Aerodynamic Performance:

PROP_DESIGN_ANALYSIS and gnuplot can be used to create plots which aid the understanding of aircraft propeller performance. Some of the available plot types are shown below. The performance maps were made with PROP_DESIGN_MAPS_CS. This is the version of PROP_DESIGN that lets you evaluate constant speed propellers. It is available in the PROP_DESIGN_UNDOCUMENTED folder. All of the screenshots below are for the included General Atomics Predator B example.

Hot Shape CAD Models:

Below are renderings of hot shape aircraft propeller and hot shape fan CAD models. I created them using PROP_DESIGN, Rhino, and KeyShot. The renderings are of four of the included examples; Airbus A400M, Delta Computer Case Fan, General Atomics Predator B, and the Piaggio Avanti II. These renderings should give you an idea of all the different shapes PROP_DESIGN can create.

Four different chord distribution options are available; constant, elliptical aligned along chord / 4, elliptical aligned along chord / 2, and scimitar (elliptical aligned along the trailing edge).

Aerodynamic Loads:

PROP_DESIGN_ANALYSIS outputs steady state aerodynamic forces and moments along the span (a.k.a. the quarter chord line) of the blade. These are for use with structural analysis software such as FEA. It should be noted that, the affect of centrifugal force is typically much more dominate than the affect of the aerodynamic loads. It is not uncommon to ignore the aerodynamic loads and only apply centrifugal force. For high horsepower engines, aerodynamic loads will become more significant. To be safe, you can run a structural model with and without aerodynamic loads. This will allow you to see how important they are to your specific application. All loads act at the airfoil's quarter chord point.

It is easier to apply thrust and torque force rather than lift and drag. This is because lift and drag vectors change with angle of attack. You should not apply lift and drag with thrust and torque force, since thrust and torque force result from lift and drag. Doing so will cause error.

PROP_DESIGN_ANALYSIS also outputs lift, drag, and pitching moment coefficients along the span of the blade. These coefficients are non-dimensional. They are output for completeness more than anything.

Orientation of Aerodynamic Loads:

The screenshots below indicate load locations and directions. Dark blue arrows designate the thrust vectors, red arrows designate the torque force vectors, and green arrows designate the pitching moment vectors. Vectors are shown in the positive direction. Note, positive pitching moments act to increase angle of attack while negative pitching moments act to decrease angle of attack. The orange line represents the axis of rotation. Notice that, for swept blades:

  • The thrust vectors (dark blue arrows) are parallel to the axis of rotation and perpendicular to the span of the blade
  • The torque force vectors (red arrows) are mutually perpendicular to the thrust vectors and the span of the blade
  • The pitching moment vectors (green arrows) are mutually perpendicular to the thrust and torque force vectors

The magenta lines are mutually perpendicular to the dark blue and light blue lines. The sweep angle (delta) is the angle between the magenta line and the red line. Delta is coded to always be zero at the root of the blade and increase smoothly to the value specified at the tip.

Spanwise distance is shown with the light blue lines, in the pictures below. The light blue lines always start at the axis of rotation and end at the quarter chord points, even though it was not possible to show this in all of the pictures below. The span of the blade can be thought of as a line starting at the axis of rotation and connecting all quarter chord points. Thus the span of the blade is essentially the blade itself and is not shown with a special line. Do not confuse spanwise distance with the span of the blade.

It is worth noting that the load vector orientation is the same for truly swept blades, swept airfoils, or any combination of the two. The PROP_DESIGN mesh is based on a truly swept blade. Thus, the pictures below reflect the internal computations. Applying aerodynamic loads to straight blades is much easier, since all vectors are aligned with the global coordinate system.