Extending delays in SU motors

I saw Fred Shecter's post on TRF about humidity extending delays in BP motors. If you dump the BP powder in a SU, apply a tiny drop of water to hole (to "humidify" the delay grain), dry external residue, then replace the ejection charge, will this delay the delay? I realize it's probably impossible to calibrate the additional time (if any), but in an altitude shot with a small rocket (think F32) that needs more than a

15 sec. delay, for instance, it won't matter so much in terms of late delay damage.

Anybody done this?

Reply to
slowslide
Loading thread data ...

This won't work.

The humidity-related delay lengthening was in BP motors. The delay grain in BP motors is a slower-burning BP mixture. In APCP motors (like the SU F32 you are talking about), the delay grain is a slower-burning APCP formulation.

Unlike BP, APCP is not water-permeable. In cured form, it's essentially a block of rubber. All you will do is lessen the chance of lighting the BP ejection charge (since there will almost certainly be residual moisture in the "touch hole").

- Rick "Bad idea" Dickinson

Reply to
Rick Dickinson

Take the delay charge out, bond a piece of ICI plastic igniter cord a.k.a. slowburn into the hole, cut it to whatever additional delay you want (1 inch per second) and put the end of the PIC into an ejection charge.

Dead easy.

Chris

Reply to
Chris Eilbeck

I doubt it would work with a composite delay grain; it wouldn't absorb moisture like the BP-based materials in an Estes-style motor.

What might work would be if you could get some fuse with a known burning rate, and set it between the existing delay grain and the ejection powder. (A little blob of powder taped in a bit of baggie around one end; the other end stuck through the touch-hole in the forward bulkhead...)

-dave w

Reply to
David Weinshenker

PolyTech Forum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.