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non rc balsa glider - 6/15/2003 10:50:18 PM   
Zorak



Posts: 133
Joined: 11/30/2002
From: Framingham, MA,
Status: offline 		I have tried constructing several different balsa gliders which have no rc controls, just throw it and watch it go until it drops basically. They have all been very simple, wings, vertical and horizontal stabilizers attached to just a stick of thick balsa in the middle. When I throw just the "fuselage" (stick part) with the vertical and horizontal stabilizers it flies about 10 feet. However, whenever I add wings of any kind, it goes about one foot, then points straight up the tumbles to the ground. So far just putting a straight piece of cardboard has worked better as wings than a really nice airfoil design that took a long time to make. Can anyone help me as to why this is happening?
Thanks
       Post #: 1

non rc balsa glider - 6/16/2003 12:53:49 AM   
rogerflies


 

Posts: 344
Joined: 1/8/2002
From: Thomasville, GA, USA
Status: offline 		Where is the CG? It sounds like the planes are seriously tail heavy. For starting out, balance the plane at the wing spar and add weight to the nose until it is just a little lower than the tail.

When you launch the plane, don't throw it really hard. Just walk fast, and gently toss the plane straight ahead.

After trying these things, post a reply to let us know how it worked, and we'll go from there.

Roger

_____________________________

"New ideas in launching equipment."

(in reply to Zorak)
       Post #: 2

non rc balsa glider - 6/16/2003 1:27:38 AM   
BMatthews



Posts: 9004
Joined: 10/4/2002
From: Burnaby, BC, CANADA
Status: offline 		I don't think there ARE any spars Roger....

Zorak, you're obviously venturing into the very basics of flight here and good on ya for taking this method to learn. But the short answer is that Roger is quite right in that your balance point has been ignored.

Basically, assuming you're working with flat sheet surfaces here, you want the model to balance at about the 1/3 chord point behind the leading edge of the wing. From there use some hot breath to slightly warm the rear of the stabilizer and "steam" in some small amount of up elevator to achieve the longitudinal (fore and aft) balance you need for level flight. Simply put the nose weight (modeling clay is perfect but a short nail or a bit of solder wrapped around the nose does equally as well) will make the model nose dive slightly and the up elevator provides a speed sensitive countering force to balance that nose diving. Play with the balance point and up elevator until you get a nice glide and you've got your stable flight point.

On your next project try gluing some chordwise short lengths of copper wire to the trailing edges of the stabilizer and fin so you can bend in your adjustments and the copper wire will help hold them in place. Short cut lines near the fuselage stick will let the rear edges bend easier as the stick won't be fighting the adjustment bends.

I did a quick google.com search using the key words "model airplane aerodynamics" without the quotes and got lots of promising hits. Give it a try and I suspect you'll find some good info that will help a lot.

From here you can try lots of different planforms like deltas, saucers, flying wings and stuff like that. Good luck and happy learning.

PS: The more technical answer to why your glider is nosing up so strongly is that your balance point is at or behind the aircraft's neutral point and basically it's trying to fly backwards. But if you try flying it that way the airflow will change again and it'll just try to flip the other way. It's all in balancing the forces that are at work.

Oh, and there's lots of us folks that fly fancy versions of what you're using here. We call them free flight hand launch gliders and it's not at all unusuall to loose them in thermals. Even in dead air and with a good throw it's common to get flights of around a minute. Try that google thing using "free flight hand launch glider" or just "free flight hlg" and you can find some sites with plans for the fancier ones.

_____________________________

Witty saying to be plagarized shortly.....

(in reply to Zorak)
       Post #: 3

non rc balsa glider - 6/16/2003 1:42:43 AM   
probligo



Posts: 354
Joined: 5/13/2002
From: opononi, NEW ZEALAND
Status: offline 		Zorak, welcome to the real world of model gliders.

May your stay be a very long, and exciting, one. These small, and has been said, very basic models are the most challenging and the most rewarding of any that have ever been built.

As Roger and Brian have already said, you need to add some weight to the front.

Where it should "balance" after is a matter of conjecture but if the wings are flat sheet somewhere between 33% and 50% chord will be about right.

Keep in touch and let us know how you progress.

BTW, my e-maddy is around someplace - like probligo at yahoo (in the right form) will get to me quick as...

(in reply to Zorak)
       Post #: 4

non rc balsa glider - 6/16/2003 2:50:39 AM   
Zorak



Posts: 133
Joined: 11/30/2002
From: Framingham, MA,
Status: offline 		Wow! I got it working! I will post a pic soon.
I balanced the plane under a point around a half chord and wrapped solder around screws on the nose until it balanced more. I think I understand the concept of balancing much better now. The plane is the equivalent of a torque problem, with the elevator rotating the back of the plane down, and the weight on the nose rotating in the opposite direction. When these are equal it flies steady. I am thoroughly happy Can't wait to experiment with different designs

(in reply to Zorak)
       Post #: 5

non rc balsa glider - 6/16/2003 4:52:43 AM   
KJohn


 

Posts: 264
Joined: 2/19/2003
From: Medina, OH, USA
Status: offline 		I have often thought about setting up some type of 'consistant launch' method. It would allow me to try a different wing on the same fuselage and launch it in the same way each time.

One way would be to place the plane on a skateboard and let it to roll down a board the same way and the same speed each time. It the end of the board the skatebaord would be forced to 'stop' and the plane would slide free. I would then measure the distance that the wing took the plane. This would have to be indoors or on a flat calm day outdoors. If I tried to launch by hand I am sure it would vary from one toss to the next.

(in reply to Zorak)
       Post #: 6

non rc balsa glider - 6/16/2003 5:54:38 AM   
BMatthews



Posts: 9004
Joined: 10/4/2002
From: Burnaby, BC, CANADA
Status: offline 		Either a skateboard or a launch rail with a dropping weight. The speed of the launch would be controlled by the model weight and the distance the weight drops.

But for most of the basics a seried of hand tosses will usually tell you what you need to know.

_____________________________

Witty saying to be plagarized shortly.....

(in reply to Zorak)
       Post #: 7

free flight hlg pictures - 6/17/2003 4:39:43 AM   
Zorak



Posts: 133
Joined: 11/30/2002
From: Framingham, MA,
Status: offline 		Here are a couple photos of my very first working glider. Note how much weight I ended up adding! I used toothpicks to hold the camber of the wings, and the pictures dont show it but the horizontal stabilizer is angled down slightly. Between when these pictures were taken and now, the left wing was cracked when it arrived unexpectedly at rake

Is there something I can coat the wings with to make them less readily broken?

http://www.geocities.com/tgohan/airplane1.jpg
http://www.geocities.com/tgohan/airplane2.jpg

(for geocities you have to drag these links to the title bar)

(in reply to Zorak)
       Post #: 8

non rc balsa glider - 6/17/2003 6:31:23 AM   
BMatthews



Posts: 9004
Joined: 10/4/2002
From: Burnaby, BC, CANADA
Status: offline 		Two ways to reduce the amount of nose weight needed. Move the wing back to make the nose longer or use thinner and lighter wood for the tail and taper the fuselage.

For your next one you may want to try using some dihedral for lateral stability. With the wings flat like that it'll want to drop off into a spiral dive to one side or the other.

For thin wings with camber curved into the wood like you're doing simple arced ribs of balsa are often used to hold the camber in place. Another option is to look into Jedelsky type construction although you'd want it to be a bit bigger for that sort of construction.

_____________________________

Witty saying to be plagarized shortly.....

(in reply to Zorak)
       Post #: 9

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