L4/5 - Longitudinal Stability Flashcards
What is the static margin?
The distance in which the CG can move rewards before reaching the neutral point (the aerodymanic centre of the aircraft). The greater the Static margin the greater the longitudinal stability.
What is the difference betwen stick fixed and stick free stability?
Stick fixed is when the stick is fixed so the elevator stays at a constant position
Stick free is when the elevator is allowed to float freely with the prevailing airflow.
What is the trim tab?
A tiny extra control surface on the back of the elevators and rudder, controlled by the trim wheel.
What happens as the CG moves towards the forward limit?
Nose is heavier on takeoff
Higher stall speed
More thrust and therefore fuel required to maintain speed
Nose down tendancy
A positive change in AOA required a negative change in moment for stability and so…?
The gradient of Cm/AoA is negative. <0
What are the two requirements for static stability?
dCm/dAoA < 0
Cm0 must be > 0
What is the Trim angle of attack?
The neutral point. The angle of attack at which the sum of moments = 0.
What is an Unbalanced Airplane?
Where the gradient is correct however Cm0 < 0.
What is the wings contribution to stability?
The wing is usually destabalising and so a horizontal tail is required to balance out the wing.
See lectures to details tail calcs
See lectures to details tail calcs
How do you find the Stick Fixed neutral point?
You reaarange the picthing moment equation for the wing
