Dec 28 meeting notes:

Location: Norwood Autocraft, plus a stop at Long Range Systems

In attendance:

John Carmack
Phil Eaton
Russ Blink
Neil Milburn
Bob Norwood

Next meeting will be Tuesday at LRS if the peroxide shows, Norwood’s if it doesn’t.

Consolidated Freight picked our peroxide up from X-L on Tuesday, so it should be here any day now.  Really.  We hope.

The shipping method is worth a mention:  we are getting a five gallon container of 98%, but it is shipped in a 55 gallon drum.  Another empty five gallon container is included to keep it from falling over, and an inch of water with a lot of stabilizers is poured into the bottom of the drum, so if there is a leak internally, it will become highly stabilized.

I have been unable to find a reasonable size commercial space that fits our needs.  I may start looking at building something, but an interim plan I am considering is to find a local chemical company that would be willing to store a 55 gallon drum of peroxide for us, and let us just pick up a gallon or two at a time as we need it.

Phil has our flight waiver at the FAA for the dumb rocket.

Phil has all the needed launch site info for the insurance company, but needs to get it to them, then I need to get them a check.

Phil needs to place an order for our launch rail and base.

The silver screens still haven’t shown up.

We still need to have some of the new metal foam silver plated and sintered.  We should get the exact process parameters from the plating shop this time.

Neil and Phil brought the dumb rocket components tonight, and everything fits together fine.  It is being assembled with a 98mm engine mount, so we can test it with conventional HPR motors, then install our peroxide motor with an adapter.

We hope to launch it on an L-600 (roughly what the peroxide motor should be) with the tank loaded with water and functional electronics at Shoot For The Stars next month, if it doesn’t get rained out for the fourth time.

My wife had her graphic artist create some Armadillo Aerospace artwork, and we will get some of it transferred to mylar adhesive for the rocket.  Did we settle on a white paint job? 

Depending on when the flight computer arrives, I will either have a dumb GPS telemetry relay for it, or we will run the full flight computer with multiple sensors and blinking lights to test actuation.

I think I found the flight computer I want: http://www.winsystems.com/products/sbcs/lbcplus.htm

It is a bit overkill, but it has four serial ports built in, and the video and ethernet will let me do normal software development on it just like any other computer.

I am waiting to hear back from them with a quote for everything I need.

I made large changes to the VTVL simulator last week, primarily to validate the canted engine roll control and tolerance of variability in engine placement and efficiency.  It works surprisingly well.  If you run it in full manual mode (which is basically unusable), you can see the cross coupling between roll and the other axis, but with the computer doing the angle seeking, It Just Works.  This is very good news  four fixed engines gives full three axis attitude control.

I am officially changing my axis naming for the simulator so that “roll” is the conventional rocketry use (around the axis of primary thrust), instead of having it be “yaw” as it is in my games.

We test-fitted things on the VTVL platform tonight, and found that some things don’t fit.

The top crossbar and engine mounting tabs are perfect, but the engine canting tabs are an inch or two too short.  We could still use them by swiveling the engine mounts a bit to the side, but we are having new pieces cut anyway, because the solenoid mounting holes were also off.  We left the solenoids and tank with Bob to test fit.

We are still waiting on the two sticks of thin tubing for the tank mount and landing legs.

We moved the electronics platform from under the crossbar to above it.  This means the electronics will need separate crash protection, but it allows the bottle bars to be welded directly to the crossbar, and save seven inches or so of leg height.

We had originally planned on having the distribution manifold on top of the crossbar, but things work out a lot more symmetrically with it directly connected under the bottle.  Unfortunately, that means that the four hoses we made are now too short.

With the engines under the crossbar instead of add the bar ends, we need more 90 degree fittings.

The solenoids require a check valve between them and the bottle to use vacuum loading, which complicates the bottle to manifold connection.  Phil and I fitted everything together to put the fill port ahead of a check valve ahead of the distribution manifold, but it is a pretty ungainly mess.  It may actually be better to use a check valve per engine, which would let us put the fill port on one of the extra manifold ports, and save eight inches or so of connected fittings.

Russ needs to tap his bottle manifold out to quarter NPT from 1/8”.  It isn’t critical for the VTVL, but we will need the flow in the dumb rocket.

If we are going to use Russ’s manifold instead of the NOS one (and the arguments are good for it), we should look into adding blow off valves somewhere else in our plumbing.

I just ordering 30’ of 3 teflon hose, 8 1/8” to 3 90 degree fittings, 4 straight 3 hose ands, and 4 45 degree 3 hose ends.

Stuff to do over the next couple meetings:

Finish the VTVL and dumb rocket assembly.

I will bring two laptops and radios next week and demonstrate how the real flight telemetry system will work.

Assemble and test battery packs for the VTVL vehicle.  We should get several identical packs made, so we can do back to back testing in one sitting without worrying about recharging or running out.  We should test them with all four solenoids hooked up and running a high duty cycle to make sure they won’t run out too fast.  I am getting an unregulated 12v to regulated 5v power supply for the flight computer, so hopefully everything we need to run can work off of one of the two voltages.

Experiment with the big automotive fuel injectors.  We should take a look at the spray pattern and see how much pressure they can open under.  They won’t flow enough for our current uses, but they might be a good optimization point for other projects.

If we have peroxide, this is the test plan I propose:

Russ: make sure we have plenty of nitrogen!

Continue with 100ml test runs on the small engine until we really have it sorted out.  The existing cycle of a 100 msec pulse followed by a 300 msec delay, then full on for ten seconds (which will exhaust everything) should also be followed until we are reliable, then we can experiment with PWM duty cycles.

Use 85ml of 98% peroxide and 15ml of distilled water (I will bring a jug next week), which will give us 83% concentration.  There still seems to be some debate about the maximum concentration usable with silver catalysts, with some sources citing 85% and others citing 90%.  If we get good reusability out of our catalysts at this level, we can increase the concentration to 90%.

Michael at X-L cautions that diluting the 98% takes a fair amount of mixing, and that it will generate a bit of heat.

Start off with 200 psi pressure and the .040” jet.  If it works reliably, increase the pressure to 450 psi and possibly larger jets.

We currently have all of our decent silver foam packed into the small engine, but there was already some erosion on some of the discs.  If we get degrading performance with subsequent runs, we are probably still either washing the silver off or poisoning it.

We should try a pack of the pure silver screens when they arrive.  That will lay rest to the washing vs poisoning argument.  If we are poisoning, we should get some nitric acid so we can experiment with cleaning the pack after each run.

We need to experiment with better injector plates.  If nothing else, I want to block off the central holes in the current plate.  Just putting a dime behind the plate should be a step in the right direction.  Darin: email around the specs you got from the laser cutting shop.

We can test Juan’s motor, but we will run through our peroxide pretty quickly with it.  500ml should be enough to get a look at it.