Tom Speer's Home Page

Welcome to my homepage. Here you'll find information on aerodynamics, landyacht and multihull sailboat design, and hydrofoils. 

Nearly everthing is theoretical, for the simple reason that I can't afford the testing to get experimental data. Where possible, I've validated these calculations against published results, but if anyone has any relevant experimental data, I'd love to see them. 

New: Updated wingmast aerodynamics paper using XFOIL results

Everthing on this site is for educational purposes only. I make no warranty as to the suitability or accuracy of these results or tools for any specific purpose. Commercial use forbidden without express permission of the author. 



Optimum Planforms



Optimum Planforms







Planar Planforms



Optimum planforms for sail rigs and hydrofoils having a single, planar lifting surface. 














Wingmast Aerodynamics

PDF Version



The basic aerodynamic features of two-dimensional sections that consist of a symmetrical airfoil with a thin sail extending from the trailing edge. A simple method for designing wingmast shapes is presented, which does not require a computer to produce masts with good aerodynamic performance. The effects of various mast sizes are explored, and the effects of both under- and over-rotation of the mast compared to the design condition. 





Rigid Wing Sail Rigs

20% Chord Flap

30% Chord Flap

40% Chord Flap

50% Chord Flap



Rigid wing rigs take the wingmast a step farther, and elimiate the sail entirely. A single, symmetrical airfoil does not produce high lift and as a result the acceleration of a yacht so equipped is very poor. So rigid wing rigs typically have two or more symmetrical airfoils hinged so that they form a slotted flap when deflected. This produces more lift than the wingmast/sail combination.

The main wing element of these airfoils was designed to a similar aerodynamic philosophy as the wingmast sections - providing for a smooth forward movement of the transition point as angle of attack increases, so as to have robust characteristics at low Reynolds numbers. The NACA 0012 provides a good section for the flap because of its front loading, which allows the whole flap to be used for the airfoil's pressure recovery. Any tendency of the flap to form a leading edge pressure peak can be suppressed by adjusting the slot gap.





External Flap Airfoils

Theory vs NACA data for NACA 23012

Riblett GA30-612 with GA37-315 flap

C506F ultralight airfoil



External flaps are separate airfoils that are positioned near the trailing edge of the main wing. They are were used on the Junkers trimotor and several ultralight aircraft. External flaps can provide high lift with low drag and give the designer lots of flexibility. 

The NACA tested the 23012 airfoil with a 23012 airfoil as a 20% chord flap, and the data are compared here with the computational method. The GA30-612 with a GA37-315 flap is used on some popular ultralights, and the theoretical data presented gives some insight in to how the combination works. The C506F is my own design, made for a designer working on an all-metal ultralight. The the key requirements were very high lift, ease of manufacture, and good handling qualities.















Sections for Proa Boards and Rudders




Design of three families of sections for shunting proas.  These sections have fore-aft symmetry and rounded edges.  Complete coordinates and XFOIL computed data are presented.






Sections for Sailing Hydrofoils



Design approaches and typical results for hydrofoils which must operate at low Reynolds numbers (small chord lengths and low speeds), as well as avoid cavitation at high speed. 





Chapter 1 Cavitation Inception on Foils, Struts and Pods

Chapter 2 Choice of Foil System for Optimal Performance

Chapter 3 Ventilation Inception of Surface Piercing and Submerged Foils and Struts

Chapter 4 Trim, Altitude and Pre-Takeoff Resistance of Hydrofoil Craft

Chapter 5 Longitudinal Stability (Controls Fixed)



Hydrodynamics of Hydrofoil Craft
Subcavitating Hydrofoil Systems

Technical Report 463-1
Hydronautics Incorporated

This is the most comprehensive reference on hydrofoil design I've found. It presents the engineering relationships and typical results for all aspects of hydrofoil design, covering both fully submerged and surface piercing foils.

These PDF files are no longer available online.  They can be found on the AMV CD-ROM #1 from the International Hydrofoil Society.





Generic Hydrofoil Analysis



A simple analysis of hydrofoil performance and comparison with test data. Included are comparisons with Alexander Graham Bell's HD-4 full scale test data and Hanno Smits' tow tank data. The approximate analysis is also applied to fully submerged T foils and surface-piercing V foils and ladder foils.

The lessons learned are:
- The simple analysis is adequate to predict the most important influences on hydrofoil performance. - Fully submerged foils are the most efficient for a given design point.
- Surface-piercing foils can be competitive with fully submerged foils when the requirement is to operate over a wide range of speeds.
- Pitch trim is vitally important to the performance of surface-piercing foils, especially V foils which vary their span as well as their area as a function of their depth of submergence.

I am deeply indebted to Hanno Smits and to the Bell estate for their generous permission to use their data in my analysis.



Design Tools



Design Tools







Simple Landyacht Velocity Prediction Program



An executable MathCad model of a landyacht performance with a rigid wing rig. (requires MathCad)





Lifting Line Analysis Spreadsheet



An Excel spreadsheet which can compute optimal planforms for wings, cat rig sails, and single hydrofoils. Will also compute the lift and induced drag for arbitrary planforms, including ground or free surface effects.













Landyacht with Rigid Wing Rig



Landyacht testbed build by Landyacht Design Interchange Association (LYDIA). (Apologies for the large size of this file!) This was a proof-of-concept vehicle used to try out new ideas in landyacht design and to investigate technical issues associated with the twin wing landyacht concept. The yacht was sailed with both direct mechanical control of the wing and with the wing free to pivot, controlled only by an aerodynamic surface on a tail boom. 

The aerodynamic control was found to be effective for an aft tail but was not workable when configurred as a canard. The partial span flap was effective in providing aerodynamic twist for high winds, but caused excessive drag due to the abrupt change in span loading which increased induced drag and caused stalling of the wing immediately above the flap.





Wind Tunnel Test Report



Wind tunnel test data and performance prediction of the landyacht built by LYDIA. The tests were performed by Matt Brown, Daphne Marschalk and Ricardo Camerena at San Diego State University under the direction of Dr. Joseph Katz. Model components were supplied by LYDIA. The surprising discovery from this test was the high drag created by the wheels - 30% to 40% of the total aerodynamic drag was created by the rear wheels alone. Also investigated was the effect of sealing the gap between wing and body which significantly improved the performance.





Simple Landyacht Velocity Prediction Program



HTML version of a landyacht performance model. Not executable, but shows all the derivation and sample results.





Performance of a Class IV Design



Predicted performance for a notional landyacht powered by a rigid wing. The results are realistic, however reliable data for an actual design are not available to completely prove out the method. 





Single Wing Parametric Study



A parametric study of the effects of wing planform on the efficiency and heeling moment of an isolated wing as would be used as the sail rig for a landyacht. The study is only concerned with lift and induced drag - airfoil parasite drag is not included. Interference with the ground is accounted for, but interference effects of the body are not included. 





Twin Wing Concept



The origin and rationale for a landyacht which is powered by two rigid wings mounted in an "A" frame arrangement. Results include renderings of the concept and initial feasibility studies. Compared with a conventional landyacht, light air performance is degraded, but higher speeds in high winds are indicated. The twin wing concept has completely different load paths, which may result in a lighter structure. 





Twin Wing Parametric Study



A parametric study of the effects of wing planform on the efficiency and heeling moment of two isolated wings as would be used as the sail rig for a landyacht. This is a companion study to the single wing parametric study above, and the effects of the twin wing configuration are compared with the corresponding single wing configuration. 













Cruising Trimaran Design Case Study 



This area has been moved to its own website at 






Comments and questions? Contact