Propeller efficiency, Other Engineering

PROPELLER EFFICIENCY:

The propeller is 80 - 87% efficient up to approximately 400 mph.  Generally, beyond this performance will fall off, although new materials and improved blade technology are tending to increase efficiency.

This efficiency can be expressed as followed:

Propeller efficiency  =    Work done by propeller/work done by engine *  100

The drag on an aircraft travelling at 300ft/sec is 1100 lbs and if the engine produces 750 Shaft Horsepower the propeller efficiency is as follows:

Work          =  Force  *  Distance

Drag =  Thrust (in level flight)

Work Done by Propeller / Sec    =       Thrust *  Speed

                                                         =       1100  *  300 ft lbs

Work Done by Engine                           =       HP / Sec

                                                         =       750  *  550 ft lbs (1 HP)

Propeller Efficiency                      =   (1100*300)/(750*350) * 100  =  80%

Note that if the aircraft is stationary with engine running, thrust is produced, but as there is no forward movement, propeller efficiency is zero.  At high forward speeds the slip could be zero, i.e. no angle of attack, therefore no thrust.  With no thrust the propeller efficiency is zero.

When power is changed into thrust, the drag (or torque) created by the propeller limits engine speed.  To be efficient, obviously the propeller should absorb all the power available.  This is achieved by making a compromised design as power absorption creates limitations.

Propeller design with regard to diameter, number of blades and blade shape is governed by the power to be absorbed.  The tip speed must not approach the speed of sound or efficiency will be lost; this limits diameter.  Aircraft design also limits propeller design.  Low slung engines mounted close to the fuselage require small diameter propellers; larger propellers require a longer undercarriage.

  • Diameter
  • Blade Angle
  • Chord
  • Change of Angle of Attack
  • Camber of Aerofoil

In higher powered engines, a reduction gear is usually fitted.  This allows the engine to run at its most efficient speed while allowing the propeller to turn at its most efficient speed.

 

Posted Date: 9/14/2012 2:36:26 AM | Location : United States







Related Discussions:- Propeller efficiency, Assignment Help, Ask Question on Propeller efficiency, Get Answer, Expert's Help, Propeller efficiency Discussions

Write discussion on Propeller efficiency
Your posts are moderated
Related Questions
Applications of the subject strength of materials

Also called 1-bit DAC or sigma-delta DAC. It uses pulse-density modulation (PDM) which encodes the signal amplitude by the relative density of the pulses. The output voltage has on

WHAT IS ZENER DIAOD?

if the response of a signal is h(t) then the cascading of two responses h1(t) and h2(t) is given by

Explain the following observations: cells of Escherichia coli fermenting glucose grow faster when NO3 - is supplied to the culture and then grow even faster when the culture is hig

tell me about where we download notes for electronics syllabus

Fire prevention – bays or zones: To prevent the spread of a fire within an aircraft/engine nacelle, it is divided up into sections or zones, each being separated by a fireproof

Solvency Ratios: Profitability Ratios: The profitability ratios determine the capacity of the company to generate the profits with the amount of shareholders investment. Again hig

OUTPUT CHARACTERISTICS: Figure shows a "Common Emitter" amplifier stage. Common Emitter Amplifier Stage With no base/emitter bias applied, there will be no collector

Fire risk assessment process: This is the main part of the FRA process.    Here we consider the risk, measure it against what we consider acceptable and, if we consider that t