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Sig Wonder planform

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cluttonfred

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Actually, I should have said that I'd avoid main wheels on the wings. The Catto Acro-X layout would work well with bicycle landing gear (single main wheel and a steerable nosewheel) with outrigger wheels or skids on the lower wing tips.
 

cluttonfred

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wonder 2.jpg

Getting back to the Sig Wonder planform, I wonder if anyone has any ideas on how to manage two possibly-related issues: the sharp transition between the short- and long-chord wing sections and potentially poor stall behavior.

As in the Fauavel unswept tapered planform there is a potential for the up elevator to a wash out the center section and prevent it from stalling, leading to stalling the wing tips first. For this sort of design to work as a sport plane, it would need docile handling, and that means stalling the center section first while the outer panels with the ailerons remain unstalled to maintain control.

My first thought would be to use completely different airfoil sections for the center section and outer panels to try to tune the stall behavior along with full-chord wing fences to separate the flow, but the Sig Wonder RC model appears to use a consistent airfoil section with the rear center section almost like a big fixed central flap. The result is a drastic decrease in the effective thickness of the airfoil as well as a drastic increase in the Reynolds number because of the long chord. I wonder if angling that flap slighty downward to increase the effective incidence of the center section would be enough to ensure docile stall behavior? In that case, maybe a particularly thick, flat-bottom airfoil would work well, something like a Clark YM-18, NACA 4418, or Goe 679 that remains thick enough aft for the "flap" extension.

clarym18-il_l.png naca4418-il_l.png goe679-il_l.png

That "flap" approach would complicate the structure a bit since the rear center section would be somewhat thin, but I wonder if the aerodymics of a consistent wing tip to tip until about 3/4 of the short chord would provide more predictable handling without the need for full-chord wing fences and two separate airfoils considering this would be a relatively low-speed and low-wing-loading application.
 

Victor Bravo

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I asked Jim Marske about that elevator-induced tip stall phenomenon, and he said (point blank) that it simply did not happen on any of the flying wings he tested. I don't know if that was limited to his own tapered and forward swept wings, or whether that includes straight Backstrom or Fauvel planforms.
 

cluttonfred

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Al Backstrom definitely thought elevator-induced stall was an issue with a straight plank and only used tip elevons on his designs.

Following up on my previous post, here is what I was trying to describe in terms of the center section being essentially a large fixed flap tacked on to the outer section wing airfoil. The multiple positions of the flap are not intended to show movement, rather that the angle of the flap could be tweaked in development to tune the stall behavior of the center section. I have not shown the actual elevator.

sig wonder flap goe 679.jpg

Structurally it would be more complicated than that because the center section neutral point would be about 21 inches aft of the outer section neutral point. That would be good for allowing the pilot's head to stick up behind the main spar (there would be an auxiliary spar for the center section as well) but bad for low speed handing as you'd need to set the rearmost CG location quite far forward so you'd still have safe forward CG with the center section stalled.
 

Tiger Tim

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Getting back to the Sig Wonder planform, I wonder if anyone has any ideas on how to manage two possibly-related issues: the sharp transition between the short- and long-chord wing sections and potentially poor stall behavior.
Here’s one way to handle the long chord section:

Would the stall be that nasty on something like this? I would think it would be a lot like stalling a plank, but possibly more benign.
 

cluttonfred

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That T-Tray is essentially a constant cross-section wing back to the main spar with the fixed flap portion starting there. That's an interesting intermediate approach between Wonder's flap starting at the rear spar and just using two completely different airfoils and would probably result in a lighter build than the Wonder because the spars in the flap section could be taller and more efficient. Here's a revised drawing with the T-Tray fixed flap and a pic of an uncovered T-Tray model.

sig wonder flap goe 679 v2.jpg t-tray 005.jpg

This gives me ideas about eliminating the rear fuselage and building the rear flap as a cantilever unit as the flap ribs could easily be made into load-bearing triangular trusses. The effect would be like a twin-boom design with the space between the booms and the tail filled in to add wing area.

I am still worried about stall behavior since, even without tip stall, stalling the center section would shift the neutral point forward drastically (like in a sharply forward-swept wing). I think it would still work but you might want stall strips on the center section and the plane would always need to be balanced fairly far forward.
 
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TFF

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The problem with the Rans S11 was the center did not stall at the same time as the tips and would fly on the center. Unlike a standard plane in a stall which is add power after the stall, the S11 wants you to have power to pull you through the stall. The faster it flew the better it flew. The model Wonder does not have moving rudders, aileron elevator only. A lot of rudder at slow speed may have it spin like a top. Like a Ercoupe, limit control movement is probably the best way to tame. You can’t stall a plane if you can’t overload the wing per speed, limit elevator. I would limit rudder too.
 

Tiger Tim

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the plane would always need to be balanced fairly far forward.
I don’t think I’d plan on having that ducktail in the middle contribute to any lift at all. In fact, I see it as either an exceptionally short coupled horizontal stabilizer or if you prefer as a reflexed extension of the trailing edge. In either case it ought to allow a little more forgiving (of builder error) airfoil to be used for the balance of the wing.
 

TFF

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I think it not being an airfoil would make it viable aerodynamically. Too much competing kills it. There could be some taper, but wing tail works. Wing inside a wing is way more complicated.
 

Bill-Higdon

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Pops

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That CL combat with flying wings sure brings back a lot of good memories. We had a lot of fun.
 
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cluttonfred

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While I can see that might be a perception that needs to be overcome, the Sig Wonder is a very different beast than the Rans S-11 Pursuit. Check out the factory clip below (especially the shots of it flying overhead) and you will see that the Rans was a very low aspect ratio lifting fuselage more akin to some of the pointier NASA lifting bodies of the 1960s but with with little wings attached. Something like the Wonder does not attempt to gain any lift from the fuselage, just from an extended airfoil-profile center section so would be far more akin to the proven low aspect ratio designs like the Arup or Piana-Canova designs than the S-11.


The Sig Wonder looks too much like a simplified discredited Rans S11, that didn’t end well and was never resurrected
 
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