engine thrust angle / adverse yaw
02-20-2005 | 05:24 PM
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From: san jose,
CA
engine thrust angle / adverse yaw
I have my first true giant scale plane, a 1/3 scale Citabria. 131" WS, 38 lbs. Bought used. Installed a friends G-62 with Pro Zinger 22-10 to see if that would be enough engine. In general, plane flies great, and very scale like. So, I purchased a used Sachs 4.2 (a little more power is always good) and am in the process of installing.
Set up the G-62 with 2 deg right thrust, 0 deg up/down (as best I could). Thought I had the right thrust nailed because plane needs little if any rudder correction from idle to full power. However, the adverse yaw when using ailerons only is really powerful on left banks, much more tame on right banks. On left aileron banks, the plane will actually go right and climb. I understand that coordinated rudder is necessary, and is part of the fun of learning to fly the plane in a truly scale like manner. The problem I want to try to correct is the difference between left and right turns. Very stable and linear in right turns, but in left turns, using left rudder, a little too much rudder makes the plane bank (roll) way more than the stick movement should. When trying to tighten up the turn with more rudder, actually needs some opposite aileron to keep it from banking too much. Right turns don't do this - just bank with both aileron and rudder, and then hold enough rudder to keep it turning. I've been told this is just due to engine torque, etc.
So - question is - is there a balance between right thrust and the difference in left vs right turns? Should I back off the right thrust, and put up with a little pulling to the left under power? Would that help even out the turns? Or is this just the way I should expect this plane to act?
doug
Set up the G-62 with 2 deg right thrust, 0 deg up/down (as best I could). Thought I had the right thrust nailed because plane needs little if any rudder correction from idle to full power. However, the adverse yaw when using ailerons only is really powerful on left banks, much more tame on right banks. On left aileron banks, the plane will actually go right and climb. I understand that coordinated rudder is necessary, and is part of the fun of learning to fly the plane in a truly scale like manner. The problem I want to try to correct is the difference between left and right turns. Very stable and linear in right turns, but in left turns, using left rudder, a little too much rudder makes the plane bank (roll) way more than the stick movement should. When trying to tighten up the turn with more rudder, actually needs some opposite aileron to keep it from banking too much. Right turns don't do this - just bank with both aileron and rudder, and then hold enough rudder to keep it turning. I've been told this is just due to engine torque, etc.
So - question is - is there a balance between right thrust and the difference in left vs right turns? Should I back off the right thrust, and put up with a little pulling to the left under power? Would that help even out the turns? Or is this just the way I should expect this plane to act?
doug
02-20-2005 | 09:37 PM
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From: St. Charles, MO
RE: engine thrust angle / adverse yaw
Dick H. should be able to answer your question with his experience level in the big machines.
With the big machine there is a lot of spiral airflow from the propeller. There will be an asymmetric flow on the vertical-rudder combination. If you have trimmed it level in normal flight be sure the ailerons and rudder arn't working against each other. Such that removing the right rudder allows the left aileron become effective. Check that the wings are not warped, vertical and horizontal tails are straight and not warped. Be sure all controls move the same amount and are set absolutely at neutral.
I do know that a lot of full scale machines have a slightly offset vertical fin to get a balanced level flight, and some use trim tabs on the ailerons.
With a Citabria you might look at what the real one requires and or flys like. There might be a site somewhere that describes it. Meanwhile you need a guy that has trimmed out a big model.
With the big machine there is a lot of spiral airflow from the propeller. There will be an asymmetric flow on the vertical-rudder combination. If you have trimmed it level in normal flight be sure the ailerons and rudder arn't working against each other. Such that removing the right rudder allows the left aileron become effective. Check that the wings are not warped, vertical and horizontal tails are straight and not warped. Be sure all controls move the same amount and are set absolutely at neutral.
I do know that a lot of full scale machines have a slightly offset vertical fin to get a balanced level flight, and some use trim tabs on the ailerons.
With a Citabria you might look at what the real one requires and or flys like. There might be a site somewhere that describes it. Meanwhile you need a guy that has trimmed out a big model.
