CapFlight 2000
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Aerodynamic Model

Lift Cooef chart

The CapFlight 2000 Aerodynamic model has been improved.  It calculated lift and drag as the shuttle enters the earth asmosphere.  The air density is calculated from 400,000 feet and the aerodyanmic forces start to build up as the shuttle falls below 300,000 feet.  The lift and drag values are adjusted for control surface position, including the elevons, body flap, speed breaks and landing gear extension.

The elevons are controlled by the computer to respond the control stick inputs.  As the control stick is moved left/right a roll rate is commanded.  The elevons are then commanded to move, one up and the other down, to create the desired roll rate.  Then they nuterialize. Pitch is controlled similarly.  Both pitch and roll inputs can be entered as the same time.  Yaw is automatically adjusted.

The chart above show the change in the lift cooeficient for elevon deflection at across varying angles of attack. Charts for all the important aerodynamic parameters were used to derive up to 5 order polynomials like the following so that lift and drag can be calculated. 

The basic lift equasion is:

Lift Force = -(Q Bar * Lift Area * (Wing  Lift Coef + Speed Break Lift Coef + Langing Gear Lift Coef) / 2)

where Q Bar is dynamic pressure:  Q Bar  = Air Density * (Air Velocity) ^2  / 2

Lift Cooef  =  -3.49020E-10x^5 - 1.88441E-08x^4 + 1.24431E-06x^3 + 8.22887E-05x^2 - 2.80333E-03x + 6.71123E-04 where x is the elevon setting.  Different formula are used for each mach number range and angle of attack.   


logo Copyright (c) 2006 Theodore S. Kyle
Launch of STS 114, Return to Flight, July 26, 2005
Background Photo by NASA