Hello,
On March 21, 2018, I have published
https://stunthanger.com/smf/open-forum/rabe-rudder-necessity-or-just-another-gizmo-from-the-past. This message generated a lot of interest and comments.
After 1.5 years and about 300 pattern flights with two full scale F2B electric models, I have decided to add my own observations regarding the Rabe Rudder (RR).
My latest model, Big Red, based on Igor's Max Bee II, uses RR. The deflections of the RR in Big Red were based on the corresponding deflections in Patrick MacKenzie's Max Bee II. The maximum deflection was 35-36 degrees with the elevator fully down, 8 degrees with the elevator neutral and 0 degrees with the elevator fully up.
Patrick is flying "soft corners".
At the time I started trimming Big Red (May 2019), I was not yet able to fly really tight corners. They were, using Paul Walker's terminology, "soft" or, using my own description "very soft". Now, I have learned to make the "pivoting corners" (ref: Paul Walker Trim Flow series) in most of the maneuvers requiring them. Big Red pivots nicely, for example in the corners of the outside squares, but the large RR deflection cause the momentary yaw problem - the plane wags its tail to the inside of the circle. Apparently the RR generated yaw moment in the pivoting outside corners is momentarily larger than the gyroscopic moment acting about the model vertical axis originating in CG.
I have decided to decrease the maximum deflection of the RR to about 20 degrees outside with the elevator fully down, 2 degrees with the elevator neutral, and 2 degrees inside (yes, inside...) with the elevator fully up.
Max Bee II elevator surface area is 10.75 in.^2.
Going flying now - almost no wind and cloudy. If the test pattern flights demonstrate that the "inside tail wagging", especially noticeable in the outside squares corners and also in the second turn of the hourglass decreases, I am going in the right direction.
Anticipating the question: the model has been carefully trimmed following the Paul Walker's Trim Flow Chart. The lead-outs position, the outside wing tip weight, the thrust axis angles and, most of all, the CG location, seem to provide a very good grooving and turn sensitivity. The horizontal and inverse horizontal flights are symmetrical, the wings are in the plane of the lines and the round maneuvers are symmetrical and easy to perform. Lap time: 5.18-5.22 sec.
Igor's wing airfoil provides the exceptional tolerance for the CG location - moving the CG (+) (-) 0.25" does not change the model flight quality, at least for me. This unique feature will be the subject of one of my next threads.
Happy Flying,
M