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Model Forum / General / Rockets / September 2007Sky Ripper flight report
Since it seems so quiet, I thought I'd post a quick launch report... I flew my second ever hybrid Saturday, a Sky Ripper H155. Other than forgetting to install the vent tube, the launch went very smoothly. After futzing around for a bit at the pad to get the vent in place, the fill and ignition were textbook perfect - it went on the first attempt! I really like the Sky Rippers and their AP grain ignition system. It is very reliable and works with any 12V system. It was my first ever dual deploy, and it gets a passing grade, but I lost the fin can to my stretched HiTech H45 in the process :( The apogee event was a bit hot and fried the nylon cord tethering the fin can to the rest of the rocket resulting in a fubar'd fin can. But the motor case was unscathed. The main fired as intended at 500 feet and brought the rest of the rocket down in reasonably good shape. The two shear pins in the nosecone tore the airframe a bit - next time I'll add a wrap of glass instead of just CA'ing the holes in the LOC tube. And the main charge was also a bit hot resulting in the chute needing some holes patched : ( But I consider it mostly a success. I'll build a new fin can, this one a bit longer to take the next longer SRS 38mm case - maybe even the longest (36") case - and be back in business. I hate losing the old unit; it was my L1 bird. But it's pretty much beyond hope with two breaks in the 2.6" airframe. I also used only a single switch on the altimeter this time. In the past, I've had one switch for power plus one per charge, but this time, having accumulated some experience with the RRC2, I kept the arming sequence simple and just had one screw switch to turn after getting the rocket on the pad. I'm really getting to like the hybrids. These SRS motors jump off the pad. With the apparently lower average thrust than comparable impulse solids, I tend to envision slow liftoffs - and potentially harmful weathercocking - but that's just not the case. They have no problem building good rod speed. And, after having prepped them a couple times, there's really no more complexity than assembling a 38mm AT case. In fact, building the SRS case might even be easier. Having the added hose hookup at the pad increases the challenge, but the sum total of it isn't really much different than solids. I'm already getting psyched for the next one. Doug The difficulty of learning curves is more perceived than actual... Doug Make sure to put some CA in the holes when drilling cardboard to reinforce - expecially for shear pin use - it helps to spread the thin stuff all around the area too.. I have seen folks glue in razor blades because they are thin but I have not tried that - not sure if I would myself - the CA really helps. Barry > Since it seems so quiet, I thought I'd post a quick launch report... > [quoted text clipped - 49 lines] > Doug > The difficulty of learning curves is more perceived than actual... On Sep 26, 3:57 pm, <locprecis...@sbcglobal.net> wrote: > Make sure to put some CA in the holes when drilling cardboard to reinforce - > expecially for shear pin use - it helps to spread the thin stuff all around > the area too.. Hi, Barry, I had applied some CA to the holes, but apparently not enough. I'll keep working on it, though. BTW, the Plano Hobbytown now carries LOC again, hooray! In fact, I believe the alt bay I used on this flight was purchased there (or else from Quikburst). > I have seen folks glue in razor blades because they are thin > but I have not tried that - not sure if I would myself ... I'd be afraid that would make it too easy to shear the pins thus potentially defeating the purpose, eh? BTW2: I looked for you at LDRS in Amarillo last summer to buy you a cocktail as payback for the replacement rings you sent me for my MMA. I still owe you :) Doug >> I have seen folks glue in razor blades because they are thin >> but I have not tried that - not sure if I would myself ... > > I'd be afraid that would make it too easy to shear the pins thus > potentially defeating the purpose, eh? The other trick is to glue very thin brass shims to the BT or NC. This helps shear the shear pins. > The main fired as intended at 500 feet and brought the rest of the > rocket down in reasonably good shape. The two shear pins in the > nosecone tore the airframe a bit - next time I'll add a wrap of glass > instead of just CA'ing the holes in the LOC tube. And the main charge > was also a bit hot resulting in the chute needing some holes patched : Doug- Having never used shear pins, I'd be interested to know more deatils on this. Were you using nylon screws for shear pins? How much BP did you use, and how long is the chamber it pressurized? Tim >> The main fired as intended at 500 feet and brought the rest of the >> rocket down in reasonably good shape. The two shear pins in the [quoted text clipped - 9 lines] > >Tim There used to be a good article on it on Rocketry Online's Info Central. They also have a BP calculator that allows you to input shear pins. When everything works correctly, the chamber is not pressurized for very long - I'd say under1 second. Anyway, look on ROL, Info Central or Rocketry Planet. Most people use 2-56 or 4-40 nylon screws. I've also heard of people using white round plastic stuff for making models. Sorry I forget the official name. It is usually sold in hobby and craft stores. >>> The main fired as intended at 500 feet and brought the rest of the >>> rocket down in reasonably good shape. The two shear pins in the [quoted text clipped - 12 lines] > using white round plastic stuff for making models. Sorry I forget the > official name. It is usually sold in hobby and craft stores. Styrene plastic rod. I used the 4mm and it worked perfectly. I found that I had to use a cig lighter to melt a top to the pin so it resembles a nail. Ted Novak TRA#5512 IEAS#75 >>> Were you using nylon screws for shear pins? How much BP did you use, >>> and how long is the chamber it pressurized? > Styrene plastic rod. I used the 4mm and it worked perfectly. I found > that I had to use a cig lighter to melt a top to the pin so it resembles > a nail. That's what I used. I got it from the Plastruct display at the hobby store. But mine are 1/16" (~1.6mm). I used a soldering iron to forge nailheads onto them, then applied some tape to hold them in. Two pins were used on this rocket. I can't remember if I tested this setup or not. Which means I should have done it (again) to be sure. On two other rockets, a 2.3" bird and a 3" airframe, I've applied glass and run ground tests with the pins, so I felt I had a decent handle on using them and getting the amount of powder right. As for preparing this airframe for pins, I pretty much followed what Barry outlined in his post. The forward 1" of airframe was soaked (inside) with thin CA, then the pin holes were treated as well. Besides Barry's post, I've seen this (glassless) technique described several times on the web, so I thought, at least hoped, it could be done without tearing. I used about 1.5g of powder. The airframe is 20" long (x2.6") minus 3" of coupler and 2" of nosecone shoulder, so the powder was a bit heavy (blow it out or blow it up :) but that shouldn't affect the shearing, should it? Anyway, I'll keep tinkering with this one. Maybe apply some brass to improve the shearing per Alex' suggestion. Yesterday, I bought a new tube, coupler and rings to build a new lower section with, this time long enough for the 36" SRS case. I'm really getting to like the hybrid thing :) Doug >>>> Were you using nylon screws for shear pins? How much BP did you use, >>>> and how long is the chamber it pressurized? [quoted text clipped - 34 lines] > > Doug I have three flights on a 5.38" LOC airframe using nylon 2-56 screws as shear pins. All I did to the airframe was soak a little CA into it around the holes and I cannot see any deformation. The thicker tube might be a factor.  SignatureDavid W. Schultz http://home.earthlink.net/~david.schultz ------ "What you don't know should be a goad to make you try and find out, not an excuse to bliss out and sit drooling into your filet mignon." -- PZ Myers >>>> Were you using nylon screws for shear pins? How much BP did you use, >>>> and how long is the chamber it pressurized? [quoted text clipped - 34 lines] > >Doug Good ideas. Whatever you do, don't forget to ground test BEFORE you fly it. Also remember that the amount of BP is determined by how many shear pins you use, their thickness and the volume of the airframe that you will be pressurizing. >>>>> Were you using nylon screws for shear pins? How much BP did you use, >>>>> and how long is the chamber it pressurized? [quoted text clipped - 41 lines] >you use, their thickness and the volume of the airframe that you will >be pressurizing. I forgot to mention friction. > > The main fired as intended at 500 feet and brought the rest of the > > rocket down in reasonably good shape. The two shear pins in the [quoted text clipped - 9 lines] > > Tim Should have used pickle forks... SignatureTweak |
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