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Stability vs. controllability
Closer AC to CG: weaker stability, greater controllability
Further AC from CG: stronger stabiliy, reduced controllability
Occurs as a/c yaws or rolls into sideslip. Side forces cause increased yaw - directional instability
Results from strong directional stability relative to weak lateral stability
Results from strong lateral stability relative to directional stability
How to improve transonic flight?
Sweep and low thickness to chord ratio
1) Cause the root to stall at a lower AOA
2) 3.5o causes the tip to stall at a higher AOA
Combined effect is that the root and tip stall at approximately the same time.
Advantages/disadvantages of swept wing
A: Higher speeds, structurally stronger
- 1) Less CL
- 2) Prone to tip stall
- 3) Spanwise flow
- 4) Leading edge vortexing
- 5) High induced drag at low speed
With two pilots, CG moves...
forward. Increased stability
CG Forward Limits
CG Aft Limits
Upper fuselage/center wing to do not move CG (No answer, just know)
Disadvantage of swept wing:
High AOA Stall
Slight nose down pitch Mach 0.8
Second indicator of impending stall
Accelerated stalls with no external stores - 20o pitch up
Is thrust neutral on longitudinal stability
mass air flow in slugs / sec
What happens to TR in the following?
2) Weight increase
3) Altitude increase
1) TR shifts up and left
2) TR shifts up and right
3) TR shifts right