Elastic Launched Glider B

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Re: Elastic Launched Glider B

Postby SOCoach » February 21st, 2015, 11:25 am

My ELG students are 8th grade girls who are working pretty hard at this event, but they get tired of sanding pretty quickly. We are using 1/8 or 3/32 thick balsa for wings at the start and sand them down. Can we start with 1/16 thick balsa and make that work?

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Re: Elastic Launched Glider B

Postby bernard » February 21st, 2015, 12:53 pm

SOCoach wrote:My ELG students are 8th grade girls who are working pretty hard at this event, but they get tired of sanding pretty quickly. We are using 1/8 or 3/32 thick balsa for wings at the start and sand them down. Can we start with 1/16 thick balsa and make that work?

When I did this event for Division C last year, I tried balsa sheets that were 1/32". 1/16" and 3/32" thick. For the thicker sheets, it definitely takes a lot longer to go through (I made a glider just a few days ago with a rather thick sheet since that was all I had left). I think a 1/16" thick sheet would work well, since your wings will likely be much thinner than that (the glider I made a few days ago had a trailing edge of about 2-3 sheets of paper thick). 1/16" is also thick enough so if you want a thicker leading edge it would work well.

If you have 1/8" or 3/32" balsa sheets left and don't want to let them go to waste, you could start with a lower grit sandpaper and once you're close to what you want use a very high grit sandpaper. I've made the mistake of using low grit sandpaper for too long and it has left gashes on my wings which have been hard to even out with high grit.
"One of the ways that I believe people express their appreciation to the rest of humanity is to make something wonderful and put it out there."

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Re: Elastic Launched Glider B

Postby SOCoach » February 21st, 2015, 3:25 pm

Thanks for the advice, I'll try that. I have good students with good intentions, but not enough patience. :)

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Re: Elastic Launched Glider B

Postby jander14indoor » February 22nd, 2015, 9:26 am

Probably just saying this another way, but sanding a glider wing should not be an exercise in patience. We're talking well less than an hour, should be much less.
Either the paper is too fine to start (or possibly dull) or the balsa is to hard (heavy, dense). Starting with 100 grit is probably appropriate, keep the force light. When close, switch to 150 grit, maybe finishing off with 220 grit.
You may also need to stop periodically to knock (vacuum) the dust off the paper so it doesn't clog and stop cutting. Some of the stearate coated or open coat papers might help there.

Make sure you use long sanding blocks to sand evenly. I use a piece of melamine covered shelving cut to 11 inches long by about 2 inches wide for the convex portions. For concave portions you will need some form of shaped block.

Jeff Anderson
Livonia, MI

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Re: Elastic Launched Glider B

Postby bjt4888 » February 22nd, 2015, 10:24 am

SOCoach,
I am 100% in agreement with Jeff Anderson regarding sanding, sandpaper grits and sanding block shape and size. I'll add that my favorite sandpaper for grits 220 through 100 is 3M Sandblaster and my favorite extra fine sandpaper (320 through 600 grit), if you want to use it (not really necessary), is Gator Waterproof.

Also, as I have mentioned before, I have posted various narratives in Hip Pocket Aeronautics Science Olympiad discussion thread describing sanding of a 1/16" sheet wing down to target weight for a 4.0 gram flapper glider (this year, and also narrative for last year's HS event w/ a 3.0 gram glider of smaller span). A wing blank 1/16" thick of 6.0 lb/cu ft wood will weigh about 3.4 grams.

If you are intending to build to the 4.0 gram minimum weight, you will not want to use anything thicker than 1/16" as a starting point for a low-ceiling glider (up to 30-35 ft, or even a little more). Once a 1/16" thick wing blank that weighs 3.4 grams is properly sanded, it will weigh about 2.2 grams.

Brian T.

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Re: Elastic Launched Glider B

Postby SOCoach » February 24th, 2015, 6:30 pm

Thanks for the ideas - Those will be a big help. We will start with 1/16 balsa and go from there.

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Re: Elastic Launched Glider B

Postby tanjil2001 » March 2nd, 2015, 3:34 pm

hello im competing in the science Olympiad and its my schools first year and its happening this week so i have some last minuet questions one question is what is the lip balm test what is the purpose for it and i needa little better understanding of what the flight log is so may i get someone to help me :geek:

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Re: Elastic Launched Glider B

Postby jander14indoor » March 2nd, 2015, 5:50 pm

The lip balm test is a safety test. On launch these gliders can move VERY fast. To keep from having everyone, including the spectators, from having to wear armor, the tips are meant to be blunt. The cap is the objective way to check this. Place it over the tip, you shouldn't be able to touch the bottom of the cap.

The flight log is just a record of every test flight. You have to record certain info on each flight, and pick some data of your own. If you intend to be successful, you should have more data per flight, and more than the 10 minimum flights. The idea behind the requirement to present a flight log is to get across the importance of taking data in science and engineering.

Read back up through this discussion thread and look at last years for more info.

Jeff Anderson
Livonia, MI

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Re: Elastic Launched Glider B

Postby NASA123 » March 4th, 2015, 5:18 pm

Hello everyone!

I am new to Elastic Launched Gliders, and am using the Freedom Flight Models kit. Our flights are EXTREMELY inconsistent, with some arching beautifully at launch and others gliding beautifully across the room (with the same glider). I am pretty sure our launch methods are okay, as we try to be as exact as possible, although we do launch them by hand. We have tried adding weight to the front, to the back (terrible idea, I know, we had nothing else to try), changing the angle of incidence of the wings, and experimenting with launch angles and rubber sizes. I was thinking of adding elevators to the wings to try making the flights more consistent and controllable. Is this a good idea? If so, how big should they be compared to the wings?

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Re: Elastic Launched Glider B

Postby bjt4888 » March 5th, 2015, 9:26 am

NASA123,
Congratulations on constructing an excellent glider! Read my description of trimming a flapper glider here:

http://www.hippocketaeronautics.com/hpa ... ic=16492.0

Be sure to set the center of gravity per the plans for your glider and be sure your flap deflection (the downward curve of the flaps) is set per plans and consistent between the right and left wings. Nothing flexing or moving that shouldn't be moving is important for these gliders. All glue joints should be good. No piece of wood should be too thin or flexible and the tape connection of the pylon to the fuselage should be tight. Flaps should be properly sanded thin to be sure that they are flexible enough. You will see in my description of trimming a flapper that establishing the correct incidence angle of the wing is a key (as the wing is adjustable by removing the tape, adding a shim and retaping. With a properly drooped flap, most flapper gliders require the forward portion of the wing to be angled down slightly (around 1/25" or 1/64" shim). Once all of the above is set, determining the launch inclination angle and bank angle and rubber stretch is all that is left.

Read the thread I have posted the link to above.

Brian T.

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Re: Elastic Launched Glider B

Postby NASA123 » March 5th, 2015, 10:04 am

Thanks bjt4888! This is a huge help!

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Re: Elastic Launched Glider B

Postby wlsguy » March 5th, 2015, 12:48 pm

NASA123 wrote:Hello everyone!

I am new to Elastic Launched Gliders, and am using the Freedom Flight Models kit. Our flights are EXTREMELY inconsistent, with some arching beautifully at launch and others gliding beautifully across the room (with the same glider). I am pretty sure our launch methods are okay, as we try to be as exact as possible, although we do launch them by hand. We have tried adding weight to the front, to the back (terrible idea, I know, we had nothing else to try), changing the angle of incidence of the wings, and experimenting with launch angles and rubber sizes. I was thinking of adding elevators to the wings to try making the flights more consistent and controllable. Is this a good idea? If so, how big should they be compared to the wings?


Definately insuring the trim of your glider is correct is the first step but, since you said you can get good flights and bad flights, this may not be the problem.

It's likely you are not controlling the 3 launch variables (pullback distance, left to right wing tilt, and launch angle).
If these are not controlled (the angles to ~ 5 degrees and the pullback distance to ~ 1cm) your flights will vary.
The more these vary, the more inconsistant your results.

As I once heard Jeff Anderson say;
"....this event is not about building an airplane, it's really about understanding and controlling the different variables. An airplane is just a fun way to do it"

Good Luck,
John Hance

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Re: Elastic Launched Glider B

Postby BananaPirate » March 6th, 2015, 2:12 pm

Hi everyone,
So my partner and I have constructed a few Freedom Flight models now. The build quality is getting a lot better, but we seem to have hit a wall. Our glider sometimes drops a few feet right after transition. After that it flies smoothly, but the time is only around 15 seconds, in a ceiling of at least 25 feet. Is it too heavy? It weighs around 5.1 grams.

Thanks for the help!

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Re: Elastic Launched Glider B

Postby jander14indoor » March 7th, 2015, 5:41 am

Yes, too heavy. Weight is critical in the flying event. Lift MUST equal weight, not a rule, physics. The only way to increase lift (assuming good design and proper trim) is to fly FASTER, which for a glider means you must descend faster. This increases drag meaning you have to descend still faster.

You are 25% over weight, lose that and you should immediately push the time up around 5 seconds.

Then work on the transition. Dropping 2 ft in a 25 ft gym is 10% of your time. Another couple of seconds.

Jeff Anderson
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Re: Elastic Launched Glider B

Postby BananaPirate » March 7th, 2015, 7:44 pm

Ok, thanks for the help!


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