Aerodynamic Forces on an Aircraft Flashcards
Bernoulli/Euler
Static Pressure+Dynamic Pressure=Total Pressure Pressure Energy+KE=Total Pressure
For Bernoulli to be true
Static+Dynamic Pressure are local values Total pressure is constant for the flow, but only if no energy is dissipated in the flow, the fluid is inviscid and irrotational
The subscript infinity denotes
Freestream conditions
Centre of Pressure, Cp=
(P-Pinfinity)/0.5pinfinityVinfinity^2
Lift
Acts at 90o to the flow
Drag
Acts parallel to the flow and to oppose the aircraft motion
Pitching Moment
Acts about a defined axis
Defined about the LE or quarter chord point
Lift, Drag and Pitching Moment are…
Independent of aircraft size and speed
The CL,CD and CM are functions of which 3 dimensional parameters?
Angle of attack
Mach no.- High Speeds
Reynolds No.- Low Speeds
How does lift occur?
Comes from the differnce in pressure between the lower and upper surfaces of the wing.
It is a mix of Bernoullis and Circulation theory
What causes a wing to stall?
Onset of flow seperation
What governs flow seperation?
Reynolds No.- At low speeds
Mach No.- For high speeds, shock-induced
To land and take-off what is required?
Low speeds typically 1.3 Vmin
2 sources of Drag
- Surface Friction drag (Skin Friction Drag) - a direct result of fluid viscosity
- Pressure Drag- Form (due to shape), Induced (due to Vortices at wing tips) and Wave (due to shock formation at high speeds)
Profile Drag
A combo of skin friction and form drag
