piston launchers

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JJSR

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I'm wondering how many times you use/clean your piston launchers?

I usually bring three with me to compete with, because they soot up and don't slide well after a launch. In between events I take them apart knock out the soot and sand the piston and tube some.

While getting rockets ready this morning for a competition in two weeks, I had the idea to sprinkle some baby powder in the tubes which seems to have a lubricating affect on the piston. will this work in the long run or will the powder make it worst?
 
I'm wondering how many times you use/clean your piston launchers?

I usually bring three with me to compete with, because they soot up and don't slide well after a launch. In between events I take them apart knock out the soot and sand the piston and tube some.

While getting rockets ready this morning for a competition in two weeks, I had the idea to sprinkle some baby powder in the tubes which seems to have a lubricating affect on the piston. will this work in the long run or will the powder make it worst?

I've found that my best piston head has a relatively loose fit and that I can use the piston tubes many times before replacement. The only part of the tube that routinely fouls is the top end right next to the engine. If that happens, I just cut the tube an inch or two shorter. I start off with a full 34" length, so for duration events, it doesn't affect the result all that much.
 
Sometimes it helps a stubborn piston. I do the same - usually get 3-4 flights out of a piston tube. I make my pistons from coupler stock, with a balsa plug in one end, coated with CA and sanded smooth. I often put a bit of epoxy in the balsa plugged end to protect it from the exhaust.

I don't know what kind of pistons you are using, but I usually just use the CHAD (Cheap and Dirty) pistons - a length of BT-5 or 20, a couple glued in one end, and a piston inserted into the other. A wooden dowel completes the piston assembly - I just fold the igniter wires back on the motor and push the piston tube over the motor and wires. Fold the remainder of the wires back down and you are ready to go. When cleaning the tubes (sandpaper wrapped around a dowel), I blow out the residue, put the cleaned piston in and blow into the business end - if it is clean enough, the piston will whack into the stop with a loud "thunk".

The pistons usually last several years - if I sand down through the CA, I just give it another soak, let dry and sand smooth again.

Oh, and I usually fly the models out of the club's Medalist tower using the piston only for the boost. I've never tried launching a model using only the piston.
 
I used to try to squeeze every bit of use out of the tubes, but now I just replace if they get gnarly. I've got 3-4 launches out of a piston tube in the past, but now only 1, maybe 2. A sticking piston tube is a real bummer when you're counting on a flight that just has to qualify. A fresh tube removes one more variable that could scrub the flight. Tubes are cheap. I might keep them for some other use if I need to. The pistons themselves last much longer.
 
You can buy a gun cleaning kit that has wire brushes as well as small square pads that can be pushed up and down inside the tube. I find that they were extremely well to keep the crud out. In any event, it's usually the top of the tube that suffers the most damage and can be cut off for reuse.
 
One other little tip on using pistons - I put a wrap of silver Mylar tape around the rocket end of the piston tube. It both helps to quickly tell me which end is which, and also keeps the end of the tube from deforming after the first use. As mentioned in a previous post, if the tube gets too badly messed up , you can cut a couple inches off and reapply some new tape. If you don't have any silver tape, I got mine at Blick's.

Also, be sure to write your name on both you tubes and your dowels - in the heat of the moment of launch and tracking where the rocket landed, I rarely get mine back immediately. It saves confusion over what belongs to whom if there are several piston tubes built up at the pad.
 
You can also roll your own piston tubes out of fiberglass. I've done that for FAI competitions. They end up being extremely lightweight and clean up with water. I've actually brought a small spray bottle to the field and could blast any crud out of the tube with a shot of water. Three or four wraps of .75oz fiberglass makes a usable tube, though you can go with a few more wraps for more durability.

I've made carbon fiber tubes also, and they're pretty much indestructible. However, they are pretty darn heavy and probably affect the flight of the rocket too much.
 
It's probably a nice way to get started. Someone showed me how to make cardboard pistons years ago and I placed a large order for tubes and centering rings from BMS and made dozens of them. The Sunward kit seems nice that it comes with a base. Supporting the piston from down below can get difficult.
 
Ugh! I've been out of the "loop" so long that I do't know where to get started!

What is the largest motor/diameter you have use with a piston? Does it just work with black powder motors?
 
I've used up to a D motor with a piston at a NARAM competition. I'm not familiar with anyone using a piston with a composite motor, but in theory, it might work. The slower huffing and puffing start of a composite motor might pop it off the piston before full ignition occurs. There'd have to be some sort of way to exhaust that initial pressure prior to launch.
 
Ugh! I've been out of the "loop" so long that I do't know where to get started!

What is the largest motor/diameter you have use with a piston? Does it just work with black powder motors?

Pistons will work with composite motors, but I've never seen it done reliably. I've used a piston launcher with every Estes motor 24mm or smaller. It would probably work with the 29mm motors too, but there are better motor options available at that point.

The easiest way to get started with pistons is to use a spent Estes or Quest engine casing. Cover the nozzle with a piece of masking tape, then pour a few grams of 15 minute epoxy behind the nozzle from the top end. Let cure. Cut shorter if desired. Use a 1/2" dowel from home depot or your LHS as a support rod. Sharpen one end with a pocket knife and drive it into the ground for support. (Alternately, use your choice of launch pad base.) Slide your piston tube over the support, then put the piston head on top of the dowel.

Here's an excellent article on pistons by Chan Stevens from the March/April 2009 edition of Sport Rocketry.
https://www.nar.org/wp-content/uploads/2014/05/Piston-Launchers-Stevens.pdf
 
Chan shared that technique with me prior to him writing the article. A generous guy who has always shared his techniques with others.

What I ended up doing was ordering a hundred small balsa disks from BMS. They probably were a custom order and I'm not sure if Bill is still doing those. But if you don't need that many, then simply cut out a bunch of small squares of balsa and glue them to the top of the coupler piece. Once dried, it takes about a minute with a piece of sandpaper to round off the square balsa so that it is circular in shape and glued on the top of the coupler. It takes awhile to soak the couplers with CA and sand them smooth. But what you end up with are nice lightweight pistons that actually last a long time.
 
Hi all, I have access to a CNC lathe and whipped up a number of aluminum piston heads in 13, 18, and 24mm sizes. The 10.5mm pistons are already heading to the internats team with Steve Kristal. These are basically the same piston heads that Pat B had made up a few years back, without the set screw to hold them on the piston rod. The through hole is 0.271" in diameter and fits 1/4 inch brass tubing fairly well -- a 1/4 inch dowel with a bit of tape. They are 1.2 inches long.

If anyone is interested, contact me at [email protected]

Mikey
 
Do you use those "as-is" or do you put a wrap of Teflon tape on them?

How long do they last?

i have my own design for aluminum piston heads, and I'm still using the ones I made over four years ago. Just wipe them down with a wet wipe when you're done for the day.
 
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