In spite of the wedge rudder trim tab that came with the rudder, I'm having to apply a noticeable amount of right rudder.
The RV-4 builder's manual mentions that misaligned gear leg fairings can produce a significant deflection of the skid ball.
My question is: Can I use intentional misalignment of one or both gear leg fairings instead of an (additional) rudder trim tab?
Having a hard time visualizing which way they should be adjusted.
But also, what are the aerodynamic consequences (drag?) of doing this?
Finn
The short answer is YES gear leg fairings can cause yaw and yes they cause aerodynamic drag. Both are true but we try to minimize it. Using them to adjust for something else that is out of trim or rig will cause drag but it may be very small. However everything hanging out in the breeze is drag regardless.
When you say "noticeable amount of right rudder", you mean in level cruise flight? Right? How is roll trim? Where is the elevator trim tab in level cruise flight (solo)?
When finishing my first RV-4 long ago. I endlessly adjusted, rigged to get wings level in cruise with no trim tab. I tried to get elevator pitch trim tab to have little to no tab deflection in cruise (solo). Last I wanted yaw zero in cruise flight without a tab. I was mostly successful. I ended up with a tiny rudder wedge. No shame in a small rudder trim tab.
GEAR LEGS are forward of CG. So looking down on the airplane, if you move gear leg trailing edge to the right it will will swing the nose LEFT (like pushing on the left rudder pedal and and making the skid ball go right.If you move the gear leg fairing trailing edge to the LEFT (looking down at the airplane) the opposite will occur. So if you have to push on the RIGHT rudder to make the plane not skid in wings level, level cruise flight, you would move one or both gear leg fairings trailing edges to the left. This pushes nose right.
Keep in mind (not to get too complicated) the spiral slip stream of from the prop will cause different effect on the left and right gear leg fairing and vertical Stab and Rudder even in level flight. So it is normal for the noise to be slightly nose left (slightly). The yaw will change with airspeed, but you are saying "noticeable amount of right rudder."
Check all your rigging. Make small adjustments. Take good flight test notes. Change one thing at a time. Have a flight test plan written out and don't get to focused on the yaw and not fly the plane. Good LUCK (and always fly safe).
PS LEFT TURNING tendencies (slip stream, gyro precision, torque and P-factor) is always there. In level flight it is mostly (spiral) slip stream and torque. Monster rudder tabs on RV's should not be necessary, assuming the vertical stab was installed per plans and the airframe is straight you should not have to apply noticeable rudder in level cruise.
Aileron and flap rigging can cause roll which can also induce yaw... so double check all the rigging.
Often over looked is engine mounting. Some times you need to SHIM engine to get thrust line correct, due to small tolerances in engine mount and firewall. The thrust line should be straight or slightly right to cancel left turning.
Whatever you do try to find neutral of gear leg fairings. By neutral I mean the chord line of fairing is in line with with airframe airflow in level flight. Air flow around plane is complex and variable, but for reference we use wing chord line or top edge of cockpit longeron. Finding the level chord line of gear fairings is not easy, due to gear leg angles and taper of fairing. Make sure when setting your references with no weight on wheels per plans. Set up some repeatable reference system so you know what you have now and what you are adjusting to. I chased my tail a few times rigging. Be methodical. Do easy stuff first. Don't adjust and pray. Do you flight test and record results. Wash, rinse, repeat. Again make sure the whole plane is in rig. If you did not build it check wing incidence angles and vertical stabilizer. Sometimes planes are built a little off (they are armature built after all.)
I bonded and glassed on wood stiffeners to my gear legs which set the fairings position in stone (by the way stiffeners made the plane feel solid and had no shimmy ever). I had no adjustments of fairing after that. However I flew the plane with no gear leg fairings or wheel pant fairings (which can cause yaw). So I knew the affect before and after. In the end a tiny wedge was bonded to the rudder.
Consider taking the fairings off (gear leg and wheel pants) and flying like that. If you still have big rudder input with gear/wheel fairings off during level cruise flight you might have other issues.
FYI I had the original metal gear leg fairings which were narrow chord. Ones on later models were wider slightly. The aftermarket TEAM ROCKED gear leg fairings are even wider (chord) and have a greater effect in all axes. This is what I have for my RV-7. Richard Vangrunsven does NOT approve or like wide chord gear leg fairings on his airplanes designs, because it reduces the effectiveness of the rudder to get out of spins. The gear leg fairings act opposite of vertical stabilizer and reduces yaw stability. However the wide fairings do reduce drag and look cool. I did NOT fool with my gear leg fairings on later planes. I just tried to get the "straight" or parallel to wing chord line. Any other adjustments are done with vert stab, trim tab, rigging overall or engine thrust line as needed.