Sunday, December 26, 2010

Building three simultaneously = efficiency!

I'm taking advantage of my two-week break from work to complete construction on:
  1. 4" Extreme DarkStar - This was my gift to myself this year after seeing KO's success with the all-fiberglass kit. I've decided to break this one in with the pink M1676 Pro75 motor.
  2. Madcow Rocketry 4" fiberglass Nike Smoke - Thanks to the kind generosity of my parents who bought this kit for me for Xmas I plan to select motors with reckless abandon on this one.
  3. 3" Vertical Ass... - This is my abbreviated kit bash of the Vertical Assault parts from Giant Leap Rocketry.
Those are the second and third all-fiberglass rockets I've built and they seem to go together quite nicely. Here are the first two in my studio for scale:
And here's the build progress on the Vertical Ass... I took this opportunity to neatly cut exact diamond shapes from the 3" tube to perfectly fit the fin can shape:
Here's the clamping setup while the epoxy cures:
And I'm very pleased with the final cured form of the assembly:

Thursday, December 16, 2010

Further analysis for DRM II's first flight

I was chatting with my aerospace buddy Chris at work today and, having seen the blog entry and data below, he was as confused as I about the barometric altitude curve shape. I normally plot barometric altitude as that's accepted as the official peak. Accelerometer-based altitudes can suffer from integration errors caused by wobble, spin, coning or other undesirable flight behavior. Chris asked if it might have been caused by a Mach transition effect but I only hit Mach 0.58 so I was nowhere near the transonic region (0.8-1.2). I continued to ponder this irregularity and think I can explain the difference. In this alternate plot from the Raven you can see that the accelerometer-based altitude is shaped as one would expect with air-starts (slight slope increase when they kicked in):
I remembered that the aluminum tube that connects the electronics bay to the motor area was not plugged. When I pulled the camera it had a bit of smoke residue on it and the electronics board smelled sooty. This 7.5" rocket produces a great deal of base drag that I think forms a vacuum. I think that's why the barometric curve is steeper than the accelerometer curve and why there's an inflection point after the air-starts burned out. Then base drag decreased at that point which might have increased the pressure in the electronics bay just enough to flatten out the barometric curve in that weird region. In any event the rocket turned only once and otherwise flew straight up so I'm going believe the accelerometer curve in this particular case. Let me know if you have other thoughts. I'll definitely plug up the conduit with clay next time to reduce this pressure tomfoolery.

Sunday, December 12, 2010

Der Red Mix mark II... For The Win!

Last weekend I flew DRM mark II for the first time on a central L730 Classic and 2 x I345 White Thunder air-starts 1 second after the L burned out. I couldn't be more pleased with the outcome. First off there was pretty much zero wind all day at Plaster City though that came at the cost of a persistent cloud ceiling at roughly 6-7k feet. I had prepped a bit the night before and mounted the Flip MinoHD video camera and altimeters/battery holders on the board and also assembled the recovery system. On the drive out I decided I didn't want to char the innards of DRM II with black powder and so committed to investing in the Rouse Tech CD3 Jupiter ejection kit with 28 and 35g CO2 cartridges. This added about 45 minutes to the prep once purchased and built so I flew at noon. Thanks KO for shooting some prep shots:
[Note to self: stop talking whilst being photographed.] I got out to the pad and realized it's pretty difficult to get that 6+ foot long, 26 pound thing on the rail myself. Luckily a few folks helped. Here's my buddy Frank reminding us where ALL of his flights land:
I was confident that I'd fixed all the problems from last time with this build and prep so all that remained was to push that button. The liftoff was much faster than I'd anticipated and I'd estimate that flame to be 6 feet long:
The ascent was beautifully straight and essentially rotation-free. It appeared to me that the 2 x I345 White Thunder air-starts kicked in before the L730 Classic had burned out. The video and altimeter data would prove me wrong, however:
Note the single rotation over the mile of ascent! I'm very pleased indeed. Watch full-screen on YouTube in 720p HD for best effect. Here also is the unabridged version of the video from liftoff to shut-off (~5.5 mins). Here's a recovery shot and altimeter data from both the Parrot2 and Raven:

The average barometric peak of the two altimeters was 5,550'. Also note the clear velocity decrease after the L730 burned out and then the spike as the I345s kicked in. Yay, data. Next time I plan to fly 5 motors (1 on the ground then 2 in the air then 2 more in the air). I'll shoot for Lucerne on January 8th to get some different video scenery. Great success!! Oh and here are some other shots from that day as well.