1. AAE 556 Aeroelasticity Lecture 7-Control effectiveness
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Reading
Sections
These sections are painfully worked example problems – read through them to understand principles discussed in class
Section has a virtual work example – wait to read this until next week
Skip 2.19 for now (will do next week)
Read 2.20, and
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3. Our next goal learn about 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
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Ailerons are required for lateral stability They become increasingly ineffective at high speeds
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.
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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
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6. Herman Glauert’s estimators for CLd and CMACd
The flap-to-chord ratio is
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7. 1 DOF idealized model – no camber Sum moments about the shear center
Linear problem (what does that mean?) e
Remember
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8. Solve for the twist angle due only to aileron deflection d
Lift
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9. The aeroelastic lift due to deflection
Compare answer to the lift computed ignoring aeroelastic interaction
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The aileron deflection required to generate a fixed increases as q increases
Aileron deflection increases as q approaches reversal
The required control input is …
Is aileron reversal an instability?
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11. The most common definition for the reversal condition
Is it possible that I deflect and aileron and get no lift?
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?
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12. How do I make the numerator term in the lift expression equal to zero?
L=0, reversal
L=infinity, divergence
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13. Solve for the q at the reversal condition
numerator=0 or
Why the minus sign?
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Understanding what the aileron does Two different ways to compute pressure distribution resultants due to aileron deflection
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15. Force equivalence the same moment at the AC with 2 different models+
Solve for the distance d to find the CP distance from the AC = Ld d e
A lift force at d produces the same result at the AC as a lift force and moment at the AC
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16. Aileron center of pressure depends on the aileron chord
mid-chord
Distance aft of 1/4 chord
All-movable surface AC
Aileron flap to chord ratio, E
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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
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