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New Design (Unfinished) - Ram Jet
I had the crazy idea of making a model rocket that (kind of) looks like a ramjet engine. I've got it started but it's not stable yet. I think it needs a TON of noseweight at this point but I'll keep playing with it.
I inset the rear tube with the engine hoping the smoke and flame coming out the back would look more like engine exhaust. I was also thinking of using three canted engines to make it even more spectacular. But at that point I think I needed something like 12 oz of nose weight. I've been playing with body tube sizes and nosecone shapes but nothing seems to help. I think the internal fins would help keep the whole thing stable going up, but I'm not sure whether I believe RockSim as far as stability goes. Also, I'm not quite sure how to shorten the fins in the ring tail - I don't want them going all the way up the nosecone. That would make it difficult for the parachute to deploy. Comments are welcome.
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-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- Dale Marshall, San Antonio Texas NAR #90990 Semroc SAM #083 BAR Since 2008 Enjoying model rocketry since 1977. The Spotted Dragon -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- |
#2
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Quote:
Congratulations! Now you're sounding like one of us... Quote:
I'm not sure you can do this without having some external fins. If you had a gimbaled engine, then a computer would be in charge, but we don't have that. We have to hang it out in the breeze. There may be a compromise 'minimal fin size' that will work, but I think you will still have something visible on the outer surface of the tube...
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Craig McGraw BARCLONE Rocketry -- http://barclone.rocketshoppe.com BARCLONE Blogsite -- http://barclone.wordpress.com BARCLONE Forum -- BARCLONE Forum BARs helping BARs SAM 0044 AMA 352635 |
#3
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Update!
I've changed things around significantly, and added a "skinny" portion near the aft end but I'm not sure how to cover it (I guess a custom transition is in order). The first try with a single 18mm engine only made it to 115 ft and had a horrible DV. So I put in three engines (I'm thinking canted since three won't fit in the body tube I'm using) and after adding a LOT of noseweight it makes it to 330 ft and has an excellent DV. Take a look. I'm going to modify the engine to 24mm next to see what happens.
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-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- Dale Marshall, San Antonio Texas NAR #90990 Semroc SAM #083 BAR Since 2008 Enjoying model rocketry since 1977. The Spotted Dragon -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- |
#4
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Feyd,
Look this revision over and see if it is closer to what you wanted. I'm getting between 460' and 483' on three C6-3 engines, and the Dv numbers are from 16 FPS to 26 FPS. Length: 14.50" Diameter: 3.70" (RT-99) Fin Span: 10.04" Weight: 3.61 oz Model reaches safe flight V on a 36" x 1/8" standard rod. I'm not sure this can be done without having some fin area, and it took quite a bit of tweaking to get this combination to work right. I'm still trying to eliminate the ballast (I hate adding dead mass to a design!). Your idea is a good challenge, Feyd! Thanks for presenting it!
__________________
Craig McGraw BARCLONE Rocketry -- http://barclone.rocketshoppe.com BARCLONE Blogsite -- http://barclone.wordpress.com BARCLONE Forum -- BARCLONE Forum BARs helping BARs SAM 0044 AMA 352635 |
#5
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Thanks, I'll have to play with your model a bit. I was trying to make it look as much as possible like an actual engine. I was thinking the airflow over the internal fins would keep it stable. So I'm not sure RockSim is taking that into account.
__________________
-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- Dale Marshall, San Antonio Texas NAR #90990 Semroc SAM #083 BAR Since 2008 Enjoying model rocketry since 1977. The Spotted Dragon -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- |
#6
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I think it does, but once RockSim is told it has a 'ringfin' component, it gives that more significance than the pylons (or any custom-shape fins) inside. Sometimes, RockSim gives totally bogus numbers. Take a look at the stability margin when you switch from 'Barrowman' to 'RockSim' calculations on the first tab. Barrowman says it's stable...
__________________
Craig McGraw BARCLONE Rocketry -- http://barclone.rocketshoppe.com BARCLONE Blogsite -- http://barclone.wordpress.com BARCLONE Forum -- BARCLONE Forum BARs helping BARs SAM 0044 AMA 352635 |
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