Quickstart:
The Airfoil Calculator can be used to calculate the shape (x,y coordinates), pressure distribution, lift and pitching moment coefficients of NACA and DHMTU airfoils, both with and without ground effect. Only members of The WIG Page can use the Airfoil calculator, but non-members can preview its output by clicking on the thumbnails.
The Airfoil Calculator is easy to use, just fill out the desired parameters, press "calculate airfoil" and click one of the four thumbnails for viewing the results.
Note that the pressure distribution is calculated with a potential flow model, this means that separation (e.g. stall) is not modelled. So the results must be used with care, extreme pressure gradients may be the result of a calculation, but in reality they cannot exist and separation will be the result.
Furthermore the calculations are only 2D, but 3D pressure distributions will often be entirely different, expecially for low aspect ratio wings in ground effect.
The most well-know airfoil family is the NACA collection of airfoils. Although these may not be regarded as particularly suitable for the main wing of a WIG craft, they will find application for horizontal and vertical tails and for parts of the wing, for example the wingtip.
The DHMTU series of airfoils, however, are designed specifically for use in WIG craft, Is is easy to choose the design parameters of this airfoil so that its mean line will become S-shaped. This enhances stability of WIG craft.
Please note that selecting a DHMTU airfoil for a WIG does not guarantee good performance or stability. Airfoil design is an integral part of WIG design.
Airfoil generators are available for the following airfoils. An image of the airfoil and a table with co-ordinates is generated. Only members of this site have full access to the airfoil generators. More information about the extra features for members of The WIG Page is found in the members section. Non-members can preview the airfoil generator functions by using the default airfoils, so just click on generate foil, without making any changes.
These airfoils are very easy to use, since they only have 3 parameters. As a consequence they are not very sophisticated, but still some of the foils are very useful for tails and aerodynamic shapes, specifically the 00xx foil.
The first two digits of the designation are related to the mean line and the last two indicate the thickness as a percentage of the mean line. The first digit indicates the maximum ordinate of the mean line as a percentage of the chord and the second indicates the position of that maximum ordinate in tenths of the chord, starting at the nose.
For example: a NACA0012 airfoil has 12% thickness and no camber and a NACA2409 airfoil is 9% thick and has 2% camber at 40% of the chord.
These airfoils were developed by the Department of Hydromechanics of the Marine Technical University (DHMTU) of St. Petersburg specifically for use in ground effect. These foils are characterised by a flat centre section on the bottom and (if desired) an S-shaped mean line. As opposed to the NACA airfoils, these airfoils are not defined by a mean line and a thickness distribution, but by separate definitions for the upper and lower side, since the shape of the lower side is very important in ground effect.
DHMTU sections have 8 parameters, one for the nose radius, 4 for the lower surface and 3 for the upper surface. The general format of a DHMTU airfoil is:
DHMTU a-b.c-d.e-f.g.h
where:
| a = | maximum ordinate of the upper surface (%c) |
| b = | position of the maximum ordinate (%c) |
| c = | ordinate of the start of the flat section (%c, below the horizontal is positive) |
| d = | position of the start of the flat section (%c) |
| e = | ordinate of the end of the flat section (%c, below the horizontal is positive) |
| f = | position of the end of the flat section (%c) |
| g = | slope parameter of the upper trailing edge |
| h = | nose radius parameter |
Note that all (x) positions are measured from the nose.
For example: a DHMTU 12-40.2-10.3-60.21.3 has a noticable S-shaped mean line, both due to its 'reflexed' aft lower side and its slightly reflexed upper side. Its thickness on the upper side is 12% at 40% of the chord, the flat section on its bottom runs from 10% to 60% chord and from 2% to 3% below the horizontal. Finally its nose radius parameter is 3 and its trailing edge parameter is 21.