5 years ago



Propeller Weight

Propeller Weight Generalization A weight estimating equation (ref. 2) was derived for preliminary propeller selection studies. The propeller geometric parameters (diameter, number of blades, activity factor) and the operational parameters (SHP, RPM, Mach number) incorporated in this formula are those which experience has shown to have the most predominant effect on propeller weight and the exponents have been established empirically to best fit the weight trends of current general aviation propellers and those anticipated for the 1980 time period. The equation is presented on Table II. The weight equation of Table I1 provides a useful tool for estimating propeller weight for any general aviation aircraft installation in this decade within *lo’% accuracy. However, it must be remembered that parameters other than the basic geometric and performance characteristics used in this equation effect propeller weights. These are variations in propeller environmental temperatures, type of control system and the degree to which individual manufacturers design.for minimum weight. Propeller Cost Generalization A cost equation (ref. 1) was generalized using end user price lists and weights obtained for representative industry propellers in the five general aviation aircraft categories shown in Table I. The equation is defined as follows: where: C C c1 Z LF LFl - average original equipment manufacturer, 0. E .M. propeller cost for a number of units/year, $/lb. - single unit 0. E. M. propeller cost $/lb. LF ” LF1 - learning curve factor for a number of units/year - learning curve factor for a single unit B - number of blades 13

F - single unit cost factor E - empirical factor For the computer program, an 89% slope learning curve was assumed. F and E factors were generated to evaluate costs of 1969 and the projected costs of 1980 time periods. The factors for propellers installed on each aircraft category are listed be- low. 196 9 19 80 Category I F 3.5 E 1.0 Quantity 19 F 10 3.5 E Quantity 1.0 2230 I1 3.7 1.5 2810 3.7 1.5 5470 I11 3.2 3.5 1030 3.2 3.5 1990 IV 2.6 3.5 29 5 3.5 3.5 6 80 V 2.0 3.5 3.4 65 3.5 36 8 Computer Program The performance generalization for conventional and multi-bladed propellers and the corresponding noise, weight and cost generalizations described in the previous text have been computerized. The computer program has been coded in FORTRAN Tv and has been run on the IBM System/370. With this computer program, the aforementioned propeller performance characteristics can be readily calculated for a range of selected propeller geometries and desired operating conditions. Examples of parametric studies made with the computer program are presented in another section of the text. There are four performance computation options available. First, if an engine is specified, then the operating condition is defined with the horsepower and the cor- responding propeller thrust is computed. Second, if a propeller thrust requirement is defined then the thrust is included as input and the horsepower is computed, thus indicating engine size. Third, for operating conditions defined by horsepower or thrust, it is possible to define the tipspeed corresponding to 50% stall. This would be the tipspeed for minimum noise. Fourth, reverse pitch angle and the corresponding reverse thrusts for a range of landing ground roll velocities operating at the fixed reverse pitch angle are computed. The corresponding noise (PNdB), weight and cost for the first three options are calculated. The weight and cost are calculated for both the 1969 and 1980 time period where costs are based on the 89% slope learning curve and the unit costs and quantities selected by Hamilton Standard from available surveys. There are the options of varying learning curve, unit costs, and quantities. The required inputs for all options of this computer program are the following: 14

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