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May 6 and 10 meeting notes

May 6 and 10 meeting notes


A whole lot of miscellaneous notes:


We are talking to Yet Another Parachute Vendor for the full size vehicle: Strong Parachutes.  They are already working on parachutes for Starchaser, so the odds of them getting cold feet on us are probably slim.  We are hopeful about getting a main canopy for helicopter drop tests of a full size vehicle by July.


We have continued some alternate propellant engine tests with 50% peroxide and the XCOR igniter, but we haven’t had any success to speak of yet.  We did manage to foul the spark plug in the igniter once, and overheat it a bit so that one solder joint melted, but the problems were easily fixed.  We have little doubt that a 70% peroxide / kerosene biprop would light up easily with our current setup, but the 50% peroxide mixes cease combustion when the igniter torch goes out.


We have one more direction to pursue before giving up on the 50% mixtures:  peroxide / methanol with a pre-heated platinum catalyst.  This has some interesting possibilities, because methanol burns catalytically in contact with hot platinum (a significant aspect of how glow fuel based engines work, and it also functions with propane in catalytic heaters), and hot platinum is also a good catalyst for peroxide decomposition.  I will be testing some catalysts from Catalytic Products International www.cpilink.com , which may also turn out useful even if we stick with 90% peroxide.  One thing that this will force us to look at is catalyst pre-heaters, because platinum is a much poorer catalyst than silver at room temperature.  Even silver packs could probably benefit from pre-heating, which would likely make startup much more consistent.  We are experimenting with some heating elements and temperature sensors for this.


We hope to have some 70% peroxide for tests soon, and our efforts to secure additional 90% peroxide seem to be looking up a little.


In support of our alternate propellant work, I just bought the rather expensive "Handbook of Reactive Chemical Hazards."  A couple extracts:

Acetone and hydrogen peroxide readily form explosive dimeric and trimeric cyclic peroxides, particularly during evaporation of the mixture.  Many explosions have occurred during work-up of peroxide reactions run in acetone as solvent ... A general warning against using acetone as a solvent for peroxide oxidations is given.

Furfuryl alcohol ignites in contact with 85% peroxide within 1 s.


Detonability limits of mixtures with 2-propanol have been measured.  Approximately stoichiometric combinations of 50% hydrogen peroxide and the alcohol could be made to detonate, as could a wider range of mixtures with higher test peroxide.


It is worth noting that the entire book seems to be basically a collection of empirical observations and anecdotes from the last fifty years, which isn’t really as rigorous as I was hoping for.  The accuracy may be a bit questionable as well – we testing furfuryl alcohol with 90% peroxide, and it doesn’t self ignite at all.  Perhaps the case of ignition involves combinations of additives or stabilizers in the two chemicals that were not present in our samples.


Neil has been busy doing meetings with government officials regarding launch licensing and operations.


Joseph has been laying the foundation for our new peroxide storage facility and test stand support building.


We have been doing some final work on the sub-scale vehicle, so as soon as we get more 90% peroxide, we should be ready to fly.


The flaky damaged Esteem wireless bridge has been replaced with a brand new unit, which we have mounted vertically so it can stay in the factory shielded case.


The entire electronics bulkhead has been mounted on a vibration isolating ring which is side bolted into the tube, instead of sliding the electronics bulkhead down over studs coming from angle brackets bolted to the side of the tube.  It is likely that the damaged Esteem was the only thing really being effected by vibration, but we decided to proactively attack vibration and shock for the future.  We had originally intended to use four bonded rubber isolator mounts in place of the mounting studs, but the stamped angle brackets weren’t really square enough to provide a good base, and we were finding we needed more points of support around the outer ring anyway.  I milled a complete 24” OD ring out of ½” thick aluminum, and we bonded a ½” wide strip of fairly soft foam rubber on top of it.  Because we use nutserts on the inside of the tube to retain the bolts that hold the nose cone to the body, I had to add cutout pockets to the ring to allow it to slide by them.  I made equidistant pockets on the mill, but it turned out that we had just sort of eyeballed the nutsert placement on the tube, so we had to do some last minute hacking to make it fit.  The honeycomb electronics bulkhead was sanded and bonded directly to the foam rubber with RTV.  We sanded 1/8” off the outer diameter of the bulkhead, so it now has a nice multi-axial vibration mount when inside the tube.  This may lose some bandwidth from the inertial sensors, but most of the isolation should be well above 100hz.


We did a drag test on our Kevlar drogue chute to see how much load the vehicle would see at burnout deployment, and how fast it would need to be going to deploy the main chute.  We had a hanging scale hooked up to the parachute cable, but getting a good deployment was trickier than we expected.  We first tried just tossing it out the back of Phil’s suburban, but the base drag was so high that we couldn’t get it to inflate at all.  We then tried out the sun roof, which didn’t work much better.  Finally, we rigged up a pulley on the end of a six foot wooden beam, and stuck that out the sun roof, which worked fine.  The chute produces about 35 pounds of drag at 50 mph (22 m/s).  In theory, a deployment at 200 mph would give 16x, or 560 pounds of drag on our release latches.


We hung the small vehicle from the hoist, and hung weight from the parachute release chain underneath it.  The releases worked fine at a terminal velocity (weight of the vehicle) test, and nothing broke when we hung 900 pounds from it, but the latch bodies did bend a bit.  We will probably have to build some stronger releases when we want to fly this vehicle with a large propellant load.


Matt is finally done with his heavy work load, so we have some pictures of work from Saturday:


http://media.armadilloaerospace.com/2003_04_11/newShop.jpg (those are our empty peroxide drums that we just had sent back from our storage warehouse, since we no longer have anything to actually store there)







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