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Washout on airplane wings...

NewHeli

Key Veteran

Pittsburgh, Pennsylvania, USA

This is a continuation of my post "High speed plank design"...

I've made great progress on the wing (that is all I have been working on at this point), but now I've been told that I need to build in some washout in the wingtips (to prevent tip stalls). The wing has a 13.5 root chord and 7.4 tip, with a tapered leading edge (trailing edge is almost square to fuselage). I am using the NACA 0012 airfoil (quite thin), so the root chord thickness is 1.5? (not sure) and the tip is 0.8. The wing tip is rounded, and the wingspan is about 59.

The person that told me to put washout in seems to know what he is talking about, but can anyone else argue or support his theory? He seems positive that the design will tip stall. (Apparently adding about 1.5 to 3 degrees of negative incidence to the tip, it will stall after the root, preventing tip stalls). I would jump right in and do this, but my concern is having a "twisted" aileron (this would be hard to build). Flaps also help prevent tip stalls, but that would add weight. I'm trying to keep this plane to about 7 pounds, with a 91 engine, retracts, radio gear, and everything else, adding a flap servo is probably not going to help.

If you would like to see the plane, it is a free flight model (that I'm scaling up to RC) from the FF sport section of the September MA 2005. Also I could email you the plans if you would like to help.

Thanks,
Nathaniel

Nathaniel Rice
Team HeliWholesaler/Miniature Aircraft
Team YS Engines

12-09-2005 Over year old.
cessna151

Veteran

Missouri... Originally Indiana

Flaps also help prevent tip stalls, but that would add weight.
Flaperons.

--Eagles may soar high, but weasels don't get sucked into jet engines!--

12-09-2005 Over year old.
HOMEPAGE  
NewHeli

Key Veteran

Pittsburgh, Pennsylvania, USA

I thought of that, but the ailerons are on the outer "half" of the wing--not full span, so that might not work. Or maybe spoilerons?

Nathaniel

Nathaniel Rice
Team HeliWholesaler/Miniature Aircraft
Team YS Engines

12-09-2005 Over year old.
CeeJay

Heliman

Alexandria, LA - USA

Wash out in a planks wing

Yea, washout does work to make the root of the wing stall first which then allows the stall condition to proceed from the root and travel out to the tip as the bird progresses into full stall. It makes a bird that is in the initial stages of stalling to have the beggining of the stall to occur up close to the fuselage or wing root area. This normally results in the nose dropping, and can in fact stop the bird from stalling fully by the resulting increase in airspeed due to the drop of the nose.

The effect of warping the wing 1.5 to 3 degrees like that usually will prevent the bird from performing what is referred to as a tip stall. That is where one wing end basically stalls while the opposite wing is still producing lift. When that happens the bird basically performs a snap roll, in the direction of the stalled wing, to inverted and drops the nose towards the ground. Both of which are bad things to have happen if your are low, and slow, such as when on approach to a landing.

Now if this is a wing on a racing bird, this could be detrimental to your endeavors. IE RACING. Doing this will slow the speed of your bird due to added drag. So if speed is your thing, then you might want to reconsider just making sure you keep your speed up on your approach to landing and not worry it.

CeeJay

12-09-2005 Over year old.
NewHeli

Key Veteran

Pittsburgh, Pennsylvania, USA

Thanks for the advice. I may just do that.

Nathaniel

Nathaniel Rice
Team HeliWholesaler/Miniature Aircraft
Team YS Engines

12-09-2005 Over year old.
JitsuGuy

Key Veteran

Tulsa, Oklahoma

Plus if you drink beer while flying, it really makes the plane look a lot faster and is harder to control.

12-09-2005 Over year old.
cessna151

Veteran

Missouri... Originally Indiana

Be careful now, he's only 17.

Aileron location shouldn't matter when it comes to flaperons or spoilerons, i think. And with a good computer radio you can do either in small amounts or none at all to see which works best. I would build it for speed then experiment.

--Eagles may soar high, but weasels don't get sucked into jet engines!--

12-09-2005 Over year old.
HOMEPAGE  
CK_

Senior Heliman

Redondo Beach, CA

I ran your wing in a 3D panel code to get the lift coefficient distribution. Here's what it looks like at ten degrees angle of attack.

Looks like it's going to stall around the 50% span region. Not a real good situation. If you want speed then you don't want to twist the wing. One solution is to tailor the airfoil along the wing to give a high max lift coefficient at the tip and a low max lift coefficient at the root to force the root to stall first. You could use a thin airfoil with a relatively sharp leading edge toward the root and transition to a fat airfoil with a much rounder leading edge at the tip. You could even use a symmetric root airfoil and transition to a cambered tip airfoil to give you aerodynamic washout without the geometric twist.

BTW, the rounded wingtips make the wing harder to build and increase the tip stall tendancy. I would get rid of them.

Chris

12-10-2005 Over year old.
JitsuGuy

Key Veteran

Tulsa, Oklahoma

Oh sorry, didn't know he was 17.

12-10-2005 Over year old.
zoom boy

Key Veteran

N.E. Lincolnshire UK

What CK said

Just look at a fighter jet, vs an airliner, there are not many fighter aircraft with reflex in them.

There are some inflight pics of planes like the F-16 or F/A-18 that show what looks like reflex, but thats actually the wing bending up at the trailing edge when its loaded in a turn.

Fast, little to no reflex, slow, some reflex, generally speaking.

Another thing that you could try is wing fences, like on the Mig-15 and Su-17 aircraft, these are not that common these days, because winglets have taken over, but a wing fence would be easier to build and it can be nearly anywhere on the wing.

What they do is they reduce spanwise airflow at high AoA, and that can decrease the problem of tip stall.

12-10-2005 Over year old.
NewHeli

Key Veteran

Pittsburgh, Pennsylvania, USA

Hmm guess I will have to consider dropping the round tips.

Will inboard flaps (inner 50% of wing) prevent tip stalls? If so, I will take the chance with the weight.

CK_, did you understand the plans? Did you see where the aileron was? It starts right were the servo linkage is, and goes to the tip. If I put flaps on the other side of that, on the inboard side...

Thanks alot

Nathaniel

Nathaniel Rice
Team HeliWholesaler/Miniature Aircraft
Team YS Engines

12-10-2005 Over year old.
NewHeli

Key Veteran

Pittsburgh, Pennsylvania, USA

Oh BTW, can anyone tell me how far the actuation rod on a 60 size mechanica retract moves? Like how far it moves in/out to extend/retract the gear?

Thanks,
Nathaniel

Nathaniel Rice
Team HeliWholesaler/Miniature Aircraft
Team YS Engines

12-10-2005 Over year old.
Hawk4flyer

Senior Heliman

Deland,Florida

Depending on the retracts, 1 & 1/8 inch.

CK_ is right on the money with how the wing will perform. I would go with changing the LE radius. This is easy to do without radical design changes.

I'd have to think about what radius to make it. But, you should be able to make the radius 1/4' from root to tip and achieve the same results.

This is in fact how I do it.

12-10-2005 Over year old.
HOMEPAGE  
NewHeli

Key Veteran

Pittsburgh, Pennsylvania, USA

1.25 inches? Wow, I was figuring on 3/4--guess I'll need to draw in a bigger servo arm... BTW they are going to be GP 60 size retracts.

So is it that easy? Just changing the LE radius, without changing airfoil or thickness? If I change airfoil or thickness, it WILL lead to major design changes...but just the LE radius might be doable.

I have been talking to Colin Mill through PM's, he says the wing might also have a high G flick, meaning in high banked/tight turns or possibly even loops, the tips will stall and cause a sort of snap roll--that would not be cool. However, I don't plan on doing any severly tight turns like a funfly plane, but I do hope this thing will knife edge...

Thanks,
Nathaniel

Nathaniel Rice
Team HeliWholesaler/Miniature Aircraft
Team YS Engines

12-10-2005 Over year old.
Hawk4flyer

Senior Heliman

Deland,Florida

Yes, the LE "trick" will help with tip stalling.

The short explanation is..

A sharper LE radius will cause the wing to stall at a lower angle of attack. The blunter the LE the higher the angle at stall.

In reallity your changing the airfoil by changing the LE radius. It will no longer be a NACA0012. (at the tip).

Racer type planes have to make really tight turns around the pylons. So they will stall during high G turns. Tip stalling would be really bad at 100 mph. ( Also known as "high speed stalls") Most pylon racers have some washout in the wings to keep them level.

Anyway, good luck.

12-10-2005 Over year old.
HOMEPAGE  
CK_

Senior Heliman

Redondo Beach, CA

NewHeli,
If you added flaps inboard of the ailerons then yes, it would help with tip stall but this only works when the flaps are deployed. If the flaps are up and the wing stalls for any reason then it will roll inverted. If you solve the problem by twisting the wing then don't be tempted to fly inverted because the wing twist will be adding to the tip stall tendancy then. If you don't plan on flying inverted then you should be using an appropriate cambered airfoil with washout as required for efficiency and stall characteristics. If you want to be able to fly inverted then you can decrease the taper or tailor the airfoil or both. What you could do is keep the airfoil thickness constant. That will make the percent thickness vary from something like 9% at the root to 15% or so at the tip. It also makes the wing easier to build because the ribs are perpendicular to the spars and the spar shear webs are all the same height.

zoom boy,
Reflex and washout are two different things. Washout is the twist of the airfoil chord line down the length of the wing. Reflex is aft camber in the airfoil's mean line that causes the trailing edge to bend up. Most airliners and fighter jets use some washout. http://www.aerospaceweb.org/question/planes/q0099.shtml

Chris

12-11-2005 Over year old.
NewHeli

Key Veteran

Pittsburgh, Pennsylvania, USA

Changing the LE radius will technically change the airfoil, but here is my question--assuming I want to keep the same max-thickness line (the main spar) down the wing, and I make the LE radius larger, this will make the length of the rib in front of the spar shorter--correct? Is this ok? I guess what I'm trying to say is that the airfoil will have the same shape as the 0012 Behind the spar, but a different one in front of it. Is this ok?

I don't want to decrease taper or rid of the rounded tips becuase that is part of the uniqueness (is that a word? ) of the plane.

Nathaniel

Nathaniel Rice
Team HeliWholesaler/Miniature Aircraft
Team YS Engines

12-11-2005 Over year old.
zoom boy

Key Veteran

N.E. Lincolnshire UK

Yes, oops, thanks for reminding me (not the first time i've mixed them up, but I know what I mean), but to bring reflex into it
Fast, little to no reflex, slow, some reflex, generally speaking.
In faster (what he wants) planes like fighters (the ones I've seen wing sections for that is) there tends to be either no reflex or a little bit, and if you look at some airliners there tends to be more.

Also reflex bending the trailing edge up, is changing the mean camber line, so it will affect the washout (but not with respect to span)

12-11-2005 Over year old.
NewHeli

Key Veteran

Pittsburgh, Pennsylvania, USA

I went ahead and changed the LE radius on rib 8 (those of you who have my plans). The normal radius was .15, now its .25. I'm counting the "tip" as rib 8 and out...or should it be 7? That would make the radius a bit tougher...

Should I am for the same bigger radius on rib 9 or should I go even bigger?

Thanks,
Nathaniel

Nathaniel Rice
Team HeliWholesaler/Miniature Aircraft
Team YS Engines

12-11-2005 Over year old.
AirWolfRC

rrProfessor

42½ N, 83½ W

NewHeli, what are you really trying to accomplish ?

Washout serves only one purpose, prevent sharp (sudden) stall characteristics by letting the root of the wing stall before the tips instead of the whole wing stalling at the same time.
A thicker (percentage) airfoil at the tips can do the same thing.
Stall strips can do the same thing.

If you want low speed handling without a sharp stall, thick wing and washout.

If you want same handling right-side-up and up-side-down (3D), no washout and symetric airfoil.

If you want speed, no washout and a thin wing.

Wolfgang

12-14-2005 Over year old.
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