PPL PPL Aircraft Systems and Powerplant 2 — Questions and Answers
Question 1: What does manifold pressure (MAP) indicate in a piston aircraft?
- Fuel pressure in the fuel lines
- The absolute pressure in the engine intake manifold, used to set power (Correct answer)
- Oil pressure at the engine
- Barometric pressure at cruise altitude
Correct answer: The absolute pressure in the engine intake manifold, used to set power
Manifold pressure measures the absolute pressure of the air-fuel mixture in the intake manifold and is the primary power-setting indicator in many aircraft.
Question 2: What happens to a normally-aspirated engine's power output as altitude increases?
- Power increases due to reduced aerodynamic drag
- Power decreases because lower air density reduces the mass of air entering the engine (Correct answer)
- Power stays constant up to the service ceiling
- Power increases until the critical altitude
Correct answer: Power decreases because lower air density reduces the mass of air entering the engine
As altitude increases, air density decreases, so the engine ingests less air mass per stroke, reducing combustion energy and power output.
Question 3: What is the purpose of the mixture control in a piston aircraft?
- To control engine RPM
- To adjust the fuel-to-air ratio to maintain proper combustion as altitude and air density change (Correct answer)
- To activate carburetor heat
- To control throttle position at cruise
Correct answer: To adjust the fuel-to-air ratio to maintain proper combustion as altitude and air density change
The mixture control adjusts the fuel-to-air ratio because air density decreases with altitude, requiring less fuel to maintain the correct stoichiometric ratio.
Question 4: What color arc on the tachometer indicates the normal continuous operating range?
- Red arc
- Yellow arc
- Green arc (Correct answer)
- White arc
Correct answer: Green arc
The green arc on the tachometer indicates the normal continuous operating RPM range approved by the manufacturer.
Question 5: What is the purpose of the alternator on a modern piston aircraft?
- To start the engine
- To continuously charge the battery and supply electrical power during flight (Correct answer)
- To power the magneto ignition system
- To cool the engine at high power settings
Correct answer: To continuously charge the battery and supply electrical power during flight
The alternator converts mechanical energy from the engine crankshaft into electrical energy to power avionics and continuously recharge the battery.
Question 6: What does a high Cylinder Head Temperature (CHT) reading above the red line indicate?
- Normal cruise power setting
- Potential engine damage from overheating requiring immediate action (Correct answer)
- Lean mixture condition only
- Low oil pressure condition
Correct answer: Potential engine damage from overheating requiring immediate action
CHT gauges monitor engine heat; exceeding the red line limit indicates the engine is overheating and damage to cylinder heads or valves may occur.
PPL PPL Aircraft Systems and Powerplant 2
What does manifold pressure (MAP) indicate in a piston aircraft?