#21
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Wellll...let me measure it real quick....OK...heres a quick sketch...
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Gerald Wallace...BAR in Ky. BoRocks Rocketry Systems jonrocket.com "An armed society is a polite society." - Robert Anson Heinlein "Its a tale, told by an idiot, full of sound and fury, signifying nothing" - MacBeth |
#22
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And I see I got the rings "close". All I did was match the ring location to the simulated shroud where they would touch.
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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 |
#23
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Thanks for checking it for me. However, I'm curious... what engines did you simulate it with? I was intending to build it for 18mm... but I can see that the lower mass of 13mm engines might contribute positively to the stability.
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NAR # 115523 Once upon a better day... SAM #0076 My site: http://rocketry.gonnerman.org |
#24
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Now I have not put the components on a scale but bear with me for a second here... If your bird is a T-20 using 18mm motors the difference in stability vice a 13mm motor in a T-20 tube should be negligible. Now...assuming friction fit...For the 18mm version your gonna have the motor and motor block. For a 13mm version (still using a T-20) your not only gonna have the 13mm motor and motor block, your also gonna have 2 centering rings and a motor tube. I think the weight difference will be very small with a minimal effect on stability. I have an 18mm version around here somewhere...I just can't find the freakin' thing. Let me just grab the scale instead of guessing.... OK...13mm Estes A10 + 2 CR0520 + motor tube = .3oz 18mm Estes A8 + motor block = .6oz Well....more difference than I expected but I believe .3oz is negligible in a bird this stable. Tell ya what...I'll find out the easy way tomorrow afternoon...I'll just throw one together and let er' rip. Bo
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Gerald Wallace...BAR in Ky. BoRocks Rocketry Systems jonrocket.com "An armed society is a polite society." - Robert Anson Heinlein "Its a tale, told by an idiot, full of sound and fury, signifying nothing" - MacBeth |
#25
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I just revised the Spike (Solo's Nail) plan, adjusting the centering ring sizes to match the shroud diameter at those locations. See attached... Motors are the A10-3T and A3-4T; the A3 is the better motor overall with a Dv of 8 FPS. Margin with the A10 is 1.56, and with the A3 is 1.04. The shroud could be tweaked a bit more to get a higher margin.
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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 |
#26
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Hmm. Honestly, if it's that close, I'd just throw a few grams of noseweight in and call it good.
Thanks!
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NAR # 115523 Once upon a better day... SAM #0076 My site: http://rocketry.gonnerman.org |
#27
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Bumping an old, old thread to show off my just-finished version of Bohica's Dead Ringer. I built it with an 18mm motor mount, because something down in my reptilian brain refused to believe it'd go far on a 13mm motor; reptilian brain is probably wrong as usual, but it wouldn't shut up so 18mm it was.
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Rich Holmes Camillus, NY Secretary / newsletter editor Syracuse Rocket Club http://richsrockets.wordpress.com |
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