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September 6, 2003 notes

September 6, 2003 notes


I am going to start putting a link to each Armadillo update at Frontier Files Online, a Slashdot-like message board system run by the Al Differ of JP Aerospace and the Space Frontier Foundation.  I get a lot of useful suggestions from people by email, but it will probably be interesting to let everyone publicly discuss Armadillo technical issues, and my replies to specific comments will probably be of interest to more people than just the comment author.




We had a pretty light week, because delivery of our big catalyst order was delayed again.  They are now projecting a ship date of next Friday, but I am trying to get them to ship three 5.5” rolls earlier so we can do engine testing next Saturday.  Engineering designs certainly do benefit from using standard parts that are available for next-day shipping from McMaster-Carr, but there are a few specialty items that we just need to deal with longer lead time suppliers on.


Don Stark is reporting that he has the first five gallons of concentrated 90% peroxide ready for us, but I told him we don’t really want to start using it until we have at least 20 gallons on hand, enough for us to ground test, hover test, and flight test the small vehicle, barring problems.  We have contracted for five hundred gallons of peroxide from him, which will be enough to do all the tests we want with the small vehicle, and fly the big vehicle a couple times with silver screen based engines if the mixed monoprop engines wind up not working out.  If the mixed monoprop engines do work out, we will wind up sitting on most of the 90% peroxide until we get back to working on biprop engines for upper stages.


We had an interesting experience looking for replacement zippers for our space suit – the seamstress that we had given it to was looking all over the DFW area for appropriate heavy-duty zippers, and finally found some at a tent / awning fabrication shop.  It turns out that the owner was actually involved in making the original space suits for the monkeys way back in the early 60’s US space program.  He knows exactly what to do, so we just turned the project over to him.


Several readers suggested mooring line snubbers for line shock absorbing for our big hover tests.  They were cheap, so I bought a couple of each size, but it turns out that they aren’t nearly strong enough for us.  The thickest snubbers, designed for 1” diameter lines, broke with only about 900 pounds of force.  This is probably still a good direction to investigate, they must have larger snubbers of some kind for ocean going ships of various kinds.  It still seems to me like there should be some arrangement used with steel cable that operates on the same principles as wire rope isolators, which would allow us to use them without insulation.




We have matching press plates for both the 5.5” and 12” diameter engines now.  The next engine we build will have the pack plates welded in with the assembly under moderate pressure to prevent any warping.  We should have laser cut pack plates from Global Stencil for both engine sizes next week.




We finished up the preheat system for the full size vehicle.  Four quick connect lines go to each engine and meet at a manifold on the ground, which is connected to 50’ of line leading to the propane and air tanks.  We plan on using compressed air tanks instead of an air compressor in the field, because an air compressor capable of supplying 16 cfm sustained is very large.  Because the air tanks will be significantly emptied during the preheat, I bought a dual stage regulator to minimize the pressure drop.  If the air flow dropped off, the fuel mixture would go closer to stoichemetric, and we would start melting screens in the engine.  I am still a little concerned that even if the air flow stays constant in CFM, the density will be increasing due to the reduced temperature as the bottle empties.  The flow meters we are using are not temperature insensitive, so there is some self-correction, but it may still be a factor.  We changed to a larger flow meter on the air side, so we can measure enough to preheat four engines at once.  Small check valves in our preheat system limited us to flowing 14 cfm, so we will have to replumb some of those to ½” to get the flow to our desired 16 cmf.  At 14 cfm, one air bottle ran four a bit over 4 minutes, which is borderline for a full preheat, so we will probably take two bottles.




We changed the compression thread on the spring cannon over to a 1” diameter acme thread with a bronze nut and added a big T handle, which makes the compression a lot smoother.  We noticed that our retention cable that keeps the spring and piston from flying out of the cannon is fraying a bit.  At first, we thought this was from the shock, but it turns out that it gets pinched by one of the shackles during compression.  We tried another mounting point, but it didn’t fix the problem.  When we build a 6” ID cannon, we will have a lot more room to give it a separate mounting point.





We built some simple strap clamps to allow us to bolt the hatch on the vehicle without requiring air pressure to push it in place.


We prepped five 1” KZCO valves for the big engine development and deployment.  Our prep work consists of venting the ball valves, bridging over the thermal cutoff control (if we are flying, we would rather have a valve motor die trying to operate than cut off when it gets a little hot), and soldering some terminals on the driver board.


The welded distribution manifold still leaks, so we started working on a replacement that would be configured with two ports on two sides, instead of one port on four sides, which will avoid the need for a big 90 degree fitting.  I was boring the main 3.75” deep by 1.8” wide hole on the mill using helical interpolation with a 1” diameter end mill, but half way down it grabbed and broke the bottom cutting edge off the bit.  It would have been faster to just bore it manually on the lathe, but I tend to prefer building parts on the CNC mill, because it makes building the part a second (or third) time a lot easier.




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