Elastic Launched Glider C

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Re: Elastic Launched Glider C

Post by illusionist » December 2nd, 2012, 2:03 pm

Speaking of launching...

How do you avoid hitting the launch handle? Having a 0-0 (the ideal?) incidence would mean that no lift is produced, which would mean that the glider travels in a straight line and is destined to collide with the top of the handle, right? Also, the rubber is pulling the glider toward the top of the handle, so that creates a direct path of collision...

My handle is a wooden dowel with a screw on top, sticking up about 1/4", which the rubber is looped around.
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Re: Elastic Launched Glider C

Post by jander14indoor » December 2nd, 2012, 7:59 pm

0-0 does NOT mean no lift. Remember, incidence is against an arbitrary reference, it is NOT the angle of attack. Also, the 0 incidence angle is not in general the zero lift angle, though its not uncommon either. In addition, the hook is probably below the center of gravity and will pull the nose up giving a positive angle of attack.

If you look on the AMA glider site you will find a picture of a typical launch, the glider is generally well above the end of the launcher.

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Re: Elastic Launched Glider C

Post by chalker7 » December 3rd, 2012, 6:47 am

314chocolate wrote: If you are truely staying to the same ratios, wouldn't the effect of the increased wing area be negated by the increased weight? But if you don't scale up the wood when you do the model, that would throw the calculations off.
Ah, so here's the confusion. When you perform a scale model simulation, you have to make sure EVERYTHING is at a reduced scale to ensure comparable and scalable results. For gliders this would mean wing area, wood thickness, mass, ceiling height, launch height and launch speed (at minimum.) The last 5 are incredibly hard (or maybe impossible) to control for, but of particular importance to this conversation is wood thickness. Wood only comes in standard thicknesses from the hobby store and unless you are very good at careful sanding, it's tough to get it to a precise other thickness. This means that when scaled up, you are unlikely to actually scale everything up proportionally.
You're probably better off just going with a design that is based off of an established design (like the simple simon,) scaled up by area to close to the maximum but not by wood size. That design is pretty overbuilt and the wood sizes listed should be able to handle the extra forces that come from a bigger model.
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Re: Elastic Launched Glider C

Post by theging » December 3rd, 2012, 9:30 am

jander14indoor wrote:0-0 does NOT mean no lift. Remember, incidence is against an arbitrary reference, it is NOT the angle of attack. Also, the 0 incidence angle is not in general the zero lift angle, though its not uncommon either. In addition, the hook is probably below the center of gravity and will pull the nose up giving a positive angle of attack.

If you look on the AMA glider site you will find a picture of a typical launch, the glider is generally well above the end of the launcher.

Jeff Anderson
Livonia, MI
The event I referenced (the wing exploding into a dozen pieces) was the only time an event like that has happened to me. However, my hook was a good 15 centimeters in front of my center of gravity, as it is with almost all of my planes. I have no idea what would have caused that even though most of my planes are similar and this has never happened before. Perhaps my hand slipped or something...

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Re: Elastic Launched Glider C

Post by fanjiatian » December 5th, 2012, 5:40 pm

No matter what I do, the wing of my glider (Simple Simon) keeps hitting the launching handle. I've shattered a few gliders in this way.
I've tried tilting the glider away, but that doesn't seem to work.
Any tips?

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Re: Elastic Launched Glider C

Post by wlsguy » December 6th, 2012, 4:54 am

fanjiatian wrote:No matter what I do, the wing of my glider (Simple Simon) keeps hitting the launching handle. I've shattered a few gliders in this way.
I've tried tilting the glider away, but that doesn't seem to work.
Any tips?
For those people having trouble with the wing shearing at launch.
It is possible to hit the launch handle but, from our team's experience, it is normally caused by wing stresses.
The high speed stress caused the wing to shear off.
When we watch the video of a NG launch, the wing never came close to the handle.

Now, if you are sure you are actually hitting the handle, try something different.
Check out the handle in the Trial event rules. It is more of a launch pad and reduces the number of handle strikes.
http://soinc.org/sites/default/files/up ... tglide.pdf

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Re: Elastic Launched Glider C

Post by chalker7 » December 6th, 2012, 6:26 am

wlsguy wrote: Now, if you are sure you are actually hitting the handle, try something different.
Check out the handle in the Trial event rules. It is more of a launch pad and reduces the number of handle strikes.
http://soinc.org/sites/default/files/up ... tglide.pdf
I agree with wisguy, but we could be wrong depending on the configuration of your launch handle. What does it look like, where is the rubber band attached, etc? A picture would be most helpful.
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Re: Elastic Launched Glider C

Post by wlsguy » December 6th, 2012, 7:00 am

chalker7 wrote: ...... we could be wrong depending on the configuration of your launch handle. What does it look like, where is the rubber band attached, etc? A picture would be most helpful.
I guess I assumed (bad move on my part) the OP was using a typical AMA launch handle. If this is not the case, it could change everything.
I agree, Chalker7's request for a picture of the launch handle would be most helpful.

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Re: Elastic Launched Glider C

Post by fanjiatian » December 7th, 2012, 6:02 pm

http://i47.tinypic.com/a02g2.jpg[/IMG]
http://i45.tinypic.com/359fyia.jpg[/img]

Definitely not a typical AMA handle, I couldn't find any links showing how to build a handle.
There's a hook on the end of the handle with the rubber band, that end points away from me when I launch my glider.

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Re: Elastic Launched Glider C

Post by retired1 » December 7th, 2012, 6:53 pm

I have kits from 3 respected glider people and all just use a wooden dowel with a 1/4 to 3/8 saw cut in one end. Tie a knot in the band forming a loop, put the loop over the rod and then thread the band back thru the slit.
Some people just tie a knot around the stick, but I do not like that idea. Some people will just tie a couple of knots that are large enough that they will not pull back thru the slit. Both legs of the band go in the slit.
Someone used a tiny screw in the top of the dowel and hooked the band onto that. I do not care for that idea either, but it should work better than your hook. The catapult in the first picture is too short. Your glider will have to accelerate extremely fast or it will not reach a 35' ceiling. Hard on gliders.
A visual example is Kirk's videos of constructing the SO Lit'l Sweep glider at this site, near the bottom.

Good luck.

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