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And another thing, igniting with motors

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DynaSoar

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The "flash pan" idea for starting many clustered motors gave me an idea. Might it be possible to start a large engine by pointing a small engine with igniter up the nozzle of the larger?
 

wwattles

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It would, but then what happens to the smaller motor? It would still be burning (presumably) and would have to go somewhere (out) so the main motor can burn properly. Now you've got an unguided rocket motor, still burning, falling/shooting from the rocket. Not a safe combo, if you ask me!

WW
 

edwardw

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What kind of motor are you talking about? Composite, BP? I know for my bigger EX grains (75mm and 98mm) I throw a 29mm grain inside the very top and light that. It really gets going and shoots the flame down the core and has great ignition.

Edward
 

BlueNinja

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If you were using an AP motor, it wouldn't work. 2 reasons.

a)AP needs heat and pressure to burn, unlike BP. This is because there is a gap between the AP and the combustion, if that gap is too small it will CATO too big it will chuff.
b)If you light an AP (most AP is core burning, not totally but it's not an end-burner either) motor at the bottom, it will still have cold air in the top that needs to be pushed out. Until this cold air is pushed out, it will chuff.


Blue
 

Ryan S.

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actually it would work and has, a guy wrote an aritcle about it in an HPR magazine a year ago or so. He used an A to ignite a 1939. Essentially he put the thing way up inside and ignited it. All the heat ignited the M. I think the chunk of cardboard vaporized

The fact that AP has a diffusion flame doesnt really matter in this situation. But if it did, that would actually work to your advantage since the little motor would pressurize the core faster.

You really need to stick the motor inside the bigger motor though, unless your smaler motor has sparks then you could prusumable fire it upwards and ignite the bigger motor at the top. This is kinda how the spaceshuttle ignites its outboard SRBs There is a thing at the top that blasts sparks down the core.
 

edwardw

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I personally would be worried about having that A motor in the core. What if it became stuck or plugged the nozzle for a second...you could have a CATO right there.

Edward
 

solrules

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Some hybrids use cut up 18/24mm reloads as starter grains to burn through the nitrous fill hose as well as start the fuel burning.

As edwardw said, large motors use small grains as staters, for example a P motor ignitor for the Black Brant II Project is pretty complex.
 

DynaSoar

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Originally posted by wwattles
It would, but then what happens to the smaller motor? It would still be burning (presumably) and would have to go somewhere (out) so the main motor can burn properly. Now you've got an unguided rocket motor, still burning, falling/shooting from the rocket. Not a safe combo, if you ask me!

WW
That would be a rather dumb design.

I was thinking of an engine tube with a small base holding the starting engine nozzle up sitting on the pad, and the big bird lowered down until it's sitting on the starter.
 

Todd Knight

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I have been away for a few days but I wanted to post on this. The article was in ER, I believe, by Bruce Lee. The gist of the article concerned instant starts on larger, in this case M-1315, clusters. He uses a small 1/4A booster motor. He drilled out the delay/smoke grain and inserted the motor in reverse and attached an e-match. This acted like a end burner with no nozzle. Basically it is the Cessaroni pellet idea applied to an AT motor. He used this successfully in his Bomb Pop rocket with 2 m-1315s on a couple of different flights.

This is a very good article for people thinking about a larger cluster design that could be unstable if all the motors are not lit off the pad. For single motor flights I still recomend the boosted igniter with some BT propellant, Quickbust or a dipped (Iginterman). Maybe not instant on, but it works consistantly and may not create any warranty issues if something goes wrong.
 

rocwizard

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WEdge bailed out on that comlex ignitor metioned on his site for the BB2. After hearing about how well the thermite ignitors worked in the Liberty project, he's going with those. more can be read in another thread. Now that's instant on!:D You have to be careful not to use to much of the mix or it will happily cato your motor. About 1 gram of it per 1000ns of motor you are igniting. From the tests that Wedge was doing about a 100 yards from the flightline, you could feel a small concussion from it, so there are alot of gases and heat being produced very quickly that instantly bring your motor up to operating pressure.
 
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