I am a bit confused by terms used in side thrust discussions. Some say a model plane tends to veers to the left as a result of engine torque, some say torque has nothing to do with it, it is because the stream of air behind the prop is rotating clockwise, the rudder and vertical fin is normally above the thrust line, so the spiral of air will push it to the right. In most trimming charts it is said that if the plane veers left ad right thrust, to me thrust is the hi pressure stream behind the prop, so if you turn the engine to the right to prevent it from veering to the left, you are adding left thrust not right thrust ? The same applies to up and down thrust.

The term 'right thrust' means you are shifting the engine shaft toward the right (as viewed from behind the plane) which means the result of the forward thrust (pull) is angled to the right a little bit more. Same with 'down thrust', the engine shaft is angled downward to create a little more pull toward the bottom of the plane.

The thrust terms do not apply to the column spinning air created by the propeller but rather to the resultant angle of thrust created by the shifting of the engine.

Don

Thanks for the reply Don,
I except that this is the way the term is used by modelers and would be ridiculous to try and change it now. But we must admit that is confusing to newcomers and technically incorrect because thrust is not “pull”, it is the high pressure behind the prop so you are actually applying left thrust to make the plane veer right.
To sum it up: We move the Prop side of our engine shaft to the side we want the plane to veer and call it “that side” thrust, I think I got it.

I think you understand what you need to do to get the plane to fly in a straight line, and your reasoning for why it is required is correct (ie it's to do with spiralling air striking the fin, not a torque or centrifugal reaction). But, the thrust on the plane is definitely acting forwards (and a bit to the right)!

Newton once said that force = mass x acceleration. He was quite a clever guy because he also figured that every action (ie force) has an equal and opposite reaction (ie if I push you, you push me back).

So, the propeller accelerates a column of air backwards. The mass of the air being moved, multiplied by the acceleration of that air, gives you the force that the propeller is applying to the air. And because every action has an equal and opposite reaction, this results in a force (ie thrust) on the plane that acts forwards.

Therefore, the thrust on the plane is forwards, not backwards. If you want to think of it this way, you could say that the thrust on the air is backwards, which is why if you put your hand in the prop wash it gets pushed backwards. And therefore, if you rotate the engine to the right a bit, the air is being accelerated to the left a bit and you get a resulting force on the plane to the right.

The terms are indeed technically correct!

James

Thanks James,
You have cleared it for me. “The engine does work on the gas and accelerates the gas to the rear of the engine; the thrust is generated in the opposite direction from the accelerated gas”
I have learned something new again!
Cheers piet