Aerodynamic Drag Force.
0,5(de)(Cd)A(V2+Vair) 2 N
Fd = 0,5(de)(Cd)A(V2+Vair) 2 N
Where (de) is density of air or atmosphere through which the rocket flies.kgs/m3
Cd Aerodynamic form drag coeficient
A is the cross sectional area of the rocket m2
V2 is the actual velocity of the rocket m/s
Looking at the formula for determining the drag force restricting the rocket.
We can say that Fd is directly proportional too: (de)(Cd)A
But more importantly Fd increases with (V2)2
The faster it travels the more significant the value of Fd becomes
The main restraining aerodynamic ‘Drag’ force can be reduced by
So reducing the diameter of the bottle used but maintaining the enclosed volume will help dramatically. Bigger is not always better.
If the nose cone resembles the shape of a brick then there is a considerable resistance created as the rocket punches its way through the atmosphere.
Usually you avoid launching rockets when the weather conditions are poor.
Minimum aerodynamic drag for an optimised projectile volume of minimum exposed surface area.
Cd values of 0.1 and less
For a parachute what we want is to increase aerodynamic drag to a maximum to decelerate the descent of a valuable payload or rocket. So we need maximum drag produced by a system of low mass. Typical Cd = 0.75 to 1.5
|Parachute rate of fall Excel Table|
|Some examples of aerodynamic drag coefficients Cd for some basic shapes and forms.|
|An introduction to boundary layer aerodynamics|
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©John Gwynn and sons2003
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