It's 3 weeks from launch date, construction and ground testing for the Defiance-H is done. Now that the rocket is ready, I can do the final calculations on center of gravity and descent rate. I assembled the fuel grain in the combustion chamber, did an over all weighing of the rocket, then balanced the rocket on a roller to determine the center of gravity.
Here are the specs and predicted specs:
Over All Length: 192.25"
Nose to CG: 120.125"
Nose to Barrowman CP: 153.43"
Stability Margin: 33.305"
Weight no N2O w/Fuel: 73.4 lb.
Fuel Grain Weight: 9.6 lb.
Fuel Use: 6.17 lb.
Burn Out Weight: 67.23 lb.
N2O Load: 35 lb.
Lift Off Weight: 108.4 lb.
Descent Rate Under 4' Drogue: 79.07 fps
Descent Rate Under 4' Drogue & 10' Main: 29.36 fps
Initial Thrust: ~875 lbf
Thrust to Weight Ratio: 8.07:1
Time to Apogee: 39.6 sec.
Apogee: 25,000'
Time Under Drogue: 303.5 sec. (5.06 min.)
Time Under Main: 34.06 sec.
Total Descent Time: 5 min. 37.5 sec.
Altimeter Setup:
RMCS
Pyro 1 Apogee no delay
Pyro 2 Apogee 1 second delay
Pyro 3 at 1,000'
LED enabled, sample rate 50 Hz.
RRC2X
Mach Delay 25 seconds
Main at 1,000'
Apogee Charge: 10 grams 3F black powder
PIRM2 Main Charge: .6 grams 3F black powder (1" straw measure)
Altimeter power supply: 3) Energizer Max 9 volt batteries. 2 in parallel for main power, 1 for RMCS pyro power. All tested 9.4 volts or higher, 6.4 amps or higher. Batteries zip tied and hot glued at base.
Launch Valve PIRM2 Charge: .35 grams Red Dot (1" straw measure)
Line Cutter Charge:
Pre heater Grain:
I'm one week out from launch day, I had to restrain myself from performing final prep work on the rocket until now. As you can see from the data above, the altimeters are loaded and ready to fly. I also drilled the N2O vent hole in the tank today, I decided to go with a .032" vent hole to keep chilling and loss in the tank to a minimum. I also picked up a second N2O tank this week, and purchased more plumbing to allow me to connect the two tanks in parallel. The dual tanks should help to keep the N2O temperature/pressure up. In the past I've had a single N2O supply tank ice up while filling a run tank. The dual tanks should reduce the amount of N2O drawn from a single tank, which means less liquid turning to vapor and less chilling.
The waiver has arrived as well. The bad news is that my FAA contact told me I probably wouldn't be able to fly from this location again. Apparently there is a jet path over this site at 18,000'. I'm not sure how far I'll have to move, if it's just a few miles, that shouldn't be a big deal, but if it's more than that, I may be looking at Alton again. Alton isn't ideal either since it falls in the take off/landing path of the Sioux City airport. Finding a suitable launch site is really a PITA, unless you know someone, it's hard to just drive up to a persons home and get them to let you launch rockets...
I decided to test a slightly larger pre heater grain for this engine. I've been using about 10 to 15 grams of APCP, but with a larger engine I may need a bit more to ensure good ignition. I used a pre cast grain for a small 29 mm motor, cut the inhibitor layer off and drilled a 3/16" hole down the middle. The hole down the center is for the wood dowel that holds the grain in place in the combustion chamber.
Click Here for a short video of the burn.
Here's a vid cap several seconds into the burn.
The burn looked pretty good, a nice symmetrical ball of flame and sparks. It looks like I'll have about 17 seconds from ignition until the propellant starts falling off the dowel. I did only use one igniter on this test, where I use two (one on each side of the grain) on a flight. That brings up a good point, I have quite a number of pyro events that all must happen for a launch to be successful, so I double up on igniters on the pre heater grain, and double e-matches on both the line cutter and the main valve PIRM2. That makes for 11 e-matches/igniters for the 5 pyro events of the launch and flight. (2) Line cutter, (2) pre heater, (2) main valve, (3) apogee and (2) main.
Sometimes I wonder if I think too much about what could go wrong... Probably not though! In this case I worried about the nose cone bulkhead tearing off the nose cone itself. For some insurance I ran some 9/16" tubular nylon under the "U" bolt on the inside of the nose cone bulkhead, then ran it through the telemetry bulkhead. To make sure the telemetry module stayed together, I ran some steel cable through the bulkhead and around the mounting board in two places. Now if the nose cone snaps at the end of the shock cord with too much force and breaks the bulkhead mount, the fiberglass nose cone will fly off but the telemetry package will stay attached to the shock cord.
Here's the other side of the telemetry board.
It may be overkill, but you can see I have 3 tie wraps on each set of batteries. I also used hot glue to help retain the battery packs. While hot glue isn't super strong. What it is, is flexible. It grips the mounting board with amazing strength yet should provide some shock protection for the battery packs. It's hard to see in the picture, but the GPS output connector simply slides into a slot on the top/back of the GPS. I routed out a slot in the board for the connector to reset into, that should go a long way to retaining it. I also used hot glue to glue the connector to the GPS for added strength. The GPS really can't go anywhere, since it's wedged in between the lower bulkhead and the batteries, and when inserted into the 3" tube it presses against the tube wall as well.
I did one last test with the telemetry unit all wired up and ready to fly. As expected it all worked fine, batteries are all fresh and should give me some 10 to 12 hours of transmit time.