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 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%
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(*) 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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