Stage Ignition

[Stewart32]

Is it permited to ignite the sustainer via fuse?

 

[Missileman]

I believe it is permitted (not 100 percent sure, but have read of it being used) however in what context?
I have heard of fusing being used for example where the fuse is lit by the staging charge of the booster motor.
However using a fuse, for example , that is lit at launch, would be a tricky venture as timing would be very dificult and probably inacurate at best.

 

[powderburner]

I have never tried to ignite an upper stage motor using any kind of fuse. Take all the following comments accordingly.

I am not even sure what fuse you would use. Cannon fuse? (that heavily-coated stuff with a little BP up the middle) Jetex fuse? (if it is even still available) What?

It would seem that using a fuse would introduce its own set of risks and unknowns. What holds the fuse securely into the nozzle while the booster is burning? Does the attachment (fuse to nozzle) block or plug the nozzle? Are you sure the fuse will light reliably? Does the fuse have enough thermal energy to reliably light the upper stage motor?

Are you sure you can't just use a regular motor-to-motor setup? Are you trying to get some sort of optimum coasting/delay between stages?

 

[Karl]

Ive gap staged a D12-0 to a D12-5 , and to make sure it staged i shoved 2" of QuickMatch down the nozzle , but i folded the QM to make a tight fit in the nozzle , and made sure it was touching the propellant.
-Karl

 

[shockwaveriderz]

stewart, sure it is.....the fuse can be ignited either by electronic means or by the ejection charge particulate from the booster engine....

see the gap staging thread for additional info

 

[Karl]

If you havent got allready , the Rocketry Handbook by G.L Stine ? Should tell you everything you need to know about rocketry.
Yep , i dont think blackpowder can be ignited electronically , as blackpowder is ignited much more easily than Composite rocket propellant , so electronics wouldnt be required.
Has anyone ever seen a Composite rocket engine , staged to a Black-Powder engine?
-Karl

 

[graylensman]

Originally posted by powderburner
Are you sure you can't just use a regular motor-to-motor setup? Are you trying to get some sort of optimum coasting/delay between stages?

The reason booster motors have a zero-delay is to eliminate coasting time at staging... all the other forces acting on a rocket become more "forceful" when there's no thrust to counter them. So you run the risk of the model arcing over before staging if its heavy at the very least.

 

[jflis]

I've staged composites to composites and composites to BP many times in the past.

I've got several old aerotech booster motors. You use a piece of jetex fuse that goes into a hole in the top of the booster motors (that gets ignited at motor burnout) that then feeds into the nozzle of the sustainer.

I am not aware of any composites that allow for this any more

jim

 

[powderburner]

Originally posted by graylensman
The reason booster motors have a zero-delay is to eliminate coasting time at staging... all the other forces acting on a rocket become more "forceful" when there's no thrust to counter them. So you run the risk of the model arcing over before staging if its heavy at the very least.

By asking my qstn, I was not advocating that any sort of interstage delay system be used. I was trying to figure out why Stewart would not want to use the regular staging system of direct ignition. It is simple, cheap, and quite reliable.

I have seen analyses showing that optimum altitudes (for NAR competition applications) can be obtained through the use of small delays between stages, but this adds a whole 'nother wrinkle. You would have to add electronics, on-board batteries, and separate upper stage ignition, and you would have to assure very high-quality timing of the whole thing to get any of the altitude benefit. It looks like a lot of trouble to go through for only a few extra feet.

 

[Bob Stephenson]

Originally posted by graylensman
The reason booster motors have a zero-delay is to eliminate coasting time at staging... all the other forces acting on a rocket become more "forceful" when there's no thrust to counter them. So you run the risk of the model arcing over before staging if its heavy at the very least.

Whilst keeping the rocket pointed in the right direction when it stages (ie straight up) is extremely important there is another fundamental reason why boosters have zero delay. In order to attain maximum height you want to transfer the maximum momentum to the upper stage/s when they are lit.

Basically the longer you wait the slower the rocket is travelling at staging. The extra height attained through coasting would not make up for the lost momentum...

Gravity is always the greatest enemy for any rocket (but it sure helps you get them back after a good flight )

Cheers

(Evil) Bob