PROP_DESIGN

Introduction:

PROP_DESIGN is an open source aircraft propeller design program. PROP_DESIGN allows for the design of straight and swept aircraft propellers. PROP_DESIGN can be used for effective velocities of 0 to Mach 1.3 and all altitudes covered by the U.S. Standard Atmosphere of 1976. Maximum aircraft propeller efficiencies of approximately 90% can be achieved.

PROP_DESIGN can also be used in the design of many products which are very similar to aircraft propellers:

Airboat Propellers
Box Fans
Computer Case Fans
Ducted Fans
Hovercraft Thrust Axis Propellers
Propfans (a.k.a. Open Rotors, Ultra-High Bypass Engines (UHB), and Unducted Fans (UDF))
Turbofans

Formulation:

PROP_DESIGN utilizes vortex theory, does not rely upon the Betz condition, nor does it rely upon Theodorsen's theory of propellers. PROP_DESIGN utilizes a purely analytical formulation, with a few exceptions. Empirical data was used to create the airfoil, atmospheric, and stall models.

The empirical data, utilized by PROP_DESIGN, is freely available online. Reputable sources were referenced:

Airfoil Model; NASA Technical Reports Server (NTRS)
Atmospheric Model; United States Committee on Extension to the Standard Atmosphere (COESA)
Stall Model; Sandia National Laboratories

You can use your own airfoil and stall models, if desired. You will have to edit and re-compile the Fortran 77 source code, in order to do so, however. Using your own airfoil and stall models may improve accuracy. Editing the airfoil and stall models is not too difficult, as the source code is very clean. The portions which define the airfoil and stall models only consist of a few lines of code.

PROP_DESIGN executes quickly, and requires little computational resources, because it does not attempt to solve the Euler, Navier-Stokes, or Boltzmann equations. Rather, the Biot-Savart law and the Kutta-Joukowski theorem are utilized to iterate upon induced angle of attack and circulation.

PROP_DESIGN is based on a code called PROPSY, described in the following publications:

'The numerical determination of circulation for a swept propeller', 1996, by Markus Tremmel

'Numerical Determination of Circulation for a Swept Propeller', 2001, by M. Tremmel, D. B. Taulbee, J. R. Sonnenmeier

I made many corrections and improvements to PROPSY. In fact, at this point, PROP_DESIGN is almost an entirely different program. Therefore, one should not expect the results of the two codes to be the same. Rather than publish these changes in a traditional way, I decided to publish them online. This was done to make it easy, and free, for people to obtain them.

Some other formulations, that aircraft propeller design and/or analysis codes rely upon, include; blade element theory, test/empirical data, Theodorsen's theory of propellers (a form of test data), the Betz condition, and I have even seen one code based on marine propeller theory. For a number of reasons, I do not recommend that you use such codes. One important reason is that the simplifications that these formulations utilize are no longer necessary. The simplifications were made to create design and/or analysis procedures that could be implemented at the time the formulations were created. These simplifications affect the accuracy of the results. Modern computers allow us to remove these simplifications. In general, if an aircraft propeller design and/or analysis code relies upon a formulation created prior to 2010, you should not use it for anything other than a historical reference.

Other than PROP_DESIGN, the only other software I would use in the design and/or analysis of an aircraft propeller would be CFD. However, CFD is much more compute intensive than PROP_DESIGN. Therefore, it is best to start with PROP_DESIGN and move on to CFD only if necessary.

Feature Summary:

Handles effective velocities up to Mach 1.3 (approx. equivalent to aircraft traveling at Mach .8)
Handles altitudes up to, 282,152.23097 feet (53.437922532 miles), the mesosphere
Extremely precise; less than .001% error in the two variables that it iterates upon
Based on a unique implementation of vortex theory, by Anthony Falzone, circa 2010
No Betz condition
No Theodorsen theory
No marine propeller theory
No test data other than the airfoil, atmospheric, and stall models
Computes straight and swept aircraft propeller performance
Computes ducted and unducted aircraft propeller performance
Computes the static condition, the case where there is no forward motion of the propeller
Finds the optimum propeller geometry for a given operating condition
Compares any two aircraft propellers
Creates aircraft propeller performance maps
Exports information that you can use to quickly and very accurately model the propeller in MoI and/or Rhino
Requires few computational resources (i.e. minimal CPU, memory, and storage requirements)
Runs quickly, even on netbooks and laptops
Can be used to benchmark Fortran compilers and x86 processors
Can be used to burn-in/load test x86 processors
Free, open source, public domain software; therefore, there are no restrictions on what you can do with it

Limitations:

PROP_DESIGN does not apply to the design of helicopters, marine propellers, or wind turbines. PROP_DESIGN does not allow for counter-rotation. PROP_DESIGN does not allow for back pressure. Examples of back pressure include; fans operating near a ceiling or wall, computer case fans with filters attached, and fans attached to CPU or GPU coolers. PROP_DESIGN does not allow for a pitched and/or yawed propeller rotational axis. Examples of a pitched and/or yawed propeller rotational axis include; oscillating fans, aircraft maneuvers, the E-2 Hawkeye aircraft, and tiltrotor aircraft such as the Bell Boeing V-22 Osprey. PROP_DESIGN does not consider the affect that wind has on propeller performance. Well educated users should be able to modify PROP_DESIGN, in order to remove the existing limitations.

Notes:

PROP_DESIGN does not calculate aircraft propeller noise levels. This is due to the fact that an efficient aircraft propeller is also a quiet aircraft propeller. Since you normally strive for an efficient design, there is no additional effort required to achieve a quiet design. To calculate aircraft propeller noise levels, I recommend the procedure described in the following document:

'Prediction Procedure for Near-Field and Far-Field Propeller Noise', 1977, SAE AIR1407 1977-05-01

The document also contains information showing what characteristics increase aircraft propeller noise. The document is based on empirical data collected by Hamilton Standard.

The geometry PROP_DESIGN outputs is termed the hot shape. The hot shape is the geometry required to provide the desired aerodynamic performance. FEA is needed to find the corresponding cold shape. The cold shape is the geometry that is manufactured. Centripetal force will deform the cold shape into the hot shape, at a user specified shaft angular velocity. If you manufacture the hot shape, you will not achieve the desired performance.

PROP_DESIGN is unproven. It is up to the user to verify his or her design. To do this, I recommend comparing the results you obtain with PROP_DESIGN against test data that you collect. The typical aircraft propeller design process is as follows:

Determine the required hot shape using PROP_DESIGN
Make an aircraft propeller blade hot shape CAD model, using output from PROP_DESIGN
Perform FEA, to determine the cold shape and structural integrity of the propeller
Perform CFD analysis, to further study aerodynamic characteristics of interest
Perform FSI analysis, to determine flutter characteristics
Perform CAA analysis, to determine acoustic characteristics
Build and test actual prototypes
Compare predictions to test data, resolve all discrepancies
Fulfill all applicable FAA regulations

These steps are normally performed by a group of qualified engineers. Several of these steps are conducted in parallel, in order to reduce the time to market. As you can imagine, getting a FAA certified aircraft propeller to market is a very time consuming and expensive endeavor.