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Author Topic: Wing leading edge sweep back?  (Read 2460 times)

Offline Larry Wong

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Wing leading edge sweep back?
« on: January 13, 2017, 06:51:34 AM »
Is there a ideal sweep to design of a wing for stunt ? Or just what looks good! Sweep  = dihedral =lift!
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Offline Mark Scarborough

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Re: Wing leading edge sweep back?
« Reply #1 on: January 13, 2017, 11:57:28 AM »
there is absolutly an "ideal " sweep for a stunt wing, given a specific combination of span, chord, flap size, flap distribution, elevator size, horizontal stab size, distance from CG to elevator, incidence angle, power system, atmospheric conditions, and trim,, ( just to name a few)

bottom line, there is no way to answer this question realistically,, of course there is an optimal configuration for a given system.....

remember, a stunt plane is a system, no one factor determines its success, but it can determine its failure,,
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Offline Tim Wescott

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Re: Wing leading edge sweep back?
« Reply #2 on: January 13, 2017, 12:05:23 PM »
Mark, you forgot pilot preference.

Co, whatever is optimum, the optimum is probably broad.  What I gather from talking to pilots in the Pacific Northwest, and seeing on these boards, is that wing taper and keeping the flap line unswept is what's important.  When you find your best wing and flap taper, then the straight flap hinge line pretty much dictates the leading edge sweep.

However -- the traditional "stunt trainer" wing uses a no-taper wing with tapered flaps (and, hence, a dead straight leading edge), and you can do pretty well with one of those.  The difference seems to be in how they handle the wind.

Build a few.  Try 'em out.  Report back.  Remember that you haven't tested the model until it's fully trimmed and you've flown in all sorts of wind.
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Offline Howard Rush

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Re: Wing leading edge sweep back?
« Reply #3 on: January 13, 2017, 08:53:47 PM »
Quote from: Co_Pilot<>< on January 13, 2017, 06:51:34 AM
Sweep  = dihedral =lift!

Sweep * kα = dihedral = dcl/dβ = probably not what you want for stunt
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Online Trostle

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Re: Wing leading edge sweep back?
« Reply #4 on: January 14, 2017, 12:02:10 AM »
One would think that with the low Reynold's Numbers we are talking about, there would seem to be a practical limit on how much LE sweep could be.  More sweep with a straight flap hinge line will mean smaller wing tips and lower Reynolds's Number at the tips and less lift being generated by the wing.  Then the Australian Firecracker comes along and it seems to do OK.  Also, there is a  1960 Classic design by Curtis Comer called the Sky Dancer.  This has performed well at VSC in the hands of several builders.  (Plans were published in Model Aviation, Dec 94.)  Both of these airplanes had tips nearing 50% of the root chord.

And then, Al Rabe comes up with his S5 designs where he forces smaller tips in his quest for scale appearance with a corresponding comparatively smaller wing area/comparatively higher wing loading and he makes those airplanes work very well.  He does this by keeping the wing loadings within reason with construction using near super human building skills and using airfoils he developed for his designs.

So, the answer to how much LE sweep for our stunt ships is somewhere up there in Mark Scarborough's post.

(S5 = Super Semi Scale Stunt Ship)

Keith

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Offline Will Davis

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Re: Wing leading edge sweep back?
« Reply #5 on: January 28, 2017, 09:12:12 AM »
The Curtis Comer Skydancer has more sweep than more traditional models, I have built 2 and competed at VSC, Nats  and brodak's  with mine. Others that have built sky dancers that I know of include Curtis, Larry Draughn and Roy Decamera.

All flew well and used OS 35 s for power . Built per the published plans, the forward lead out exits the leading edge of the wing.. Very difficult to make adjustable .

I still fly mine on occasion, 24 year old model . Last competition was 3 years ago at brodak's in classic expert,

The top photo is Roy's model, very nice finish and well built model,  perfect Roy de camera workmanship.

The red Skydancer is the original with Curtis , photo 1992 I built my model from measurements  taken from original Skydancer . the cad drawings were done from our measurements  for the publication .

The red and white is mine at 1993 NATS

Back to the original question on leading edge sweep. I asked Curtis about his design thoughts on the wing , he  designed it to penetrate the wind , fly well with some different airfoil thoughts foot the time , the high point of the wing is moved forward on the root, then back on the tip, he had some aerodynamic reason for all of this.

In reality I  always thought he was caught up in the 50's to early 60's  saber jet and mig jet look.  Then a b17 flew over and he got the rudder design idea.

« Last Edit: January 28, 2017, 11:37:28 AM by Will Davis »
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