PML piston chipped

[astrowolf67]

Just wondering, the piston on my son's PML Tiny Pterodactyl got chipped yesterday. It's a small chip, about a half inch up, quater inch wide on the bottom shoulder. It appears that it will still function as intended, but for safety, I figure I'd better ask. Is it still safe to use? The only thing I can figure, is the top of the body hit it during deployment, as there's no paint missing anywhere else.

 

[wyldbill]

Should be OK. I'd sand the rough edges off and make sure it slides OK. This is usually caused by too large a BP charge according to PML. See Pg. 57 of their FAQ

 

[Justin Horne]

I had one chip too. However, it was caused by a charge that was VERY early... On my intruder too, first flight.. The piston strap zippered the quantum tube all the way down to the forward certering ring! I salvaged the fins, and will rebuild it... Nice rocket, I recommend it.. Tond of places to make fillets though!!

Justin

 

[Stymye]

I've been thinking about a pml kit , but I repeatedly read things about brittleness,shrinkage,pistons hanging...

I don't want to have to overbuild the kit just to keep it from breaking..
or worry about a piston hanging and destroying the entire rocket

or am I just seeing one side more often
and there are actually alot of PML kits that have launched/recovered sucessfully more than a dozen times without something breaking?

 

[Justin Horne]

I'd say go for it! The kits build really well, and are very strong. In my post, the rocket had launched on an I285 and was still moving very fast...However, in the future, I will use glassed phenolic versus the quantum, although it is very good.

As for the piston sticking, if using Quantum, put the tube in the freezer. Then, try to use the piston. Sand the piston so it works smoothly. The piston is now perfect for the smallest the tube will almost certainly ever be, and will work just fine for all other temps.

I have another PML kit that is great.. With how many that are sold, it's no wonder you here how many break. They really are very good kits, in my opinion.

Justin Horne

 

[astrowolf67]

Stymye, I'm with Justin, go for it. This is the first damage to the Tiny Ptero, and it's nothing that under/over building could have helped, just one of those times where everything collided during deployment. And, it's still fully functional. The PML quantum kits are some of the most durable I've seen, and prepping them is a breeze if you use the piston. The piston can be left out, with no major modification, and you can use a nomex pad in place of it easily.

Todd J's blue and orange Pterodactyl Jr came in ballistic, and slammed into a paved road down at Ardmore on his first L1 attempt. It only ruined the nose, and cracked one fin fillet.

 

[lalligood]

You can easily reinforce the coupler by double-walling the piston. That means...

1) Order a new piston (coupler) sleeve.
2) When it arrives, cut it length-wise so that the radius shrinks (& overlaps) when you squeeze it.
3) Test fit inside the existing piston. Mark the overlap.
4) Trim off the overlap so that the edges butt against each other when you slide back into the piston.
5) Epoxy into place.

That's it!

 

[Johnnie]

Todd J's blue and orange Pterodactyl Jr came in ballistic, and slammed into a paved road down at Ardmore on his first L1 attempt. It only ruined the nose, and cracked one fin fillet.

Todd J has come along way since then, as he will go for "3" at the 7/10/04 launch in Manchester...

I own one PML/Quantum kit, a 4" Endeavor, and I used the piston as a bulkhead stop in the booster...it is glued in permanently. There is no motor ejection, as this bird uses electronic dual deploy.

I have seen the piston work, and I have seen it blow through the parachute on ejection, and fall to the ground in a tangled mess. When the phenolic swells from humidity, it will bring a 4" AMRAAM down and fence post it...with no damage to the rocket I might add.

Buy one, they are of the highest quality...but get out your wallet.

 

[Stymye]

thanks for the info guys
overall it sounds like PML kits are pretty tough..I guess I need to save up and go for it.!