Will it fly??

A few of us nut bars in our local club have been having a rather tongue in cheek debate over the last few years. On one side we have a VERY limited number of believers, on the other side the majority, are the most vocal nonbelievers. The debate centers around weather a model air craft with the wing covered in window screen would fly.
On the yes side, the premise of given enough power a brick would fly, on the no side all manner of semi half baked aerodynamic gems of wisdom. You may now realize how little we really have to talk about at our (help get us though the winter) Club meetings.

This discussion was born when I shared my experience with a CG Gentle Lady which had a two color film covering on the wing. On launch, on a high start the wing shed the covering from the spar to the trailing edge (Black Barron over Monokote not a good combo). The resulting flight sans more than 50% of the wings covering was to say the least uneventful. I achieved a flight that was very similar in duration to the six previous flights of the day. So began the debate… Like why bother with covering at all? And it went downhill from there. … Have some fun all… Bert

Uh, yes and no. What do you mean by "fly"? Do you consider a hovering plane to be "flying"?

If the wing must produce the lift via traditional Bernoulli effects, as opposed to the engine holding the plane in the air, then no, it won't work. The screen allows air to pass through it, so you will not get the Bernoulli effect velocity profile and pressure delta needed to move the wing upward (i.e., lift). It might be simpler to imagine what would happen even if you could get a pressure delta between the upper and lower surfaces. The higher pressure air would simply pass through the wing to the upper surface, without taking the wing with it. This all discounts the fact that the screen will have some miniscule resistance to air passing through it. In theory, I guess, you could get the thing to produce enough lift if you could get it moving fast enough, but that couldn't happen in reality, because the engine you would need to do so would make the plane heavier and require more lift... (a never-ending death spiral as we say in the design world).

Like you say, though, a brick can fly- that is, made to stay airborne- with enough engine. It's just another physical way of getting it to stay there- no wing lift, just engine thrust.

This debate is borne of an apples to oranges comparision.

First lets consider the "screened" wing. The screen will have some small resistance to air passing through it as mentioned before, but given enough flow some of the air would follow the airfoil shape. This would give you the classic differential pressure between the top and bottom, but because it's a screen the air would try to flow through the wing from bottom to top. Again, given enough air and enough differential you could probably get some lift out of it, but it would be very inefficient. So it might work, but not well.

In the case of your glider, you retained the covering on the first 1/3 of the wing. This is really the most critical part. So the wing was still able to generate some lift. I can't imagine it was too efficient, but luckily for you it behaived all right and you were able to save the model. However, I doubt you'd win any endurance contests with it.

Metal or vinyl screen?

Gnat size or larger??

This are important things to consider

Yes it will fly if the screen can offer enough resistance to air passing through it.

HI…
Well it seems I have sparked a rather anemic debate. One consolation is like in our little club, we have folks on both sides. One theory advanced by one of the full scale guys in our group is that the screen represents a contaminated airfoil and will not allow the generation of lift.
It seems I may just have to spend some time in the Lab (He means shop) with the wind tunnel (he means blow side of a shop vac) and a rather sophisticated airfoil (He means piece of wing from wrecked aircraft) and see what kind of data I can accumulate.

bert.

I think you should just take your least expensive plane peel the covering off put on some screen and go fly!!

If it works your a hero!!

good luck,


Weskel

ps, I think it will fly, but not very good....

is it possible that the turbulant air flowing over the wing could form a bit of a "surface" for the pressure differential to act on ? it wouldnt be the greatest, as air would still be sucked through the wing, but as long as the plane is advancing forward at a fast enough pace ...

would probably need twice as much wing surface as the same plane w/ proper wings tho

This is all second hand, but here goes...

Several years ago, there were two brothers working on a plane for the SAE Aerodesign competition. It was a sizable plane with a 72"+ wingspan and 10"+ chord, and was powered by a K&B .60 engine. The wing was built-up with 3/32" ribs and a carbon fiber I-beam spar. Then the wing was wrapped with a thin carbon fiber skin. During the first flight, the aircraft would barely leave the runway with almost no weight (SAE Aerodesign is a weight lifting competition where the brothers were expecting to lift ~26+lbs). The plane then crashed while trying to climb out of ground effect. When the brothers held the broken wing up to the light they saw thousands of tiny holes through the carbon fiber skin (due to the weave of the fabric).

In other words, the concept would probably not work, except possibly at the right Reynolds number, and with the right screen, and airfoil, or with a huge amount of power, etc.

taylorcraft1947

Was the original covering lost from the top AND the bottom of the wing?
If only one side, then it could fly as described.
If both sides were lost, then the chord shortened a WHOLE lot, and the c.g. ended back to the trailing edge of the "improved" wing.
Which would have resulted in a plane-shaped hole (front view) in the ground.
With only one side lost, there's no path for the lower side pressure to the upper side thru the extant covering, so the plane would continue to fly.
As the GL has a center-of-the-rib spar set, the initial description seems odd..
Unless the only covering lost was that aft of the somewhat short-spanned leading edge sheeting on the upper surface of the GL.

on stuff like this it would be nice to find a local university to give you access to a windtunnel for a couple of tests.

Now that's what I need..a wind tunnel. Why you ask? I am scared to lunch the Starship Enterprise (when it's completed) I'm trying to think of a safe way to test a plateform that was designed in someones mind for space travel and not for the atmosphear. The CG is back behind the engin leaving the disc (total lifting surface) ahead of the power.

Of course I could add another wing structure along the back side of the nacells but then it's not the star ship.

Any ideas????

Lawrence
Omaha, Nebraska

Lawrence, I've seen a couple of those flying.

Berta, maybe this is some form of "laminar air flow" wing?

If you were to use a nylon screen with very small mesh... coupled with light wing loading plane, I'd fully expect it to fly. I've been camping in my modern tent with winds strong enough to send more than a few tents cartwheeling down the river bed. There was so much resistance in the screen mesh on this thing, you could barely feel any air movement inside with ALL the windows open. Guess the next time I upgrade, I'll have to cut out the screens and do some covering.

Why just yesterday I walked out of the shop with my uncovered Kadet Senior and it nearly blew out of my hands....

I gotta believe there is some point (an inverse relationship) where the screen reaches sufficient solidity for a given horsepower to fly the "screen plane". It probably be easier for us modelers than full size a/c designers because we can easily achieve higher power loadings and we don't have to find a volunteer to go up in our screen plane.

Seriously, there must be some value of wing open area that would still support flight. If I really wanted to answer the question, I think I would start with 5-10% open area and begin testing. I would continue to increase the open area until the plane no longer lifts off the ground. To give the screen plane a chance, I would begin by putting the open area in the rear of the airfoil. You know, it may be that the open area could be increased even more if the screen plane could be rocket assisted to some given velocity. But that's for later after the ROG method is explored.

....or you could just use your imagination....

The good old theory of flight !!!
Imagine a flat wing section, pulled into the air by a good old MDS engine, it flies, until the engine stops, then it basically falls out of the sky, all be with a shallow glide, then lets imagine a fully aerofoil section ( english) , pulled again by the good old MDS , it gains height, the engine stops, it falls to earth.
It is NOT the wing section at all making the aeroplne fly, it is the engine pulling the aeroplane through the sky that keeps it up there. so the theory of flight, as good as it sounds, relies upon something pulling the aircraft through the air, most of us have flown flat plate wing models, and they fly, some cases very well, What happens when the engine stops? Yep, it falls to earth, what about the latest NACA aerofoil section ? works while being pulled through the air, engine stops, it falls to earth, just a bit quicker than the flat plate. ? don't believe me? try it.

Footnote, we are talking powered models here, gliders fall to earth no matter what. !!!

hey chris with gliders they don't nassicarily HAVE to fall to the ground immediatly they can thermal around leeching off the heat lift caused by that annoying bright thing that breaks up our night

Someone could try a method often used by model designers to detemine CG on oddball designs. Build a hand launched free flight glider with a framed up wing, cover it with some form of gauze from a fabric shop, or a party supplies shop, and see if it flies. Very cheap way to expirement and maybe satisfy some curiosity.

I could be wrong, but it seems to me that at low angles of attack and high speeds the screen would behave not much differently than solid covering, but at a high angle of attack it would loose almost all lift. If you look at a screen door edge on and then start to increase the angle, it starts out looking like a solid sheet until you reach the angle that you can see thought it. At the angle of attack that you can't see through the wing ( I guess I'm thinking of a flat plate to keep it simple), when viewed from the front, it should deflect enough air to provide lift.... unless your planning on using chicken wire.....

Maybe I'll just try to fly my Kadet Sr. with no dope on the silk....

I've seen some WW1 scale jobs fly with a very light dope coating over silk that was definitely porous, but the mesh is so fine it was probably acting like a sealed surface at this size.

Hi All… Just thought I would revive this old tread with an up date.

Early this summer one of the more adventurous in our group had some limited success with the screen covered wing. He used an old overweight Kadet Mark 2 fuse, a leftover semi symmetrical wing with a self designed airfoil, and old worn out beater of a 40 2 stroke. As you can see by the chosen test bed, he was not overly confident in the end result.
The leading edge of the wing was balsa sheeted top and bottom and remainder of the wing was covered with screen, top and bottom. The entire wing was then covered with film.

The plane was test flown successfully. For each subsequent flight 2 bay sections of film was removed. The plane flew each time with a continuing decline of performance.
With the last 2 bays of screen removed the plane did not have enough runway to get of the ground. Those there to witness, all agreed that a stronger 40 would have defiantly put the plane in the air.

When flying the plane was predictable however it was very sluggish. The power-off sink rate was impressive.
The result however entertaining for those of us present is inconclusive in so much as the critical area of the wing was balsa sheeted. Perhaps screen sheeting on the leading could provide the next chapter… bert

Now that's what I'm talkin' about when I say "empirical testing"!