April 9 and 13, 2002 meeting notes

 

In attendance:

 

John Carmack

Phil Eaton (Tuesday)

Russ Blink

Joseph LaGrave

 

 

New Engines

 

Our stainless steel CNC work from DynaTurn came in, and it turned out wonderful.  I had them make 11 engines, including catalyst chambers, nozzles, spreading plates, and retaining plates, so we would have enough for two complete vehicles’ attitude control, two rotor tip engines, and one test mule.  These pieces are combined with Smalley spiral retaining rings as anti-channel rings, pre-cut stainless screens, copper vacuum flange gaskets, and pure silver screens that we cut with an arbor punch in our hydraulic press.  We grind down the top of an aluminum –4 AN fitting for a jet holder, and use Edelbrock stainless steel flare jets for metering.  We finally got a pressure gauge installed on our hydraulic press, so we now have accurate measurements of the compression that we do after each anti-channel ring is installed.  For these 1” diameter cat packs, we go to 500 psi indicated, which, if the external press barrel is fully loaded, works out to about 1500 psi on the screens.

 

 

With a 0.080” jet under an NOS Pro-Race solenoid, these engines make a very smooth 30 pounds thrust at 600 psi tank pressure, which is adequate for our attitude control needs in a balanced engine.  There is a pretty severe pressure drop through our packs, which consist of usually 57 20 mesh stainless discs and 70 32 mesh pure silver discs, but we can live with it.  Plated screens can get by with less total screens of a coarser mesh, but we value the fact that we have yet to have a pure silver based pack wear out at all.  I am going to have a batch of 2” catalyst pack engines machined next week, which can serve as larger attitude

 

It has been interesting running the stainless steel engines, because on a long run, they glow quite visibly red hot.  The brass engines get every bit as hot, but don’t visibly glow even on long runs at night.

 

We fitted four of the new engines, all fully bedded in, to the big lander, and carried it out for a simple ground test of the attitude engines.  This was also the first test of our new fill equipment on a vehicle, as opposed to the test stand.  We washed the entire system with five gallons of water, because it had been sitting around for several months now.  We then loaded two gallons of peroxide, and Russ suited up and set in the seat to run the engines with the manual push button controller.  After warming (which still involves an initial gush of liquid, unlike the foam packs), all four engines were initially perfectly smooth, far better than our previous engines.  After a little bit of running, one of the engines started to have severe pulsing oscillations, sounding like a machine gun.  We had heard this type of roughness with the foam engines, and we were always wondering if it was a plumbing issue, or because the engines didn’t have jets in them.  We were disappointed to hear it with the new engines.  It is worth noting that they were still catalyzing perfectly, while the foam engines would have probably been shot by the end of those runs, which totaled about 60 seconds of firing time on each engine.

 

To determine if it was related to the plumbing, we switched two of the engines, leaving the plumbing and solenoid constant.  On the second load of two gallons, the same engine, in its new position, continued to show the roughness.  After a little while, a second engine started behaving the same way, and later a third one started to intermittently do it.

 

We are rather confused at the moment.  We did note that the first engine to show the problem was the number 0 engine, which we did a longer set of break in runs on, so it seems to be a wear or bedding in issue, but we have run similar packs for many minutes of fire time without showing the problems.  There are three differences of note:  the packs are now stainless steel, which will retain somewhat more heat, these runs are at 500+ psi, while all our recent work has been at 250 psi on the test stand, and these are vertical firing instead of horizontal.

 

Next week, we are going to take off the first rough engine and run it on the test stand at the same feed pressure.  That will be an interesting data point one way or the other, but in all likelihood, we will wind up opening each engine and adding a couple screens.  The higher heat retention and pressure has probably squashed the silver a little flatter, so we expect the packs to be a bit loose.  It may just become standard practice to add a few more stainless screens after running, or perhaps use a higher pack compression during assembly to deform the silver around the stainless earlier.

 

We are looking forward to getting the big lander back in the air.  We still have to make a screen based main engine, but once we do, we should be able to finally get through long enough series of tests to safely get a person in the air.  I also have a significantly changed software architecture to begin using, and we have the laser altimeter to test.

 

New Rotor

 

Our new rotor is assembled.  The list of improvements:

 

Hub bar made of 7068 aluminum, instead of 6061, for a 2.5x strength increase

Hub bar inserted and bonded length more than tripled

Better prep for the metal filled epoxy bonding, including a dilute nitric acid wash

Using 180ksi strength cap screws with proper grip lengths for retention, three #10 and two ¼” on each hub bar, and two ¼” on each tip engine mount

Using Kevlar-phenolic board for insulation between the tip engine and the engine mount

Tip engine mounts made out of 7068 aluminum instead of brass, for a tip mass savings

Tip engine chambers machined down to save over half their mass

Tip engine chambers in stainless, for a slight mass saving and a significant pressure rating increase

Tip engines retained by #10 cap screws instead of #8

Rotor hard line tubing changed to 8000 psi rated stainless tubing, instead of 2000 psi rated aluminum

 

The test stand uprights have been rebuilt, with a sturdier bearing mount.

 

The blades are set at 20 degrees of pitch, instead of the 10 degrees the old ones were at.  There are concerns about exactly how the rotor retention strength should be calculated due to multiple attachments and bonding on a long shaft, so we will probably not spin this much faster than the original, although the higher pitch will give significantly mote lift.  We will be doing test spins next week, with computer control of the RPM.