Piston Launchers and higher engine classes

I heard/read from someplace/somebody that the increased pressurization from a piston launcher causes it to "chuff" ? I thought I also heard or read that somebody had solved that problem? If this is so, what causes the "chuffing"....some form of pressure mixmatch? shockie B)

That depends on propellant formulation. Original errortech motors were low metals and that certainly was the case. I would think a WL motor would tend to do that less.

Jerry

Koen O. Loeven hath so eloquently decared:

AP motors often burn for a fraction of a second before coming up to pressure. I could see the motor inflating and extending the piston without producing liftoff velocity, then heading off in some unpredictable direction. A vented piston, with just enough leakage to release that preliminary burn, might work, providing you could calculate (or guesstimate) how much venting and how much friction to provide.

Seriously, what problem are you trying to solve with the piston launcher ? It might have been solved another way already.

/ArtU

there's an excellent article by Scott Johnsgard, Jr. is in Apogee's E-zine Issue #47 (04/15/01) at

- iz

ArtU wrote:

that explains the purpose of a piston launcher, yes.

I am asking what purpose this modeler needs to solve ? The use of the piston as explained by apogee works for small light cardboard models mostly in NAR altitude events if the model is of optimim weight.

If Koen wishes to solve say a HRP altitude record, other means might be more elegent, then using a piston on APCP.

BTW, I had an inverted empty 24mm aerotech "e" engine as the "form" for my cheap and dirty tower launcher for B PD. I simply glued 3 18" Spruce spars to the side of the empty engine, quick tower for T-50 sized models.

Anyway, I swear, that the B engine firing INTO the nossle of the empty "E" motor does something, even if that something is just better noise, cause It really moves out and roars. At a NAR Meet they said, THAT Was a B motor ?

/ArtU

Might be as simple as testing something Jerry mentioned on the newsgroup.

Jerry

and that would be ? curious minds are inquiring to know.

/ArtU

He/someone was talking about poplugs and I suggested a piston (surrogate for launcher) and also suggested a tower.

Then it morphed to composites and the discussion was historical comments about composites being chuffy with pistons. I posted that higher metals propellants were less chuffy and someone else posted that venting the piston helps which is true.

So the executive summary is a zero volume piston (dowel on bottom with tube as moving element, with a small hole perhaps 1/8"+ in it and dowels on the top of the piston tube as a tower and the piston tube itself can have lugs on a rod.

Use an endburner with higher than normal metals or a short core motor with high metals such was WL or WS or FS and PRAY.

If it fails? Stick your head between your legs and kiss your ass goodbye :)

I've watched this thread for awhile now and think I may have some experience that is relevant. First, I've launched several flippy fin rockets using a 5 foot long section of ABS pipe that is closed at one end with a screw-in plug. The rocket is loaded into the tube nose first from the open breech. the igniter must be at least 18" long. wadding is stuffed around the base of the rocket to help protect it from the heat of the exhaust. the igniter leads are then threaded through a hole in the screw cap. The cap is then secured. With the tube locked in the upright position, the rocket is launched. The tube acts as a gun barrel and the wadding serves to help confine the exhaust. Needless to say, it rips out of the tube. I've used G55s. F102s, and an assortment of other 24mm motors ranging from E-G and all have worked perfectly.

The second method I've used uses the same tube but this time, it's 4" in ID. The fins of the rocket are fixed rater than folding and a seal is maintained using Styrofoam spacers that act like a sabot. Ignition is done the same way and the results are the same as well except that acceleration out of the tube is faster due to the lower weight of the rocket and the much better seal at the breech. Not exactly a piston launcher but the result is very much the same.

Higher altitude by harnessing the initial exhaust just as with the estes class events.

Koen

those sound like closed breech launchers to me..... shockie B)

Is this commonplace for ALL APCP motors? Or is it common for the larger JJKLM motors as opposed to the smaller EFGH composite motors? Or is it a function of the propellant type? Can "painting the walls" help with the initial ignition ?

I could see the motor inflating and extending the piston without

Interesting design problem... create a movable psiton head attachment assembly that can vent and not vent at different times...

Function of propellant type and IGNITER TYPE. Most consumer motors have unoptimized through the nozzle igniters.

No.

What is "just enough"? :)

You don't want to "paint the walls". Your igniter will throw hot slag onto the walls of the grain. This starts it burning. If the walls are coated, the coating gets hit with hot slag. The coating burns and then lights the grain. Sand the core of your grains with 80 grit and use a hot igniter that throws a lot of slag. This will give you the best results.

This is just what I wanted to do for a project, so thanks for the post RJ.

It might help Koen with his ideas as well.

I was figuring using a centering ring on the bottom split into three tri-sections each with a foam sabot attached to it.

Must looks "T I T S" flying out the top with the Sabot flying away to the sides !

I can't wait !

also, those flippies, are they from aero-con ? I had been thinking about getting one of those to play with this winter, yes the dual stager.

/ArtU

R. J.s post seems to make real sense to me.

Aerocon is the source. I think you idea using the centering ring is on target. Might I suggest making the ring out of corrugated cardboard coated with epoxy? it's easy to work with, light and readily available.

Kewl !

/ArtU