Swept leading edge Vs. straight.

[Gordon Tarbell]

What would be the disadvantages of using a non tapered constant cord wing in a plane for stunt competition. Seems all the competitive designs have swept back leading edges and airfoils decreasing in thickness toward wingtips. Is the constant cord non tapered wing design a deal breaker for having competitive flight characteristics?

[Howard Rush]

See http://stunthanger.com/smf/open-forum/leading-edge-sweep/ , replies 16 through 27, particularly those from Igor Burger.

Many good stunters have constant-chord wings.  Examples are the twin Pathfinder and Dan Banjock's air racer thing.

[RknRusty]

See http://stunthanger.com/smf/open-forum/leading-edge-sweep/ , replies 16 through 27, particularly those from Igor Burger.

Many good stunters have constant-chord wings.  Examples are the twin Pathfinder and Dan Banjock's air racer thing.

My reading tells me that rearward swept tips spill the air off with less turbulence, letting the upper and lower layers recombine behind the wing without draggy vortices.

My F. Twister wing is non-tapered in every direction, ending with blunt flat tips. It's not the expert caliber airframe you guys in the Big Leagues fly, so I don't know if it rates a spot in this conversation, but it's a topic that interests me, so I chipped in.
Rusty

[Howard Rush]

My reading tells me that rearward swept tips spill the air off with less turbulence, letting the upper and lower layers recombine behind the wing without draggy vortices.

I recommend the nonfiction section in the library. 

[RknRusty]

I recommend the nonfiction section in the library. 

Thanks for the tip, card's in my wallet.
I never paraphrase anything I've read from a source that doesn't seem to me to be reliable. So I blew this one, I don't know where I saw that. Maybe reading about the A-380 wings.
I apologize

[Serge_Krauss]

Wow, Howard! I re-read that entire thread and got as frustrated as the first time. I read my own post there and thought, "Oh good, I already said what I want to say!" Of course it wasn't understood anyway. I really did not like that altercation.

So, I'll repeat here what I think was relevant in that thread.

Disadvantages of un-tapered wing:

1) The Hershey-bar-shaped wing is structurally at a disadvantage because it has more of its lift near the tip, which applies more bending torque to the root ('has an excessive root bending moment'). It needs a heavier root structure than a tapered wing to resist bending and breakage.

2) Having the large tip chord allows larger aerodynamic twisting torques at the tip. Without excessive added structure, the wing is more liable to deform in maneuvers.

3) The MAC and therefore the aerodynamic center of the wing is farther out than on a tapered wing. This gives gusts a larger leverage to roll the plane. (Elliptical wings are the best in this respect for any given aspect ratio).

4) Tapered wings have closer to the theoretically most efficient (elliptical) lift distribution. Rectangular wings are penalized some by excessive tip losses - higher drag than wings of the same area with taper, which increases the span.

5) Tapered wings are felt by many to be the most aesthetically pleasing.

Advantages of rectangular wings.

1) they are easier to build: All ribs are the same, except the sheeted ones; spars, leading edges, trailing edges, and sheeting can be continuous across the root section; and symmetry, squareness, etc. are easier to measure and maintain in construction, with less detailed jigging.

2) Associated with #1, the performance hit is not so great for work saved.

I don't think the constant-chord wing is a deal breaker, but it probably will take more of a hit in performance in gusty weather and at the highest levels of competition.

I've probably left stuff out, but I'm on borrowed time with this computer, which shows signs of packing it in at any time.

SK

[Gordon Tarbell]

Thank you for the reply SK. That is what I wanted to know on this. My biggest concern was centered around effects of wind on the wing. We do have to deal with varying amounts of wind and turbulence while trying to carve out a decent pattern for scores.

[Tim Wescott]

I recommend the nonfiction section in the library. 

How about the section in Wikipedia on wingtip rake?

I can remember, but can't put my finger on, a reference that shows that the rake of the trailing edge itself does matter, in that it can cause the trailing vortex to come off of the wing further away from the tip (if it's forward sweep) or closer to the tip (if it's backward rake).  This is important because the location on the wing where the vortex comes off is more or less what determines the induced drag -- so if you can encourage the vortex to leave at the tip, instead of inboard of the tip, your induced drag goes down.  The raked wingtips that Boeing is adopting on some planes encourages the vortex to separate right at the wing tip instead of a bit inboard.

BUT: Induced drag probably isn't the most important thing on our stunters.  A swept-forward wing, with it's greater induced drag, may work well because of all the other good things its doing at the same time it's making the plane slow down more in the square corners.

[RknRusty]

Hey Tim, that's a much more eloquent version what I had in mind before being swept toward the non-fiction literature. I mentioned the A-380 in my second post, but the 777 has... I better be careful... Might, as far as I know, have a similar wingtip specifically for that purpose.

However, I'll resist posting in here without a reference in front of me. Or better yet, just shutup and read. I'm a simple electronics guy on R&R, rusty and retired
Rusty
and retired

[Howard Rush]

Sorry, Rusty.  There's a heap of misinformation written about stuff like this, and it's hard to separate wheat from chaff.  Here is an old NACA paper on tapered wings: http://www.dtic.mil/dtic/tr/fulltext/u2/049045.pdf  .  Figure 4 is pertinent to Serge's item 4 in his excellent summary above.  I first saw it in Abbott and von Doenhoff's book (von Doenhoff was George Aldrich's cousin), and decided my aspect-ratio-4 combat planes were OK without taper.  See the attached pdf for the lowdown on wing tips.

That said, there's not much point in doing fancy stuff to minimize induced drag in stunt planes: they have about the right amount, and the disadvantages of things like swept tips, although small, probably outweigh the advantages. 

[RknRusty]

Thanks Howard, I understand. And in the engineering forum, I feel like we overlap the lines between models and full sized planes too. Both of which I find fascinating and have since I was a kid.
Rusty

[Scientifiction .]

Sweep of the High Point ( Max. Thickness ) is consider by some at the drawing board , for positive yaw stability .
Light Loadings and low lateral polar inirtia on a straight wing likely wont require that for smooth air .

previous incarnation of this flew good in wind , 20 knots your hanging on HARD , on grass kicking the heels in
for consecutive manouvres , in winter . Two Hands at 25 knots and the winds pushing it along as quick as youd
like to go , Likely to turn into a wind surfer , without the board .

Very Ridgid bellcrank to elevator . Stretching 016 solids @ 20 Plus. Twanging a line in Sq Bottoms on .018 7 strand,
though no ill effects except on the nerves , and arm strain .  So thereabouts is the practical limit , for that ship .

The ELIPTICAL Tips on the straigh ( no taper ) diheadral wing give goog clean vortice free airflow .
A bit of pressure in those conditions . Has two or three cunning dodges in the control system ' enabling ' this performance .
And built like a brick * house , ER - Strong . Tissue over silk & spruce spars .. New ones somewhat lighter as theres other
things to use when the yachts are planing .

Highly Tapered Wings give good lateral ( roll ) stability in Rough Air . For Flying in 30 - 40 Kt Air Id consider essential .

[Scientifiction .]

if you step outside the Nobler Derivative concept , you start with pretty much a clean sheet of paper ,



Just DONT use a FP 40 .

This piece of trash actually PREFERS Wind .

[phil c]

Just from observation, a constant chord wing seems to turn quicker(less speed loss) for a 90deg. corner, maybe 120deg.  That can help, as long as you let the plane straighten out and get back up to speed.    A strongly tapered(tip chord less than 70% of root) seems to not turn quite as fast, but the taper makes it much less sensitive to gusts.

[Paul Smith]

According to the non-fiction aeronautical book I believe, the totum pole of planforms goes like this:

Elliptical
Triple taper
Simple taper
Rectangle

But the percent difference is so small that it doesn't make much difference in a small, very light, and massively over-powered model.

The British spent massive labor building a small number of Spitfires, which flew the best.  Other countries built bigger numbers of simple planes that flew well enough.

[Paul Smith]

A non-taper wing puts the center of lift outboard and builds up stress in the center.  This stress must be dealt with using heavy material.

A taper wing moves the stress inboard and has a thicker and inherently stronger center section.  This saves weight.

[Scientifiction .]

The British spent massive labor building a small number of Spitfires, which flew the best.  Other countries built bigger numbers of simple planes that flew well enough.

Who won the War , Then !


( the Titles Hogwash )



Actually , they built over 20.000 ., about the same as most others , bar the Il2 Stormovic .
Even a well flown Hurricane could take on Me 109s, and out turn a FW 190 if it saw it coming .

A trick in the mist was to dive a Spit in front of a Me 109 and sucker him into a speed dive , watching the altimeter .
With a better pull out , if you left it late enough the Me 109 would pull out , underground .  

Tempest & Yak 3 were probably the most dangerous , offensively , of the ' interceptors ' .