Sport Rocketry

up in the piston tube for guidance and support and also for the pis- ton to rest on. How to Use a Piston Launcher The first step in using the piston launcher is to put your prepped rocket onto the piston tube (with the piston head already inside the piston tube). The engine should extend out of the rocket by 3/8" to 1/2" so that it can be fit into the piston tube. The end of the engine is essentially friction fit into the top of the piston tube. The tighter the better. When inserting the motor into the piston tube, the igniter leads are bent out, and up. With Estes igniters, I first put the ignit- er and igniter plug in the engine and then remove all the igniter tape. Then I bend the igniter leads up along the sides of the motor. Then the engine is inserted into the piston. See Figures 2 and 3 showing the steps. Figure 2 shows the rocket with the Mylar tape for friction fit with the igniter snaked around the sides. Figure 3 shows a close up of the rocket on the piston. Make 34 MAY/JUNE 2021 SPORT ROCKETRY a stop on the central dowel by wrapping tape around the dowel so that when the piston tube rests on this stop the piston head is about 2" below the engine nozzle. Figure 4 shows the view of the entire as- sembly. Mount the piston/rocket on your stand or in your tower and hook up the clips. That's it! You're now ready to launch once that "cow sucking" thermal arrives! A longer piston launcher can be made by coupling lengths of tubing using tele- scoping tubing that fits over the outside of the piston tube. For 13mm pistons, use a piece of BMS T5Plus-34. The tricky part is making sure the tube joint is smooth so the piston does not get caught on it while still having a good piston/tube seal. Typically if using a 1/2" aluminum or brass piston head, it will be too loose in a 13mm piston tube. This may allow some gasses to escape that you are trying to capture to give the rocket the addition- al boost. I use 1/2" Mylar tape from ASP Rocketry wrapped around the piston head until the piston fits snugly, but not too tight. How tight is that? With my half inch brass piston heads I keep adding wraps of tape on the piston until it slides down the tube freely without the back end covered, but slides slowly or stops when the I cov- er the backend of the piston tube with my finger. The dowel rod and dowel stop position I use to support the piston launcher in my tower allows the piston head to slide down a couple of inches from the top of the pis- ton tube. This is based on R&D reports that show better performance that way. I generally use a piston tube only once. The exhaust residue buildup at the top of tube reduces the performance in subse- quent launches. Others simply cut off a few inches, but then you are stuck with a shorter piston tube. What I do is take the used piston tubes and generally discard the top 6 inches, and then use the rest of the tube for building additional rockets. A brush can be used to remove exhaust resi- due also. That's it. It really isn't that hard. An adjacent page has a plan/illustration that shows everything I described in this arti- cle. There are many great R&D reports on piston launchers in the members only area of the NAR website if you want to learn more. Otherwise, if you still have ques- tions on piston launchers please don't hes- itate to contact me. My contact info is on the NAR Website. C L E A N . S I M P L E . R E L I A B L E . T H I N K I M P U L S E . IMPLSLaunch . com

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