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Old Dec 23, 2012, 01:00 PM
less is more
Knoll53's Avatar
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Quote:
Originally Posted by Stupot46 View Post
One of they guys using a split fin on the slope forum said just the same thing,he could virtually stop it dead with the set up you describe.I'll have to have a read at the Optic6 manual,see if I can figure out how to do it.
Stuart
With the Optic 6, I'd put the split rudder on the throttle stick then use one of your programs to mix the elevator to the throttle stick. Works a treat.

This way you can ease into the braking/elevator compensation thing. Depending on your airspeed, you may want to ease into it to avoid a drastic pitch change.

Kent
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Old Dec 23, 2012, 01:45 PM
the anthropocebo effect
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Joined Jan 2007
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I like the airbrake idea of the split drag rudder requiring down elevon, so you get flaps for landing.

It looks like everyone is right, except possibly me. Dr.Drela's calculation is right, as usual. A 1 in 10 swept rudder hinge line has essentially no pitch effect on a tailed airplane. The keys are a fairly modest 5.7 degree hinge sweep and a tailed airplane.

Even the 25 degree rudder hinge line sweep on my old BoT has very minimal effect because the stabilizer is so much more powerful. I fly my BoT with minimal elevator throw because the planform has very bad tip stall characteristics, and I have honestly never noticed any up elevator effect from the 25 degree rudder hinge line sweep. It should be pretty noticeable too, since I basically cruise around at minimum sink speed, just above stall speed, all the time with that thing. A touch of up makes it stall, but a lot of rudder does not. Rudder hinge line sweep is cosmetic on a tailed airplane, and the touted up elevator effect would probably be undesirable anyway.

On a plank flying wing, with the low pitch stability and high pitch sensitivity, the effect of a swept rudder hinge line will be quite a bit more noticeable. The force is still pretty small until the hinge sweep angle gets past 15 degrees. I haven't quite worked out how much elevon correction would be need for a typical plank. I am still not clear why you would want an up elevator effect from the rudder - if it worked, it would likely stall the glider on turn initiation and not be very useful. The drag from rudder deflection with a fin above the CG will create the same sort of magnitude nose up pitch moment as a 15 degree rudder hinge line sweep angle.

If the drag centre of a split rudder is high above the CG, it will have a much larger effect than a modestly swept (less than 15 degrees) rudder hinge line. Coupling that effect with down elevons is a great idea for landing a plank, as long as you program the coupling in and test at altitude first.

Kevin
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Last edited by kcaldwel; Dec 23, 2012 at 01:57 PM.
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Old Dec 23, 2012, 03:12 PM
I don't like your altitude
Stupot46's Avatar
Joined Sep 2011
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Thanks for the feedback,greatly appreciated.
Been thinking about how to operate it.Some sort of Y system.Maybe a slot in the fin,about to the mark on the pic.Two thin wire/ carbon rods into a single tube,soldered/epoxied into one just before the servo.(fill the slot after installation)
One of the guys(must find that thread again) mentioned putting magnets on each fin half to stop them parting during flight.(possible flex in the rods in a turn?)
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Old Dec 23, 2012, 03:48 PM
less is more
Knoll53's Avatar
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Nice summary Kevin. The magic of the split rudder swept hinge line is that there is no horizontal stabilizer to get in the way, so that split rudder becomes a useful up elevator input.

With this finding, I'm quite eager to build a small heavy plank just to use this braking system.

Kent
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Old Dec 23, 2012, 04:57 PM
I don't like your altitude
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Found some thin music wire" amongst my souvenirs".this could do the job,maybe a thinner tube.
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Old Dec 23, 2012, 06:01 PM
I don't like your altitude
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http://www.rcgroups.com/forums/showt...ing+plank+down

This is the thread I mentioned earlier.A long read,but worth it.Some more from Marcus in there.
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Old Dec 24, 2012, 06:37 AM
I don't like your altitude
Stupot46's Avatar
Joined Sep 2011
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Mk2 fuselage.I would have struggled to get a rudder servo in the first one,so this is broader and deeper.This will allow me to mount the wing low enough to fair it into the nose.
Needs a name,so it will be Thks2
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Old Dec 25, 2012, 01:01 AM
I don't like your altitude
Stupot46's Avatar
Joined Sep 2011
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A Xmas tail.Bit of blending/ filling this should be ok.
Off to do Santa stuff,seasons greetings to all.
Stuart
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