Question

A propeller engine for a model airplane is measured to have a jet velocity of 50 kilometres per hour. When strapped to a fixed support it is measured to produce 10 Newtons of thrust. Determine the mass flow through this propeller (in kilograms per second):

Answer 1

We can use the equation for thrust generated by a propeller:

Thrust = Mass flow rate x (Jet velocity + Air velocity) + Propeller efficiency x Power

Since the propeller is strapped to a fixed support and not moving through the air, we can assume that the air velocity is zero. Therefore:

Thrust = Mass flow rate x Jet velocity

Solving for mass flow rate:

Mass flow rate = Thrust / Jet velocity

Substituting the given values:

Mass flow rate = 10 N / (50 km/h) = 10 N / (13.89 m/s) = 0.720 kg/s

Therefore, the mass flow through this propeller is 0.720 kilograms per second.