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JSBSim Aerodynamics: Difference between revisions
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== QBar == | == QBar == | ||
QBar, or dynamic pressure, is the product of velocity^2*(air density)/2 | QBar, or dynamic pressure, is the product of velocity^2*(air density)/2 | ||
* ''' | * '''QBarUW''' Use this value for formula involving Alpha. It is the value of QBar restricted to the vertical plane. | ||
* ''' | * '''QBarUV''' Use this value for formula involving Beta. It is the value of QBar restricted to the horizontal plane. | ||
* It is possible to calculate other dynamic pressures for special purposes, such as QBarU for control surfaces. | |||
The Greek letter rho or "ρ" is commonly used for air density. Normally, Qbar is based on the total free stream velocity, V[inf], so: | |||
qbar = 1/2*ρ*(V[∞])^2 | |||
V[∞] is a vector and can be broken down into components commonly called U, V, W. By definition, U, V, and W are all at right angle to each other, so we use Pythagoras to say: | |||
'''(V[∞])^2 = U^2 + V^2 + W^2''' | |||
and rewrite | |||
'''qbar = 1/2*ρ*(U^2 + V^2 + W^2)''' | |||
QbarUV drops the vertical component, W, and just uses: | |||
'''qbarUV = 1/2*ρ*(U^2 + V^2)''' | |||
QbarUW drops the horizontal component and just uses: | |||
'''qbarUW = 1/2*ρ*(U^2 + W^2)''' | |||
And for the special case of qbarU, only use the axial component. | |||
'''qbarU = 1/2*rho*(U^2)''' | |||
Since its one dimensional, preserving the sign to show direction is valid: | |||
'''qbarU = 1/2*ρ*(U*abs(U))''' | |||
Qbar, qbarUV and qbarUW, can not have signs because they are multidimensional, use the reported alpha or beta angles to decide where the pressure is coming from. | |||
== Metrics == | == Metrics == | ||