February 19 and 23, 2002 Meeting Notes

 

In attendance:

 

John Carmack

Phil Eaton

Russ Blink

Neil Milburn

Joseph LaGrave (Sat)

 

Tuesday water cooled biprop engine tests

 

All of these tests were with the cat pack composed of 50 80 mesh silver screens alternated with 20 mesh stainless screens, with a spring stainless anti-channel ring every 20 screens. The pack continued to light up almost instantly through all tests, but almost all the runs were rough.

 

The water cooled chamber has had the throat bored out to 0.375” from 0.25”, in the hopes of increasing our mass flow enough so that we can move up from the smallest (0.018”) fuel jet, allowing us to bracket the rich/lean area. The chamber was slightly deepened to 3.125” to the top of the converging angle, and is 1.00” in diameter. Depending on if you count the converging cone and the fuel injector ring, that give somewhere around an L* of 23, which is a bit on the low side.

 

I took a few low quality videos this time.

 

run 1:

I wanted to see how much we could possibly flow through the cat pack, so we bolted the fuel injector ring onto the cat pack just as a retainer, with no chamber or nozzle at all. The results were interesting. It took a lot longer than expected, showing that the 80 mesh screens are extremely restrictive to gas flow, and that we aren’t likely to see much increased thrust even though the new nozzle is over twice the area of the previous one. It was smooth for ten seconds, then very rough for the last three seconds.

 

The exhaust was clearly subsonic, with the engine only registering five pounds of thrust. The retaining plate had 0.25” diameter holes in a 0.25” thick plate, so that was not enough room for the gas to get to sonic velocity. We have run some motors in the past that worked ok with multiple tiny nozzles, so I will probably make a thicker retaining plate with actual converging / diverging cones the next time we try this.

0.120 peroxide orifice, no nozzle

 

run 2:

0.060 peroxide 0.018 fuel, 250 psi

bad fuel solenoid connection

 

run 3:

0.060 peroxide 0.018 fuel, 250 psi

solenoid worked, no fire

This was the exact combination that had worked well last Saturday, but the larger throat seems to have changed the characteristics. Cat packs make scaling trickier, because a change in chamber pressure will effect flow through the pack differently than flow through the fuel orifice.

 

run 4:

0.060 peroxide 0.020 fuel, 250 psi

change battery

rich? no fire?

 

run 5:

0.060 peroxide 0.018 fuel, 250 psi

no fire

 

run 6:

0.080 peroxide 0.018 fuel, 250 psi

fire

 

run 7:

0.070 peroxide 0.018 fuel, 250 psi

fire

 

run 8:

0.070 peroxide 0.022 fuel, 250 psi

fire

http://media.armadilloaerospace.com/2002_02_19/steam.mpg

We saw our cooling water jet burp steam on this run, so we turned up the water flow for later runs.

 

run 9:

0.070 peroxide 0.026 fuel, 250 psi

fire

 

run 10:

0.070 peroxide 0.030 fuel, 250 psi

some fire, rich cloud

http://media.armadilloaerospace.com/2002_02_19/tooRich.mpg

This brackets the rich end of the burnable range.

 

run 11:

0.070 peroxide 0.018 fuel, 250 psi, 475 peroxide 25 water

did not light

This was a test of reduced (85%) peroxide concentration, which is reported to be necessary when using regenerative cooling and silver screen catalyst packs. We need to get this to light.

 

run 12:

0.070 peroxide 0.018 fuel, 250 psi, undiluted peroxide

fire

This was a long burn test.

http://media.armadilloaerospace.com/2002_02_19/longBurn.mpg

 

Almost all of the runs were rough, but one or two were smoother for no apparent or repeatable reason.

 

We measured our cooling water flow (after increasing it after run 8) to be 450 ml of water flowing in 20 seconds, which is about how much peroxide is flowing through the engine, so we aren’t far off from something that could use the peroxide for regenerative cooling.

 

Saturday engine tests

 

We built a new catalyst pack with only 20 80 mesh silver screens, then 30 20 mesh silver screens (still with stainless screens between each silver screen). Because we are out of fresh catalyst, all of these are from previously run engines. There were a couple noteworthy things when the pack was taken apart:

 

The 80 mesh silver screen on the top had a neat hole punched in it directly under the pipe fitting. I had been leading with a silver screen as a minimum latency arrangement for attitude engines, but after seeing this I have changed to leading with stainless. This is also probably an argument for a spreading plate, but the smoothest runs we ever saw were with a screen pack with no spreading plate.

 

The 304 stainless spiral anti-channel rings had lost most of their spring. They were still a tight fit, and seemed to be doing the job, but no longer actively pressing against the walls. After over five minutes of hot fire, it probably isn’t surprising. If we find that we really do need the spring pressure, Smalley does offer the spiral retaining rings in Inconel X-750.

http://www.mwspring.com/select.htm

Lists 304/316SS as good to 550 F for springs, which is certainly exceeded by a good margin. The Inconel is listed as 750-1100 F max temperature, which is still below what the lower rings will see, but would certainly be an improvement.

 

I used new rings when rebuilding the pack.

 

Russ bored out the combustion chamber slightly from 1.0” to 1.1” diameter, which increases the L* from 23 to about 27. We were hoping this would help light with the 85% peroxide.

 

Russ also made a completely new channel wall combustion chamber to replace the simpler water jacketed chamber, but we didn’t get around to firing it today:

media.armadilloaerospace.com/misc/cooledEngine.jpg

If it seals well and cools well, we will probably make a new one out of aluminum and try full regenerative cooling with peroxide.

 

Matt was back, so we have some good quality footage, but things weren’t running as well as they were the last couple times. We also had a leaky gasket on a couple of the early runs.

 

http://media.armadilloaerospace.com/2002_02_19/engine_tests_02-23-02.mpg

 

run 1:

new cat pack: 20 x 80 mesh, 30 x 20 mesh

070 peroxide, 018 fuel

fire, rough biprop, moderately smooth monoprop

 

run 2:

same, monoprop only

decently smooth, but not great

 

run 3:

quarter inch more pack compression, adding a spacer. This was a LOT of pressure.

more rough

 

run 4:

adjust feed line on the test stand to try to avoid theoretical bubbles

somewhat smoother

 

run 5:

same, with fuel

not lighting?

not full decomposition?

 

run 6:

0.022 fuel

reasonably smooth, didn’t light

 

run 7:

retest

new battery for solenoid

moderately smooth

we are out of kerosene, which is why the last run didn’t light

 

run 8:

more kerosene in tank

difficulty lighting, but finally did catch for a rough run

 

run 9:

replace pack spacer with 6 20 mesh silver + 7 stainless screens to get a bit more active area

still had trouble lighting

 

run 10:

We hooked up our ethane tank to see if we would have better luck lighting a gaseous fuel. The ethane tank was at 480 psi (Ethane is listed as 540 psi vapor pressure @ 70°F), which we regulated down. We knew we were going to need a lot larger orifice for the gas than for kerosens.

ethane, 070 ethane at 300 psi, 070 peroxide

rough, did not light

 

run 11:

0.120 ethane

no fire

 

run 12:

480 psi ethane (max)

no fire

minor noticeable change, but probably still not rich enough to light. The tiny solenoid is probably the restricting factor for gas flow right now, so we will have to change to a larger one when we try again.

 

run 13:

back to the other all 80 mesh cat pack to repeat a run from Tuesday.

070 peroxide, 020 kerosene

barely lit, very rough

The all 80 mesh cat pack instantly warmed up on its first run of the day, but it took a couple of tries to get the kerosene to light today, while on Tuesday with these parameters, it would instantly light on every push. We aren’t sure what is going on with this. We are wondering if the increased chamber diameter might actually be hurting the performance by cooling the decomposed peroxide as it flows out of the narrower fuel injection ring.

 

The mostly-20 pack is a lot smoother than the all-80 pack, but still not nearly as smooth as the all-20 pack we tested a few weeks ago, and it doesn’t seem to be getting 100% decomposition. When our screen order finally arrives, we will try to replicate the untra-smooth all-20 packs.

 

Rotor test

 

On January 5, we did our first spin test that just used a single engine on a marginally balanced rotating hub. We have addressed several issues we had with that test:

 

The test stand has secure legs.

The “rotor” is increased to 1/4" stainless pipe from 1/8” to give more rigidity.

We have a pair of balanced engines.

We have a tachometer sensor on the shaft.

We mounted the tank directly above the rotary seal with an AN-swivel union instead of a length of hose.

 

The test went flawlessly, and we let it spin up to just under 500 rpm with brief pulses of peroxide.

 

media.armadilloaerospace.com/misc/rotorTipEngines.jpg

 

http://media.armadilloaerospace.com/misc/secondSpin.mpg

 

The initial burst out of the engines was left over water from the water test we ran before we loaded peroxide.

 

We are tilting the engines down a bit so it acts like the rotor has more inertia, but it still doesn’t have much of any drag, so it spins up fast, and takes quite a while to slow down. Our big rotor blades should be here any day now, but we will have to reconfigure for spinning on top of our new vertical test stand, because it will be 27’ in diameter…

 

This current configuration uses a hollow rotating shaft that the peroxide flows through. This allows an inexpensive axial rotary joint, but makes it impossible to mount a parachute on the other side of the rotor, which we would like to do for the fast vehicles. We are probably going to be moving to an over-the-shaft rotary seal that would allow us to have a solid, static shaft, with the tapered roller bearings mounted on the hub instead of the vehicle:

http://www94.thomasregister.com/olc/rotarysystemsin/011.htm

I was quoted $3100 for this in 316 SS, which is a bit pricey, but it directly solves our problem. The RPM range is going to be a little marginal on it, but we should get by, because we will only need to see 500 RPM for a couple minutes at a time.

 

We need to get the tach sensor interfaced with a computer and work on automatic RPM control. There is a very long lag when turning the flow on and off, but I need to get some actual graphs on the response rate, then try to auto-control it. I’m not sure yet if we will use PWM on a solenoid, or see if we can get one of our KZCO ball valves in 1/4".