2 Divergence Flashcards
What is ‘Divergence’?
The phenomenon that occurs when the moments due to aerodynamic forces overcome the restoring moments due to stiffness.
(Causing the wing to fail, so we want this to be as big as possible)
Structural failure
what is Theta0?
The initial angle of incidence between the wing and the airflow
What is theta?
The angle the wing will rotate through, very often the twist
What is GJ?
Torsional rigidity
What is U for divergence?
Strain energy
In the legrange equation, what is T?
T is the kinetic energy
In the Lagrange equation, what is
The Dissipative function
In the Lagrange equation, what is U?
Strain energy
What does the first term of the legrange equation simplify to?
From kinetic energy (T) equation simplifies to
What is the second term of the legrange equation simplify to?
Using the Dissipative function
What does the third term of the legrange equation simplify to?
Using the strain energy (U) equation
Whats the equation for variable chord c(y) for a tapered wing?
What bit of the legrange equation do we need for divergence?
The third and final terms
What is the equation for work done for divergence?
Moment * the angle moved
What is the equation for Moment?
L x ec
What is ec
- e is the percentage of chord from aerodynamic centre to cg
- c is the chord
What does subscript 1 mean?
Means that the parameter is just for an aerofoil
What does subscript w mean?
Means that the parameter is for the whole wing
What is the q divergence equation for a 2D aerofoil?
- K is the stiffness of the wing
- a1 is the CL slope of a 2D aerofoil
- e is the percentage chord from the ac to cg
- c is the chord
what is the elastic axis?
The centre of rotation
What is the CL for a symmetric wing with some twist?
What is the CL for a cambered wing with some twist?
What is the expression for the chord of a linearly tapered wing, where Cr is the chord at root and Ct is the chord at the tip?
How do we get the strain energy for bending?
(Bending is always quadratic)
