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