Totally far out. Any MPEGs down the line?
John Carmack wrote: > It is so nice when things make analytical sense... > > We did tube hover tests today. It was cold, but no longer humid, so once > the engines warmed up they were clear, which was a relief. What was > frustrating was that we did the first test with 250 psi tank pressure, and > even though I wound up throttling all the way up, all the tube did was > scoot sideways a little bit. This did not make sense, because the test > stand results indicated it should have over 500 pounds of lift with a > straight shot to the engine. We had modified our procedure to do the > engine warmup pulses while the pressurization hose was still regulating the > vehicle tank, so there was no drop in pressure, and it had plenty of time > to get the initial pressurization cool-down pressure drop compensated for. > > We loaded up again, and went to 300 psi, the highest I want to take this > tank. It did the same little scooting thing. We were fairly mystified, so > we pulled it back inside and very carefully balanced out two scales to > weigh the vehicle (280 pounds without the parachute and draw tower), then > used one of those scales with a hydraulic jack to calibrate the test stand > load cell. Everything checked out. At 300 psi, it should have been > pulling almost a full G of acceleration. > > I checked the motor valve calibration to see if it might have only been > opening halfway, but that was right on. > > It finally hit me: > > Krushnik Effect! > > The base flare is only held about three inches off the ground by the wire > rope isolator feet, so the rush of gas from the main engine has to > accelerate a fair amount to escape radially. The 4' diameter flare base > has 1800 square inches of area, so even a small pressure drop would > overcome the 250 or so pounds of net engine thrust. > > We cut some more polyethylene blocks to stand the entire thing another 3.5" > off the ground, and tried again. It was a good thing I was ready for it, > because during throttle up, the vehicle basically "popped" off the ground > at a pretty good clip. A caught it just before it came up on the tether, > and got it back down. When it hit the ground it knocked off most of our > foot extensions, so it was sitting at a crooked angle, but everything came > through nicely. I just blew all the peroxide out the attitude engines, > rather than try and lift off from a 20 degree tilt, but the test was a > great success. It flies nice and straight while accelerating under > guidance. It should be a pretty flight when we go to altitude. > > If the weather cooperates, we will do parachute tests on Saturday, then we > will be ready to fly (probably in Oklahoma, it looks like). > > John Carmack > > _______________________________________________ > ERPS-list mailing list > [EMAIL PROTECTED] > http://lists.erps.org/mailman/listinfo/erps-list -- >>>>>>>>>>>>>>>>----<<<<<<<<<<<<<<<<< ........ Alex Fraser N3DER ......... ......... [EMAIL PROTECTED] ....... [~]_>^</\-[~]_>^</\-[~]_>^</\-[~]_>^< _______________________________________________ ERPS-list mailing list [EMAIL PROTECTED] http://lists.erps.org/mailman/listinfo/erps-list
