Faceted Airfoil Approximated Design for Foiled Surf Sailboard

I had been wrote to Australian Moth Design Forum about Faceted airfoil design idea 16 years ago and they built one and found the foil does not instantly escape jump from the water and increases the time of moth in water without collapse.

I had been inspired from F117 Stealth aircraft faceted wing airfoil.

Now I dont know the exact dimensions or specifications of curved foils for surf sailboard but I do need to know approximated conversion of curved airfoil to faceted airfoil and get help to know facets dimensions and angels. I dont know whether bottom is flat or not but I need your help to build a faceted foil for surf sailboard.

This would be the simplest , cheapest and safest to use foil.

Thank you,
Umut
Istanbul

 

I asked same question to the gpt. It drew 8 faceted design and I requested simplest design and it drew 4 surfaced design. In reality does 4 faceted design work ?

Windsurf Foil Design Using Simplified Faceted Airfoil
⚙️ 1. Front Wing (Main Lift)

• Airfoil: Simplified 4-facet (above)
  
  
• Span: 90 cm
  
  
• Chord: 15 cm
  
  
• Area: ~1350 cm² (good lift for cruising and early takeoff)
  
  
• Aspect Ratio (AR): 9021350=6\frac{90^2}{1350} = 61350902=6 → efficient and stable
  
  
• Material: 3–4 mm aluminum sheet or 3D-printed plug + fiberglass
  
  
• Angle of Attack: +2.5° relative to fuselage (for early lift)
  
  
• Construction: 4 flat segments top, 4 bottom (cut with laser/CNC or bend manually over jig)
  

2. Rear Stabilizer (Horizontal Tail)

• Airfoil: Same 4-facet profile (inverted)
  
  
• Span: 45 cm
  
  
• Chord: 10 cm
  
  
• Area: ~450 cm²
  
  
• Angle of Attack: –1.5° relative to fuselage (provides pitch stability)
  
  
• Material: same as front wing
  

3. Fuselage

• Length: 75 cm (front wing 60 cm from mast; rear wing 15 cm behind)
  
  
• Cross-section: 2×2 cm square bar or teardrop if faceted
  
  
• Material: Solid aluminum or stainless steel
  
  
• Wing Mounting: Bolted or welded (welded is stronger for open-sea use)
  
  
• Wing angle interface: Can use tapered spacer shims or cut angled slots
  

️ 4. Mast

• Height: 85 cm (adjustable if modular)
  
  
• Profile: Symmetric faceted foil (same 4-panel logic, mirrored)
  
  
• Thickness: ~14 mm max thickness; 10–12 cm chord
  
  
• Material: Aluminum or stainless steel (TIG-welded) OR laminated carbon over foam core
  
  
• Mounting: Deep Tuttle box or plate mount with 4 bolts
  

Construction Overview
Part Material Notes
Wings Aluminum 6061 or stainless 3–4 mm sheet, laser cut or hand bent
Fuselage Solid aluminum bar 20×20 mm; pre-drilled or welded joints
Mast Faceted Al sheet or carbon Symmetric; full weld or modular
Connection M8 bolts + Loctite Stainless hardware, marine-grade
Performance Expectations
Feature Estimate
Takeoff Speed 8–10 knots
Cruising Speed 12–18 knots
Max Stability High — forgiving for open water
Weight Limit Up to 100–110 kg rider + gear
Upwind Performance Good (moderate AR front wing)

 

The F117 faceted design was caused by the "stealth" requirement, not aerodynamics.

 

Absolutely. Particularly if it is of a rectangular shape with the a ratio of width to length of no more and no less than 7.62

 

An airfoil with two facets, one upper and one lower, works. Commonly known as a flat plate. they have been used on many boats as centerboards and rudders. Disadvantages are stall at low angle of attack, particularly at low speeds, which means lower maximum lift, and higher drag.

 

Very good idea Umut, the simplicity of the faceted design has potential for DIY foils. I think we can take inspiration from existing profiles (such as GO FOIL or SABFOIL) and translate them into flat surfaces. Even if the base is not completely flat, a model with 5 or 6 well-oriented facets could work. Can't wait to see your sketches or 3D models!

 

My understanding is that the F-117 has facets only because computing power was scarce at the time of it's design and the multi-faceted shape was a result of this.The succeeding F-22 and f-35 have compound curved surfaces and presumably,due to progress,a lower radar signature and better aerodynamics.I am having difficulty visualising a way in which an amateur could accurately create such a faceted shape with realistic expectations of good performance.I am aware of the technique Dr Mark Drela advocates for creating foil sections and it works nicely,but it is time consuming for foils with curved planforms.Since he originally published the idea we have seen the widespread adoption of hobby CNC machinery and 3D printers and these can create accurate realisations of any combination of section and twist the human mind can devise.I believe they will allow the use of more sophisticated foil sections and allow better performance than a faceted foil is likely to achieve.I suspect that some experimenting with turbulator strips on conventional foils might also be worth investigating,but that is a bit esoteric for performance dinghies that have to deal with a range of conditions.