Building a balsa sailplane

[Tuur]

As a project for school we need to construct a (model)sailplane, which fits in a box of 60x60 centimeters. It has to be made for 70% of balsa wood.

In two weeks, we'll hold a competition. The goal of the competition is to get the plane as far as posible (in a straight line).

I have some questions about aerodynamics though...

- The plane needs to fly as far as possible. Which type of plane should I contstuct to obtain this goal? Do I need a fast plane, or a slower "sailor"? The plane doesn't have any controls, and is launched by hand.

To make my further questions a bit more clear, I made some illustrations;

Here you have a front view of the wings. Which one is the best? As the plane doesn't have any controls, it's VERY important to maintain a straight course here. If the wings are built in a V-shape, it'll be more stable. What's the best combination? 1, 2 or 3? Or something else?


Winglets. Do I need them? Are they efficient if used on such a small scale (wing span ca 70cm)? And if I use them, would it be better if they bended downwards too?


The wings again. Is it better to use a wing which is swept a bit backwards, or a straight one? Do I need a long & small wing, or a more delta-shaped one?


The vertical tail fin & winglets. What's the profile of the vertical tail fin? Is it shaped like a droplet to have less resistance? Or is it better to have more resistance (to maintain course)?.


The tail. Do the horizontal tailfins need to be angled? Or is it better to build a V-tail? Which one will best maintain a perfect straight course? Personally I think nr 1.


I know airliners fly with a small nose-up attitude. What's the exact advantage of this? Do I need to construct my plane to fly with the nose up a bit too?


The wing profile. Is a hollow "bird" wing better? A "clean" & fast wing, or a slower wing, like if the flaps were extended?

I know it are a bunch of questions, but it would be great if someone could shed a light on this

Thanks,

Tuur

[Buzz]

I can't help you with answers, but I can really suggest going to the library, there are some good books about aerodynamics of airplanes (at least in Hasselt)...

[Avro]

- The plane needs to fly as far as possible. Which type of plane should I contstuct to obtain this goal? Do I need a fast plane, or a slower "sailor"? The plane doesn't have any controls, and is launched by hand.

You just said that the goal of the competition is to fly the furthest. So I suggest you build a plane with some good lift capabilities (even at low speeds) and not especially a "high" speed configuration.

I know airliners fly with a small nose-up attitude. What's the exact advantage of this? Do I need to construct my plane to fly with the nose up a bit too?

About the attidue of your plane: What you need to achieve or at least try to achieve is that the air which strikes against your leading edge will almost be tangent to your leading edge. This means that you will have to build a wing which will have a deeper camber than what you've drawn.

The wing profile. Is a hollow "bird" wing better? A "clean" & fast wing, or a slower wing, like if the flaps were extended?

First of all don't take wing number 2 . As you may see, you've designed number 2 with sharp edges underneath. This isn't that good. Those sharp edges will create losses due to the fact that some part of the air will stagnate and re-circulate in that area.

To begin with you need a clean line without sharp changes in direction. Secondly you will need to build a wing which will give you a good lift. This means that you will have to build a wing with a deep camber. This means that the wing shouldn't be straight like in point number 1. I don't know if you see what I mean. If not, just bend your wing number one (but not in a symmetric way) - like on a real plane. This will enable you to get more lift.


I hope this helps as a start and don't hesitate to make some tests to be sure that your idea works well.