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Author Topic: What about cat launch?  (Read 1698 times)
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hermit
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« on: February 20, 2008, 10:34:39 PM »

I think I'd like to try something a little simpler before I foray into towliners and such, so what about catapult launched? First off I guess I'd need some kind of plan, a little advice about some basics, and then spring!
The first questions that come to mind are- Lightest possible wood for wings. yes? A hard piece for the fuse, yes? I would think very little decalage? What size for catapult rubber? Only a start.

Doug
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Sundance12
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« Reply #1 on: February 20, 2008, 11:33:09 PM »

Hi Doug:

I will try to find a few designs for cat launch gliders from my library and send you a plan.

Bruce
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hermit
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« Reply #2 on: February 28, 2008, 08:25:03 PM »

After cutting some sheet for the Jenny, I wound up with a piece of pretty light 1/16 that was really unusable, so I made up a little 8" cat launch glider this morning. Didn't take a pic sorry, and now it might be too late cause it's hanging off a wire at the top of light standard! Anyway, it was great fun trying to get the thing to do something good, a few loops, a few spiral dives, even a few good launch and transition to glide flights. Certainly different than powered flight. A hoot really! Twang! Thar she goes!

So here's the question. Anybody got some general tips about these things? Incidence? dihedral? moment arm length? Are stab and fin areas about the same as for a powered model? Angle of launch? Balance point? I may get it back yet, got it out of the Elm tree once, and seemed to making some progress with a few real nice glides after transition.

Doug
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« Reply #3 on: February 29, 2008, 12:11:26 AM »

Doug,

 I'll send you plans for the Sweepette 8 when I get a chance. The moments on a CLG are much different than on a rubber model. For any model between 6 and 12" span, I usually start with .5 deg incidence, 1/64" left rudder offset, and 1/16" washin in the left wing inboard panel. And maybe a touch of washout in the wingtips if I want a really hot flight pattern. The washout will actually make some CLG's nose over slightly from a vertical launch, making it easier to get them to fall off to the left and transition. And I usually set the CG around 40% MAC. Stab should be 20-30% of the wing area, rudder as small as you can get it and not have dutch rolling. For the small ones, I seal the wings with CA to stiffen them up and waterproof them. Otherwise, it's easy to dissentigrate the wings on a full launch. And the noise from such an event is something you'll never forget. Then again, the buzzing whistle of a rocket glider that's a touch overpowered is pretty unforgettable, too.
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hermit
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« Reply #4 on: February 29, 2008, 11:47:15 AM »

Thanks Josh. The smallness of the glider was more from the size of sheet I had than anything. Bigger might be better huh?

Doug
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« Reply #5 on: February 29, 2008, 04:18:01 PM »

Bigger might be better huh?

Nah. The little ones are a little more sensitive, but I get more fun out of them and find that it takes a lot less time to finish one. And they don't break as easily in the event of a crash. And with the small ones, you can hold onto the extended tailboom without sacrificing stretch distance. Larger ones require the stab to be on a platform so you can hold the model under the wing so as to be able to stretch the catapult band farther. And I hope that somehow that made sense... Embarrassed
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« Reply #6 on: March 02, 2008, 04:44:50 PM »

I don't know what the turn around time is on getting plans uploaded, but I just submitted the Sweepette 8 plans to the plans repository. I just finished a new one this afternoon and decided to use hard balsa for the fuse. I'm still not entirely sold on the idea, but it seems reasonably durable and is incredibly light. This one floats unlike any example of this design I've yet built. Come to think of it, I've now built 6 of them. Unfortunately only 3 are still in existence, one of which was given away. I guess I need to build more of them.
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hermit
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« Reply #7 on: March 02, 2008, 05:12:01 PM »

Thanks Josh, I'll watch for it.
Doug
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« Reply #8 on: March 02, 2008, 10:24:56 PM »

Ok, the plan is now available. And have a look at the latest one. Chose to make the fuse from hard balsa instead of bass wood, something that I once considered to be total stupidity. It seems to handle the launch very well, though, and results in an incredible weight savings. I did some night flying this evening after church using the glow of the street lights. The wind was negligible, so drift wasn't a concern. I put in about 20 flights, 4 of which went past the minute mark, an impressive performance for such a small model. Except for a few tweaking flights, the model did not fail to break the 50 second mark throughout the flying session. I reckon a second one will need to be built soon. This one might not stay around for long.

So I say all that to say this: built it, you'll like it!
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