Help Me With This (Paper) Airplane

[jyl]

Okay, to the pilots on the board (full-scale and scale):

I need your help with a paper airplane.

My son wanted to know how airplanes fly. I used construction paper and scotch tape to make him a wing, and using a fan we saw how it produced lift. Then he wanted an airplane. So with some more construction paper I made him an airplane. See photos below. It is about a foot long with a penny and three paper clips as ballast in the nose.

The problem is that it doesn't fly as well as I'd like. If it is tossed gently and released when pointing slightly nose-down, it glides beautifully to a smooth landing. But if it is tossed harder, or is released when nose-up or nose-flat, it tucks its nose under in an ever-steeper dive until it strikes the ground vertically.

We're going to build another plane this week (out of sturdier paper), and I'd like some tips on what is wrong with this one, and how to improve the next one.
- Where should the center of gravity be? Right now it is about 1/2" aft of the thickest part of the wing.
- Should the wing be bigger? Positioned further forward or rearward?
- Should the horizontal stabilizer be tilted? Have an airfoil shape? (I'll build some trim tabs into the horizontal stabilizer and the wing next time.)

[BlueSkyJaunte]

Needs some dihedral, for one thing.

A bigger stab (chord-wise) for another.

General rule of thumb in HLGs that I've built is that CG is at the maximum camber, which should be about 1/3 back from the leading edge. I suspect your airfoil has a bit too much camber--lots of lift at low speed but huge drag coefficient.

[mikester]

Too much camber there, reduce it some and add some chord in the wing and you won't loose much lift. The CG for an unpowered plane such as this should likely be at about 25% of the chord since you're depending on gravity. If that falls too fast move it back but likely not more than 33%.

How old is your son?

If he's old enough you might consider a small radio controlled plane. These days they have a lot of ready to fly models that aren't too bad on the wallet and actually do fly.

try www.horizonhobby.com or www.towerhobby.com

[island911]

EVERYTHING you need to know about paper airplanes is here (entry #4)
Hawaiian Shirt day (or, more corporate BS)

[jyl]

Woah there.

"Stab" means the horizontal stabilizer and bigger "chord" means increase the leading-edge to trailing-edge dimension?

What is "dihedral"? Does that mean the angle of the wing to the body, i.e. tilt the wing up a bit at the leading edge?

So the wing needs to be thinner (upper surface to lower surface dimension) and with a bigger chord.

[M.D. Holloway]

JYL - that wing should be like 12 inches longer! There is no way that thing will gain any lift. When scaling down, the density of the material is not liner, were as the demnsions are. Imagine if your son wanted to take one of his hot wheels and scale it up - the diecast chassis would weigh 12 tons!

Pull that wing off and stick a slab of Balsa wood through it...

[mikester]

Originally posted by jyl
Woah there.

"Stab" means the horizontal stabilizer and bigger "chord" means increase the leading-edge to trailing-edge dimension?

What is "dihedral"? Does that mean the angle of the wing to the body, i.e. tilt the wing up a bit at the leading edge?

So the wing needs to be thinner (upper surface to lower surface dimension) and with a bigger chord.

Stab is the horizontal stabilizer in the tail, Chord is the depth from the leading edge of the wing to the trailing edge.

The first thing I would do is try to get the CG right and see what it does.

[Brother]

Make the wing mount adjustable. If you slid the wing back a few 1/8ths it would probably fly better.

If you can find a package of Whitewings Paper airplanes at a hobby store you would be money. It will probably run 10-20 bucks and you would get some nice models.

Dihedral is going to be tough to create on your own without some stiffer paper.

You might think of picking up a control line model as well. It is an airplane on the end of the string that you fly by standing in the center of a large circle and having the plane fly around using centrifugal force.

[HardDrive]

Why not get a simple kit of some kind? They have balsa kits for rubber band powered planes.

[masraum]

The "wing" at the back should be symmetrical, instead of asymmetrical like the lift producing wing in the front.

[Rex Walter]

JYL,

There are several good suggestions here. I think your wing is too thick. The airflow cannot follow the upper surface if it changes direction too quickly. The suggestion about just using a flat piece of balsa wood may work. What is happening, is that as the nose goes up, or the speed goes up, the airflow separates off the top surface, and you stall - the nose drops and it hits the floor.

The horizontal stabilizer (stab) could be symmetrical (the same curve upper and lower surface - but the job of the stab is to push down - so you can install the stab upside down. The wing will naturally want to pitch nose down, and the stab counteracts this by creating the opposing pitching moment. I would also make the stabs chord (front to back length) longer - maybe the same as the vertical tail (although that looks pretty big also).

Rex

[targa911S]

Christ you guys ARE rocket scientists!

[304065]

John,

When the wing generates lift, it also generates a nose-down pitching moment. Try this at home: remove the horizontal stabilizer and throw the plane. It should exhibit the same nose-over behavior you observed.

Now, put the horizontal stabilizer back on, but upside down from the way you had it before, so the fat part of the stabilizer is pointed toward the ground. Now throw.

You should notice a difference in flight behavior. If it noses UP, reduce the size of the horizontal stabilizer or decamber the airfoil.

I used to fly a Piper Arrow, which is basically a Cherokee with retractable gear and a constant-speed prop. It has a "stabilator" or all-flying horizontal tail. The airplane is actually a couple knots faster with two passengers in the back, because the required angle of attack (a pilot's term for the size of the bite the stabilizer takes) is lower for sustained level flight, because the aft CG makes the plane fly with the nose higher during cruise. Therefore, you don't have to trim the stabilizer so far away from the zero degree position -- and we know that as angle of attack increases, so does lift, but so too does drag. So the less you deflect the stabilizer, the less drag you create. . . a couple knots faster.

[304065]

Rex beat me to it!