Excuse Me: Flight 1

Flight 1

Saturday May 26, 2007 at FITS 2007.

Summary: Failure...

Dimensions:

12' x 5.5", 14.5" span

Dry weight:

25 lb

Tanked pad weight:

38 lb

Spent weight:

32 lb

Preheater:

immediate ignition

Ignition:

less than 2 seconds

Liftoff:

quick acceleration

Boost:

7.5 sec burn, 5 sec blowdown

Coast:

very slow left roll

Drogue deployment:

didn't see, 2 charges fired, airframe separated

Drogue descent:

fast & flopping all over

Main deployment:

1000' charge didn't clear nosecone, 800' charge did; nose cone & its' harness executed a 1/2 overhand knot through the lower upper airframe harness; knot prevented main bundle from opening

Landing:

came in without main @ ~75 fps, upper end of lower airframe impacted first in soft dirt

Damage:

upper end of lower airframe mushroomed back to top of motor; many nosecone dings; all easily reparable

Max acceleration:

162 ft/sec/sec; 5.0 G

Max speed:

663 ft/sec; Mach 0.6

Altitude:

Missileworks RRC2X-40K:	8118'
GWiz MC barometric:	7973'
GWiz MC accelerometer:	8109'

Failure Analysis:

NC harness did a half over-hand knot through the body harness, knotting the main bundle closed
it did so because I chose to go drogue-less at the last minute, and the pieces were flapping all over
I went drogue-less because I couldn't get the drogue & harnesses to fit at the away cell (I couldn't prep in camp & transport a 12.5' load) the same way I had at home
the fit didn't work because I chose to use the 1/2" Kevlar, which as was so thoroughly pointed out, is 100X or more overkill
the end result is that I'll fix the dings, repair the forward end of the booster, switch to 1/4" Kevlar plus something TBD to inhibit zippers (short pieces of 2" nylon?) and try again with my 2nd reload

Photos:

M 'n M Photo courtesy of & ©2007 Brad Wright	Me 'n Excuse Me Photo ©2007 Andrew MacMillen
Launch! Photo courtesy of & ©2007 Bill Clugston	Clean flame Photo courtesy of & ©2007 Bill Clugston

Multimedia:

Slideshow (3.8MB MOV)	Video (1.3MB WMV)
Photos & video courtesy of & ©2007 Rockets Magazine

Gwiz data:

Summary	Overlay
Overlay detail	Acceleration
Acceleration detail	Gwiz vs. TMT * * F=MA; neglects drag but includes decrementing mass

RockSim projected an altitude around 12K' (even with a finished weight mass override) whereas the flight only achieved 8K'. The much lower thrust fully explains this, but since the supply tank was near optimal pressure, I'm uncertain why the flight & impulse was so much lower than expected.

Motor:

Ratt M900 parts	M900 hybrid grain
Grain burn through	Inside grain
Inside grain detail
The grain was burned through at the phenolic pre-combustion chamber shoulder after the flight. Since the case is un-damaged, this most likely occured during the low pressure & heat blow-down phase. After discussing this with Rattworks, I discovered that my X-injector is a beta release version that only has 2 crossing slots, so the nitrous is directed mostly sideways and impinges on the grain exactly at the pre-combustion chamber shoulder. The release version injector has both slots and a hole in the tip to direct some of the nitrous down the chamber. An upgrade will solve this problem, and hopefully improve the thrust.

FITS 2007 Sunset

Excuse Me