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Model Forum / General / Rockets / November 2007Here's an actual rocket post.. mid level engine in a small rocket?
Howdy everyone. I haven't posted here before, but I'm seeking advice and I figured this newsgroup could benefit a little from an on topic post.. basically, I had a fatboy kit sitting around and decided to stuff a 29mm motor in it. I'm starting by beefing up the engine section - plywood centering rings and a thicker cardboard engine tube. I've got two questions though: the top of the engine tube is only a few inches from the bottom of the nose cone. Should I be worried about this or take any precautions against burning my chute? (using a loc 12" nylon w/ kevlar shock cord) Secondly, are the balsa fins included with the kit up to this setup in terms of both size and strength? I usually epoxy fins to the engine tube and then do a heavier epoxy fillet on the fin/airframe. I'm probably going to need to add quite a bit of weight to the nose cone too.. could I just use the weight difference between the oem engine section and my souped up one as the amount to add, or would I be better off just putting a string on it and spinning it around? any input/thoughts would be appreciated. Thanks, Jesse <snip> >I'm probably going to need to add quite a bit of weight to the nose cone >too.. could I just use the weight difference between the oem engine >section and my souped up one as the amount to add, or would I be better >off just putting a string on it and spinning it around? No, you should add enough nose weight to move the CG back to where it was on the original kit. Measure with the motor you intend to fly inserted.  SignatureDarren J Longhorn http://www.geocities.com/darrenlonghorn/ NSRG #005 http://www.northstarrocketry.org.uk/ /UKRA #1094 /L2 /RSO http://www.ukra.org.uk/ I put an F21 in a 2:1 scale Overdrive (the 1:1 takes an A3T). Had to use a heavy nosecone to make it stable, and one flight was all it could take. When I retrieved it, some of the fins were partially shredded and the paint just ahead of the engine was all blistered. Oh, and yes, it was worth it :-) hehe! I wonder if it would help if I paint the inside of the main tube with some high temp paint. It does sound like I have to ditch the balsa fins then, eh? Jesse > I put an F21 in a 2:1 scale Overdrive (the 1:1 takes an A3T). Had to > use a heavy nosecone to make it stable, and one flight was all it > could take. When I retrieved it, some of the fins were partially > shredded and the paint just ahead of the engine was all blistered. > > Oh, and yes, it was worth it :-) > hehe! > [quoted text clipped - 3 lines] > > Jesse I made a 7 C motor cluster in a Fat Boy. All those ejection charges going off at once barbecued the inside. On a later model I lined the interior with aluminum duct work tape and that worked great. Another method is to line the tube with couplers. > I made a 7 C motor cluster in a Fat Boy. All those ejection > charges going off at once barbecued the inside. On a later > model I lined the interior with aluminum duct work tape and > that worked great. Another method is to line the tube with > couplers. For clusters like these, I use a mix of plugged motors with regular (ejection) motors. I get the reliability of a few redundant charges but don't have 5 or 7 or 9 of them going off at once. [Depending on the rocket, I may have to plug the motors. I can get A10-PT's, D11-P's and E9-P's, but for B6-0 and C6-0 motors, I cut a 1/2" length of 1/2" dowel and epoxy it into the forward end. Works great. (Shhhh, don't tell anybody I said that...)] Doug >> I made a 7 C motor cluster in a Fat Boy. All those ejection >> charges going off at once barbecued the inside. On a later [quoted text clipped - 12 lines] > > Doug After the first barbecue I went to a mix of 3 C6-5's and 4 C6-7's. Since they didn't all go off at the same time and the tube was lined with aluminum tape it worked nicely. why not just use c-60's???? jc >>> I made a 7 C motor cluster in a Fat Boy. All those ejection >>> charges going off at once barbecued the inside. On a later [quoted text clipped - 16 lines] > they didn't all go off at the same time and the tube was lined with > aluminum tape it worked nicely. >> After the first barbecue I went to a mix of 3 C6-5's and 4 C6-7's. Since >> they didn't all go off at the same time and the tube was lined with >> aluminum tape it worked nicely. > > why not just use c-60's???? Because they eject at motor burnout since they have no delay. You could fill them with epoxy but that's the dreaded M word, modification! Plus, that requires that you work on the motors before going to the field, the 5's and 7's were always ready in the flight box. But the best reason is that seven motors all dumping tracking smoke looks awesome! >>> After the first barbecue I went to a mix of 3 C6-5's and 4 C6-7's. >>> Since they didn't all go off at the same time and the tube was lined [quoted text clipped - 9 lines] > But the best reason is that seven motors all dumping tracking smoke looks > awesome! I'll unequivically concede that last point! <G> jc Hmmm, the dreaded M word. I still have an old Vaughn Brothers kit ( L'l Wild Thing) that uses 8 A engines (13mm) and one C engine. I use the old hot-glue plug technique all the time. I must be a very bad boy. SignatureR J Talley Teacher/James Madison Fellow "What? Me Worry? Alfred E Newman > Hmmm, the dreaded M word. I still have an old Vaughn Brothers kit ( L'l > Wild Thing) that uses 8 A engines (13mm) and one C engine. I use the old > hot-glue plug technique all the time. I must be a very bad boy. And how many motors have I modified? Well, they don't call me the Clustermeister for nothing! > I made a 7 C motor cluster in a Fat Boy. All those ejection charges > going off at once barbecued the inside. On a later model I lined > the interior with aluminum duct work tape and that worked great. Here's a tip I got from Jim Flis: Stagger the ejection charges. In my shortened Rikter Recker, I use one E9-6 and two E9-8s (er, or the other way around, it's been a while). So in your Fat Boy, make half the engines have a longer delay so they don't all go off at once. I recently (well, a couple of years ago) built a 29mm Fat Boy. I used balsa (not the punky balsa that came with the kit but some good C grain stuff), yellow glue, and the paper centering rings. I did add some nose weight to move the cg back to where it should be. I also used a kevlar strap for the shock cord and a nylon chute w/nomex bag. The airframe was essentially stock, except for motor tube. See binaries group for pictures. The glue along fin roots is not a built-in epoxy fillet, it is a repair. You can see by the fin tips, this is a flying rocket, not a static model. |
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