Elastic Launched Glider C

bjt4888
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Re: Elastic Launched Glider C

Postby bjt4888 » June 17th, 2013, 9:17 am

Paragraph 5 should read "...Richard Peterson based designs..."

Brian Turnbull
AMA 77545 (and 342672)

calgoddard
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Re: Elastic Launched Glider C

Postby calgoddard » June 17th, 2013, 10:05 am

Potential damage to gliders from a free-standing launch device is a red herring. Such damage is extremley unlikely to occur. Students that design and perfect free-standing launch devices for indoor balsa gliders, such as the winners of the ELG event at the 2013 SciOly Nationals, should not be penalized by stifling their engineering creativity. Our regionals are the largest in the country and last year there was only one such device in the ELG event and it caused no problems for any competitor whatsoever, during practice or during the official competition. The SciOly ELG event should not be a mirror image of the AMA catapult glider event. Free-standing launch devices help competitors safely and successfully address the challenges of practicing in one ceiling height and competiting in a different ceiling height through careful collection and analysis of launch data.

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Re: Elastic Launched Glider C

Postby erikb » June 19th, 2013, 11:41 am

In addition to leaving the official flight count at two, I would suggest one new rule to require the launch device to be a hand-held piece of wood (or other non-metallic material) of 6” maximum length with a 7” maximum length rubber loop attached to one end. The purpose of this suggestion is not to make the event more similar to the AMA event, but to limit the possibility of large launch devices damaging co-competitior’s gliders during practice sessions.
Here is the take from one of those teams with a large floor standing launcher.

In our state the kids get all the settings they needed to fly any ceiling height (as long as the diameter of the glider circle does not change) days in advance. So in other words. They would trim to an approximate bunt height of the ceiling then use the device to gather the roll, pitch and band pull needed to compete for a range of heights above and below the estimated height given by the event supervisors. They then used that data the day of the competition to compete. The kids had all the data they needed to put a glider right next to the ceiling with an amazing drop in just a few minutes at the regional and the state meet.

At nationals they could not, since the difference of lift due to the air density was too great and they had to adjust to the point the data they gathered was useless.

However, for any team in the same altitude and approximate humidity they could use that data and compete with little time needed for trimming. That means any team from either coast could prepare days in advance and be competitive for nationals next year in florida, with just a few minutes of trim to adjust for temperature and humidity.

So while it did not work as planned for us at nationals, during the state competitions it did.

As for the hand held AMA sticks. With us, the majority of the events the kids competed in were AMA. They are just as efficient with the stick as the catapult. However, the stick is not a precise skill but a skill of knowledge, expertise and intuition. More importantly it would be very hard to get more then gross estimations of pitch, roll and turn. Data would be an estimation at best.

No matter how much it frustrates me, Science O is not AMA. AMA is the perfect flight, in perfect conditions with hours to prepare. If it was an AMA event at nationals this year, the kids would have been pushing 30 second flights in that room. With Science O, you get what you get, go for it.

At least with the catapult they can use scientific principles to get close enough. And then it comes down to who is the most prepared team.

So for Science O, not only is the catapult desirable, i will argue that it is exactly what a team needs to be doing for a scientific event.
Last edited by erikb on August 25th, 2013, 7:19 am, edited 1 time in total.
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arooj1a2b3c
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Re: Elastic Launched Glider C

Postby arooj1a2b3c » August 24th, 2013, 10:08 am

I don't know if this has been covered before, but how does the effect of having dihedral only at the wing tips differ from a plane with dihedral at the center of the wings and the wing tips?

erikb
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Re: Elastic Launched Glider C

Postby erikb » August 25th, 2013, 7:15 am

I don't know if this has been covered before, but how does the effect of having dihedral only at the wing tips differ from a plane with dihedral at the center of the wings and the wing tips?
Dihedrals for full wings help with stability. They prevent rolling and sliping. The larger the Dihedral the better the stability. (flat being no dihedral) However they reduce lift and add just a smidgen of drag.

So the object is to find the right Dihedral for the wings you are using that allows the glider to transition well but not drop faster because of the Dihedral.

Wiglets, or the edges of the wing reduce drag by blocking the air from slipping over the tip to the low pressure area on top of the wing. Reducing the drag by reducing the air swirl on the tip of the wing.

Not a lot of designs for duration gliders have winglets because there is such a small amount of drag due to tip vortexes. The gliders are moving very slowly (or should be). In addition, there is a saying and i believe it. "Don't add weight to reduce drag." breaking the wing and gluing it at the tips will add weight.

Polyhedral wings are broken in the middle or closer to the edges but, not at the tips. They are a compromise that does not loose as much lift but does not give as much stability. You see a lot of these designs in the unlimited class where the wings can be longer and the added weight of the glue joint is negligible to performance.
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Poudre High School, Fort Collins CO.


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