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Monday, June 14, 2004
Armadillo Aerospace News: Streamlined hovers and landings
Armadillo Aerospace: We completed the streamlined subscale vehicle and conducted several hover tests this week. Total vehicle weight is 310 pounds dry.
We did some drop tests from the hoist to evaluate the shock absorber landing gear, and they did a very good job, even when the vehicle was swung before release. Without any bounce, the vehicle just settles down, even at slight angles.
It has been raining a lot, and it wouldn’t let up for us at all on Tuesday, but we really wanted to test things out, so we put a big plastic bag over the rocket nose to give some extra cover to the electronics, and went ahead and gave it a try. The flight control software had been modified to predict acceleration some time in the future to compensate for the time lag between moving the valve and engine chamber pressure changing, which should smooth out the up/down oscillations in hover and landing modes.
We stood the vehicle up on the big foam blocks so we didn’t need to trust it to come down straight, but this put them too close to the engine on the narrow vehicle, and we burned off a lot of the aluminum covering we added. We are probably going to get some stainless foil next time.
This engine didn’t warm up as nicely as the engine on the lander, which we attribute to the lack of a compressed hot pack. After it finally got warm, the hover looked very good, but it ran out of propellant before it landed, which made us very happy we had done a block launch instead of a ground launch. We did another run with extra propellant, and everything went normally. The acceleration prediction seemed to be working very well.
At hover, the chamber pressure was only 100 psi, so on a boosted hop with even a 0.5G stabilize level, we are looking at a 50 psi chamber pressure, which is certainly going to separate inside the nozzle. We seem to have pretty good luck with even separations, but we have certainly seen some single-wall attachment separations, which I have been very concerned about disrupting flights. We decided to cut off some of the nozzle, taking it down to only about a 1.8x expansion ratio. This will be underexpanded on boost, and still rather overexpanded during coast, but it will hopefully be a reasonable compromise. Read More
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