If you choose to build the motor before going to the field, do not install the BP ejection charge until just before you fly it. If you do not fly an assembled motor, it can be kept "on standby" for months if you loosen the closures to take the pressure off of the o-rings, but only if the BP has not been installed. If you try to do this with BP installed, you stand a good chance of some of it working its way between the delay grain and the forward closure. That is not a good thing.

To keep ypu from forgetting to add the BP later, wrap some masking tape around the forward end of the casing as if you are making a thrust ring - that will prevent you from inserting the motor into your rocket. Remove the tape after you have added the BP charge.


Bill

I have had a 29mm Aerotech case loaded with a G64-4 reload.....for over two years now. Never had the nerve to fire it. I think all the BP for the ejection charge is in there, too. Should I dissasemble this thing and start over using fresh BP? Then launch it in something I can afford to lose? I have had my share of 'no ejections' and lost those birds, which is why I was reluctant to use it.
Allen

I keep hearing this advice, but I can't see any evidence for it. Did this come from Gary?

A single use motor uses the same components, O-rings and all. They stay permanently compressed. Of course, it is impossible to loosen them. But I can't see any reason to take the pressure off the o-rings once the motor has been assembled and tightened. The only risk I see is an accidental loosening of the closures, and that loosening would have to be on the order of at least half a turn to be of any significance at all as far as letting BP work so far into the delay well that blowaround would occur. A wrap of tape around each end would serve as a reminder that the motor is ready, a prevention of vibrational loosening, and an indicator if it does gets accidentally loosened.

On five occasions over the past 19 years, I've prepped H and I motors from three weeks to seven months before flights with no consequences, and I've built many hobby line motors days in advance with no problems. Knock on wood, I've never had any anomalies with RMS motors. Granted, I don't fly that many (10-15 a year until 2002, two or three a year since then) but that's still over 100 motors flown, with a large percentage built at least a day in advance.

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Roy
nar12605

If you look at the LMS motors and EMK kits by RCS, they only use a single delay oring, and it's in radial compression around the outside of the delay, which is different than Aerotech hobbyline motors, where all three orings need to be compressed by threading the closures tightly. There might be another oring pre-installed on the fwd closure, but it's in radial compression also.

I am pretty confident this is the same construction used in the AT single use line today, nothing like RMS. In the past, no o-rings were used in AT SU at all, only epoxy.

Attached Files

f27r_2-pk_lms_in_20204.pdf (579.6 KB, 52 views)

There have, indeed, been o-rings in past SUs. In 1989, I cut through a number of spent casings to see what the construction of the motors was like, and since I was using a hand saw (hack saw and razor saw) I was surprised to find the resistance caused by the o-rings.

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Roy
nar12605