Wings without volume? (made from a single layer of foil)

[Elthy]

Hello! For a project at university we have to build planes from steel-foil that can glide well. Now im looking at wing profiles but everything i find is about wings with a volume, thus they need at least 2 layers of steel foil to make.

We want to use a single layer of foil since thats lighter and way easier to build. To read about that i would need words i could google, sites about paper-planes dont help me much since those usualy have low aspect-ratio (while our plane will look more like a glider-plane). Could you help me with decent google keywords or even better pages that discuss the aerodynamics of such wings?

Edited April 24, 2016 by Elthy

[kunok]

That kind of wings has almost no moment of inertia so aren't useful. https://en.wikipedia.org/wiki/Moment_of_inertia . Is the same reason the beam has shape of H. They aren't single layer for structural reasons. It will be harder to make one, at least a monoplanes (a biplane should be fairly easy thought)

In aerodynamics they are far better than the others, the most thin wings are of fighters, start looking there.

[Nuke]

the wright flier had very thin wings. but it got its ridgidity from a network of wires that also allowed for wing twisting for roll control. i believe the lower camber on those wings was actually negative creating more of a cupped wing shape. overall thickness is the sum of the upper and lower camber i believe.

structurally speaking you are going to need some support. you can still pull off single sheet wings if you fold in creases to act like ribs and roll up the leading and trailing edges as spars. something like that might work.

[PB666]

Bernoulli's motion allows for near mass-less wing structure. The problem however is that for most aircraft because of the moment of inertia of air traveling around a wing, the joint between the wiing and the pressure hull of the craft (Or that which centers the pressure hull) needs to be the strongest part of the craft. So you need some structure tapering from the joint to the wind tip. To give an example, a high speed jet traveling at high altitude can be struck by a blind sheer, you have seen instances were passengers have been injured and luggage tossed from the overhead compartments, but the wings did not break off, this is because the wings are designed to withstand several g-forces during flight. 

In addition, most commercial aircraft take advantage of the strength needed to store fuel in the volume of the wing. When you talk about high speed travel, the sears haack volume of the wing will be critical, since you want air to travel slightly faster over than under, but the wing itself volume should gradually increase and decrease and you do not want the boundary layer to detach (particularly from the top of the wing as this causes high-speed stall). Otherwise you create hideous drag elsewhere on the craft.

 

[wizzlebippi]

How big will this glider be?  If you want to build something large, a sheet or two of foil won't do it, but at the right scale it could get the job done.  Also, for small enough wings, the shape of the airfoil doesn't matter as much because even airfoils behave like flat plates. 

[Elthy]

Structural support wont be a big problem since we can use steel-wire and capillary tubes for structure. The gilder will be somewhere areound 1-1,5m wing span and can wheight up to 400g (we were told that good ones often stay way below 100g)

3 hours ago, wizzlebippi said:

Also, for small enough wings, the shape of the airfoil doesn't matter as much because even airfoils behave like flat plates. 

Since the main "body" of the aircraft will be only a capillary tube it will be a single wing (not divided by the body) around 1-1,5m and with a chord of about 15cm. Is that so small the shape stops mattering? (BTW: the gilder will be thrown, so only low speed)

[Shpaget]

How thick is that steel foil you have?
If it's thin enough for a 1-1,5m wing span glider to stay below 100 g, then it must be orders of magnitude too thin to be of any structural value.

Like others have said, in order for a wing to be strong enough to hold up a plane, it needs to have some thickness. Otherwise it will just flop around.

Why do you have to use the steel foil? Can't you pick some other material? Take a look at F1D models. They are ultralight rubber band powered planes that are usually under 1 g and the best ones fly for more than half an hour (record is 45 minutes, IIRC).

[kerbiloid]

Sounds like Powered paragliding but with chute made of foil. Looks also.

[Elthy]

Its 0,01mm thick, so it wont add much weight. Its made from stainless-steel and quite expensive (thats more limiting than wheight). The project is part of a compitition called "Stahl Fliegt" (steel flies) and we cant use anything with an iron content of less than 70% to archive a long and far flight (when thrown at 9m height). The glider gas to fit in a m^3 and has to weight less than 400g.

[kerbiloid]

As you are going to use super-thin canvas under a stress, probably you in any case will need to treat this as a "thin envelope under pressure" in terms of Strength of Materials discipline.
So, probably you anyway will use a large curvature radius and make it like a segment/sector of sphere. I.e. a deltaplane or a paraglider.
A disadvantage of the steel foil - it's less elastic than polymers.

(V-1 was made of steel, but not one-layer.)

Edited April 25, 2016 by kerbiloid

[PB666]

2 hours ago, Elthy said:

Its 0,01mm thick, so it wont add much weight. Its made from stainless-steel and quite expensive (thats more limiting than wheight). The project is part of a compitition called "Stahl Fliegt" (steel flies) and we cant use anything with an iron content of less than 70% to archive a long and far flight (when thrown at 9m height). The glider gas to fit in a m^3 and has to weight less than 400g.

you want something with a gentle curve. 

https://en.m.wikipedia.org/wiki/Airfoil

[wizzlebippi]

9 hours ago, Elthy said:

Structural support wont be a big problem since we can use steel-wire and capillary tubes for structure. The gilder will be somewhere areound 1-1,5m wing span and can wheight up to 400g (we were told that good ones often stay way below 100g)

Since the main "body" of the aircraft will be only a capillary tube it will be a single wing (not divided by the body) around 1-1,5m and with a chord of about 15cm. Is that so small the shape stops mattering? (BTW: the gilder will be thrown, so only low speed)

It's not just chord length, but speed as well. Calculate your expected takeoff and cruise Reynolds Numbers. There's a transition around 250-300k, above which airfoil shape matters a lot more. As a point of reference, RC aircraft operate around this transition.

[EnderKid2]

Under cambered wings give great lift to weight, but have higher drag.

[insert_name]

Are you able to make structural parts with volume

[KerikBalm]

beginner hanggliders are "single surface" with only one fabric(dacron) layer, and are basically like what you describe

[Shpaget]

How are you going to attach pieces together? If only 70%+ iron is allowed, does that mean glues are out of the picture (soldering as well)? Welding such a thin foil is impossible.

[kerbiloid]

[pincushionman]

I was going to say it's not that much different from a paper airplane, but the I remembered those are folded, so it's not a single ply.

How much of this steel foil do you get to play with? If you need to do some quick small-scale prototyping (to determine "yes, these shapes might work to produce lift"), you might be able to get away with aluminum foil, coathanger wire, and tape (all cheap and easy to get)

[AngelLestat]

You can have a airfoil without close the shape below, that is how sailboats and frisbees work.
I dont know much about aerodynamics, but I guess this can work:

With an angle of attack from 7 to 15 might be fine.. Low angles will require faster launch speeds.

Shape:

Then you need to choose the wings angle like this:

For gliders I will choose polyhedral, but it will be hard to bend the foil shape like that, so dihedral should work to gain some stability.

About the plane shape.. I can not help you with that..  you will require to do some research or just try to copy a design taking care that it keeps is center of mass.

PD: Make a a launching pad of wood with an elastic rubber, so you can control the launch angle and speed to test. 

Edited April 26, 2016 by AngelLestat

[problemecium]

Look up "Science Olympiad" plane designs. It's been a few years so I'm not sure if they still do it, but one of the bigger events used to be a balsa glider competition, which sounds like a similar thing to what you're doing.

[Elthy]

While curved airfoils are proably the best shape they are also hard to manufacture, so we will propably give a flat surface a try. Also i think those may be calculable without using professional simulator programs or similar, which would help a lot. Ive seen a lot of diagrams showing the lift/drag to AoA of airfoils, do you know any calculator for simple ones on the internet?

Edited May 1, 2016 by Elthy