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Propulsive efficiency comparison for various gas turbine engine configurations. The calculation is somewhat different for reciprocating and turboprop engines which rely on a propeller for propulsion since their output is typically expressed in terms of power rather than thrust. The equation for heat added per unit time, Q, can be adopted as ...
It helps in understanding the efficiency of the propeller at different speeds and is particularly useful in the design and analysis of propeller-driven vehicles.It is the ratio of the freestream fluid speed to the propeller, rotor, or cyclorotor tip speed. When a propeller-driven vehicle is moving at high speed relative to the fluid, or the ...
A propeller imparts momentum to a fluid which causes a force to act on the ship. [1] The ideal efficiency of any propulsor is that of an actuator disc in an ideal fluid. This is called the Froude efficiency and is a natural limit which cannot be exceeded by any device, no matter how good it is.
Consider the element at radius r, shown in Fig. 1, which has the infinitesimal length dr and the width b. The motion of the element in an aircraft propeller in flight is along a helical path determined by the forward velocity V of the aircraft and the tangential velocity 2πrn of the element in the plane of the propeller disc, where n represents the revolutions per unit time.
The logarithmic term with weight ratios is replaced by the direct ratio between / = where is the energy per mass of the battery (e.g. 150-200 Wh/kg for Li-ion batteries), the total efficiency (typically 0.7-0.8 for batteries, motor, gearbox and propeller), / lift over drag (typically around 18), and the weight ratio / typically around 0.3.
P R curve for the light aircraft with the drag curve above and weighing 2000 kg, with a wing area of 15 m² and a propeller efficiency of 0.8. W = (ρ/2).S.V 2.C L and P R = (ρ/2η).S.V 3.C D. The extra factor of V /η, with η the propeller efficiency, in the second equation enters because P R = (required thrust)× V /η. Power rather than ...
where is propulsive efficiency (typically 0.65 for wooden propellers, 0.75 metal fixed pitch and up to 0.85 for constant-speed propellers), hp is the engine's shaft horsepower, and is true airspeed in feet per second, weight is in lbs. The metric formula is:
Propeller-driven airliners had useful load fractions on the order of 25–35%. Modern jet airliners have considerably higher useful load fractions, on the order of 45–55%. For orbital rockets the payload fraction is between 1% and 5%, while the useful load fraction is perhaps 90%.