Elastic Launched Glider B

[foxfire]

I noticed many of the best flying gliders at the competition had combination wood and paper wings. Where can I find a kit or schematic with such as design? Thank you!

[builderguy135]

Our plane crashed and the horizontal stab broke in half during competition. Is there a way to make the planes stronger, or would that not be worth the extra weight?

Anything above 3 grams is not worth the extra weight. If the stab is savable, reglue it but try to keep the glue at a minimum. If it's not, then cleanly cut it off and remake a stab. The planes only have to be as strong enough to survive the initial launch. Stabs generally aren't broken that often, so you can keep it light without having many issues.

[jander14indoor]

I noticed many of the best flying gliders at the competition had combination wood and paper wings. Where can I find a kit or schematic with such as design? Thank you!

I'm a little doubtful that they were wood and PAPER, more likely wood and white foam.
Freedom Flight https://www.freedomflightmodels.com/kits.php
and
J&H Aerospace http://jhaerospace.com/product-category ... ts/page/3/
are the two kits I'm aware of that combine foam and wood. There may be others.
If you spend some time searching the web you may find similar designs to make yourself.

Jeff Anderson
Livonia, MI

[jander14indoor]

Our plane crashed and the horizontal stab broke in half during competition. Is there a way to make the planes stronger, or would that not be worth the extra weight?

Little to NOTHING is worth extra weight in the flying events if it takes you over the rule minimum. Except PERHAPS wing area, but then only if you can increase area MUCH faster than weight. Weight kills time terribly fast. And weight in the tail is particularly bad as it drives you to add USELESS weight to the nose to get the CG right.

BUT that does not mean you can't do things that make the plane stronger WITHOUT adding weight. Change where the weight is located.

Example, some of the more sophisticated glider designs have balsa leading edges for strength, but the trailing half of the wing is a very light foam that can't handle the crashes. Its used for another reason too, but that is one benefit.

Even without foam, you can do something similar with an all balsa wing. Select a small strip of hard (dense) balsa, say 1/8 inch wide and glue it to the edge of your wing stock that is a softer, lower density. The hard strip is then oriented to the leading edge of the wing.

You can do much the same by careful selection of your wood for the wing. Select sheet stock appropriate for the design, here's some critera. Look at the surface, you want to use B-grain balsa, half the sheet should have the sparkly surface of C grain, the other half should be moving towards the boring surface of A-grain. Now, hold the sheet up to a strong light and look through it. You'll probably see the C-grain is darker, that means heavier denser, and the A-grain is lighter (less dense). If not, put that stock back and look for another sheet. Once you've found that ideal sheet, cut the wings out so the dark (dense/hard) wood is along the leading edge, and the light along the trailing edge.

Careful use of carbon fibers can be VERY effective. A couple of strands glued to the leading edge can add a lot of strength with minimal weight penalty. Most of the ELG kit manufacturers have moved to carbon fiber fuselage sticks. I THINK at least one of them either offers the rods for these sticks, but can't see it right now.

Hope that helps.

Jeff Anderson
Livonia, MI

[NewSciolyer]

What is the recommended proportion of weight for the gliders? (Ex. Wings take up X% of the weight, Hortizontal Stab takes up X%)
Or what is the recommended weight for each piece? Thanks!

[bjt4888]

New,

I would recommend:

Wing (complete with pylon): 1.75 grams
Fuselage: 0.65 grams
Stabilizer: 0.2 grams
Fin: 0.05 grams
Front hook: 0.1 grams
Nose ballast: 0.25 grams

Of course, all components must be adequately stiff. This means judicious use of carbon, light foam and low density wood.

Brian T

[Nathanfrommars]

New,

I would recommend:

Wing (complete with pylon): 1.75 grams
Fuselage: 0.65 grams
Stabilizer: 0.2 grams
Fin: 0.05 grams
Front hook: 0.1 grams
Nose ballast: 0.25 grams

Of course, all components must be adequately stiff. This means judicious use of carbon, light foam and low density wood.

Brian T

Brian,

We are trying to reduce the weight from 4g to below 3.5g. The other parts are reduced some weight except the Stab and Fin. What kind of balsa wood or foam can achieve the following? Stabilizer: 0.2 grams Fin: 0.05 grams

Thanks,

Nathan

[bjt4888]

Nathan,

Good job working on the critical details.

5.0 lb cu ft balsa (c-grain necessary for stiffness) sanded to .025” thick stabilizer will weigh 0.2 grams. Of course, the stabilizer area should be about 15% of the wing area. It is easiest to get low density wood like this in slightly thicker sheets, like 1/16” thick sheets, cut the stabilizer blank from the thicker sheet, and sand using a “thickness sanding jig” to .025”. A typical size 3” x 36” sheet of balsa 1/16” thick that averages 5.0 lb cu ft will weigh 9.0 grams. The stabilizer blank cut from this sheet will weigh 0.5 grams. After sanding to .025” it will weigh .020 grams.

One more trick. It can be difficult to buy a 5.0 lb cu ft sheet of 1/16” c-grain wood. So, if you buy a slightly easier to find 5.5 - 6.0 lb cu ft sheet you can probably find light sections of the sheet (hold it up to a light bulb and look for areas without any dark (heavy) streaks) and cut the stabilizer and fin blanks out of this part of the sheet.

Good luck.

Brian T

[Nathanfrommars]

Nathan,

Good job working on the critical details.

5.0 lb cu ft balsa (c-grain necessary for stiffness) sanded to .025” thick stabilizer will weigh 0.2 grams. Of course, the stabilizer area should be about 15% of the wing area. It is easiest to get low density wood like this in slightly thicker sheets, like 1/16” thick sheets, cut the stabilizer blank from the thicker sheet, and sand using a “thickness sanding jig” to .025”. A typical size 3” x 36” sheet of balsa 1/16” thick that averages 5.0 lb cu ft will weigh 9.0 grams. The stabilizer blank cut from this sheet will weigh 0.5 grams. After sanding to .025” it will weigh .020 grams.

One more trick. It can be difficult to buy a 5.0 lb cu ft sheet of 1/16” c-grain wood. So, if you buy a slightly easier to find 5.5 - 6.0 lb cu ft sheet you can probably find light sections of the sheet (hold it up to a light bulb and look for areas without any dark (heavy) streaks) and cut the stabilizer and fin blanks out of this part of the sheet.

Good luck.

Brian T

Thank you! We are going to try it out.

Nathan

[Nathanfrommars]

How to calculate the area of wing if it has flaps? Including flaps or not?

Thanks,

Nathan