I just wanted to get someones opinion on the best ignigters to use, or
modifications that can be made in order to ignight a cluster. My
cluster will consist of a central J350 and two outboard H128's. I want
them to all be lit on the ground simultaneously, and I figure that the
J350 will come up to pressure after the outboards do.
Is there any way to compensate for this by modifying the J350's igniter
or anything like that?
Thanks a lot,
If the J350 has enough thrust to achieve liftoff on its own, then what
you can do is use a G-Wiz LC accelerometer flight computer in the "cluster
mode" (selectable by a jumper on the circuit board), where it fires one
of its pyro outputs when it sees a launch detect.
Ignite the J350 from the ground-based firing system, and use the G-Wiz to
start the outboards when it detects the acceleration from the J350.
Your thinking is a little backwards...
All though you might like to have the J come up to pressure first , most
likely it won't.
I've flown numerous clusters & the smaller motors kick up first because
there is less volume to pressurize. You could use 2 igniters or a double
dipped igniter for the J to ensure that it does light first & just a plain
single dip for the H's.
I think he said that he does expect the J350 will take longer.... so maybe
you reading is a little backwards? :-) Just messing with you, don't get
Also, it is important to know that all you have to do is get the propellant
for all motors lit before the rocket lifts off; they don't all have to come
up to pressure. If the H128's come up and start to lift the rocket, and the
J350's propellant is lit at the top but comes up to pressure as the rocket
is going up the rod/rail, that would be OK. What is NOT ok is that the
igniter gets pulled out before the propellant gets lit.
Your suggestion of 2 igniters in the J is a good one; I think I'll try that
for my next cluster.
Well, so long as the H's have enough thrust to get the rocket stable by the
end of the rail. Anyone see that video of a LOC magnum on 2 rocketflite
motors and a kosdon I500? The smaller motors lit first, the rocket left the
rail, pretty much stopped, and then the I500 kicked in. Someone posted it up
on here a while ago...
nice strip of thermalite in the J might increase your odds but it might be
better to air start those H's for safety's sake. Do this with electronics
or a strip of shrink wrapped sheathed thermalite that has a small unsheathed
portion under the nozzle of the J.
Get a package of Pyrodex 50 caliber, 30 gain pellets (not powder). A 50
cal pellet should fit in the core of an AeroTech 38mm motor. Put one
pellet in the top of the core of the top grain of the J350. Cut a pellet
so that about 1/2 of a pellet fits in the top of the top grain of each
H128s. Use Daveyfire N28F (F, not B, although a B would probably work,
too) igniters. Make sure the Daveyfires touch the pellets. The
Daveyfires will ignite the Pyrodex, which will ignite the propellant. As
long as the pellet ignites you will have a built-in igniter that will
continue to try to ignite the propellant until the pellet is consumed.
I've used this method with AeroTech 38mm, 54mm and 75mm motors and get
instant ignition. In 54mm and larger motors I stick a toothpick into the
smoke grain and CA pellets onto it. (Pyrodex pellets have a hole through
Daveyfire N28F (F not B) igniter and copper thermite for instant