paully_321

I am nearly done with my new Tiger 60 arf. I noticed the firewall is not square to the rest of the plane and It looks to be on purpose. The hatch covering the fuel tank is also cut at the same angle.

Is this on purpose, and if so why? If it is wrong what should I do to fix it.

Pictures below...The square is flush to the side of the fuse in both, but one side is square and the other is not.

Paul

ChuckW

Don't worry, the angle is intended. Often, the designer will incorporate various engine thrust angles to improve the flying characteristics of the airplane.

In your pictures, it looks like the blind nuts for the motor mounts are also off-center to the left. This is to compensate for the angle and keep the spinner close to the center line.

It all looks a little weird the first time you see it but the designer knows what he is doing.

Stickbuilder

It's done to compensate for people not wanting to use the rudder at all times. When flying full scale, you either have a trim tab to adjust, or you spend a lot of time dancing on the pedals, and sadly, most model flyers don't use the rudder enough.

Bill, AMA 4720
WACO Brotherhood #1

Flypaper 2

It's to compensate for torque and P factor which tends to pull the nose to the left on take off. The right thrust pulls it back to the right.

JohnW

My Feedback: (6)

Right thrust on models is to counter the asymmetrical slip stream caused by our single engine single propeller planes.

Torque, p-factor, etc. really don't come into play.

P-factor is reversed when inverted, which means we'd need left thrust to counteract it. For a real world example, we use right thrust in pattern ships, which spend 50% of their life upside down, yet they track true both inverted and rights side up, so right thrust isn't because of P-factor.

Torque only has a roll effect, not a yaw effect. The torque in most planes is small due to the mass of the propeller is so small compared to the mass of the plane.

Gyroscopic effects can sometimes be felt with abrupt pitch changes or on large enough planes, but right thrust doesn't fix that.

cruzomatic

My Feedback: (17)

I agree with what the others said. Don't worry about it, it's normal.

Mr Cox

The prop is also spun in the air with a resistance so this torque made on the prop by the engine has to have a counterforce/torque. With a prop spinning anticlockwise the plane will roll clockwise (when viewed from the front) i.e. the plane rolls to the left.

JohnW

My Feedback: (6)

Yes, torque will cause the plane to roll to left, but this is countered with right aileron, not right thrust.

Mr Cox

Yes I agree to that.
But it also depends on the plane. Without ailerons but with dihedral in the wing, righthand thrust can be used to counteract this torque rather than using the rudder.

JohnW

My Feedback: (6)

I understand your point, with dihedral, right thrust produces right yaw, which couples to right roll due to the dihedral, which opposes torque. But, I guess should have added that I just don't see how there could be enough torque present to cause a problem in our models. If I understand what you are saying, to counter torque on a non dihedral plane, we would need a throttle->aileron mix to counter torque? Right thrust won't do it since the coupling is gone with no dihedral. So I don't understand why torque is a problem only on dihedral planes. I just haven't ever seen the need for a throttle->aileron mix so unless I'm missing something or misunderstood, I’d think the roll component you are fixing is really yaw from the slipstream that coupled into roll due to the dihedral in the wing, nothing to do with the engine torque.