PROP_DESIGN contains many examples, to help get users started. The included examples relate to the following products:

• Airbus A400M Military Transport
• Delta TFB1212GHE Computer Case Fan
• General Atomics Predator B UAV
• Mooney Acclaim Type S Single-Engine Piston Aircraft
• Piaggio Aero P180 Avanti II Twin-Engine Turboprop Aircraft

These products were chosen as PROP_DESIGN examples, because they cover the typical operating range of aircraft propellers. These products were designed, built, and tested prior to the existence of PROP_DESIGN. The PROP_DESIGN example input files are based on information found on the internet. Thus, the PROP_DESIGN example designs may or may not be similar to the actual product designs.

Two additional examples are also provided:

• Hovercraft and VTOL Examples
• Modern Turbofan Example

The 'Hovercraft and VTOL Examples' are intended to show how PROP_DESIGN integrates into vehicle design projects. The 'Modern Turbofan Example' was done out of curiosity and proved to be very enlightening. I believe all PROP_DESIGN users will find this example to be very interesting. More information, regarding the additional examples, can be found below.

Below is an application of a diffuser. Moreover, a diffuser was used to create static pressure for the plenum chamber of a hovercraft. The diffuser is shown in gray. The ducted fans are shown in light blue. The plenum chamber is shown in white. The parts in black are where the cargo and/or passengers would go.

The hovercraft and VTOL examples use the same fans. The hovercraft example uses half the fans of the VTOL example (3 out of 6 fans). Thus, the hovercraft example uses half the power of the VTOL example. The hovercraft example can lift approx. 2.7x the weight of the VTOL example, while only using 25% of the power (1 out of 4 fans). This comes with one major limitation, hovercrafts can only float inches above the ground.

The hovercraft example has a lift-to-thrust ratio of approx. 11, at takeoff. However, traditional aircraft are much more efficient than that. Aircraft wings made with NACA 65A009 airfoils have a peak Lift/Drag (i.e. lift-to-thrust) ratio of approx. 90.5. Typical cars and trucks are also more efficient than hovercraft. Cars and trucks have a Weight/Drag (i.e. lift-to-thrust) ratio of approx. 33.3.

Below is an example of a VTOL aircraft. The ducted fans are shown in light blue. The fixed position thrust vectoring nozzles are shown in white. The parts in black are where the cargo and/or passengers would go.

VTOL aircraft will be more efficient than helicopters and quadcopters. They will also be able to travel at much higher speeds. This is due to the air flow into the blades. An axial flow orientation is ideal. However, VTOL aircraft are much less efficient than traditional aircraft. All VTOL have a lift-to-thrust ratio of one. Aircraft wings made with NACA 65A009 airfoils have a peak Lift/Drag (i.e. lift-to-thrust) ratio of approx. 90.5. So VTOL aircraft should only be used when absolutely necessary.

I wanted to see if PROP_DESIGN could be used to design turbofans. I found that it could be. You can also add a stator if you like. Using a stator will double the thrust or half the power, depending upon how you choose to use it. If you want to half the power, then you would design the rotor for half the thrust. You use the stator to generate the other half. These are rules of thumb. You may not get exactly half the thrust or half the power, but you can get very close to that. I found PROP_DESIGN had no problems creating designs very similar to what you see on commercial jets. For this example, the static thrust at sea level is over 115,000lbf. The stator was designed to double the thrust at the cruise condition (Mach .7 at 32,000ft). There are 22 rotor blades and 21 stator blades. NACA 65A009 airfoils are used.

One thing I recently looked into was airfoil interaction effects. I found that the airfoils need to be at least three chord lengths apart to act independently. This means that high blade count devices could have accuracy issues. Moreover, even though my turbofan example matched the performance of similar designs, I'm not sure the predictions are accurate. I would use the code with caution for these types of cases.