Static Test # 2 – DECA 8 grain Rocket Motor, KNDX, March 27, 2010

Second time right. Perfect static test.

Goals:

  • Evaluate use of 8 bates grains stacked on top of each other in a 54mm motor.
  • Use a 5gr igniter charge consisting of 2,5gr commercial BP and 2,5gr magnesium to boost the start up pressure for instant ignition.
  • Use checklist for motor assembly
  • Use isopropanol for grain priming
  • Test Viton o-rings “46x4mm Precisie O-ring FPM (Viton®) 75° compound 51414”
  • Measure temperature of casing near the nozzle

Excel file – 54mm, 8 BATES grains, KNDX 6535 Static Test II – 27.03.10.xls

Video – DECA_14_-_Static_Test_II_-_27.03.2010

Thrust curve

 

  1. Peak thrust – 910N
  2. Average thrust – 680N
  3. Burn time – 1,8s
  4. Total thrust – 1366Ns
  5. Propellant weight – 1155,5,gr
  6. ISP, delivered – 120,5s

 

Pc . At = ( F / g ) / CF

Pc • 2,02=  ( 910 / 9,81 ) / 1,10

Pc = 36,5 Bar

CFmax = 1,26

Throat aera ( At = 2,02 )

(g = 9,81 m / s)

Notes:

  1. Grain making proces is as described here is excellent and resulted in 8 beautiful bates grains. Average density of 99%, AGAIN!   However, release of the tapered core took some more persuasion then previous releases with the newly machined core.
  2. Weight of the motor – loaded but excluding igniter – was 2633gr of which 1155,5gr of KNDX.
  3. Pyrogen coating: 4 top grains all surfaces, lower 4 grains only the ends coated with commercial 3F BP.  BP needs to be grinded in a mortar before being mixed with isopropanol. Isopropanol evaporates much less rapid then the aceton based NC lacquer thus giving you more time to work.  Total coating on all grains = 2,3gr BP.
  4. Igniter: 5,0gr (2,5gr commercial 3F BP + 2,5gr of magnesium).
  5. Weather was fair, temperature during testing 9-11° C.
  6. Again, the bolt holes in the casing do cause significant damage to the o-rings and slice off small sliffers or leave cutting marks when inserting the nozzle or forward closure. No leakage at all.
Conclusion:
  1. 8 bates grains seems to works just fine although the burn time was longer than expected. No erosive buring was evident. Burn time was the same as test #1.  This could be either a result of the 9° C temperature or the high density.
  2. Igniter worked better than expected. Magnesium solved the instant ignition problem for this motor. Please be carefull: This is a potentially dangerous mix. In the presence of moisture, the Mg will react, generating heat, to the point where ignition of the BP may occur. I wouldn’t recommend mixing this up in advance.
  3. Checklist worked like a charm, easy breezy motor assembly. Small notes to be revised and version as per 19.04.2010 can be found here.
  4. 100% isopropanol (IPA),  as obtained from a local printing office, works OK for priming the grains and given the results of the test it will be used for all future priming jobs.
  5. Viton o-rings from Eriks were of excellent quality and performed better than the NBR o-ring which melted after the burn. However, the bolt holes consistently made 12 evenly spaced cuts in the o-ring (12 cuts from 2 rows of 6 bolt holes). O-rings are therefore considered as single use. Could be re-used for the recovery electronics bay.
  6. Temperature peaked 170° C at 30s after burn out.  Quick search on the internet reveals that the aluminium temperature should be kept at under 250° C to prevent degradation of the aluminium.

Library:

DECA 14 – 2010 Rocket Motor – Assembly & Propellant Loading Manual – 17-05-2010 – All you need to know.

DECA14 11 DEGR 600NPV 27-3-2010 – Raw data from test: 600N/VDC

54mm mold spring loaded – Compression mold drawings