Rabe Rudder - necessity or just another gizmo from the past - continuation

[Matt Piatkowski]

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

[Matt Piatkowski]

Good news! My approach works well.
Tail wagging visible before disappeared, that is, I cannot see or feel it.
I have to ask somebody on the outside of the circle to check the model movements in corners but I know already that on my Pattern skill level it is much better.

The model seems to carry now a bit more momentum leaving the corners, a crucial and very important difference that allows to better make, for example, the horizontal eight corner #10. This is the inside corner but before the RR angles change the model was using more energy and momentum in the horizontal eight left square outside corners and was barely making the corner#10.

Also, the batteries drain decreased slightly, from 1850 to 1800-1820 mAh. Both measured in similar weather, 69-70 deg.F., cloudy and no wind. This indicates a positive effect of smaller RR outside deflection that acts like an air brake. Less air braking converts into less battery drain.

I am very pleased with the way the entire Big Red (Max Bee II) project progresses. Again, please remember that the above observations and results are valid for my current flying style, this particular model, lap times, lines length, propeller, battery, Spin66 ESC and Igor's active timer having certain setup.

Happy Flying,
M

[Dee Rice]

I found that it works well for some ships and not needed on most...........depends on design, weight, and the pilots style.

Trivia question..........What  design did Al first use his moveable rudder on?   

[Trostle]

Trivia question..........What  design did Al first use his moveable rudder on?

The first design that Al Rabe published with the movable rudder was his first Mustang showing Cavalier colors (red and white) in the June 1969 issue of American Aircraft Modeler.  In the accompanying article Al explained he tried out his idea of a movable rudder to compensate yaw on all pitching maneuvers on "a simple straight-wing stunt ship called Oriental, designed by Dee Rice."

Al had that Cavalier Mustang at the 68 Olathe Nats where I had the privilege to fly it.  I was impressed.  Al, this being his first Nats appearance, qualified in the top 10 for the finals that year but had to leave before the delayed finals were completed - but that is another story.

Keith

[Brett Buck]

As before - it's not a necessity in any sense of the word. It can be made to work and be a beneficial improvement in many case. However, in practical use, it usually doesn't end up improving anything and frequently creates problems far in excess of the precession it is supposed to be correcting for. Not because the idea is wrong, but because it is not adjusted correctly, usually with VASTLY, orders of magnitude, too much movement.

[Bootlegger]

  For Dee Rice, my money is he used it on a Dee Rice Oriental...  So there  LOL LOL

[Steve Helmick]

Most I've seen moved VERY little, especially since it's highly unlikely that more than 15 to 20 degrees of elevator is ever actually used. Too much was ALWAYS bad.  Steve

[Air Ministry .]

Ya musta seen this fred : ?

https://stunthanger.com/smf/stunt-design/rabe-rudder/

last para ,



Comes out a lot clearer if you click away on Keiths Post on the link above .