RASAero Comparison with Flight Data

LOC/Precision Caliber IspTM

 

Presented below is a comparison of the RASAero flight simulation with flight data for a LOC/Precision Caliber Isp™ high power rocket, powered by an I205 rocket motor, which was flown with a Blacksky AltAcc axial accelerometer and barometric altimeter instrumentation unit.  The rocket reached an altitude of 3964 ft as measured by the barometric altimeter.  The RASAero rocket file for this rocket (CalIsp1.alx1) is included in the RASAero software download.

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LOC/Precision Caliber Isp™ high power rocket, I205 rocket motor, barometric altimeter altitude 3964 ft.

 

 

 

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RASAero scale rocket drawing for the LOC/Precision Caliber Isp™ rocket, including Center of Gravity (CG) and Subsonic Center of Pressure (CP).

 

 

 

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RASAero aerodynamic data plot for the LOC/Precision Caliber Isp™ rocket; power-on and power-off drag coefficient (CD) versus Mach number, plot zoomed in to Mach 0-1.2.

Note that because of the small nozzle exit diameter (nozzle exit area), there is little difference between the power-on and power-off drag coefficients.  The primary start of the transonic drag rise at approximately Mach 0.90 can be seen in the plot, although the drag begins to increase at Mach 0.80 due to the transonic drag rise for the rail guides (which are equivalent to vertical cylinders in the flow around the rocket).

 

 

 

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Measured axial acceleration, accelerometer-based velocity, on-board measured barometric pressure, barometric altimeter altitude, and accelerometer-based altitude for the LOC/Precision Caliber Isp™ rocket on an I205 motor.

Data from Blacksky AltAcc axial accelerometer and barometric altimeter on-board instrumentation unit.

 

 

 

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RASAero flight simulation predicted acceleration and velocity for LOC/Precision Caliber Isp™ rocket on an I205 motor.

Compare predictions to accelerometer-based flight data from Blacksky AltAcc on-board instrumentation unit presented in previous plots.

In the early part of the flight the accelerometer-based altitude and velocity are considered more accurate than the barometric altimeter altitude due to the absence of any pitot tube corrections or pressure lag corrections to the on-board measured barometric pressure.  At apogee the barometric altimeter altitude is considered more accurate than the accelerometer-based altitude, due to trajectory and attitude effects not taken into account in the one-dimensional integration (assuming a straight-up flight) of the body axial acceleration data.  For the RASAero flight simulation predicted axial acceleration note the similarly shaped plot of acceleration versus time compared to the on-board measured axial acceleration, with a peak axial acceleration of approximately 500 ft/sec2.  For the RASAero flight simulation predicted velocity note the similarly shaped plot of velocity versus time compared to the accelerometer-based velocity, with a peak velocity of just over 700 ft/sec.

 

 

 

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Barometric altimeter altitude and accelerometer-based altitude for the LOC/Precision Caliber Isp™ rocket on an I205 motor.

Data from Blacksky AltAcc axial accelerometer and barometric altimeter on-board instrumentation unit.

In early part of flight accelerometer-based altitude is considered more accurate.  At apogee barometric altimeter altitude is considered more accurate.

 

 

 

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RASAero flight simulation predicted altitude versus time plotted through apogee for LOC/Precision Caliber Isp™ rocket on an I205 motor.

Compare prediction to accelerometer-based altitude data for early phase of flight and barometric altimeter apogee altitude data from Blacksky AltAcc on-board instrumentation unit presented in previous plot.

Again, at apogee the barometric altimeter altitude is considered to be more accurate than the accelerometer-based altitude.  Again note the similarly shaped plot of altitude versus time from liftoff through apogee.  For the LOC/Precision Caliber Isp™ rocket on an I205 motor the RASAero flight simulation predicted altitude is 3871 ft, an error of only -2.35% compared to the barometric altimeter measured altitude of 3964 ft.

 

 

 

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On-board measured barometric pressure and barometric altimeter altitude from launch through apogee to landing, including parachute descent, for LOC/Precision Caliber Isp™ rocket on an I205 motor.

Data from Blacksky AltAcc on-board instrumentation unit.

 

 

 

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RASAero flight simulation predicted altitude versus time from launch through apogee to landing, including parachute descent, for LOC/Precision Caliber Isp™ rocket on an I205 motor.

Compare prediction to barometric altimeter altitude data, including parachute descent, from Blacksky AltAcc on-board instrumentation unit presented in previous plot.

For the RASAero flight simulation prediction note the similarly shaped plot of altitude versus time for the parachute descent.  Based on the barometric altimeter altitude data from apogee to landing the parachute descent time was 241 sec.  The RASAero flight simulation predicted parachute descent time is 218.83 sec, an error of only -9.20% in the parachute descent time from apogee to landing.
 
 
 
Summarizing the flight; for the LOC/Precision Caliber Isp™ rocket on an I205 motor the RASAero flight simulation predicted altitude is 3871 ft, an error of only -2.35% compared to the barometric altimeter measured altitude of 3964 ft.