IOPT Select one or more design variables to be optimized:

1 - AFDES, Activity Factor per blade.

2 - DIAM, Propeller diameter.

3 - PITCH, Propeller geometric pitch.

4 - RPM, Engine RPM.

5 - VCRS, Cruise velocity.

Variables not selected remain fixed for the duration of the run.

Example: IOPT=1,2,4,5 allows activity factor, diameter, engine speed and VCRS to be varied by the optimizer.

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 usually 1 for a pusher) and better efficiency.

2 - Constant angle-of-attack pitch distribution for blunt nose.

ABMIN The minimum blade design angle-of-attack for cruise referenced to the zero-lift-line. Used as an alternative to CLDES to prevent the propeller from being too lightly loaded. An angle-of-attack of about 1.2 degrees is needed for the Clark Y airfoil and for the R.A.F. 6 airfoil and an angle of around 2.5 to 3 degrees is more typical.

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.

CLDES Design lift coefficient. Use to specify a specific desired lift coefficient. Takes precedence over ABMIN. Usually use the lift coefficient for minimum drag: 0.25 for Clark-Y, 0.4 for R.A.F.-6.

DMAX Maximum diameter limit, inches

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). One way to estimate ADRAG is to try a few different values along with a reasonable simulation of the recommended size propeller until you can match the aircraft published design performance. With test flight speed, power and propeller known, ADRAGcan be determined automatically by the PROP OPTIMIZER Advanced program from power required at a recorded cruise performance point, i.e., at ALTCRS, RPMCRS which defines the horsepower produced and delivered to the propeller and VCRS 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 and SPAN are used to find induced drag and KS the slipstream 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. Activity factor is a very important design parameter which is generally ignored since it must be computed rather than simply measured like pitch and diameter.

ALTCRS Density altitude for optimized cruise propeller design, feet

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. The greater the drag coefficient of the body, the lower KS will be. KS could be in the region of 0.1 to 0.5 for a powered high-drag parasail and would be zero for a flat plate facing into the wind.

DIAM Initial or reference propeller diameter, inches

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.

PITCH Geometric pitch taken at the airfoil chord line at 75% of tip radius, inches. Manufacturers usually use this value. Absolute pitch, also called experimental pitch, is taken at the airfoil zero-lift-line. It is higher since the zero-lift-line is above the chord line. Effective flight pitch, which is the product of diameter times advance ratio, varies widely depending on speed and rpm and under power is lower than absolute pitch. Drag and, in climb, gravity are always acting to reduce effective pitch. When comparing computer simulation to flight results, these differences should be kept in mind.

RPMCRS Reference flight rpm used when calibrating the program from the measured cruise rpm and velocity for determining ADRAG. 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.

VCRS Design target velocity for cruise, MPH, or recorded true airspeed for determining ADRAG.

WTGRSS Aircraft gross weight, lb. Enables the program to calculate the induced drag.

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.

AFDES Activity factor per blade. The higher the activity factor, the more power a blade can absorb (or is required). For a given diameter, activity factor increases with blade width.

ALPHA Blade angle-of-attack at the 75% radius, degrees. The angle the incoming air flow makes with the airfoil zero-lift-line.

ANGLE Blade pitch angle at 75% tip radius station measured with respect to the plane of rotation, degrees.

CL Blade lift coefficient. Design lift coefficient for cruise.

CP Power coefficient: A non dimensional ratio relating power required to air density, propeller speed squared and propeller diameter raised to the fifth power. Power required is proportional to the fifth power of diameter for other factors being equal.

CT Thrust coefficient: A non dimensional ratio relating thrust produced to air density, propeller speed squared and propeller diameter raised to the fourth power. Thrust produced is proportional to the fourth power of diameter for other factors being equal.

CS SPEED_POWER coefficient, J/CP^(1/5). A design parameter used in determining maximum efficiency for cruise propellers.

DIAM Propeller diameter, inches

DRAG Aircraft drag, pounds

ETA Propeller efficiency: ETA=CT*J/CP

A measure of how much power is delivered to the air stream by the propeller relative to power delivered by the engine. This value includes compressibility, profile drag and relative diameter corrections.

ETA COMPRESS CORRECT: A factor indicating the percentage propeller efficiency is reduced due to sonic compressibility effects at the blade tip. Zero indicates no compressibility losses. The optimizer tries to design on balance to minimum loss.

ETA PROFILE DRAG CORR: An efficiency correction due to blade width or total activity factor and represents the induced losses.

ETA DIAMETER CORRECT: Corrects for the relative influence of body and engine nacelle size to propeller diameter. Assuming that the reference point is accounted for in the effective pitch and ADRAG calibration, this correction is the increase or decrease in efficiency from the calibrated reference point.

FFGPH Fuel flow in gallons per hour

FFPPH Fuel flow in pounds per hour

HPA Maximum Horsepower Available from the engine at any given engine rpm.

J Advance ratio J=(V*88)/(RPM*DIAMETER) Where: V=mph, DIAMETER=ft. In flight the propeller advances a distance of J times the DIAMETER per revolution.

MPG Aircraft miles per gallon of fuel

NB Number of blades

PITCH Pitch of chord line at the 75% radius station, inches. The geometric or theoretical advance of the propeller per revolution.

RHO Atmospheric density, slugs

SFC Specific fuel consumption, lb/hp/hr

SHP Shaft horsepower required at the propeller shaft before efficiency losses.

THRUST Propeller thrust, pounds

THP Net Thrust Horsepower delivered to the atmosphere by the propeller after efficiency losses and required for flight, (THP=SHP*ETA).

TPMACH Tip Mach number

V Aircraft velocity, miles/hour

VS Speed of sound, feet/second

VT Tip speed, feet/second

NRUN Number of trial designs run

PAYOFF Objective or merit function. A quantitative measure of the design goal such as maximum velocity or climb rate.