Motor Integrated to Airframe

Not a whole lot to report from our past work party. The most significant event to occur was the mounting of our motor to the airframe. The kerosene flex line is a bit too long and will be more so when we add fittings to purge this line. The stainless steel braided hose can be seen in the photo below at the bottom of the motor.
We also need to figure out how to best plumb the lines from the main LOX valve to the LOX dome including fittings to purge this line as well. As you can see in the photo below the stainless steel braided LOX hose would need to make a tight radius bend to connect with the LOX dome flare fitting. Www.anplumbing.com has a great selection of aluminum Earl's AN fittings and has a 90 degree adapter fitting we may be able to use. The alternative is to route the line outside the airframe for the static test.
Paul Breed has gratiously donated new pressure transducers to us. These transducers have a 0-5VDC output and integrate better to the elctronics. We will be monitoring via telemetry pressure in the helium tank, LOX tank, kerosene tank and the combustion chamber.

We also changed out a valve on the SSPS to allow us to pre-fill the "dome-dump" accumulator more easily.

This upcoming week is spring break, so I'm not too sure how many students are planning on being in town. Once the motor is fully plumbed we can begin our final testing.

--- Carl

Motor Prep, Ignition and Oher Details

Motor Prep
Our missing LR101 motor was finally returned to us. After sitting idle for 6 months it has accumulated quite a bit of visible surface rust on the exterior. The motors are entirely 4130 steel except for a copper wire which spirals between the walls forming the cooling passages. We're not sure how much rust may be in the cooling passages since they are nearly impossible to inspect. I took this motor to Sheffield Platers to have them electroless nickel plate it. I'm hoping this will clean off all the rust and offer protection from further rusting. They said it will cost $90. In the mean time, Steve Harrington (our other rocket project adviser and head honcho at Flometrics... and my boss) has offered us one of Flometrics LR101 motors, which we have begun to modify for use in our system. This involves cutting off the spindles which were orginally used to mount & gimbal the motor. Also, a hole is tapped so that a AN fitting can be screwed to the motor to plumb the kerosene in (see picture below).



Rust has been an enemy to us in the past. We have had injectors completely clog up with rust particles that were in the cooling passages. If we use this motor we'll have to make sure the inside is free of rust since the cooling passages were never plated in the original Rocketdyne process. Someone in the past suggested we recirculate naval jelly through the cooling passages which seems to work pretty well, so we will do that as a precaution. Also, sometime ago I made the tooling to make filter screens for the LOX and Kerosene. The screens nest over the injector.


The LR101 is getting to be pretty rare. It's my understanding that Rocketdyne is no longer allowing them to go on the surplus market due to the liability. They now destroy any motors they do not use... what a shame :-( I have heard that these motors are starting to go for up to $4000. Our educational budget (is $0.00 a budget?) can not afford this, so we're talking about reproducing our own based on the LR101. We have two designs: A sheet metal formed/welded one (see pics below) and a machined design (Devin, can you post pics of your design... I don't have it).
I hope to send out drawings to have these parts quoted in the next week or two. I also need to talk to our welder to determine what details/features he will need to make these parts weldable. Ideally I'd like to have them made from stainless steel to, once and for all, put this rusting issue to bed, however, a proper thermal analysis will need to be done, since stainless doesn't have the thermal conductivity the existing 4130 steel has.

Igniters
The original motor used hypergols for ignition. I have been told by a Rocketdyne engineer familar with these motors that a pyrotechnic igniter will work and the flames should spread out radially as close to the injector face as possible to insure propellant ignition without letting too much liquid propellant build up in the combustion chamber. These are sometimes referred to as radial outward-firing igniters or ROFI's. As far as I know, all the amatuer groups lighting this motor use pyrotechnic igniters.

No one on our team has a pyrotechnics license, so we will have to count on others for an igniter. I don't really want to have to make igniters. I'm trying to get some experts to provide them. Ken Mason, who has fired hundreds of LR101's with legendary Bob Truax, makes his on ROFI's. Ken has been a valuable resource and knows so much about these engines. I am hoping that either him or Kevin Baxter at the Friend's of Amatuer Rocketry can help us with an igniter.
Just in case that falls through, we thought about using automotive flares to make an igniter. I'm assuming they are DOT legal so they should be okay to use by mortal folks like us. We took one apart and the flammable substance is some yellow powder (sulfur and something else is my guess... anyone know for certain the composition?). We carefully (slowly) drilled a 1/8" hole in the end and inserted a nichrome wire folded in half so that the two wire ends stuck out the end of the flare. We glued that in with some 5 minute epoxy (see below... they are road flares... not dynamite folks!).

We then cut off a 1.5 " section of the flare containing the nichrome wires and inserted them in a phenolic fabric tube which had 5 radial 3/16" diameter ports for the flames to emit from. We capped both ends with wooden dowel caps using 5 min. epoxy and allowed the wires to come out of two of the ports.

We tested it by connecting the nichrome wires to long leads and touching them to a 12VDC battery. As soon as I can figure out how to post videos, I'll do so! Just as expected fire came out of the radial ports, however, it wasn't as uniform as I would have expected. Maybe 5 ports was too many. Perhaps 4 1/8" diameter ports will create more back pressure and better distribute flamey stuff from all the ports. The flare igniter burned for over 30 seconds, but by 15-20 seconds the phenolic casing was starting to burn through.


Plumbing
The Soft Start Pressurization System was finally plumbed to each of the propellant tanks tanks. A check valve goes between the SSPS and each tank to insure that no cross-contamination from propellant vapors can occur.

A small leak was found in a helium fill line fitting. We fill the composite pressurant tank through the Circle Seal regulator in the SSPS. The fitting is a straight adapter -- 3/16" tube to 1/8" NPT. The tubing then has to make a 180 degree bend and was probably stressesd. We'll replace it with a 90 degree elbow adapter. I've ordered new fittings.

Next we will plumb the MPVA to the motor via flex hoses. If our motors aren't ready we'll probably add some orifices to each propellant line to similuate the pressure drop through the motor and start high pressure and cryotesting. Paul Breed has offered to let us use the balance of a LN2 dewar he just ordered.

--- Carl

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