Quantcast

igniting 2nd stage BP motor

The Rocketry Forum

Help Support The Rocketry Forum:

rocketsonly

Well-Known Member
Joined
Apr 7, 2004
Messages
877
Reaction score
0
Hey, say you have a 2 stage rocket. The first stage is a composite reloadable motor. So you ignite that easily. Would there be an ejection charge in order to eject the 1st stage off? Then how do you ignite the 2nd stage if it's a BP motor?
-Matthew
 

sandman

Well-Known Member
Joined
Jan 18, 2009
Messages
10,468
Reaction score
5
Composite to black powder staging can only be done with electronics.

That's it...no other alternatives!

Sorry.

sandman
 

powderburner

Well-Known Member
Joined
Jan 18, 2009
Messages
7,356
Reaction score
4
You would not need an ejection charge from the first stage to separate the upper stage----as soon as the upr stg motor fires up, the stages will come apart. This is the normal method for staging BP-to-BP. The booster motor (lower stage) does not have an ejection charge. The last bit of propellant in the booster motor burns down to a thin wall and then bursts forward, pushed by the pressure of the booster combustion chamber. The thin wall fractures into bits which (usually) go into the nozzle of the upper stage motor and ignite it. All this takes place while the two stages are still hooked together. After the upr stg fires up, the motor exhaust pressurizes the inter-stage volume and pops the booster loose.
 

rocketsonly

Well-Known Member
Joined
Apr 7, 2004
Messages
877
Reaction score
0
The thin wall fractures into bits which (usually) go into the nozzle of the upper stage motor and ignite it.
Usually? How reliable is this method?

-Matthew
 

loopy

Well-Known Member
Joined
Dec 13, 2009
Messages
4,570
Reaction score
1
Originally posted by rocketsonly
Usually? How reliable is this method?

-Matthew
For BP to BP, it's pretty reliable - especially if you're using motors of the same diameter, i.e. C6-0 to C6-7 or B6-6, and the motors are taped together with the ejection end of the booster taped to the nozzle end of the sustainer. Darn clost to 100% in that case. It becomes slightly less reliable if "gap staging" (staging the motors while they're not butted up against each other), or staging different diameter motors. If staging 24 to 18 mm (D12-0 to C6-7, for example), you may want to drill a few vent holes in the rocket in the area of the staging. This will keep the booster ejection from overpressurizing the area and popping the booster off before the sustainer ignites. I've done this on my Commanche 3 with great success on full bore D12-0, C6-0, C6-7 flights. Only one failure in 5 attempts.

Loopy
 

powderburner

Well-Known Member
Joined
Jan 18, 2009
Messages
7,356
Reaction score
4
My experience has been that direct staging works better. That may only be a fluke due to the variabilities of trying to use a small database for statistics.

For dozens of flights (50-60?) using direct staging (top of booster in contact with base of upper stage motor casing, casings taped together) I have not had an in-flight failure-to-stage. The only failure I remember was a booster nozzle blow-out on the launch pad.

I have less experience at gap staging (motors separated by a few inches, held together by prayer) and have had two instances of failure-to-stage. This of course resulted in two worthless piles of rocket remnants. But I have only launched this configuration (a gap-staged rocket, not the piles of parts) probably 15 or 20 times.
 

shockwaveriderz

Well-Known Member
Joined
May 25, 2002
Messages
2,466
Reaction score
1
There was a thread close to this topic just recently that has a lot of good information:

http://www.rocketryforum.com/showthread.php?s=&threadid=7432

and another thread from way back:

http://www.rocketryforum.com/showthread.php?s=&threadid=853

when in doubt, use the search function, it is your friend.....


pss....Both these threads mention the use of a mercury switch....I just want the potential reader to know there are 2 kinds of mercury switches: there is the one you want to use and the one you don't want to use. The one you don't want to use is also called a mercury tilt switch. This is because the mercury will make contact with the contacts at small angles of attack from the vertical......NOT good in rockets....actually they make numerous mercury tilt swicthes with differing angles of attack form say 5 degrees to maybe 15 degrees....obviously this is not what you want...You can tell a mercury tilt switch from a regular mercury switch by looking at its contacts... the mercury tilt switch will have different length contacts while the mercury switch, the one that you do want, the contacts are the same length

You can get mercury switches here:

http://www.kelvin.com/

http://www.kelvin.com/Merchant2/mer...uct_Code=270062&Product_Count=&Category_Code=
 

Loki

Well-Known Member
Joined
Apr 17, 2009
Messages
279
Reaction score
0
Originally posted by sandman
Composite to black powder staging can only be done with electronics.

That's it...no other alternatives!

Sorry.

sandman
Yes there is! Thermalite. See my post in another thread on this topic.
 

BlueNinja

Well-Known Member
Joined
Jan 18, 2009
Messages
2,690
Reaction score
1
I would think a D12-18mm would be more reliable because teh 18mm fits nicely inside the 24mm motor...
 
Top