Session: 01-14 Propellers and Open Rotors II

Paper Number: 153475

Improving Propeller Performance Using a Hybrid Airfoil Propeller Design 

The primary method currently used for propeller design is the Blade Element Momentum Theory or BEMT.  BEMT combines momentum theory with blade element theory to calculate the thrust and torque on a propeller blade.  Momentum theory describes the loss of pressure (momentum) when passing air through a rotor plane. Blade Element Theory divides the propeller blade into small, independent, 2-D airfoil sections.  Aerodynamic forces are summed along the span of the blade to find the forces and moments exerted on the propeller. BEMT uses an iterative procedure to calculate the lift and drag leading to optimum thrust and torque for minimum induced losses.  Wisniewski and Van Treuren have shown that a double break propeller design, reducing the thrust production at tip, leads to minimum induced drag and improved performance making the propeller more efficient (lower drag) and quieter. A hybrid design, using two different airfoils, can can improve efficiency even more.

    A series of tests were performed on a commercial and three custom propellers.  The design point was 5 lb_f of thrust at 7,000 ft under static conditions.  Data taken compares RPM, power required, and SPL at the design point.  The commercial propeller was a KDE CF215, a 21.5 x 7.3 propeller which is 21.5 inches in diameter.  The custom propeller had a 21.5 inch diameter, a 2.25 inch chord which tapered to an oval tip.  A baseline propeller was designed with an SG6043 airfoil at 4.5 AoA with standard BEMT methods.   A 50_94 double break propeller with only the SG6043 airfoil was then designed and tested.  Last, a hybrid 50-94 double break propeller was designed and tested.  It is a hybrid propeller because it uses a combination of a SG6043 airfoil for the hub to the first break and then transitions to a SG6041 airfoil for at the tip.  The reduced drag with the SG6041 leads to lower power required than the 50_94 propeller using only the SG6043.  Care should be given to choosing appropriate airfoils for the hybrid propeller designs that have low drag coefficients over the range of tip airfoil AoAs.  When this condition is satisfied, the hybrid configuration shows the most promise for both efficiency and a reduction in SPL.  

Presenting Author: Kenneth Van Treuren Baylor University

Presenting Author Biography: Dr Ken Van Treuren is Professor Emeritus in Mechanical Engineering at Baylor University. In 1977 he earned his B.S. in Aeronautical Engineering from the USAF Academy studying gas turbine propulsion. He was then awarded a Guggenheim Fellowship to study hydrocarbon combustion for his M.S. in Engineering at Princeton University. After serving 10 years as a USAF pilot in KC-135 and KC-10 aircraft, he completed his DPhil in Engineering Sciences at the University of Oxford, United Kingdom in gas turbine impingement cooling. Dr Van Treuren returned to the USAF Academy to teach heat transfer and propulsion systems until his military retirement in 1998. At Baylor University for the past 26 years, he taught courses in fluid mechanics, energy systems, propulsion systems, heat transfer, and aeronautics. Research interests include renewable energy, small wind turbine aerodynamics, and noise generation as it applies to the urban environment. Currently, he designs small Unmanned Aerial System propellers, reducing noise and power requirements. He is a Fellow of the ASME and an Associate Fellow of the AIAA.

Authors:

Kenneth Van Treuren Baylor University
Charles Wisniewski USAF Academy
Devin O'dowd USAF Academy