Ditch the piston?

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derpderpmd

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Literally just finished my PML Quicksilver and foolishly attached the lug rails with screws which of course prevent the piston from working freely. I could remove the foreward one with a lot of effort, but can I just ditch the piston and convert it to just a standard burrito wrap method? Any drawbacks or things to take into consideration? This newbie thanks you in advance!
 

timbucktoo

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You say lug rails, are you referring to the brass tube they include with kit or are you using rail buttons? I have epoxied the launch lugs in the past. If you are using rail buttons, I would ditch the piston.
 

Rocketclar

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Too bad, I like piston ejection and even made a FG one for my L3 project. If you ditch the piston, just make sure that your recovery stuff (burrito) doesn't get hung up on the back of the nuts for the rail buttons.
 

jimn

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I have several PML kits where I used the piston and rail buttons. The piston just has to be above the top button.
 

K'Tesh

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If possible, I'd convert the piston into a 1/2 moon baffle.
 

OZRoc

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Remove the screw(s) from the top linear rail lug and epoxy it back on. Tape over the hole on the inside, after sanding the inside hole blemish, and use the hole as an extra "key" for the epoxy. May be a bit of finessing with the piston movement but all should be good.

.... Just re-read the post. Looks like you epoxied as well as screwed? If you can remove the screws or drill them out just augment with epoxy as above.
Cheers
 

Voyager1

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Remove the screw(s) from the top linear rail lug and epoxy it back on. Tape over the hole on the inside, after sanding the inside hole blemish, and use the hole as an extra "key" for the epoxy. May be a bit of finessing with the piston movement but all should be good.

.... Just re-read the post. Looks like you epoxied as well as screwed? If you can remove the screws or drill them out just augment with epoxy as above.
Cheers
I used this technique on a couple of builds when I couldn’t install the forward rail lug below the piston position and it was very successful. The lugs never came off!
 

Mike Haberer

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Ditch the piston. I had a PML Bull Puppy where the piston bound do to not cleaning it and it became a lawn dart. Since the piston uses a tube coupler, convert it into a baffle. You can notch out bulkheads a little to slide over the rail lug. It won't matter at all in terms of the ejection charge getting to the laundry (you can epoxy over the forward bulkhead to plug that opening) and you don't need to use a burrito, or wadding, or dog barf. I put baffles in any airframe from BT-50 to 4" if the airframe is long enough to handle it.
 

JimJarvis50

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Nothing like a piston thread! Oh, maybe a glue thread? Anyway, I highly recommend pistons. I have them in most of my rockets and my belief is that they significantly increase the chances of getting the main out. I don't like loose pistons though. Sometimes, the PML pistons are a little loose.

If you don't use the piston, then make sure that whatever is above the separation point has enough mass to pull out the chute. Most of the time, it is that mass, and not the BP, that ejects the chute. Even though the kit has a payload section, consider adding a little mass to it to make sure the chute gets pulled.

Jim
 

dr wogz

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also depends on where you fly. The tube (plastic) and the piston (Phenolic) expand / contract at different rates. So, flying in cold weather (freezing or below) = piston seazed. flying in summer (+25°C) = piston is super loose.

I say ditch. I did with mine after 2 or 3 flights..
 

Rocketclar

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Also, if you use piston ejection, you do need to really clean out the tube after every flight so that the piston will slide easily. I also talc the piston(s) before use. This is really important in cold weather with QT. With most of your HP rockets, you should have a small vent hole in the various sections to help minimize the bottled up atmospheric pressure from popping the rocket apart when you don't want it to. That's one reason for shear pins. The vent hole(s) also help with pushing the piston into place.
 

Funkworks

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A picture of the screw tips inside the airframe would be interesting.
 
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