Rocket lengths
#1
Posted 01 December 2005 - 03:43 PM
I am brand new to this forum as you can proberly tell, so bear with me. My interest at the moment is BP rockets, small and large. The amount of information available through these pages is excellent if you are prepared to look.
One piece of information I don't seem to be able to find, even though I have read virtually all threads, is the LENGTH rockets should be.
As an example, is there an optimum length of the tube for a 2 and 4 oz rocket? How long should the core be if a core burner? How long should the core be?
I have made a few with different tube lengths with various degrees of sucsess, but it would be good to standardise things.
Any help would be apreciated
#2
Posted 01 December 2005 - 05:59 PM
Casing lenght: 10 Tubes ID's, for example 4oz. has and ID of 1/2" so the casing lenght is 5"
Core lenght: 7 ID's
That's basicly it.
#3
Posted 01 December 2005 - 06:48 PM
Some general specs
Casing lenght: 10 Tubes ID's, for example 4oz. has and ID of 1/2" so the casing lenght is 5"
Core lenght: 7 ID's
That's basicly it.
Cheers,
That is exactly what I needed. Great site by the way.
#4
Posted 02 December 2005 - 03:30 AM
Some general specs
Casing lenght: 10 Tubes ID's, for example 4oz. has and ID of 1/2" so the casing lenght is 5"
Core lenght: 7 ID's
That's basicly it.
I'd like to add; "Amateur Rocketry" book says the core distance to the delay is equal to the distance to the inside of the tube wall. I suppose that means the 'burn-out' is all at once and doesnt end-burn for a period. Although, maybe you want it to end-burn for a while... As always, there is only ONE answer.
Edited by GBthriller, 02 December 2005 - 03:32 AM.
#5
Posted 02 December 2005 - 10:17 AM
There will be some "end burning" but it gives next to no thrust to the rocket especially one carrying a substantial payload. The actual core of the motor is gone in probably 1 to 1.5 seconds in a 1# rocket. After that it is merely delay til the passfire is hit. This is why you can switch compositions above the core to say, a glitter formula. My favorite for this is Winokur 39 as it locks in nicely. D1 will work decently as well. This adds a very nice tailed effect which varies from the charcoal tail given off during ascent. This delay comp is only added after the solid charge of rocket propellant is pressed above the top of the core. It pays to mark your drifts once you figure out where you want these changes to take place. Drill through the clay top plug and into the delay to set your timing.
#6
Posted 02 December 2005 - 11:21 AM
#7
Posted 02 December 2005 - 11:30 AM
#8
Posted 03 December 2005 - 04:17 PM
#9
Posted 04 December 2005 - 12:18 PM
#10
Posted 04 December 2005 - 01:12 PM
2oz Stick-3/16" Round dowel, 18" long (bp)
4oz Stick-1/4" Square, 24" long (whistles)
8oz Stick-3/8" Square, 36" Long (bp)
1# Stick is 1/2" Square, 36"-40" Long (bp)
All sticks are clear pine which yields a nice balance of strength/weight and is either free or cheap. Square sticks have proven better for guidance. The round sticks on the 2oz seem to not matter. After firing many dozens of these I've "not yet" had one go errant. The fact is that they are so fast they tend to go straight up with not much arcing involved. They are also never tasked so much as to slow them down a whole lot.
I only bother to balance the 2oz and 4 oz motors. The larger motors there is no need and it would be detrimental to do so. Consider a 36" .5" square stick attached to a 1# motor. There is typically 4" of stick contacting the case thus leaving 32" in free air. Try to balance a rocket with a header that weighs only 300 grams. You would need to; A) add a ton of weight to the end of the stick B) use a much heavier (thicker) stick or C) a much longer stick. Why take away from the rockets capability? I used to try to balance all my rockets until I was told not to bother by someone who knows quite well. Too, eventually it was impossible and thus it was abandoned on the bigger sizes. The small rockets that may carry 15-50 grams? Sure, balance them but only within reason. If your motor is worthy then there is little need. You will just be wasting lift capacity on a stick with more potential energy on its way back down.
Edited by Maineiac, 05 December 2005 - 02:05 AM.
#11
Posted 06 December 2005 - 06:33 PM
#12
Posted 15 December 2005 - 10:39 PM
i think it was 1/2 the ID, but i can't remember.
thanks, i'm making up some new tooling at the weekend, and i want it to be decent.
#13
Posted 15 December 2005 - 11:07 PM
#14
Posted 16 December 2005 - 03:51 PM
Your recollection is correct. 1/2 the tube ID is the traditional nozzle size.
ok thanks, just wanted to make sure.
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