Auto conversions & gear boxes

[Dave Covert]

I notice that most auto engine conversions use a gear box between the engine
and the prop. Why is that? Is it because an auto engine's peak HP is too
high for a prop to swing? Is it because auto engines weren't designed to be
pulled around by their crankshafts and don't have proper thrust bearings?
Both?

Are there any auto/motorcycle conversions that don't require gear boxes?

Dave

[ET]

"Dave Covert" > wrote in
:

> I notice that most auto engine conversions use a gear box between the
> engine and the prop. Why is that? Is it because an auto engine's peak
> HP is too high for a prop to swing? Is it because auto engines weren't
> designed to be pulled around by their crankshafts and don't have
> proper thrust bearings? Both?
>
> Are there any auto/motorcycle conversions that don't require gear
> boxes?
>
> Dave
>
>
>

The sonex can use a VW conversion attached directly.

http://www.aeroconversions.com/ or www.sonex-ltd.com

--
ET >:)

(Future student pilot and future Sonex Builder)


"A common mistake people make when trying to design something
completely foolproof is to underestimate the ingenuity of complete
fools."---- Douglas Adams

[Corky Scott]

On Fri, 20 Feb 2004 16:27:38 GMT, "Dave Covert"
> wrote:

>I notice that most auto engine conversions use a gear box between the engine
>and the prop. Why is that? Is it because an auto engine's peak HP is too
>high for a prop to swing? Is it because auto engines weren't designed to be
>pulled around by their crankshafts and don't have proper thrust bearings?
>Both?
>
>Are there any auto/motorcycle conversions that don't require gear boxes?
>
>Dave

Dave, this is kindof the Auto Conversion 101 question no. 1. The
answer is pretty much all of the above.

Auto crankshafts aren't designed for bending loads, so if you bolt a
prop to one, you are taking a big chance that the prop loads
transferred directly to the hub of the crankshaft you bolted the prop
to, could fail the crankshaft, just behind the prop hub.

Many of the early VW direct drive engines did fail in this manner.
This resulted in a lot of changes to the VW engine when used as an
airplane engine, one of the changes was to redesign the crankshaft.
Not all VW engines get so modified though, even today.

Props have an rpm range in which they are most effective. There are
an incredible number of variables, but diameter, shape, cord, pitch,
thickness all play a part in prop design. A bitty prop turning very
fast just isn't as effective as a large prop turning slower. The
smaller prop, with it's smaller diameter has less thrust because much
of the prop is blowing air against the nose of the airplane. It's a
lot more complicated than that but that's the gist.

Auto engines are tiny when compared to direct drive airplane engines.
Take a 180 hp Lycoming. It's cubic inch displacement is 360. They
turn the prop at around 2600 to 2700. The Ford V-6 in airplane trim,
puts out 180 hp also. It displaces 232 inches and makes it's power at
4800 rpm. No prop will work at that rpm. To harness the power, it
needs to be turned slower. Enter the prop speed reduction unit.

The psru takes care of keeping the bending loads off the crankshaft
and reduces prop speed to a more useable rpm.

Yes there are motorcycles that are being used in airplanes, the BMW
comes to mind.

Corky Scott

[Gig Giacona]

"Dave Covert" > wrote in message
...
> I notice that most auto engine conversions use a gear box between the
engine
> and the prop. Why is that? Is it because an auto engine's peak HP is too
> high for a prop to swing? Is it because auto engines weren't designed to
be
> pulled around by their crankshafts and don't have proper thrust bearings?
> Both?
>
> Are there any auto/motorcycle conversions that don't require gear boxes?
>
> Dave
>
>

Because the RPMs at which the motor is producing the proper amount of power
would be spinning the prop to fast.

[Richard Lamb]

Dave Covert wrote:
>
> I notice that most auto engine conversions use a gear box between the engine
> and the prop. Why is that? Is it because an auto engine's peak HP is too
> high for a prop to swing? Is it because auto engines weren't designed to be
> pulled around by their crankshafts and don't have proper thrust bearings?
> Both?
>
> Are there any auto/motorcycle conversions that don't require gear boxes?
>
> Dave

Some people think aircraft engines are "old fashioned technology"
and have not kept up with developments in auto engine field.

They point out that aircraft engines haven't changed much in
over 50 years.

Some people feel that auto engines can be used to power airplanes.

To some extent, all three of these ideas are true.

Aircraft engine do not run like car motors.

Aircraft engines run at much higher sustained power settings and
constant rpm for long periods of time.

And then there is the propeller...
Turning the propeller is what it's all about.

The propeller converts the engine's power into thrust.
As always, when energy is converted, there are losses.

Moving through the air at very high speeds, the propeller
makes lift (thrust, which is power successfully converted into
forward motion) and drag (pure conversion losses).

So, propeller efficiency is extremely important.

If the propeller is only 50% efficient, half of the
power generated by the engine is wasted in losses.
Yes, literally.

Only one hard rule for propellers - longer is better.

But longer blades mean lower RPM because the tips of the
propeller blades MUST stay below the speed of sound (yep,
Mach 1, really) for any efficiency at all.

Part of the reason for this is the huge increase in drag
as the tip enters the transonic (speed) region.

It takes TORQUE to turn that propeller - not horsepower.

A given propeller needs to turn at a given RPM, which
will require a given amount of torque.

If the engine makes enough torque to turn the propeller at
that RPM, a direct drive set up may be possible.

There are a lot of other minor details that may get in the way -
Harmonic Resonance is a big one.
But, it may be possible to run this combination direct drive.

If the engine needs to turn at a higher RPM to make adequate
power, some kind of gearing would be necessary to reduce engine
RPM to propeller RPM. Notice that reducing RPM will increase
torque proportionally. Seems like a nice trade off.

Now the engine should be running at an RPM near the peak of its'
torque curve. This is for best engine operating economy.

And the (longer) propeller is running at a comfortable (lower)
RPM for good efficiency. Life is wonderful.

Except for the weight.
Auto engines are seldom as light as possible.
Then we add more weight in the form of a gearbox and such.
Radiators full of heavy (hot!) fluids.
External oil sump?
Mounting?
Propeller gyroscopic forces operating on the crankshaft?

Weight is critical to any flying machine.
(Go back and look at how birds are built)

So...
Think of it as evolution in action.

The reason our old antique Lycosourus engines are the way they
are is that they evolved into a very narrow niche.

They turn propellers to pull airplanes.

They make very high torque
at very low RPM,
and are as light as possible.
They are tremendously reliable and fairly efficient.

Prices are high because of limited production and high demand.
Simple economics.

But the economics of engine development (and risk assesment) are
anything but simple.

I have a big bore VW (2180cc) on my parasol.
That's a converted car motor.

There is a weatlh of prior art using VW engines for small airplanes
(if one is inclined to use it).

What works, and what doesn't. (eg: breaking cast crankshafts)

Mine is a very simple conversion, using high quality (GPAS) parts
built by a little German perfectinist.
I trust it - so far.

I also don't push it beyond conservative limits.

All VW engines are 40 hp engine (IMHO).
Some can make more power than that - for a while.
This one is _rated_ at 70 hp.
But will reach thermal limits of the fin area and overheat
if not throttled back (to roughly 40?)

It's a fairly expensive motor.
The jugs and pistons are standard parts, but the crank (!) and
accessories and machine work are all specialty items.
A new 2180 can easily go over $5000 with a few bells and whistles.

But the weight, power, reliability, and operating cost are all within
reason for this particular airplane.

The airplane itself can land slowly, around 35 mph.

The chances of getting down safely if the engine quits are a lot better
at 35 than they are at 53.

To me, it seems like a reasonable risk for the potential rewards.

But...

Your milage may vary.

Richard

http://www.flash.net/~lamb01


PS: I've read of a Curtiss Hawk replica that uses a direct drive Chevy
350.
It's supposed to make roughly 190 hp?
It would obviously be a heavy motor.
Not something you'd hang on a glass slipper.
But on a big old biplane with a looong prop
it seems to be just the ticket.

[Barry S.]

On Fri, 20 Feb 2004 18:08:35 GMT,
(Corky Scott) wrote:


>Auto engines are tiny when compared to direct drive airplane engines.
>Take a 180 hp Lycoming. It's cubic inch displacement is 360. They
>turn the prop at around 2600 to 2700. The Ford V-6 in airplane trim,
>puts out 180 hp also. It displaces 232 inches and makes it's power at
>4800 rpm. No prop will work at that rpm. To harness the power, it
>needs to be turned slower. Enter the prop speed reduction unit.

Speaking of Fords! How's your project coming?

__________________
Note: To reply, replace the word 'spam' embedded in return address with 'mail'.
N38.6 W121.4

[Tom Cummings]

> Are there any auto/motorcycle conversions that don't require gear boxes?

The Corvair engine operates successfully in direct drive configuration.
See http://www.flycorvair.com/

[Badwater Bill]

Nice job Richard. Nice Job.

I might just add one more comment to clear something up a bit. When
you chose a prop, you design it so the tip speeds don't exceed 0.80
Mach, or 80% the speed of sound. As the propeller tips approach
speeds over that, the airflow can become super sonic even though the
prop tip is well below Mach-1. As you mentioned, that takes a lot of
energy that is wasted and is not available for thrust to create a
shock wave and sustain it.

When I was the test pilot on the OMABP RV-6A project, we used the
Chevy Vortec V-6 engine, the PSRU was specifically designed to turn
the prop at tip speed below 80% the speed of sound. Jess Meyers also
used a reduction ratio number that was about equal to the square root
of 2 to eliminate harmonics that could have resulted in reversed
torque pulses reflecting back into the engine. By using a reduction
ratio of 1.41 (or close to it) he eliminated many sympathetic
harmonics that may have occured.

BWB

[Dave]

But with the stock Corvair engine having its peak torque at 3000 (or
4000-4500 for a modified unit) it would still be best to gear it down
for a prop speed around 2500 right?

Dave

Tom Cummings wrote:
>>Are there any auto/motorcycle conversions that don't require gear boxes?
>
>
> The Corvair engine operates successfully in direct drive configuration.
> See http://www.flycorvair.com/
>
>

[Richard Lamb]

Badwater Bill wrote:
>
> Nice job Richard. Nice Job.
>

Thank you sir!

I've heard or read that reasonable limits are about
750 feet per second for wood props
and 800, or a little more for metal props.

However...

I've seen 3000 rpm static on my engine and prop (62x29 Tennessee).
That's 811 fps tip speed! Static?
(And yes, she sings a bit at full throttle)

That could come up another couple hundred rpm at higher speed.
But 3200 rpm = 865 fps?
Holy cow!

Not bad for 40 hp, huh.

Cruise at 2800 rpm gives a stately 757 fps at 75 mph.
Fuel burn looks like just over 3 gallons per hour.


Giving credit where credit is due.
This engine was built by my neighbor, Oscar the Grouch.

Oscar is a retired police officer, and life long racing addict.

Oscar gives good motor.

He has three VW powered airplanes of his own.

His wife's "car" is a 1960's slingshot dragster with a small
block Chevy. Hand formed gloss black and gold(leaf!) aluminum body.

Grandma turns 8.80 and 152 mph in the quarter mile.


And!
Just in case the skeptics in the audience disbelieve?

I believe our (Zuehl) spring fly-in will be in May this year.
Drop in and see for yourself...

Richard

[Badwater Bill]

>I believe our (Zuehl) spring fly-in will be in May this year.
>Drop in and see for yourself...
>
>Richard

Oscar the grouch! That's funny. I could tell you stories about some
of the old men who built the RV-6A I flew. Man, the list of grouches
was long and deep. It was a project where retired men could go each
day and be insulted, embarrased, confronted and ridiculed. It didn't
matter what your background was, everybody hated you until you proved
you had some value. Once you were in, it was okay, but God help you
if you made a mistake on something. I goofed a couple times. That
was 8 years ago and I still remember how I felt as if it were
yesterday.


BWB

[Richard Lamb]

Badwater Bill wrote:
>
> >I believe our (Zuehl) spring fly-in will be in May this year.
> >Drop in and see for yourself...
> >
> >Richard
>
> Oscar the grouch! That's funny. I could tell you stories about some
> of the old men who built the RV-6A I flew. Man, the list of grouches
> was long and deep. It was a project where retired men could go each
> day and be insulted, embarrased, confronted and ridiculed. It didn't
> matter what your background was, everybody hated you until you proved
> you had some value. Once you were in, it was okay, but God help you
> if you made a mistake on something. I goofed a couple times. That
> was 8 years ago and I still remember how I felt as if it were
> yesterday.
>
> BWB

Big grin!

Kinda like here?


Richard

[Norman Yarvin]

In article >,
Badwater Bill > wrote:

>When I was the test pilot on the OMABP RV-6A project, we used the
>Chevy Vortec V-6 engine, the PSRU was specifically designed to turn
>the prop at tip speed below 80% the speed of sound. Jess Meyers also
>used a reduction ratio number that was about equal to the square root
>of 2 to eliminate harmonics that could have resulted in reversed
>torque pulses reflecting back into the engine. By using a reduction
>ratio of 1.41 (or close to it) he eliminated many sympathetic
>harmonics that may have occured.

What, in order to have the ratio between the two be an irrational number?
That's not actually going to help eliminate resonances, unless you get
lucky -- and you are about equally likely to get lucky with any number of
about the same size, irrational or not.



--
Norman Yarvin http://yarchive.net

[Tim Ward]

"Norman Yarvin" > wrote in message
...
> In article >,
> Badwater Bill > wrote:
>
> >When I was the test pilot on the OMABP RV-6A project, we used the
> >Chevy Vortec V-6 engine, the PSRU was specifically designed to turn
> >the prop at tip speed below 80% the speed of sound. Jess Meyers also
> >used a reduction ratio number that was about equal to the square root
> >of 2 to eliminate harmonics that could have resulted in reversed
> >torque pulses reflecting back into the engine. By using a reduction
> >ratio of 1.41 (or close to it) he eliminated many sympathetic
> >harmonics that may have occured.
>
> What, in order to have the ratio between the two be an irrational number?
> That's not actually going to help eliminate resonances, unless you get
> lucky -- and you are about equally likely to get lucky with any number of
> about the same size, irrational or not.
>
>
>
> --
> Norman Yarvin http://yarchive.net

Just out of curiosity, how would you get any ratio to be an irrational
number?

Tim Ward

[Cy Galley]

"Tim Ward" > wrote in message
...
>
> "Norman Yarvin" > wrote in message
> ...
> > In article >,
> > Badwater Bill > wrote:
> >
> > >When I was the test pilot on the OMABP RV-6A project, we used the
> > >Chevy Vortec V-6 engine, the PSRU was specifically designed to turn
> > >the prop at tip speed below 80% the speed of sound. Jess Meyers also
> > >used a reduction ratio number that was about equal to the square root
> > >of 2 to eliminate harmonics that could have resulted in reversed
> > >torque pulses reflecting back into the engine. By using a reduction
> > >ratio of 1.41 (or close to it) he eliminated many sympathetic
> > >harmonics that may have occured.
> >
> > What, in order to have the ratio between the two be an irrational
number?
> > That's not actually going to help eliminate resonances, unless you get
> > lucky -- and you are about equally likely to get lucky with any number
of
> > about the same size, irrational or not.
> >
> >
> > --
> > Norman Yarvin http://yarchive.net
>
> Just out of curiosity, how would you get any ratio to be an irrational
> number?
>
> Tim Ward
>
> By definition a rational number is any number that can be expressed as a
fraction of two whole numbers.

[Tim Ward]

"Cy Galley" > wrote in message
news:ehd_b.377778$xy6.1992385@attbi_s02...
>
> "Tim Ward" > wrote in message
> ...
> >
> > "Norman Yarvin" > wrote in message
> > ...
> > > In article >,
> > > Badwater Bill > wrote:
> > >
> > > >When I was the test pilot on the OMABP RV-6A project, we used the
> > > >Chevy Vortec V-6 engine, the PSRU was specifically designed to turn
> > > >the prop at tip speed below 80% the speed of sound. Jess Meyers also
> > > >used a reduction ratio number that was about equal to the square root
> > > >of 2 to eliminate harmonics that could have resulted in reversed
> > > >torque pulses reflecting back into the engine. By using a reduction
> > > >ratio of 1.41 (or close to it) he eliminated many sympathetic
> > > >harmonics that may have occured.
> > >
> > > What, in order to have the ratio between the two be an irrational
> number?
> > > That's not actually going to help eliminate resonances, unless you get
> > > lucky -- and you are about equally likely to get lucky with any number
> of
> > > about the same size, irrational or not.
> > >
> > >
> > > --
> > > Norman Yarvin http://yarchive.net
> >
> > Just out of curiosity, how would you get any ratio to be an irrational
> > number?
> >
> > Tim Ward
> >
> > By definition a rational number is any number that can be expressed as a
> fraction of two whole numbers.

Yes, I know. Since we're talking about a reduction ratio, it didn't make
any sense. An irrational ratio?
It's... irrational.

Tim Ward

[Pete Schaefer]

Easy. Just use one gear with 1.4264 teeth in it.

"Tim Ward" > wrote in message
...
> Just out of curiosity, how would you get any ratio to be an irrational
> number?

[Corky Scott]

On 20 Feb 2004 14:19:16 -0600, Barry S. > wrote:

>On Fri, 20 Feb 2004 18:08:35 GMT,
(Corky Scott) wrote:
>
>
>>Auto engines are tiny when compared to direct drive airplane engines.
>>Take a 180 hp Lycoming. It's cubic inch displacement is 360. They
>>turn the prop at around 2600 to 2700. The Ford V-6 in airplane trim,
>>puts out 180 hp also. It displaces 232 inches and makes it's power at
>>4800 rpm. No prop will work at that rpm. To harness the power, it
>>needs to be turned slower. Enter the prop speed reduction unit.
>
>Speaking of Fords! How's your project coming?
>
>__________________
>Note: To reply, replace the word 'spam' embedded in return address with 'mail'.
>N38.6 W121.4

Slowly. I have the engine assembled and is currently mounted in the
airframe. But there's everything else to do. The airframe has yet to
be blasted and painted. I think that can happen this summer. On the
other hand, we are planning some major kitchen redo's and trust me,
ALL of my attention had better be on that.

I've built an engine test stand that will allow me to wheel the engine
outside and run it, with the prop installed. I'd like to get some 30
or so hours on the engine before it gets it's final installation onto
the airframe. I decided this after listening to a crusty old DAR
speak at a local EAA meeting. It sounded to me like he'd be REALLY
unhappy with such an engine unless I could show him that it had been
thoroughly tested.

At this point, I'm being educated about headers. I was going to just
bend up a bunch of tubes, weld them to be what I need, get them jet
coated and call it good. Then I started doing some research.

It turns out that the diameter of header tubing is critical to the
performance of the engine. Larger diameter is not necessarily better.
In fact in almost all aircraft type applications, bigger is virtually
for sure not better. The exhaust header flange has openings that are
1.75" in diameter. This matches the exhaust port opening in the head.
But the tubing diameter should be 1.5", or possibly even 1 3/8" in
diameter. Also, the length of the runners should be at least over 30
inches, and 36 would be better. In addition, each tube should be as
close in length to each other as possible. Finally, the collector
needs to be about 1 78" diameter and it should be 18" long.

Reality is rearing it's ugly head. The lengths I mentioned literally
won't fit without welding the headers into loops. Not going to
happen.

I think the best I can do is get the runners as long as I can make
them and make sure they are of equal length, and get the proper
collector as that also has a huge affect on engine operation.

Why is it so important to have the runners be the same length?
Because different length runners cause different scavenging effects
within the combustion chamber. You will end up with an engine that
does not respond to ignition adjustments nor mixture adjustments as
some combustion chambers will run rich and some lean. "A series of
single cylinder engines flying loosely in formation." Quote from John
Deakin.

Many builders of the Ford V6 have complained that their engine ran
rough at maximum power. Huge effort was made to modify the intake
manifold to correct the problem. But I have not seen a single picture
of an exhaust manifold where the effort was made to create equal
length exhaust headers of the proper diameter.

I talked with a header manufacturer who told me he had heard of Dave
Blanton because a bunch of builders had asked him about headers. He
told me they all wanted to ignor his advice about tubing diameter.
They all wanted to use bigger tubing than was dictated, because they
all thought bigger was better. It's not.

Why is it so important to have the proper diameter tubing? Because
the bigger the diameter the slower the velocity of the gasses inside
it, and visa versa, up to a point. Eventually you can have exhaust
tubing in a diameter too small such that exhaust flow is restricted.
Large diameter tubing tends to cause the engine's power to peak at
extreme rpms. The smaller the diameter of the tubing, the more low to
midrange power you have.

But everyone wanted to use 1.75" tubing because that's what the
exhaust port was. 1.75" tubing would be what you would use if you
wanted flash horsepower from the engine at 8,000 rpm, like at the
dragstrip.

The header manufacturer also had a lot to say about "Zoomie" type
headers. These are headers without collectors, basically straight
pipes. Not only are these tubes also usually too large a diameter,
they leave off the collector which is crucial to the proper design of
the header system.

So with all this information, I'm taking my time with the header
design. Obviously something so important to the proper running of the
engine is not something I'm going to throw together without using
proper design criteria.

Corky Scott

[Norman Yarvin]

In article >,
Tim Ward > wrote:

>"Norman Yarvin" > wrote in message
...
>> In article >,
>> Badwater Bill > wrote:
>>
>> >When I was the test pilot on the OMABP RV-6A project, we used the
>> >Chevy Vortec V-6 engine, the PSRU was specifically designed to turn
>> >the prop at tip speed below 80% the speed of sound. Jess Meyers also
>> >used a reduction ratio number that was about equal to the square root
>> >of 2 to eliminate harmonics that could have resulted in reversed
>> >torque pulses reflecting back into the engine. By using a reduction
>> >ratio of 1.41 (or close to it) he eliminated many sympathetic
>> >harmonics that may have occured.
>>
>> What, in order to have the ratio between the two be an irrational number?
>> That's not actually going to help eliminate resonances, unless you get
>> lucky -- and you are about equally likely to get lucky with any number of
>> about the same size, irrational or not.
>
>Just out of curiosity, how would you get any ratio to be an irrational
>number?

Not with gears! But a belt can provide any ratio. Of course any
irrational number can be approximated arbitrarily well by a rational
number... but the idea is just to choose a number that can't be
approximated well by a ratio of small numbers, not one that's genuinely
mathematically irrational. (Indeed, the latter concept is almost
meaningless in engineering, which is why I felt free to use "irrational"
as shorthand for the former concept.)

The idea isn't complete nonsense. If you had two identical assemblies,
linked by a belt drive, it'd be exactly the thing to do. You wouldn't
pick a 2:3 ratio, for instance, since that would mean the second harmonic
of one would resonate with the third harmonic of the other. But a
propeller and an engine are nowhere close to identical; their resonant
frequencies don't have anything to do with each other in the first place,
so there's no point in trying to do anything to throw them out of match
with each other. (Unless you get unlucky; if resonance problems show up
in testing, then you can try re-machining one of the belt pulleys to a
different diameter, or ordering new gears for a slightly different gear
ratio.)


--
Norman Yarvin http://yarchive.net

[Jay]

For props, bigger is better for static thrust (look at a helecopter)
but what about for top speed, a more desireable figure of merit for
fixed wing aircraft? I seem to remember hearing somewhere that for
top speed there is an optimal prop length that is not infinite. You
need to generate a stream of air that is going faster than the speed
that you want to fly.

I think it relates to why you see high bypass jet engines on sub sonic
airliners but no-bypass engines on supersonic jet fighters.

[Corky Scott]

On 23 Feb 2004 09:32:01 -0800, (Jay) wrote:

>For props, bigger is better for static thrust (look at a helecopter)
>but what about for top speed, a more desireable figure of merit for
>fixed wing aircraft? I seem to remember hearing somewhere that for
>top speed there is an optimal prop length that is not infinite. You
>need to generate a stream of air that is going faster than the speed
>that you want to fly.
>
You just described the reason no piston engined WWII fighter ever flew
faster than the speed of sound. The prop needed to produce enough
thrust to pull the airplane into supersonic speed, but the prop was
running into the wall of drag as the tips neared supersonic speed and
the fuselage was producing enormous drag too.

The prop tips would have to go supersonic if the airplane was to go
that fast too, and props of that era were not designed for supersonic
speeds.

Even going straight down at full power, just too much drag. They went
fast enough to scare the bajeebers out of a number of pilots though.
:-) They also went fast enough to lock up the controls and in some
cases, cause the destruction of the airplane... and the pilot.

Corky Scott

[x]

> of one would resonate with the third harmonic of the other. But a
> propeller and an engine are nowhere close to identical; their resonant
> frequencies don't have anything to do with each other in the first place,

What resonance characteristics does a propeller have, and why?

> so there's no point in trying to do anything to throw them out of match
> with each other. (Unless you get unlucky; if resonance problems show up
> in testing, then you can try re-machining one of the belt pulleys to a

[Big John]

Corkey

The P-40 wouldn't go supersonic. Had a few hours in bird and took one
to about 20K and rolled over at full thottle. Huffed and puffed on way
down and I started my pull out about 10K and was level about 3K.

Bird did not have a Mach meter, only a ASI. As I remember only got a
little over 400 mph max (high drag, low power).

That one dive conviced me it was a subsonic aircraft :o)

Big John

On Mon, 23 Feb 2004 19:45:15 GMT,
(Corky Scott) wrote:

>On 23 Feb 2004 09:32:01 -0800, (Jay) wrote:
>
>>For props, bigger is better for static thrust (look at a helecopter)
>>but what about for top speed, a more desireable figure of merit for
>>fixed wing aircraft? I seem to remember hearing somewhere that for
>>top speed there is an optimal prop length that is not infinite. You
>>need to generate a stream of air that is going faster than the speed
>>that you want to fly.
>>
>You just described the reason no piston engined WWII fighter ever flew
>faster than the speed of sound. The prop needed to produce enough
>thrust to pull the airplane into supersonic speed, but the prop was
>running into the wall of drag as the tips neared supersonic speed and
>the fuselage was producing enormous drag too.
>
>The prop tips would have to go supersonic if the airplane was to go
>that fast too, and props of that era were not designed for supersonic
>speeds.
>
>Even going straight down at full power, just too much drag. They went
>fast enough to scare the bajeebers out of a number of pilots though.
>:-) They also went fast enough to lock up the controls and in some
>cases, cause the destruction of the airplane... and the pilot.
>
>Corky Scott

[Blueskies]

Corky,

Do you have any details available about your engine test stand, such as how you restrain it, instrumentation, cooling?

Also, a buddy of mine was talking about an engine build he did, and how he used water to match each header tube volume,
old news I'm sure...

--
Dan D.



..
"Corky Scott" > wrote in message ...
> On 20 Feb 2004 14:19:16 -0600, Barry S. > wrote:
>
> >On Fri, 20 Feb 2004 18:08:35 GMT,
> (Corky Scott) wrote:
> >
> >
> >>Auto engines are tiny when compared to direct drive airplane engines.
> >>Take a 180 hp Lycoming. It's cubic inch displacement is 360. They
> >>turn the prop at around 2600 to 2700. The Ford V-6 in airplane trim,
> >>puts out 180 hp also. It displaces 232 inches and makes it's power at
> >>4800 rpm. No prop will work at that rpm. To harness the power, it
> >>needs to be turned slower. Enter the prop speed reduction unit.
> >
> >Speaking of Fords! How's your project coming?
> >
> >__________________
> >Note: To reply, replace the word 'spam' embedded in return address with 'mail'.
> >N38.6 W121.4
>
> Slowly. I have the engine assembled and is currently mounted in the
> airframe. But there's everything else to do. The airframe has yet to
> be blasted and painted. I think that can happen this summer. On the
> other hand, we are planning some major kitchen redo's and trust me,
> ALL of my attention had better be on that.
>
> I've built an engine test stand that will allow me to wheel the engine
> outside and run it, with the prop installed. I'd like to get some 30
> or so hours on the engine before it gets it's final installation onto
> the airframe. I decided this after listening to a crusty old DAR
> speak at a local EAA meeting. It sounded to me like he'd be REALLY
> unhappy with such an engine unless I could show him that it had been
> thoroughly tested.
>
> At this point, I'm being educated about headers. I was going to just
> bend up a bunch of tubes, weld them to be what I need, get them jet
> coated and call it good. Then I started doing some research.
>
> It turns out that the diameter of header tubing is critical to the
> performance of the engine. Larger diameter is not necessarily better.
> In fact in almost all aircraft type applications, bigger is virtually
> for sure not better. The exhaust header flange has openings that are
> 1.75" in diameter. This matches the exhaust port opening in the head.
> But the tubing diameter should be 1.5", or possibly even 1 3/8" in
> diameter. Also, the length of the runners should be at least over 30
> inches, and 36 would be better. In addition, each tube should be as
> close in length to each other as possible. Finally, the collector
> needs to be about 1 78" diameter and it should be 18" long.
>
> Reality is rearing it's ugly head. The lengths I mentioned literally
> won't fit without welding the headers into loops. Not going to
> happen.
>
> I think the best I can do is get the runners as long as I can make
> them and make sure they are of equal length, and get the proper
> collector as that also has a huge affect on engine operation.
>
> Why is it so important to have the runners be the same length?
> Because different length runners cause different scavenging effects
> within the combustion chamber. You will end up with an engine that
> does not respond to ignition adjustments nor mixture adjustments as
> some combustion chambers will run rich and some lean. "A series of
> single cylinder engines flying loosely in formation." Quote from John
> Deakin.
>
> Many builders of the Ford V6 have complained that their engine ran
> rough at maximum power. Huge effort was made to modify the intake
> manifold to correct the problem. But I have not seen a single picture
> of an exhaust manifold where the effort was made to create equal
> length exhaust headers of the proper diameter.
>
> I talked with a header manufacturer who told me he had heard of Dave
> Blanton because a bunch of builders had asked him about headers. He
> told me they all wanted to ignor his advice about tubing diameter.
> They all wanted to use bigger tubing than was dictated, because they
> all thought bigger was better. It's not.
>
> Why is it so important to have the proper diameter tubing? Because
> the bigger the diameter the slower the velocity of the gasses inside
> it, and visa versa, up to a point. Eventually you can have exhaust
> tubing in a diameter too small such that exhaust flow is restricted.
> Large diameter tubing tends to cause the engine's power to peak at
> extreme rpms. The smaller the diameter of the tubing, the more low to
> midrange power you have.
>
> But everyone wanted to use 1.75" tubing because that's what the
> exhaust port was. 1.75" tubing would be what you would use if you
> wanted flash horsepower from the engine at 8,000 rpm, like at the
> dragstrip.
>
> The header manufacturer also had a lot to say about "Zoomie" type
> headers. These are headers without collectors, basically straight
> pipes. Not only are these tubes also usually too large a diameter,
> they leave off the collector which is crucial to the proper design of
> the header system.
>
> So with all this information, I'm taking my time with the header
> design. Obviously something so important to the proper running of the
> engine is not something I'm going to throw together without using
> proper design criteria.
>
> Corky Scott

[Blueskies]

If I remember correctly, the nose down full throttle was a tactic used to escape the zero's. They knew they would not
break the plane and the enemy often did. Same was true of the Wildcat, no limitation, plane would reach terminal
velocity...

--
Dan D.



..
"Big John" > wrote in message ...
> Corkey
>
> The P-40 wouldn't go supersonic. Had a few hours in bird and took one
> to about 20K and rolled over at full thottle. Huffed and puffed on way
> down and I started my pull out about 10K and was level about 3K.
>
> Bird did not have a Mach meter, only a ASI. As I remember only got a
> little over 400 mph max (high drag, low power).
>
> That one dive conviced me it was a subsonic aircraft :o)
>
> Big John
>
> On Mon, 23 Feb 2004 19:45:15 GMT,
> (Corky Scott) wrote:
>
> >On 23 Feb 2004 09:32:01 -0800, (Jay) wrote:
> >
> >>For props, bigger is better for static thrust (look at a helecopter)
> >>but what about for top speed, a more desireable figure of merit for
> >>fixed wing aircraft? I seem to remember hearing somewhere that for
> >>top speed there is an optimal prop length that is not infinite. You
> >>need to generate a stream of air that is going faster than the speed
> >>that you want to fly.
> >>
> >You just described the reason no piston engined WWII fighter ever flew
> >faster than the speed of sound. The prop needed to produce enough
> >thrust to pull the airplane into supersonic speed, but the prop was
> >running into the wall of drag as the tips neared supersonic speed and
> >the fuselage was producing enormous drag too.
> >
> >The prop tips would have to go supersonic if the airplane was to go
> >that fast too, and props of that era were not designed for supersonic
> >speeds.
> >
> >Even going straight down at full power, just too much drag. They went
> >fast enough to scare the bajeebers out of a number of pilots though.
> >:-) They also went fast enough to lock up the controls and in some
> >cases, cause the destruction of the airplane... and the pilot.
> >
> >Corky Scott
>

[Big John]

Dan

The P-38 had high speed dive problems. After a number crashed they
went back and retrofitted them with 'dive' brakes (narrow strips on
top of wing that could be raised to increase drag). These slowed the
bird down enough it could be pulled out

The P-47 also had some dive problems. It wanted to tuck at high speed
in a dive. To recover you kept full throttle on and when you got to a
lower altitude you slowed down in the thicker air and regained enough
control to recover.

The P-51 was red lined at 505 mph. I have had it up to that speed and
didn't have any problems recovering from dive.

I have friends who were in Europe and told of far exceeding the 505
red line when getting away from 109/190's. The 109 had a structural
problem in their tail and it would come off if they got too fast in a
dive (per word passed to our fighter jocks).

All of this in a time and land far away :o)

Big John

On Tue, 24 Feb 2004 11:58:03 GMT, "Blueskies" > wrote:

>If I remember correctly, the nose down full throttle was a tactic used to escape the zero's. They knew they would not
>break the plane and the enemy often did. Same was true of the Wildcat, no limitation, plane would reach terminal
>velocity...

[Charlie Smith]

>
> Not with gears! But a belt can provide any ratio. Of course any
> irrational number can be approximated arbitrarily well by a rational
> number... but the idea is just to choose a number that can't be
> approximated well by a ratio of small numbers, not one that's genuinely
> mathematically irrational. (Indeed, the latter concept is almost
> meaningless in engineering, which is why I felt free to use "irrational"
> as shorthand for the former concept.)
>
> The idea isn't complete nonsense. If you had two identical assemblies,
> linked by a belt drive, it'd be exactly the thing to do. You wouldn't
> pick a 2:3 ratio, for instance, since that would mean the second harmonic
> of one would resonate with the third harmonic of the other.

I struggle with understanding how you will throw a dangerous harmonic down a
viscoelastic belt. I guess it could be done but it doesn't seem as if it
could be done easily. Metal gears or similarly high modulus materials will
have an extremely low tangent delta and therefore have good
transmissibility. Vibration along a broad spectrum of frequencies should be
efficiently transmitted in such materials. Rubber doesn't transmit
frequency very efficiently unless its a glass; then it doesn't bend either
(unless you bend it very, very, very slowly). More likely you select the
ratio that gets you your desired prop RPM at the desired engine RPM. The
rubber belt should be an excellent (not perfect) vibration decoupler.

Charlie Smith
KIS Cruiser 4021

[[email protected]]

Pete Schaefer > wrote:
: Easy. Just use one gear with 1.4264 teeth in it.

: "Tim Ward" > wrote in message
: ...
:> Just out of curiosity, how would you get any ratio to be an irrational
:> number?

Actually, that wouldn't work either, since 1.4264 = 14264/10000. Now, if you
found the mystical gear with sqrt(2) teeth... then you'd be in business... :)

-Cory


--
************************************************** ***********************
* The prime directive of Linux: *
* - learn what you don't know, *
* - teach what you do. *
* (Just my 20 USm$) *
************************************************** ***********************

[Morgans]

"Big John" > wrote in message
>
> The P-38 had high speed dive problems. After a number crashed they
> went back and retrofitted them with 'dive' brakes (narrow strips on
> top of wing that could be raised to increase drag). These slowed the
> bird down enough it could be pulled out
>
Wasn't part of that fix also a mass balancer on the elevator, that was a
blob raised up on an arm above the elevator?
--

Jim in NC


---
Outgoing mail is certified Virus Free.
Checked by AVG anti-virus system (http://www.grisoft.com).
Version: 6.0.593 / Virus Database: 376 - Release Date: 2/20/2004

[Richard Lamb]

wrote:
>
> Pete Schaefer > wrote:
> : Easy. Just use one gear with 1.4264 teeth in it.
>
> : "Tim Ward" > wrote in message
> : ...
> :> Just out of curiosity, how would you get any ratio to be an irrational
> :> number?
>
> Actually, that wouldn't work either, since 1.4264 = 14264/10000. Now, if you
> found the mystical gear with sqrt(2) teeth... then you'd be in business... :)
>
> -Cory
>
> --

Maybe we can ask Jim to design a pi detector.

That's a tough one,
A lot harder than the BS detector...

[Richard Lamb]

Morgans wrote:
>
> "Big John" > wrote in message
> >
> > The P-38 had high speed dive problems. After a number crashed they
> > went back and retrofitted them with 'dive' brakes (narrow strips on
> > top of wing that could be raised to increase drag). These slowed the
> > bird down enough it could be pulled out
> >
> Wasn't part of that fix also a mass balancer on the elevator, that was a
> blob raised up on an arm above the elevator?
> --
>
> Jim in NC

More likely the mass balance was used to raise the flutter speed of the
elevator. Get it up above the airplane's speed range.

Also, while on the subject of P-38 lore...

I thought the dive brakes retro on the P-38 was on the bottom of the
wing?

Part of the problem was that even though the airplane was traveling at
less than transonic speed, there were places that the "air" was getting
supersonic and creating shock waves.

(I put that in quotes, because it's really the airplane that's moving,
not the air. The air just gets out of the way - rapidly. Can't blame
it.)

Then, as speed builds, the shock waves move aft?

The Bell X-1 had some problems with the shock waves moving aft on the
elevator. Moved right back to the elevator hinge line and elevator
control was rather - uhm - nonexistent?

The airplane also had a variable incidence stabilizer for elevator trim.
Chuck tried flying the airplane with the trim switch and the "all
flying"
tail, or stabilator was born.

If this is happening on the wing, as the pressure point moves aft the
nose tucks down very nicely!

As pressure increases due to decreasing altitude, the airplane might
slow
enough to return to normal subsonic conditions, and regain control.

But you'd best be hauling that nose up now!


Let's say you recover control at 25,000 feet?
You are pointed straight down at 500 mph.

You are going a little faster than 8 miles a minute,

and you are slightly more than 4 miles up...

I think it takes about 1.6 seconds from initiation
for the seat to clear the airframe...


Richard

[Big John]

Morgans

I remember reading something about the mass balancer as you call it
but can't remember what it was the solution for. It could have been to
prevent the elevator from causing trouble when in the shock wave at
high mach?

Here is what I found on Internet. They say the strip was on the bottom
of the wing but I thougth I remembered it to be on the top. In any
event it stopped the dive problem.

Quote

Earlier Lightnings had problems with high-speed dives. When the
airspeed reached a sufficiently high value, the controls would
suddenly lock up and the Lightning would tuck its nose down, making
recovery from the dive difficult. In the worst case, the wings of the
Lightning could be ripped off if the speed got too high. This problem
caused the Lightning often to be unable to follow its Luftwaffe
opponents in a dive, causing many of the enemy to be able to escape
unscathed. The problem was eventually traced to the formation of a
shock wave over the wing as the Lightning reached transonic speeds,
this shock wave causing the elevator to lose much of its
effectiveness. The problem was not cured until the advent of the
P-38J-25-LO, which introduced a set of compressibility flaps under the
wing which changed the pattern of the shock wave over the wing when
they were extended, restoring the function of the elevator.

Unquote

Big John

On Tue, 24 Feb 2004 16:03:44 -0500, "Morgans"
> wrote:

>
>"Big John" > wrote in message
>>
>> The P-38 had high speed dive problems. After a number crashed they
>> went back and retrofitted them with 'dive' brakes (narrow strips on
>> top of wing that could be raised to increase drag). These slowed the
>> bird down enough it could be pulled out
>>
>Wasn't part of that fix also a mass balancer on the elevator, that was a
>blob raised up on an arm above the elevator?

[Blueskies]

Yes, the only two 'modern' fighters of that era with no dive limitations were the p-40 and f-4f...

A guy named Reggie told me a story about when he was flying a Spit over the channel and a 109 jumped him. he flipped the
spit over into a dive and the 109 chased him on down. He was getting pretty low so he started a hard pull out of the
dive. He looked over his shoulder and saw the 109 try to pull out inside him. As the g's built he saw the 109 breakup
and fall into the channel. Reg was a good ol brit who had a nice plane down in Santa Paula...

--
Dan D.



..
"Big John" > wrote in message ...
> Dan
>
> The P-38 had high speed dive problems. After a number crashed they
> went back and retrofitted them with 'dive' brakes (narrow strips on
> top of wing that could be raised to increase drag). These slowed the
> bird down enough it could be pulled out
>
> The P-47 also had some dive problems. It wanted to tuck at high speed
> in a dive. To recover you kept full throttle on and when you got to a
> lower altitude you slowed down in the thicker air and regained enough
> control to recover.
>
> The P-51 was red lined at 505 mph. I have had it up to that speed and
> didn't have any problems recovering from dive.
>
> I have friends who were in Europe and told of far exceeding the 505
> red line when getting away from 109/190's. The 109 had a structural
> problem in their tail and it would come off if they got too fast in a
> dive (per word passed to our fighter jocks).
>
> All of this in a time and land far away :o)
>
> Big John
>
> On Tue, 24 Feb 2004 11:58:03 GMT, "Blueskies" > wrote:
>
> >If I remember correctly, the nose down full throttle was a tactic used to escape the zero's. They knew they would not
> >break the plane and the enemy often did. Same was true of the Wildcat, no limitation, plane would reach terminal
> >velocity...
>

[Dave]

Or how about a gear who's circumference was exactly 3 times its
diameter? Now THAT would be an irrational gear! <g>

Dave


wrote:
> Pete Schaefer > wrote:
> : Easy. Just use one gear with 1.4264 teeth in it.
>
> : "Tim Ward" > wrote in message
> : ...
> :> Just out of curiosity, how would you get any ratio to be an irrational
> :> number?
>
> Actually, that wouldn't work either, since 1.4264 = 14264/10000. Now, if you
> found the mystical gear with sqrt(2) teeth... then you'd be in business... :)
>
> -Cory
>
>

[Big John]

Richard

You talk like you have been in the business.

Your right, the speed brakes were at about 30% chord on the bottom of
the wing.

The mass balance was directed by the AAC to correct elevator flutter
but Kelly Johnson said they were not needed and tests they ran proved
him right. However AAC said put on so they did. Kelly said that a
number of Pilots were killed when they bailed out and hit the weights
:o(

My roommate bought the farm turning final on his second flight
checking out in '38 at Kimpo Air Base, Korea. Probably got slow and
stalled the bird?

Big John

On Tue, 24 Feb 2004 21:39:43 GMT, Richard Lamb >
wrote:

>Morgans wrote:
>>
>> "Big John" > wrote in message
>> >
>> > The P-38 had high speed dive problems. After a number crashed they
>> > went back and retrofitted them with 'dive' brakes (narrow strips on
>> > top of wing that could be raised to increase drag). These slowed the
>> > bird down enough it could be pulled out
>> >
>> Wasn't part of that fix also a mass balancer on the elevator, that was a
>> blob raised up on an arm above the elevator?
>> --
>>
>> Jim in NC
>
>More likely the mass balance was used to raise the flutter speed of the
>elevator. Get it up above the airplane's speed range.
>
>Also, while on the subject of P-38 lore...
>
>I thought the dive brakes retro on the P-38 was on the bottom of the
>wing?
>
>Part of the problem was that even though the airplane was traveling at
>less than transonic speed, there were places that the "air" was getting
>supersonic and creating shock waves.
>
>(I put that in quotes, because it's really the airplane that's moving,
>not the air. The air just gets out of the way - rapidly. Can't blame
>it.)
>
>Then, as speed builds, the shock waves move aft?
>
>The Bell X-1 had some problems with the shock waves moving aft on the
>elevator. Moved right back to the elevator hinge line and elevator
>control was rather - uhm - nonexistent?
>
>The airplane also had a variable incidence stabilizer for elevator trim.
>Chuck tried flying the airplane with the trim switch and the "all
>flying"
>tail, or stabilator was born.
>
>If this is happening on the wing, as the pressure point moves aft the
>nose tucks down very nicely!
>
>As pressure increases due to decreasing altitude, the airplane might
>slow
>enough to return to normal subsonic conditions, and regain control.
>
>But you'd best be hauling that nose up now!
>
>
>Let's say you recover control at 25,000 feet?
>You are pointed straight down at 500 mph.
>
>You are going a little faster than 8 miles a minute,
>
>and you are slightly more than 4 miles up...
>
>I think it takes about 1.6 seconds from initiation
>for the seat to clear the airframe...
>
>
>Richard

[Bob Chilcoat]

According to Warren Bode in his definitive book on the P-38, the bob weights
in the center of the elevator were mandated by the Army after one of the
YP-38's shed its tail in a dive. Further dive tests seemed to indicate that
the problem was tail flutter at certain speeds. The bob weights were added
but did not solve the problem. Wind tunnel tests eventually traced the
"flutter" problem to buffeting from turbulence off the joint between the
wing and the center fuselage pod. After a fillet was added to soften this
joint, the "flutter" problem disappeared, but the Army would not let Johnson
remove the bob weights. He hated them (the elevator was already
counterbalanced by concealed weights in the tail cones) and felt that their
only contribution was to kill a few pilots who hit them in bailouts. The
"compressability tuck" problem was investigated at the same time, but was
only solved by means of the dive brakes that were added to the P-38J-25-LO
and subsequent models. As it turned out, the compressability problem could
not occur in any P-38's if dives were initiated below 25,000 feet. Since
most P-38 operations during the war were below that altitude, few pilots
encountered the problem in combat.
--
Bob (Chief Pilot, White Knuckle Airways)

"Morgans" > wrote in message
...
>
> "Big John" > wrote in message
> >
> > The P-38 had high speed dive problems. After a number crashed they
> > went back and retrofitted them with 'dive' brakes (narrow strips on
> > top of wing that could be raised to increase drag). These slowed the
> > bird down enough it could be pulled out
> >
> Wasn't part of that fix also a mass balancer on the elevator, that was a
> blob raised up on an arm above the elevator?
> --
>
> Jim in NC
>
>
> ---
> Outgoing mail is certified Virus Free.
> Checked by AVG anti-virus system (http://www.grisoft.com).
> Version: 6.0.593 / Virus Database: 376 - Release Date: 2/20/2004
>
>

[Big John]

Bob

Your right

I posted a follow on to thread covering essentially what you said and
it never made it? I have had several disappeared like that and need to
find out what is happening. I thought at first someone was going in
and deleting my posts but I normally don't get into a Peeing contest
with most posters and need to be censored :o).

In any event, glad you posted so some of the young ones will know what
happened a long time ago in a land far away :o)

Big John

On Wed, 25 Feb 2004 10:37:57 -0500, "Bob Chilcoat"
> wrote:

>According to Warren Bode in his definitive book on the P-38, the bob weights
>in the center of the elevator were mandated by the Army after one of the
>YP-38's shed its tail in a dive. Further dive tests seemed to indicate that
>the problem was tail flutter at certain speeds. The bob weights were added
>but did not solve the problem. Wind tunnel tests eventually traced the
>"flutter" problem to buffeting from turbulence off the joint between the
>wing and the center fuselage pod. After a fillet was added to soften this
>joint, the "flutter" problem disappeared, but the Army would not let Johnson
>remove the bob weights. He hated them (the elevator was already
>counterbalanced by concealed weights in the tail cones) and felt that their
>only contribution was to kill a few pilots who hit them in bailouts. The
>"compressability tuck" problem was investigated at the same time, but was
>only solved by means of the dive brakes that were added to the P-38J-25-LO
>and subsequent models. As it turned out, the compressability problem could
>not occur in any P-38's if dives were initiated below 25,000 feet. Since
>most P-38 operations during the war were below that altitude, few pilots
>encountered the problem in combat.

[Norman Yarvin]

In article <Ubw_b.390034$na.638038@attbi_s04>, x > wrote:
>> of one would resonate with the third harmonic of the other. But a
>> propeller and an engine are nowhere close to identical; their resonant
>> frequencies don't have anything to do with each other in the first place,
>
>What resonance characteristics does a propeller have, and why?

Anything that is solid vibrates, and has resonant frequencies.
Beyond that, I haven't done any detailed analysis.


--
Norman Yarvin http://yarchive.net

[Norman Yarvin]

In article >,
Charlie Smith > wrote:

>> Not with gears! But a belt can provide any ratio. Of course any
>> irrational number can be approximated arbitrarily well by a rational
>> number... but the idea is just to choose a number that can't be
>> approximated well by a ratio of small numbers, not one that's genuinely
>> mathematically irrational. (Indeed, the latter concept is almost
>> meaningless in engineering, which is why I felt free to use "irrational"
>> as shorthand for the former concept.)
>>
>> The idea isn't complete nonsense. If you had two identical assemblies,
>> linked by a belt drive, it'd be exactly the thing to do. You wouldn't
>> pick a 2:3 ratio, for instance, since that would mean the second harmonic
>> of one would resonate with the third harmonic of the other.
>
>I struggle with understanding how you will throw a dangerous harmonic down a
>viscoelastic belt. I guess it could be done but it doesn't seem as if it
>could be done easily. Metal gears or similarly high modulus materials will
>have an extremely low tangent delta and therefore have good
>transmissibility. Vibration along a broad spectrum of frequencies should be
>efficiently transmitted in such materials. Rubber doesn't transmit
>frequency very efficiently unless its a glass; then it doesn't bend either
>(unless you bend it very, very, very slowly). More likely you select the
>ratio that gets you your desired prop RPM at the desired engine RPM. The
>rubber belt should be an excellent (not perfect) vibration decoupler.

Yeah, a belt is a lot less rigid than the metal of the rest of the
system, and absorbs a lot more. The lack of rigidity is why it makes
sense to talk about the individual resonant frequencies of the two parts
it connects -- they'll only be weakly coupled -- rather than talking
about the resonant frequencies of the combined system. But these belts
aren't exactly rubber bands; most of the stress is taken by fibers in the
belt, and the rubber mainly provides the frictional surface.


--
Norman Yarvin http://yarchive.net

[Bob Chilcoat]

John,

I saw your post on the same subject after I sent mine. Sorry for the
duplication, but at least yours did make it to my newsreader at least. My
late father (http://users.erols.com/viewptmd/Dad.html) flew the P-38, among
many other aircraft, and we still have his "Flight Manual" for it (and one
for the P-40, and the B-25). I remember reading warnings about
"compressability" in the manual when I was younger, and wondering what that
was all about. My brother in Columbus has the manuals now, so I can't refer
to it.

--
Bob (Chief Pilot, White Knuckle Airways)


"Big John" > wrote in message
...
>
> Bob
>
> Your right
>
> I posted a follow on to thread covering essentially what you said and
> it never made it? I have had several disappeared like that and need to
> find out what is happening. I thought at first someone was going in
> and deleting my posts but I normally don't get into a Peeing contest
> with most posters and need to be censored :o).
>
> In any event, glad you posted so some of the young ones will know what
> happened a long time ago in a land far away :o)
>
> Big John
>

[Corky Scott]

On Tue, 24 Feb 2004 11:46:41 GMT, "Blueskies" > wrote:

>Corky,
>
>Do you have any details available about your engine test stand, such as how you restrain it, instrumentation, cooling?
>
>Also, a buddy of mine was talking about an engine build he did, and how he used water to match each header tube volume,
>old news I'm sure...
>
>--
>Dan D.

I fabricated the engine stand using a lot of OTLAR measurements.

I pulled some 1 1/4" tubing out of the pile (I bought a pile of tubing
for a Skybolt kit years ago and still have at least half of it left.
I always seem to find enough of what I need for projects like this. I
think the cost for the tubing worked out to something like 10 cents on
the dollar.) and welded a large rectangle. Then I welded plates on
each of the corners and scrounged up four casters from around my shop
and drilled bolt holes in the plates and bolted them on. It has two
swiveling and two that don't. They are largish,solid rubber
commercial casters and I have no idea where I found them originally
but I've had them in the shop for years. I didn't pay anything for
them, I remember that.

Then I duplicated the engine mount rails and bolted them to the
engine. I suspended the engine over the base and fitted and welded
support legs from the rails to each corner of the base. Removed the
engine and welded everything.

Then I added 3/4" diagonal tubing fore and aft between the support
legs so that the engine could not shift or sway. That REALLY
solidified things.

What I'd **like** to do is remove the instrument panel from the
cockpit and mount it on the stand and use what instruments are
necessary to monitor engine performance. That way I don't have to
fabricate two instrument panels. I have not cut any holes for
instruments yet so that's in the near future. Actually buying some
instruments is also in the near future. ;-)

I'll need: Oil pressure, oil temperature, tachometer, water pressure,
water temperature and an EGT guage. It probably wouldn't hurt to have
a cylinderhead temperature guage too. I'm leaning towards digital for
the tach and possibly the temps as well but have not made up my mind
on which of the numerous choices to use.

Or I could just use some scrap plywood since I only need the
instruments that monitor engine performance so the test stand panel
could be smallish. Or I could cut up some of the 1/8" sheet aluminum
from the huge panel I scored for free. Using that stuff takes a lot
more work than using plywood though.

The radiator is sitting below the engine at present, but I think I'm
going to have to move it a bit so that the exhaust system can clear
it. The plan is for the exhaust to wrap under and behind the engine
and tuck right behind the Griffin radiator, when I get it. But for
now, the radiator I picked up from the auto parts place will do the
job. It's a Ford Taurus radiator so I know it's adaquate for the
task. If I pick up the custom radiator before all is installed back
on the airframe, I'll likely fabricate the entire cooling duct system,
including the exhaust augmentation, just to make sure the system cools
properly.

I will leave the engine installed in the fuselage for the moment, so I
can fabricate the exhaust and make sure that it fits the airframe
properly, then the exhaust will be removed from the engine and the
engine transferred to the test stand and the exhaust system
re-installed.

I'll route hoses to the radiator as necessary and weld on a pan to
hold the battery. I'll also have a "gas tank" somewhere on the base
of the stand and will have to use a fuel pump to get the gas up to the
carburetor, probably a submerged type, or something that goes in-line
and I'll just bond on a fuel line out of the gas tank.

I've built the stand tall enough that the prop can be mounted to the
engine.

When I get ready to fire it up, I'll literally have to chain the stand
down so that it does not try to hurtle off into the woods like some
demented woods buggy run amuck.

I may lift the whole thing into the back of the pickup and drive up
into the woods to do the extended running so that the neighbors don't
complain. I'll strap it down for the trip, and for running it, of
course.

I'll probably pitch the prop so that the engine can run to it's
maximum rpm while on the test stand. This will be necessary because
I'll need to make sure the engine can manage full power for extended
periods, plus there may be some tuning and adjustments required that
show up only at full power.

The test stand is roughly patterned after the engine test stands I
worked with while training as an auto mechanic at the Rhode Island
Trades Shops. Those engines did not have props bolted to them though.

If anyone would like to see what the test stand looks like, send me an
e-mail and I'll enclose a picture and send it to you. It's in rough
form right now, not completed, but I have some shots of the engine
bolted in place so you'll get a good idea of what I'm trying to
accomplish. Plus, since it's in the unpainted stage, I can still make
lots of modifications to it, should anyone have any ideas.

Corky Scott

[bryan chaisone]

Bravo! Professor Lamb...
Well done! Well done indeed... Even a simple layman Like myself can understand.

Bryan

Richard Lamb > wrote in message >...
> Dave Covert wrote:
> >
> > I notice that most auto engine conversions use a gear box between the engine
> > and the prop. Why is that? Is it because an auto engine's peak HP is too
> > high for a prop to swing? Is it because auto engines weren't designed to be
> > pulled around by their crankshafts and don't have proper thrust bearings?
> > Both?
> >
> > Are there any auto/motorcycle conversions that don't require gear boxes?
> >
> > Dave
>
> Some people think aircraft engines are "old fashioned technology"
> and have not kept up with developments in auto engine field.
>
> They point out that aircraft engines haven't changed much in
> over 50 years.
>
> Some people feel that auto engines can be used to power airplanes.
>
> To some extent, all three of these ideas are true.
>
> Aircraft engine do not run like car motors.
>
> Aircraft engines run at much higher sustained power settings and
> constant rpm for long periods of time.
>
> And then there is the propeller...
> Turning the propeller is what it's all about.
>
> The propeller converts the engine's power into thrust.
> As always, when energy is converted, there are losses.
>
> Moving through the air at very high speeds, the propeller
> makes lift (thrust, which is power successfully converted into
> forward motion) and drag (pure conversion losses).
>
> So, propeller efficiency is extremely important.
>
> If the propeller is only 50% efficient, half of the
> power generated by the engine is wasted in losses.
> Yes, literally.
>
> Only one hard rule for propellers - longer is better.
>
> But longer blades mean lower RPM because the tips of the
> propeller blades MUST stay below the speed of sound (yep,
> Mach 1, really) for any efficiency at all.
>
> Part of the reason for this is the huge increase in drag
> as the tip enters the transonic (speed) region.
>
> It takes TORQUE to turn that propeller - not horsepower.
>
> A given propeller needs to turn at a given RPM, which
> will require a given amount of torque.
>
> If the engine makes enough torque to turn the propeller at
> that RPM, a direct drive set up may be possible.
>
> There are a lot of other minor details that may get in the way -
> Harmonic Resonance is a big one.
> But, it may be possible to run this combination direct drive.
>
> If the engine needs to turn at a higher RPM to make adequate
> power, some kind of gearing would be necessary to reduce engine
> RPM to propeller RPM. Notice that reducing RPM will increase
> torque proportionally. Seems like a nice trade off.
>
> Now the engine should be running at an RPM near the peak of its'
> torque curve. This is for best engine operating economy.
>
> And the (longer) propeller is running at a comfortable (lower)
> RPM for good efficiency. Life is wonderful.
>
> Except for the weight.
> Auto engines are seldom as light as possible.
> Then we add more weight in the form of a gearbox and such.
> Radiators full of heavy (hot!) fluids.
> External oil sump?
> Mounting?
> Propeller gyroscopic forces operating on the crankshaft?
>
> Weight is critical to any flying machine.
> (Go back and look at how birds are built)
>
> So...
> Think of it as evolution in action.
>
> The reason our old antique Lycosourus engines are the way they
> are is that they evolved into a very narrow niche.
>
> They turn propellers to pull airplanes.
>
> They make very high torque
> at very low RPM,
> and are as light as possible.
> They are tremendously reliable and fairly efficient.
>
> Prices are high because of limited production and high demand.
> Simple economics.
>
> But the economics of engine development (and risk assesment) are
> anything but simple.
>
> I have a big bore VW (2180cc) on my parasol.
> That's a converted car motor.
>
> There is a weatlh of prior art using VW engines for small airplanes
> (if one is inclined to use it).
>
> What works, and what doesn't. (eg: breaking cast crankshafts)
>
> Mine is a very simple conversion, using high quality (GPAS) parts
> built by a little German perfectinist.
> I trust it - so far.
>
> I also don't push it beyond conservative limits.
>
> All VW engines are 40 hp engine (IMHO).
> Some can make more power than that - for a while.
> This one is _rated_ at 70 hp.
> But will reach thermal limits of the fin area and overheat
> if not throttled back (to roughly 40?)
>
> It's a fairly expensive motor.
> The jugs and pistons are standard parts, but the crank (!) and
> accessories and machine work are all specialty items.
> A new 2180 can easily go over $5000 with a few bells and whistles.
>
> But the weight, power, reliability, and operating cost are all within
> reason for this particular airplane.
>
> The airplane itself can land slowly, around 35 mph.
>
> The chances of getting down safely if the engine quits are a lot better
> at 35 than they are at 53.
>
> To me, it seems like a reasonable risk for the potential rewards.
>
> But...
>
> Your milage may vary.
>
> Richard
>
> http://www.flash.net/~lamb01
>
>
> PS: I've read of a Curtiss Hawk replica that uses a direct drive Chevy
> 350.
> It's supposed to make roughly 190 hp?
> It would obviously be a heavy motor.
> Not something you'd hang on a glass slipper.
> But on a big old biplane with a looong prop
> it seems to be just the ticket.

[bryan chaisone]

Bill the Grump,

Between this statement, "When I was the test pilot!". and all of your
stories, you are a legend in your own right. Or is that in your own
mind?

You are a character... LOL. We do enjoy you here, even if you are the
Grump.

Bryan


(Badwater Bill) wrote in message >...
> Nice job Richard. Nice Job.
>
> I might just add one more comment to clear something up a bit. When
> you chose a prop, you design it so the tip speeds don't exceed 0.80
> Mach, or 80% the speed of sound. As the propeller tips approach
> speeds over that, the airflow can become super sonic even though the
> prop tip is well below Mach-1. As you mentioned, that takes a lot of
> energy that is wasted and is not available for thrust to create a
> shock wave and sustain it.
>
> When I was the test pilot on the OMABP RV-6A project, we used the
> Chevy Vortec V-6 engine, the PSRU was specifically designed to turn
> the prop at tip speed below 80% the speed of sound. Jess Meyers also
> used a reduction ratio number that was about equal to the square root
> of 2 to eliminate harmonics that could have resulted in reversed
> torque pulses reflecting back into the engine. By using a reduction
> ratio of 1.41 (or close to it) he eliminated many sympathetic
> harmonics that may have occured.
>
> BWB

[bryan chaisone]

Richard Lamb > wrote in message >...
>
> Maybe we can ask Jim to design a pi detector.
>
> That's a tough one,
> A lot harder than the BS detector...

I've got a pie detector! It's right below my eyes. I can smell pies
from at least a football field away, UP WIND! Oh... You're talking
math aren't you? Damn, all you college boys make me feel
unedumacated.

Bryan "the monk" Chaisone
http://www.alexisparkinn.com/rogue's_gallery_a-h.htm#C

[Richard Lamb]

bryan chaisone wrote:
>
> Bravo! Professor Lamb...
> Well done! Well done indeed... Even a simple layman Like myself can understand.
>
> Bryan
>

Golly! Thanks.

I didn't mean to know that much, but I came by it honestly.

;)

Richard

[Richard Lamb]

bryan chaisone wrote:
>
> Bravo! Professor Lamb...
> Well done! Well done indeed... Even a simple layman Like myself can understand.
>
> Bryan
>

Golly! Thanks.

I didn't mean to know that much, but I came by it honestly.

;)

Richard

[Peter Dohm]

Corky Scott wrote:
>
> On 20 Feb 2004 14:19:16 -0600, Barry S. > wrote:
>
> >On Fri, 20 Feb 2004 18:08:35 GMT,
> (Corky Scott) wrote:
> >
> >
> >>Auto engines are tiny when compared to direct drive airplane engines.
> >>Take a 180 hp Lycoming. It's cubic inch displacement is 360. They
> >>turn the prop at around 2600 to 2700. The Ford V-6 in airplane trim,
> >>puts out 180 hp also. It displaces 232 inches and makes it's power at
> >>4800 rpm. No prop will work at that rpm. To harness the power, it
> >>needs to be turned slower. Enter the prop speed reduction unit.
> >
> >Speaking of Fords! How's your project coming?
> >
> >__________________
> >Note: To reply, replace the word 'spam' embedded in return address with 'mail'.
> >N38.6 W121.4
>
> Slowly. I have the engine assembled and is currently mounted in the
> airframe. But there's everything else to do. The airframe has yet to
> be blasted and painted. I think that can happen this summer. On the
> other hand, we are planning some major kitchen redo's and trust me,
> ALL of my attention had better be on that.
>
> I've built an engine test stand that will allow me to wheel the engine
> outside and run it, with the prop installed. I'd like to get some 30
> or so hours on the engine before it gets it's final installation onto
> the airframe. I decided this after listening to a crusty old DAR
> speak at a local EAA meeting. It sounded to me like he'd be REALLY
> unhappy with such an engine unless I could show him that it had been
> thoroughly tested.
>
> At this point, I'm being educated about headers. I was going to just
> bend up a bunch of tubes, weld them to be what I need, get them jet
> coated and call it good. Then I started doing some research.
>
> It turns out that the diameter of header tubing is critical to the
> performance of the engine. Larger diameter is not necessarily better.
> In fact in almost all aircraft type applications, bigger is virtually
> for sure not better. The exhaust header flange has openings that are
> 1.75" in diameter. This matches the exhaust port opening in the head.
> But the tubing diameter should be 1.5", or possibly even 1 3/8" in
> diameter. Also, the length of the runners should be at least over 30
> inches, and 36 would be better. In addition, each tube should be as
> close in length to each other as possible. Finally, the collector
> needs to be about 1 78" diameter and it should be 18" long.
>
> Reality is rearing it's ugly head. The lengths I mentioned literally
> won't fit without welding the headers into loops. Not going to
> happen.
>
> I think the best I can do is get the runners as long as I can make
> them and make sure they are of equal length, and get the proper
> collector as that also has a huge affect on engine operation.
>
> Why is it so important to have the runners be the same length?
> Because different length runners cause different scavenging effects
> within the combustion chamber. You will end up with an engine that
> does not respond to ignition adjustments nor mixture adjustments as
> some combustion chambers will run rich and some lean. "A series of
> single cylinder engines flying loosely in formation." Quote from John
> Deakin.
>
> Many builders of the Ford V6 have complained that their engine ran
> rough at maximum power. Huge effort was made to modify the intake
> manifold to correct the problem. But I have not seen a single picture
> of an exhaust manifold where the effort was made to create equal
> length exhaust headers of the proper diameter.
>
> I talked with a header manufacturer who told me he had heard of Dave
> Blanton because a bunch of builders had asked him about headers. He
> told me they all wanted to ignor his advice about tubing diameter.
> They all wanted to use bigger tubing than was dictated, because they
> all thought bigger was better. It's not.
>
> Why is it so important to have the proper diameter tubing? Because
> the bigger the diameter the slower the velocity of the gasses inside
> it, and visa versa, up to a point. Eventually you can have exhaust
> tubing in a diameter too small such that exhaust flow is restricted.
> Large diameter tubing tends to cause the engine's power to peak at
> extreme rpms. The smaller the diameter of the tubing, the more low to
> midrange power you have.
>
> But everyone wanted to use 1.75" tubing because that's what the
> exhaust port was. 1.75" tubing would be what you would use if you
> wanted flash horsepower from the engine at 8,000 rpm, like at the
> dragstrip.
>
> The header manufacturer also had a lot to say about "Zoomie" type
> headers. These are headers without collectors, basically straight
> pipes. Not only are these tubes also usually too large a diameter,
> they leave off the collector which is crucial to the proper design of
> the header system.
>
> So with all this information, I'm taking my time with the header
> design. Obviously something so important to the proper running of the
> engine is not something I'm going to throw together without using
> proper design criteria.
>
> Corky Scott

Another trick that was popular on cars years ago, to bring a broad band
of peak torque into the "mid range" of 2500 to 4000 rpm; was to bring
the shortest practical header pipes which could be long enough to converge
at a reasonable included angle into collectors in groups of 3 which
would fire 240 degrees apart on six and twelve cylinder engines, or in
pairs which would fire 360 degrees apart on 4 and 8 cylinder engines.

On a V6, that would be be end of the story, and a collector having
about the same diameter as the header pipes should continue the same
inertial effect out to the exit or muffler. On V8 and in-line 4
cylinder engines, the resulting initial collectors were about as long
as the header pipes before converging into a final collector.

My expectation is that "tubing headers" made this way for V8 engines
with 90 degree cranks should be only marginally useful. However, they
should work well for all V6 engines, as well as V8 engines with single
plane cranks.

I am still (at a minimum) a couple of years away from testing this
recollection on any project. My own goal would be to achieve the
desired torque curve with an exhaust system length of 4 feet or less.

However, it appears from your post that you have found a competent
exhaust fabricator who can give you some additional guidance.

Peter

[Peter Dohm]

Tim Ward wrote:
>
> "Norman Yarvin" > wrote in message
> ...
> > In article >,
> > Badwater Bill > wrote:
> >
> > >When I was the test pilot on the OMABP RV-6A project, we used the
> > >Chevy Vortec V-6 engine, the PSRU was specifically designed to turn
> > >the prop at tip speed below 80% the speed of sound. Jess Meyers also
> > >used a reduction ratio number that was about equal to the square root
> > >of 2 to eliminate harmonics that could have resulted in reversed
> > >torque pulses reflecting back into the engine. By using a reduction
> > >ratio of 1.41 (or close to it) he eliminated many sympathetic
> > >harmonics that may have occured.
> >
> > What, in order to have the ratio between the two be an irrational number?
> > That's not actually going to help eliminate resonances, unless you get
> > lucky -- and you are about equally likely to get lucky with any number of
> > about the same size, irrational or not.
> >
> >
> >
> > --
> > Norman Yarvin http://yarchive.net
>
> Just out of curiosity, how would you get any ratio to be an irrational
> number?
>
> Tim Ward

There is another word I don't recall. Basically, the idea is to even out
the wear in the gearbox--especially if it is a spur gear system--to give
dramatically longer life to the psru.

Peter

[Tim Ward]

"Peter Dohm" -KNOW> wrote in message
-KNOW...
> Tim Ward wrote:
> >
> > "Norman Yarvin" > wrote in message
> > ...
> > > In article >,
> > > Badwater Bill > wrote:
> > >
> > > >When I was the test pilot on the OMABP RV-6A project, we used the
> > > >Chevy Vortec V-6 engine, the PSRU was specifically designed to turn
> > > >the prop at tip speed below 80% the speed of sound. Jess Meyers also
> > > >used a reduction ratio number that was about equal to the square root
> > > >of 2 to eliminate harmonics that could have resulted in reversed
> > > >torque pulses reflecting back into the engine. By using a reduction
> > > >ratio of 1.41 (or close to it) he eliminated many sympathetic
> > > >harmonics that may have occured.
> > >
> > > What, in order to have the ratio between the two be an irrational
number?
> > > That's not actually going to help eliminate resonances, unless you get
> > > lucky -- and you are about equally likely to get lucky with any number
of
> > > about the same size, irrational or not.
> > >
> > >
> > >
> > > --
> > > Norman Yarvin http://yarchive.net
> >
> > Just out of curiosity, how would you get any ratio to be an irrational
> > number?
> >
> > Tim Ward
>
> There is another word I don't recall. Basically, the idea is to even out
> the wear in the gearbox--especially if it is a spur gear system--to give
> dramatically longer life to the psru.
>
> Peter

I can see how having the numerator and denominator of the ratio relatively
prime might be a benefit. Then the same configuration would only turn up
once every product of the two numbers revolutions.
That's kind of a convoluted sentence, but I don't know how else to put it.

Tim Ward

[Peter Dohm]

Tim Ward wrote:
>
> "Peter Dohm" -KNOW> wrote in message
> -KNOW...
> > Tim Ward wrote:
> > >
> > > "Norman Yarvin" > wrote in message
> > > ...
> > > > In article >,
> > > > Badwater Bill > wrote:
> > > >
> > > > >When I was the test pilot on the OMABP RV-6A project, we used the
> > > > >Chevy Vortec V-6 engine, the PSRU was specifically designed to turn
> > > > >the prop at tip speed below 80% the speed of sound. Jess Meyers also
> > > > >used a reduction ratio number that was about equal to the square root
> > > > >of 2 to eliminate harmonics that could have resulted in reversed
> > > > >torque pulses reflecting back into the engine. By using a reduction
> > > > >ratio of 1.41 (or close to it) he eliminated many sympathetic
> > > > >harmonics that may have occured.
> > > >
> > > > What, in order to have the ratio between the two be an irrational
> number?
> > > > That's not actually going to help eliminate resonances, unless you get
> > > > lucky -- and you are about equally likely to get lucky with any number
> of
> > > > about the same size, irrational or not.
> > > >
> > > >
> > > >
> > > > --
> > > > Norman Yarvin http://yarchive.net
> > >
> > > Just out of curiosity, how would you get any ratio to be an irrational
> > > number?
> > >
> > > Tim Ward
> >
> > There is another word I don't recall. Basically, the idea is to even out
> > the wear in the gearbox--especially if it is a spur gear system--to give
> > dramatically longer life to the psru.
> >
> > Peter
>
> I can see how having the numerator and denominator of the ratio relatively
> prime might be a benefit. Then the same configuration would only turn up
> once every product of the two numbers revolutions.
> That's kind of a convoluted sentence, but I don't know how else to put it.
>
> Tim Ward

You are exactly right. The remaining problem with spur gear reduction units is
that the same portions of the crankshaft pulley will always take the power
pulses--unless there is also a clutch, fluid coupling, etc. Therefore,
planetary or epicyclic drives are usually preferred unless an offset is also
needed.

Supposedly, the problems are mitigated by a hi-vo chain drive for engines of six
or more cylinders, or by a cog belt drive. Both have the advantage of spanning
approximately half of the teeth on each pulley. Unfortunately, I doubt that
some of the belt drive designers know much more than I do.

At the moment, the Geshwender drive (which is back in production despite Mr G's
death) looks like the most reliable scheme for much more than 100 horsepower,
any may still be the best value in the long run.

[Corky Scott]

On Tue, 09 Mar 2004 03:18:59 GMT, Peter Dohm
-KNOW> wrote:
>
>At the moment, the Geshwender drive (which is back in production despite Mr G's
>death) looks like the most reliable scheme for much more than 100 horsepower,
>any may still be the best value in the long run.

I agree, but add that this psru was originally designed for high
output engines, engines that start with around 400 horsepower.

For those interested, the reason Fred designed the psru in the first
place was to provide a less expensive engine alternative for crop
dusters. The engine he used was a Ford big block V8. I think that
smaller psru's may be available now but I haven't checked for a while.

When I called him to talk about his psru a year before he died, he
talked me out of using it because it was overkill to use that psru on
an engine putting out only 190 or so hp.

Corky Scott

[Peter Dohm]

Corky Scott wrote:
>
> On Tue, 09 Mar 2004 03:18:59 GMT, Peter Dohm
> -KNOW> wrote:
> >
> >At the moment, the Geshwender drive (which is back in production despite Mr G's
> >death) looks like the most reliable scheme for much more than 100 horsepower,
> >any may still be the best value in the long run.
>
> I agree, but add that this psru was originally designed for high
> output engines, engines that start with around 400 horsepower.
>
> For those interested, the reason Fred designed the psru in the first
> place was to provide a less expensive engine alternative for crop
> dusters. The engine he used was a Ford big block V8. I think that
> smaller psru's may be available now but I haven't checked for a while.
>
> When I called him to talk about his psru a year before he died, he
> talked me out of using it because it was overkill to use that psru on
> an engine putting out only 190 or so hp.
>
> Corky Scott

I agree about it being overkill. An it is not cheap either. However, it looks
like something you can trust.

It's really an interesting dilemma that I will have to face when I get ready to
build. If you don't require true short field capability, and only need a two
seater; you can give up a little power and thrust, and build a v6 version of
Steve Wittman's Tailwind installation.

I admit that I am willing to give up a lot of "utility" for the few features
that I think I need. I really don't consider landing speed very important, but
want adequate cabin width at my own elbows and shoulders.

The basic point is that I believe that I can power my first project with direct
drive. Probably an engine in the 3.8 to 4.3 liter displacement range turning a
56 to 60 inch diameter prop and developing 130 to 150 horsepower. That should
be enough for a cruising speed of about 130 kts tas.

To be really blunt about it, I could probably design a better airplane with
similar performance around a 110 hp corvair engine--if I knew of a source for
*new* heads and crank cases.

I also recognize that such an installation won't work on a Christavia MK4, which
needs a longer prop. Therefore, you really don't have a choice. You are
building the airplane that those 2400 to 2500 rpm engines were designed for! If
you use an automotive conversion, you need a psru. Hypothetically, you could
get about 170 hp from a 350 cid v8 turning a 72 inch prop at crankshaft rpm; but
you would be lugging the engine, so the smaller engine with the psru would last
longer and would still be at least 50 pounds lighter after allowing for the
drive shaft and thrust bearing adapter on the v8.

Peter

[Corky Scott]

On Wed, 10 Mar 2004 01:27:46 GMT, Peter Dohm
-KNOW> wrote:


>
>I also recognize that such an installation won't work on a Christavia MK4, which
>needs a longer prop. Therefore, you really don't have a choice. You are
>building the airplane that those 2400 to 2500 rpm engines were designed for! If
>you use an automotive conversion, you need a psru. Hypothetically, you could
>get about 170 hp from a 350 cid v8 turning a 72 inch prop at crankshaft rpm; but
>you would be lugging the engine, so the smaller engine with the psru would last
>longer and would still be at least 50 pounds lighter after allowing for the
>drive shaft and thrust bearing adapter on the v8.
>
>Peter

I'm building a Christavia Mk4 and have the Ford 3.8 installed in it
right now. The psru I'll be using was one of the products put out by
NW Aero before Johhny Lindgren acquired the business. Johhny made the
psru for the Ford V6's available for a while but does not do so any
longer because very few people seem interested in it.

He does have psru's for Chevy V6's and V8's though and I bought all
the things I need for my engine from him. Things like the camshaft,
distributer, alternator and brackets, and the proper sized pulleys to
drive everything. He can still get them.

The original psru has undergone considerable modification and looks
like a very nice unit. The top and outer drive cog bearings are now
lubricated by an enclosed oil bath, rather than by grease that must be
injected periodically by the owner.

There was a failure written up by a guy who had a Chevy V-8 in his
Lancair. The drive cog bearing seized and the belt broke. He landed
short and the airplane flipped over when the wheels dug into the soft
ground but the guy was ok. Saw some pictures of it in Contact!
magazine. The drive cog bearing had overheated and seized and the guy
admitted he did not really know how much to grease it, or how much to
put in while greasing and apparently hadn't for a while.

I'd call those bearings pretty critical parts and I'd want to have
maintenance logs telling me exactly when they were last greased.

The engine, by the way, continued to run fine and the owner was
planning to get the updated psru, which he felt was a better design.

The Chevy V6 is a pretty good engine and has a good track record when
used in airplanes but it's considerably heavier than the Ford V6
because it has cast iron heads, intake manifold and timing chain
cover. All the afore mentioned parts are aluminum in the Ford, which
makes it the lightest V6 of that type of design in the US.

You can buy all kinds of aluminum parts for it (the Chevy) to lighten
it up, but the aluminum heads are competition models and the intake
valves and air passages are designed for max power at high rpm and
they don't adopt very well to moderate output levels. You can also
buy aluminum intake manifolds for it and probably aluminum oil pans
too. It's just that each purchase takes you beyond the cost of the
original engine. I've said this before but if money were no object,
or if I had no mechanical background, I would not be converting an
auto engine. I'd just bite the bullet and spend the $10,000 to
$15,000 it takes to get a reasonable, well maintained Lycoming or
Continental. I still think it's incredible that engines can cost that
much, but they do.

Corky Scott

[Corky Scott]

On Wed, 10 Mar 2004 14:29:29 GMT,
(Corky Scott) wrote:


>
>He does have psru's for Chevy V6's and V8's though and I bought all
>the things I need for my engine from him. Things like the camshaft,
>distributer, alternator and brackets, and the proper sized pulleys to
>drive everything. He can still get them.

Clarification: Sorry, this paragraph is confusing. What I meant to
say is that Johnny does not offer the psru for the Ford anymore, but
he does still offer some parts for it. Or at least I was able to get
them from him.

The distributer is machined for him and he installs dual sensors so
that you can run two electronic ignition systems. The distributer is
set up with advance weights so that the engine can be started at zero
degrees BTDC and then advances to it's running timing setting after
the start. This makes for easy starting.


>You can buy all kinds of aluminum parts for it (the Chevy) to lighten
>it up, but the aluminum heads are competition models and the intake
>valves and air passages are designed for max power at high rpm and
>they don't adopt

Adopt should be adapt.

>very well to moderate output levels. You can also
>buy aluminum intake manifolds for it and probably aluminum oil pans
>too. It's just that each purchase takes you beyond the cost of the
>original engine. I've said this before but if money were no object,
>or if I had no mechanical background, I would not be converting an
>auto engine. I'd just bite the bullet and spend the $10,000 to
>$15,000 it takes to get a reasonable, well maintained Lycoming or
>Continental. I still think it's incredible that engines can cost that
>much, but they do.
>
Corky Scott

[Peter Dohm]

Corky Scott wrote:
>
> On Wed, 10 Mar 2004 14:29:29 GMT,
> (Corky Scott) wrote:
>
> >
> >He does have psru's for Chevy V6's and V8's though and I bought all
> >the things I need for my engine from him. Things like the camshaft,
> >distributer, alternator and brackets, and the proper sized pulleys to
> >drive everything. He can still get them.
>
> Clarification: Sorry, this paragraph is confusing. What I meant to
> say is that Johnny does not offer the psru for the Ford anymore, but
> he does still offer some parts for it. Or at least I was able to get
> them from him.
>
> The distributer is machined for him and he installs dual sensors so
> that you can run two electronic ignition systems. The distributer is
> set up with advance weights so that the engine can be started at zero
> degrees BTDC and then advances to it's running timing setting after
> the start. This makes for easy starting.
>
> >You can buy all kinds of aluminum parts for it (the Chevy) to lighten
> >it up, but the aluminum heads are competition models and the intake
> >valves and air passages are designed for max power at high rpm and
> >they don't adopt
>
> Adopt should be adapt.
>
> >very well to moderate output levels. You can also
> >buy aluminum intake manifolds for it and probably aluminum oil pans
> >too. It's just that each purchase takes you beyond the cost of the
> >original engine. I've said this before but if money were no object,
> >or if I had no mechanical background, I would not be converting an
> >auto engine. I'd just bite the bullet and spend the $10,000 to
> >$15,000 it takes to get a reasonable, well maintained Lycoming or
> >Continental. I still think it's incredible that engines can cost that
> >much, but they do.
> >
> Corky Scott

It looks like you've made the right choices for the type aircraft, and
I'm eager to read about the flight experiences.

Peter

[wes marso]

longer is better not only applies to propellers, i'll wager!
"Richard Lamb" > wrote in message
...
> Dave Covert wrote:
> >
> > I notice that most auto engine conversions use a gear box between the
engine
> > and the prop. Why is that? Is it because an auto engine's peak HP is too
> > high for a prop to swing? Is it because auto engines weren't designed to
be
> > pulled around by their crankshafts and don't have proper thrust
bearings?
> > Both?
> >
> > Are there any auto/motorcycle conversions that don't require gear boxes?
> >
> > Dave
>
> Some people think aircraft engines are "old fashioned technology"
> and have not kept up with developments in auto engine field.
>
> They point out that aircraft engines haven't changed much in
> over 50 years.
>
> Some people feel that auto engines can be used to power airplanes.
>
> To some extent, all three of these ideas are true.
>
> Aircraft engine do not run like car motors.
>
> Aircraft engines run at much higher sustained power settings and
> constant rpm for long periods of time.
>
> And then there is the propeller...
> Turning the propeller is what it's all about.
>
> The propeller converts the engine's power into thrust.
> As always, when energy is converted, there are losses.
>
> Moving through the air at very high speeds, the propeller
> makes lift (thrust, which is power successfully converted into
> forward motion) and drag (pure conversion losses).
>
> So, propeller efficiency is extremely important.
>
> If the propeller is only 50% efficient, half of the
> power generated by the engine is wasted in losses.
> Yes, literally.
>
> Only one hard rule for propellers - longer is better.
>
> But longer blades mean lower RPM because the tips of the
> propeller blades MUST stay below the speed of sound (yep,
> Mach 1, really) for any efficiency at all.
>
> Part of the reason for this is the huge increase in drag
> as the tip enters the transonic (speed) region.
>
> It takes TORQUE to turn that propeller - not horsepower.
>
> A given propeller needs to turn at a given RPM, which
> will require a given amount of torque.
>
> If the engine makes enough torque to turn the propeller at
> that RPM, a direct drive set up may be possible.
>
> There are a lot of other minor details that may get in the way -
> Harmonic Resonance is a big one.
> But, it may be possible to run this combination direct drive.
>
> If the engine needs to turn at a higher RPM to make adequate
> power, some kind of gearing would be necessary to reduce engine
> RPM to propeller RPM. Notice that reducing RPM will increase
> torque proportionally. Seems like a nice trade off.
>
> Now the engine should be running at an RPM near the peak of its'
> torque curve. This is for best engine operating economy.
>
> And the (longer) propeller is running at a comfortable (lower)
> RPM for good efficiency. Life is wonderful.
>
> Except for the weight.
> Auto engines are seldom as light as possible.
> Then we add more weight in the form of a gearbox and such.
> Radiators full of heavy (hot!) fluids.
> External oil sump?
> Mounting?
> Propeller gyroscopic forces operating on the crankshaft?
>
> Weight is critical to any flying machine.
> (Go back and look at how birds are built)
>
> So...
> Think of it as evolution in action.
>
> The reason our old antique Lycosourus engines are the way they
> are is that they evolved into a very narrow niche.
>
> They turn propellers to pull airplanes.
>
> They make very high torque
> at very low RPM,
> and are as light as possible.
> They are tremendously reliable and fairly efficient.
>
> Prices are high because of limited production and high demand.
> Simple economics.
>
> But the economics of engine development (and risk assesment) are
> anything but simple.
>
> I have a big bore VW (2180cc) on my parasol.
> That's a converted car motor.
>
> There is a weatlh of prior art using VW engines for small airplanes
> (if one is inclined to use it).
>
> What works, and what doesn't. (eg: breaking cast crankshafts)
>
> Mine is a very simple conversion, using high quality (GPAS) parts
> built by a little German perfectinist.
> I trust it - so far.
>
> I also don't push it beyond conservative limits.
>
> All VW engines are 40 hp engine (IMHO).
> Some can make more power than that - for a while.
> This one is _rated_ at 70 hp.
> But will reach thermal limits of the fin area and overheat
> if not throttled back (to roughly 40?)
>
> It's a fairly expensive motor.
> The jugs and pistons are standard parts, but the crank (!) and
> accessories and machine work are all specialty items.
> A new 2180 can easily go over $5000 with a few bells and whistles.
>
> But the weight, power, reliability, and operating cost are all within
> reason for this particular airplane.
>
> The airplane itself can land slowly, around 35 mph.
>
> The chances of getting down safely if the engine quits are a lot better
> at 35 than they are at 53.
>
> To me, it seems like a reasonable risk for the potential rewards.
>
> But...
>
> Your milage may vary.
>
> Richard
>
> http://www.flash.net/~lamb01
>
>
> PS: I've read of a Curtiss Hawk replica that uses a direct drive Chevy
> 350.
> It's supposed to make roughly 190 hp?
> It would obviously be a heavy motor.
> Not something you'd hang on a glass slipper.
> But on a big old biplane with a looong prop
> it seems to be just the ticket.

[Jay]

I think longer is only better in terms of static thrust, not
necessarily top aircraft speed.


"wes marso" > wrote in message >...
> longer is better not only applies to propellers, i'll wager!