Background

The Tornado code is a vortex lattice method programmed to be used in conceptual aircraft design and in aerodynamics education. The work on the code begun in 1999 at the Department of Aeronautics at the Royal Institute of Technology, in Stockholm, Sweden. The first version was released in 2001 together with the users manual and code description. The work done was a part of the masters Thesis of Tomas Melin, the code developer.

The aircraft geometry in Tornado is fully three dimensional with a flexible, free-stream following wake. Tornado allows a user to define most types of contemporary aircraft designs with multiple wings both cranked and twisted with multiple control surfaces. Each wing may have taper of both camber and chord. The Tornado solver solves for forces and moments, from which the aerodynamic coefficients are computed. Aerodynamic derivatives can be calculated with respect to: angle of attack, angle of sideslip, roll-, pitch-, and yaw- rotations, and control surface deflection. If necessary all of these conditions may be applied simultaneously. Any user may edit the program and design add-on tools as the program is coded in MATLAB (tm), and the source code is provided under the GNU-General Public License.

The core method stems from [Moran], but is modified according to [Melin] in order to accommodate a three dimensional solution and trailing edge control surfaces. The most notable change is the extension of the theory of the horseshoe vortex into the vortex-sling concept. The vortex sling is essentially a seven segment vortex line, which, for each panel, starts in the infinity behind the aircraft, reaches the trailing edge, moves upstream to the hinge line of the trailing edge control surface, then forward to the quarter chord line of the panel in question, going across the panel and then back downstream in an analogous way. The issue of the wake passing trough the geometry at certain flight conditions is resolved by a collocation point proximity detection routine which automatically removes the influence from a vortex thread passing too close to a collocation point.

The code is generally distributed in the hope that it will be useful, but without any warranty; without even the implied warranty of merchantability or fitness for a particular purpose. However, validation comparisons have been made by [Melin] in which the code output is compared with experimental data. The test case is a Cessna 172, for which the Cessna Aircraft Company have released flight test data [Cessna] and for which computation results from AVL and PMarc, a vortex lattice method and a panel method respectively, was available

Code Development History

2010-03-20
Release of the upgraded version of Tornado (134)
Unsteady derivatives added
Neutral point search added
Trimmed polars added
New strip theory friction function added
Compressibility function added
Lots of small tweaks

2007-12-20:
Release of the upgraded version of Tornado (134)
Solver system changed
Change directory command changed to functional form
Variable directory names added in config.m
Aircraft trim function added
New solver added, vectorised 6 times faster
Symmetric solver removed
Simple solution now computes derivatives as well
Zero lift drag prediction added
Definition plots added
Result data exporter added

2007-08-07:
Release of the upgraded version of Tornado (132).
New Camber model added, more accurate than before.
Viscosity added to ISA
Subfunctions moved inline
Symmetric solver added
Editor fixed to vork with new foil standard
Batch function added. (tornadobatch.m)
Rotation in boundary condition error fixed

2007-04-05:
Release of the upgraded version of Tornado (131b).
Splash screen added.
Trefftz plane analysis tool added
Altitude - density function added (ISA)
New paneling distributions
Prandtl Glauert Compressibility correction added
New 3-view drawing
Center of gravity added to geometry
Offline validation tool added
Code cleanup.

2006-12-13:
Release of the upgraded version of Tornado (130b).
Wind alignment in body system fixed

2005-10-18:
Release of the upgraded version of Tornado (129b).
Wake alignment fixed
Normal position on panel fixed
Wind to body transform modified
Sideslip computation modified
Standard (Horseshoe) VL method added

2004-11-04:
Release of the upgraded version of Tornado (128b).
Rudder setting problem fixed

2004-07-21:
Release of the upgraded version of Tornado (127b).
Case sensitivity fixed
File converters for geometry files from pre v125 "fOld2New"
Converter from v125 to 126: "f_version_geo_transform"
Rudder matrix transpose problem which resulted in 'index array out of bounds' fixed

2004-05-08:
Known problems
Version 126b does not work on case sensitive system

2004-03-18:
Release of the upgraded version of Tornado (126b).
Major memory structure changes
More efficient solver (solver8), with vectorized computing
Spell-check etc...
Side force/Drag swap in post processor fixed

2003-02-17:
Release of the upgraded version of Tornado (1.23b).
Reference point position changed to geometry property
Downwash matrix condition computed in solver6
Input function changed to accommodate new variable
Diffbatch changed to accommodate new variable
fOld2New function created to translate old geometry files into new
fLattice_setup created. It's a Wrapper for geosetup and wake setup etc.

2002-02-11:
Release of the upgraded version of Tornado (1.20).
New Cmac computation added
Graphical C_mac and refpoint added
Span load computation and graph added
Beta sign inconsistency corrected
Wake roll inconsistency corrected
Wake length edited
NACA profile slope error corrected
Refpoint move to MAC added
Input questions fixed for flapped asymmetric wings
Mean geometric chord added (not used yet)

2001-11-07:
Release of the upgraded version of Tornado (1.19)

2001-10-10:
Release of the upgraded version of Tornado (1.16)

2001-01-23:
Release of the first alpha version of Tornado

2001-01-23:
Pre-release beta development remarks available in the program.

References

[Cessna] L.L Leisher et al, Stability derivatives of Cessna aircraft, Cessna Aircraft company. 1957.
[Melin] Melin.T, Tornado, a vortex lattice MATLAB implementation for Linear Aerodynamic Wing applications", Masters thesis, Royal Institute of Technology (KTH),Sweden, December 2000.
[Moran] Moran, J "Computational Fluid Dynamics", Weily&Sons, 1984