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 zerolift
drag estimation, an important feature most simulation programs
do not possess.
Comparison between the various flight simulations is complicated
by the difference in motor thrusttime curve data for each computer
program. The 821 Ns AeroDRAG & Flight Simulation data represents
TMT thrusttime data within the program while 850 Ns 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 Ns) *
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 Ns) *
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 Ns) *
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 Ns)
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 Ns)
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 Ns)
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 Ns)
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 Ns)
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 Ns)
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 Ns) *
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 Ns)
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 PullDown
Motor List option where averagethrust and burntime determine
total impulse. Please use the FreeForm Thrust Curve option to
model the actual thrusttime variation of a particular rocket
motor.
(**) Average acceleration (G's) does not catch the short duration
acceleration spike from a motor's actual thrusttime 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 OnLine
AeroDRAG & Flight Simulation uses many of the rocket motors
listed in the ThrustCurve.org
database.
