1. AAE 556 Aeroelasticity Lecture 6-Control effectiveness
Purdue Aeroelasticity

2. Purdue Aeroelasticity
Today’s goals
Review what we have done with the 2 DOF model and draw some conclusions
Begin the study of control effectiveness
Purdue Aeroelasticity

3. Purdue Aeroelasticity
Reading review
Sections
Some of these sections are painfully worked example problems – work through them to understand principles discussed in class
Skip 2.19 for now (next week)
Read 2.20, and
Purdue Aeroelasticity

4. Summary-Develop 2 DOF segmented aeroelastic finite wing model
Torsional springs
fuselage
wing tip
wing root
Torsional degrees of freedom
Purdue Aeroelasticity

5. Purdue Aeroelasticity
Lift re-distribution due to aeroelasticity Wing sections support ½ the total W
Observation - Outer wing panel carries more of the total load than the inner panel as q increases
Purdue Aeroelasticity

6. The aeroelastic stiffness matrix determinant is a function of q
The determinant is
where
When dynamic pressure increases, the determinant D tends to zero – divergence occurs
Purdue Aeroelasticity

7. Twist deformation vs. dynamic pressure parameter
Unstable q region
panel twist, qi/ao
divergence
Outboard
panel (2)
determinant D is zero
Purdue Aeroelasticity

8. How do we determine divergence for an MDOF system?
The general form of the aeroelastic static equilibrium equations is
n degrees of freedom
Perturb the system by an amount
Euler question – “Is there an equilibrium solution to the following relationship?”
Purdue Aeroelasticity

9. Purdue Aeroelasticity
Static stability
The static stability test reduces to the existence of a homogeneous matrix equation that must hold if the system is neutrally stable ?
Purdue Aeroelasticity

10. Purdue Aeroelasticity
Linear algebra says...
only if … or
This nth order determinant is called the stability determinant or the characteristic equation
Purdue Aeroelasticity

11. Our next goal control effectiveness
Demonstrate the aeroelastic effect of deflecting aileron surfaces to increase lift or rolling moment
Examine the ability of an aileron or elevator to produce a change in lift, pitching moment or rolling moment
Reading – Sections
Purdue Aeroelasticity

12. Purdue Aeroelasticity
Setting the stage
Many of the uncertified minimum ultralights, and perhaps some of the certificated aircraft, have low torsional wing rigidity. This will not only make the ailerons increasingly ineffective with speed (and prone to flutter), but will also place very low limits on g loads.
Purdue Aeroelasticity

13. Purdue Aeroelasticity
The ability of an aileron or elevator to produce a change in lift, pitching moment or rolling moment is changed by aeroelastic interaction
aileron
deflection
Purdue Aeroelasticity

14. Herman Glauert’s estimators for CLd and CMACd
The flap-to-chord ratio is
Purdue Aeroelasticity

15. 1 DOF idealized model – no camber Sum moments about the shear center
Linear problem (what does that mean?) e
Remember
Purdue Aeroelasticity

16. Solve for the twist angle due only to aileron deflection d
Lift
Purdue Aeroelasticity

17. The aeroelastic lift due to deflection
Compare answer to the lift computed ignoring aeroelastic interaction
Purdue Aeroelasticity

18. One definition for the reversal condition
Is this possible?
We usually use an aileron to produce a rolling moment, not just lift. What is the dynamic pressure to make the lift or rolling moment zero even if we move the aileron?
Purdue Aeroelasticity

19. How do I make the numerator term in the lift expression equal to zero?
L=0, reversal
L=infinity, divergence
Purdue Aeroelasticity

20. Solve for the q at the reversal condition
numerator=0 or
Why the minus sign?
Purdue Aeroelasticity

21. Purdue Aeroelasticity
Summary
Control surfaces generate less lift because the control deflection creates a nose-down pitching moment as it generates lift.
At a special dynamic pressure (a combination of airspeed and altitude) the deflection of an aileron creates more downward lift due to nose-down deflection than upward lift
Purdue Aeroelasticity