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.


Bench-marking and validation are part of the beta phase of the on-going development.
The first benchmark shows good agreement between predictions and wind tunnel test results.


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

Alpha and beta phases, and first version

The alpha phase was closed on November 15th, 2019.
The beta phase was due to last until end of June 2020, but has been extended until November 30th, 2020.


flow5 is available under a commercial licence on a subscription basis. The intent of the commercial license is to provide support to the on-going development.
For beta-backers, subscriptions are available for the duration of the beta phase + 1 year of use.
On the long term, nothing is firm, but the intent is that flow5’s price remains affordable for students and private individuals.


flow5 has been designed to run on all configurations which support xflr5.
Compatibility with future ARM-based macOS configurations is not guaranteed and will depend on the availability of Intel’s MKL library on the new platform.
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.