Elastic Launched Glider C

Smithy0013
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Re: Elastic Launched Glider C

Postby Smithy0013 » February 7th, 2014, 7:51 pm

So whats up with all the really Low aspect ratios I keep seeing. They do suprisingly well which is not what i expected and theyre much more common this year than last

bjt4888
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Re: Elastic Launched Glider C

Postby bjt4888 » February 8th, 2014, 8:58 am

smithy0013,
Reducing aspect ratio is a common design idea used to increase performance in span limited model airplane classes with weight minimums. This was not so much a factor last year as there was no weight minimum. AMA CLG classes have a required maximum chord of 3", but SO does not. Increased chord on SO gliders means increased wing area. If this can be accomplished without increasing weight above the 3 gram minimum, you have reduced wing loading. See plans of AMA classes like: P-30, F1-D and Limited Penny Plane. These are rubber band classes, but the concept is highlighted. All of the successful designs in these classes are low aspect ratio compared to similar classes without span maximums and weight minimums.

Bjt4888

science8
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Re: Elastic Launched Glider C

Postby science8 » February 8th, 2014, 8:26 pm

This is for a friend. I was wondering where I could order the scholastic kit and the Stan buddenbaum kit and if both are adjusted to the new rules. Links would be appreciated

calgoddard
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Re: Elastic Launched Glider C

Postby calgoddard » February 10th, 2014, 3:20 pm

The optimum aspect ratio for the wing of a catapult launched glider (CLG) depends on the ceiling height and the class of CLG being flown. Minimum wing loading becomes more important as ceiling height decreases.

For very slow flying indoor rubber powered propeller airplanes, such as Limited Penny Planes (LPPs), the wing chord can be as much as 30% of the wing span. They have built up wings covered with delicate plastic film. The leading edge (LE) and trailing edge (TE) of the wing of an LPP are normally straight (perpendicular to the longitudinal axis of the motor stick) except for some straight taper on the LE of the upwardly canted tip sections.

A CLG typically has a solid balsa wing so that it can be launched at over 50 mph. The LE of the wing of a CLG often has a continuous curve from tip to tip. Look at published plans available on the Internet that show aspect ratios that are appropriate for small CLGs, such as the plan for the Feather Shooter.

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Re: Elastic Launched Glider C

Postby calgoddard » February 10th, 2014, 3:43 pm

At our regionals last year (2013) about a half dozen teams flew canard CLGs. I was quite surprised to see this as under the 2013 Elastic Launched Glider (ELG) rules they received no bonus. I was further surprised that they generally flew well. As best I can recall the top flight time for any of these canard CLGs was around 18 seconds. As already noted, the optimum incidence for the stabilizer of a canard CLG and the optimum center of gravity for a canard CLG are quite different from those of a traditional CLG, i.e. one with the main wing in front of the stabilizer. Further confounding me was the fact that these canard CLGs appeared to have white foam stabilizers and main wings. Observers are strictly segregated from competitors at our regionals and no pictures can be taken, except of you own team, so I was hampered in my subsequent attempts to investigate the design. I was very impressed by the students' ingenuity.

baker
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Re: Elastic Launched Glider C

Postby baker » February 10th, 2014, 5:04 pm

This is for a friend. I was wondering where I could order the scholastic kit and the Stan buddenbaum kit and if both are adjusted to the new rules. Links would be appreciated
Found this for Scholastic, Chuck Markos
http://www.amaglider.com/?p=view&a=cmar ... r-kit-2014

Let us know how it flies if you get it. Not sure if anybody has tried it yet...

bjt4888
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Re: Elastic Launched Glider C

Postby bjt4888 » February 12th, 2014, 3:46 pm

I would like to thank calgoddard for clarifying my response regarding aspect ratio. I agree that my post relates to low ceiling gliders. And, of course, my mention of lightweight rubber classes like Limited Pennyplane was with regards to aspect ratio design analysis only. This does not mean that I was recommending copying the exact aspect ratio of a Pennyplane. And, Calgoddard is of course correct in stating that I was not recommending use of the pennyplane structure or rectangular wing planform. With a 3.0 gram minimum this year, the thin balsa wing is probably the best place to start. Although, for the very adventurous, take a look at composite foam core wing construction in the F1N glider thread on Hip Pocket Aero. I do believe that it is instructive to look at dissimilar classes with similar rule limitations to glean possible avenues of creative design. For instance, the most interesting and informative postings I have found on the web related to canard design are written by Don Stackhouse relating to large outdoor radio control gliders. I found a couple very interesting tidbits regarding dutch roll and foreplane volume ratio in Don's posts.

I agree with calgoddard too that the Feather Shooter is an excellent wing planform design. Other elements of the design like the method of creating the wing airfoil by reflex sanding undercamber and a wing highpoint thickness of 0.038" out of a 1/8" thick sheet might be quite challenging for a beginner. My favorite AMA design is the current national champion glider by Bill Gowen called the WIF7. Bill posted a plan for a simplified version of this glider that met the 2013 Science Olympiad rules on the Hip Pocket Aeronautics forum last year.

I do definitely believe that the event designers have created an excellent opportunity for creative solutions this year by adding a weight minimum of 3.0 grams. For low ceiling competition (less than about 50'), many modifications of AMA style designs should be considered, including: airfoil, planform, aspect ratio, etc. See Bill Gowen's AMA category II CLG national record holder plan also posted in the Hip Pocket Aeronautics forum. Have fun and keep building and testing and solve the canard design!

bjt4888

ethancorvids
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Re: Elastic Launched Glider C

Postby ethancorvids » February 21st, 2014, 9:30 am

Does anyone know roughly what times will get a medal for regional and state? What should I use as my goal?

calgoddard
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Re: Elastic Launched Glider C

Postby calgoddard » February 21st, 2014, 11:55 am

Does anyone know roughly what times will get a medal for regional and state? What should I use as my goal?
The answer largely depends on the ceiling height at the competition venue.

ethancorvids
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Re: Elastic Launched Glider C

Postby ethancorvids » February 21st, 2014, 5:58 pm

Does anyone know roughly what times will get a medal for regional and state? What should I use as my goal?
The answer largely depends on the ceiling height at the competition venue.
O.k. Can you give examples? What would you expect for a 20ft ceiling? What about a 30ft ceiling?
Thanks.


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