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Author Topic: WING PROFILE  (Read 1310 times)

Offline FLOYD CARTER

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WING PROFILE
« on: April 07, 2009, 03:31:29 PM »
It seems that, ever since the first Nobler, stunt designers have been hooked on swept-back leading edges.  I've flown both swept-back L.E. and "barn door" wings, and neither has what I would consider an advantage, or a disadvantage.

Certainly, straight wings are easier to build, especially if all ribs are exactly the same.

I'd like to know what I'm missing in the way of aircraft performance by using a perfectly straight wing, with no L.E. sweep (but tapered flaps) and no variation in rib thickness.

ps Have mercy.  I'm an electrical engineer, not an aero engineer.

Floyd
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Offline John Miller

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Re: WING PROFILE
« Reply #1 on: April 07, 2009, 04:27:44 PM »
You are right Floyd. There are a lot of good flying straight winged aircraft out there, I can think of at least 3 right now.

What the tapered, or swept leading edge offers is an advantage due to the effective diehydral that comes from swept leading edges.
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Offline Bob Reeves

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Re: WING PROFILE
« Reply #2 on: April 07, 2009, 04:29:53 PM »
They don't get bounced around by wind quite as much as straight wings do..
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Offline Paul Smith

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Re: WING PROFILE
« Reply #3 on: April 07, 2009, 04:43:57 PM »
A tapered wing has more of it's area inboard and hence, not as leverage applied to the centre from excess lift at the tips.

A tapered wing has more thickness and strength at the centre, where it's needed.

Lift is lost at the tips.  Smaller tips have less loss.

They figuered this stuff out in the 1930's and have built virtually all wings tapered since.

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Offline Matt Colan

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Re: WING PROFILE
« Reply #4 on: April 07, 2009, 04:47:00 PM »
Quote from: Bob Reeves on April 07, 2009, 04:29:53 PM
They don't get bounced around by wind quite as much as straight wings do..

That is why most people fly swept LE's.  My Smoothie has a straight LE but has an elliptical wingtip and it never seems to bounce around in the wind.

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Offline FLOYD CARTER

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Re: WING PROFILE
« Reply #5 on: April 07, 2009, 05:35:16 PM »
Let me refine my thesis.  I'm now thinking of 3 planes I now fly.  All have straight leading edges, but with dihedral!  WILDMAN-60/Orwick 64, GEE BEE "D"/OS46, Yates DRAGON.

Aside from the "cool" looks of a tapered wing, I'm not convinced there is any actual benefit from a straight L.E. (especially with dihedral).

Floyd
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Offline Serge_Krauss

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Re: WING PROFILE
« Reply #6 on: April 07, 2009, 10:11:18 PM »
My present project has a straight leading edge with constant chord ribs but tapered flaps. I made it that way only to simplify structure and and building. Otherwise...

Some advantages of swept leading edges, including some already mentioned:

1) Free symmetrical Dihedral effect (upright/inverted).
2) Smaller tip and greater taper reduce tip losses/induced drag in maneuvers, thus not slowing the plane as much in hard corners. Lift distribution is closer to elliptical ideal. The planes L/D is increased in turns. Overhead speed probably benefits too.
3) Root bending moment is reduced, in turn reducing structural needs and consequent weight.
4) Related to this, as previously pointed out, plane is less affected by gusts.
5) Also related is the possibility of using higher aspect ratios with reduced gust-sensitivity penalty (a.c. moves inboard with MAC).
6) Increased yaw stability.

Possible disadvantages of swept leading edges:

1-2) Aerodynamic center is further aft, moving c.g. back in fuselage. This reduces the tail moment or requires lengthened tail to maintain same TVC and lengthens the effective nose moment, which increases the polar moment of inertia, while reducing tank placement options. All solutions or adjustments for these affects can increase weight.

I'll probably think of more, but I have to move on...

SK
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Offline Leo Mehl

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Re: WING PROFILE
« Reply #7 on: April 08, 2009, 05:57:27 PM »
Yup, a double tapered wing just flys better in turbulance and wind. I don't think they are any harder to build than a strait wing once you build a few. The controls and all the stuff that goes inside a wing is the same in both. A tapered wing is harder to build on a strait board than a strait wing, but I think the extra effort is worth it. So get building Floyd! mw~ mw~ HB~>
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Offline Bill Little

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Re: WING PROFILE
« Reply #8 on: July 09, 2009, 03:48:01 PM »
Similar to the topic:  What about the swept FORWARD TE (to go with the swept back LE)?  Such as the Juno, Ares, etc.. ?

Thanks!
Big Bear
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Offline phil c

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Re: WING PROFILE
« Reply #9 on: July 15, 2009, 10:59:10 AM »
One benefit of rectangular wings is that they seem to get through square corners faster.  The plane can convert some speed into zoom for about 90 deg. of turn, get around the corner without losing too much speed, and then accelerate back up to speed for the next corner.  The more tapered the wing the less this effect occurs, although most stunters really don't have much taper to the wing. A wing with the tip 50-60% of the root can get very close to an elliptical wing in efficiency.
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Offline Randy Powell

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Re: WING PROFILE
« Reply #10 on: July 15, 2009, 12:54:21 PM »
There is also a reduction in tip votex and induced turbulence. An advantage in calm conditions.
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Offline L0U CRANE

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Re: WING PROFILE
« Reply #11 on: July 21, 2009, 11:38:23 PM »
Leading edge sweep is only a part of the picture...

Actual wing sweep is according to the quarter-chord line. Examples: Flite Streaks and Ringmasters have forward swept wings... (Measure where 1/4 back from the LE is at both root and tip, and connect the line. Since the (fixed-)flaps taper forward, the quarter-chord line on each panel does, too. Much less than the TE sweep, but still forward.)

NA Mustangs had very close to zero sweep wings; the TE sweep forward was about 3 times the LE sweep back.

Tapered planform wings, with straight-line LE and TE, can behave approximately like the aerodynamicists "ideal lift distribution" provided by the proper elliptical planform. ...And are easier to build than a correct ellipse...

Sensitivity to buffeting in turbulence isn't completely a matter of the wing taper and/or sweep. Reynolds Number factors (simply, related to the actual chord lengths, since air molecules don't change size to match them. Smaller chords perform less well than longer chords like those on people-carrying aircraft, even with the same rib airfoil shapes.) I had a model with a nicely tapered planform, that buffeted severely in turbulent wind. I had kept the same airfoil percentage from root to tip. On the next model, I split the difference between the rib max depth the root airfoil % would have at the tip chord length, and the root chord airfoil max depth. It was much less sensitive to turbulence.

And, besides, a tapered wing looks better to me, too.
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