Regarding Aircraft Engine Operations- how can I describe & explain use of the RPM and Manifold Pressure Gauges

Question

Regarding Aircraft Engine Operations- how can I describe & explain use of the RPM and Manifold Pressure Gauges

Answer 1

The manifold pressure indicates how much load is being placed on the engine as prop pitch is increased. Revolutions Per Minute is the speed the engine is turning. The higher the manifold pressure at a given RPM is, the more load being applied to the engine. Rule of thumb at cruise is 2400 rpm and 24 inches of manifold pressure.

Answer 2

The previous answer describing flight at 2400 rpm and 24 inches manifold pressure is the concept of flying "square", or 24x24.   This is a good rule of thumb.   Also, it is not advisable to fly "over square".  This means flying with engine settings like 2200rpm and 25 inches manifold pressure.  

It is okay to fly under square, or something like 2100 rpm and 19 inches manifold pressure.   I do this quite often in cruise flight.

The ability to control the engine speed independently of the throttle setting is a lot like having a manual transmission or over drive in a car.   It allows pilots to better use the efficiency gains found at higher altitudes.

Answer 3

to describe the use of rpm is how fast the prop is spining and the pressure gauges is tubes outside the plane the move depending on the pressure