PML Piston tightness

About how tight should the PML piston (sliding bulkhead) for optimum operation?

Thanks
Dan

eastvolt said:

About how tight should the PML piston (sliding bulkhead) for optimum operation?

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LOOSE. The piston should easily fall out of the rocket when turned upside-down. Assuming that you are using a QT airframe, keep in mind that QT shrinks in cold temps & expands in warm temps. Depending on where you live/fly your rockets, you might want to put your airframe in the fridge or even freezer to simulate the minimum temp that you'll fly your rocket in. Once your piston is loose in the cooled/chilled airframe, then it'll work at all warmed temps.

HTH,

Our rule of thumb for SLI: If you turn the BT vertical and it slides out, it is good.

I've always followed the rule that if you can physically blow it out from the back using your own lung power, you are good to go. I second the advice of putting the airframe in as cold an environment as possible and then making the piston slide in that. Then it will be good to go without any maintenance needs.

I do suggest takiing some 220 grit to it and wiping off the ejection residue every 3rd or 4th flight though.

SpartaChris said:

I've always followed the rule that if you can physically blow it out from the back using your own lung power, you are good to go.

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I'm glad to see I'm not the only person who tests the ejection system that way. arty: People (especially the wife) usually look at me funny when I do that.

(How do you like the new collection of smilies we have available?)

I do that for piston ejection systems only.. Most other things I fly are too large diameter, and contrart to popular belief, my mouth just isn't that big!

And I like the new smileys.. Some of them crack me up.. :rock:

Thanks for all the replies - that helps a lot!

And good tip about the temperature. That quantum tubing is Type I PVC which has a pretty nasty coefficient of expansion.

Dan