How to build a model aeroplane?

Question

using cardboard,newspaper,polyform

Answer 1

However you want really, the trick is getting it balanced to fly properly.

The centre of gravity (CofG) should be roughly 1/3rd of the way down the wing chord (Front to back) from the leading edge (Front of the wing). You can normally shift this by using extra folds or adding paperclips. If you can't get the balance just right, then nose heavy is better than tail heavy.

Once you've mastered that, try playing with canards, google it for some designs. The foreplane needs to be forward and above the mainplane with a difference in angle of attack between the foreplane and mainplane of +15 degrees.

Answer 2

There are a lot of issue with your concept.

First, structurally, cardboard does not hold up well when stressed. You can bend it easily with a push of a finger for example. Folding the cardboard, like with a paper airplane glider, will handle some of the strain/stress issue, but that will also add weight to the plane because it tends to reduce the wing area (where the lift comes from) with each fold. So you need to add more cardboard, and its weight, than if it were not folded.

Second, cardboard is relatively heavy per volume; in other words it has a fairly high density. Which means the more cardboard you add ("make it big" as one answer put it), the heavier it will be. And things don't fly until lift (L) is greater than weight (W). That is, L > W is the prerequisite for flight. W includes the weight of the cardboard, tape, and egg in this case.

Third, the wings of a plane have to generate more lift (L) than the plane cross sectional area generates drag (D). This is the so-called lift over drag (L/D) ratio where L/D > 1 is necessary for sustained flight. But where will that lift in the wings come from? You need something called camber to cause the velocity of air above the wing to be greater than the velocity underneath the wing. That's how lift is generated in part. Other lift generating factors include the magnitude of the velocity, which is generated as the plane goes through the air.

Finally, what's propelling your plane? The propulsion is what will give your plane the velocity needed for lift. If you intend to simply toss it into the air, that's one thing. But if you intend to attach a propeller, rubber band, and brackets to hold both, that will add weight to the already heavy cardboard airplane.

Don't get me wrong. I'm not saying it can't be done. But I am saying there are a lot of engineering issues that need to be overcome if you are to be successful.

PS: As you seem bent on building this thing from cardboard, here's what I'd try:

1. Get the lightest possible cardboard with the greatest strength. That would be some sort of corrugated cardboard, the corrugation adds strength without adding a lot of extra material.

2. Fold the cardboard as you would fold a paper airplane. I know of two ways to do this. One is pointy and shaped like an arrow head. The other is blunt and shaped like a flying wing (avoid this one as it is usually astable). The size of the plane is limited by the ability of the cardboard to hold its shape once folded. But make it as big as you can up to the point where the plane still holds its shape in flight.

3. Use bits of tape to ensure the folds stay put and don't unfold in flight. You may need to cut one side of the cardboard in order to fold it, corrugation resists folding; that's why the tape will be necessary to keep the folds from unfolding during flight.

4. Put a paper clip on the pointy end to move the center of gravity forward. This is necessary to offset the egg that will move the CG back and, if the CB is moved too far back, the plane will nose up and stall out. Test fly the plane without the egg to find how big a paper clip is necessary to keep the plane from stalling. Then double that size for the run with the egg.

5. Find the smallest lightest egg you can get. (Maybe a bird egg; chicken eggs may be way too big and heavy.) Tape it forward on the centerline of your cardboard plane, near the paperclip...to avoid pulling the CG too far back and stall out.

6. Toss the plane with egg into the wind, but on a day that is not gusty. The gusts could drastically change the angle of attack and stall the plane. Make sure you launch the plane from someplace where a broken egg will not cause a big problem.