Why are low-revving, high torque engines preferred?

[Oliver Arend]

This may sound like a stupid question; I realize the prop can only
turn at a certain speed to avoid transonic effects at the tips and has
to be turned with a certain torque to transmit the power needed/
produce enough thrust. So far so good.

But why does the torque have to be produced by the engine in direct
drive? Couldn't weight and space be saved by using a high-revving,
small displacement engine (such as a car or even motorcycle engine)
with a reduction gearbox? I'm aware that a reduction gearbox will add
weight (but not that much?), complexity and failure modes, and that
transmitting the forces created by the prop to the airframe could be
an issue. Does it boil down to the price? Is a Lycosaur engine cheaper
than, say, a motorcycle engine of equivalent power plus the gearbox?

Thanks in advance for enlightening me,
Oliver

[jan olieslagers[_2_]]

Oliver Arend schreef:
> This may sound like a stupid question; I realize the prop can only
> turn at a certain speed to avoid transonic effects at the tips and has
> to be turned with a certain torque to transmit the power needed/
> produce enough thrust. So far so good.
>
> But why does the torque have to be produced by the engine in direct
> drive? Couldn't weight and space be saved by using a high-revving,
> small displacement engine (such as a car or even motorcycle engine)
> with a reduction gearbox? I'm aware that a reduction gearbox will add
> weight (but not that much?), complexity and failure modes, and that
> transmitting the forces created by the prop to the airframe could be
> an issue. Does it boil down to the price? Is a Lycosaur engine cheaper
> than, say, a motorcycle engine of equivalent power plus the gearbox?

At the risk of feeding the trolls:
There are several examples of the setup you describe.
The Rotax 4-stroke engines have a (belt?) reduction.
In Europe one sees more and more BMW-motorcycle engines
driving planes through a reduction, either gear or belt.

I even seem to remember car/bike engines driving a prop through
the original gearbox, fixed in one gear; but never with good results.

The main disadvantage of automotive engines is that they were
never designed for delivering their output power over
a prolonged period of time, like an aircraft engine does.
This also applies to an even greater degree to motorbike engines.

But even in the country of Lycosaurs some people
are flying behind (or before...) car engine conversions,
you might wish to search for the Corvair engine in particular.

PS if you are interested in cheap engines for modest homebuilt planes,
read every page of Bob Hoover's blog, frequently mentioned on these pages.
Good reading both for wisdom and for technical insight!

Hope this helps,

[Capt. Geoffrey Thorpe]

"jan olieslagers" > wrote in message
...
> Oliver Arend schreef:
> At the risk of feeding the trolls:
> There are several examples of the setup you describe.
> The Rotax 4-stroke engines have a (belt?) reduction.
> In Europe one sees more and more BMW-motorcycle engines
> driving planes through a reduction, either gear or belt.

There are also several versions of Lycoming / Contintntal / other "brand
name" aircraft engines with reduction units.

Adds cost, complexity, and can result in durability issues (one more thing
to go wrong).

Sometimes it works out better, sometimes not. It all depends on the details
of your objectives.

For extra points - why do Ford V8's have overhead cams and Chevy V8's tend
towards pushrods - you would thing that one would be "better", right? Why
are they different?
































Because Ford management gives the engine designers a "horsepower per
displacement" objective and Chevy magement gives them a "horsepower per
package volume" objective.

(per engine guys who have worked at both shops)

--
Geoff
The Sea Hawk at Wow Way d0t Com
remove spaces and make the obvious substitutions to reply by mail
When immigration is outlawed, only outlaws will immigrate.

[Maxwell[_2_]]

"jan olieslagers" > wrote in message
...
|
| At the risk of feeding the trolls:
| There are several examples of the setup you describe.
| The Rotax 4-stroke engines have a (belt?) reduction.
| In Europe one sees more and more BMW-motorcycle engines
| driving planes through a reduction, either gear or belt.
|
| I even seem to remember car/bike engines driving a prop through
| the original gearbox, fixed in one gear; but never with good results.
|
| The main disadvantage of automotive engines is that they were
| never designed for delivering their output power over
| a prolonged period of time, like an aircraft engine does.
| This also applies to an even greater degree to motorbike engines.
|
| But even in the country of Lycosaurs some people
| are flying behind (or before...) car engine conversions,
| you might wish to search for the Corvair engine in particular.
|
| PS if you are interested in cheap engines for modest homebuilt planes,
| read every page of Bob Hoover's blog, frequently mentioned on these pages.
| Good reading both for wisdom and for technical insight!
|
| Hope this helps,

Ditto all the above, but also torsional vibration and resonance.

An engines crankshaft is constantly changing speed, slowing during
compression, and accelerating upon combustion. A propeller is a very large
flywheel, that likes to turn the same speed all the time. Direct drive
applications have so little flex and such a fast recovery time after each
combustion event, that the ill effects of torsional vibration and
differences between crankshaft and propeller speed are greatly minimized.
All types of reduction systems have flex or free play that allows this
speed/vibration difference to cause serious problems. Further, the design of
each reduction type causes it's resonance problems to differ greatly from
one design to the next, and one rpm range to the next, and the end results
can be utterly amazing in their ability to destroy the overall system.

Simply put, designing a reduction system is much, much more complicated than
simply choosing the right gears, belts or sheaves. Therefore the reliability
of these systems are still a good bit suspect in most peoples minds, and
properly designing solutions for these issues add more weight than the
uninitiated would suspect.

There is also the issue of in-flight restarts. If an engine looses power in
flight, due to changing fuel tanks, carb ice, etc. Direct drive engines are
much more likely to keep the engine turning until the pilot solves the
problem. Reduction engines are much more likely to stop turning and force
the pilot to rely on the electrical system for a re-start.

[Steve Hix]

In article >,
jan olieslagers > wrote:

> Oliver Arend schreef:
> > This may sound like a stupid question; I realize the prop can only
> > turn at a certain speed to avoid transonic effects at the tips and has
> > to be turned with a certain torque to transmit the power needed/
> > produce enough thrust. So far so good.
> >
> > But why does the torque have to be produced by the engine in direct
> > drive? Couldn't weight and space be saved by using a high-revving,
> > small displacement engine (such as a car or even motorcycle engine)
> > with a reduction gearbox? I'm aware that a reduction gearbox will add
> > weight (but not that much?), complexity and failure modes, and that
> > transmitting the forces created by the prop to the airframe could be
> > an issue. Does it boil down to the price? Is a Lycosaur engine cheaper
> > than, say, a motorcycle engine of equivalent power plus the gearbox?
>
> At the risk of feeding the trolls:
> There are several examples of the setup you describe.
> The Rotax 4-stroke engines have a (belt?) reduction.

Geared in the 912 series, at least.

It's the only one I've seen taken apart, so far.

[[email protected]]

On Nov 25, 9:19*am, Oliver Arend > wrote:

> But why does the torque have to be produced by the engine in direct
> drive?
------------------------------------------------------------------------------------------------------
Hahahahahahaaaa.... (wheez!)

Sorry Oliver, but that's just so funny.... I forget that most
subscribers to this list are not familiar with 'real' aircraft
engines, ALL of which incorporate some form of speed reduction.
'Real' airplane engines are those big round things with all the
jugs... or those sleek narrow things tucked into the nose of a P-51 or
an Me-109.

'Smalll' aircraft engines.... typically those below 550cid or there
abouts are an EXCEPTION and tend to use direct drive. All the rest of
the world uses 'real' engines... or did, until Frank Whittle got
someone to listen to his 'crazy' ideas.

But as to the core of your question, the reason we don't find speed
reduction units on small engines (*) is their weight. The smaller the
engine, the greater the 'overhead' for a PSRU (Prop Speed Reduction
Unit).

(*) But there are exceptions. Continental made a geared A-85... Just
look for a 'G' in the Type Number. I'm not familiar with any others
but Lycoming and Franklyn probably made them.
-----------------------------------------------------------------------------------------------------------------------------
> Couldn't weight and space be saved by using a high-revving,
> small displacement engine (such as a car or even motorcycle engine)
> with a reduction gearbox?
-----------------------------------------------------------------------------------------------------------------------------

That is correct in theory, especially if the engine or 'power unit' is
water-cooled. Rotax has recently earned a 1500 TBO for the 1300cc
power unit of their 912 engines, although the TBO of the gear
reduction unit remains around 850 hours. (Maybe a Rotax mechanic can
jump in here and give us the actual numbers.)

--------------------------------------------
> I'm aware that a reduction gearbox will add
> weight (but not that much?), complexity and failure modes, and that
> transmitting the forces created by the prop to the airframe could be
> an issue.
-----------------------------------------

First off, much of the 'issue' is bureaucratic, in that the FAA
requirements for a type certificate will presently cost about a
quarter of a million dollars to satisfy. That is, over and above your
cost of development, the PAPERWORK will add another quarter-mill to
the pot. Given the market, it simply doesn't make good economic sense
to put that kind of money into ANY aspect of 'General Aviation'
today.

But that doesn't mean small, modern engines such as you've described
aren't out there. For some nice examples of modern light-airplane
engines, take a peek behind the propeller of any of the RPV's and tell
me what you see :-) There are also some shoe-box size turbines
slinging props that beg to be bolted to a KR or similar. In the 50
to 70hp range, the hot section is out of a GPU or APU. As the United
States digs it's self deeper into Third World status we'll see more of
these units appear as surplus... if we don't sell them all to
China :-)

-R.S.Hoover

[[email protected]]

On Tue, 25 Nov 2008 09:19:01 -0800 (PST), Oliver Arend
> wrote:

>This may sound like a stupid question; I realize the prop can only
>turn at a certain speed to avoid transonic effects at the tips and has
>to be turned with a certain torque to transmit the power needed/
>produce enough thrust. So far so good.
>
>But why does the torque have to be produced by the engine in direct
>drive? Couldn't weight and space be saved by using a high-revving,
>small displacement engine (such as a car or even motorcycle engine)
>with a reduction gearbox? I'm aware that a reduction gearbox will add
>weight (but not that much?), complexity and failure modes, and that
>transmitting the forces created by the prop to the airframe could be
>an issue. Does it boil down to the price? Is a Lycosaur engine cheaper
>than, say, a motorcycle engine of equivalent power plus the gearbox?
>
>Thanks in advance for enlightening me,
>Oliver
It is done often in the ultralite world - but gear drives add
complexity. If a plane doesn't have a particular part it can't fail -
so the large displacement, slow turning torque machines still win.
Lycoming has made several geared engines over the years and none has
been particularly successfull. I believe the Merlin (or one of the
big "V" engines) was also geared.

The most common geared aircraft engine today is the Rotax 912 series.

[[email protected]]

On Nov 25, 7:47 pm, wrote:

> Lycoming has made several geared engines over the years and none has
> been particularly successfull. I believe the Merlin (or one of the
> big "V" engines) was also geared.

Both the Merlin and Allison V-12s were geared. And most of the
big radials were geared. It was one of the few ways to get more
horsepower out of a given displacement.

R-1830 radial cutaway, with gears in the front of the case:
http://aviatechno.free.fr/vilgenis/images/larges/r1830_02_730.jpg

Merlin cutaway: http://www.thunderboats.org/history/images/history0324_1.jpg

Common geared Lycs: GO-435 and GO-480. Continental had the GO-300 and
GTSIO-520.

Daimler Benz DB601a: http://www.aviation-history.com/engines/db601a-1.jpg

Geared engines are nothing new at all.

Dan

[bildan]

On Nov 25, 8:29*pm, wrote:
> On Nov 25, 7:47 pm, wrote:
>
> > Lycoming has made several geared engines over the years and none has
> > been particularly successfull. I believe the Merlin *(or one of the
> > big "V" engines) was also geared.
>
> * * * *Both the Merlin and Allison V-12s were geared. And most of the
> big radials were geared. It was one of the few ways to get more
> horsepower out of a given displacement.
>
> R-1830 radial cutaway, with gears in the front of the case:http://aviatechno.free.fr/vilgenis/images/larges/r1830_02_730.jpg
>
> Merlin cutaway:http://www.thunderboats.org/history/images/history0324_1.jpg
>
> Common geared Lycs: GO-435 and GO-480. Continental had the GO-300 and
> GTSIO-520.
>
> Daimler Benz DB601a:http://www.aviation-history.com/engines/db601a-1.jpg
>
> * * * * Geared engines are nothing new at all.
>
> * * * *Dan

One of the reasons that converting an auto engine by adding a PRSU is
complicated is that auto engine bearings are not designed for thrust
or side loads. The rear bearing of an auto engine in a car just sees
torque loads.

The PRSU has to be coupled to the crank in the same way as an auto
transmission which means that the small gear or pulley has to 'float'
on its own bearing and couple to the engine's flywheel through
something like a flex coupling.

Geared radial and a few in-line engines used a planetary gearsets.
This is easier since the "sun gear" sees no thrust or side loads. The
"ring gear" sees all those loads.

[Dana M. Hague[_2_]]

On Tue, 25 Nov 2008 19:29:06 -0800 (PST),
wrote:

> Both the Merlin and Allison V-12s were geared. And most of the
>big radials were geared. It was one of the few ways to get more
>horsepower out of a given displacement.

Gearing an engine doesn't increase the horsepower; it multiplies the
torque and divides the rpm down to a more usable (by the propeller)
level. It does allow you to build a faster turning (and thus higher
horsepower) engine and still be able to use it.

In general, the way to get more horsepower out of a given displacement
is to turn the engine faster, within limits of course. With the
higher rpm's come increased wear and heat. In the "old" days (up to
the mid 1930's or so) the available materials weren't adequate for a
high revving engine, so low rpm's were the norm, and by happy
coincidence the avilable rpm's were pretty well matched to propeller
sizes convenient for the aircraft. As the technology advanced and
higher rpm's became reasonable, reduction drives began to appear,
especially on higher powered military aircraft... with some compromise
(as others have pointed out) in reliability.

Most of the small aircraft engines in use nowadays are derived from
those 1930's engines, with only minor improvements. The A-65, for
example, was redlined at 2300 rpm; the A-75, if I recall correctly,
was the same engine upgraded to turn a little faster, and today's
0-200 turns around 2600 rpm if I'm not mistaken. By contrast, modern
car engines are redlined at up to 8000 rpm.

There two main reasons we're still using the "old style" aircraft
engines. First is cost; not only does the gearing and such cost more
money, but the existing engine designs are long amortized. Developing
a new engine costs a lot of money, especially with the costs of
_certifying_ a new engine. Second is reliability and longevity; a big
slow turning engine is more reliable and lasts longer than a smaller
fast turning engine of the same horsepower.

Where we _are_ seeing reduction drive engines is in the ultralight /
light sport area, where weight is much more critical. The ultralight
movement introduced fast turning 2-stroke engines, mostly snowmobile
derived, to aviation. When your engine turns 6500 rpm you NEED a
reduction drive! For an ultralight, light weight is far more
important than a 2000 hour TBO. In the case of the Rotax 912, a
geared 4-stroke, Rotax was already used to building engines with
redrives, so it made sense for them to take that approach.

-Dana
--
The gene pool could use a little chlorine.

[Tech Support]

Merlin in 51 had a 2-1 gear reduction. 3000 rpm gave 1500 rpm prop
speed as I recall.

Big John



On Tue, 25 Nov 2008 19:29:06 -0800 (PST),
wrote:

>On Nov 25, 7:47 pm, wrote:
>
>> Lycoming has made several geared engines over the years and none has
>> been particularly successfull. I believe the Merlin (or one of the
>> big "V" engines) was also geared.
>
> Both the Merlin and Allison V-12s were geared. And most of the
>big radials were geared. It was one of the few ways to get more
>horsepower out of a given displacement.
>
>R-1830 radial cutaway, with gears in the front of the case:
>http://aviatechno.free.fr/vilgenis/images/larges/r1830_02_730.jpg
>
>Merlin cutaway: http://www.thunderboats.org/history/images/history0324_1.jpg
>
>Common geared Lycs: GO-435 and GO-480. Continental had the GO-300 and
>GTSIO-520.
>
>Daimler Benz DB601a: http://www.aviation-history.com/engines/db601a-1.jpg
>
> Geared engines are nothing new at all.
>
> Dan
>

[Morgans[_2_]]

<Tech Support> wrote in message
...
> Merlin in 51 had a 2-1 gear reduction. 3000 rpm gave 1500 rpm prop
> speed as I recall.

Many of the old big "V" and inline engines were 2:1, and were using the
front end of a very strong camshaft as the prop drive, weren't they?
--
Jim in NC

[Peter Dohm]

"Dana M. Hague" > wrote in message
...
> On Tue, 25 Nov 2008 19:29:06 -0800 (PST),
> wrote:
>
>> Both the Merlin and Allison V-12s were geared. And most of the
>>big radials were geared. It was one of the few ways to get more
>>horsepower out of a given displacement.
>
> Gearing an engine doesn't increase the horsepower; it multiplies the
> torque and divides the rpm down to a more usable (by the propeller)
> level. It does allow you to build a faster turning (and thus higher
> horsepower) engine and still be able to use it.
>
> In general, the way to get more horsepower out of a given displacement
> is to turn the engine faster, within limits of course. With the
> higher rpm's come increased wear and heat. In the "old" days (up to
> the mid 1930's or so) the available materials weren't adequate for a
> high revving engine, so low rpm's were the norm, and by happy
> coincidence the avilable rpm's were pretty well matched to propeller
> sizes convenient for the aircraft. As the technology advanced and
> higher rpm's became reasonable, reduction drives began to appear,
> especially on higher powered military aircraft... with some compromise
> (as others have pointed out) in reliability.
>
> Most of the small aircraft engines in use nowadays are derived from
> those 1930's engines, with only minor improvements. The A-65, for
> example, was redlined at 2300 rpm; the A-75, if I recall correctly,
> was the same engine upgraded to turn a little faster, and today's
> 0-200 turns around 2600 rpm if I'm not mistaken. By contrast, modern
> car engines are redlined at up to 8000 rpm.
>
> There two main reasons we're still using the "old style" aircraft
> engines. First is cost; not only does the gearing and such cost more
> money, but the existing engine designs are long amortized. Developing
> a new engine costs a lot of money, especially with the costs of
> _certifying_ a new engine. Second is reliability and longevity; a big
> slow turning engine is more reliable and lasts longer than a smaller
> fast turning engine of the same horsepower.
>
> Where we _are_ seeing reduction drive engines is in the ultralight /
> light sport area, where weight is much more critical. The ultralight
> movement introduced fast turning 2-stroke engines, mostly snowmobile
> derived, to aviation. When your engine turns 6500 rpm you NEED a
> reduction drive! For an ultralight, light weight is far more
> important than a 2000 hour TBO. In the case of the Rotax 912, a
> geared 4-stroke, Rotax was already used to building engines with
> redrives, so it made sense for them to take that approach.
>
> -Dana
> --
> The gene pool could use a little chlorine.

To expand the above points just a little:

IIRC, snowmobiles are/were derived from chain saws--which required an engine
light enough for a man to carry and use as a hand held tool. That made them
an obvious choice for another application were light weight was the most
critical factor--even at the cost of reliability and maintenance
intervals...

[Tech Support]

Jim

Gear boxes had bearings designed to handle prop loads. Engine only saw
torque and no thrust or side loads, etc.

Only engine I can remember was either a Lyc or Con that drove prop off
cam shaft. Was not very popular for some reason and only lasted a few
years????

Someone with experience with those engines might want to chime in and
comment.

Big John
**************************************************
On Thu, 27 Nov 2008 07:15:24 -0500, "Morgans"
> wrote:

>
><Tech Support> wrote in message
...
>> Merlin in 51 had a 2-1 gear reduction. 3000 rpm gave 1500 rpm prop
>> speed as I recall.
>
> Many of the old big "V" and inline engines were 2:1, and were using the
>front end of a very strong camshaft as the prop drive, weren't they?

[GTH]

Morgans a écrit :
>
> Many of the old big "V" and inline engines were 2:1, and were using the
> front end of a very strong camshaft as the prop drive, weren't they?

Rolls Royce and Allison V engines were (are) overhead camshafts.
The prop reduction gear was driven from the nose of the crankshaft.
According to Rolls Royce, the Merlin XX drive ratio was 0.42.

Best regards,
--
Gilles
http://contrails.free.fr

[Charlie[_2_]]

Tech Support wrote:
> Jim
>
> Gear boxes had bearings designed to handle prop loads. Engine only saw
> torque and no thrust or side loads, etc.
>
> Only engine I can remember was either a Lyc or Con that drove prop off
> cam shaft. Was not very popular for some reason and only lasted a few
> years????
>
> Someone with experience with those engines might want to chime in and
> comment.
>
You don't often see that because any torsional resonance problems get
amplified at an even-multiple ratio, like the cam's 2:1 ratio. Note the
final drive ratio of almost any reduction gear train & it will be some
odd number like 2.17:1, 2.85:1, etc. (Those are the options available on
a common reduction drive for rotaries, & the planetary gear set comes
from a heavy duty Ford automatic trans.

BTW, someone mentioned 'no thrust or side loads' with planetary gears.
There can actually be very high thrust loads if the gear set uses
helical cut gears instead of spur gears to get more contact area for a
given gear thickness. The drive mentioned above had to have a thrust
bearing added to its input shaft after early testing because it
destroyed the light duty thrust bearing on the rotary's E-shaft.

Charlie

[[email protected]]

On Nov 27, 11:58*am, Tech Support <> wrote:

> Only engine I can remember was either a Lyc or Con that drove prop off
> cam shaft. Was not very popular for some reason and only lasted a few
> years????

The Continental Tiara 6-285. Kept breaking that shaft, IIRC.
There's still a TCDS on it so there's a few out there yet.

Dan

[Dana M. Hague[_2_]]

On Thu, 27 Nov 2008 09:37:54 -0500, "Peter Dohm"
> wrote:

>IIRC, snowmobiles are/were derived from chain saws--which required an engine
>light enough for a man to carry and use as a hand held tool. That made them
>an obvious choice for another application were light weight was the most
>critical factor--even at the cost of reliability and maintenance
>intervals...

I've never heard that, seems unlikely... they are really very
different, except for both (along with outboard motors) being
2-strokes. All for the same reason of light weight.

-Dana
--
If you glue a piece of toast, butter side up, to your cat's back, and drop it from a high place, which way will it land?

[Morgans[_2_]]

"Charlie" > wrote

> You don't often see that because any torsional resonance problems get
> amplified at an even-multiple ratio, like the cam's 2:1 ratio. Note the
> final drive ratio of almost any reduction gear train & it will be some odd
> number like 2.17:1, 2.85:1, etc.

Perhaps an even larger factor is to get different teeth meshing together in
a cycle, each time around. it is better to not have the same mesh, time
after time, although what you say about harmonics is also a factor.

In the really big "warbird"engines, the gearboxes had to be built so
hell-for-stout to deal with the HP levels, the harmonics were not as much of
an issue because the resonance was hard to achieve with the components being
so stiff.
--
Jim in NC

[Morgans[_2_]]

> wrote

> The Continental Tiara 6-285. Kept breaking that shaft, IIRC.
> There's still a TCDS on it so there's a few out there yet.

TCDS??
--
Jim in NC

[[email protected]]

On Nov 28, 6:47 am, "Morgans" > wrote:
> > wrote
>
> > The Continental Tiara 6-285. Kept breaking that shaft, IIRC.
> > There's still a TCDS on it so there's a few out there yet.
>
> TCDS??
> --
> Jim in NC

Type Certificate Data Sheet. See
http://www.airweb.faa.gov/Regulatory_and_Guidance_Library%5CrgMakeModel.nsf/0/1376F796A5B3E1D58525670E00481FC2/$FILE/E12ce.PDF

Any U.S. certified aircraft, engine or appliance has a TCDS. Look
up your airplane. Listing here:
http://www.airweb.faa.gov/Regulatory_and_Guidance_Library/rgMakeModel.nsf/MainFrame?OpenFrameSet

Dan

[Tech Support]

When I flew the Merlin we were told in ground school the prop turned
half engine rpm. Probably because that termonology easier to remember
than 0.42 ratio.

Power was adjusted using engine rpm (and MP) so prop speed never
entered into the equation during flight.

Big John
************************************************** ****************************

On Fri, 28 Nov 2008 00:05:28 +0100, GTH >
wrote:

>Morgans a écrit :
>>
>> Many of the old big "V" and inline engines were 2:1, and were using the
>> front end of a very strong camshaft as the prop drive, weren't they?
>
>Rolls Royce and Allison V engines were (are) overhead camshafts.
>The prop reduction gear was driven from the nose of the crankshaft.
>According to Rolls Royce, the Merlin XX drive ratio was 0.42.
>
>Best regards,

[Morgans[_2_]]

> wrote
>
> Type Certificate Data Sheet. See
> http://www.airweb.faa.gov/Regulatory_and_Guidance_Library%5CrgMakeModel.nsf/0/1376F796A5B3E1D58525670E00481FC2/$FILE/E12ce.PDF
>
> Any U.S. certified aircraft, engine or appliance has a TCDS. Look
> up your airplane. Listing here:
> http://www.airweb.faa.gov/Regulatory_and_Guidance_Library/rgMakeModel.nsf/MainFrame?OpenFrameSet

Duh! I should have known that. Too much turkey! <g>
--
Jim in NC

[Peter Dohm]

"Dana M. Hague" > wrote in message
...
> On Thu, 27 Nov 2008 09:37:54 -0500, "Peter Dohm"
> > wrote:
>
>>IIRC, snowmobiles are/were derived from chain saws--which required an
>>engine
>>light enough for a man to carry and use as a hand held tool. That made
>>them
>>an obvious choice for another application were light weight was the most
>>critical factor--even at the cost of reliability and maintenance
>>intervals...
>
> I've never heard that, seems unlikely... they are really very
> different, except for both (along with outboard motors) being
> 2-strokes. All for the same reason of light weight.
>
> -Dana
> --
> If you glue a piece of toast, butter side up, to your cat's back, and drop
> it from a high place, which way will it land?

Today, thanks to a substantial market with plenty of discretionary money,
engines for snowmobiles and ultralights have improved drastically.
Gardening equipment also runs far more reliably today--and a portion of that
improvement may have come from improvements made first on ultralights and
snowmobiles.

But it was not always so--and I recommend that you ask a few of the old
timers why they used to refer to some ofthe ultralight areas by nicknames
such as "the killing fields".

Peter

[Morgans[_2_]]

"Peter Dohm" > wrote
>
> IIRC, snowmobiles are/were derived from chain saws--which required an
> engine light enough for a man to carry and use as a hand held tool. That
> made them an obvious choice for another application were light weight was
> the most critical factor--even at the cost of reliability and maintenance
> intervals...

Snow machines were survival, for people living WAY up north. Reliability
was life and death, or could be.

Lightness was also important, so the sled footprint could be smaller, and
not sink too deep, and still haul more.

Bombardier made snow machines (and engines) by the name of skii-doo. Only
one more step to sea-doo, and to ultralight engines.
--
Jim in NC

[[email protected]]

On Fri, 28 Nov 2008 08:30:06 -0500, Dana M. Hague
> wrote:

>On Thu, 27 Nov 2008 09:37:54 -0500, "Peter Dohm"
> wrote:
>
>>IIRC, snowmobiles are/were derived from chain saws--which required an engine
>>light enough for a man to carry and use as a hand held tool. That made them
>>an obvious choice for another application were light weight was the most
>>critical factor--even at the cost of reliability and maintenance
>>intervals...
>
>I've never heard that, seems unlikely... they are really very
>different, except for both (along with outboard motors) being
>2-strokes. All for the same reason of light weight.
>
>-Dana
Some of the first ultralights DID run chainsaw motors - just like the
go-cart crowd. Some of the small aircooled outboard engines were also
used - and some early snowmobiles also used a converted aircooled
outboard. (horizontal twin Johnson Snow Cruiser and OMC)

[Maxwell[_2_]]

"Peter Dohm" > wrote in message
...
|
| "Dana M. Hague" > wrote in message
| ...
| > On Thu, 27 Nov 2008 09:37:54 -0500, "Peter Dohm"
| > > wrote:
| >
| >>IIRC, snowmobiles are/were derived from chain saws--which required an
| >>engine
| >>light enough for a man to carry and use as a hand held tool. That made
| >>them
| >>an obvious choice for another application were light weight was the most
| >>critical factor--even at the cost of reliability and maintenance
| >>intervals...
| >
| > I've never heard that, seems unlikely... they are really very
| > different, except for both (along with outboard motors) being
| > 2-strokes. All for the same reason of light weight.
| >
| > -Dana
| > --
| > If you glue a piece of toast, butter side up, to your cat's back, and
drop
| > it from a high place, which way will it land?
|
| Today, thanks to a substantial market with plenty of discretionary money,
| engines for snowmobiles and ultralights have improved drastically.
| Gardening equipment also runs far more reliably today--and a portion of
that
| improvement may have come from improvements made first on ultralights and
| snowmobiles.
|
| But it was not always so--and I recommend that you ask a few of the old
| timers why they used to refer to some ofthe ultralight areas by nicknames
| such as "the killing fields".
|
| Peter
|
|

I'm an old timer, with a good bit of experience in ultralights, but I don't
recall engine reliability being all the bad in the early days, or having
much to do with the early ultralight fatalities.

[Dana M. Hague[_2_]]

On Fri, 28 Nov 2008 14:01:36 -0500, "Peter Dohm"
>But it was not always so--and I recommend that you ask a few of the old
>timers why they used to refer to some ofthe ultralight areas by nicknames
>such as "the killing fields".

Most of the early ultralight fatalities were due to lack of training
and the occasional structural failure, not engine failure... not that
there weren't frequent engine failures, too. And even at that, many
of the engine failures were pilot related... either not knowing
anything about engines (again, lack of training) or pilots who thought
they could treat a 2-stroke just like a Continental 0-200. How many
pilots fried their Cuyuna engines because they didn't have an EGT to
keep track of the temperatures?

-Dana (who first flew an ultralight in the 1980's, and still flies a
Cuyuna powered ultralight today(yes, with EGT and CHT))


--
People in cars cause accidents. Accidents in cars cause people.

[Dana M. Hague[_2_]]

On Fri, 28 Nov 2008 14:39:46 -0500, wrote:

> Some of the first ultralights DID run chainsaw motors - just like the
>go-cart crowd. Some of the small aircooled outboard engines were also
>used - and some early snowmobiles also used a converted aircooled
>outboard. (horizontal twin Johnson Snow Cruiser and OMC)

True. The first ultralights used either a McCulloch 101 (a target
drone engine) or the Chrysler-West Bend engines of about 9HP (from a
two man chainsaw, I believe). However, the snowmobile engines (Cuyuna
and then Rotax) quickly supplanted them.

-Dana

--
People in cars cause accidents. Accidents in cars cause people.

[Maxwell[_2_]]

"Dana M. Hague" > wrote in message
...
| On Fri, 28 Nov 2008 14:39:46 -0500, wrote:
|
| > Some of the first ultralights DID run chainsaw motors - just like the
| >go-cart crowd. Some of the small aircooled outboard engines were also
| >used - and some early snowmobiles also used a converted aircooled
| >outboard. (horizontal twin Johnson Snow Cruiser and OMC)
|
| True. The first ultralights used either a McCulloch 101 (a target
| drone engine) or the Chrysler-West Bend engines of about 9HP (from a
| two man chainsaw, I believe). However, the snowmobile engines (Cuyuna
| and then Rotax) quickly supplanted them.
|
| -Dana

I don't recall the original use for the McCulloch engines, but I think the
West Bend was just simply an industrial engine, designed to be sold on
mowers and alike. But IIRC, probably because of it's high horsepower for the
era, snow blowers were responsible for most of it's success.

[Highflyer]

> wrote in message
...
> On Fri, 28 Nov 2008 08:30:06 -0500, Dana M. Hague
> > wrote:
>
>>On Thu, 27 Nov 2008 09:37:54 -0500, "Peter Dohm"
> wrote:
>>
>>>IIRC, snowmobiles are/were derived from chain saws--which required an
>>>engine
>>>light enough for a man to carry and use as a hand held tool. That made
>>>them
>>>an obvious choice for another application were light weight was the most
>>>critical factor--even at the cost of reliability and maintenance
>>>intervals...
>>
>>I've never heard that, seems unlikely... they are really very
>>different, except for both (along with outboard motors) being
>>2-strokes. All for the same reason of light weight.
>>
>>-Dana
> Some of the first ultralights DID run chainsaw motors - just like the
> go-cart crowd. Some of the small aircooled outboard engines were also
> used - and some early snowmobiles also used a converted aircooled
> outboard. (horizontal twin Johnson Snow Cruiser and OMC)

I seem to recall that my first powered ultralight was an Easy Riser
powered by a 10 HP West Bend Chain Saw engine with a belt
reduction made and marketed by our own Chuck Slusarcyk. :-)

Highflyer
Highflight Aviation Services
Pinckneyville Airport ( PJY )

[Highflyer]

I think if you look at the engine cutaways or blueprints, you will see
in the drive train a torsion shaft that functioned as a torsion bar to
keep the gears engaged in the same direction and soak up some of
the inevitable torque variations around the revolution of the crank.
Engines that didn't have that were a bit fussier to run and had some
blanked out RPM ranges where you got extreme gearbox wear.

That was a problem with the ill fated Cessna 175 with its GO-300
engine. It performed a LOT better than the 172 that it shared an
airframe with, but got a reputation for eating gearboxes. The
gearbox also got a reputation for being as expensive as the engine
to overhaul. The main problem was running them in the same RPM
range as the O-300 they were used to from their 170/172. The
GO-300 was good from 2800 to 3200 RPM. Below 2800 it was
best to go all the way to idle. Then the gearbox only transitioned
once from driving to driven. People tried to run them at 2400 RPM,
which just "felt" better to an old 172 pilot. At that RPM the gearbox
would beat back and forth from driving to driven every time a cylinder
fired. A few hundred hours of that would destroy a set of
gears! :-)

Highflyer
Highflight Aviation Services
Pinckneyville Airport ( PJY )

"Morgans" > wrote in message
...
>
> "Charlie" > wrote
>
>> You don't often see that because any torsional resonance problems get
>> amplified at an even-multiple ratio, like the cam's 2:1 ratio. Note the
>> final drive ratio of almost any reduction gear train & it will be some
>> odd number like 2.17:1, 2.85:1, etc.
>
> Perhaps an even larger factor is to get different teeth meshing together
> in a cycle, each time around. it is better to not have the same mesh,
> time after time, although what you say about harmonics is also a factor.
>
> In the really big "warbird"engines, the gearboxes had to be built so
> hell-for-stout to deal with the HP levels, the harmonics were not as much
> of an issue because the resonance was hard to achieve with the components
> being so stiff.
> --
> Jim in NC
>