ORIGINAL: multiflyer
Spiraling slip stream is only one of the propeller effects that right thrust can help. The larger reason for right thrust is P-factor at slow speed. If the prop disk is not exactly perpendicular to the air stream, the blades will see different AOA on opposite sides of the disk. This shows up the most during slow flight. Nose high attitude tilts the prop arc back causing the descending blade (on the right) to take a bigger bite out of the air, and the rising blade (on the left) to take a smaller bite. Basically offsets the center of thrust to the right causing a yaw to the left. Right thrust compensates. As speed builds and nose lowers the effect reduces and the right thrust eventually becomes a nuisance, but aerodynamic stability is much greater now. So, adding more right thrust is a good compromise – but for flying right side up only. During inverted flight the right thrust is now left thrust but the P effect is still the same.
This is why aerobatic planes usually have just a little or no right thrust, while trainer and sport planes usually have noticeably more - they just spend more time right side up and are optimized for that.
A better solution of course is counter rotating props or pure jet power. There is no way to make one prop perfect.
Multiflyer
Multiflyer,
with all the respect, you are wrong.
It is well known why right thrust is introduced, in this is ONLY for spiraling slipstream and NOT for P-Factor!!! If you are not convinced about that, I can give you a link of a good explaination of a well known aero engineer, which states that very clearly.
Also, it is wrong also the fact that aerobatic planes have usually no right thrust: my pattern plane, which is designed by one of the F3A top pilots of the world, has FOUR degrees of right thrust. Obviously, you could build it without right thrust, and there are well known pilots that do that (namely, Chip Hyde), but they introduce another trick to compensate for spiraling right thrust.
I agree about the contro-rotating props though!
Dick, I appreciate your input, from your experience when such a side area distribution is constructed, it can be said that less right thrust is required?
Again, thank you all guys.