Contra-rotating engine revisited

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?


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"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.

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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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

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

There's still some asymmetrical engine torque,

No, there is not.

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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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.

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.

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.