Mike, all good questions. To some degree there is I bit of personal preference involved in when the air-starts go and how. The thing you want to do is take the most important safety factors of the flight and work on those first. For instance, there is no way you can go wrong if you use one igniter on the ground to fire the L motor, if the L has enough power to fly the rocket on it’s own (which it sounds like that is the case). Think of it as launching a normal single motor rocket, you can use any igniter you want in the L motor and it can take all the time in the world to fire if it needs and when it does go, it will go straight up since it is a single motor.

Since you have the luxury of onboard electronics for air-starting, take advantage of it. This is when the personal preference comes in. You can use the launch detection mode (liftoff) to fire a pair of the J motors or all four. The launch detection mode is like firing the motors on the ground, typically, the motors running off of launch detection ignite before the rocket leaves the rail. You could fire a pair at launch detection (liftoff) and another pair later, either before, during or after the first pair or the L motor burns out. Whatever you choose, you can be creative with it as long as the air-starts happen while the rocket is still moving and pointed up. Again, the most important thing is that you already have the L motor up to pressure before any of the J motors fire so even if only one J motor fires, you are more then likely still going to have a very safe flight and you won’t damage the rocket.

As far as igniters in the J motor, use the looped fuse over the head of an e-match method that we talked about before on your other air-start. Since you are hooking to a timer, you want to use an e-match for its reliability and sensitivity. Take about an inch or two of thermalite fuse and fold it in the middle, tape the soldered head of the e-match to prevent any shorting against the fuse (thermalite fuse has metal wire on the outside), make sure to leave the pyrogen on the e-match still exposed. Tape both ends of the fuse to the e-match just below the head of the e-match so that there is a small gap between the head of the e-match and the fuse. Dip the head of the e-match and the fuse in some pyrogen, not o much, just enough to lightly coat everything. When it comes time to instilling these into the motors you will have to do it at the pad since you will need to take the forward end of the motor apart to install the air-start igniters.

Take the front end of the motor apart so that the top of the upper grain is exposed. Slide the leads down through the nozzle, you are putting the igniter in backwards. Use a sliver of a toothpick (not much, just enough to hold it in place) to stick through the top of the igniter (between the little gap that you left between the head of the e-match and the fuse). The sliver will need to be long enough so that you can rest it horizontally on top of the upper grain and it will not be able to slide far enough to drop out. Put the motor back together properly and install the motors in the rocket then hook up the air-start igniter leads to your timer in the method you choose to fire them. Hook them up in parallel and make sure your timer is OFF when hooking them up. Just remember that through this whole process you are installing igniters in motors that are not in a rocket or on a rail, so be very careful and keep unnecessary people away.

The sliver of wood is there to hold the igniter in the top of the motor under G loading.

Art

Question: 5.... This will be My first apogee (drogue) ejection with
electronics. Any suggestions? I have Missile Works and Perfect Flite.

Do it just like you do your main deployments now. Charge size may very but for the most part it is the same. Ground test if you can, use redundant charges if you can. Since this is a flight that could see positive G’s then negative G’s through out motors firing and shutting down, I would use shear pins in both main and drogue.

Art

Excellant advice from Art. The CTI motors are consistently easy to light with the supplied ignitors and a little help inside doesn't hurt for airstarts. Adam Boggs and Jason Chamberlin have both flown the L730. And the answer to #35 - I'd go ahead and do that if I were you.

Question: 2... Does the L730 ignite fast?

the smaller motors come up to pressure faster, smaller area to pressurize.

Question: 3... Any special considerations in getting them to light
all at one time?
(such as extra long leads to keep motors connected
to power as long as possible)(Adding a little help to the end of the
match on the L)

If this is not a two stage then the length of the igniter only maters when installing it and that it makes it all the way to the top if it is a CTI and in the center or at the top of the top grain on any other motor.
I would have the electronics light the Js at some point
after liftoff.

Question: 4.... If air starting the Js. What is suggested as the number of seconds after liftoff?

you want to make sure that the rocket does not lose much speed before lighting the air starts to keep a nice straight flight.

Also if your going for as much altitude as you can get, waiting longer to start air starts is more efficient. Still you have to take in consideration of what James said. If you wait to long your rocket will start going horizontal, and going horizontal that fast after your J's are done burning will end with extremely bad zippering.

Hey Mike,

The CTI L730 does light pretty fast. I have flown it twice in a 13 pound rocket with great results, both flights over 10k.

I second Joe, I would do that if I were you.

Jason Chamberlin

After flying the Delta II back in 2004 I would go with starting the central motor (assuming it can safely lift the rocket) and then lighting the other motors via onboard electronics. We did the Delta II reverse, and the 6 on the ground (CTI Pro38) and the M on the ground also. The 6 Pro38's lifted the rocket about 6", then the M kicked in. Looking back it would have been nice to light the M, have it lift the rocket and then have a breakwire light the Pro38's. That way you are already moving and getting stable when you have the other motors kick in.

As for igniters, Art has it down. That method will work very well - an e-match is the way to go on that - low current and reliable.

Edward