Kurt

Flying 4x4 5-14-02a  28mm aluminum engine cast nozzle 3-grain Bates configuration

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"Kurt" was my first 4x4 airframe.  It flew well three times, but was disabled by CATO on Christmas Day 2001.

The remnants sat around for awhile.  Then I realized a need for a slightly lighter airframe for use with these aluminum engines, somewhat smaller than the PVC engines for which the original 4x4 was designed.  So I cut off what was left of the engine bay,  glued the splinters back together, and made a shorter version.  With a new set of dorky fins and a really odd paint-job, "Kurt" is ready to fly again. He is about three pounds lighter, good for testing these "Low-G" class engines.

Pre-Flight

The funny green thing is a foam ear-plug.  I find these to be really good nozzle sealers.  Notice in the second photo how the nozzle protrudes a bit from its tubing.  This nozzle was a bit loose after casting.  I tried to drive it out with a rod and hammer and that was as far as it would go.  I static-tested it with a full charge - it stayed put.  So I figure it has found its spot
 

Click on the photo above to load a video of this flight  (1.6 meg MGP file, 10 seconds of video)

Quick summary: Flight duration:  Thrust duration:  Altitude at apogee:  Grain configuration:  Grain Dimensions       Length:       OD:       Core:  Total fuel:  Nozzle throat:  Kn / PSI       Initial:       Max:       Final:  Launch weight:  Total Impulse:

6.7 seconds  0.76 seconds  51 meters  3 outside-inhibited Bates grains  1.85 inch (each grain)  1.0 inch  0.375 inch  101 grams KN/sucrose  0.25 inch  216 / 650  256 / 850  237 / 800  3.29 kg  108 N-sec

Calculated thrust curve is asymmetrical because the grains are a bit longer than the ideal Bates dimension for this diameter.

Post-Flight

Note that the nozzle has shifted forward.  This is unexpected.  Apparently, the inertia of a sudden stop is significant.  I also suspect that the thin aluminum tube heats more quickly than the massive aluminum nozzle, thus expanding a bit and loosening the nozzle.  I have sometimes drilled and tapped small holes in the nozzle region and inserted small setscrews to lock the nozzle in place.  This worked OK, but then I found a better way.

Details:  Spreadsheet output:
 

LumberCalc	Version 1d			Data for flight 5-14-02a	"Kurt" - 7-poundish 4x4
Measured:				Calculated:
Distance *	Feet	Meters		Rise/Run at apogee:	0.653529	< ratio of height on pole at apogee / distance to pole
A. Camera to measuring pole	5.1	1.554404		Rise/Run at burnout:	0.211765	< height on pole at burnout / distance to pole
B. Camera to launcher	280	85.33984
C. Camera to touchdown	231	70.40536		Height at apogee:	50.89203	< distance to apogee * rise/run ratio at apogee
D. Launcher to touchdown	59	17.98232		Height at burnout:	18.07197	< distance to burnout * rise/run ratio at burnout
E. Rise on pole at burnout	1.08	0.329168		Rise height after burnout:	32.82007	< height at apogee - height at burnout
F. Rise on pole at apogee	3.333	1.015849
* Letters A-F refer to drawing on Sheet 2				Rise time, burnout to apogee:	2.588044	< calculated from rise height, deceleration by gravity
				Time, launch to apogee	3.348044	< boost time + rise time
Time	Seconds			Fall time, apogee to ground	3.222752	< calculated from height at apogee & gravity
Thrust duration	0.76			Total Flight time (calculated)	6.570796	< calculated boost + rise + fall time)
Descent from apogee	3.3			%Error between flight times:	0.016201	< comparing measured vs. calculated times
Total flight time (measured)	6.679
				Velocity at burnout (m/sec)	25.36283	< calculated from rise height, deceleration by gravity
Weight	Kilograms			Acceleration, actual (m/s^2)	33.37215	< velocity at burnout / thrust duration
Fuel charge	0.1007			Acceleration, felt (m/s^2)	43.17215	< actual acceleration + gravity
Total launch weight	3.2925			Thrust (Newtons)	142.1443	< felt acceleration * total weight
				Total Impulse (N-Sec)	108.0297	< thrust * thrust duration
				Isp (N-Sec/kg)	1072.787	< total impulse / mass of fuel charge
Jimmy Yawn				Seconds	109.4681	< Isp / gravity
jyawn@sfcc.net
5/14/02				Height (of doubtful accuracy)	53.361	< calculated from measured fall time

Click here to download a copy of this spreadsheet, Excel format

Graph of wavefile extracted from video:

Events:
0.6 seconds, Ignition switch clicks
1.45 seconds, Thrust begins*
2.2 seconds, burnout (tapering-off noise is echo)
8.4 seconds, vehicle hits ground

*The ignition switch is right by the camera and the launcher is 280 feet away.  Thus the ignition delay is about 1/4 second less than the .wav file would suggest.

JY
5/15/02