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Model Forum / General / Rockets / December 2003Piston 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 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) > Has anyone successfully used piston launchers for RMS engines in the G/H/I > range? Any special considerations other than guidance? > > Koen > I heard/read from someplace/somebody that the increased pressurization from > a piston launcher causes it to "chuff" ? 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 > I thought I also heard or read > that somebody had solved that problem? If this is so, what causes the [quoted text clipped - 5 lines] > > > > Koen  SignatureJerry Irvine, Box 1242, Claremont, California 91711 USA Opinion, the whole thing. <mail to:01rocket@gte.net> Please bring common sense back to rocketry administration. Produce then publish. http://www.usrockets.com My articles valuable? Donate at iKobo.com c/o my email. Koen O. Loeven hath so eloquently decared: > Has anyone successfully used piston launchers for RMS engines in the G/H/I > range? Any special considerations other than guidance? > > Koen 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. Signature.. the elven we were there before they were > AP motors often burn for a fraction of a second before coming up to > pressure. 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 > 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. Interesting design problem... create a movable psiton head attachment assembly that can vent and not vent at different times... > > AP motors often burn for a fraction of a second before coming up to > > pressure. > > 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? Function of propellant type and IGNITER TYPE. Most consumer motors have unoptimized through the nozzle igniters. > Can "painting the walls" help with the initial ignition ? No. > 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 What is "just enough"? :) > > preliminary burn, might work, providing you could calculate (or > > guesstimate) how much venting and how much friction to provide. > > Interesting design problem... create a movable psiton head attachment > assembly that can vent and not vent at different times... SignatureJerry Irvine, Box 1242, Claremont, California 91711 USA Opinion, the whole thing. <mail to:01rocket@gte.net> Please bring common sense back to rocketry administration. Produce then publish. http://www.usrockets.com My articles valuable? Donate at iKobo.com c/o my email. 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. > > AP motors often burn for a fraction of a second before coming up to > > pressure. [quoted text clipped - 16 lines] > > the elven > > we were there before they were 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 > > AP motors often burn for a fraction of a second before coming up to > > pressure. [quoted text clipped - 12 lines] > Interesting design problem... create a movable psiton head attachment > assembly that can vent and not vent at different times... > > AP motors often burn for a fraction of a second before coming up to > > pressure. [quoted text clipped - 3 lines] > function of the propellant type? > Can "painting the walls" help with the initial ignition ? 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) > 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. hmmm or designing the piston size to account for it > Has anyone successfully used piston launchers for RMS engines in the G/H/I > range? Any special considerations other than guidance? Seriously, what problem are you trying to solve with the piston launcher ? It might have been solved another way already. /ArtU > Koen 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 >>Has anyone successfully used piston launchers for RMS engines in the G/H/I >>range? Any special considerations other than guidance? > 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 http://www.apogeerockets.com/education/newsletter47.asp 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 > [ and see other interesting articles in the Apogee archive > at http://www.apogeerockets.com/education/newsletter_archive.asp ] [quoted text clipped - 8 lines] > > > > /ArtU > I am asking what purpose this modeler needs to solve ? Might be as simple as testing something Jerry mentioned on the newsgroup. Jerry SignatureJerry Irvine, Box 1242, Claremont, California 91711 USA Opinion, the whole thing. <mail to:01rocket@gte.net> Please bring common sense back to rocketry administration. Produce then publish. http://www.usrockets.com My articles valuable? Donate at iKobo.com c/o my email. >>> Might be as simple as testing something Jerry mentioned on the newsgroup. and that would be ? curious minds are inquiring to know. /ArtU > > I am asking what purpose this modeler needs to solve ? > > Might be as simple as testing something Jerry mentioned on the newsgroup. > > Jerry > >>> Might be as simple as testing something Jerry mentioned on the > newsgroup. > > and that would be ? > curious minds are inquiring to know. 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 a.s goodbye :) > /ArtU > > > > I am asking what purpose this modeler needs to solve ? > > > > Might be as simple as testing something Jerry mentioned on the newsgroup. SignatureJerry Irvine, Box 1242, Claremont, California 91711 USA Opinion, the whole thing. <mail to:01rocket@gte.net> Please bring common sense back to rocketry administration. Produce then publish. http://www.usrockets.com My articles valuable? Donate at iKobo.com c/o my email. 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. SignatureR. J. Talley Teacher/James Madison Fellow NAR #69594 NRA #133073736 > > > >>> Might be as simple as testing something Jerry mentioned on the [quoted text clipped - 27 lines] > > > > > > Might be as simple as testing something Jerry mentioned on the newsgroup. those sound like closed breech launchers to me..... shockie B) > 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 [quoted text clipped - 48 lines] > > > > Might be as simple as testing something Jerry mentioned on the > newsgroup. >>The fins of the rocket are fixed rater than folding and a seal is maintained >>using Styrofoam spacers that act like a sabot 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 > 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 [quoted text clipped - 48 lines] > > > > Might be as simple as testing something Jerry mentioned on the > newsgroup. 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. SignatureR. J. Talley Teacher/James Madison Fellow NAR #69594 NRA #133073736 > >>The fins of the rocket are fixed rater than folding and a seal is > maintained [quoted text clipped - 77 lines] > > > > > Might be as simple as testing something Jerry mentioned on the > > newsgroup. > 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 > > >>The fins of the rocket are fixed rater than folding and a seal is > > maintained [quoted text clipped - 88 lines] > > > > > > Might be as simple as testing something Jerry mentioned on the > > > newsgroup. Another thought here, the sabot sections must not melt when subjected to the exhaust gasses. Foam will melt unless sealed with something. How about using mat spray over the foam and then laying down a layer or two of aluminum foil? Or, what about making the sabot sections out of balsa? Or, gee I really like this one, making them out of shirt backing or tablet backing and coating them with epoxy? Remember, they are primarily spacers. The ring at the bottom will do the sealing. SignatureR. J. Talley Teacher/James Madison Fellow NAR #69594 NRA #133073736 > > 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 [quoted text clipped - 111 lines] > > > > > > > Might be as simple as testing something Jerry mentioned on the > > > > newsgroup. >>Foam will melt unless sealed with something. But wont they be tossed up in the air while they just start to melt ? I was thinking of pink foam. Used as ejection charge plugs in rocket competition already. > Another thought here, the sabot sections must not melt when subjected to the > exhaust gasses. Foam will melt unless sealed with something. How about using [quoted text clipped - 125 lines] > > > > > > > > Might be as simple as testing something Jerry mentioned on the > > > > > newsgroup. > Seriously, what problem are you trying to solve with the piston launcher ? > It might have been solved another way already. > > /ArtU Higher altitude by harnessing the initial exhaust just as with the estes class events. Koen > > Seriously, what problem are you trying to solve with the piston launcher ? > > It might have been solved another way already. [quoted text clipped - 5 lines] > > Koen R. J.s post seems to make real sense to me. Art, LDRS BBL altitude. $1000 gets lots of people thinking. RDH8 > > Has anyone successfully used piston launchers for RMS engines in the G/H/I > > range? Any special considerations other than guidance? [quoted text clipped - 5 lines] > > > Koen It will be interesting if you get the piston launcher to work for the BBL. RDH8 > 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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