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.
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.
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
Reply to
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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