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Timers for sustainer ignition

I'm getting ready to work on a Launch Pad plan-pak of a Standard RIM-67 booster for their Standard AGM-78 kit. The plans describe how to construct an air-start circuit involving a piston within one of the booster motor thrust blocks. A piston is held forward by a D12-0 motor before and during thrust. Upon burnout, the back pressure from the motor forces it to the rear, allowing the piston to be pushed back by the spring of a switch which allows the switch to close, thus completing a circuit and igniting the sustainer motor. A very nice solution, but .......

After having seen how much gunk gets deposited on the inside of the body tube I'm more than a little nervous about the long-term viability of this device, especially since there is really no way to get in there and clean things out. My thought is to switch over to a timer based solution, specifically the PerfectFlite MT3G miniTimer3 with g-switch. The timer and battery would be positioned at the nose of the sustainer, which is where the plans call for the battery placement anyway. I'd be able to do away with the mechanical switch, the wiring running between the booster and sustainer, and could use an additional motor with an ejection charge in the booster (the booster is a 3xD12-x cluster; 2 -0's and 1 -3 to deploy the booster parachute). The idea of using more than one motor to deploy the parachute is appealing to me; I'd hate to have only 2 of the 3 motors light and end up with neither of them being able to deploy the chute!

I'd very much appreciate hearing from anyone with experience in this area, either for this specific application (the TLP kit/plan-pak) or for the basic concept in general.

TIA,

-Scott

Reply to
Scott Oliver
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I built the staging switch described in the instructions. I knew that it would gum up, but mine did so after two flights. The third flight resulted in a lawn dart for the sustainer. I rebuilt the switch with one of my designs, and it worked great the first flight. The second flight it did not.

I recommend the electronic timer, of a G-Wiz altimeter.

John

Reply to
John Stein

Scott, perfect flite timer 3's are great for air starting and one of it's designed reasons to being. I flew my airstart last month with it.

The "G" switch needs .5 seconds of 2 gs to fire

Art

Reply to
ArtU

Hi Scott, I don't have the TLP kit & I use composite motors, but I also use a timer in the sustainer and it has worked fine every time. This method eliminates some potential problems, and you'll be very happy with it. BTW, as was stated in this thread the PerfectFlite MT3G does take .5 sec. after lift-off to arm, but I seem to remember the timer automatically compensates for this so there is no need to set it for a .5 sec. shorter timing period. I guess that's why the timer range begins at .6 seconds. Larry Lobdell Jr.

Reply to
Larry Lobdell, Jr.

I'd be just as worried about 2 of 3 lighting and end up with neither being able to ignite the sustainer. Unless it has altimeter deployment as well.

Bob Kaplow NAR # 18L TRA # "Impeach the TRA BoD" >>> To reply, remove the TRABoD!

Reply to
Bob Kaplow

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