Very low aspect ratio planes?

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berridos

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I got it)). The mixer creates artificial washout. However that mixer doesnt solve the adverse yaw produced by induced lift when rolling. Wonder how they use the winglets in that mixer. The kinematic looks incomplete.
 

Urquiola

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If I remember it well, the F-104 on exhibirion at Speyer Science and Technology museum in Germany, reduced to skeleton, allowing to think any homebuilder could make one, had some type of moving part in the leading edge, going down as to increase camber, thus lift at low speed I'd say.
About the Larry Heuberger's Delta in the image above, same as in the atached 3-View of Hoffman Flying Wing, mr Hoffman changed into workable plans the concepts by Snyder, the inventor of Arup machines, and the Roy Scroggs Dart, all have a counter-dihedral receeding wing, while my first option will be as in my Icon, by R B Johnson, patent US1887411. It's just about Dutch Roll? For sure, any 'Ground Effect', specially disturbing at landing, will be reduced with an ordinary dihedral,Hoffman 3vu.jpg receding wing thickness on the lower side. Comments? Blessings +
Anybody having data about 'Wingspan' of R J Thompson 'Flying Flounder'? It went airborne
 

Urquiola

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I'm not sure about having failed in explaining the doubt.
The type of wing construction I'd endorse is as 'A' in the attached image, but the Hoffman, the Scroggs and other are arranged the opposite way: 'B'.
My choice was made thinking in allowing air flow going outwards when approaching the ground, a flat bottom of wing perhaps worsening the ground effect, the airplane rebounding or even put upside downWing tapering types.jpg. I'ts rather about the architecture of bottom side of wing than just the leading edge. Blessings +
 

Riggerrob

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CF-104, CF-8 and several other jet fighters have hydraulically drooped
Leading edges to increase wing camber, increase lift and reduce landing speeds. They also have flaps and drooling ailerons to increase camber (and lift) along the trailing edges.

CF 104, Harrier, and many other jets have anhedral (down ward tilting wing tips) to improve roll stability. You see, sharply swept wings add to roll stability so much that the airplane might develop Dutch roll, but drooping wings reduce stability close to neutral for more stable flight.
 

rotax618

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The secret to slow flight in Low Aspect homebuilt airplane has very very little to do with airfoil and high lift devices, it relies on 3 functions, they are Planform, Wing Loading and Available Thrust.
the planform must ensure a stable vortex is formed at high alpha, the wing loading MUST be lower than conventional planform aircraft to compensate for the increased induced drag at high alpha, obviously, as Zimmerman demonstrated if you have sufficient thrust you can reduce speed to zero while maintaining height.
 

berridos

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The beauty lies in targeting those three factors while keeping cruise acceptable.
 

berridos

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The induced drag of LAR is horrible and the adverse yaw much more significant then in traditional planes. The way to overcome this is create several elevons per side and to tailor the lift distribution for any given situation.
For example in cruise you dont want to build in static washout as it will increase drag. The minimal id would be by flexing the inboard elevon up and the outboard elevon minimally down so that you achieve an eliptical lift distribution.
In case of turning, the way to avoid id is by deflecting on one side both elevons slightly down and on the other side the inboard elevon slightly down and the outboard elevon strongly up. (outboard elevons should have a sharp super frise setup).
In approach setup you want the inboard elevons to have strong up deflections with the outward ailerons having significant downward deflections in order to increase washout ,and add massive stability and avoid tip stall.
All this is filled with massive nonlinearities and is a very delicate subject on LAR.
Its pretty impossible to build a mechanical mixer for these situations.
Is there any lightweight reliable fly by wire mixer? RC models can do this without problem with isolated servos.
 

berridos

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Thinking out loud, maybe one solution would be to use the akaflieg mixer (approach safety configuration-strong dynamic washout) and put adjustment servos on the elevon leverarms depending on the flight regime (cruise min id regime). If those servos fail they just get stuck in the wrong position, but arent critical to safety. I am not activating the elevons with servos, just changing the leverarm.
Would need to think how to adjust for the 3 to 1 aileron movement in a mechanical way.
 
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Urquiola

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About 'Dutch Roll' and some LAR designs, a few months ago, while driving, I watched a car towing an small trailer, that made exactly the banking movement called 'Dutch Roll'. Any comment? Blessings +
 

danmoser

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The induced drag of LAR is horrible and the adverse yaw much more significant then in traditional planes. The way to overcome this is create several elevons per side and to tailor the lift distribution for any given situation.
Berridos, can you please provide a source of information for the "much more significant" adverse yaw of low AR designs?
My understanding and experience indicates that the adverse yaw phenomenon becomes stronger as aspect ratio increases... implying that very low AR designs should have little if any adverse yaw.
If I my current understanding of adverse yaw is wrong, I am eager to learn why.

Does anyone know if the Facetmobile exhibited adverse yaw tendencies?

I have not observed any discernible adverse yaw when flying an AR=2 model glider with simple 3-servo elevon & central rudder controls.. not a lot of rudder needed to make turns.. but maybe others have made different observations?

I have also observed that when banking into a turn in a sailplane, the adverse yaw is extremely noticeable, necessitating a lot of extra initial rudder input when starting into a turn.
 
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