Rocket twisting around the line

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BlackLotus
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Location: Boonies, Nevada

Rocket twisting around the line

Post by BlackLotus » Wed Mar 05, 2008 10:01 pm

My son is largely finished with his space derby ship and has just started painting it. It is very light so I thought I would give it a test in the basement on just two rubber bands (make sure it wasn't going to tear apart.)

I put up some fishing line that I had in the tackle box (new stuff) and hooked it up. With 100 winds, the thing regularly starts off by twisting up and over the fishing line. This slows it down a great amount. When it does this, the thing only makes it 10 - 15 yards before running out of steam. When it somehow resists the urge to circle the string, it takes off and runs a good 20 yards, very quickly.

I'm wondering if the type of line could be the problem, or the fact that I am starting it by moving my finger away from the prop? Any ideas?



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GravityRacer
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Re: Rocket twisting around the line

Post by GravityRacer » Sat Mar 22, 2008 7:57 am

Maybe this is too late to help you...

You are observing the reaction torque of the propeller accelerating to speed. This means your rocket is REALLY light. That's one trick to winning this race. I sanded the nose over a little at a time to an angle opposite the direction of spiralling around the line so that I counteracted the reaction torque. The propeller ends up pointing off line.

What I have done for ADULT space derby is carve a kit until I could see light in several places. I lightened, feathered and polished the propeller, and made the hanger a space frame. I even drilled through the middle of the rod that holds the rubber bands at the back. The whole thing weighs 9 grams, including the rubber bands.

Hope this helps.



BlackLotus
Master Pine Head
Master Pine Head
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Joined: Tue Jan 15, 2008 10:02 am
Location: Boonies, Nevada

Re: Rocket twisting around the line

Post by BlackLotus » Sat Mar 22, 2008 12:29 pm

I suspect you are correct. After the boy put on sanding sealer, two coats of white, two coats of blue and his stickers, it no longer turned around the line. I suspected something like the weight. After all that paint it still ended up 17.7g with prop, 3 rubber bands, dowel and everything.



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