Twin Wing Landyacht Concept

Goal - 100 kt/200 kph/120 mph with course racing landyacht

• Current World Record is 94 mph with one-way asymmetrical yacht

Problem - Landyacht speeds are limited by three factors:

• stability - rolling (heeling) moment limits available aerodynamic force
• skidding - tire traction limits available aerodynamic force
• efficiency - drag limits apparent wind angle (beta) which caps

Empirical Data -Limited

• Annual NALSA speed trials - historical yacht speeds & yacht speed/wind speed ratio
• SDSU wind tunnel test - rear wheels alone account for 30% to 40% of total aerodynamic drag

Design Approach - Twin Wing Concept

• Inclined wing, displaced from centerline, reduces effective moment arm
• Aerodynamic downforce adds to traction w/o adding inertia
• Structural load paths eliminate large bending moments in axle, body - lighter weight
• Delta wheel fairings
• Concept sketches:
  rear quarter
  front quarter
  top
  right side
  front
  rear

Twin Wing Rationale

• Consider a single wing, set to windward & inclined to leeward
• Projection of lift vector passes close to leeward wheel (Fig. 1)
• Force vector could pass through contact patch, producing zero moment
• Produces downward component
• Reflecting wing for other tack produces two, mutual supporting wings in an A-frame
• Pilot controls each wing separately to control rolling moments
• Initial feasibility looks promising, but light wind performance is a problem.

Delta Wheel Fairings

• Best landyachts today use simple flat plate over wheel hub - minimum "frontal" area
• Must work at + 15 - 30 degrees beta; zero beta drag is relatively unimportant
• Traditional fairings increase "frontal " area, do not consider separation due to beta
• Fat delta provides streamlined shapes in streamwise cutting planes

Aerodynamic Issues

• Fairing shaping for fully attached flow
• Wing/fairing & Wing/Wing interference
• Low Reynolds number performance
• Span/chord length tradeoffs (induced drag vs Reynolds number)
• Body shape
• Overall configuration sizing and optimization

Aerodynamic Tools:

• Eppler PROFIL: single element airfoil design
• MCARFA: multiple element airfoil analysis
• CMARC: 3D analysis

Tool Deficiencies:

• Mesh generation - difficult to handle wing/fairing geometry
• Multiple element airfoil design
• Inability to handle laminar separation bubbles or modest trailing edge separation

Progress to Date:

• 2D airfoil design
• Parametric study of 2 wings
• Representative fairings & wing intersections modeled