CPL Aircraft Systems and Aerodynamics 3 — Questions and Answers
Question 1: What is the aerodynamic effect of deploying leading-edge slats?
- They increase wing camber and allow higher angles of attack before stall (Correct answer)
- They reduce induced drag by modifying spanwise airflow
- They act as speed brakes to reduce airspeed rapidly
- They deflect exhaust gases to increase thrust
Correct answer: They increase wing camber and allow higher angles of attack before stall
Leading-edge slats increase wing camber and create a slot that energizes boundary layer airflow, allowing the wing to sustain lift at higher angles of attack and lower speeds.
Question 2: In a pressurized aircraft, what does 'differential pressure' refer to?
- The difference between fuel pressure at the injector and manifold pressure
- The difference between cabin pressure and outside ambient pressure (Correct answer)
- The pressure drop across the cabin air filter
- The difference between static and pitot pressure
Correct answer: The difference between cabin pressure and outside ambient pressure
Differential pressure (delta-P) is the difference between the pressurized cabin pressure and the ambient outside air pressure, which determines structural loads on the fuselage.
Question 3: What is 'propeller slip' in aviation?
- Sideways movement of the propeller disc due to gyroscopic precession
- The difference between the theoretical pitch distance traveled and the actual distance advanced per revolution (Correct answer)
- The angular velocity difference between engine shaft and propeller hub
- Vibration in the propeller caused by blade tip vortices
Correct answer: The difference between the theoretical pitch distance traveled and the actual distance advanced per revolution
Propeller slip is the difference between the geometric pitch (theoretical distance advanced per revolution) and the effective pitch (actual distance advanced), caused by the propeller working against air resistance.
Question 4: What is the relationship between aspect ratio and induced drag?
- Higher aspect ratio produces more induced drag for the same lift
- Lower aspect ratio produces less induced drag for the same lift
- Higher aspect ratio produces less induced drag for the same lift (Correct answer)
- Aspect ratio has no effect on induced drag
Correct answer: Higher aspect ratio produces less induced drag for the same lift
A higher aspect ratio wing generates less induced drag for the same lift coefficient because the wing tips are farther apart, reducing the strength and influence of wingtip vortices.
Question 5: During engine start, why is it critical to avoid 'hot starting' a turbine engine?
- Hot starts increase fuel consumption and reduce engine life
- Excessive turbine inlet temperature during light-off can cause thermal damage to turbine blades (Correct answer)
- A hot start causes compressor surge immediately after ignition
- It floods the combustion chamber with unburned fuel
Correct answer: Excessive turbine inlet temperature during light-off can cause thermal damage to turbine blades
A hot start occurs when turbine inlet temperature exceeds limits during the start sequence, which can cause severe thermal damage to turbine blades and combustion components.
Question 6: What aerodynamic phenomenon is described by 'ground effect'?
- Increased parasite drag caused by proximity to the runway surface
- Reduction of induced drag due to interference with wingtip vortex formation near the ground (Correct answer)
- Increased lift caused by air compressed between the wing and ground
- Static charge buildup on airframe when operating near terrain
Correct answer: Reduction of induced drag due to interference with wingtip vortex formation near the ground
Ground effect reduces induced drag by limiting downward airflow from the wingtips, weakening vortices and reducing induced angle of attack when the wing is within approximately one wingspan of the ground.
Question 7: What is the function of a 'firewall' in a piston aircraft?
- An avionics protection circuit that prevents electrical surges from reaching cockpit instruments
- A fire-resistant bulkhead separating the engine compartment from the cabin to contain engine fires (Correct answer)
- A valve that shuts off fuel flow when cockpit smoke is detected
- A heat shield protecting the oil cooler from exhaust gases
Correct answer: A fire-resistant bulkhead separating the engine compartment from the cabin to contain engine fires
The firewall is a fire-resistant barrier (typically stainless steel) between the engine compartment and the cabin, designed to contain an engine fire for a minimum of 15 minutes.
CPL Aircraft Systems and Aerodynamics 3
What is the aerodynamic effect of deploying leading-edge slats?