Components Mounted in Airframe

This past Sunday's work party had 7 students in attendance: Alyson, Judy, Jerry, Eddie, Alex, Joquin and Devin, the project manager. Also present was Brett, an industry engineer helping the project and myself.

Soft-Start Pressurization System (SSPS)
The SSPS was tested at high pressure tested and mounted in air frame. During bench testing one of the brass AN nuts on a stainless steel braided hose was over-tightened and stripped. I new one was ordered. This didn't stop us from testing... it just meant we had to test each Mity Mite regulator independently, by swapping the remaining flex line between regulators. To test we connected the system to a 2200 psi air supply. I also put a ball valve on each regulator output with a .028" orifice to mimic the actual load and an upstream pressure gauge to make sure we were getting the required output pressure. With the ball valves closed we set the output pressure on the Circle Seal hand-loaded regulator. This is the regulator that will "reload" the domes and, hence, change the propellant tank pressure. We set this reg to 500 psi. We loaded the dome-dump accumulator (DDA) (the sphere in the system) to 100 psi just using shop air with an air nozzle gun. This would allow the regulators to initially pressurize the propellant tanks to 100 psi and hopefully start the motor in a benign manner. When we opened the ball valves on the reg output, air would flow through the orifice at a modest rate. Then we energized the dome-dump solenoid (DDS) with 12 VDC from a power supply. The gauge on the DDA changed from 100 psi to 500 psi in about 1 to 1.5 seconds and the air output of the mity mites immediately increased. I think this event happens much quicker than 1-1.5 seconds, but there is some dampening in the pressure gauge. We'll see when we test with water in our tanks and we can actually track the tank pressure with our pressure transducers. After testing, we mounted the SSPS in the airframe. At our next work party we'll replace the broken flex hose and plumb the Mity Mite outputs to the propellant tanks. we also need to reroute the helium fill line which allows us to remotely load helium into our composite pressurant tank. Here are some pics...



Main Propellant Valve Assembly (MPVA)
We tweaked the MPVA to allow full range of motion. Initially when we commanded the pnuematic actuator to open the ball valves they only opened about 70%. of the 90 degree rotation. We had made a geometry error when mounting the pnuematic actuator. We simply drilled new mounting holes for the actuator and that solved everything. Now we get 100% opening. The whole assembly is quite rigid and we cycled it at least 50 times that day. We probably overbuilt the structure it is mounted to, but we wanted to make sure it was rigid, unlike previous versions. We may add some lightening holes and machine away some material in it when we're ready to fly it, but for our static test this will do.

Motor Mounting Bulkhead
The titanium sheets covering the bottom bulkhead were giving us a real hard time. New sheet metal skins made from 6061 aluminum. Here it is mounted. The 8 small holes are what our engine mounts to. The large hole on the left is where the LOX line exits the airframe to connect to the motor. We need to add a hole for the kerosene plumbing.



Other:
Our electronics were built and donated by Paul Breed at Netburner (see Paul's blog: Unreasonable Rocket). Our electronics allow us to transmit data from the rocket to a ground station. Basically we monitor pressure in both the propellant tanks and the motor combustion chamber. If time and resources permit I would like to add a transducer to the helium supply and DDA. There is also an accelerometer which we could use to sense altitude and GPS which updates at 5 Hz. All this data is sent over a 1 Watt Maxstream transmitter.
Here the electronics are mounted in the airframe:

For the flight we are also going to try to have a wireless camera mounted to transmit live video of the flight from the rocket. We also will have two commercially available rocket altimeters to initiate the recovery via parachute deployment. We haven't selected altimeters at this time, so any recommendations or suggestions would be appreciated.

LOX tank insulated
We used fiberglass insulation to insulate the LOX tank. We left the top and bottom of the tank un-insulated so that we could leak check the fittings at the top & bottom. We will also need to insulate the LOX line leading to the MPVA.
Motor woes...
One of our former students was entrusted with our LR-101 motor and has gone MIA. We exhausted every effort to get a hold of him to get the motor back. This is a big deal! We have a spare motor, but we'll need to modify it to get it into a configuration for our vehicle. We'll start this at our next work party.


--- Carl