Top Quality Aerodynamics Software Since November 1, 1999

Flight Simulation Comparison BACK
AeroDRAG & Flight Simulation performs flight simulations of single and multiple stage rockets using the basic equations of rocket motion to determine rocket velocity, altitude and acceleration using a finite difference procedure. In this latest version, Cd can vary with rocket velocity and air density varies with altitude. The ability to model the variation of Cd with velocity is important for accurate high speed and high altitude rocket predictions. For comparison with other flight simulation programs a model having a 4.0236 inch diameter (10.22 cm), total rocket mass 8.839 lb (4009 gms), drag coefficient 0.70 and powered by a J275 RMS motor was analyzed using AeroDRAG's Flight simulation routine. The results are for rockets launched from sea level with an air temperature of 77 degrees F. AeroDRAG & Flight Simulation results compare well with these flight simulation programs and performs subsonic, transonic and supersonic zero-lift drag estimation, an important feature most simulation programs do not possess.

Comparison between the various flight simulations is complicated by the difference in motor thrust-time curve data for each computer program. The 821 N-s AeroDRAG & Flight Simulation data represents TMT thrust-time data within the program while 850 N-s AeroDRAG & Flight Simulation data represents equivalent WinRoc total impulse data for a J275 motor input manually.

Drag Estimate Validation
AeroDRAG has been validated using experimental NACA drag coefficient data.


Flight Simulation Comparison Data (Cd = 0.70)
AeroDRAG (J275 = 821 N-s) *
Peak altitude = 907.7 meters
Max velocity = 153.1 m/sec
Apogee time = 13.8 sec
Avg acceleration = 5.0 g's **
AeroDRAG (J275 = 850 N-s) *
Peak Altitude = 944.5 meters
Max velocity = 158.5 m/sec
Apogee time = 13.9 sec
Avg acceleration = 5.2 g's **
AeroDRAG (J275 = 819 N-s) *
Peak altitude = 905.0 meters
Max velocity = 152.7 m/sec
Apogee time = 13.8 sec
Avg acceleration = 5.0 g's **
wRASP (J275 = 819 N-s)
Peak Altitude = 908.2 meters
Max velocity = 158.6 m/sec
Apogee time = 13.2 sec
Max acceleration = 7.6 g's
WinRoc (J275 = 850 N-s)
Peak Altitude = 953.9 meters
Max velocity = 161.1 m/sec
Apogee time = 13.7 sec
Max acceleration = 7.1 g's
Popular Simulation (J275 = 819 N-s)
Peak altitude = 943.2 meters
Max velocity = 160.6 m/sec
Apogee time = 13.5 sec
Max acceleration = 7.7 g's
CompuRoc (J275 = 817 N-s)
Peak Altitude = 935.9 meters
Max velocity = 149.6 m/sec
Apogee time = 13.6 sec
Max acceleration = 7.3 g's
CompuRoc (J275 = 851 N-s)
Peak altitude = 974.8 meters
Max velocity = 154.9 m/sec
Apogee time = 13.8 sec
Max acceleration = 7.6 g's
Altmark (J275 = 821 N-s)
Peak Altitude = 918.3 meters
Max velocity = 163.0 m/sec
Apogee time = 13.3 sec
Max acceleration = 7.2 g's

Cd Effect on Maximum Rocket Altitude
A large slender high power rocket may be designed to have a Cd in the range of 0.30 to 0.50. This means that by using the old default value of 0.75 a rocketeer may greatly underestimate the actual altitude attained by his/her rocket. As a consequence an FAA waiver may be busted!! The following chart displays the effect of using a Cd of 0.40 instead of 0.70 as illustrated in the above example. In this example a rocketeer may underestimate maximum altitude by 239.7 meters (786.4 feet) by using 0.70 for Cd instead of 0.40. AeroDRAG & Flight Simulation not only computes drag coefficient (Cd) but performs flight simulations too.


Cd Effect on Rocket Performance (Cd = 0.40)
AeroDRAG (J275 = 850 N-s) *
Peak Altitude = 1,190.9 meters
Max velocity = 170.2 m/sec
Apogee time = 15.96 sec
Avg acceleration = 5.15 g's **
WinRoc (J275 = 850 N-s)
Peak Altitude = 1,193.6 meters
Max velocity = 170.8 m/sec
Apogee time = 15.70 sec
Max acceleration = 7.1 g's
Difference
-0.23%
-0.35%
+1.65%
 

(*) Thrust Curves use the Pull-Down Motor List option where average-thrust and burn-time determine total impulse. Please use the Free-Form Thrust Curve option to model the actual thrust-time variation of a particular rocket motor.
(**) Average acceleration (G's) does not catch the short duration acceleration spike from a motor's actual thrust-time variation. However, the lower average acceleration provides a more conservative estimate of the suitability of a motor for a particular model rocket for safe liftoff. Rule of thumb indicates a safe liftoff can be achieved using a motor producing an average acceleration of about 4 G's.

Thrust Curve Data On-Line
AeroDRAG & Flight Simulation uses many of the rocket motors listed in the ThrustCurve.org database.



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