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Rocket
Motor Testing
ROCKET MOTOR TEST STAND (RMTS)
RMTS DEVELOPMENT
The development of the Rocket Motor Test
Stand (RMTS) was undertaken to better define the thrust-time
characteristics of rocket motors for improved flight performance
analysis. An AeroTech RMS-38/360 rocket motor using an I161-6w
reload kit was hot fire tested using the RMTS on March 28, 1998.
This system is capable of recording the thrust-time characteristics
of rocket motors generating up to 331 pounds of maximum thrust.
Overall test-bed dimensions for the RMTS are 19 5/8" long
x 12" wide x 16 1/2" high. The RMTS is fabricated from
6061-T6 aluminum using 3/4" thick plate for the rocket motor
mounting components of the main chassis. The rocket motor translation
plate is supported by two pairs of linear bushings which slide
on two precision steel shafts. Shaft alignment is maintained
by two 2" square shaft support members bolted to a 1/4"
thick x 19 5/8" long x 12" wide plate. The 1/4"
plate is bolted to two 3 1/2" x 3 1/2" x 25 1/2"
wood beams mounted on two concrete blocks. Rocket motor thrust
is measured by a Celtron single-point load cell with a rated
safe overload of 331 pounds. A 12 volt, 4 AH lead-acid battery
is used to excite the strain gage circuitry in the load cell.
The Celtron load cell has a full scale output of 2.0 mV/V. Finally,
a DATAQ Instruments data acquisition module is used to record
the thrust-time waveform to a laptop computer located 100 feet
from the RMTS. The DATAQ DI-158-UP data acquisition module is a 12 bit,
4 channel A/D converter and was selected because it was inexpensive
($199) and connects to the USB port all standard
Windows XP computers. In addition, if required this 4 channel
device can be used to measure any four combinations of thrust,
temperature and pressure.
ROCKET MOTOR HOT FIRE TEST
RMTS OPERATION AND DATA RECORDING
A 26 item countdown check list was used to
safely and efficiently operate the RMTS in the field in accordance
with the Tripoli Safety Code. An AeroTech Copperhead igniter
was used to start the rocket motor using standard high power
rocket electrical ignition equipment. WINDAQ waveform recording
software was used to process the data stream being sent from
the load cell mounted on the RMTS. From within WINDAQ the Gain
was set to 100 and the sample rate was set to 240 samples per
second. Prior to motor start the environmental temperature was
recorded as 56 degrees Fahrenheit. Then, after giving an audible
5 second countdown the rocket motor operated normally and the
thrust waveform data was successfully recorded by the WINDAQ
software onto the laptop computer's hard drive. This concluded
the first use of the RMTS on a warm spring day.
RMS-38/360 (I161) THRUST-TIME PLOT
DATA REDUCTION AND PLOTTING
The data reduction of the successful test
of the Rocket Motor Test Stand (RMTS) was accomplished using
the DATAQ Instruments WINDAQ Playback software. A range of waveform
data was selected and copied to a file in spreadsheet format.
Then, the Microsoft Works Spreadsheet computer program was used
to plot the thrust-time data. The resulting plot indicates that
the maximum thrust is about 50 pounds and the burn-time is approximately
2.4 seconds. Finally, a graphical analysis of the RMTS thrust-time
data indicates that the Total Impulse (I) of the RMS-38/360 (I161)
motor is 78 lbf-sec.
Rocket Motor Thrust-Time Response by
In-Flight Measurement
A rocket flight using an IA-X96 Cambridge accelerometer
was performed to produce in-flight data to verify the thrust-time
response recorded by the RMTS. The Cambridge accelerometer was
flown aboard a modified single stage Quantum Leap rocket. The
Cambridge IA-X96 recorded the Quantum Leap's time dependant values
of acceleration, altitude, and velocity. The maximum values of
acceleration, altitude and velocity recorded by the accelerometer
were respectively: 10.22 G's, 2,355 ft. and 291.18 mph (427 ft/sec).
The Quantum Leap weighed 4.5 pounds at liftoff and used an RMS-38/360
(I161-10 w) rocket motor for propulsion. |