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Characterizing SF propellant APCP

Objectives:

Determine the following empirical parameters:

  • Max Pressure
  • Average Pressure 
  • max Force
  • Average Force 
  • Total Impulse
  • Grain Mass

From these parameters determine the following parameters for the propellant:

  • ISP
  • C*
  • a
  • n

Four burns were performed using identical propellant grains in a static  test motor.  Pressure was measured using a 2500PSI pressure transducer and force measured with a 100 kg load cell.  

Calibration:

Pressure calibration was performed from the manufacturers datasheet and verified using a compressor.  The compressor only allowed us to test at ~120PSI which was far from full scale for the tests.  Uncertainty in pressure measurements is +- 10 PSI

Force calibration was performed using one of the team members balancing on the load cell given his known weight.  While the team member professed to know his weight and the calibration was full scale, it provided difficult for him to balance on the load cell platform consistently so our repeatability was low.  Uncertainty in force measurements is +- 10 lbs. 

Data:

Burn 1:  21/64" Nozzle Diameter

Pressure vs Time 21/64 Nozzle APCP SF propellant
Force vs Time 21/64" Nozzle APCP SF propellant

 

  • Max Pressure 1458 +- 10 PSI
  • Average Pressure 822 +- 10 PSI
  • max Force 85 +- 10 lb
  • Average Force 72 +- 10 lb
  • Total Impulse 161 lb . s +- 20 lb.s

Visual Observations:

Low smoke. Substantial nozzle erosion from 21/64 to 25/64".

Burn 2: 23/64" Nozzle Diameter

Pressure vs Time 23/64 Nozzle APCP SF propellant
Force vs Time 23/64" Nozzle APCP SF propellant

 

  • Max Pressure 854 +- 10 PSI
  • Average Pressure 606 +- 10 PSI
  • max Force 73 +- 10 lb
  • Average Force 61 +- 10 lb
  • Total Impulse 155 lb . s +- 23 lb.s

Visual Observations:

Low smoke. Substantial nozzle erosion from 23/64 to 26/64"

 Burn 3: 25/64" Nozzle Diameter

Pressure vs Time 25/64 Nozzle APCP SF propellant

Force vs Time 25/64" Nozzle APCP SF propellant

 

  • Max Pressure 662 +- 10 PSI
  • Average Pressure 519 +- 10 PSI
  • max Force 68 +- 10 lb
  • Average Force 59 +- 10 lb
  • Total Impulse 158 lb . s +- 24 lb.s

Visual Observations:

Low smoke. Substantial nozzle erosion from 25/64 to 26/64"

 Burn 4: 23/64" Nozzle Diameter Second Burn

Pressure vs Time 23/64 Nozzle APCP SF propellant

Force vs Time 25/64" Nozzle APCP SF propellant

 

  • Max Pressure 1367 +- 10 PSI
  • Average Pressure 773 +- 10 PSI
  • max Force 81 +- 10 lb
  • Average Force 65 +- 10 lb
  • Total Impulse 155 lb . s +- 22 lb.s

Visual Observations:

Low smoke. Substantial nozzle erosion from 23/64 to 26/64"

Notes: 

Grain mass was not recorded at the time of the experiment so is estimated from propellant density and grain geometry. Assuming a propellant density of 0.06 lb/ in^3 and 2 grains with a 52mm diameter and 19mm core we obtain the following.

  • Grain Mass .86 lb +- .2lb 

Nozzle erosion was significant during all test. 

ISP Calculations:

Propellant ISP 183s - 53 + 86s. These large uncertainties are due to the uncertainty in the propellant mass and the force scale calibration.   The author is only confident that the propellant ISP is between 130 s and 270 s which is hardly useful.  With accurate values for the mass of the propellant grains, the uncertainty could be reduced substantially.



 

 

 

 

 

 

 










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