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December 2 - 15, 2001 Notes

December 2 - 15, 2001 Notes


The new vehicle, all set:




We were all set for a series of flights that was intended to end with our first manned liftoff today. The vehicle was ready, the computers were ready, we had plenty of peroxide and plenty of nitrogen, we had ballast measured, the ambulance was standing by and…


The engines started running cloudy.


At first we thought it was because it was cold and drizzling, but two of the attitude engines did completely clear up, while two stayed far too cloudy to fly with. We vented all the peroxide out of one of the clear engines, and by the time it was done, it was starting to cloud up as well.


In our rush of progress on the vehicle systems, we never did really solve our catalyst pack wear problems. We only get about 120 seconds of fire time on a fresh pack before the engines start clouding up – that is usually three flight days with two or three flights each. Now that we are flying larger and larger vehicles, it is only going to get worse. We need to address this. An old reference book referred to pack lifetimes in HOURS for some engines.


We are just about out of our current batch of plated foam, so we are going to get a new batch made with a different process. Our very first couple sheets of foam were plated so thick that the foam was “crunchy”, and broke off in little pieces when bent. That seemed to last very well in our original tiny 20 pound motors, but other factors, like total pack depth, and high pack compression, may also have played a part. The big batch of foam was plated thinner, and seemed to have worse wear characteristics from the start. We have also been told that we should have the plated silver sintered onto the foam before use, but we will just be guessing on parameters.


If foam plated thicker and sintered works out, that will be great, because we won’t have to change our engines. If we have to go to a silver screen based pack, we are going to have to make brand new engines, because screens require about twice the pack depth of the foam packs. They also take about four times as long to warm up (Mark Henry said that his specially plated screen packs warm instantly, but Juan Lozano’s screen packs and our pure silver screen packs are significantly slower) and weigh several times as much (not that the weight is an issue…). Long life is probably the most important thing for us, although really long warmup times might be a bit of a problem if a person is sitting on the vehicle.


We built a proper pure silver screen catalyst pack for one of our test engines tonight. We used our hydraulic press to push our cutter through about 14 layers of screen at a time, which worked out very nicely. We compressed 52 silver screens into the area normally occupied by about 23 of our compressed foam discs. When we test fired the engine, we were appalled to see liquid peroxide gush right out of the engine on the warmup pulse. This was right after water testing everything, so it was a cold, damp pack, but still… We had stopped doing warmup pulses altogether on the foam packs. It made 30 pounds of thrust, but even after multiple warmup pulses, it never ran clear. We believe that we need twice the pack depth with the pure silver screens.


We are going to make a quick test motor with twice the pack depth to see if we can get stable performance out of a pure screen pack, then we will run it for a couple minutes and see how it ages.


We have a bunch of other miscellaneous stuff going on as well:


The laptop remote piloting program has been modified to show a realtime graph of tank pressure, which we are now using as a fuel gauge for flight – it changes the entire background color when it goes below a warning level, which is visible even in your peripheral vision. We are now using exact, specific amounts of peroxide and pressure for the flights to make this repeatable. The initial decay of pressure as the tank cools after filling is a bit of an issue, but we are putting the warning at a conservative level.


We should be spinning a pair of little engines on a shaft within a couple weeks. I got a couple 1800 rpm rotary seals from www.rotherm.com for the shaft. They aren’t very peroxide compatible, but they will be downstream of the valve, so we are going to see how they do.


We are looking at using an airboat prop from http://www.airboatprops.com/ for our first lifting tests. It won’t be optimized for high speed, but they can be configured for over 2000 pounds of static lift. A rocket driven prop will give us about a 6x lift multiplier at liftoff – the props deliver up to four pounds of lift per shaft horsepower, and a tip engine generates about 1.5 shaft horsepower per pound of thrust. The lift multiplier goes down as speed increases, going negative into pure drag at some point around mach one.


We are buying a bar of TZM alloy molybdenum to make some test nozzles for our hybrid engines. This maintains good strength over 3000 deg F, but it needs an oxidation protection layer. I had been hoping to use ruthenium, which is cheaper and high melting than platinum, but I have been told that it is difficult to get a pinhole free ruthenium plating, so we may wind up with platinum plating.


I finally got the LCD panel working with our flight computer, but the digital signal is touchy enough that I couldn’t put an extension between the panel and the computer. The next generation electronics box will probably have the panel mounted directly on it. I also ran into a similar signal extension problem trying to run a USB joystick through our normal CPC connectors – two feet of unshielded, untwisted wire seems to be too crappy even for low bandwidth USB devices.


Our one-watt 802.11b systems should be here soon.


I am looking at possibly buying this laser altimeter: http://www.laseroptronix.com/flyg/altm400.html There are a couple radar altimeters I am also looking at, but they are more expensive. I am very excited about getting a fast altimeter integrated with our systems, because then we will be able to get good auto-hover and auto-land running. I am probably going to implement that in the simulator soon.


We are preparing to do some test composite fabrication. We are going to try making bulkheads for our 2’ filament wound tubing, and see if they can hold enough pressure to act as a pressurized cabin or a propellant tank for the rotary pumped engines. We are going to just use city water pressure to hydrotest them to 50 psi or so.



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