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Big vehicle work

Hover test hanging points

May 20 and 24, 2003 Meeting Notes


Hover test hanging points


The big vehicle will be hover tested hanging from four climbing ropes under a big crane.  We usually lift the cabin with chains through eye nuts on the seat belt harness backup plates towards the middle of the honeycomb bulkhead, but for load points that may take a pretty good shock, we want to feed directly into the cone metal.  If we just grabbed at the top, it would certainly bend the metal on a hard hit.  We have some 2” square blocks of milled aluminum already welded in up there as a secondary catch in case the main bulkhead bond ever lets go, but it took some work to arrange for lifting points from there.


If we had thought it all the way through earlier, we would have drilled ¾” holes in each of our bulkhead backup blocks before we welded them in, which would have let us just tie the rope off around a bolt through there, but we can’t get a big drill in with them already mounted.  We turned some little bars that we carefully welded in with lots of back-side water cooling to keep from cooking the nearby epoxy bond, but we were still a bit unsure of the joint strength. We decided to drill a hole through the bracket from the outside of the cabin, and thread the rope through that, then tie off to the bar, so it is pulling into the block instead of out of it.  There is a danger of cutting the rope like this, so we are going to smooth it out pretty carefully.


Ballast peg / helicopter lift point


When we do the parachute canopy helicopter drop test we want to simulate the full vehicle configuration as much as possible, so we are going to have to add a few hundred pounds of ballast at the bottom end to stand in for the full size engines and backup parachute weight.  We decided the easiest thing to do was make a peg sized for Olympic barbell weights that could fit through the manway flange.  I originally intended to machine the matching screw thread into it so it would thread through, but it turns out the manway has a metric thread on it, so we are going to live with just a smooth bore and a sturdy clamp holding the weights in place to keep it in position.


The end of the peg will also be the main lifting point for the helicopter, and the temporary parachute attachment point.





Electronics mounting flange


We intend to have a period of overlap where we are using exactly the same electronics in both the subscale and full size vehicle, so we built an oversize top pressure flange for the tank that has vertical supports where the circular electronics bulkhead from the small vehicle can be directly bolted in.  It has the 12 hole bolt circle and a pressure transducer tap underneath the electronics board, and a Viton O-ring on the bottom.  To hold the O-ring in place during assembly and still be peroxide compatible, I used some Teflon pipe sealant.  We also put some big lifting points on the plate, which will allow us to put chains through the open cabin hatch and down to the manway flange for horizontal lifting of the vehicle.


To make sure everything sealed well, we did a minor pressurization test of the tank with the electronics flange on top, and the existing manway flange on the bottom.  An entire tall nitrogen bottle at 2500 psi only took the tank to 52 psi, so we are going to need a bunch of bottles to pressurize for flight tests.  An argument can be made that we would be better off with a shorter tank for our pre-launch license flights, because we can’t load more than 200 gallons of peroxide (the tank is 850 gallons) without hitting the launch-license impulse limit, but we are going to have to change the tank for the larger carbon fiber one to make the full 100km flights.  This tank is basically the same mass as the larger carbon tank will be, but we could have used a somewhat smaller tank and added more ballast.


We galled one of the stainless manway bolts and had to cut it off to get the manway off after the test.  A couple people have recommended Braycote as a peroxide compatible lubricant / anti-seize, but Krytox is similar, and available from McMaster, so we will probably use that.  When we put the manway back on for the ballast peg, we used some of our normal anti-seize on the bolts, but we will have to have everything apart and cleaned before we load any peroxide into it.




Tank / cabin coupling


Baldwin fabrication was able to rush out a new 11” conical coupling section for us this week, since we found the 7” ones we got last week too short for comfort.  These will work fine, so we used extra care aligning everything with laser levels and surveying equipment, and bonded the section to the tank.  The fiberglass and aluminum were both prepared with a power belt sander and coarse paper, then cleaned with alcohol, then painted with epoxy, then covered in fiberglass filled epoxy.  After settling the coupling back down to our marked points, a filet of filled epoxy was built up at the bottom to fair the tank into the aluminum coupling, and we used empty caulking tubes filled with fiberglass/epoxy to put another bead on the inside.  We covered the outside with peel ply, so we can put an extra wrap of fiberglass around the joint on Tuesday.


This looks like it is going to work out well – we will be able to transfer the entire cabin section to a different tank with only a day’s worth of work.




The electronics mounting flange bolts in place of the small aluminum lifting plate shown at the top of this image.


Transport cradle


Joseph did some work on the transport cradle for the big vehicle.  We should be testing moving the entire thing around next week.  We talked about a lot of options for building trailer mounted lifts and winches for flight operations, but we decided it is simplest to just rent a crane for flight operations, and just let the trailer be horizontal transportation.  We have castors on the cradle for moving the tank around the shop, and just stand it of on wood blocks when we strap everything down on the trailer.




Coming up


I am putting together a separate little computer system for the helicopter drop test, so in case something does go wrong, we don’t wreck all the expensive electronics.  I got another 50G triaxial accelerometer, so we will have acceleration data for both the cabin end and the engine end, which may hit harder as the vehicle falls over.


We will get the cabin fully  mounted on the coupling flange.


We are working on some lifting devices to allow the entire vehicle to be tipped and moved with a forklift.


We are working on engine mounting for the 6” engines.  We will be doing the hover test with just four big-nozzle 6” engines, but we will probably be adding the 12” engine in the center when we want to start flying it fast.


We need to build our launch stand that fits around the mounted engines.


It is looking like we will have the big vehicle ready for hover testing by the time we secure our large scale peroxide supply.  We are currently hopeful we will be flying the small vehicle within a month, and the large vehicle a month after that.


http://www.armadilloaerospace.com/n.x/Armadillo/Home/Widget%60s%20Corner (I moan and complain that it is “propellant” or “peroxide”, but since I’m not actually paying for any artwork… :-) )





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