An analysis tool for planes and sails operating at low Reynolds numbers

flow5 is a potential flow solver with built-in pre- and post processing functionalities. Its purpose is to make preliminary designs of wings, planes and sails reliable, fast and user-friendly.

Flow solver

flow5 uses a potential flow solver which includes the following methods:

  • A non-linear Lifting-Line Theory method which follows the methodology described in the report NACA-1269
  • Two VLM methods using quad ring vortices and horseshoe vortices.
  • A volume quad panel method based on the report NASA 4023
  • Two triangular panel methods based on Galerkin formulations. The first uses uniform source and doublet densities on panels, the second uses uniform source and linear doublet densities. The benefit of triangular methods is their ability to describe general 3d surfaces including fuselages. In addition, the linear method improves the accuracy of the predictions in cases of high local pressure gradients.

The wake can be represented either by conventional straight vortex lines and flat panels, or by using a Lagrangian description with vortex particles. The latter method is the way forward and is recommended for its better predictions.

Viscosity is accounted for by interpolation of 2d viscous data, and by a viscous loop used to derive a solution which satisfies both the 2d viscous properties and the 3d inviscid flow solution.
Note: XFoil is not part of flow5, the program uses xflr5 as an external back-end to generate the 2d viscous data.


In the case of airplane, the first benchmark shows good agreement between predictions and wind tunnel test results.
A comparison of measured sailboat performance with predictions in real life sailing conditions shows that panel codes are only valid in narrow upwind conditions.


flow5 includes the core capabilities of xflr5 for plane analyses, and of sail7 for boat analyses. A number of new features have been introduced to improve on these two applications and to make the analyses more user-friendly, versatile and accurate.
User Interface (UI)
3d Galerkin formulations
Plane analyses with fuselage
Non linear control polars
Vortex Particle Wake
Intel MKL
CAD Interfaces
2d Interactive Boundary Layer solver

Development status

The alpha phase was closed on November 15th, 2019.
The beta phase has ended on December 6, 2020.
flow5 v.02 has been the first formal version of the application, released on December 6, 2020.
The major part of the development has been completed with the release of flow5 v7.19 on October 18, 2021.

The main activity is now code maintenance, bug corrections and minor improvements. There are still some ideas for new features such as the parametrization of viscous behaviour as a function of flap settings. These however will likely be implemented at a slower pace than has been the case during the first part of the development.


Since the developement has reached a milestone with the release of flow5 v7.19, flow5 is now proposed under a permanent licence at a fixed price for all intended usages. This replaces the subscription model that has been active during the first two years of the development.


flow5 has been designed to run on all configurations which support xflr5.
flow5 v7.10 has been tested successfully on Mac mini M1 with the Rosetta 2 translator.
Performance scales with the speed and number of processor threads.
Check-out the detailed hardware requirements before purchasing flow5.

Bug reports and feature requests

Until a ticket functionality similar to the one available for xflr5 is added to this website, please use the discussion section to report a bug or request a feature.
Check out also the troubleshooting section to fix the most common issues.


xflr5: xflr5 is an analysis tool for airfoils, wings and planes operating at low Reynolds Numbers
sail7: sail7 is a tool designed for the analysis of sail boat performance
XFoil : XFoil is an interactive program for the design and analysis of subsonic isolated airfoils

Video tutorials

flow5 – video tutorials

Documentation and resources

A tentative online documentation is under construction, focusing first on user questions and comments, and on the most recently introduced features..
The presentation documents and project files used in the demonstration videos can be downloaded from this page.


flow5 ® is a registered trademark in France of the company Cère-Aéro.