Wing shape question

[Patrick Plawner]

Hi,


I got this new plane, from someone who already build it. I looked at the user manual and it looks ok but something cought my attention yesterday.

Looking at the plane, standing on the ground, on it's landing gear.

The plane designed for aerobatics, and E3D.

#1 - The wing is in light V shape
#2 - The upper cambered surface is more or less flat as the bottom cambered surface is roundish, and longer than the top surface.


All your comments on the above are most welcome.


My own comments:
#1 - E3D is not much better with flat wing ? What is the advantage of light V shape, except maybe more stable ???
#2 - I learned that lifting is created, in a part, by air speed acceleration, so symetrical wing should be the limit, but not the bottom longer than the top ??? What did I miss ? Is this not an issue at our low speed ? But why would any wing be build this way ? Don Sims just proposed a funny good one, as he suggested that the plane was designed to fly inverted :)


Here are few pictures to show you the thing.



The first picture shows how to install the servos and the carbon fiber spar into the wing, and show then the shape of it.

[Patrick Plawner]

This is now, the wing installed, from the side

[Patrick Plawner]

And view from a different angle. The side of the wing has some angle too, which also stablelize the plane, while flying non inverted.

[steve lewin]

I guess that by "light V shape" you mean the wing has some dihedral i.e. tips of wing are higher than the centre. Many aerobatic low wing planes have some dihedral. It compensates for the fact that the wing is below the thrust line.

As for the airfoil, are you sure he didn't fit the wing the wrong way up ;). I have seen many planes with an airfoil similar to that but with the most curved part on the top (they are commonly called semi-symmetrical).

OTOH Don may not have been joking, that shape may be an attempt to compensate for some of the other aerodynamic problems that low wing planes can have. Why not just fly it and see how it works ?

Steve

[Patrick Plawner]

Yes Steve, I meant dihedral, just I never remember how to spell it right so writing "V shape" was safer :)


I will try it as it is, just sounded weird.

[Sparky Paul]

Looking at the drawing of the spar installation, there's more curvature on the top, which is proper.
It appears to be semi-symmetrical.
I suspect the wing on the model is installed upside down!
When you fly it, you'll be surprised. It wll fly!
Better inverted, but it will fly.

[Patrick Plawner]

The thing is, on the drawing, the upper part is the one that get the servo, and goes actually as the down side of the wing.

You can't really make a mistake when building the wings as the side is curved.


I am telling, something is weird with the design, I think.

[Patrick Plawner]

To illustrate it, here is the drawing for the servos. Corrolating the 2 pictures, you'll see more what I mean...


Look at the red circle, it will indicate which side is the top of the wing.

[Patrick Plawner]

I assume that they intended that adding the wingspar should not impact the wing curve, and therefore, it would be symetrical, but it seems that it does impact the shape, at least the one I got.

[Patrick Plawner]

I tried the plane and I am not sure if it is just some controls to adjust or not, but the plane flies, indeed, better inverted.

Actually, inverted, it climbs, and starts to loop even, without any elevator.

While non inverted, I need to add evelator to maintain altitude.


Since I have only few flights, I still need to make sure it s not coming from something else, but that's what I noticed so far.