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Output

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Program Output


Overview

Program output is displayed on the screen. It can be printed by printing the screen using the  File|Print  command from the menu. The data set can also be saved as a binary file using the menu command  File|Save  It contains the date and time at which it was produced and a list of both the input parameters (repeated for the record) and parameters computed from the input data that are "global" in the sense that they apply to the aircraft in general and to all elements of the propeller.

Units in the output first column are generally SI. An authoritative set of conversion factors are found in the Units section. In most cases the USCS units (mostly equivalent to 'English' units) are displayed in a second column.

Propeller

The screen display shows both the input data parameters flagged with an "@" symbol at the first of the line and the data derived from the input.

Some properties such as the kinematic viscosity, used for computing Reynolds number are computed and displayed for interest but does not affect the pitch distribution calculated. In this case it is shown because the kinematic viscosity for normal flying conditions is usually significantly lower than the value for the standard atmosphere used in so many places.

The data items are followed by a table of blade station (blade radius), the suggested pitch and corresponding blade angle at that station as well as other data that applies to each station. This data can be computed ant many, finely divided, chord positions by entering a small value of "Delta R" for station spacing.

Be sure to read the  Calculations  section to find out more about the information in the output data and how they are arrived at.

Terms

The "flight helix pitch" is the pitch of the spiral figure the propeller makes in space as it moves. This is the advance of the blade for one revolution. Computed as the quotient of the velocity and the engine speed in Hertz it is in the area of 80 to 200 millimeters for many control line applications. See Prop Motion For an illustration, explanation, and several examples of flight helix pitch for several records and very competitive racing classes,

The "ideal efficiency" is the efficiency a propeller would have if the airfoil sections had no drag. This is analogous to the induced drag of a wing and an efficiency that can not be improved on given the input diameter, flight speed, thrust (computed from the aircraft drag area), and rpm.

The "effective diameter" is the diameter of a propeller with an infinite number of blades that would have the same ideal efficiency. In practical terms the effective diameter and efficiency is less with a single blade propeller than with a two-blade propeller. The single blade is used and may have better over all efficiency because the increased blade chord will have a higher Reynolds number and, because of this, less profile drag

The "aircraft drag area" is the frontal area with a drag coefficient of 1 that has the same drag as the aircraft and lines. The line drag has to include the effect of pilot lag in racing. In these events the pilot is usually required to have the handle behind a line drawn from the center of the circle to the aircraft and this adds to the drag. The line drag including this factor may be estimated from the line drag program.

If you don't have an estimate and don't have some aerodynamic data you can get a crude guess as to what it is. Get an estimate of the engine power at full speed. Multiply this by propeller efficiency. (Use 0.6 as a guess if you don't have something better). Convert this number to Watts if you are not using SI units. Divide the power by the airspeed in meters/second. This is the thrust required. Compute the dynamic pressure as speed squared times air density divided by 2.0. Look at the example output sheet for the density value. Near sea level the dynamic pressure is about 0.6* (speed m/s)^2. Divide the thrust estimate by the dynamic pressure and multiply by 10000 to convert to cm^2. Typical values range from 10 to 200 over all speed/racing types. Look at the output to see what power the program estimates is required.

Airfoil data output are the angle of zero lift referenced to the pitch gage measurements and the angle above zero lift desired for best lift/drag. The considerations are somewhat involved and are necessary to read to use this program properly. Start with the Airfoil Data page.