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Counteracting Torque on Plane Propellers?


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Greetings Kerbal Forums,

I have no idea how to counteract the torque on a propeller plane like those in World War 1.  I've been trying to make a Fokker-style plane, but I have this problem where my airplane will have a clockwise rotation when going fast on the runway and especially taking off, leading to many a KIA Kerbals.  This is not due to landing gear - they are as they should be, vertical relative to the ground, and the plane does not exhibit any veer due to parts bending.  Center of gravity is slightly forward of center of lift as it should be.  I cannot send a picture of the aircraft as any design I try from the bottom up exhibits this torque.

 

I wish to not use engines nor RCS thrusters as that would defeat the purpose of it being WW1 style.

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Hello, and welcome aboard!

I'm far from an expert on this subject, but that said: what you're seeing is an inherent issue in single-engine propeller planes.  Due to the principle of conservation of angular momentum, if your propeller spins in one direction, the rest of your plane is going to want to spin in other other direction -- basically so the two balance out.  You can eliminate this by using multiple propeller that spin in different directions (so that the torque from each cancels out), but that's not an option if you want a single-engine for replica purposes.  

I believe real-life planes largely manage this through the control surfaces -- i.e., using the ailerons to counter the roll force.   Unfortunately, control surfaces don't work well at very low speeds.  So you may want to try to throttle up gradually, so that by the time you're applying full torque, you're at least going fast enough to have some roll control.  You can also try using more/bigger control surfaces, or increasing the control authority slider.

Another, less authentic way to deal with it is to use lots and lots of reaction wheels, which can apply a compensating torque.  

Also, the more massive your plane is, the less effect you'll see from the torque - but if you have to scale up your prop to get to the desired speed, that may just cancel out. 

 

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You can clip a counter-rotating object inside the plane, to hide it.

The sizes and torques of airplanes and their engines is not precisely analgous to the "real world". So if you are trying to create replica stuff -- you are going to need to make some small concessions between functionality and looks. Often by using clipping.

 

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In real life, single-engine planes typically have their engines pointing very slightly off-center.  This compensates somewhat for the pitch and yaw components of the torque on the plane, at least at certain speeds, and seems to help in KSP.  However, about all you can do for the roll component is fight it with aileron trim.

SAS doesn't deal well with single-engine torque.   As such, I always use contra- or counter-rotating props, not single-engine.

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I flew variants of the single engine plane pictured below for quite some time (an hour or more). I tried adding a couple of reaction wheels and I tried reducing the motor size to 30%. I tried reducing torque on takeoff. Nothing helped. Having said that, it was quite easy to takeoff and fly. By using SAS on takeoff and making one small steering adjustment I repeatedly ran the entire length of the runway before lifting off. After climbing out I turned SAS off and used trim to counteract the engine torque. Regular small input was necessary but it was not difficult or onerous. Landing deadstick was easy since I no longer had to deal with the torque.

This whole thing was made a lot easier by having spent a lot of time flying a multiple engine plane which does not have any issues with torque and with which I learned to contend with settings for variable prop pitch, engine rpm and torque.

Before that I had tried another single engine plane and found it very difficult.

GWjDgri.png

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