Piston Launchers and higher engine classes

Has anyone successfully used piston launchers for RMS engines in the G/H/I range? Any special considerations other than guidance?
Koen
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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)

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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

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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.
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the elven
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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...

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

No.
What is "just enough"? :)

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Jerry Irvine, Box 1242, Claremont, California 91711 USA
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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.

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I believe it is commonplace for APCP motors as noted by Jerry. It's my understanding that the larger the motor the larger the core. Therefore the longer it takes to pressurize the core's void.
So the 'fraction of a second' is a function of the size of the motor.
As to the effects on a piston launcher, I've never used one or seen one used, but I could see the 'fraction of a second' burn cause the effects detailed below.
Ken Baldwin CAR S825 replace nospam with telus to reply

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I've seen it on FGH, have not flown enuf E's to be sure. I had to learn this in order to take those liftoff shots I do so well (look at zak orions descon entry)

hmmm or designing the piston size to account for it
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Seriously, what problem are you trying to solve with the piston launcher ? It might have been solved another way already.
/ArtU

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there's an excellent article by Scott Johnsgard, Jr. is in Apogee's E-zine Issue #47 (04/15/01) at http://www.apogeerockets.com/education/newsletter47.asp
[ and see other interesting articles in the Apogee archive at http://www.apogeerockets.com/education/newsletter_archive.asp ]
- iz
ArtU wrote:

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G/H/I
?
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Might be as simple as testing something Jerry mentioned on the newsgroup.
Jerry
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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.
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those sound like closed breech launchers to me..... shockie B)

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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.
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