THE THEORETICAL PERFORMANCE OF HIGH EFFICIENCY PROPELLERS
Abstract
The vortex lattice method has been developed to analyze the performance of propellers, and the techniques of numerical optimization has been devised to determine the optimum propeller blade shapes. Results are given for NASA SR-1, SR-2, SR-3, NACA 109622 and CESSNA 172 propellers. Comparison of the predicted power coefficients and the experimental results show good agreement at different advance ratios J. The ideal efficiency shows good agreement for a two blade propeller except that a slight under estimate of the induced effect causes a slight over estimate of the ideal efficiency. A discussion has been shown in Chapter 2. By using vortex lattice method, investigation has been given for propeller proplet, which is a small airfoil section, mounted at the tip to improve the efficiency. The efficiency improvement is 2% - 6.85% depending upon the propeller blade employed. The load distribution for a propeller-proplet combination is different from that of propeller alone. Proplet increases the load distribution along the blade radius especially near the tip. A cant angle (beta)(,w) of the proplet controls the distribution. Optimum condition can be approached by assigning a negative value of (beta)(,w) (toed out proplet). The proplet heights are closely related to the improvement of the efficiency. A linear function between the percentage of improvement in efficiency and proplet height has been found within the twice proplet height boundary. The propeller blade shape optimization uses sequential unconstrained optimization technique to find the optimum blade shape under the constraint of constant power coefficient. Propeller blade shape input data are based upon SR-2, Purdue model, and CESSNA 172. The result of efficiency for each propeller blade obtained by this method is slightly higher than that of Goldstein. The optimum value of (beta)(,w) for Purdue model is -5.6(DEGREES), which makes the pitch distribution near the tip slightly less than that of propeller alone, to approach the optimum condition of the propeller.
Degree
Ph.D.
Subject Area
Aerospace materials
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