Sunday, January 1, 2017

Lucerne Dry Lake, November 2016: The L1500 is a bad-ass!

As noted previously, and now that it seems to be out of production, my Madcow's 8" Mega Cowabunga was finally complete and ready to go.  I selected Aerotech's 98/5120 5089L1500 Blue Thunder beastie for a first flight and that was a good, thrusty choice as the hefty stub weighed 39 lbs on the pad.

Near the beginning of the video I included a CD3 ejection test with a 16g cartridge, 98/2560 motor assembly, and three shear pins as a worst-case pressure combination.  I also seek to minimize nosecone velocity since it alone weighs 10 pounds and I want to optimize separation and stress/strain at ejection.  This 16g cartridge was so gentle that I bumped up to 25g for the flight to add margin.
     The motor defied thermodynamics and self-assembled (😁) without issue. I followed Aerotech's revised assembly guidelines that now include bonding of grains to the liner for certain reloads:

This also represented the inaugural test of my 3D printed electronics bay for a stroll.  It houses two Featherweight Raven altimeters with Power Perches and the two halves are bolted through against the airframe wall and down against the top centering ring like so:

I used a stock, heftier CTI dipped match for ignition which proceeded expeditiously.  From a distance the rocket appeared to wobble a bit off the rod but stability should be rock solid so... more on that in a bit.  Again I used a deployment bag for a 12' Rocketman 'chute and both proved good choices as recovery proceeded in a beautifully uncomplicated manner:

Here are the data from the altimeters in very solid agreement:
  • Raven 1 (70G/30G) peaks [graph, tabular]:
    • Altitude, barometric: 6,208'
    • Velocity: 541 MPH
    • Acceleration, axial:  11.44G
    • Acceleration, lateral: 8.93G
  • Raven 3 (70G/30G) peaks [graph, tabular]:
    • Altitude, barometric: 6,182'
    • Velocity: 545 MPH
    • Acceleration, axial:  11.67G
    • Acceleration, lateral: 9.64G
  • Averages:
    • Altitude: 6, 195'
    • Velocity: 543 MPH
    • Acceleration, axial: 11.55G
    • Acceleration, lateral: 9.29G
Now about that liftoff torque... It took several views of the slow-mo pad video to (mostly) realize what happened. Lucerne's pads use a hinge as an airframe support at the bottom of the rail and I probably did not have that aligned axially with the rail slot. Additionally it's now obvious to me that nozzle's throat was not aligned with the apex of the roof-shaped thrust deflector. This high-thrust motor therefore vectored its thrust toward the camera and induced a clockwise moment of the pad from the thrust deflector upward. Now why would everything above the pad's legs be allowed to rotate ~70 degrees? No idea but, rest assured, I'll be checking that and other alignments from now on. Here's the unfortunate but minor and reparable damage to the bottom 1515 Delrin rail guide:

Overall I consider this flight to have rocked! Subsequently I purchaseed both CTI 4807L3150 Vmax and AT 4668L2500 Super Thunder reloads for future, authoritative sky-hole-punching.  Oh how the viciousness will delight.

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