Manifold pressure Flashcards
What does a manifold pressure gauge measure in a piston aircraft engine?
It measures the absolute pressure of the fuel/air mixture inside the intake manifold, also known as Manifold Absolute Pressure (MAP).
What does the manifold pressure gauge indicate when the engine is not running?
It indicates ambient air pressure, approximately 14.7 psi (29.92 in Hg).
How is power output related to manifold pressure at constant RPM and altitude?
The power output is directly related to the fuel/air flow being delivered to the combustion chamber; as throttle setting increases, MAP increases, leading to more power.
What happens to the manifold pressure indication when the engine starts?
The manifold pressure decreases to a value less than ambient pressure, for example, idle at 6 psi (12 in Hg).
How does the manifold pressure gauge indicate engine failure or power loss?
It shows an increase in manifold pressure to a value corresponding to the ambient air pressure at the altitude where the failure occurred.
What is the characteristic of a normally aspirated engine regarding manifold pressure and altitude?
The power developed by a normally aspirated engine decreases with a decrease in atmospheric pressure, meaning less mixture is inducted at higher altitudes.
Why does the power output of a normally aspirated engine decrease at higher altitudes?
At higher altitudes, atmospheric pressure is lower, reducing the amount of mixture entering the cylinders and therefore decreasing the power output.
What is the typical atmospheric pressure at 10,000 feet altitude, and how does it affect manifold pressure?
The atmospheric pressure is about 10 psi at 10,000 feet, and this results in only a third of the required mixture entering the cylinders, reducing power to about a third of sea-level power.
What is supercharging or boosting in the context of manifold pressure?
Supercharging or boosting artificially increases pressure and mixture density to maintain sea-level manifold pressure at higher altitudes.
How does supercharging help overcome the limitations of a normally aspirated engine at high altitudes?
It uses a centrifugal air pump, driven by the engine crankshaft, to increase the pressure and density of the air/fuel mixture entering the cylinders.
Why is the use of a direct-reading pressure gauge mainly restricted to small aircraft?
Because it becomes impractical to pipe the pressure to the cockpit in larger or more complex aircraft.
How is manifold pressure measured and displayed in more complex aircraft?
The pressure is measured at the source and transmitted electrically to the pilot’s instrument displays.
What is the process of converting manifold pressure into an electrical signal for display purposes?
It involves converting mechanical movement into an electrical output at the measuring source and then reversing this conversion for display on a mechanical indicator.
Name three types of devices used to convert manifold pressure into an electrical signal.
Synchronous transmission (synchro system), inductive transmitter, and potentiometer system.
