What is the critical mach no?
Speed at which the airflow over a wing becomes sonic.
Describe the characteristics of MCrit?
- Initial mach buffet
- Increase in drag due to the breakdown of airflow
- Mach tuck
- Possible loss of control
Describe mach tuck
A nose down change in attitude after MCrit
Why does the centre of pressure move aft as speed increases beyond MCrit?
- Shockwaves form on upper surface towards leading edge. Causes rearwards shift in centre of lift.
- Swept wing experiences shock wave at thick wing root. Loss of lift inboard leads to a lift force being further aft.
What does a mach trimmer correct for?
Mach tuck
When does an aircraft stall?
When critical angle of attack is exceeded, regardless of airspeed.
Recovery must therefore reduce AoA
What four qualities effect an aircraft’s stall speed?
- Weight
- Altitude
- Wing design/lift
- Configuration
What type of aircraft design is associated with a superstall or deep stall?
T-tailed aircraft
What prevents dutch roll?
Yaw dampers
What are the four flying quality penalties experienced at very high level?
- Restricted operating range
- Reduced manoeuvrability
- Reduced aerodynamic damping
- Reduced stability
What is adverse yaw?
Yawing motion in the opposite direction to the turning/rolling motion of the aircraft. Due to the drag on the down-going aileron being greater than that on the up-going aileron.
What devices are best at producing roll?
Spoilers, but the roll comes at the cost of lift.
What are the 3 purposes of spoilers?
- Roll Control
- Air speed brakes
- Ground lift dumpers
What factors contribute to a change in the pitching moment due to flap extension?
- Increase in lift due to increased wing area
- Rearward movement of centre of pressure
- Increase in down wash
- Increase in drag
