Blade Element Theory (BET)

What is BET ?

If we look at an aeroplane wing flying in a straight line the lift produced by it is easily calculated by using the lift formula restated here without explanantion for clarity.
Lift Force = CL ½ ρ V2 S
A problem arises if we try and apply this to a rotating wing such as a helicopter rotor blade. Although the blade is rotating with a constant RPM if we look at two parts of the blade, one near the root and the other near the tip it is apparent that they both travel different distances in one revolution. Since V is a velocity it relates to distance moved in a period of time, as a result the V2 element of the lift formula varies along the blade. In order to calculate the actual lift produced by the blade we can consider the blade to be made up of a number of very thin strips of blade all travelling at the same angular velocity (RPM) but with different linear velocities enabling us to calculate using the lift forumula the lift produced by each of the thin strips (or elements, hence the name) . If we now add up all of the lift forces produced by the thin strips we now have a good idea what the lift force produced by that blade will be.

This theory also holds for the calculation of Drag and Centrifugal Force and when individual element forces are calculated results which approximate reality can be achieved.

Application of Blade Element Theory

Finding The Lift Produced By A Blade Mathematically

 
Example Content

Web References

None Specified

Bibliography