Optimum Planforms


Design Tools




Wingmast Aerodynamics

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 large masts are shown to have a greater operating range of angle of attack. Maximum lift for both small and large masts is similar. 

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.

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