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Jan 02, 2001 meeting notes

Jan 02 meeting notes:

Location: Long Range Systems

In attendance:

John Carmack
Phil Eaton
Russ Blink
Neil Milburn

Next meeting on Thursday at 6:15 for more engine tests!

The X-L peroxide finally came in today.  The freight charge was $175.  Because it is 31 degrees here right now, the stabilizing water was frozen around the peroxide jugs.

The five gallon sample jugs have spigots on them, which makes dispensing test samples very convenient, although it does drip a bit after closing.  We were expecting to have to make a vacuum pump to siphon it out, but this works great.  The lead time on this order was pretty long, but there were some issues with X-L dropping support for 90% during the processing of our order (we changed it to 98%), so I hope the next batch goes through faster.

I was concerned about the very cold peroxide, but as Michael warned us, it does heat up noticeable when you mix distilled water into it, so it wasn’t a problem.  I would like to hear an explanation for this heating behavior, if anyone has any ideas.

We made three test firings with 85% mixtures:  The first one was at 200 psi with the .040” jet, the second one was at 400 psi with the .040” jet, and the third one was at 400 psi without any jet at all and twice the peroxide (200ml total).  The results are available in Excel format at
media.armadilloaerospace.com/misc/jan02.xls.  The jetted flow was definitely less than last time, due to the far denser catalyst pack in the current motor.
We saw excellent catalytic reaction on all of them, with the exhaust turning completely transparent after the first half-second or so.  We took video of it, but there isn’t much to see with it working well…

There are two factors that changed since our last test runs:  we are using X-L peroxide instead of our self distilled, and the catalyst pack is compressed to 3x the density instead of loosely packed.  We didn’t intend to change two factors, but Russ’s still cracked in the cold weather before we could try the compressed pack with our stuff.

When we disassembled the motor, the nozzle side of the pack was pristine, so we don’t seem to be washing the catalyst off, either.

The only problem is that we only got about half the thrust we wanted.  Removing the metering jet only made minor differences in the flow through the engine, even though it makes a huge change when water testing without chamber pressure.

We are limited right now by the nozzle size.  Russ is going to drill out the nozzle tomorrow, and we will test again on Thursday.  The current nozzle might be roughly appropriate for an AP motor, but for monoprop peroxide, it has both too small of a throat and too large of an expansion ration.

Juan’s specs for the 100lb motor are:
300 psi chamber pressure
0.245 in2 throat area (0.56” diameter)
0.895 in2 exit area (1.07” diameter)

Scaling down to something in the 15lb thrust range would give:
0.036 in2 throat area (0.22” diameter)
0.134 in2 exit area (0.41” diameter)

Russ: measure the current size exactly for our records before cutting it out.  You should also measure your big motor.

I am guessing that the pulsation at the end of the third run is caused by the chamber pressure being very close to the supply pressure, instead of having a healthy drop across the pack.

We might also want to add some more foam disks at the nozzle side of the pack, even if they aren’t silver plated, just to reduce the open gap at the injection point.  Our 200 msec warm up pulses weren’t even enough to get it solidly pushed into the pack in the current form.  Both the slightly shorter pack and the longer feed hose contributed.

I brought a bunch of chemistry glassware for dealing with the peroxide.  We still need to get a better washing facility than the sink on the other side of the building.

The new 3 hose, 90 degree fittings, and 45 degree hose ends for the VTVL platform are here.

The magnetometer got shipped off today from JP Aerospace, and I also ordered a different one from
http://www.precisionnavigation.com/ as a backup.

Bob said that the remaining tubing for the VTVL platform will be in on Thursday, so we should have the framework assembled next Tuesday.

I got the price quote from WinSystems for the single board computer I want for the flight computer:  In small quantities:
LBC-586PLUS-133-C         $695
SDK2-LBC-104               $895
PCM-DC/DC-12-500-3        $200 (3A capacity, 9-36VDC input, 12V nominal)

That sounds reasonable to me, so I am going to order it after I get a little clarification on the flash disk subsystems.

The software is nearly ready to go for the ground station and flight computer.  It is nicely configurable between running the simulator, connecting to a remote simulator, or connecting to real remote hardware.  I did wind up running into a problem with my current control law when I added some latency to the communication link.  It is currently going into increasing oscillations, so I have a bit more work to do there.

Stuff to do soon:

Get the water to the garage sink at LRS turned on again.

Get some of the metal foam off to the silver plater.  Get the process parameters they use for our records.

Make a vent hose for the vacuum pump, so we don’t need to worry about accidents when it is pressurized.  We can tie the hose down to the other end of the fill cart.

Pick up another compressor, in case the current pump dies.

We might want to have another N2 bottle handy, because at 400psi, we go through it pretty fast.

Vise grips.  Eventually, Russ needs to cut flats on the little engine for easier disassembly.

Metal pipe clamps for the engines to test stand.


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