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EX Motors



This motor is a KNSU G-167 with a total impulse of 115N-sec (calculated). I have not yet run a static test, But have 7 successful burns, including three flights. The burn time measured in static and flight tests matches the calculated burn time of .7 seconds, and the rockets got off the pad in a hurry and flew in the neighborhood of the estimated altitude.


The motor is constructed from 1" PVC pipe and fittings. The delay is constructed like but is installed via a PVC reducer, which I find simpler and more convenient. I have not had any problems with this arrangement, but when I had to substitute two reducers, 1" to 3/4" and then 3/4" to 1/2", instead of the single reducer I had trouble with the delay and fuel both igniting reliably because the distance between the two was increased by over an inch.

The first three test motors were case bonded. I knew this was not the best idea, and after a failure I switched to casting in Estes BT-10 tube, which is the perfect diameter.
The nozzle is cast into a 1" PVC bushing with a section of 1" pipe as shown below I find this to be an improvement over similar PVC motors with cast nozzles because the short length allows me to access and work on the nozzle from both ends.


Despite four failures out of 10 I think this has the makings of a reliable design. All of the failures were departures from the stated design and failed at the point of departure. I plan to continue with this design.

  1. PVC9-3: Case bonded fuel unbonded. Moved to inhibited grains.
  2. PVC9-4: Tried simplified friction fit nozzle. Nozzle ejected. Possibly also too much BP boost charge. Moved to BP+Mg igniters for more flame, less explosion.
  3. PVC9-8: Delay did not light. Substituted PVC fitting moved it too far from fuel.
  4. PVC9-10: Delay lit, fuel did not. Ejection charge deployed chute and lit fuel. See above comment on PVC fitting.


Static Test (1,2,3)

Flights (7,8,9,10)

Subpages (2): Igniters Nozzles
Bill Kuker,
Feb 21, 2009, 8:55 AM
Bill Kuker,
Feb 21, 2009, 8:56 AM