ATPL Tech Questions Flashcards
In laymans terms describe how a jet engine works
A fan on the front sucks air in. Some of the air goes through a compressor in the middle of the engine. The compressor compresses the air which heats it up. The air then passes into the combustion chamber which is injected with fuel and ignited. The exhausted air then exits via the rear and drives the turbine which drives the compressors and the fan
What does FADEC control?
Full authority digital engine control.
Electronically monitors and adjusts the engine functions. functions such as engine start, mixture, propeller pitch, fuel flow
Why are jet engines more efficient at high altitude?
Air is cooler and cool air expands more when heated. Expansion of air drives the combustion engines.
Air is less dense therefore the aircraft flies faster than low altitude for same thrust.
Jet engines - more efficient at high rpms. Air density is less at altitiude which means more RPM is required which means they are more efficient.
What is Dutch roll?
Oscillating instability caused by strong laterall stability and weak directional stability.
Common on jet aircraft.
Distrubance in yaw/roll. Oute going wing span is increased and therefore produces more lift and this in turn creates more drag. This drag forces the aircraft to yaw towards the downgoing wing. A lift force is created on the fin which produces a force in the opposite direction and the process repeats.
Leading edge slats
Re-engersies the airflow at high angle of attacks. High speed air from beneath the wing passes through to the upper surface.
Delays the stall. Critcal AoA increased
Flaps
Krueger - Increases camber and the depth of the wing. Reduces stall speed and increases lift. Hinged. Produces same amount of lift at lower airspeeds
What happens if sweep angle is increased?
Stall speed is increased
Higher sweep angle = more spanwise flow and less chordwise accelerating air.
How does a swept wing work?
Splits the airflow into 2 components to trick the wing into thinking it is flying slower. Spanwise and chordwise airflow. spanwise flow travels along the leading edge and does not accelerate. Chordwise flow which acceleates is reduced. Less accelerating air thus higher Mcrit.
Airflow flows at an angle and this increases the effective chord of the wing but wing thickness remains unchanged. Reduces the thickness to chord ratio. Creates a higher Mcrit.
Swept wing stall effects and how to reduce the effects
Stalls at wing tip due to spanwise flow. CP moves fwd and creates a nose up tendency.
Loses aileron authority.
Vortex generators renergise the airflow and help increase aileron effectiveness.
Washout/twist - Increases camber at the wingtip and delays the stall.
Dihedral/Anhedral
Dihedral - Inclined upwards and increase stability in the roll axis
Anhedral - Inclined downwards - less stable - helps high wing become less stable as they are stable anyway.
What is wing load?
Total mass of the aircraft divided by the area of its wing.
High wing loading = greater takeoff/landing distance and higher stall speeds.
What causes a lower Mcrit speed?
Wing thickness - Thin wing will have a higher Mcrit,
Camber of a wing ( high camber of a wing will cause air to accelerate faster)
Weight of the aircraft - Heavier aircraft will require more lift to be produced and therefore more acceleration over the surface of the wing.
What is coffin corner
An aircrafts absolute ceiling.
Low speed buffet meets high speed buffet
Stall speed increases with altitude due to the reduction in air density and thus causing a reduction in lift.
As altitude increases, temperature decreases and local speed of sound decreases so the critical mach number decreases.
Increase in weight = increase in stall speed = lower coffin corner
Adverse aileron
Upgoing wing produces more lift = more drag = yaw in the opposite way to the turn.
What is V2
Safe single engine climb speed. Must be held until AA as a minimum. Ensures min climb gradient is achieved. at screen height
