(Courtesy of Star Rocketry)
Please share any lessons learned that you feel other HYPERTEK Rocketeers will benefit from!
The new RG L and RG M injector bells are a challange to properly seat the fill stem into the kline valve. Before you insert the fill stem you may want to make a mark 16 7/8" from the tip of the fill stem for the L motor system and 19 3/8 for the M motor system. When you have it properly seated this mark will be even with the bottom of the fuel grain.
The new drop fill stem assemblies are also prone to binding after a few launches. If the fill stem binds it will not slide out of the kline valve and the O2 will toaste your fill stem and injector bell. To remedy this take the brass bushing out of the fill stem assembly. This will allow the fill stem to drop freely and not bind.
We are having some problems getting our motors lit and could use your help!
your O2 pressure to about 90 PSI. The most important part is the following:
Place a piece of masking tape on your ignition wire so that at least 2" is above the top end of the tape. Then put the top edge of the tape 3/4" down from the top of the O2 filler tube and wrap the tape around the tube. Now bend 1" of the top 2" lead of the ignition wire down so it is about at a 60 to 90 degree angle from the filler tube. When you slide your rocket over the ignition wire you will have to bend it down a little more so that it will slide through the nozzle. You want the end of the wire to touch or be as close to the inside wall of the fuel grain as possible. This should light your fuel grain up with no problem.
On the "L" grains I actually tape the ignition wire to the grain (Click Here For Illustration).
You could also do this for your "J" grains if you would like but I do not think you will have a problem if you follow the procedure I outlined above.
Motor Tube Lengths Vary on 1685cc & 2800cc Motor Systems.
If you plan on using both the 1685cc & 2800cc motor systems in your rocket be sure to build your motor tube for the 1685cc motor system. Due to the different neck configurations on the tanks the 2800cc motor system ends up taking 1/4" more motor tube space. By building your motor tube to fit the 1685cc configuration you can just add a 1/4" motor tube spacer to accommodate the 2800cc configuration.
Ignition technique for "L" fuel grains - tape to inside wall of fuel grain.
Cut a length of ignition wire and instead of taping it to your fuel stem tape it to the inside wall of your fuel grain with tape ( I use the thin black 1/2" electric tape). Feed ignition wire through the nozzle and out the other end that screws to your motor assembly. Then put a piece of tape on the ignition wire so that about 1" of wire extends beyond the tape. Pull on the ignition wire at nozzle end to feed the taped piece back into the fuel grain until the tip of the ignition wire is about 1/2" to 1" from the bottom of the threaded area of the fuel grain. Click Here For Illustration
SPECIAL SAFETY NOTICE:
If you have the old "J" fuel grains with the ribs/finlets (Click Here For Illustration) on the inside of the fuel grain - DO NOT USE THEM!!! They tend to CATO upon launch!
Never use any lubricants other than silicone grease.
I used petroleum jelly once and blew my fuel grain apart as well as the booster section of my rocket! Krytox reacts with the magnesium in the EFX grains and also causes fuel grain failure - photo below of Bill Beggs' Sudden Rush on I310 EFX with Krytox!
Never reuse a fuel grain.
My 12 Volt battery got low and did not provide enough juice to keep my N2O lit when the tie strap melted through. The rocket went up about 75' with a cloud of liquid N2O blowing out through the fuel grain nozzle. I reused the fuel grain which apparently had developed a hair line crack due when it hit the ground after being super cooled by the unlit N2O flowing through it. The fuel grain exploded when the N2O lit this time and pressurized the fuel grain.
Ensure that you actually see the "white" liquid vapor of the N2O venting and do not just assume the normal change of tone when filling the motor system means it is full.
I was filling the motor system and heard a change in tone which normally meant the N2O was venting. The N2O supply tank actually had actually run out of liquid N2O and by the time I did the countdown the rocket took off running on vapor! It launched and went about 329' into the air. Luckily no damage.
Use Ematches verses flash bulbs for your ejection charges. Ematches seem more reliable.
I was using flash bulbs but had one that tested good fail on my apogee charge. The rocket came in ballistic from about 4000'. The main charge fired at 300' but the chute was instantly shredded and the rocket was a total loss. The HYPERTEK motor system is the only part that survived! Ematches have been much more reliable for me.
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