Sunday, October 12, 2014

Updated: Der Red Mix mark II Skidfest at ROCTober 2014

After talking it up for over a year I finally flew my scratch-built Der Red Mix mark II on a full complement of seven burly Skidmark motors (as always switching to 720p in full-screen mode is the shit):

A formidable liftoff featuring loud, flaming titanium granules:

And notably angled ascent:

I arrived at the lake bed later than I'd have preferred but the conditions were perfect all day with light, intermittent wind and perfectly clear skies.  I had prepped all the electronics two months ago so I only needed to load up the seven Skidmark motors, set up the CD3 ejection system, mount the Flip Mino camera inside, and button everything up.  Upon checking in with the RSO he seemed confident in my design and flight plan but cautioned that the far pads were angled away from the spectators.  He specifically asked me not to adjust the rail to a more vertical orientation (and that's some foreshadowing).  Kurt Gugisberg was out at the pads and helped me to get the 30.5 pound rocket loaded up on the rail.  I powered up the two Ravens, installed the air-start igniters, started the Flip camera, closed the electronics bay door, installed the central motor ignitor, and was ready to go.
     The ignition of the central CTI 2010K675 was instantaneous as expected and, at a 7.3:1 thrust-to-weight ratio, the ascent was expeditious.  Now normally I would have set the launch angle at 1-2 degrees from vertical because this rocket is incredibly stable and there was no wind.  Instead the angle I was asked not to change was closer to 4-5 degrees from vertical so the angle you see it the picture above is real.  The one second air-start gaps I programmed into the altimeters seemed a bit long but the sequential pairs of 543I297, 258H180, and 176H123 Skidmarks otherwise popped as expected.  By the time the H123 pair fired the rocket appeared to be approaching a horizontal flight path but, in reviewing the onboard video above, that was mostly an optical illusion.  From the ground it also appeared that the ejection was 3-4 seconds too late but the video once again proves that wrong and the 'chute popped right at apogee.  Unfortunately the initial launch angle essentially lobbed the rocket on an arc rather than straight up so that extra velocity at apogee served to zipper the top of my rocket rather severely.  I can repair it but, from now on, I'm trusting myself to set the optimal launch angle. Once again DRMII stuck the landing:

Here's the zipper damage from the energetic ejection (Grrr...):

And here's the interesting thrust curve showing acceleration surges from the four motor phases in red on the left of the graph:

The altitudes from the Raven 2 (tabular, graph) and Raven 3 (tabular, graph) only differ by 10 feet (!) and average to 4,483 feet above ground level.
     So I'll repair the damage, shorten the air-start delays to 0.1-0.5 seconds, and fly DRMII again soon with a K815 Skidmark in the center. I'm not yet sure of the outboard motors but they'll likely max out the motor tube lengths.  Thanks for reading!

Addendum: I found more shots of this flight on David Reese's Flickr photo stream:
Thanks again, David!!

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