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 cant 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
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
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 cant
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
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 days
worth of work.
The electronics mounting flange bolts in place of the small
aluminum lifting plate shown at the top of this image.
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.
I am putting together a separate little computer system for
the helicopter drop test, so in case something does go wrong, we dont 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
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
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.
(I moan and complain that it is propellant or peroxide, but since Im not
actually paying for any artwork