Contra-rotating engine revisited

[Chris W]

The previous post on this topic got me wondering. Just how different
would the two engines need to be? I'm no expert, but it seems to me
cam shaft(s), magnetos, and prop are the parts that would be different
from one side to the other. I almost forgot, reverse the polarity on
the starter motor. What am I missing?


--
Chris W
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[Steve Foley]

"Chris W" > wrote in message
...
> The previous post on this topic got me wondering. Just how different
> would the two engines need to be? I'm no expert, but it seems to me cam
> shaft(s), magnetos, and prop are the parts that would be different from
> one side to the other. I almost forgot, reverse the polarity on the
> starter motor. What am I missing?

How about an engine with the crankshaft running out the front and back, so
you could mount a prop on the either end? That way you could have
counter-rotating props using the same engine.

[Mxsmanic]

Steve Foley writes:

> How about an engine with the crankshaft running out the front and back, so
> you could mount a prop on the either end? That way you could have
> counter-rotating props using the same engine.

There's still some asymmetrical engine torque, since the engine itself
turns in only one direction.

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[Chris W]

Mxsmanic wrote:
> Steve Foley writes:
>
>> How about an engine with the crankshaft running out the front and back, so
>> you could mount a prop on the either end? That way you could have
>> counter-rotating props using the same engine.
>
> There's still some asymmetrical engine torque, since the engine itself
> turns in only one direction.
>

I think he meant you could mount the engine backwards, then it would be
spinning the other way. With the crank going out both ends you could
mount the prop on it, no mater which way it was in the plane. Seems to
be more work than what some twins do now if you ask me. Mounting the
engine in backwards, would not a simple matter.

--
Chris W
KE5GIX

"Protect your digital freedom and privacy, eliminate DRM,
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[Steve Foley]

"Mxsmanic" > wrote in message
...
> Steve Foley writes:

> There's still some asymmetrical engine torque,

No, there is not.

[Mxsmanic]

Steve Foley writes:

> No, there is not.

Unless the engine is weightless and frictionless, it will exert torque
on the airframe whenever it is turning, even if there are no props.

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[Roy Smith]

In article >,
Mxsmanic > wrote:

> Steve Foley writes:
>
> > No, there is not.
>
> Unless the engine is weightless and frictionless, it will exert torque
> on the airframe whenever it is turning, even if there are no props.

No, that's not true. If there is no prop, the engine will only exert
torque on the airframe when its rotational speed is changing.

My mom used to have a 1960-something Buick with a big-ass V8 and a mushy
suspension. You could set the thing rocking just by revving the engine in
neutral.

[tom418]

Vacuum pumps are different (although these are accesories)
"Chris W" > wrote in message
...
> The previous post on this topic got me wondering. Just how different
> would the two engines need to be? I'm no expert, but it seems to me
> cam shaft(s), magnetos, and prop are the parts that would be different
> from one side to the other. I almost forgot, reverse the polarity on
> the starter motor. What am I missing?
>
>
> --
> Chris W
> KE5GIX
>
> "Protect your digital freedom and privacy, eliminate DRM,
> learn more at http://www.defectivebydesign.org/what_is_drm"
>
> Gift Giving Made Easy
> Get the gifts you want &
> give the gifts they want
> One stop wish list for any gift,
> from anywhere, for any occasion!
> http://thewishzone.com

[buttman]

This is annoying. "COUNTER-rotating" is the term you want.
"CONTRA-rotating" is when you have two different blades on the same
shaft spinning in different directions. About 50% of the time one of
these terms gets used, they get them mixed up.

http://en.wikipedia.org/wiki/Contra-rotating_propellers
http://en.wikipedia.org/wiki/Counter-rotating_propellers

Chris W wrote:
> The previous post on this topic got me wondering. Just how different
> would the two engines need to be? I'm no expert, but it seems to me
> cam shaft(s), magnetos, and prop are the parts that would be different
> from one side to the other. I almost forgot, reverse the polarity on
> the starter motor. What am I missing?

[Mxsmanic]

Roy Smith writes:

> No, that's not true. If there is no prop, the engine will only exert
> torque on the airframe when its rotational speed is changing.

The forces that compel the engine to rotate in one direction engender
equal and opposite forces that tend to rotate the airframe in the
opposite direction.

> My mom used to have a 1960-something Buick with a big-ass V8 and a mushy
> suspension. You could set the thing rocking just by revving the engine in
> neutral.

That's because the amount of torque changes with the rotational speed
of the engine. However, as long as it is turning, it is exerting
torque on the rest of the car.

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[Mxsmanic]

tom418 writes:

> Vacuum pumps are different (although these are accesories)

What is the logic behind using vacuum to power instruments? Why not
just use an electric motor, or compressed air?

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[Capt. Geoffrey Thorpe]

"Chris W" > wrote in message
...
> The previous post on this topic got me wondering. Just how different
> would the two engines need to be? I'm no expert, but it seems to me cam
> shaft(s), magnetos, and prop are the parts that would be different from
> one side to the other. I almost forgot, reverse the polarity on the
> starter motor. What am I missing?
>
>
> --
> Chris W
> KE5GIX
>

Camshaft as you said.
Crank - they drill the holes for the oil to the rod bearings in a different
spot.
Magneto - the impulse has to work in the other direction. I don't know if
there are changes to the points for avaition applications.
Oil pump - has to pump in the other direction
Starter - the bendix is different, the brushes are re-located
Alternator - it may have a different cooling fan
vacuum pump
Prop as you said
Mechanical Tach, or the drive (I assume)

--
Geoff
The Sea Hawk at Wow Way d0t Com
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When immigration is outlawed, only outlaws will immigrate.

[TxSrv]

Mxsmanic wrote:
> What is the logic behind using vacuum to power instruments? Why not
> just use an electric motor, or compressed air?
>

Why don't you just think about what FAA's answer to that one is.
So obvious a Caveman can figure it out. Plus, compressed air
can be and is used. But not electricity, unless....

F--

[Jose[_1_]]

> Anyone for the "Dutch Roll" discussion next?

Isn't that a cinnamon roll where you supply your own cinnamon?

Jose
--
"There are 3 secrets to the perfect landing. Unfortunately, nobody knows
what they are." - (mike).
for Email, make the obvious change in the address.

[Bucky]

Chris W wrote:
> The previous post on this topic got me wondering. Just how different
> would the two engines need to be?

If propeller direction is all that you need to change, could you just
add a reverser gear?

[Steve Foley[_2_]]

"TxSrv" > wrote in message
. ..


> So obvious a Caveman can figure it out.

Too many Geico ads?

[Steve Foley[_2_]]

"Bucky" > wrote in message
ups.com...
> Chris W wrote:
>> The previous post on this topic got me wondering. Just how different
>> would the two engines need to be?
>
> If propeller direction is all that you need to change, could you just
> add a reverser gear?
>

How about one engine in the middle, with chain driven gears turning the
props on the wings.

Oh, wait. I think that's already been done.

[Peter Dohm]

Please do not feed the trolls!

[Peter Dohm]

Please do not feed the trolls!

[Jim Macklin]

MXs Maniac, sounds like a handle for a motocross rider or
wannabe...

Test for torque.

Jump your YZ400 and while in the air, open the throttle, why
does the front wheel move and which direction? Stab the
rear brake just before landing, why is that a bad idea?


Get your MSFS and setup the P51 Mustang with the big HS
prop. In flight at 75 mph and 100 feet, slam the throttle
wide open, report what happens?


"Nomen Nescio" > wrote in message
...
| -----BEGIN PGP SIGNED MESSAGE-----
|
| From: Mxsmanic >
|
| >That's because the amount of torque changes with the
rotational speed
| >of the engine. However, as long as it is turning, it is
exerting
| >torque on the rest of the car.
|
| Dammit! I'm calling MIT tomorrow to demand my money back.
| Those *******s told me that it was proportional to angular
| acceleration.
|
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| Version: N/A
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[Mxsmanic]

Nomen Nescio writes:

> Dammit! I'm calling MIT tomorrow to demand my money back.
> Those *******s told me that it was proportional to angular
> acceleration.

You'd have to demonstrate that they explained it incorrectly; if you
misunderstood, no refund is likely to be forthcoming.

--
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[Matt Barrow]

"Jim Macklin" > wrote in message
...
> MXs Maniac, sounds like a handle for a motocross rider or
> wannabe...
>
> Test for torque.
>
> Jump your YZ400 and while in the air, open the throttle, why
> does the front wheel move and which direction? Stab the
> rear brake just before landing, why is that a bad idea?
>
>
> Get your MSFS and setup the P51 Mustang with the big HS
> prop. In flight at 75 mph and 100 feet, slam the throttle
> wide open, report what happens?

For him, it probably causes the infamous "Blue Screen of Death".

[Morgans[_2_]]

"Chris W" > wrote in message
...
> The previous post on this topic got me wondering. Just how different would
> the two engines need to be? I'm no expert, but it seems to me cam shaft(s),
> magnetos, and prop are the parts that would be different from one side to the
> other. I almost forgot, reverse the polarity on the starter motor. What am I
> missing?

Not speaking to the other items, but electric motors seldom run as well in both
directions. It has to do with the timing, or how far ahead of the rotation that
the magnetic fields, or windings are switched.
--
Jim in NC

[Morgans[_2_]]

"Bucky" > wrote
>
> If propeller direction is all that you need to change, could you just
> add a reverser gear?

Before you come in here and play with big boys, you better put on your galoshes,
bucky.

And stop following that MX, from the sim group, where ever he goes. He and you
are going to get your fingers stepped on.

Maybe get a clue, too.

Oooh, that was mean. I take it back.
--
Jim in NC

[tom]

With two stroke engines it is easy. I did this once. All I needed to
do was exchange the field wires in the starter to turn it backwards,
and modify the advance mechanism in the distributor so the spark was
advanced in the new direction. It ran fine. This was to enable a
motorcycle engine to be used in a go kart, where the engine was mounted
backwards, behind the rear wheels. It was a twin Yamaha and the go
kart would pop wheelies like crazy.

tom

Chris W wrote:
> The previous post on this topic got me wondering. Just how different
> would the two engines need to be? I'm no expert, but it seems to me
> cam shaft(s), magnetos, and prop are the parts that would be different
> from one side to the other. I almost forgot, reverse the polarity on
> the starter motor. What am I missing?
>
>
> --
> Chris W
> KE5GIX
>
> "Protect your digital freedom and privacy, eliminate DRM,
> learn more at http://www.defectivebydesign.org/what_is_drm"
>
> Gift Giving Made Easy
> Get the gifts you want &
> give the gifts they want
> One stop wish list for any gift,
> from anywhere, for any occasion!
> http://thewishzone.com

[Morgans[_2_]]

"Nomen Nescio" > wrote

> Dammit! I'm calling MIT tomorrow to demand my money back.
> Those *******s told me that it was proportional to angular
> acceleration.

Naahhh. Just go ahead, and put in for an official change in the laws of
Physics. I'm sure they must need changed, if MX says it is due to something
else. Not.
--
Jim in NC

[tom]

Sorry, but you are wrong here. As long as there is no load external to
the engine, it's own friction torque will have no external
manifestation. There will be an external torque, momentarily while the
engine is accelerated or de-accelerated.

tom


Mxsmanic wrote:
> Steve Foley writes:
>
> > No, there is not.
>
> Unless the engine is weightless and frictionless, it will exert torque
> on the airframe whenever it is turning, even if there are no props.
>
> --
> Transpose mxsmanic and gmail to reach me by e-mail.

[Jose[_1_]]

> Naahhh. Just go ahead, and put in for an official change in the laws of Physics.

That will have to be brought up before the Grand Canonical Ensemble. I
don't think they are meeting again for another two years.

Jose
--
"There are 3 secrets to the perfect landing. Unfortunately, nobody knows
what they are." - (mike).
for Email, make the obvious change in the address.

[Mxsmanic]

tom writes:

> Sorry, but you are wrong here. As long as there is no load external to
> the engine, it's own friction torque will have no external
> manifestation. There will be an external torque, momentarily while the
> engine is accelerated or de-accelerated.

If you run the engine in zero gravity, does the crankshaft spin while
the engine remains still, or does the engine spin while the crankshaft
remains still, and why?

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[Capt.Doug]

>"Chris W" wrote in message
> The previous post on this topic got me wondering. Just how different
> would the two engines need to be? I'm no expert, but it seems to me
> cam shaft(s), magnetos, and prop are the parts that would be different
> from one side to the other. I almost forgot, reverse the polarity on
> the starter motor. What am I missing?

Prop governor and oil pump drive gears if not on camshaft. Floating
crankshaft balance weights may be slightly different if those are used.

D.

[Neil Gould]

Recently, Morgans > posted:

> "Nomen Nescio" > wrote
>
>> Dammit! I'm calling MIT tomorrow to demand my money back.
>> Those *******s told me that it was proportional to angular
>> acceleration.
>
> Naahhh. Just go ahead, and put in for an official change in the laws
> of Physics.
>
Sorry, but that change isn't scheduled before the release of Real World
2.0.

Neil

[Bucky]

Morgans wrote:
> And stop following that MX, from the sim group, where ever he goes.

huh?

[Kingfish]

Steve Foley wrote:
>
> How about an engine with the crankshaft running out the front and back, so
> you could mount a prop on the either end? That way you could have
> counter-rotating props using the same engine.

Two props mounted on a common crank would turn in the same direction,
so they wouldn't be contra-rotating (I assume that is what you meant)
but might be counter-rotating if they turn in the opposite direction of
the other engine's props.

Come to think of it, if an engine had contra-props mounted front & back
(like the old Dornier Do X flying boat from the 30's) the props' torque
would cancel each other's out but would there still be a torque
reaction from the direction of engine rotation? I'm assuming the Do X
props were contra-rotating, not 100% sure on that.

[Steve Foley]

"Kingfish" > wrote in message
ups.com...
>
> Steve Foley wrote:
>>
>> How about an engine with the crankshaft running out the front and back,
>> so
>> you could mount a prop on the either end? That way you could have
>> counter-rotating props using the same engine.
>
> Two props mounted on a common crank would turn in the same direction,
> so they wouldn't be contra-rotating (I assume that is what you meant)
> but might be counter-rotating if they turn in the opposite direction of
> the other engine's props.

What I meant was putting a clockwise spinning prop on one wing, and turning
the other engine around, so it would be a counter-clockwise spinning prop on
the other wing.