PROP OPTIMIZER INPUT DEFINITIONS PROP OPTIMIZER PROGRAM Copyright 1993 Donald R Bates - All Rights Reserved BATES ENGINEERING, 2742 Swansboro Road, Placerville, CA 95667 Phone/FAX 916-622-1886 PROP OPTIMIZER INPUT DEFINITIONS ---------------------------------------------------------------------------- CONTROL NPAYOFF Select design objective merit function for optimization: 0 - ADRAG and BACAL flight calibration 1 - Point design analysis (may vary RPM only using IOPT=3) Calculates point performance for one set of design variables. 2 - Maximum VCRS (cruise velocity) NOTE: PROP OPTIMIZER Advanced has additional options to find the maximum rate of climb and minimum horsepower required for a given design cruise speed. IOPT Select one or more design variables to be optimized: 1 - AFDES, Activity Factor per blade 2 - DIAM, Propeller diameter 3 - RPM, Engine RPM Variables not selected remain fixed for the duration of the run. Example: IOPT=1,2,3 allows activity factor, diameter and engine speed to be varied by the optimizer while reduction factor is fixed. NOTE: PROP OPTIMIZER Advanced has additional options to find the optimum speed for maximum rate of climb and optimum gear ratio for geared engines. PDES Selects radial pitch angle distribution for design output: 0 - Constant geometric pitch distribution (default). 1 - Constant angle-of-attack pitch distribution for slender nose or pusher (KS must equal 1 for a pusher) and better efficiency. 2 - Constant angle-of-attack pitch distribution for blunt nose. ---------------------------------------------------------------------------- DESLIM AFLIM Lower and upper bounds on the single blade activity factor, AFDES. The default is 60 to 150 which is about the practical range. If the optimizer can not converge to a solution in the desired range different try different limits. DLIM Minimum and maximum diameter limits, inches TDMAX Maximum blade thickness/diameter ratio to prevent excessive hub thickness. A value greater than zero must be input to trigger blade airfoil coordinates output. ---------------------------------------------------------------------------- DESVAR ABDES The minimum design blade angle-of-attack for cruise referenced to the zero-lift-line. This prevents the propeller design from being too lightly loaded. Normally, you will want to run the propeller at the angle for best efficiency which the program automatically finds if ABDES=0 or is omitted. This usually gives the propeller blade a lift coefficient in the minimum drag range. This is about CL=0.2 and an angle-of-attack of about 1.2 degrees for the Clark Y airfoil. You can determine the loading angle of your present propeller by running the ADRAG calibration. ADRAG Equivalent flat plate drag area of your aircraft in square feet. (Typically: F-51 Mustang= 2.7, Cassutt= 0.9, Miller JM-2= 1.0, KR-2= 1.4, Q2= 1.5, Falco= 2.2, RV-6A= 2.3, Varieze= 1.75). With test flight speed, power and propeller known, ADRAG can be determined using NPAYOFF=0. This option computes ADRAG based on the power required calculation at a recorded cruise performance point, i.e., at ALTCRS, RPMREF which defines the horsepower produced and delivered to the propeller and VDES is the recorded cruise velocity. ADRAG is used to calculate the parasite drag component of the total drag. Total drag is parasite + induced + slipstream drags. WTGRSS, SPAN and KS are needed to calculate ADRAG and the total drag. AFDES The initial design single blade activity factor. When input, AFDES makes the program start with this value. The resulting propeller is scaled from the input or default CHORD values. Otherwise, AFDES is calculated from the input CHORDs or the default NACA propeller. The practical range is about 60 to 150 per blade. ALTCRS Density altitude for optimized cruise propeller design, feet BACAL Calibration increment to the rated blade angle at 75% tip radius. When BACAL is input, the program outputs both effective and rated pitch. To determine BACAL, use the NPAYOFF=0 input option and input propeller data recorded for cruise performance at maximum power. BACAL is used as a reference to relate the manufacturer's airfoil and pitch measurement to the program output. If not known, BACAL is usually in the 1-5 degree range and approximately the zero lift angle-of-attack with the opposite sign. KS Propeller slipstream constant for drag generated on other aircraft components. Drag added is KS*CT/J^2 times parasite drag. KS varies from 1 for tail mounted pushers to 13 for a very clean streamline body. NACA TR 640 suggests 2.5 for 1938 vintage aircraft. Modern homebuilt tractors may be slightly higher, possibly about 3, and powered self-launch sailplanes slightly lower due to the large wing area outside of the slipstream. The high value for clean streamline bodies is due to the relatively low drag without the propeller compared to the added drag due to the slipstream effect. This term may be negated by setting KS to zero but there is much test data to support it and 2.5 is the program default. NOTE: PROP OPTIMIZER Advanced can determine KS automatically. DIAM Initial propeller diameter, inches DREF Reference propeller diameter, inches, for calculating the efficiency correction for diameter changes. It is the diameter of the propeller used to determine ADRAG for the reference performance calibration. OSWALD Aircraft efficiency factor due to W.B.Oswald. This term directly affects induced drag. If the aircraft designer does not provide this value, most aircraft are in the 0.70-0.95 range and you may omit this input and use 0.825 the program default. This term has about a 1% effect on cruise performance since induced drag is small at high speeds and maybe about a 5% influence on climb performance for relatively moderate climb speeds. In the August 1993 issue of the EAA Experimenter, Professor Ribbons explains how to determine e from flight testing. PCTPWR Percent of sea level power available to use for CRUISE design. This number, in percent (=<100), requires that the program design to the smaller of PCTPWR/100 times maximum available sea level power or of maximum available power for the cruise altitude. PITCH Effective pitch taken at the zero-lift-line at 75% of tip radius, in inches. When BACAL is input, both effective and rated pitch at the manufacturer's reference line, usually the airfoil bottom or chord line will be output. When doing the BACAL calibration, input rated PITCH and effective PITCH and BACAL will be calculated by the program (NPAYOFF=0). When running point designs (NPAYOFF=1), the input pitch will be assumed to be rated pitch and effective pitch will be calculated using BACAL. Otherwise, in all optimizations, the program calculates pitch and ignores any input PITCH value. REDFAC Engine/propeller rpm gear reduction factor. RPMREF Reference flight rpm used when calibrating the program from the measured cruise rpm and velocity for determining ADRAG and the angle calibration term, BACAL. Also the initial design cruise rpm when running point designs and optimizations. SPAN Wing span, ft. Needed, along with weight, to calculate induced drag for a more accurate determination of ADRAG and rate of climb. VDES Design target velocity for cruise, MPH, or recorded true airspeed for determining ADRAG. VDES is needed to start the solution. WTGRSS Aircraft gross weight, lb. Enables the program to calculate the induced drag and rate of climb. ---------------------------------------------------------------------------- TABLES STA Stations as a fraction of blade radius from 0.2 to 1.0 at tip for corresponding CHORD values. When omitted, defaults to the NACA reference propeller. CHORD Blade chord values corresponding to STA values, inches. If omitted, the program defaults to the NACA propeller blade shape and activity factor. The final blade shape is ratioed to these initial values. TCTAB Blade thickness/chord ratios corresponding to STA values. A thinner blade delays compressibility losses when tip speeds are above the critical Mach number. The NACA efficiency correction for tip loss was developed for the thickness for the outer half of the blade or the average at 75%R. When omitted, defaults to the NACA propeller. RPMTAB RPM table for horsepower and specific fuel consumption Extend this table to a low enough range for about 800 propeller rpm to provide enough latitude for the optimizer to work during its search procedure for static thrust conditions. Input this data even if you are using a fixed rpm for cruise. HPTAB Horsepower available values (maximum) corresponding to RPMTAB. Use the maximum sea level horsepower curve which the program will correct for altitude. Use the PCTPWR input to provide any other desired power level. SFCTAB Specific fuel consumption corresponding to RPMTAB, lb/hp/hr., Used to output fuel flow for reference only - optional.