propeller - blade element theory (2)
DESCRIPTION
This is a presentation which covers some theories on the performance of a propeller when analyzed and treated as an infinitesimal blade element from its root to tip chord, how the twist angle of each station contributes to the uniformity of airflow, and the general topics related to blade element analysis.TRANSCRIPT
PowerPoint Presentation
Basic Helicopter and Propeller DesignAE 511Reported by:De Leon, Francis Carlo S.Dimaculangan, Deo MarYANOInstructor: Dr. Jay Jack ManzanoTHE BLADE ELEMENT THEORY
The Blade Element TheoryPropeller Design2
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BLADE ELEMENT THEORY (BET) is a mathematical process originally designed byWilliam Froude(1878),David W. Taylor(1893) andStefan Drzewieckito determine the behavior of PROPELLERS.
William Froude
David W. Taylor
Stefan DrzewieckiKindly press Enter.to go to the next slide.
It involves breaking a blade down into several small parts then determining the forces on each of these small blade elements.
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The blade is composed of aerodynamically independent, narrow strips or elements.Physical Assumption
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Free Body Diagram for the Analysis of a Blade Element
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Explanation of the FBD
VrVr is the rotational speed of the propeller, measured in RPM.Blade angle Alpha, becomes the effective angle of attack for the aerodynamic analysis of the cross-section airfoil. Kindly press Enter.to go to the next slide.
VrBut when the aircraft starts its forward motion, forward velocity VF comes into existence.We must consider a resultant VR (the resultant velocity component that now acts upon the blade cross-section.)
VFVRKindly press Enter.to go to the next slide.
Vr
VFVRThe effective angle of attack Alpha, becomes a little relatively smaller than when the propeller was not moving forward.This was due to the new resultant relative air velocity component that aerodynamically acts upon the blade cross-section.Kindly press Enter.to go to the next slide.
Vr
VFVR
This aerodynamic activity produces Lift and Drag forces, and from these forces, the propellers Thrust Force and its Torque becomes able to be calculated.Kindly press Enter.to go to the next slide.
Upon calculating the an elements Thrust/Torque, the whole Propeller Blades Thrust/Torque is then the sum of the values of all the infinitesimal blade elements, from its root to its tip.TIPROOTKindly press Enter.to go to the next slide.
Example:For two blades, Thrust computed from BET analysis is multiplied by 2.
For three blades, Thrust computed from BET analysis is multiplied by 3.
For four blades, Thrust computed from BET analysis is multiplied by 4.And so onKindly press Enter.to go to the next slide.BLADE ELEMENT THEORY (BET) has proven that basic aerodynamics can be applied to almost anything that will come in contact with airflow.This fundamental theory has helped produce a lot of propellers that we see today from small aircrafts to large ones.
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Basic Helicopter and Propeller DesignAE 511Reported by:De Leon, Francis Carlo S.Dimaculangan, Deo MarDizon, John Kevin M.Instructor: Dr. Jay Jack Manzano