Basic principles - propeller, Other Engineering

BASIC PRINCIPLES :

The purpose of a propeller is to convert the power developed by the engine into a useful force called 'Thrust'. This force must be equal to and opposite in direction to 'Drag' in order for the aircraft to remain in level flight without acceleration.

Aircraft propellers, whether powered by reciprocating engines or turbine engines, accelerate a large mass of air through a small velocity change, as opposed to the turbojet, which accelerates a small quantity of air through a large velocity change.

The cross section of a propeller blade is similar to that of an aerofoil and it will behave in a similar manner when moving through the air. As the blade is rotating as well as moving forward, the blade will meet the air at a positive angle of attack. This will produce 'lift' which acts along the axis of rotation of the engine, thus causing forward movement of the airframe as a result of thrust. The blade can be thought of as a rotating wing in essence.

There are two types of propeller, fixed pitch and variable pitch. The first section will deal with the fixed pitch propeller.


Propellers can be installed in several configurations: that of a 'tractor' in which the propeller is mounted forward of the engine, and 'pusher' in which the mounting is aft of the engine.

Increase in power output has resulted in the development of four and six bladed units, but there is a limit to R.P.M. and efficiency, generally accepted to be approximately 500 m.p.h. However, recent advances in computer design, composite materials and blade aerodynamics, plus the continued development of the fan engines, do seem to indicate that the propeller, albeit in a vastly different form to the Wright Brothers' model, will be around for many years to come.

The propeller blade is of Aerofoil section with some changes in terminology and the forces produced as it moves through the air are roughly equivalent to the forces of lift and drag produced by an aircraft wing.  These forces are called thrust and torque and are shown in comparison with an aerofoil.

1993_propller.png

Newton's Second Law states that Force = Mass ´ Acceleration and Thrust being a force, the same expression applies, being equal to the mass of air handled and the speed of the slipstream, less the speed of the aeroplane.  Therefore, the power expended in producing thrust depends on the mass of air moved per second.  On average, thrust constitutes 80% of the total horsepower absorbed by the propeller (torque).  The other 20% is lost in friction and slippage.  For any speed of rotation, the horsepower absorbed by the propeller balances the horsepower delivered by the engine.

Posted Date: 9/14/2012 2:20:48 AM | Location : United States







Related Discussions:- Basic principles - propeller, Assignment Help, Ask Question on Basic principles - propeller, Get Answer, Expert's Help, Basic principles - propeller Discussions

Write discussion on Basic principles - propeller
Your posts are moderated
Related Questions
how can we determine the crystal structure of material by having interplanar spacing d?

what is the basics suggetion for the education values

In the previous discussion, we investigated the static aeroelastic behaviour of straight (unswept) wings. These wings are characterised by an effective decoupling of wing bending a

in which type of armature winding Equaliser ring dummy coils are used

create 22 elements in scalar hint:for loop or any loop statement and append to previous variable element by elements

Assume that a movie is two hours long, that the frame rate is 30 frames per second, and that the resolution per frame is 1080i (1920×1080 pixels per frame), and that each pixel is

identify the role of the regulators and problems associated with regulation

We now have some idea about what models are available to simulate the flow over an aerofoil, and also how to use the Hanley package to apply these methods. Keep referring to you

Provided a 1D array of integers, find all combinations of 3 values from this set such that: a+b+c=0 For example, if one were provided with the set [3 1 3 -4 -6], the resulting answ

defination of leverage,objectives,enterpritation,analysis,conclusion,references,review of literature.