light twins? [Archive] - AviationBanter

Gordon Arnaut

July 25th 05, 02:31 PM

Thanks for the info, Rusty.

How much does the 13b single rotor weigh? And how much does it cost to get
the e-shaft shortened?

I think I saw a picture of that drone you mentioned. It's an air-cooled
rotary made by the Israelis, I believe.

I too would love to see a small two-rotor, preferably air-cooled and with
aluminum end housings. That would make a very nice little engine.

There is an outfit here in Canada that is promising to produce some small
rotaries for light planes, but I don't know how far along they are. A German
outfit makes single-rotor go-kart engines, as well as an UL version.

Regards,

Gordon.

"Bellsouth News Server" > wrote in message
.. .
> Hi Gordon,
>
> Yes, by single rotor, I mean a shortened 13B engine. This requires a few
> custom made pieces, primarily the eccentric shaft, but these are probably
> going to become more available as the Sport Pilot class of planes comes
> online.
>
> Mazda did make smaller engines, but it was a long time ago. The 10A ended
> production in 74 I believe. The 12A was a good engine, and it's "only"
> been out of production for 20 years. The 13B is by far the most commonly
> available engine today, though it won't be too many years before the
> Renesis will take over that honor. Unfortunately, the smaller engines
> aren't all that much lighter, since it's the rotor housing and rotor that
> get narrower. Also, as the 13B advanced, the rotors got lighter, to the
> point where a late model 13B rotor is probably lighter than a 10A rotor.
> I haven't looked at the weights, so that's just my estimation. Bottom
> line is that the 13B, and Renesis are about the only realistic choices for
> single rotor conversions at this time.
>
> What would be better than a single, would be a smaller two rotary. There
> are any number of these popping up, but like so many other new engines we
> see, they just never seem to materialize, and if they do, they're so
> expensive that they lose their appeal. There are some very attractive
> rotaries made for UAV/target drone use, but they aren't sold for manned
> aircraft, and I haven't been able to figure out what the TBO would be.
> Can't imagine the life expectancy of a target drone is very many hours :-)
> Getting parts for these odd engines would be a problem as well.
>
> Cheers,
> Rusty
>
>
>> I'm intrigued by your twin-wankel idea. I appreciate the elegant
>> simplicity of the wankel design myself and try to keep abreast of what's
>> happening in the rotary avaition community.
>>
>> When you say single-rotor, are you talking about a 13b that has been
>> shortened? I wonder too about the smaller displacement Mazdas -- you
>> never hear much about those, but I would assume they should be lighter
>> than the 13b.
>>
>> Regards,
>>
>> Gordon.
>>
>
>

Frank van der Hulst

July 25th 05, 08:46 PM

Bellsouth News Server wrote:
> What would be better than a single, would be a smaller two rotary.

Whatever happened to the motorcycle rotaries? IIRC Suzuki had a 500cc
rotary in a motorcycle about 20 years ago. And Norton too?

I'd guess that a rotary of this size would be ideal for a microlight
aircraft.

Mark Smith

July 25th 05, 10:49 PM

Frank van der Hulst wrote:
>
> Bellsouth News Server wrote:
> > What would be better than a single, would be a smaller two rotary.
>
> Whatever happened to the motorcycle rotaries? IIRC Suzuki had a 500cc
> rotary in a motorcycle about 20 years ago. And Norton too?
>
> I'd guess that a rotary of this size would be ideal for a microlight
> aircraft.

All this talk about the rotary engine.

If they were this great, would there not be at least a couple cars
running them ?
--
Mark Smith
Tri-State Kite Sales
1121 N Locust St
Mt Vernon, IN 47620
1-812-838-6351
http://www.trikite.com

Anthony W

July 26th 05, 04:30 AM

Frank van der Hulst wrote:
> Bellsouth News Server wrote:
>
>> What would be better than a single, would be a smaller two rotary.
>
>
> Whatever happened to the motorcycle rotaries? IIRC Suzuki had a 500cc
> rotary in a motorcycle about 20 years ago. And Norton too?
>
> I'd guess that a rotary of this size would be ideal for a microlight
> aircraft.

They faded into history...

Tony

Bellsouth News Server

July 26th 05, 02:25 PM

> How much does the 13b single rotor weigh? And how much does it cost to get
> the e-shaft shortened?

The basic engine with stock housings is about 120-125 lbs, but you could
lose 25 lbs of that in exchange for around $3000 if Racing Beat ever
finishes their aluminum side housings. The e-shaft can be cut down from a
stock shaft, but it's no small job, so it's better to buy a new one, or find
one that someone else has made. Over the years, lots of these have been
built, including a number of shafts that were made by NASA. In the near
future, there will be a much better availability of these I think, but
nothing definite now.

> There is an outfit here in Canada that is promising to produce some small
> rotaries for light planes, but I don't know how far along they are. A
> German outfit makes single-rotor go-kart engines, as well as an UL
> version.

Those are actually the same engine if you're talking about the German place
that I'm thinking of. The Canadian outfit bought the rights to the engine,
and will eventually start making them in Canada, though the price is pretty
high for such an unproven engine. I wish them luck, but haven't seen much
interest from the community yet.

As for other posts on this subject:

There were certainly some smaller rotaries produced, such as the motorcyle,
and even some outboard engines. I just don't think any of those were nearly
as reliable as the Mazda version has been. They also aren't that available,
or I'd love to play with one.

As for rotary engines being in cars, yes, they are. The RX-7 was sold until
2001 or 2002, and the RX-8 has a new version of the rotary called the
Renesis. Excellent engine! In the US, people still remember the seal
problems that Mazda had when they were introduced in the early 70's, which
is unfortunate. Other countries have had several cars, trucks, etc with
rotary engines, but Mazda doesn't sent them here, because we won't buy them.
The RX-7 was discontinued in the US after 95, but sold in other countries
until at least 2001. The RX-8 was said to be our last chance, and if the
sales in the US were good (and they have been), we would get the next
version of the RX-7 as well, and perhaps other rotary powered vehicles.

Cheers,
Rusty

Bellsouth News Server

July 26th 05, 02:33 PM

> The basic engine with stock housings is about 120-125 lbs,

I meant go make it clear that this is without a redrive, or any other engine
accessories. The total installed weight will be somewhere around 220 lbs
with stock housings, and the currently available (heavy, overbuilt)
redrives. The engine can make 100+ HP pretty easily, and much more with a
turbo.

Rusty

Gordon Arnaut

July 27th 05, 04:58 AM

Thanks, for the info, Rusty.

What gearbox are you using? It seems like overkill to put one of Tracy's
boxes -- or something similar -- on a single rotor.

I would think a belt drive might be engineered that would be considerably
lighter -- expecially if you use the poly-v belts.

Just to add about why rotaries aren't more popular -- a big reason is that
the auto industry is geared around the piston engine. The infrastructure of
suppliers and manufacturers is all predicated on that business model, so
there is a lot of inertia there and changing course is like trying to do a
U-turn in an aircraft carrier.

However the wankel engine has some incredible advantages, including
smoothness simplicity, ruggedness and power potential that truly puts it a
class above the piston engine. There is no question about that, as
rotary-powered race cars have proven over and over -- until they are banned
because they simply have an unfair advantage.

Regards,

Gordon.

"Bellsouth News Server" > wrote in message
...
>> The basic engine with stock housings is about 120-125 lbs,
>
> I meant go make it clear that this is without a redrive, or any other
> engine accessories. The total installed weight will be somewhere around
> 220 lbs with stock housings, and the currently available (heavy,
> overbuilt) redrives. The engine can make 100+ HP pretty easily, and much
> more with a turbo.
>
> Rusty
>
>
>

Corky Scott

July 27th 05, 01:19 PM

On Tue, 26 Jul 2005 23:58:12 -0400, "Gordon Arnaut"
> wrote:

>However the wankel engine has some incredible advantages, including
>smoothness simplicity, ruggedness and power potential that truly puts it a
>class above the piston engine. There is no question about that, as
>rotary-powered race cars have proven over and over -- until they are banned
>because they simply have an unfair advantage.
>
>Regards,
>
>Gordon.

It's true that the rotory offers some interesting advantages, one of
which is the ability to continue to run and produce power after the
engine has lost compression due to overheating and warped side seals.

It will make power right to point where you shut it down, but you
won't get it started again because of low compression.

I guessing that it's disadvantages were enough that it never appealed
to big auto makers to work on them. Wankel itself was unable to make
it a success and it's hard to argue that Mazda has either. It's fuel
consumption and inherently dirty emissions which require a lot of
technology to clean up plus the investment in machine tools to create
it just didn't seem worth it to the bean counters, I suppose.

And the public did not seem to care much that it was available. When
Mazda first brought it out, it had a number of quirks that the buying
public had trouble getting used to. It had a cold temperature
starting assist that consisted of an injector that added pure
antifreeze from a seperate tank into the intake manifold. This of
course created a dense white cloud of smoke, which the owner was told
was normal, and it was, but it sure made owners nervous to see it.
And the owner had to refill the tank, which they often did not do,
which resulted in hard cold weather starting. Add this to the manual
choke, which the RX-7's had for many years and which the public had
difficulty using and it's easy to see why it was popular only for a
limited number of people.

Then there was the stench of the exhaust. Nothing smelled worse, not
even a diesel, and you could not tune it away. When properly adjusted
for emissions, it stank most powerfully, it felt like it was actually
burning your nostrils.

Mechanics didn't like it because it had two ignitions called a leading
and trailing ignition and originally, the distributer held three sets
of points in two layers. Not easy to adjust and naturally
problematic.

That of course went away with the advent of electronic ignition, and
eventually the engine was fuel injected and everything was computer
controlled. But converting such an engine for use in an airplane is
not without it's challenges.

Corky Scott

Bellsouth News Server

July 27th 05, 01:39 PM

Hi Gordon,

I'm starting out with one of Tracy's RD1C drives, which is 2.85:1, and good
for way more power than I'll make wiht the single rotor. Unfortunately,
it's about 45 lbs stock. Speaking with Tracy, there's probably about 5 lbs
of weight that can be removed without losing any strength, and perhaps more
if you're willing to sacrifice strength in the drive. That wouldn't be a
problem for the single rotor, but if you ever wanted to use it on a two
rotor, it would be.

Richard Sohn has a running 12A single rotor now, and he's using a Hirth G-40
gearbox. At last report, his total engine weight was 170 lbs, which is
pretty great. He's custom made many of the parts on his engine to save
weight, and might produce them if it all works out well. He's currently on
a slow, and careful development and test program, and eventually plans to
put the engine in his Avid, which I believe is flying with a Subaru. It
will be interesting to see how the Hirth box works out, but I'm not sure how
much lighter it really is in the long run. I've asked Richard for the total
weight, but since so much of the adaptation is dependent on his custom end
housings, he hasn't been able to come up with a number. My guess is
something around 30 lbs total for the drive.

I asked about belt drives, and found that someone was making one for the
single rotor that David Atkins is selling. So far, I haven't heard any
reports of how that worked, if it even got finished. One other fellow who
makes belt drives told me that he refused to make such a drive for Atkins,
because it wouldn't be strong enough. His point was that the single rotor
is still full sized, and gives the same strength power pulses as the two
rotor does. Because of this, he felt the drive has to be as strong as the
two rotor drive. This does make sense to me, but I'm sure there has to be a
way to reduce the weight further.

FWIW, my plan was to bolt together off the shelf parts, and see what it
weighs. The Kolb Slingshot that I'll be using initially will handle the
weight, when flown as a single place, and with a BRS chute to balance the
CG. Once I get a worst case weight, then I'll start working on reducing it.

Cheers,
Rusty (hiding rotary info in the light twin thread)

> What gearbox are you using? It seems like overkill to put one of Tracy's
> boxes -- or something similar -- on a single rotor.
>
> I would think a belt drive might be engineered that would be considerably
> lighter -- expecially if you use the poly-v belts.

[email protected]

July 27th 05, 03:36 PM

Saying that Rotaries have an unfair advantage is only part of the
story. In the appropriate classes, they were raced for years, often
successfuly. But they were still hated because they were so LOUD.
Unbearably, explosively loud without big heavy mufflers - which got to
be mandatory in many venues This might not matter much for a target
drone or a tiny cart engine but it does everywhere else.

[email protected]

July 27th 05, 03:36 PM

Bellsouth News Server

July 27th 05, 04:08 PM

> I guessing that it's disadvantages were enough that it never appealed
> to big auto makers to work on them. Wankel itself was unable to make
> it a success and it's hard to argue that Mazda has either.

How can you say that Mazda hasn't made this successful? Sure, the initial
introduction had it's share of problems, but since the RX-7 made the
re-introduction of the rotary here in the US, the engine has been as
troublefree as any engine produced. Emissions was one of the biggest
problems, but the newly redesigned Renesis engine cleaned that up, as well
as taming a bit of the bark, and overly hot exhaust. Fuel consumption in
aircraft use does not seem to be any worse than any other engine of the same
power range. The truth is that other manufacturers tried the rotary, but
didn't feel like it was worth developing, since they were perfectly happy to
churn out piston engines. Only Mazda seems to have had the willingness to
stick with it, and make it successful.

> But converting such an engine for use in an airplane is
> not without it's challenges.
>
> Corky Scott

What challenges does it present, that aren't shared by any other auto
engine? Heck, it already has dual ignition. These days, two rotor engines
are not nearly the challenge that some engines would be, because Tracy Crook
sells engine controllers, monitors, and gear drives. Conversion Concepts
makes excellent mounts. About the only thing missing is an off the shelf
intake, and exhaust, which aren't far behind.

Cheers,
Rusty
13B powered RV-3 flying (2500+ fpm climb, 200 mph cruise)
Kolb Slingshot being converted from 912S to single rotor almost as I type

Bob Kuykendall

July 27th 05, 05:34 PM

Earlier, Bellsouth News Server wrote:

> How can you say that Mazda hasn't made
> this successful? Sure, the initial
> introduction had it's share of problems,
> but since the RX-7 made the re-
> introduction of the rotary here in the
> US, the engine has been as troublefree
> as any engine produced.

Well, Corky didn't say that Mazda hasn't made the Wankel rotary a
success. He only said that it's hard to argue it:

Earlier, Corky Scott wrote:

: Wankel itself was unable to make it a
: success and it's hard to argue that
: Mazda has either.

That the vast majority of Mazda cars are powered by conventional piston
engines supports Corky, at least when you consider the aspect of
commercial success. And it is undeniably commercial success by which
car manufacturers measure themselves and each other. Sure, the RX-7 and
RX-8 motors seem to be trouble-free, but at what cost?

And further, since most of the patents that cover the Wankel
innovations are now expired or are about to expire, you'd expect to see
other manufacturers adopting the Wankel. That you don't see this tends
to support Corky's argument that for the vast majority of engine
applications the Wankel's disadvantages outweigh its advantages.

Personally, I think that Wankel rotaries continue to be part of Mazda's
automobile offerings only because it would be harder sell an RX-series
car without them. I believe that Mazda decided to continue the Wankel
heritage of the RX only after carefully balancing the greater cost per
unit horsepower of their rotary against the whizz-bang (Okay,
whizz-hummm in this case) technical appeal in the RX package. An RX
without a rotary would be like a Mustang without three-element
taillights or a Buick without fake exhaust portholes.

Thanks, and best regards to all

Bob K.
http://www.hpaircraft.com/hp-24

Bill Daniels

July 27th 05, 06:19 PM

I think there are theoetical factors against the Wankel-type rotary.

The combustion chamber shape is far from ideal and there isn't a straight
forward way to correct that. As a result, the engine leaks a lot of heat in
exhaust gasses as well as through the cooling system so there is less energy
going into producing power. All else equal (and it rarely is), the rotary
will have worse specific fuel consumption than a crank and piston.

Old pistons have one rarely discussed advantage. In the interval between
ignition and the beginning of the power stroke, piston motion is very low
and the volume of the combustion chamber is close to constant. This allows
combustion to run to completion under near ideal conditions of temperature
and pressure. That squeezes more heat calories, and therefore power, out of
the fuel-air mixture.

Bill Daniels
(I loved my RX-7)

[email protected]

July 27th 05, 09:03 PM

A rotary made by Midwest (originally used in Norton motorcycles) and
now produced by Diamond has been very successfully used to power self
launched sailplanes made by Alexander Schleicher. I fly an ASH-26E
powered by a 50hp single rotor wankel.

More info is at
http://www.as-segelflugzeuge.de/englisch/produkte/ash26/e_ash26_main.htm

-Tom

[email protected]

July 27th 05, 09:05 PM

The Norton engine is alive and kicking - now being produced by Diamond
and they're thinking of making a 2 rotor version with 100 hp.

-Tom

Corky Scott

July 27th 05, 09:28 PM

On Wed, 27 Jul 2005 10:08:35 -0500, "Bellsouth News Server"
> wrote:

>How can you say that Mazda hasn't made this successful? Sure, the initial
>introduction had it's share of problems, but since the RX-7 made the
>re-introduction of the rotary here in the US, the engine has been as
>troublefree as any engine produced. Emissions was one of the biggest
>problems, but the newly redesigned Renesis engine cleaned that up, as well
>as taming a bit of the bark, and overly hot exhaust. Fuel consumption in
>aircraft use does not seem to be any worse than any other engine of the same
>power range. The truth is that other manufacturers tried the rotary, but
>didn't feel like it was worth developing, since they were perfectly happy to
>churn out piston engines. Only Mazda seems to have had the willingness to
>stick with it, and make it successful.

Now now Bellsouth, let's not get too worked up over this. I agree on
most aspects of the rotory but a raging success in the automotive
world it has not ever been. Sure you can get it in old RX-7's and new
RX-8's, but that's it. If it were such a great alternative, everyone
would be trying to build one.

I don't quite understand how Tracy manages to get the kind of fuel
burn he claims but I suspect he isn't running it very hard because the
amount of surface area the rotors are exposed to as they rotate is
much greater than that in a piston type engine. This much greater
combustion chamber exposed surface area means much more fuel can
condense on the surface. It means it's going to get poorer gas milage
inherently, unless you unleash the electronics engineers to do their
magic with fuel injection and all the other gadgets that are used to
emeliorate the situation.

The problem is, you don't get that stuff when you put it in a
homebuilt airplane unless you rip out all the sensors and the entire
wiring harness to go along with it.

So yes, it's a very very solid engine but like so many things in
aviation, it has it's compromises.

Corky Scott

Russell Duffy

July 27th 05, 11:35 PM

> Now now Bellsouth, let's not get too worked up over this. I agree on
> most aspects of the rotory but a raging success in the automotive
> world it has not ever been. Sure you can get it in old RX-7's and new
> RX-8's, but that's it. If it were such a great alternative, everyone
> would be trying to build one.

Hi Corky,

Finally fixed the "Bellsouth News Server" name. I left that all generic
after the last time I got spam attacked on one of these groups. We'll see
if it comes up as my real name this time.

Certainly the rotary cost's Mazda a bit more to make, but I would assume
that's true of any automakers flagship engine. They also don't put their
top engine in everything they make. Ever heard of a Dodge Hemi Neon :-)
Seriously, the rotary is a bit of a specialty engine, but those of us who
bet our lives on them believe that those special qualities are what makes
them the best choice. Still, if they have to be in every vehicle on the
road to be a raging success in the automotive world, then I guess they're
not :-)

Breaks over, back to the single rotor in the garage.

Cheers,
Rusty

Ernest Christley

July 27th 05, 11:37 PM

Bill Daniels wrote:
> I think there are theoetical factors against the Wankel-type rotary.
>
> The combustion chamber shape is far from ideal and there isn't a straight
> forward way to correct that. As a result, the engine leaks a lot of heat in
> exhaust gasses as well as through the cooling system so there is less energy
> going into producing power. All else equal (and it rarely is), the rotary
> will have worse specific fuel consumption than a crank and piston.
>
> Old pistons have one rarely discussed advantage. In the interval between
> ignition and the beginning of the power stroke, piston motion is very low
> and the volume of the combustion chamber is close to constant. This allows
> combustion to run to completion under near ideal conditions of temperature
> and pressure. That squeezes more heat calories, and therefore power, out of
> the fuel-air mixture.
>
> Bill Daniels
> (I loved my RX-7)
>

Any loss of BSFC at speed is nearly all compensated for through extreme
leaning made possible by charge stratification (centrifugal force throws
gas fumes to the outside of the chamber, where the plugs just happen to
be). In real world airplane (vs. imaginary ones), there is no
difference in rotaries vs pistons. Furthermore, the BSFC Lycoming
et.al. publish is for a engine running on a test stand. In the real
world, most pilots run rich to protect valves.

--
This is by far the hardest lesson about freedom. It goes against
instinct, and morality, to just sit back and watch people make
mistakes. We want to help them, which means control them and their
decisions, but in doing so we actually hurt them (and ourselves)."

Ernest Christley

July 27th 05, 11:47 PM

Bob Kuykendall wrote:
>
> And further, since most of the patents that cover the Wankel
> innovations are now expired or are about to expire, you'd expect to see
> other manufacturers adopting the Wankel. That you don't see this tends
> to support Corky's argument that for the vast majority of engine
> applications the Wankel's disadvantages outweigh its advantages.
>

If by "vast majority", you mean automobiles, then you a absolutely
correct. An automobile is one of the worst possible applications for a
rotary. The low end torque isn't there, and Mazda has to go through all
sorts of contortions to get some. Rotaries like to rev fast and stay
that way, and really suck at the low end.

Where the engine will shine is situations where the low end grunt is
unecessary, and they can rev to 6000RPM or more and stay there..
Airplanes and power generation are two examples that come to mind.
Expect to see more AIRPLANE ENGINES using the rotary concepts as the
patents run out.

The biggest disadvantages right now is low volume. GM or Ford won't
touch a design that is meant for a few thousand per year. Mechanics
have neither the time nor inclination to learn about an engine they'll
very rarely see. But Lycoming is already working at those sorts of
volumes. It becomes a non issue.

The second quoted problem is a red herring. BSFC. The rotary leans MUCH
better than any piston engine. In actual practice in real airplanes,
fuel burn is indistinguishable.

But the advantages. An engine that will sacrifice itself to get you
home. A $500 rebuild that takes a weekend. Power to weight ratios that
already beat pistons and continue to climb. Did I mention, an engine
that will sacrifice itself to get you home.

--
This is by far the hardest lesson about freedom. It goes against
instinct, and morality, to just sit back and watch people make
mistakes. We want to help them, which means control them and their
decisions, but in doing so we actually hurt them (and ourselves)."

Ernest Christley

July 27th 05, 11:59 PM

Corky Scott wrote:
>
> I don't quite understand how Tracy manages to get the kind of fuel
> burn he claims

he reaches up and turns down that mixture button. The charge stratifies
in a rotary, pushing the fuel charge out to the plugs.

but I suspect he isn't running it very hard because the
> amount of surface area the rotors are exposed to as they rotate is
> much greater than that in a piston type engine. This much greater
> combustion chamber exposed surface area means much more fuel can
> condense on the surface.

Running at 6000RPM vs 2500 doesn't leave much time for fuel condensing.
It is true, though. The rotary doesn't get complete fuel burn,
especially at the little pointy ends of the chamber. But the
counterpoint is that most pilot run rich to keep from cooking their
valves. No valves in a rotary.

Besides, all that extra energy left in the exhaust need not be wasted in
an airplane engine.

It means it's going to get poorer gas milage
> inherently, unless you unleash the electronics engineers to do their
> magic with fuel injection and all the other gadgets that are used to
> emeliorate the situation.
>
> The problem is, you don't get that stuff when you put it in a
> homebuilt airplane unless you rip out all the sensors and the entire
> wiring harness to go along with it.

Tracy is an electronics engineer 8*)
I bought 42lb Ford injectors, still have to get LS1 (from GM I believe)
coils. Tracy's controller is around $800. All the other sensor you
need are attached to the engine when you pull it out of the car. You
get them unless you go through a lot of trouble to leave them behind.

>
> So yes, it's a very very solid engine but like so many things in
> aviation, it has it's compromises.

Have I mentioned in this thread that it will sacrifice itself to get you
home. Even on one rotor, it will keep making enough power to keep most
GA planes in the air until you shut it off. To me, it takes a lot to
compromise away that much safety.

--
This is by far the hardest lesson about freedom. It goes against
instinct, and morality, to just sit back and watch people make
mistakes. We want to help them, which means control them and their
decisions, but in doing so we actually hurt them (and ourselves)."

Charlie

July 28th 05, 01:41 AM

Mark Smith wrote:
> Frank van der Hulst wrote:
>
>>Bellsouth News Server wrote:
>>
>>>What would be better than a single, would be a smaller two rotary.
>>
>>Whatever happened to the motorcycle rotaries? IIRC Suzuki had a 500cc
>>rotary in a motorcycle about 20 years ago. And Norton too?
>>
>>I'd guess that a rotary of this size would be ideal for a microlight
>>aircraft.
>
>
>
> All this talk about the rotary engine.
>
> If they were this great, would there not be at least a couple cars
> running them ?
Mazda RX-8 Renesis. The 6 speed manual transmission model makes around
250 hp without being turbo or super charged. The core 'short block'
engine weighs around 170 lbs. They are perfectly happy making rated hp &
more all day long as long as they have proper oil & water temps.

The reason for so much talk about them as a/c engines is that the core
engine is just about bullet proof at any power level likely to be used
in a GA aircraft. If someone made a small 2 rotor it would likely be
slightly heavier than a 2 stroke of equivalent power but much lighter
than a 4 stroke & have much higher reliability than the 4 stroke. The
guys flying the 2 rotor Mazda engines say the fuel burn is only slightly
worse than Lycomings of equivalent power so there's not much penalty there.

It's actually better suited to a/c use than in cars, due to the way it
responds to intake tuning & the fact that it's not very fuel efficient
until power output is at a high level, unlike piston engines. The cars
have incredible Rube Goldberg intakes to keep the engine 'on the pipe'
over a wide range of rpms; this isn't needed in an aircraft. It responds
to intake tuning like 2 strokes respond to exhaust tuning. (It's a true
4 stroke engine, though.)

More than you ever wanted to know?

Charlie

Gordon Arnaut

July 28th 05, 04:03 AM

Excellent points, Ernest.

As far as the combustion chamber efficiency is concerned, the rotary is at a
slight disadvanatage -- at least in theory. However, the piston engine has
more friction and pumping losses.

Think of just the power required to drive the camshaft and open the valves
against the springs. The rotary doesn't have a cam, or valves. Also a lot
less bearing surfaces to cause frictional losses.

I agree with the opinion that the rotary is ideally suited for airplanes. I
understand that with Tracy's controller the engine will happily run 200
degrees lean of peak. Try doing that with a Lycoming.

Most important all, the thing is almost impossible to break, as Ernest
pointed out. As long as the supporting systems are properly implemented --
and therein lies the rub -- the engine itself is practically bullet proof.

Regards,

Gordon.

PS: Rusty, thanks for the info on the gearbox. That Hirth box or something
similar sounds like a good way to go. 170 lbs is outstanding for a 100hp
engine -- could be even more with peripheral porting.

Best of luck with your Kolb project. I hope you will have some pictures
available.

"Ernest Christley" > wrote in message
. com...
> Corky Scott wrote:
>>
>> I don't quite understand how Tracy manages to get the kind of fuel
>> burn he claims
>
> he reaches up and turns down that mixture button. The charge stratifies
> in a rotary, pushing the fuel charge out to the plugs.
>
> but I suspect he isn't running it very hard because the
>> amount of surface area the rotors are exposed to as they rotate is
>> much greater than that in a piston type engine. This much greater
>> combustion chamber exposed surface area means much more fuel can
>> condense on the surface.
>
> Running at 6000RPM vs 2500 doesn't leave much time for fuel condensing. It
> is true, though. The rotary doesn't get complete fuel burn, especially at
> the little pointy ends of the chamber. But the counterpoint is that most
> pilot run rich to keep from cooking their valves. No valves in a rotary.
>
> Besides, all that extra energy left in the exhaust need not be wasted in
> an airplane engine.
>
> It means it's going to get poorer gas milage
>> inherently, unless you unleash the electronics engineers to do their
>> magic with fuel injection and all the other gadgets that are used to
>> emeliorate the situation. The problem is, you don't get that stuff when
>> you put it in a
>> homebuilt airplane unless you rip out all the sensors and the entire
>> wiring harness to go along with it.
>
> Tracy is an electronics engineer 8*)
> I bought 42lb Ford injectors, still have to get LS1 (from GM I believe)
> coils. Tracy's controller is around $800. All the other sensor you need
> are attached to the engine when you pull it out of the car. You get them
> unless you go through a lot of trouble to leave them behind.
>
>>
>> So yes, it's a very very solid engine but like so many things in
>> aviation, it has it's compromises.
>
> Have I mentioned in this thread that it will sacrifice itself to get you
> home. Even on one rotor, it will keep making enough power to keep most GA
> planes in the air until you shut it off. To me, it takes a lot to
> compromise away that much safety.
>
>
> --
> This is by far the hardest lesson about freedom. It goes against
> instinct, and morality, to just sit back and watch people make
> mistakes. We want to help them, which means control them and their
> decisions, but in doing so we actually hurt them (and ourselves)."

Corky Scott

July 28th 05, 12:57 PM

On Wed, 27 Jul 2005 22:47:34 GMT, Ernest Christley
> wrote:

>The second quoted problem is a red herring. BSFC. The rotary leans MUCH
>better than any piston engine. In actual practice in real airplanes,
>fuel burn is indistinguishable.
>
>But the advantages. An engine that will sacrifice itself to get you
>home. A $500 rebuild that takes a weekend. Power to weight ratios that
>already beat pistons and continue to climb. Did I mention, an engine
>that will sacrifice itself to get you home.

All good points. I didn't mention this (at least not recently) but I
had a 13B in my shop at one time that I was going to use for my
airplane.

This was a number of years ago before Tracy began developing his
rotory. I had started with a Buick/Olds 215 cid aluminum V8 but had
sold it because it was too hard to find parts for it.

I was getting increasingly nervous about using the 13B because I knew
I had to fabricate my own intake manifold and exaust system. I had
been an auto mechanic who worked on Mazda's, including the RX7's so I
knew something about them. The intake manifold looked to be almost as
big as the engine, which is why all the folks I'd been talking with
were recommending it be junked and a smaller one fabricated.

Remember, this was in the early 90's, not now.

But the thing that really put me off was the heat of the exhaust
system. It ran something like 500 degrees hotter than piston type
exhaust systems and required a thick wall stainless steel system.
Even with such a system, all that heat seemed a little scary to me.

So I sold that and now have the Ford V6 which is running well at this
point and seems to have all the power I need.

Corky Scott

Gordon Arnaut

July 28th 05, 02:36 PM

Rusty,

I've just been thinking about that fellow's contention that a single rotor
needs a redrive as strong as a two-rotor, because the power pulse of a
single is just as strong.

As far as I can see, this cannot be valid. If I'm thinking this through
correctly, each rotor will make three power pulses for each revolution of
the rotor, or one revolution of the e-shaft.

Even if two rotors were running out of phase, there would still be two power
strokes for each revolution of the e-shaft on a two-rotor, versus a single
power pulse per rev on a single. Your redrive would need to handle only half
the power.

Tracy's gearboxes are excellent by all accounts, but why use something so
heavy if it's not necessary? (Even so you overall weight of 220 lbs is
excellent for a 100hp engine).

Also, in terms of packaging, on a high-wing pusher like the Kolb, an upright
belt drive would put your thrust line at wing level where it needs to be,
while the engine could be down low, near the plane's vertical center of
gravity (like on the Challenger, which uses such a tall belt drive with the
Rotax 2-stroke).

I am interested in exploring just such an application with a high-wing
pusher design that I am developing. I've been looking at poly-v belts, which
you see driving the engine accessories on newer autos -- but there are
poly-v belts that will handle upwards of 500hp. You also see them on some
two-stroke UL engines.

The advantage of the poly-v over a cogged (synchronous) belt is that they
naturally dampen torsional spikes, by means of slippage. Another plus is
that the pulleys can be considerably lighter.

Regards,

Gordon.

PS: Regardsing the issue of hot exhaust on rotaries, this makes them ideally
suited to turbocharging.

"Bellsouth News Server" > wrote in message
...
> Hi Gordon,
>
> I'm starting out with one of Tracy's RD1C drives, which is 2.85:1, and
> good for way more power than I'll make wiht the single rotor.
> Unfortunately, it's about 45 lbs stock. Speaking with Tracy, there's
> probably about 5 lbs of weight that can be removed without losing any
> strength, and perhaps more if you're willing to sacrifice strength in the
> drive. That wouldn't be a problem for the single rotor, but if you ever
> wanted to use it on a two rotor, it would be.
>
> Richard Sohn has a running 12A single rotor now, and he's using a Hirth
> G-40 gearbox. At last report, his total engine weight was 170 lbs, which
> is pretty great. He's custom made many of the parts on his engine to save
> weight, and might produce them if it all works out well. He's currently
> on a slow, and careful development and test program, and eventually plans
> to put the engine in his Avid, which I believe is flying with a Subaru.
> It will be interesting to see how the Hirth box works out, but I'm not
> sure how much lighter it really is in the long run. I've asked Richard
> for the total weight, but since so much of the adaptation is dependent on
> his custom end housings, he hasn't been able to come up with a number. My
> guess is something around 30 lbs total for the drive.
>
> I asked about belt drives, and found that someone was making one for the
> single rotor that David Atkins is selling. So far, I haven't heard any
> reports of how that worked, if it even got finished. One other fellow who
> makes belt drives told me that he refused to make such a drive for Atkins,
> because it wouldn't be strong enough. His point was that the single rotor
> is still full sized, and gives the same strength power pulses as the two
> rotor does. Because of this, he felt the drive has to be as strong as the
> two rotor drive. This does make sense to me, but I'm sure there has to be
> a way to reduce the weight further.
>
> FWIW, my plan was to bolt together off the shelf parts, and see what it
> weighs. The Kolb Slingshot that I'll be using initially will handle the
> weight, when flown as a single place, and with a BRS chute to balance the
> CG. Once I get a worst case weight, then I'll start working on reducing
> it.
>
> Cheers,
> Rusty (hiding rotary info in the light twin thread)
>
>
>> What gearbox are you using? It seems like overkill to put one of Tracy's
>> boxes -- or something similar -- on a single rotor.
>>
>> I would think a belt drive might be engineered that would be considerably
>> lighter -- expecially if you use the poly-v belts.
>
>

Gordon Arnaut

July 28th 05, 02:48 PM

Tom,

Thanks for that link. What an amazing aircraft. These self-launching
sailplanes have really become a hotbed of technology. (L/D ratio of 50:1,
laminar flow over 95 percent of chord; wow.)

The fact that a rotary is used instead of the traditional two-strokes speaks
volumes about the rotary's power-to-weight performance.

Regards,

Gordon.

> wrote in message
oups.com...
>A rotary made by Midwest (originally used in Norton motorcycles) and
> now produced by Diamond has been very successfully used to power self
> launched sailplanes made by Alexander Schleicher. I fly an ASH-26E
> powered by a 50hp single rotor wankel.
>
> More info is at
> http://www.as-segelflugzeuge.de/englisch/produkte/ash26/e_ash26_main.htm
>
> -Tom
>

Russell Duffy

July 28th 05, 03:51 PM

> PS: Rusty, thanks for the info on the gearbox. That Hirth box or something
> similar sounds like a good way to go. 170 lbs is outstanding for a 100hp
> engine -- could be even more with peripheral porting.
>
> Best of luck with your Kolb project. I hope you will have some pictures
> available.

Thanks Gordon. BTW, Richard Sohn's 12A single rotor is peripheral ported.

PP vs the normal side ports is a hotly contested issue on the rotary list,
and I personally believe it's not worth doing for our 7500 rpm range. I've
been told that a good porting job on 3rd gen housings will get you the same
power as PP at the same rpm. The side ports will lose big if you're going
to run up to 9000 rpm or so, but we don't. There are a number of folks who
are very committed to the PP tests, and are using smaller than "normal" PP
ports, to improve the performance at our rpms, but until some of them are
running, and can be compared to what's already out there, we won't know.

Numbers I've heard for 7500 rpm for a single rotor with side ports are
upwards of 120 HP. Since you have to have a muffler of some type, and since
turbos seem to work pretty well as mufflers, I'm planning to use a small
Garrett turbo as my muffler. It's probaby not much heavier than a muffler,
and associated pipe would be, so it's not that much of a weight penalty. If
you choose to run the boost that you could get from the turbo, it should be
closer to 180 HP. For the Kolb, this would be insane, so I'll have to limit
the rpm, and boost to keep the power down to what the airframe can handle.
Folks have used 100 HP Rotax engines on the SlingShot, so the plan would be
to not exceed that by much, unless some 912S driver needs a lesson :-)

As you may know, Mazda went to NO peripheral ports on the Renesis, which
means they took the exhaust port off the rotor housing as well. Now all
ports are on the side housings, which allows them to have no overlap, but
still have improved power. This also has the benefit of slowing the
exhaust, which helps quiet it some, as well as reducing the temp of the
exhaust. Unfortunately, the temp seems to be picked up by the cooling system
now, so there's a bit of a trade-off there.

Cheers,
Rusty

Gig 601XL Builder

July 28th 05, 04:01 PM

What is the installed weight of a 12A?

"Russell Duffy" > wrote in message
...
>> PS: Rusty, thanks for the info on the gearbox. That Hirth box or
>> something similar sounds like a good way to go. 170 lbs is outstanding
>> for a 100hp engine -- could be even more with peripheral porting.
>>
>> Best of luck with your Kolb project. I hope you will have some pictures
>> available.
>
> Thanks Gordon. BTW, Richard Sohn's 12A single rotor is peripheral ported.
>
> PP vs the normal side ports is a hotly contested issue on the rotary list,
> and I personally believe it's not worth doing for our 7500 rpm range.
> I've been told that a good porting job on 3rd gen housings will get you
> the same power as PP at the same rpm. The side ports will lose big if
> you're going to run up to 9000 rpm or so, but we don't. There are a
> number of folks who are very committed to the PP tests, and are using
> smaller than "normal" PP ports, to improve the performance at our rpms,
> but until some of them are running, and can be compared to what's already
> out there, we won't know.
>
> Numbers I've heard for 7500 rpm for a single rotor with side ports are
> upwards of 120 HP. Since you have to have a muffler of some type, and
> since turbos seem to work pretty well as mufflers, I'm planning to use a
> small Garrett turbo as my muffler. It's probaby not much heavier than a
> muffler, and associated pipe would be, so it's not that much of a weight
> penalty. If you choose to run the boost that you could get from the
> turbo, it should be closer to 180 HP. For the Kolb, this would be insane,
> so I'll have to limit the rpm, and boost to keep the power down to what
> the airframe can handle. Folks have used 100 HP Rotax engines on the
> SlingShot, so the plan would be to not exceed that by much, unless some
> 912S driver needs a lesson :-)
>
> As you may know, Mazda went to NO peripheral ports on the Renesis, which
> means they took the exhaust port off the rotor housing as well. Now all
> ports are on the side housings, which allows them to have no overlap, but
> still have improved power. This also has the benefit of slowing the
> exhaust, which helps quiet it some, as well as reducing the temp of the
> exhaust. Unfortunately, the temp seems to be picked up by the cooling
> system now, so there's a bit of a trade-off there.
>
> Cheers,
> Rusty
>
>
>
>
>

Russell Duffy

July 28th 05, 04:04 PM

> Even if two rotors were running out of phase, there would still be two
> power strokes for each revolution of the e-shaft on a two-rotor, versus a
> single power pulse per rev on a single. Your redrive would need to handle
> only half the power.

If I understood him correctly, he was saying that each time the rotor fires,
there is a large power pulse that has to be transferred to the prop. The
belt has to be strong enough to be able to absorb that pulse. Since the
pulse you get from the single rotor is exactly the same amplitude as the
pulse from a two rotor, the belt has to be just as strong. If (big if)
that's the limiting factor of the belt strength, then it wouldn't matter how
many pulses there were. BTW, I'm an electonics guy, so not really qualified
to debate redrives.

> Tracy's gearboxes are excellent by all accounts, but why use something so
> heavy if it's not necessary? (Even so you overall weight of 220 lbs is
> excellent for a 100hp engine).

I looked around, and just couldn't find anything better than Tracy's drive
that was actually available. Amazingly, even some of the belt drives
weighed more than Tracy's drive, so at the moment, it's the best off the
shelf solution. I'm hopeful something else will come along, but it was the
best I could find for now. I also have plans to build another RV-8, or
maybe an RV-7, so the drive can be used for that eventually if I find
something better for the single rotor.

> Also, in terms of packaging, on a high-wing pusher like the Kolb, an
> upright belt drive would put your thrust line at wing level where it needs
> to be, while the engine could be down low, near the plane's vertical
> center of gravity (like on the Challenger, which uses such a tall belt
> drive with the Rotax 2-stroke).

The Kolb design has the engine on top of the wing, so the belt drive is
actually a problem for the position of the prop. Using Tracy's drive, and a
72" prop, I'm almost exactly where I need to be. It's also nice that the
drive is long enough to let the prop clear the back of the ailerons, while
keeping the engine from having to sit any farther aft for CG reasons.

> PS: Regardsing the issue of hot exhaust on rotaries, this makes them
> ideally suited to turbocharging.

See other reply :-)

Cheers,
Rusty

Russell Duffy

July 28th 05, 04:09 PM

"Gig 601XL Builder" <wr.giacona@coxDOTnet> wrote in message
news:vr6Ge.343$_t.142@okepread01...
> What is the installed weight of a 12A?

Richards single rotor (using 12A rotor and rotor housing) is about 170 lbs
at the moment, which is really low because he custom made so many items on
the engine to save weight. Using stock Mazda housings would push the weight
up to about 220 lbs at the most.

A 12A is normally a two rotor engine, which weighs pretty close to the same
as a 13B. We generally use a figure of about 330 lbs for firewall forward
weight of a two rotor.

Cheers,
Rusty

Corky Scott

July 28th 05, 04:13 PM

On Thu, 28 Jul 2005 09:36:36 -0400, "Gordon Arnaut"
> wrote:

>As far as I can see, this cannot be valid. If I'm thinking this through
>correctly, each rotor will make three power pulses for each revolution of
>the rotor, or one revolution of the e-shaft.

My recollection from my mechanicking days is that the eccentric shaft
rotates at three times the speed of the rotor. Whether this
translates into the number of power pulses you mention gives me a
headache to contemplate.

I know that this is the reason the engine could run for so long at
such seemingly high rpms: the rotors were actually spinning at one
third the rpms the eccentric shaft was going. So at 9,000 rpm
measured at the accentric shaft, the rotors are only turning 3,000.

Corky Scott

Russell Duffy

July 28th 05, 05:14 PM

>>As far as I can see, this cannot be valid. If I'm thinking this through
>>correctly, each rotor will make three power pulses for each revolution of
>>the rotor, or one revolution of the e-shaft.
>
> My recollection from my mechanicking days is that the eccentric shaft
> rotates at three times the speed of the rotor.

Abolutely right Corky. Gordon got it right in the rest of his post, so I
just figured he left out a word above, and it should have read "one PER
revolution of the e-shaft".

Cheers,
Rusty

Gordon Arnaut

July 28th 05, 08:40 PM

Rusty,

Yes, I meant exactly what you said: three power pulses per single rev of the
rotor, and one pulse per rev of the e-shaft.

Regards,

Gordon.

PS: I like that you are using a turbo as a muffler -- not much more weight,
similar or even better noise reduction, not to mention the power.

"Russell Duffy" > wrote in message
...
>>>As far as I can see, this cannot be valid. If I'm thinking this through
>>>correctly, each rotor will make three power pulses for each revolution of
>>>the rotor, or one revolution of the e-shaft.
>>
>> My recollection from my mechanicking days is that the eccentric shaft
>> rotates at three times the speed of the rotor.
>
> Abolutely right Corky. Gordon got it right in the rest of his post, so I
> just figured he left out a word above, and it should have read "one PER
> revolution of the e-shaft".
>
> Cheers,
> Rusty
>
>

Gordon Arnaut

July 28th 05, 09:08 PM

Rusty,

I don't want to beat this issue to death, and I'm not a power transmission
expert either, but this is the first time I've heard of "amplitude" as an
issue in redrive design.

Usually the redrive designer is concerned with handling the maximum torque
and will devise a load model that will encompass the worst-case operating
scenarios.

I think the guy is referring to amplitude of power pulses because the torque
coming from an internal combustion engine is not linear like in an electric
motor, or turbine -- it has torsional spikes.

Still, compared to a piston engine, the rotary is a pussy cat when it comes
to torsional issues, because it does not have the lever-arm effect of the
crankshaft throws to worry about -- which creates the bulk of the torsional
flex in a piston engine.

When it comes to belt drives, the manufacturers have two ways of rating
them: one for smooth, continuous power like electric motors, and another for
combustion engines.

They also rate them for max continuous torque, so I feel pretty safe in
saying that with a single rotor engine making half the torque, you will need
less belt. With a gearbox, the dynamic gear tooth leads will likewise be
less.

Regards,

Gordon.

"Gordon Arnaut" > wrote in message
...
> Rusty,
>
> Yes, I meant exactly what you said: three power pulses per single rev of
> the rotor, and one pulse per rev of the e-shaft.
>
> Regards,
>
> Gordon.
>
> PS: I like that you are using a turbo as a muffler -- not much more
> weight, similar or even better noise reduction, not to mention the power.
>
>
>
>
> "Russell Duffy" > wrote in message
> ...
>>>>As far as I can see, this cannot be valid. If I'm thinking this through
>>>>correctly, each rotor will make three power pulses for each revolution
>>>>of
>>>>the rotor, or one revolution of the e-shaft.
>>>
>>> My recollection from my mechanicking days is that the eccentric shaft
>>> rotates at three times the speed of the rotor.
>>
>> Abolutely right Corky. Gordon got it right in the rest of his post, so I
>> just figured he left out a word above, and it should have read "one PER
>> revolution of the e-shaft".
>>
>> Cheers,
>> Rusty
>>
>>
>
>

Corky Scott

July 28th 05, 09:23 PM

On Thu, 28 Jul 2005 16:08:46 -0400, "Gordon Arnaut"
> wrote:

>Still, compared to a piston engine, the rotary is a pussy cat when it comes
>to torsional issues, because it does not have the lever-arm effect of the
>crankshaft throws to worry about -- which creates the bulk of the torsional
>flex in a piston engine.

This may not be accurate Gordon. There was a company based up in
Washington State that produced a planetary gear box as a PSRU for the
Mazda rotory and they had a HORRENDOUS developmental period with many,
repeat many broken boxes.

They finally got something that was extremely professional looking as
machined aluminum can be, and robust and long lived. They had it on
the front of an RX4 and flew it to various air shows. One of the
developmental partners was killed in an airplane crash and for a while
the psru was still available but I don't know if it still is.

The big issue, the one that was busting props and tearing their boxes
apart was torsional vibration. I remember reading that they claimed
there was something about the rotory engine that gave it a really
powerful torque spike.

I think they eventually solved the problem with some kind of cushion
drive. But for a while it was busting one attempt after another on
the test stand, and a bunch of dead stick landings.

Corky Scott

Gordon Arnaut

July 29th 05, 03:08 AM

Thanks Corky,

My assumptions about the rotary were not based on experience, so it's good
to learn something new.

I would have expected the rotary to have less spiky torque output than a
piston, but perhaps the wobble of the rotor along its ellipsoidal path
creates enough inertia to cause some sizable spikes.

I may post a question about this to the Mazda newsletter -- once Paul gets
back from Osh. I'm sure there will be some people there with good insight on
this.

I still have to think though that maximum torque is the limiting factor in
both gear and belt design. Even if torsional vibration is an issue (with the
rotary or any engine), the way to address that is to dampen the spikes and
prevent harmonics from causing destructive resonance. Just using bigger
stronger gears is one approach, but not really the most elegant -- or
lightweight.

I notice that Tracy uses rubber doughnuts between the flywheel and the
gearbox coupling, just for that reason I would assume.

Your story is just another reminder that gearboxes are one of the big
bugaboos of any auto engine conversion -- and torsional vibration (or
resonance) is always the culprit. I know that in the Subaru community there
is not really a box that I would consider completely trustworthy.

I was hoping the rotary was less of a problem in this area. Darn.

Regards,

Gordon.

"Corky Scott" > wrote in message
...
> On Thu, 28 Jul 2005 16:08:46 -0400, "Gordon Arnaut"
> > wrote:
>
>>Still, compared to a piston engine, the rotary is a pussy cat when it
>>comes
>>to torsional issues, because it does not have the lever-arm effect of the
>>crankshaft throws to worry about -- which creates the bulk of the
>>torsional
>>flex in a piston engine.
>
> This may not be accurate Gordon. There was a company based up in
> Washington State that produced a planetary gear box as a PSRU for the
> Mazda rotory and they had a HORRENDOUS developmental period with many,
> repeat many broken boxes.
>
> They finally got something that was extremely professional looking as
> machined aluminum can be, and robust and long lived. They had it on
> the front of an RX4 and flew it to various air shows. One of the
> developmental partners was killed in an airplane crash and for a while
> the psru was still available but I don't know if it still is.
>
> The big issue, the one that was busting props and tearing their boxes
> apart was torsional vibration. I remember reading that they claimed
> there was something about the rotory engine that gave it a really
> powerful torque spike.
>
> I think they eventually solved the problem with some kind of cushion
> drive. But for a while it was busting one attempt after another on
> the test stand, and a bunch of dead stick landings.
>
> Corky Scott

Russell Duffy

July 29th 05, 04:51 AM

> I notice that Tracy uses rubber doughnuts between the flywheel and the
> gearbox coupling, just for that reason I would assume.

As I understand it, there are two ways to avoid the resonance issue. One is
to make the drive coupling tighter, and the other is to make it looser.
Powersports chose tighter I believe, and the precision they need could be
why their drive costs $6000. Tracy chose the looser path. Both work fine.
The biggest unknown I face with the single rotor is the resonance frequency,
and how it works with the rubber dampeners that Tracy chose for the two
rotor engine. I may very well have to change the durometer of the rubber
dampeners, but I won't know until I try it.

Cheers,
Rusty

Corky Scott

July 29th 05, 12:46 PM

On Thu, 28 Jul 2005 22:08:10 -0400, "Gordon Arnaut"
> wrote:

>Your story is just another reminder that gearboxes are one of the big
>bugaboos of any auto engine conversion -- and torsional vibration (or
>resonance) is always the culprit. I know that in the Subaru community there
>is not really a box that I would consider completely trustworthy.

Really? Not even Eggenfellner's? I haven't heard of any failures of
his design yet, but I haven't been actively following Subaru
conversions.

Corky Scott

Gordon Arnaut

July 30th 05, 02:31 AM

Yes, the Egg redrive has no failures yet, from what I know.

However, he seems to have taken the "build it strong as hell" approach and
doesn't use any kind of damping, such as elastomers, sprag clutch, etc. He
is also using a heavy flywheel that helps to smooth out the torque spikes.

The result is quite a heavy unit. Still his FWF package is competitive with
Lyc on a power-to-weight basis. Not bad at all.

Regards,

Gordon.

"Corky Scott" > wrote in message
...
> On Thu, 28 Jul 2005 22:08:10 -0400, "Gordon Arnaut"
> > wrote:
>
>>Your story is just another reminder that gearboxes are one of the big
>>bugaboos of any auto engine conversion -- and torsional vibration (or
>>resonance) is always the culprit. I know that in the Subaru community
>>there
>>is not really a box that I would consider completely trustworthy.
>
> Really? Not even Eggenfellner's? I haven't heard of any failures of
> his design yet, but I haven't been actively following Subaru
> conversions.
>
> Corky Scott

jetdesigner

July 30th 05, 06:24 AM

All this talk about the rotary engine.

If they were this great, would there not be at least a couple cars
running them ?
--
Mark Smith
Tri-State Kite Sales
1121 N Locust St
Mt Vernon, IN 47620
1-812-838-6351
http://www.trikite.com
[/QUOTE]

This begs the question, if Connies and Lycs were so great, would there not be at least a couple cars running them? - LOL

Jim Carriere

July 30th 05, 07:06 PM

jetdesigner wrote:
> All this talk about the rotary engine.
>
> If they were this great, would there not be at least a couple cars
> running them ?
> --
>
> This begs the question, if Connies and Lycs were so great, would there
> not be at least a couple cars running them? - LOL

Now THAT is funny (LOL too)

Ernest Christley

July 31st 05, 07:24 PM

jetdesigner wrote:
>
> This begs the question, if Connies and Lycs were so great, would there
> not be at least a couple cars running them? - LOL
>
>

The answer to the question is that the rotaries power curve does not
lend itself well to automobile applications. If you drove around town
at 120mph, it would be another story. In real life, you want to punch
the gas and have your vehicle jump out ahead of oncoming traffic. The
rotary doesn't have that power down low.

Mazda has gone through hell and back to make the rotary work in a car,
but it is an overly complicated mess to deal with. Turbos...adjustable
intake...a ridiculously complicated exhaust system. It's a work of art,
but still barely a decent auto engine.

In the airplane, build an intake tuned to 6000rpm (give or take), build
a stainless steel muffler and your ready to go.

--
This is by far the hardest lesson about freedom. It goes against
instinct, and morality, to just sit back and watch people make
mistakes. We want to help them, which means control them and their
decisions, but in doing so we actually hurt them (and ourselves)."

Charlie

July 31st 05, 08:38 PM

Gordon Arnaut wrote:
> Yes, the Egg redrive has no failures yet, from what I know.
>
> However, he seems to have taken the "build it strong as hell" approach and
> doesn't use any kind of damping, such as elastomers, sprag clutch, etc. He
> is also using a heavy flywheel that helps to smooth out the torque spikes.
>
> The result is quite a heavy unit. Still his FWF package is competitive with
> Lyc on a power-to-weight basis. Not bad at all.
>
>
> Regards,
>
> Gordon.
>
>
> "Corky Scott" > wrote in message
> ...
>
>>On Thu, 28 Jul 2005 22:08:10 -0400, "Gordon Arnaut"
> wrote:
>>
>>
>>>Your story is just another reminder that gearboxes are one of the big
>>>bugaboos of any auto engine conversion -- and torsional vibration (or
>>>resonance) is always the culprit. I know that in the Subaru community
>>>there
>>>is not really a box that I would consider completely trustworthy.
>>
>>Really? Not even Eggenfellner's? I haven't heard of any failures of
>>his design yet, but I haven't been actively following Subaru
>>conversions.
>>
>>Corky Scott
>
>
>
Sorry for coming in a little late on this; I usually frequent the
Flyrotary list & Rusty mentioned that this thread was alive over here.
The non-existent email address is there because I got tired of a steady
diet of spam.

Several things come to mind about the previous few messages in this
thread, from the stuff I've read in about 10 years of following
Powersport, then Tracy Crook's development trials & tribulations. This
is from memory & I never claim to have a good memory. :-)

Gearbox strength for 1rotor vs 2rotor: The big deal about a 1rotor is
that the torque curve actually reverses (goes negative) with a 1 rotor,
like a 4cyl 4stroke piston engine. With a 2 rotor, the torque curve
never actually reverses so the gear box isn't stressed as much in the
torsional resonance dept. even though there's twice the power. If you
frequent Paul Lamar's list I'm sure he will be happy to show you the
torque curve for the 2rotor. IIRC, the torque curve for a 1rotor looks
like a 4cyl piston engine, going negative between each positive torque
peak. If the system resonates & you continue to excite it without
damping the resonance, no amount of strength will keep it from breaking.

The 1st incarnation of Powersport are the guys in the northwest with the
rotary powered RV-4 that had such horrendous torsional resonance
problems *on a dyno*. Current thinking is that they had a problem with
resonance on that particular dyno with that particular engine/dyno
coupling (it was built to test V-8's) They also had severe problems
getting their P-port engine to idle properly. Others have had no problem
at all getting them to idle smoothly. The developers had racing V-8
backgrounds & some of that stuff doesn't transfer well to the rotary.
Their internal tooth ring gear, designed to keep the gearbox 'tight',
like Rusty mentioned, is very heavy, very expensive, & if it isn't heavy
enough will actually loosen up as rpm comes up & the ring gear tries to
stretch. Kind of self-defeating. The 'tight' vs 'loose' issue is really
an issue of moving resonant frequency above the operating rpm range or
moving it below the operating range. 'Tight' moves it up; 'loose' moves
it down. Manual transmission cars are 'loose', moving resonance below
normal operating rpm. You've probably experienced the automotive version
of torsional resonance if you've put a manual trans car in 2nd or 3rd &
let the idling engine try to pull the car. If the engine continues to
run, the car will move forward in big surges. That's the resonant
frequency of the drive train. I don't remember Powersport ever having a
problem with broken props or gearboxes; my memory is that they went
straight from their dyno problems to the big internal spur gear. They
did have a gearbox failure when competing in time-to-climb at SNF
because they were using nitrous & over stressed a bearing in the
gearbox. I think they were producing somewhere between 350-400hp (13B
without turbo) when that happened.

Damping torque pulses with belt slippage: inefficient & produces a lot
of heat.

I think Corky mentioned the nightmare of an intake manifold on RX-7
13B's; fortunately a much simpler & lighter intake works fine for
aircraft since low rpm torque isn't needed.

Eggenfellner: I believe they've recently had the 1st failure of one of
their gearboxes.

Charlie
(Rusty's 'hangar away from home' for the next hurricane)

jetdesigner

August 1st 05, 03:08 AM

"In the airplane, build an intake tuned to 6000rpm (give or take), build
a stainless steel muffler and your ready to go."

You made the point quite well that I was trying to make humorously. The true test of an engine is not whether it powers a car or not. The real issue, does it work well for a given application. If yes, then it is a good engine for that particular application. The rotary does have its applications, not just cars. And yes, it does work well where a constant rpm is desirable.

Using the analogy of "does it work well in a car" is parmount to rating UL engines by "does it work well in a snow mobile". Pretty darn absurd I would say.

Morgans

August 2nd 05, 08:13 AM

"Gordon Arnaut" > wrote

> The advantage of the poly-v over a cogged (synchronous) belt is that they
> naturally dampen torsional spikes, by means of slippage. Another plus is
> that the pulleys can be considerably lighter.

Gordon

Get a clue. Compare efficencies between a cogged belt sized for 100 HP,
and the necessary number of v-belts for the same 100 HP. Next, take that
percentage of power wasted for each, and calculate how much heat will be
produced by each of these two systems.

Should be no problem for a math wiz like yourself.
--
Jim (barking, foaming mad) in NC

First rule of getting out of a hole. Quit digging.

Second rule for getting out of a hole. Leave.

Gordon Arnaut

August 2nd 05, 02:25 PM

Wow. It's the brain-dead moron who took the beating of his life on the wood
species thread and was too chicken to even respond.

Now he's back here, spitting up his usual crap.

This is a pattern with Moron from NC. He jumps in slinging personal attacks
completely unprovoked and yet he doesn't know the first thing about the
subject.

If I was to ask him what the efficiencies are of cogged and poly-v belts
would he be able to give an answer? Of course not. Just watch and see. Yet
here he is badmouthing a person in a most uncalled for manner.

What a pathetic loser. Gets his pathetic little rocks off by jumping on
these lists and acting out some kind of alter ego -- a poser, a
substance-free poser.

Regards,

Gordon.

"Morgans" > wrote in message
...
>
> "Gordon Arnaut" > wrote
>
>> The advantage of the poly-v over a cogged (synchronous) belt is that they
>> naturally dampen torsional spikes, by means of slippage. Another plus is
>> that the pulleys can be considerably lighter.
>
> Gordon
>
> Get a clue. Compare efficencies between a cogged belt sized for 100 HP,
> and the necessary number of v-belts for the same 100 HP. Next, take that
> percentage of power wasted for each, and calculate how much heat will be
> produced by each of these two systems.
>
> Should be no problem for a math wiz like yourself.
> --
> Jim (barking, foaming mad) in NC
>
> First rule of getting out of a hole. Quit digging.
>
> Second rule for getting out of a hole. Leave.
>
>

Gordon Arnaut

August 2nd 05, 02:27 PM

Charlie,

Thanks for the insightful post. What exactly is the source of the torsional
vibration in the rotary? And how does it compare in severity to a piston
engine?

Regards,

Gordon.

"Charlie" > wrote in message
.. .
> Gordon Arnaut wrote:
>> Yes, the Egg redrive has no failures yet, from what I know.
>>
>> However, he seems to have taken the "build it strong as hell" approach
>> and doesn't use any kind of damping, such as elastomers, sprag clutch,
>> etc. He is also using a heavy flywheel that helps to smooth out the
>> torque spikes.
>>
>> The result is quite a heavy unit. Still his FWF package is competitive
>> with Lyc on a power-to-weight basis. Not bad at all.
>>
>>
>> Regards,
>>
>> Gordon.
>>
>>
>> "Corky Scott" > wrote in message
>> ...
>>
>>>On Thu, 28 Jul 2005 22:08:10 -0400, "Gordon Arnaut"
> wrote:
>>>
>>>
>>>>Your story is just another reminder that gearboxes are one of the big
>>>>bugaboos of any auto engine conversion -- and torsional vibration (or
>>>>resonance) is always the culprit. I know that in the Subaru community
>>>>there
>>>>is not really a box that I would consider completely trustworthy.
>>>
>>>Really? Not even Eggenfellner's? I haven't heard of any failures of
>>>his design yet, but I haven't been actively following Subaru
>>>conversions.
>>>
>>>Corky Scott
>>
>>
>>
> Sorry for coming in a little late on this; I usually frequent the
> Flyrotary list & Rusty mentioned that this thread was alive over here. The
> non-existent email address is there because I got tired of a steady diet
> of spam.
>
> Several things come to mind about the previous few messages in this
> thread, from the stuff I've read in about 10 years of following
> Powersport, then Tracy Crook's development trials & tribulations. This is
> from memory & I never claim to have a good memory. :-)
>
> Gearbox strength for 1rotor vs 2rotor: The big deal about a 1rotor is that
> the torque curve actually reverses (goes negative) with a 1 rotor, like a
> 4cyl 4stroke piston engine. With a 2 rotor, the torque curve never
> actually reverses so the gear box isn't stressed as much in the torsional
> resonance dept. even though there's twice the power. If you frequent Paul
> Lamar's list I'm sure he will be happy to show you the torque curve for
> the 2rotor. IIRC, the torque curve for a 1rotor looks like a 4cyl piston
> engine, going negative between each positive torque peak. If the system
> resonates & you continue to excite it without damping the resonance, no
> amount of strength will keep it from breaking.
>
> The 1st incarnation of Powersport are the guys in the northwest with the
> rotary powered RV-4 that had such horrendous torsional resonance problems
> *on a dyno*. Current thinking is that they had a problem with resonance on
> that particular dyno with that particular engine/dyno coupling (it was
> built to test V-8's) They also had severe problems getting their P-port
> engine to idle properly. Others have had no problem at all getting them to
> idle smoothly. The developers had racing V-8 backgrounds & some of that
> stuff doesn't transfer well to the rotary. Their internal tooth ring gear,
> designed to keep the gearbox 'tight', like Rusty mentioned, is very heavy,
> very expensive, & if it isn't heavy enough will actually loosen up as rpm
> comes up & the ring gear tries to stretch. Kind of self-defeating. The
> 'tight' vs 'loose' issue is really an issue of moving resonant frequency
> above the operating rpm range or moving it below the operating range.
> 'Tight' moves it up; 'loose' moves it down. Manual transmission cars are
> 'loose', moving resonance below normal operating rpm. You've probably
> experienced the automotive version of torsional resonance if you've put a
> manual trans car in 2nd or 3rd & let the idling engine try to pull the
> car. If the engine continues to run, the car will move forward in big
> surges. That's the resonant frequency of the drive train. I don't remember
> Powersport ever having a problem with broken props or gearboxes; my memory
> is that they went straight from their dyno problems to the big internal
> spur gear. They did have a gearbox failure when competing in time-to-climb
> at SNF because they were using nitrous & over stressed a bearing in the
> gearbox. I think they were producing somewhere between 350-400hp (13B
> without turbo) when that happened.
>
> Damping torque pulses with belt slippage: inefficient & produces a lot of
> heat.
>
> I think Corky mentioned the nightmare of an intake manifold on RX-7 13B's;
> fortunately a much simpler & lighter intake works fine for aircraft since
> low rpm torque isn't needed.
>
> Eggenfellner: I believe they've recently had the 1st failure of one of
> their gearboxes.
>
> Charlie
> (Rusty's 'hangar away from home' for the next hurricane)
>
>
>

Gordon Arnaut

August 2nd 05, 10:01 PM

Charlie,

I did get some info from Paul Lamar on the rotary list, including some
graphs of torque peaks for the 2-rotor.

However, I just looked at some torque graphs of piston engines and even a
six-cylinder will go below the zero axis into negative territory -- although
the amplitude below zero is less than for a 4-cylinder piston.

Only when you get to an 8-cylinder piston does the wave stop going into
negative territory.

I'm not really clear from Paul's graph whether the 2-rotor goes negative or
not. I would think it does, since Paul describes it as similar to a
6-cylinder piston, in terms of torsional excitation.

It is clear of course that the torque pulses from the single-rotor will be
even more uneven and will go deeper into negative territory.

Still, as you pointed out, the cure to torsional excitation is to dampen it,
not to build a stronger transmission. It should also be noted that one way
to avoid torsional vibration is not to run the engine continuously at the
rpm where excitation occurs (as with the non-counterweighted Lycoming).

With a single-rotor engine, I would think that if you dampen the harmonics
at the offending rpm, you should not need a heavy gearbox designed for the
power of the bigger engine.

Also as far as poly-v belts are concerned, the perception is that they are
not as efficient as cog belts, but this just isn't so. A properly tensioned
poly-v belt is as efficient as a cog belt, between 95 and 98 percent.
(Goodyear and other belt makers have info on this on their websites).

This is as efficient as most gearboxes -- or even slightly better.

Also the system should be properly tensioned so there is no slippage at full
power. The only time slippage will occur is when torsional excitation causes
a big torque pulse. Of course, there is no reason to run the engine at that
rpm anyway (whatever it may be on a rotary, but probably below 2000 rpm).

As far as heat is concerned, both cog belts and poly-v belts generate
similar amounts of heat -- the two or three percent of power that is lost
goes to heat. So does a gearbox.

The belt manufacturers have made great strides in poly-v technology in
recent years. This is definitely not just a bunch of v-belts strung
together.

Regards,

Gordon.

"Charlie" > wrote in message
.. .
> Gordon Arnaut wrote:
>> Yes, the Egg redrive has no failures yet, from what I know.
>>
>> However, he seems to have taken the "build it strong as hell" approach
>> and doesn't use any kind of damping, such as elastomers, sprag clutch,
>> etc. He is also using a heavy flywheel that helps to smooth out the
>> torque spikes.
>>
>> The result is quite a heavy unit. Still his FWF package is competitive
>> with Lyc on a power-to-weight basis. Not bad at all.
>>
>>
>> Regards,
>>
>> Gordon.
>>
>>
>> "Corky Scott" > wrote in message
>> ...
>>
>>>On Thu, 28 Jul 2005 22:08:10 -0400, "Gordon Arnaut"
> wrote:
>>>
>>>
>>>>Your story is just another reminder that gearboxes are one of the big
>>>>bugaboos of any auto engine conversion -- and torsional vibration (or
>>>>resonance) is always the culprit. I know that in the Subaru community
>>>>there
>>>>is not really a box that I would consider completely trustworthy.
>>>
>>>Really? Not even Eggenfellner's? I haven't heard of any failures of
>>>his design yet, but I haven't been actively following Subaru
>>>conversions.
>>>
>>>Corky Scott
>>
>>
>>
> Sorry for coming in a little late on this; I usually frequent the
> Flyrotary list & Rusty mentioned that this thread was alive over here. The
> non-existent email address is there because I got tired of a steady diet
> of spam.
>
> Several things come to mind about the previous few messages in this
> thread, from the stuff I've read in about 10 years of following
> Powersport, then Tracy Crook's development trials & tribulations. This is
> from memory & I never claim to have a good memory. :-)
>
> Gearbox strength for 1rotor vs 2rotor: The big deal about a 1rotor is that
> the torque curve actually reverses (goes negative) with a 1 rotor, like a
> 4cyl 4stroke piston engine. With a 2 rotor, the torque curve never
> actually reverses so the gear box isn't stressed as much in the torsional
> resonance dept. even though there's twice the power. If you frequent Paul
> Lamar's list I'm sure he will be happy to show you the torque curve for
> the 2rotor. IIRC, the torque curve for a 1rotor looks like a 4cyl piston
> engine, going negative between each positive torque peak. If the system
> resonates & you continue to excite it without damping the resonance, no
> amount of strength will keep it from breaking.
>
> The 1st incarnation of Powersport are the guys in the northwest with the
> rotary powered RV-4 that had such horrendous torsional resonance problems
> *on a dyno*. Current thinking is that they had a problem with resonance on
> that particular dyno with that particular engine/dyno coupling (it was
> built to test V-8's) They also had severe problems getting their P-port
> engine to idle properly. Others have had no problem at all getting them to
> idle smoothly. The developers had racing V-8 backgrounds & some of that
> stuff doesn't transfer well to the rotary. Their internal tooth ring gear,
> designed to keep the gearbox 'tight', like Rusty mentioned, is very heavy,
> very expensive, & if it isn't heavy enough will actually loosen up as rpm
> comes up & the ring gear tries to stretch. Kind of self-defeating. The
> 'tight' vs 'loose' issue is really an issue of moving resonant frequency
> above the operating rpm range or moving it below the operating range.
> 'Tight' moves it up; 'loose' moves it down. Manual transmission cars are
> 'loose', moving resonance below normal operating rpm. You've probably
> experienced the automotive version of torsional resonance if you've put a
> manual trans car in 2nd or 3rd & let the idling engine try to pull the
> car. If the engine continues to run, the car will move forward in big
> surges. That's the resonant frequency of the drive train. I don't remember
> Powersport ever having a problem with broken props or gearboxes; my memory
> is that they went straight from their dyno problems to the big internal
> spur gear. They did have a gearbox failure when competing in time-to-climb
> at SNF because they were using nitrous & over stressed a bearing in the
> gearbox. I think they were producing somewhere between 350-400hp (13B
> without turbo) when that happened.
>
> Damping torque pulses with belt slippage: inefficient & produces a lot of
> heat.
>
> I think Corky mentioned the nightmare of an intake manifold on RX-7 13B's;
> fortunately a much simpler & lighter intake works fine for aircraft since
> low rpm torque isn't needed.
>
> Eggenfellner: I believe they've recently had the 1st failure of one of
> their gearboxes.
>
> Charlie
> (Rusty's 'hangar away from home' for the next hurricane)
>
>
>

Ernest Christley

August 4th 05, 03:41 AM

Gordon Arnaut wrote:
> Charlie,
>
> Thanks for the insightful post. What exactly is the source of the torsional
> vibration in the rotary? And how does it compare in severity to a piston
> engine?
>
> Regards,
>
> Gordon.
>

The source is the same as in a piston engine. The fuel/air mixture is
has to be compressed right before it is ignited. The ignited mixture
then only provides power for about 60 degrees of rotation.

The negative peek is very small in the two rotor for two reasons.
First, the 8 to 10 pound rotor plus very large cranshaft provides a
significant flywheel effect. And second, the negative pulse is slightly
overlapped by the postive pulse of the other rotor; eg. the pressure
graph is actually the result of the overlay of the graph from two
independant rotors.

--
This is by far the hardest lesson about freedom. It goes against
instinct, and morality, to just sit back and watch people make
mistakes. We want to help them, which means control them and their
decisions, but in doing so we actually hurt them (and ourselves)."

Ernest Christley

August 4th 05, 03:56 AM

Gordon Arnaut wrote:
>
> Still, as you pointed out, the cure to torsional excitation is to dampen it,
> not to build a stronger transmission. It should also be noted that one way
> to avoid torsional vibration is not to run the engine continuously at the
> rpm where excitation occurs (as with the non-counterweighted Lycoming).

No. The only cure for torsional excitation is the move the system's
harmonic into a range that will only be seen in low power operations and
then won't be used for very long. Tracy's PSRU moved the excitation
range down to between 500 and 800 rpm (working off the top of my head
here, so the numbers may be off). A well tuned rotary will idle in the
900-1000rpm range (prop at about 1/3rd of that).

Dampening doesn't exist. Elasticity in the system may shorten the
peaks, but you'll be left with a fatter mountain. The energy has to go
somewhere. The problem is that you'll still be hitting the shaft at
it's resonant frequency, causing a vibration in it. Each hit adds a
little to the vibration. If you repeatedly hit anything at it's
resonant frequency, each hit will add to the system vibration until it
either wears out very quickly or comes apart catastrophically. That
applies to reduction units, crankshaft, and control surface skins (yes,
flutter is a form of resonant vibration). Adding some elasticity to the
shaft may make the gearbox last longer, but you won't be able to do much
in those few seconds 8*)

Here's someone who says it much better than I:

http://rotaryaviation.com/PSRU%20Zen%20Part%202.html

--
This is by far the hardest lesson about freedom. It goes against
instinct, and morality, to just sit back and watch people make
mistakes. We want to help them, which means control them and their
decisions, but in doing so we actually hurt them (and ourselves)."

Gordon Arnaut

August 7th 05, 02:41 PM

Ernest,

You are right that springs and elastomers do not technically dampen kinetic
energy, they simply store and relase it at a later time (how much later
depends on the frequency at which it is tuned).

However, both springs and elastomers can achieve our objective of clipping
of destructive harmonics if they are tuned to the resonant frequency of the
object that we want to protect from resonance.

Also, fluid dampers do exist for both engines and propellers which actually
do dampen kinetic forces by turning them into heat, just like the shock
absorber on your car.

Drive belts do this as well, including the synchronous (cog) belts which
don't actually slip but which do absorb some energy as heat.

In fact, even a propeller can be tuned efectively to do this, because it is
kind of like a spring -- it flexes at its tips with the power pulses and
then whipsaws back during the lulls. A propeller thus tuned can do the same
thing as a harmonic balancer on an engine.

Of course the trick is in the tuning. More often we are concerned about the
opposite, where they propeller may in fact add to the excitations of the
crankshaft at its resonant frequency. We see this in non-counterweighted
Lycoming four-cylinder engines, which have operating restrictions in certain
rpm ranges.

So when we talk about torsional resonance issues, there are two aspects: one
is the engine itself, and specifically the crankshaft, which shoulders the
torsional forces. The other aspect is what the engine is connected to,
whether a propeller, a gearbox, or both.

We know of course that each object has a natural frequency at which it
resonates -- the point at which external excitations cause harmonics to
build. The object's mass, stiffness and damping determine how it will
respond to an excitation force.

Obviously having smoother excitations -- such as cylinders or rotors firing
at more frequent intervals -- will result in less extreme instantaneous
torque excursions, and the engine will run smoother. Dow that mean it will
be free of torsional vibration? No. Even an electric motor has torsional
vibration because the magnets arranged around its circumference which propel
the rotor are like firing pulses -- a motor with 12 magnets will be smoother
than a motor with two magnets.

However the engine can be as smooth as butter, but if the shaft on which it
is riding is very thin, it will still flex -- and at some point will reach
its resonant frequency, and if left there for the harmonics to build up --
will break.

So that's where mass and stiffness comes into play. Look at tuning forks,
the smaller ones will vibrate at a higher frequency. Even a small excitation
will cause a lot of flex in the thin tuning fork.

It's the same with crankshafts or other shafts -- such as those in a
gearbox, or a propeller -- which are exposed to torsional forces.

For example, most V-8 engines come with a harmonic balancer, even though
they have four power pulses for each crankshaft rotation. That's because
there is enough flex in the crankshaft that the crank can begin to resonate
at some rpm within the operational range.

But look at the four-cylinder Subaru opposed engine. It has never needed a
harmonic balancer. Why? It's crankshaft is quite massive and very stiff, so
its resonant frequency is below the engine's operating range. (It is stiff
because it has five main bearings, so each crank throw is supported by two
main bearings, one on each side; plus the crank journals are quite massive).

Although I'm not yet fully up to speed on the rotary, it is quite clear that
it is similar to the Subaru in that it does not need a torsional dampening
device. That e-shaft is quite rigid and it's throw is short enough that it
will not flex the way a crankshaft will flex. So more stiffness equals a
lower resonating frequency.

So why be concerned with torsional vibration? It's because we are putting a
gearbox and propeller on this engine. Just because the rotary does not
resonate itself does not mean it won't set a gear shaft into resonance.
That's the point of the damping at the engine-gearbox coupling.

When I asked what the source was of torsional issues with the rotary, I did
not have a full grasp of the dynamics with the rotary engine -- until I
watched some helpful animations.

However, as you can see, torsional vibration is not strictly a function of
power pulses. It is a function of the many things inside the engine --
including moments of inertia, stiffness of torque shafts, etc -- plus just
as many variable in whatever it is the engine may be connected to.

Regards,

Gordon.

"Ernest Christley" > wrote in message
. com...
> Gordon Arnaut wrote:
>>
>> Still, as you pointed out, the cure to torsional excitation is to dampen
>> it, not to build a stronger transmission. It should also be noted that
>> one way to avoid torsional vibration is not to run the engine
>> continuously at the rpm where excitation occurs (as with the
>> non-counterweighted Lycoming).
>
> No. The only cure for torsional excitation is the move the system's
> harmonic into a range that will only be seen in low power operations and
> then won't be used for very long. Tracy's PSRU moved the excitation range
> down to between 500 and 800 rpm (working off the top of my head here, so
> the numbers may be off). A well tuned rotary will idle in the 900-1000rpm
> range (prop at about 1/3rd of that).
>
> Dampening doesn't exist. Elasticity in the system may shorten the peaks,
> but you'll be left with a fatter mountain. The energy has to go
> somewhere. The problem is that you'll still be hitting the shaft at it's
> resonant frequency, causing a vibration in it. Each hit adds a little to
> the vibration. If you repeatedly hit anything at it's resonant frequency,
> each hit will add to the system vibration until it either wears out very
> quickly or comes apart catastrophically. That applies to reduction units,
> crankshaft, and control surface skins (yes, flutter is a form of resonant
> vibration). Adding some elasticity to the shaft may make the gearbox last
> longer, but you won't be able to do much in those few seconds 8*)
>
> Here's someone who says it much better than I:
>
> http://rotaryaviation.com/PSRU%20Zen%20Part%202.html
>
>
> --
> This is by far the hardest lesson about freedom. It goes against
> instinct, and morality, to just sit back and watch people make
> mistakes. We want to help them, which means control them and their
> decisions, but in doing so we actually hurt them (and ourselves)."

Jim Carriere

August 7th 05, 07:48 PM

Gordon Arnaut wrote:
> For example, most V-8 engines come with a harmonic balancer, even though
> they have four power pulses for each crankshaft rotation. That's because
> there is enough flex in the crankshaft that the crank can begin to resonate
> at some rpm within the operational range.

Actually, V-8s have a harmonic balancer because they would otherwise
have a first order imbalance. The physics explanation is pretty long
and doesn't make a lot of sense anyway, but it's because the
crankpins are 90 degrees apart (inline fours don't have this
imbalance because the pins are in pairs 180 degrees apart, but they
have second order imbalance instead... that is what a pair of balance
shafts cures) and the mass on the ends of those crankpins (rods and
pistons) flinging around are at different distances along the
crankshaft. Also, the harmonic balancer on a V-8 is two weights, one
on each end of the crankshaft. A lot of people don't realize there
are two weights, not just the one on the front of the engine.

Harmonic dampers are a different animal. They will smooth out power
pulses on any engine configuration. Harmonic balancers have nothing
to do with power pulses and everything to do with complicated
vibration of large pieces of metal moving back and forth in different
directions and different places.

I think the terms balancer and damper are confused with each other
because they look almost the same- a big part attached to the front
of the crankshaft to make the engine smoother.

Ernest Christley

August 7th 05, 09:39 PM

Gordon Arnaut wrote:
> Ernest,
>
> You are right that springs and elastomers do not technically dampen kinetic
> energy, they simply store and relase it at a later time (how much later
> depends on the frequency at which it is tuned).
>
> However, both springs and elastomers can achieve our objective of clipping
> of destructive harmonics if they are tuned to the resonant frequency of the
> object that we want to protect from resonance.
>

You don't listen to or read the work of others, and you like to read
your own writing way to much.

>>http://rotaryaviation.com/PSRU%20Zen%20Part%202.html
>>

--
This is by far the hardest lesson about freedom. It goes against
instinct, and morality, to just sit back and watch people make
mistakes. We want to help them, which means control them and their
decisions, but in doing so we actually hurt them (and ourselves)."

Morgans

August 7th 05, 09:43 PM

"Ernest Christley" > wrote

> You don't listen to or read the work of others, and you like to read
> your own writing way to much.

It's called "The world according to Arnaut."

Ain't it grand? <chuckle>
--
Jim in NC

Richard Lamb

August 7th 05, 11:01 PM

Very impressive, Gordon.
Probably the most understandable description of harmonics and
resonance, and how they can destroy stuff that I've ever seen here.

Thanks

Richard

Bashir

August 8th 05, 03:35 AM

Gordon Arnaut wrote:

> So more stiffness equals a
> lower resonating frequency.

Do you want to think that one through again, Gordon?

Gordon Arnaut

August 8th 05, 03:52 AM

Thanks for pointing out my typo.

As stiffness increases so does the frequency at which it resonates, as we
see on a taut guitar string, or drum, which increase in pitch as they are
tightened.

Regards,

Gordon.

"Bashir" > wrote in message
oups.com...
> Gordon Arnaut wrote:
>
>> So more stiffness equals a
>> lower resonating frequency.
>
> Do you want to think that one through again, Gordon?
>

Gordon Arnaut

August 8th 05, 04:00 AM

Jim,

Yes there is some confusion between a harmonic balancer and damper, but the
device I'm referring to uses an elastomer tuned to a specific frequency to
clip harmonic resonance.

This has nothing to do with balance, which can be addressed in the ways you
mentioned -- counterweights, balance shafts, etc. An engine can make a lot
of vibration and shaking (up and down and side to side) and not have a
problem with torsional resonance.

The opposite is true too -- a very smooth engine can all of a sudden break
its torque shaft from torsional resonance. That's why torsional resonance is
known as the silent killer.

Regards,

Gordon.

"Jim Carriere" > wrote in message
.. .
> Gordon Arnaut wrote:
>> For example, most V-8 engines come with a harmonic balancer, even though
>> they have four power pulses for each crankshaft rotation. That's because
>> there is enough flex in the crankshaft that the crank can begin to
>> resonate at some rpm within the operational range.
>
> Actually, V-8s have a harmonic balancer because they would otherwise have
> a first order imbalance. The physics explanation is pretty long and
> doesn't make a lot of sense anyway, but it's because the crankpins are 90
> degrees apart (inline fours don't have this imbalance because the pins are
> in pairs 180 degrees apart, but they have second order imbalance
> instead... that is what a pair of balance shafts cures) and the mass on
> the ends of those crankpins (rods and pistons) flinging around are at
> different distances along the crankshaft. Also, the harmonic balancer on
> a V-8 is two weights, one on each end of the crankshaft. A lot of people
> don't realize there are two weights, not just the one on the front of the
> engine.
>
> Harmonic dampers are a different animal. They will smooth out power
> pulses on any engine configuration. Harmonic balancers have nothing to do
> with power pulses and everything to do with complicated vibration of large
> pieces of metal moving back and forth in different directions and
> different places.
>
> I think the terms balancer and damper are confused with each other because
> they look almost the same- a big part attached to the front of the
> crankshaft to make the engine smoother.

Bashir

August 8th 05, 04:13 AM

He can be taught!! Who would have thought it!?

Morgans

August 8th 05, 05:06 AM

"Bashir" > wrote in message
oups.com...
> He can be taught!! Who would have thought it!?

Heaven forbid you should have written that what he said was crap! <chuckle>
--
Jim in NC

Gordon Arnaut

August 8th 05, 04:45 PM

Ernest,

I have read Tracy Crook's piece on torsional resonance, even before you
pointed to it.

A couple of thoughts. First, Tracy has devised a good solid gearbox that has
proven itself in service with a respectable number of flight hours.

He is absolutely correct in pointing out that the crankshaft is a spring
mass, as I have said earlier. So is the propeller, and the gear shaft of the
transmission. Any complex piece of machinery is a combination of a number of
spring masses, each with its own resonant characteristics.

But let's back up a little and try to really understand this. I don't think
my earlier explanation was completely satisfactory.

The key thing to understand first is that any object will vibrate if force
acts on it to displace it in some way. In astrophysics we know that the
biggest objects in the universe vibrate, and even the universe itself
vibrates -- and has left a trace of its vibrations as it expanded after the
big bang.

A guitar string vibrates if you displace it with a pick. An engine vibrates
from power pulses. Even an electric motor vibrates from the power pulses of
its magnets.

But vibration is not resonation. Resonation is when an object vibrates at
its particular resonant frequency, at which point the harmonics (which are
vibrations that are integer multiples of the fundamental frequency; the
second harmonic is twice the frequency of the fundamental; the third is
trhree times, etc.) build on top of one another and lead to ever greater
amplitude of the vibration (the string moves back and forth in an ever-wider
arc until it breaks).

We see this in a guitar string when it breaks unexpectedly while we are
tuning it. As we were turning the tuning knob we just happen to hit the
resonant frequency and the string suddenly hear an increae in volume (and a
much richer, almost howling sound) and the vibration of the string gets
visibly bigger unti it snaps.

But if you just try to break that string by turning the knob tighter while
keeping the string perfectly still, you would be surprised how much force it
would take to snap that string in tension. On thicker strings, like on a
bass, you would not have enough strength in your hand to do it, despite the
help from the mechanical advantage of the gear knob.

It's the same thing with a crankshaft, except that the vibration is a
twisting back and forth of the shaft, rather than a swinging side to side
like on a string or a tuning fork.

That crankshaft is going to be vibrating with every power pulse because each
power pulse exterts a force on the lever arm of the crankpin which causes a
twisting of the shaft. And in the split second after the power pulse
subsides, the shaft will swing back twisting back beyond neutral -- just
like a guitar string when you displace it swings to both sides of its
neutral axis as it vibrates.

So the crankshaft will be flexing and vibrating at all times when the engine
is running. Is this bad? No. This has nothing to do with resonance.

Yet this is where all the confusion comes in. An earlier poster pointed out
that V-8 engines use balancers in order to smooth out imbalances and lessen
vibration and shaking. This is desirable because we would all rather have an
engine or any piece of equipment that vibrates less not more.

But this does nothing to address the problem of resonance.

So what causes the crankshaft to get to the point where it starts
resonating? Well, just like our guitar string it needs to be displaced with
enough force and in the right way -- force applied at just the right number
of times per second, or its frequency. Once this is accomplished, the
crankshaft will begin to resonate. It will literally ring like a bell, with
the harmonic notes all coming out and all of them joining together to cause
the amplitude of the vibration to intensify (the crank will begin to twist
back and forth in a wider and wider arc, just like the guitar string going
berserk.)

At some point, the crank cannot twist anymore and it will break.

Now if we were concerned about avoiding this situation how would we proceed?
Well, we know that an object's resonant frequency is related to its mass. If
we make a bigger crankshaft it will resonate at a lower frequency, hoepfully
below the actual operating rpm of the engine.

But this isn't alway possible. Another approach is to make that shaft
stiffer, which will actually increase the shaft's resonant frequency, but
also has a much more important benefit. It now takes much more force to
displace it, or bend it from its neutral axis.

Think of a very thick bass guitar string that is tightened as tight as you
can get it. Now try to pluck that string. You can't get it to vibrate,
because you don't have enough force in your finger to displace it far enough
from its neutral axis that it will vibrate.

So if you can make the crankshaft stiffer, it will take more force to cause
vibration, perhaps more force than the power pulses of the engine will
produce and then resonance can never set in.

So the engine manufacturers do take this into consideration and design
crankshafts that will not fail from resonance. So what's the problem?

Well the problem is when we go to attach something to the engine. And engine
isn't much good unless it is hooked up to something and doing something
useful -- like driving a propeller.

And that's where things get complicated, because now we are adding another
spring mass to the system. We now have two possible problems, either the
engine can set the propeller into resonance, or the propeller can set the
crankshaft into resonance.

And we haven't even got to the gearbox yet. Just the prop and engine is
enough of a problem that each engine and prop must be tested and certified
as a combination. You can't just bolt on any certified prop any certified
engine.

This is also why we see homebuilt aircraft breaking crankshafts or props.

So now when we add a gearbox too, we have multiplied the possible scenarios
that can go wrong. Both the crankshaft and prop are vibrating springs, with
the gearbox in the middle.

What is required is a design approach similar to the powertrain approach
used in auto industry.

However, very few people in the homebuilding community are trained in the
nuances of this particular discipline (including me). So we have people of
various technical abilities trying to tackle this problem in a bootstrap,
eyball engineering kind of way.

For example, Crook talks in his article about how springs in a clutch plate
do not work satisfactorily becuase they would be tuned for only one
frequency, while the engine oeprates over a wide range.

Yes, this is true if you are concerned about elimintaing the harshness of
everyday vibration. But if you want to stop resonance, then all you need to
do is exactly that -- tune the damping device for that one frequency.

Here again we see the issue of harshness and vibration clouding the issue of
resonance.

In any case, it is not an easy problem and the automakers have a lot fo very
thoruoghly trained people working out drivetrain issues for every new
combination of engine and drivetrain -- and they don't even have a prop at
the other end.

Regards,

Gordon.

]
"Ernest Christley" > wrote in message
.com...
> Gordon Arnaut wrote:
>> Ernest,
>>
>> You are right that springs and elastomers do not technically dampen
>> kinetic energy, they simply store and relase it at a later time (how much
>> later depends on the frequency at which it is tuned).
>>
>> However, both springs and elastomers can achieve our objective of
>> clipping of destructive harmonics if they are tuned to the resonant
>> frequency of the object that we want to protect from resonance.
>>
>
>
> You don't listen to or read the work of others, and you like to read your
> own writing way to much.
>
>
>>>http://rotaryaviation.com/PSRU%20Zen%20Part%202.html
>>>
>
>
>
> --
> This is by far the hardest lesson about freedom. It goes against
> instinct, and morality, to just sit back and watch people make
> mistakes. We want to help them, which means control them and their
> decisions, but in doing so we actually hurt them (and ourselves)."

Gordon Arnaut

August 8th 05, 07:16 PM

Just a quick additional note to clarify my point about stiffness.

Stiffness is a restraining force that acts against an excitation force -- as
we see in the taut guitar string. Mass and damping are also restraining
forces.

So it is not just that it takes more force to displace a stiff object enough
to set it to vibrating -- it is technically correct to think of stiffness as
a restraining force.

Also, since we are talking about excitation versus restraint it should be
noted that most discussions of torsional resonance fixate on the engine
power pulses as a source of exciation.

This is quite erroneous because as soon as we add a propeller we have an
object with a very large moment arm and hence inertial mass that can -- and
does -- produce very powerful excitation.

The gearbox itself can also be a source of excitation because it too has
inertia and mass, although far less than a propeller.

Another source of excitation is imbalance. We see this in the
non-counterweighted Lycoming engine in which this imbalance creates enough
of an excitation that, when combined with the excitation of a propeller can
set the crank into resonance, resulting in a broken crank.

It should be added that no piston engine is perfectly balanced. That's why
even a V-8 needs a balancer. On an opposed engine, the opppoosing cylinders
do not balance each other perfectly either because they are not operating on
the same plane. The result is a rocking couple and second order imbalance.

Apparently this is where the rotary has a big advantage because it can be
brought into perfect dynamic balance.

But the important thng to remember is that imbalance is just one of the
excitation forces that can contribute to resonance -- although not usually
in a big way.

Also, it is useful to remember that if you add a gearbox to the engine, the
concern will be with excitations coming from both the engine and prop and
setting a gear shaft into resonance. This is why redrives have such a dismal
record.

Regards,

Gordon.

"Gordon Arnaut" > wrote in message
...
> Ernest,
>
> I have read Tracy Crook's piece on torsional resonance, even before you
> pointed to it.
>
> A couple of thoughts. First, Tracy has devised a good solid gearbox that
> has proven itself in service with a respectable number of flight hours.
>
> He is absolutely correct in pointing out that the crankshaft is a spring
> mass, as I have said earlier. So is the propeller, and the gear shaft of
> the transmission. Any complex piece of machinery is a combination of a
> number of spring masses, each with its own resonant characteristics.
>
> But let's back up a little and try to really understand this. I don't
> think my earlier explanation was completely satisfactory.
>
> The key thing to understand first is that any object will vibrate if force
> acts on it to displace it in some way. In astrophysics we know that the
> biggest objects in the universe vibrate, and even the universe itself
> vibrates -- and has left a trace of its vibrations as it expanded after
> the big bang.
>
> A guitar string vibrates if you displace it with a pick. An engine
> vibrates from power pulses. Even an electric motor vibrates from the power
> pulses of its magnets.
>
> But vibration is not resonation. Resonation is when an object vibrates at
> its particular resonant frequency, at which point the harmonics (which are
> vibrations that are integer multiples of the fundamental frequency; the
> second harmonic is twice the frequency of the fundamental; the third is
> trhree times, etc.) build on top of one another and lead to ever greater
> amplitude of the vibration (the string moves back and forth in an
> ever-wider arc until it breaks).
>
> We see this in a guitar string when it breaks unexpectedly while we are
> tuning it. As we were turning the tuning knob we just happen to hit the
> resonant frequency and the string suddenly hear an increae in volume (and
> a much richer, almost howling sound) and the vibration of the string gets
> visibly bigger unti it snaps.
>
> But if you just try to break that string by turning the knob tighter while
> keeping the string perfectly still, you would be surprised how much force
> it would take to snap that string in tension. On thicker strings, like on
> a bass, you would not have enough strength in your hand to do it, despite
> the help from the mechanical advantage of the gear knob.
>
> It's the same thing with a crankshaft, except that the vibration is a
> twisting back and forth of the shaft, rather than a swinging side to side
> like on a string or a tuning fork.
>
> That crankshaft is going to be vibrating with every power pulse because
> each power pulse exterts a force on the lever arm of the crankpin which
> causes a twisting of the shaft. And in the split second after the power
> pulse subsides, the shaft will swing back twisting back beyond neutral --
> just like a guitar string when you displace it swings to both sides of its
> neutral axis as it vibrates.
>
> So the crankshaft will be flexing and vibrating at all times when the
> engine is running. Is this bad? No. This has nothing to do with resonance.
>
> Yet this is where all the confusion comes in. An earlier poster pointed
> out that V-8 engines use balancers in order to smooth out imbalances and
> lessen vibration and shaking. This is desirable because we would all
> rather have an engine or any piece of equipment that vibrates less not
> more.
>
> But this does nothing to address the problem of resonance.
>
> So what causes the crankshaft to get to the point where it starts
> resonating? Well, just like our guitar string it needs to be displaced
> with enough force and in the right way -- force applied at just the right
> number of times per second, or its frequency. Once this is accomplished,
> the crankshaft will begin to resonate. It will literally ring like a bell,
> with the harmonic notes all coming out and all of them joining together to
> cause the amplitude of the vibration to intensify (the crank will begin to
> twist back and forth in a wider and wider arc, just like the guitar string
> going berserk.)
>
> At some point, the crank cannot twist anymore and it will break.
>
> Now if we were concerned about avoiding this situation how would we
> proceed? Well, we know that an object's resonant frequency is related to
> its mass. If we make a bigger crankshaft it will resonate at a lower
> frequency, hoepfully below the actual operating rpm of the engine.
>
> But this isn't alway possible. Another approach is to make that shaft
> stiffer, which will actually increase the shaft's resonant frequency, but
> also has a much more important benefit. It now takes much more force to
> displace it, or bend it from its neutral axis.
>
> Think of a very thick bass guitar string that is tightened as tight as you
> can get it. Now try to pluck that string. You can't get it to vibrate,
> because you don't have enough force in your finger to displace it far
> enough from its neutral axis that it will vibrate.
>
> So if you can make the crankshaft stiffer, it will take more force to
> cause vibration, perhaps more force than the power pulses of the engine
> will produce and then resonance can never set in.
>
> So the engine manufacturers do take this into consideration and design
> crankshafts that will not fail from resonance. So what's the problem?
>
> Well the problem is when we go to attach something to the engine. And
> engine isn't much good unless it is hooked up to something and doing
> something useful -- like driving a propeller.
>
> And that's where things get complicated, because now we are adding another
> spring mass to the system. We now have two possible problems, either the
> engine can set the propeller into resonance, or the propeller can set the
> crankshaft into resonance.
>
> And we haven't even got to the gearbox yet. Just the prop and engine is
> enough of a problem that each engine and prop must be tested and certified
> as a combination. You can't just bolt on any certified prop any certified
> engine.
>
> This is also why we see homebuilt aircraft breaking crankshafts or props.
>
> So now when we add a gearbox too, we have multiplied the possible
> scenarios that can go wrong. Both the crankshaft and prop are vibrating
> springs, with the gearbox in the middle.
>
> What is required is a design approach similar to the powertrain approach
> used in auto industry.
>
> However, very few people in the homebuilding community are trained in the
> nuances of this particular discipline (including me). So we have people of
> various technical abilities trying to tackle this problem in a bootstrap,
> eyball engineering kind of way.
>
> For example, Crook talks in his article about how springs in a clutch
> plate do not work satisfactorily becuase they would be tuned for only one
> frequency, while the engine oeprates over a wide range.
>
> Yes, this is true if you are concerned about elimintaing the harshness of
> everyday vibration. But if you want to stop resonance, then all you need
> to do is exactly that -- tune the damping device for that one frequency.
>
> Here again we see the issue of harshness and vibration clouding the issue
> of resonance.
>
> In any case, it is not an easy problem and the automakers have a lot fo
> very thoruoghly trained people working out drivetrain issues for every new
> combination of engine and drivetrain -- and they don't even have a prop at
> the other end.
>
> Regards,
>
> Gordon.
>
>
>
>
> ]
> "Ernest Christley" > wrote in message
> .com...
>> Gordon Arnaut wrote:
>>> Ernest,
>>>
>>> You are right that springs and elastomers do not technically dampen
>>> kinetic energy, they simply store and relase it at a later time (how
>>> much later depends on the frequency at which it is tuned).
>>>
>>> However, both springs and elastomers can achieve our objective of
>>> clipping of destructive harmonics if they are tuned to the resonant
>>> frequency of the object that we want to protect from resonance.
>>>
>>
>>
>> You don't listen to or read the work of others, and you like to read your
>> own writing way to much.
>>
>>
>>>>http://rotaryaviation.com/PSRU%20Zen%20Part%202.html
>>>>
>>
>>
>>
>> --
>> This is by far the hardest lesson about freedom. It goes against
>> instinct, and morality, to just sit back and watch people make
>> mistakes. We want to help them, which means control them and their
>> decisions, but in doing so we actually hurt them (and ourselves)."
>
>

Richard Lamb

August 9th 05, 12:53 AM

Well, MY last post on this subject was accused of being pornography...

Some people have NO sense of humor

Richard

Gordon Arnaut

August 9th 05, 02:09 AM

Thanks for the generous words, Richard.

Keep in mind I'm not an expert in this field, but this process of thinking
the issues through logically is also helping me to understand things better.

I may well be wrong on some points, and I encourage those with more
experience in this field to chip in and make corrections or contributions.

Regards,

Gordon.

"Richard Lamb" > wrote in message
oups.com...
> Very impressive, Gordon.
> Probably the most understandable description of harmonics and
> resonance, and how they can destroy stuff that I've ever seen here.
>
> Thanks
>
> Richard
>

Gordon Arnaut

August 9th 05, 02:18 AM

Just one more post script about the Lycoming engine. It's interesting to
note that it is the prop that is the source of the excitations that set the
crankshaft into resonance.

The fact that the engine lacks counterweights (unbalanced) does not hurt it
one bit -- except for the unpleasantness of the shaking.

However, when you add the spring mass of that heavy prop, then that is
enough to set the crank into resonance, but only at a certain rpm -- between
2000 rpm and 2300 rpm, approximately, and only if run there for some length
of time to let the resonance build up.

It's interesting also that the problem can be solved by two ways, either
adding balance weights to the crankshafts, which some models of the same
engine employ, or using a lighter prop, like the two-blade MT, which is
STC'd without rpm restrictions.

So we see plainly that the resonance problem is not just an issue of engine
firing pulses, which is what a lot discussion seems to fixate upon.

Regards,

Gordon.

"Gordon Arnaut" > wrote in message
...
> Just a quick additional note to clarify my point about stiffness.
>
> Stiffness is a restraining force that acts against an excitation force --
> as we see in the taut guitar string. Mass and damping are also restraining
> forces.
>
> So it is not just that it takes more force to displace a stiff object
> enough to set it to vibrating -- it is technically correct to think of
> stiffness as a restraining force.
>
> Also, since we are talking about excitation versus restraint it should be
> noted that most discussions of torsional resonance fixate on the engine
> power pulses as a source of exciation.
>
> This is quite erroneous because as soon as we add a propeller we have an
> object with a very large moment arm and hence inertial mass that can --
> and does -- produce very powerful excitation.
>
> The gearbox itself can also be a source of excitation because it too has
> inertia and mass, although far less than a propeller.
>
> Another source of excitation is imbalance. We see this in the
> non-counterweighted Lycoming engine in which this imbalance creates enough
> of an excitation that, when combined with the excitation of a propeller
> can set the crank into resonance, resulting in a broken crank.
>
> It should be added that no piston engine is perfectly balanced. That's why
> even a V-8 needs a balancer. On an opposed engine, the opppoosing
> cylinders do not balance each other perfectly either because they are not
> operating on the same plane. The result is a rocking couple and second
> order imbalance.
>
> Apparently this is where the rotary has a big advantage because it can be
> brought into perfect dynamic balance.
>
> But the important thng to remember is that imbalance is just one of the
> excitation forces that can contribute to resonance -- although not usually
> in a big way.
>
> Also, it is useful to remember that if you add a gearbox to the engine,
> the concern will be with excitations coming from both the engine and prop
> and setting a gear shaft into resonance. This is why redrives have such a
> dismal record.
>
> Regards,
>
> Gordon.
>
>
>
>
> "Gordon Arnaut" > wrote in message
> ...
>> Ernest,
>>
>> I have read Tracy Crook's piece on torsional resonance, even before you
>> pointed to it.
>>
>> A couple of thoughts. First, Tracy has devised a good solid gearbox that
>> has proven itself in service with a respectable number of flight hours.
>>
>> He is absolutely correct in pointing out that the crankshaft is a spring
>> mass, as I have said earlier. So is the propeller, and the gear shaft of
>> the transmission. Any complex piece of machinery is a combination of a
>> number of spring masses, each with its own resonant characteristics.
>>
>> But let's back up a little and try to really understand this. I don't
>> think my earlier explanation was completely satisfactory.
>>
>> The key thing to understand first is that any object will vibrate if
>> force acts on it to displace it in some way. In astrophysics we know that
>> the biggest objects in the universe vibrate, and even the universe itself
>> vibrates -- and has left a trace of its vibrations as it expanded after
>> the big bang.
>>
>> A guitar string vibrates if you displace it with a pick. An engine
>> vibrates from power pulses. Even an electric motor vibrates from the
>> power pulses of its magnets.
>>
>> But vibration is not resonation. Resonation is when an object vibrates at
>> its particular resonant frequency, at which point the harmonics (which
>> are vibrations that are integer multiples of the fundamental frequency;
>> the second harmonic is twice the frequency of the fundamental; the third
>> is trhree times, etc.) build on top of one another and lead to ever
>> greater amplitude of the vibration (the string moves back and forth in an
>> ever-wider arc until it breaks).
>>
>> We see this in a guitar string when it breaks unexpectedly while we are
>> tuning it. As we were turning the tuning knob we just happen to hit the
>> resonant frequency and the string suddenly hear an increae in volume (and
>> a much richer, almost howling sound) and the vibration of the string gets
>> visibly bigger unti it snaps.
>>
>> But if you just try to break that string by turning the knob tighter
>> while keeping the string perfectly still, you would be surprised how much
>> force it would take to snap that string in tension. On thicker strings,
>> like on a bass, you would not have enough strength in your hand to do it,
>> despite the help from the mechanical advantage of the gear knob.
>>
>> It's the same thing with a crankshaft, except that the vibration is a
>> twisting back and forth of the shaft, rather than a swinging side to side
>> like on a string or a tuning fork.
>>
>> That crankshaft is going to be vibrating with every power pulse because
>> each power pulse exterts a force on the lever arm of the crankpin which
>> causes a twisting of the shaft. And in the split second after the power
>> pulse subsides, the shaft will swing back twisting back beyond neutral --
>> just like a guitar string when you displace it swings to both sides of
>> its neutral axis as it vibrates.
>>
>> So the crankshaft will be flexing and vibrating at all times when the
>> engine is running. Is this bad? No. This has nothing to do with
>> resonance.
>>
>> Yet this is where all the confusion comes in. An earlier poster pointed
>> out that V-8 engines use balancers in order to smooth out imbalances and
>> lessen vibration and shaking. This is desirable because we would all
>> rather have an engine or any piece of equipment that vibrates less not
>> more.
>>
>> But this does nothing to address the problem of resonance.
>>
>> So what causes the crankshaft to get to the point where it starts
>> resonating? Well, just like our guitar string it needs to be displaced
>> with enough force and in the right way -- force applied at just the right
>> number of times per second, or its frequency. Once this is accomplished,
>> the crankshaft will begin to resonate. It will literally ring like a
>> bell, with the harmonic notes all coming out and all of them joining
>> together to cause the amplitude of the vibration to intensify (the crank
>> will begin to twist back and forth in a wider and wider arc, just like
>> the guitar string going berserk.)
>>
>> At some point, the crank cannot twist anymore and it will break.
>>
>> Now if we were concerned about avoiding this situation how would we
>> proceed? Well, we know that an object's resonant frequency is related to
>> its mass. If we make a bigger crankshaft it will resonate at a lower
>> frequency, hoepfully below the actual operating rpm of the engine.
>>
>> But this isn't alway possible. Another approach is to make that shaft
>> stiffer, which will actually increase the shaft's resonant frequency, but
>> also has a much more important benefit. It now takes much more force to
>> displace it, or bend it from its neutral axis.
>>
>> Think of a very thick bass guitar string that is tightened as tight as
>> you can get it. Now try to pluck that string. You can't get it to
>> vibrate, because you don't have enough force in your finger to displace
>> it far enough from its neutral axis that it will vibrate.
>>
>> So if you can make the crankshaft stiffer, it will take more force to
>> cause vibration, perhaps more force than the power pulses of the engine
>> will produce and then resonance can never set in.
>>
>> So the engine manufacturers do take this into consideration and design
>> crankshafts that will not fail from resonance. So what's the problem?
>>
>> Well the problem is when we go to attach something to the engine. And
>> engine isn't much good unless it is hooked up to something and doing
>> something useful -- like driving a propeller.
>>
>> And that's where things get complicated, because now we are adding
>> another spring mass to the system. We now have two possible problems,
>> either the engine can set the propeller into resonance, or the propeller
>> can set the crankshaft into resonance.
>>
>> And we haven't even got to the gearbox yet. Just the prop and engine is
>> enough of a problem that each engine and prop must be tested and
>> certified as a combination. You can't just bolt on any certified prop any
>> certified engine.
>>
>> This is also why we see homebuilt aircraft breaking crankshafts or props.
>>
>> So now when we add a gearbox too, we have multiplied the possible
>> scenarios that can go wrong. Both the crankshaft and prop are vibrating
>> springs, with the gearbox in the middle.
>>
>> What is required is a design approach similar to the powertrain approach
>> used in auto industry.
>>
>> However, very few people in the homebuilding community are trained in the
>> nuances of this particular discipline (including me). So we have people
>> of various technical abilities trying to tackle this problem in a
>> bootstrap, eyball engineering kind of way.
>>
>> For example, Crook talks in his article about how springs in a clutch
>> plate do not work satisfactorily becuase they would be tuned for only one
>> frequency, while the engine oeprates over a wide range.
>>
>> Yes, this is true if you are concerned about elimintaing the harshness of
>> everyday vibration. But if you want to stop resonance, then all you need
>> to do is exactly that -- tune the damping device for that one frequency.
>>
>> Here again we see the issue of harshness and vibration clouding the issue
>> of resonance.
>>
>> In any case, it is not an easy problem and the automakers have a lot fo
>> very thoruoghly trained people working out drivetrain issues for every
>> new combination of engine and drivetrain -- and they don't even have a
>> prop at the other end.
>>
>> Regards,
>>
>> Gordon.
>>
>>
>>
>>
>> ]
>> "Ernest Christley" > wrote in message
>> .com...
>>> Gordon Arnaut wrote:
>>>> Ernest,
>>>>
>>>> You are right that springs and elastomers do not technically dampen
>>>> kinetic energy, they simply store and relase it at a later time (how
>>>> much later depends on the frequency at which it is tuned).
>>>>
>>>> However, both springs and elastomers can achieve our objective of
>>>> clipping of destructive harmonics if they are tuned to the resonant
>>>> frequency of the object that we want to protect from resonance.
>>>>
>>>
>>>
>>> You don't listen to or read the work of others, and you like to read
>>> your own writing way to much.
>>>
>>>
>>>>>http://rotaryaviation.com/PSRU%20Zen%20Part%202.html
>>>>>
>>>
>>>
>>>
>>> --
>>> This is by far the hardest lesson about freedom. It goes against
>>> instinct, and morality, to just sit back and watch people make
>>> mistakes. We want to help them, which means control them and their
>>> decisions, but in doing so we actually hurt them (and ourselves)."
>>
>>
>
>

Ernest Christley

August 10th 05, 04:52 AM

Gordon Arnaut wrote:
> Just one more post script about the Lycoming engine. It's interesting to
> note that it is the prop that is the source of the excitations that set the
> crankshaft into resonance.

Just like it is the wheels that push an engine around so that the car
can move.

--
This is by far the hardest lesson about freedom. It goes against
instinct, and morality, to just sit back and watch people make
mistakes. We want to help them, which means control them and their
decisions, but in doing so we actually hurt them (and ourselves)."

Ernest Christley

August 10th 05, 05:06 AM

Gordon Arnaut wrote:
> A couple of thoughts. First, Tracy has devised a good solid gearbox that has
> proven itself in service with a respectable number of flight hours.
>

That should be and indication to you to shut up and learn from your elders.

>
> But let's back up a little and try to really understand this. I don't think
> my earlier explanation was completely satisfactory.
>

Now your getting it.

> The key thing to understand first is that any object will vibrate if force
> acts on it to displace it in some way. In astrophysics we know that the
> biggest objects in the universe vibrate, and even the universe itself
> vibrates -- and has left a trace of its vibrations as it expanded after the
> big bang.
>

So, is the goal here to talk gibberish about as many subjects as
possible in the forlorn hope that there is an outside chance that you
might be right about SOMETHING!!

> A guitar string vibrates if you displace it with a pick. An engine vibrates
> from power pulses. Even an electric motor vibrates from the power pulses of
> its magnets.
>
> But vibration is not resonation.

Case in point. You obviously have no idea what you're talking about.
You read a science book once in high school and now consider yourself a
scholar. Here's a clue. Resonation requires TWO objects. You need
something to vibrate, and something to cause the vibration.

from: http://en.wikipedia.org/wiki/Resonate

In physics, resonance is an increase in the oscillatory energy absorbed
by a system when the frequency of the oscillations matches the system's
natural frequency of vibration (its resonant frequency).

> That crankshaft is going to be vibrating with every power pulse because each
> power pulse exterts a force on the lever arm of the crankpin which causes a
> twisting of the shaft. And in the split second after the power pulse
> subsides, the shaft will swing back twisting back beyond neutral -- just
> like a guitar string when you displace it swings to both sides of its
> neutral axis as it vibrates.

So close, yet so far away. If you'd shut up and read what you wrote up
to this point, you might get it. Dampeners do nothing to help the
destruction of an engine that is running at its resonant frequency.
They lower the harshness of the pulses, but the point of resonancy is
that the energy from each pulse is stored in the system until the next
pulse arrives. So you get 3sec run time vs 0.3sec? Big whup!

--
This is by far the hardest lesson about freedom. It goes against
instinct, and morality, to just sit back and watch people make
mistakes. We want to help them, which means control them and their
decisions, but in doing so we actually hurt them (and ourselves)."

Gordon Arnaut

August 10th 05, 02:39 PM

Ernest,

First off all, I described resonance perfectly accurately: You just pulled
out an encyclopedia definition that worded it another way and said exactly
what I said, that an object will resonate at its natural frequency, which
causes its oscillations to increase in amplitude.

Your saying that I am wrong is simply not true, and shows that you are
simply acting out of spite -- as demonstrated by the bitter and combative
tone of your message.

Just for the record, my discussion of resonance in engines is light years
beyond your silly encyclopedia blurb.

I explained that in order to understand resonance, it is useful to think in
terms of excitation forces -- power pulses, imbalance and outside spring
mass systems, such as a propeller, for example -- and restraining forces,
such as mass, stiffness and dampening.

You are wrong on several fundamental points: first, a damper is a
restraingin force and will do just that, it will dampen the oscillations
resulting from resonation. It does this by clipping the harmonics, which are
what cause the amplitutde of the oscillations to grow.

A damper can be a spring or an elastomer tuned to the resonant frequency, or
even a flywheel, which relies on inertia to dampen the oscillations. A sprag
clutch which allows freedom of movement in one direction but not the other,
also clips oscillations. All of these dampers work by counteracting the
energy of the harmonics. Without the energy of the harmonics, the
oscillations cannot increase.

Point blank question: Are you are saying that if you bring an object to
resonance, there is nothing that damping can do to restrain the
oscillations? I am asking again because that is exactly what you said. I
just want to confirm because this is an elementary point of understanding
resonance and if you don't understand this, then...well, I think we can draw
our own conclusions...

Also plain wrong is that resonance requires two objects. Resonance requres
only one object and an excitation force acting on it. Period. An object is
not a force.

Also, I see now that your are unable to discuss politely --throwing around
personal insults like confetti. Nice. Also, what right do you have to demand
that I "shut up?" Why don't you shut up?

Regards,

Gordon.

"Ernest Christley" > wrote in message
.com...
> Gordon Arnaut wrote:
>> A couple of thoughts. First, Tracy has devised a good solid gearbox that
>> has proven itself in service with a respectable number of flight hours.
>>
>
> That should be and indication to you to shut up and learn from your
> elders.
>
>>
>> But let's back up a little and try to really understand this. I don't
>> think my earlier explanation was completely satisfactory.
>>
>
> Now your getting it.
>
>> The key thing to understand first is that any object will vibrate if
>> force acts on it to displace it in some way. In astrophysics we know that
>> the biggest objects in the universe vibrate, and even the universe itself
>> vibrates -- and has left a trace of its vibrations as it expanded after
>> the big bang.
>>
>
> So, is the goal here to talk gibberish about as many subjects as possible
> in the forlorn hope that there is an outside chance that you might be
> right about SOMETHING!!
>
>> A guitar string vibrates if you displace it with a pick. An engine
>> vibrates from power pulses. Even an electric motor vibrates from the
>> power pulses of its magnets.
>>
>> But vibration is not resonation.
>
> Case in point. You obviously have no idea what you're talking about. You
> read a science book once in high school and now consider yourself a
> scholar. Here's a clue. Resonation requires TWO objects. You need
> something to vibrate, and something to cause the vibration.
>
> from: http://en.wikipedia.org/wiki/Resonate
>
> In physics, resonance is an increase in the oscillatory energy absorbed by
> a system when the frequency of the oscillations matches the system's
> natural frequency of vibration (its resonant frequency).
>
>
>> That crankshaft is going to be vibrating with every power pulse because
>> each power pulse exterts a force on the lever arm of the crankpin which
>> causes a twisting of the shaft. And in the split second after the power
>> pulse subsides, the shaft will swing back twisting back beyond neutral --
>> just like a guitar string when you displace it swings to both sides of
>> its neutral axis as it vibrates.
>
> So close, yet so far away. If you'd shut up and read what you wrote up to
> this point, you might get it. Dampeners do nothing to help the
> destruction of an engine that is running at its resonant frequency. They
> lower the harshness of the pulses, but the point of resonancy is that the
> energy from each pulse is stored in the system until the next pulse
> arrives. So you get 3sec run time vs 0.3sec? Big whup!
>
> --
> This is by far the hardest lesson about freedom. It goes against
> instinct, and morality, to just sit back and watch people make
> mistakes. We want to help them, which means control them and their
> decisions, but in doing so we actually hurt them (and ourselves)."

Gordon Arnaut

August 10th 05, 02:53 PM

Just one more note, about Ernest's talk of an engine "running at its
resonant frequency."

Just where do we see engine's running at their resonant frequency? I have to
wonder because if you are driving down the highway and holding a steady
rpm -- perhaps with the aid of cruise control -- I think you will want to be
sure not to run at this "resonant frequency."

How laughable. If this were true there would be cars beside the highway
every couple of miles or so.

The fact is that engines are designed not to resonate. Designers do this by
taking into account excitation forces and applying countering restraining
forces.

Mathematically the relationship is represented by :
M a + D v + K x = Me ² e sin( t - )

For simplification, the above equation can be written as:
Mass term + Damping term + Stiffness Term = Restraining Force

The restraining forces, represented by the various terms in the equation,
are what determines how a rotor behaves throughout its operating range. Any
excitation force, such as imbalance, is always in equilibrium with the
restraining forces of mass, damping, and stiffness. The amount of measured
vibration, as a result of these combined forces, will depend upon the
combined effect of all three terms in the equation.

Regards,

Gordon.

"Gordon Arnaut" > wrote in message
...
> Ernest,
>
> First off all, I described resonance perfectly accurately: You just pulled
> out an encyclopedia definition that worded it another way and said exactly
> what I said, that an object will resonate at its natural frequency, which
> causes its oscillations to increase in amplitude.
>
> Your saying that I am wrong is simply not true, and shows that you are
> simply acting out of spite -- as demonstrated by the bitter and combative
> tone of your message.
>
> Just for the record, my discussion of resonance in engines is light years
> beyond your silly encyclopedia blurb.
>
> I explained that in order to understand resonance, it is useful to think
> in terms of excitation forces -- power pulses, imbalance and outside
> spring mass systems, such as a propeller, for example -- and restraining
> forces, such as mass, stiffness and dampening.
>
> You are wrong on several fundamental points: first, a damper is a
> restraingin force and will do just that, it will dampen the oscillations
> resulting from resonation. It does this by clipping the harmonics, which
> are what cause the amplitutde of the oscillations to grow.
>
> A damper can be a spring or an elastomer tuned to the resonant frequency,
> or even a flywheel, which relies on inertia to dampen the oscillations. A
> sprag clutch which allows freedom of movement in one direction but not the
> other, also clips oscillations. All of these dampers work by counteracting
> the energy of the harmonics. Without the energy of the harmonics, the
> oscillations cannot increase.
>
> Point blank question: Are you are saying that if you bring an object to
> resonance, there is nothing that damping can do to restrain the
> oscillations? I am asking again because that is exactly what you said. I
> just want to confirm because this is an elementary point of understanding
> resonance and if you don't understand this, then...well, I think we can
> draw our own conclusions...
>
> Also plain wrong is that resonance requires two objects. Resonance requres
> only one object and an excitation force acting on it. Period. An object is
> not a force.
>
> Also, I see now that your are unable to discuss politely --throwing around
> personal insults like confetti. Nice. Also, what right do you have to
> demand that I "shut up?" Why don't you shut up?
>
> Regards,
>
> Gordon.
>
>
>
>
> "Ernest Christley" > wrote in message
> .com...
>> Gordon Arnaut wrote:
>>> A couple of thoughts. First, Tracy has devised a good solid gearbox that
>>> has proven itself in service with a respectable number of flight hours.
>>>
>>
>> That should be and indication to you to shut up and learn from your
>> elders.
>>
>>>
>>> But let's back up a little and try to really understand this. I don't
>>> think my earlier explanation was completely satisfactory.
>>>
>>
>> Now your getting it.
>>
>>> The key thing to understand first is that any object will vibrate if
>>> force acts on it to displace it in some way. In astrophysics we know
>>> that the biggest objects in the universe vibrate, and even the universe
>>> itself vibrates -- and has left a trace of its vibrations as it expanded
>>> after the big bang.
>>>
>>
>> So, is the goal here to talk gibberish about as many subjects as possible
>> in the forlorn hope that there is an outside chance that you might be
>> right about SOMETHING!!
>>
>>> A guitar string vibrates if you displace it with a pick. An engine
>>> vibrates from power pulses. Even an electric motor vibrates from the
>>> power pulses of its magnets.
>>>
>>> But vibration is not resonation.
>>
>> Case in point. You obviously have no idea what you're talking about. You
>> read a science book once in high school and now consider yourself a
>> scholar. Here's a clue. Resonation requires TWO objects. You need
>> something to vibrate, and something to cause the vibration.
>>
>> from: http://en.wikipedia.org/wiki/Resonate
>>
>> In physics, resonance is an increase in the oscillatory energy absorbed
>> by a system when the frequency of the oscillations matches the system's
>> natural frequency of vibration (its resonant frequency).
>>
>>
>>> That crankshaft is going to be vibrating with every power pulse because
>>> each power pulse exterts a force on the lever arm of the crankpin which
>>> causes a twisting of the shaft. And in the split second after the power
>>> pulse subsides, the shaft will swing back twisting back beyond
>>> neutral -- just like a guitar string when you displace it swings to
>>> both sides of its neutral axis as it vibrates.
>>
>> So close, yet so far away. If you'd shut up and read what you wrote up
>> to this point, you might get it. Dampeners do nothing to help the
>> destruction of an engine that is running at its resonant frequency. They
>> lower the harshness of the pulses, but the point of resonancy is that the
>> energy from each pulse is stored in the system until the next pulse
>> arrives. So you get 3sec run time vs 0.3sec? Big whup!
>>
>> --
>> This is by far the hardest lesson about freedom. It goes against
>> instinct, and morality, to just sit back and watch people make
>> mistakes. We want to help them, which means control them and their
>> decisions, but in doing so we actually hurt them (and ourselves)."
>
>

Gordon Arnaut

August 10th 05, 03:00 PM

And just one more thing.

I said previously that auto designers take resonance into account and design
powertrain systems not to resonate. They do this by applying restraining
forces as I mentioned in my previous message.

The key thing for us in the amateur-built aircraft community is that we are
putting together a powertrain piecemel. We take an auto engine, a prop, a
gearbox and put them all together. Sometimes this can result in resonation
of one or more pieces in the system.

What I have been doing is just trying to think through the problem and apply
known facts about resonance and known design principles.

Regards,

Gordon.

"Gordon Arnaut" > wrote in message
...
> Just one more note, about Ernest's talk of an engine "running at its
> resonant frequency."
>
> Just where do we see engine's running at their resonant frequency? I have
> to wonder because if you are driving down the highway and holding a steady
> rpm -- perhaps with the aid of cruise control -- I think you will want to
> be sure not to run at this "resonant frequency."
>
> How laughable. If this were true there would be cars beside the highway
> every couple of miles or so.
>
> The fact is that engines are designed not to resonate. Designers do this
> by taking into account excitation forces and applying countering
> restraining forces.
>
> Mathematically the relationship is represented by :
> M a + D v + K x = Me ² e sin( t - )
>
> For simplification, the above equation can be written as:
> Mass term + Damping term + Stiffness Term = Restraining Force
>
> The restraining forces, represented by the various terms in the equation,
> are what determines how a rotor behaves throughout its operating range.
> Any excitation force, such as imbalance, is always in equilibrium with the
> restraining forces of mass, damping, and stiffness. The amount of measured
> vibration, as a result of these combined forces, will depend upon the
> combined effect of all three terms in the equation.
>
> Regards,
>
> Gordon.
>
>
>
> "Gordon Arnaut" > wrote in message
> ...
>> Ernest,
>>
>> First off all, I described resonance perfectly accurately: You just
>> pulled out an encyclopedia definition that worded it another way and said
>> exactly what I said, that an object will resonate at its natural
>> frequency, which causes its oscillations to increase in amplitude.
>>
>> Your saying that I am wrong is simply not true, and shows that you are
>> simply acting out of spite -- as demonstrated by the bitter and combative
>> tone of your message.
>>
>> Just for the record, my discussion of resonance in engines is light years
>> beyond your silly encyclopedia blurb.
>>
>> I explained that in order to understand resonance, it is useful to think
>> in terms of excitation forces -- power pulses, imbalance and outside
>> spring mass systems, such as a propeller, for example -- and restraining
>> forces, such as mass, stiffness and dampening.
>>
>> You are wrong on several fundamental points: first, a damper is a
>> restraingin force and will do just that, it will dampen the oscillations
>> resulting from resonation. It does this by clipping the harmonics, which
>> are what cause the amplitutde of the oscillations to grow.
>>
>> A damper can be a spring or an elastomer tuned to the resonant frequency,
>> or even a flywheel, which relies on inertia to dampen the oscillations. A
>> sprag clutch which allows freedom of movement in one direction but not
>> the other, also clips oscillations. All of these dampers work by
>> counteracting the energy of the harmonics. Without the energy of the
>> harmonics, the oscillations cannot increase.
>>
>> Point blank question: Are you are saying that if you bring an object to
>> resonance, there is nothing that damping can do to restrain the
>> oscillations? I am asking again because that is exactly what you said. I
>> just want to confirm because this is an elementary point of understanding
>> resonance and if you don't understand this, then...well, I think we can
>> draw our own conclusions...
>>
>> Also plain wrong is that resonance requires two objects. Resonance
>> requres only one object and an excitation force acting on it. Period. An
>> object is not a force.
>>
>> Also, I see now that your are unable to discuss politely --throwing
>> around personal insults like confetti. Nice. Also, what right do you have
>> to demand that I "shut up?" Why don't you shut up?
>>
>> Regards,
>>
>> Gordon.
>>
>>
>>
>>
>> "Ernest Christley" > wrote in message
>> .com...
>>> Gordon Arnaut wrote:
>>>> A couple of thoughts. First, Tracy has devised a good solid gearbox
>>>> that has proven itself in service with a respectable number of flight
>>>> hours.
>>>>
>>>
>>> That should be and indication to you to shut up and learn from your
>>> elders.
>>>
>>>>
>>>> But let's back up a little and try to really understand this. I don't
>>>> think my earlier explanation was completely satisfactory.
>>>>
>>>
>>> Now your getting it.
>>>
>>>> The key thing to understand first is that any object will vibrate if
>>>> force acts on it to displace it in some way. In astrophysics we know
>>>> that the biggest objects in the universe vibrate, and even the universe
>>>> itself vibrates -- and has left a trace of its vibrations as it
>>>> expanded after the big bang.
>>>>
>>>
>>> So, is the goal here to talk gibberish about as many subjects as
>>> possible in the forlorn hope that there is an outside chance that you
>>> might be right about SOMETHING!!
>>>
>>>> A guitar string vibrates if you displace it with a pick. An engine
>>>> vibrates from power pulses. Even an electric motor vibrates from the
>>>> power pulses of its magnets.
>>>>
>>>> But vibration is not resonation.
>>>
>>> Case in point. You obviously have no idea what you're talking about.
>>> You read a science book once in high school and now consider yourself a
>>> scholar. Here's a clue. Resonation requires TWO objects. You need
>>> something to vibrate, and something to cause the vibration.
>>>
>>> from: http://en.wikipedia.org/wiki/Resonate
>>>
>>> In physics, resonance is an increase in the oscillatory energy absorbed
>>> by a system when the frequency of the oscillations matches the system's
>>> natural frequency of vibration (its resonant frequency).
>>>
>>>
>>>> That crankshaft is going to be vibrating with every power pulse because
>>>> each power pulse exterts a force on the lever arm of the crankpin which
>>>> causes a twisting of the shaft. And in the split second after the power
>>>> pulse subsides, the shaft will swing back twisting back beyond
>>>> neutral -- just like a guitar string when you displace it swings to
>>>> both sides of its neutral axis as it vibrates.
>>>
>>> So close, yet so far away. If you'd shut up and read what you wrote up
>>> to this point, you might get it. Dampeners do nothing to help the
>>> destruction of an engine that is running at its resonant frequency. They
>>> lower the harshness of the pulses, but the point of resonancy is that
>>> the energy from each pulse is stored in the system until the next pulse
>>> arrives. So you get 3sec run time vs 0.3sec? Big whup!
>>>
>>> --
>>> This is by far the hardest lesson about freedom. It goes against
>>> instinct, and morality, to just sit back and watch people make
>>> mistakes. We want to help them, which means control them and their
>>> decisions, but in doing so we actually hurt them (and ourselves)."
>>
>>
>
>

Gordon Arnaut

August 10th 05, 03:40 PM

Just one more point about dampers:

Ernest said: "Dampeners do nothing to help the
destruction of an engine that is running at its resonant frequency. They
lower the harshness of the pulses, but the point of resonancy is that the
energy from each pulse is stored in the system until the next pulse arrives.
So you get 3sec run time vs 0.3sec? Big whup!"

Here are the facts: dampers do not just give you an extra few seconds of
protection. They nip resonance in the bud very effectively.

Yes elastomer or spring-type dampers do delay the release of energy -- both
a spring or a piece of rubber store and relase energy at a later time,
usually a split second, as I mentioned earlier in this discussion.

However, the significance of this is not that it merely delays the onset of
resonance -- and the destruction of the engine -- by three seconds, as
Ernest would have us believe. The signficance is that by absorbing, then
releasing the energy from resonation a split second later, the timing of the
resonation is disrupted and the object cannot continue to resonate. It stops
resonation in its tracks.

Here's how it works: the first harmonic that appears with resonation is
dampened by the spring or rubber, or sprag clutch or whatever, so that
subsequent harmonics cannot be set into vibration, so the oscillation does
not build. The destructive chain is broken by disrupting the timing of the
first harmonic.

If you look at a harmonic damper of a car engine, you will see an inner
metal disk and an outer metal ring, and a strip of rubber in between. That
rubber is tuned to precisely disrupt -- or clip -- harmonics at the
crankshaft's resonant frequency. (This is a function of the density of the
rubber compound).

And this is why when you have your harmonic damper overhauled, it will come
with a new strip of rubber, replacing the old strip which has hardened and
aged and no longer absorbs energy at the intended frequency.

Springs in a clutch plate can do the same thing if they are tuned at the
same frequency as the rubber compound. A sprag clutch is another approach,
so is a flywheel (which dampens out the energy from the harmonic by the
force of its spinning inertial mass). The Eggenfellner gearbox uses uses
this approach and has the best record so far.

Ernest I am amazed that you don't even know this much, yet you have the
brass to hurl unprovoked personal insults.

Regards,

Gordon.

"Gordon Arnaut" > wrote in message
...
> And just one more thing.
>
> I said previously that auto designers take resonance into account and
> design powertrain systems not to resonate. They do this by applying
> restraining forces as I mentioned in my previous message.
>
> The key thing for us in the amateur-built aircraft community is that we
> are putting together a powertrain piecemel. We take an auto engine, a
> prop, a gearbox and put them all together. Sometimes this can result in
> resonation of one or more pieces in the system.
>
> What I have been doing is just trying to think through the problem and
> apply known facts about resonance and known design principles.
>
> Regards,
>
> Gordon.
>
>
> "Gordon Arnaut" > wrote in message
> ...
>> Just one more note, about Ernest's talk of an engine "running at its
>> resonant frequency."
>>
>> Just where do we see engine's running at their resonant frequency? I have
>> to wonder because if you are driving down the highway and holding a
>> steady rpm -- perhaps with the aid of cruise control -- I think you will
>> want to be sure not to run at this "resonant frequency."
>>
>> How laughable. If this were true there would be cars beside the highway
>> every couple of miles or so.
>>
>> The fact is that engines are designed not to resonate. Designers do this
>> by taking into account excitation forces and applying countering
>> restraining forces.
>>
>> Mathematically the relationship is represented by :
>> M a + D v + K x = Me ² e sin( t - )
>>
>> For simplification, the above equation can be written as:
>> Mass term + Damping term + Stiffness Term = Restraining Force
>>
>> The restraining forces, represented by the various terms in the equation,
>> are what determines how a rotor behaves throughout its operating range.
>> Any excitation force, such as imbalance, is always in equilibrium with
>> the restraining forces of mass, damping, and stiffness. The amount of
>> measured vibration, as a result of these combined forces, will depend
>> upon the combined effect of all three terms in the equation.
>>
>> Regards,
>>
>> Gordon.
>>
>>
>>
>> "Gordon Arnaut" > wrote in message
>> ...
>>> Ernest,
>>>
>>> First off all, I described resonance perfectly accurately: You just
>>> pulled out an encyclopedia definition that worded it another way and
>>> said exactly what I said, that an object will resonate at its natural
>>> frequency, which causes its oscillations to increase in amplitude.
>>>
>>> Your saying that I am wrong is simply not true, and shows that you are
>>> simply acting out of spite -- as demonstrated by the bitter and
>>> combative tone of your message.
>>>
>>> Just for the record, my discussion of resonance in engines is light
>>> years beyond your silly encyclopedia blurb.
>>>
>>> I explained that in order to understand resonance, it is useful to think
>>> in terms of excitation forces -- power pulses, imbalance and outside
>>> spring mass systems, such as a propeller, for example -- and restraining
>>> forces, such as mass, stiffness and dampening.
>>>
>>> You are wrong on several fundamental points: first, a damper is a
>>> restraingin force and will do just that, it will dampen the oscillations
>>> resulting from resonation. It does this by clipping the harmonics, which
>>> are what cause the amplitutde of the oscillations to grow.
>>>
>>> A damper can be a spring or an elastomer tuned to the resonant
>>> frequency, or even a flywheel, which relies on inertia to dampen the
>>> oscillations. A sprag clutch which allows freedom of movement in one
>>> direction but not the other, also clips oscillations. All of these
>>> dampers work by counteracting the energy of the harmonics. Without the
>>> energy of the harmonics, the oscillations cannot increase.
>>>
>>> Point blank question: Are you are saying that if you bring an object to
>>> resonance, there is nothing that damping can do to restrain the
>>> oscillations? I am asking again because that is exactly what you said. I
>>> just want to confirm because this is an elementary point of
>>> understanding resonance and if you don't understand this, then...well, I
>>> think we can draw our own conclusions...
>>>
>>> Also plain wrong is that resonance requires two objects. Resonance
>>> requres only one object and an excitation force acting on it. Period. An
>>> object is not a force.
>>>
>>> Also, I see now that your are unable to discuss politely --throwing
>>> around personal insults like confetti. Nice. Also, what right do you
>>> have to demand that I "shut up?" Why don't you shut up?
>>>
>>> Regards,
>>>
>>> Gordon.
>>>
>>>
>>>
>>>
>>> "Ernest Christley" > wrote in message
>>> .com...
>>>> Gordon Arnaut wrote:
>>>>> A couple of thoughts. First, Tracy has devised a good solid gearbox
>>>>> that has proven itself in service with a respectable number of flight
>>>>> hours.
>>>>>
>>>>
>>>> That should be and indication to you to shut up and learn from your
>>>> elders.
>>>>
>>>>>
>>>>> But let's back up a little and try to really understand this. I don't
>>>>> think my earlier explanation was completely satisfactory.
>>>>>
>>>>
>>>> Now your getting it.
>>>>
>>>>> The key thing to understand first is that any object will vibrate if
>>>>> force acts on it to displace it in some way. In astrophysics we know
>>>>> that the biggest objects in the universe vibrate, and even the
>>>>> universe itself vibrates -- and has left a trace of its vibrations as
>>>>> it expanded after the big bang.
>>>>>
>>>>
>>>> So, is the goal here to talk gibberish about as many subjects as
>>>> possible in the forlorn hope that there is an outside chance that you
>>>> might be right about SOMETHING!!
>>>>
>>>>> A guitar string vibrates if you displace it with a pick. An engine
>>>>> vibrates from power pulses. Even an electric motor vibrates from the
>>>>> power pulses of its magnets.
>>>>>
>>>>> But vibration is not resonation.
>>>>
>>>> Case in point. You obviously have no idea what you're talking about.
>>>> You read a science book once in high school and now consider yourself a
>>>> scholar. Here's a clue. Resonation requires TWO objects. You need
>>>> something to vibrate, and something to cause the vibration.
>>>>
>>>> from: http://en.wikipedia.org/wiki/Resonate
>>>>
>>>> In physics, resonance is an increase in the oscillatory energy absorbed
>>>> by a system when the frequency of the oscillations matches the system's
>>>> natural frequency of vibration (its resonant frequency).
>>>>
>>>>
>>>>> That crankshaft is going to be vibrating with every power pulse
>>>>> because each power pulse exterts a force on the lever arm of the
>>>>> crankpin which causes a twisting of the shaft. And in the split second
>>>>> after the power pulse subsides, the shaft will swing back twisting
>>>>> back beyond neutral -- just like a guitar string when you displace it
>>>>> swings to both sides of its neutral axis as it vibrates.
>>>>
>>>> So close, yet so far away. If you'd shut up and read what you wrote up
>>>> to this point, you might get it. Dampeners do nothing to help the
>>>> destruction of an engine that is running at its resonant frequency.
>>>> They lower the harshness of the pulses, but the point of resonancy is
>>>> that the energy from each pulse is stored in the system until the next
>>>> pulse arrives. So you get 3sec run time vs 0.3sec? Big whup!
>>>>
>>>> --
>>>> This is by far the hardest lesson about freedom. It goes against
>>>> instinct, and morality, to just sit back and watch people make
>>>> mistakes. We want to help them, which means control them and their
>>>> decisions, but in doing so we actually hurt them (and ourselves)."
>>>
>>>
>>
>>
>
>

Morgans

August 11th 05, 02:22 AM

"Ernest Christley" > wrote

> So, is the goal here to talk gibberish about as many subjects as
> possible in the forlorn hope that there is an outside chance that you
> might be right about SOMETHING!!

gordon likes to see himself type and post. He is so totally clues, it is
hard to know where to start.

My solution? Just let himself talk to himself. It is solution I wish
everyone here would adopt, and after a while with nobody playing with him,
he might go away.
--
Jim in NC

Gordon Arnaut

August 11th 05, 04:53 AM

Bashir,

Actually, I spoke too quickly when I conceded a mistake.

Tautness and stiffness are two different things. A taut string will vibrate
at a higher frequency than a loose string, but we have not changed its
inherent stiffness or elasticity (e).

If you increase the stiffness (decrease the elasticity) of an object, you
will decrease its resonant frequency, as I first stated.

The resonant frequency of a system is symbolized by "w n"

and pronounced "Omega-sub-n". An object's mass and elasticity determines its
resonant frequency, and is expressed mathematically as:

wn = ?(k/m)

K is the value for elasticity, while m is the value for mass. So we see that
lower elasticity (greater stiffness) results in a lower frequency of
resonation.

So making a crankshaft stiffer does decrease the rpm at which it will
resonate. It also increases the value of restraining force acting against
excitaiton. So the benefits are cumulative.

We can see a real-world example of this in V-8 engines which would not last
very long without a harmonic damper, even though they have much smoother
torque pulses than a 4-cylinder. The reason is that the crankshaft has to be
much longer and thereby less stiff -- or more elastic.

On most four-cylinder engines, dampers are not needed because the short,
stout crank actually resonates at a frequency below the oeprating range.
Hence resonance will never be encountered.

It's useful at this point to back up and define what resonant frequency of
an object -- or system -- really means. Stated most simply it is the
frequency at the object or system will vibrate if it is excited by a single
pulse.

The actual torsional resonance of an engine can be calculated if you know
the torsional rate of the crankshaft (which is its spring value) and its
mass moment of inertia, which is a function of crank stroke and weight,
number of journals, dimensions of the flywheel, torsional absorber,
accessories.

So now we know a little about resonance and how it affects a crankshaft. But
what happens when we attach a propeller or gearbox-propeller combination to
that engine?

Well, now we are dealing with not just an object but a system. And this
system has its own torsional resonance frequency, which is different from
that of the single object itself, like the crankshaft.

A key concept here is tranmissibility, which is the ratio between the
amplitude of the excitation torque, and the amplitude of the output torque.
In simple terms, this means that the gearbox and propeller can be subjected
to vibratory forces many times higher than the torque peaks produced by the
engine.

Here is where damping comes in. But even with damping there will be some
amplification of vibratory forces transmitted from the gearbox to the
gearbox and prop.

There is some good reading at this website, with specific info on how
torsional resonance is dealt with in designing aircraft PSRU systems:
http://www.epi-eng.com/BAS-VibBasics.htm

Regards,

Gordon.

"Bashir" > wrote in message
oups.com...
> He can be taught!! Who would have thought it!?
>

Gordon Arnaut

August 11th 05, 05:00 AM

I'm going to write out that equation for resonant frequency because the
symbols did not translate over properly.

It should read:

Omega sub-n (resonant frequency) = the square root of K (elasticity) divided
by m (mass)

If you plug any numbers into this equation you see that resonant frequency
goes down as stiffness goes up (elasticity goes down = stiffness going up).

We also see the same result if we increase mass: resonant frequency again
goes down.

This is important because we want to design an engine-gearbox-prop system
that resonates at an rpm below actual operation, if possible.

Regards,

Gordon.

"Gordon Arnaut" > wrote in message
...
> Bashir,
>
> Actually, I spoke too quickly when I conceded a mistake.
>
> Tautness and stiffness are two different things. A taut string will
> vibrate at a higher frequency than a loose string, but we have not changed
> its inherent stiffness or elasticity (e).
>
> If you increase the stiffness (decrease the elasticity) of an object, you
> will decrease its resonant frequency, as I first stated.
>
> The resonant frequency of a system is symbolized by "w n"
>
> and pronounced "Omega-sub-n". An object's mass and elasticity determines
> its resonant frequency, and is expressed mathematically as:
>
>
>
>
>
> wn = ?(k/m)
>
>
>
>
>
> K is the value for elasticity, while m is the value for mass. So we see
> that lower elasticity (greater stiffness) results in a lower frequency of
> resonation.
>
> So making a crankshaft stiffer does decrease the rpm at which it will
> resonate. It also increases the value of restraining force acting against
> excitaiton. So the benefits are cumulative.
>
> We can see a real-world example of this in V-8 engines which would not
> last very long without a harmonic damper, even though they have much
> smoother torque pulses than a 4-cylinder. The reason is that the
> crankshaft has to be much longer and thereby less stiff -- or more
> elastic.
>
> On most four-cylinder engines, dampers are not needed because the short,
> stout crank actually resonates at a frequency below the oeprating range.
> Hence resonance will never be encountered.
>
> It's useful at this point to back up and define what resonant frequency of
> an object -- or system -- really means. Stated most simply it is the
> frequency at the object or system will vibrate if it is excited by a
> single pulse.
>
> The actual torsional resonance of an engine can be calculated if you know
> the torsional rate of the crankshaft (which is its spring value) and its
> mass moment of inertia, which is a function of crank stroke and weight,
> number of journals, dimensions of the flywheel, torsional absorber,
> accessories.
>
> So now we know a little about resonance and how it affects a crankshaft.
> But what happens when we attach a propeller or gearbox-propeller
> combination to that engine?
>
> Well, now we are dealing with not just an object but a system. And this
> system has its own torsional resonance frequency, which is different from
> that of the single object itself, like the crankshaft.
>
> A key concept here is tranmissibility, which is the ratio between the
> amplitude of the excitation torque, and the amplitude of the output
> torque. In simple terms, this means that the gearbox and propeller can be
> subjected to vibratory forces many times higher than the torque peaks
> produced by the engine.
>
> Here is where damping comes in. But even with damping there will be some
> amplification of vibratory forces transmitted from the gearbox to the
> gearbox and prop.
>
> There is some good reading at this website, with specific info on how
> torsional resonance is dealt with in designing aircraft PSRU systems:
> http://www.epi-eng.com/BAS-VibBasics.htm
>
> Regards,
>
> Gordon.
>
>
>
>
>
> "Bashir" > wrote in message
> oups.com...
>> He can be taught!! Who would have thought it!?
>>
>
>

Gordon Arnaut

August 11th 05, 05:48 AM

Ernest,

There is no gibberish in any of what I said. And I wasn't talking about
"many" subjects, only one: resonance.

My point was to illustrate the difference between simple vibration and
resonance.

Since you didn't get it, I will try again. Think of a guy on a diving board
bouncing up and down. He is vibrating that board at a certain frequency (the
number of times per second he goes up and down). This is vibration.

Now when he jumps off that board, the board will continue vibrating, only
now it is resonating, because it is vibrating at its natural frequency. If
you count the number of times per second that the board bounces up and down,
you will have discovered its resonant frequency. (It's usually higher than
the frequency of the guy jumping up and down, which is why it starts
flapping).

However, the resonation does not continue or increase, because the
excitation force stopped. Only if the excitation force were to continue at
the same frequency, would the board go into HARMONIC resonance, which causes
the oscillations to increase in amplitude.

Here is an experiment you can try at home: take a think metal shaft and hold
it horizontally. Now attach one end to a wall or other solid surface so it
can't move, and provide a means of holding the other end up so the shaft
remains in the horizontal position, but free at this other end.

Now add a round disk or wheel to this free end. Grasp the disk in your hand
and turn it, causing the shaft to twist. This is what happens when the
torque pulses of the engine act on the crankshaft. When you have twisted as
far as you can, let go and count that number of times the wheel swings back
and forth per second -- if you can; it will probably be too fast to time
without special equipment.

You will now know the torsional (twisting) resonance of your shaft.

All you need to do is twist it once and let go. by definition resonance is
the vibrational frequency that results from only a SINGLE excitation.

Again, if you were somehow able to twist that shaft back and forth at
precisely the timing required to maintain its resonant frequency, you would
induce harmonic resonance.

I daresay that if you have read and considered what I have said, you will
have improved you understanding of resonance by a fair margin.

Regards,

Gordon.

"Ernest Christley" > wrote in message
.com...
> Gordon Arnaut wrote:
>> A couple of thoughts. First, Tracy has devised a good solid gearbox that
>> has proven itself in service with a respectable number of flight hours.
>>
>
> That should be and indication to you to shut up and learn from your
> elders.
>
>>
>> But let's back up a little and try to really understand this. I don't
>> think my earlier explanation was completely satisfactory.
>>
>
> Now your getting it.
>
>> The key thing to understand first is that any object will vibrate if
>> force acts on it to displace it in some way. In astrophysics we know that
>> the biggest objects in the universe vibrate, and even the universe itself
>> vibrates -- and has left a trace of its vibrations as it expanded after
>> the big bang.
>>
>
> So, is the goal here to talk gibberish about as many subjects as possible
> in the forlorn hope that there is an outside chance that you might be
> right about SOMETHING!!
>
>> A guitar string vibrates if you displace it with a pick. An engine
>> vibrates from power pulses. Even an electric motor vibrates from the
>> power pulses of its magnets.
>>
>> But vibration is not resonation.
>
> Case in point. You obviously have no idea what you're talking about. You
> read a science book once in high school and now consider yourself a
> scholar. Here's a clue. Resonation requires TWO objects. You need
> something to vibrate, and something to cause the vibration.
>
> from: http://en.wikipedia.org/wiki/Resonate
>
> In physics, resonance is an increase in the oscillatory energy absorbed by
> a system when the frequency of the oscillations matches the system's
> natural frequency of vibration (its resonant frequency).
>
>
>> That crankshaft is going to be vibrating with every power pulse because
>> each power pulse exterts a force on the lever arm of the crankpin which
>> causes a twisting of the shaft. And in the split second after the power
>> pulse subsides, the shaft will swing back twisting back beyond neutral --
>> just like a guitar string when you displace it swings to both sides of
>> its neutral axis as it vibrates.
>
> So close, yet so far away. If you'd shut up and read what you wrote up to
> this point, you might get it. Dampeners do nothing to help the
> destruction of an engine that is running at its resonant frequency. They
> lower the harshness of the pulses, but the point of resonancy is that the
> energy from each pulse is stored in the system until the next pulse
> arrives. So you get 3sec run time vs 0.3sec? Big whup!
>
> --
> This is by far the hardest lesson about freedom. It goes against
> instinct, and morality, to just sit back and watch people make
> mistakes. We want to help them, which means control them and their
> decisions, but in doing so we actually hurt them (and ourselves)."