NACA 0006 hydrofoil CFD: pressure and cavitation Designing a wing: the wing mast step by step Sections, geometry, results: the Heliciel method

This wing or foil design tutorial (getting started) shows you how to design a simple wing or hydrofoil with Heliciel: you start from a model, set the span and the chords, rebuild, then read the lift and the power. Our example is the foil of a pedal boat, with a numerical goal: 1,000 N of lift for 250 W of available power. Incidence forcing, twist and thickness distribution options are covered in the second tutorial, building a wing or foil (going further).

On this page:

• How Heliciel calculates wing performance
• Opening a hydrofoil or wing model
• The requirements of a pedal-powered foil
• Entering the half-wing dimensions
• Rebuilding and reading lift and power
• Finding the flying speed with multiple analysis
• Refining the wing to gain lift-to-drag ratio

1 : How Heliciel calculates wing performance

To compute the performance of a wing, Heliciel uses Prandtl's lifting-line theory. You can design your wing without mastering the mathematics of this method: that is the whole point of Heliciel. But the notions of induced velocities and angles it introduces help in understanding the results. They are detailed on the page on Prandtl's lifting-line theory. To review the basic principles of wing design, the page on wings, hydrofoils and sails recalls them.

Whether you build a wing or a hydrofoil, the method is the same. We therefore model a foil here without making any distinction. The problem of cavitation, specific to hydrofoils, is covered on the cavitation page.

2 : Opening a hydrofoil or wing model

We size, test and edit the plans of our wing with Heliciel . To start, we open a hydrofoil (or wing) model.

The starting models offered by the Files menu, here in an earlier version of the interface.

For this introductory tutorial, we use the simplest profile law. In the 2: Blade geometry tab, 2.2: Profiles Law sub-tab, select A) Law "constant profile": Heliciel then applies the same airfoil to all elements of the wing.

The constant profile law, here with a NACA 1408 airfoil of relative thickness 0.080 times the chord.

3 : The requirements of a pedal-powered foil

What is the goal of our wing or foil? Our example is a human-powered vehicle project: a pedal-driven boat that flies above the water. If that sounds far-fetched, we invite you to visit the human-powered hydrofoils site to see how many such projects already exist. This type of project demands a perfect command of efficiency.

Foil boats driven by pedalling.

To keep things simple, we set two starting data: an available propulsion power of 250 W (what a willing adult delivers at a steady pace) and a mass of 100 kg for the vehicle and its pilot. The force to lift equals the weight, about 1,000 N. We therefore have to make a hydrofoil wing that generates 1,000 N of lift with a propulsion power of 250 W. Our goal is to go as fast as possible with these 250 W. We proceed by successive trials of length and shape to find the best compromise.

Heliciel calculates the drag and lift of a half wing. That is handy for a foil fixed to a hull or a fuselage: only the losses at the free side are computed. For a complete, free, symmetrical wing, multiply the results by 2. Here we assume a submerged symmetrical wing, and we leave aside the connection to the hull to concentrate on the wing that generates the lift.

We start with a wing 1 m in total span. Since we model a half wing, its length is 0.5 m. Two main unknowns occupy us:

1. the speed needed to create 1,000 N of lift, i.e. 500 N for a half wing;
2. the power needed to produce that lift at that speed.

4 : Entering the half-wing dimensions in Heliciel

These results are easy to obtain. In Heliciel's tabs, you enter:

1. in 1.1: Fluid, check the fluid (sea water at 10 °C);
2. in 1.2: Objective, check that the selection is "Wings and Foils";
3. in 1.3: Operating point, enter a speed, for example 5 m/s;
4. in 2.1: Blade dimensions, enter:
   • the length of the half wing or foil: 500 mm;
   • the chord at the blade root (wing or foil): 200 mm, for example;
   • the chord at the blade tip: 100 mm, for example;
   • then click linearize in the chord distribution. Remember to linearize after each change of dimensions or of the number of elements!

Note that the thickness of your foil is set by the chord and the relative thickness, because you selected the constant profile law in tab 2.2.

The half-wing dimensions entered: 500 mm long, chords of 200 mm at the root and 100 mm at the tip, speed 5 m/s.

5 : Rebuilding the wing and reading lift and power

Our half wing is ready to be tested. Simply click the Rebuild button in the horizontal toolbar at the top right of the software:

What does Heliciel do when you rebuild?

• It looks in the airfoil performance database for the selected profile and finds the angle of attack that gives the maximum lift-to-drag ratio.
• It builds the 3D model with this angle.
• It computes drag, lift, power, resistance and the other results, taking into account downwash, the induced velocities generated by lift.

Your foil should look like this (particles were switched on from the 3D model menu):

Let us zoom on the result that interests us:

Lift of 707 N, total drag of 39.6 N (13.5 N shape drag and 26.1 N induced drag) and power of 197.9 W.

The lift is 707 N for a power of 197 W (total drag × speed = propulsion power to supply). For a complete symmetrical wing, we multiply the results of this half wing by 2:

• lift of the complete wing = 707 × 2 = 1,414 N;
• propulsion power of the complete wing = 197 × 2 = 394 W.

6 : Finding the flying speed with multiple analysis

We must lift 500 N per half wing: let us look for the speed that gives that lift. To avoid many trials, we use multiple analysis, which plots a lift and power curve against speed.

Here is the result of an analysis over the range 1 to 5 m/s:

Lift (blue) and power (green) of the half wing against fluid velocity.

The power reaches 125 W (reminder: the maximum power we can use per half wing is 250 / 2) at about 4.25 m/s, and at this speed we read about 500 N on the lift curve (approximate reading). A speed of 4.25 m/s therefore lets us lift 2 × 500 N while consuming 2 × 125 W: we "fly" at that speed.

7 : Refining the wing to raise aspect ratio and lift-to-drag ratio

We can reduce the width of the wing to increase its aspect ratio and so reduce tip losses. We gain lift-to-drag ratio, hence energy available to go faster.

In the 2: Geometry › 2.1: Blade dimensions tab, we narrow the wing tip from 100 to 50 mm and the root goes from 200 to 150 mm. Do not forget to linearize to update the shape.

Root chord of 150 mm, tip chord of 50 mm.

We rebuild to update the geometry and the performance at 4.25 m/s. The reduced area has dropped the lift to 250 N. We run a new graphical analysis from 4 to 8 m/s to find the lifted mass and the speed at 125 W:

Lift and power of the refined half wing, from 4 to 7 m/s.

Let us read the speed and the lift for 125 W: about 5.5 m/s and 430 N of lift (approximate reading). We gained speed, but the lift is a little low, since we need 500 N per half wing: the foil area will have to increase a little. Now it is up to you to invent the best compromises for your project.

This tutorial ignores one point: with 250 W at the propeller shaft, it is in practice impossible to deliver 250 W of propulsion power. The efficiency of the propeller and of the transmission parts reduces the power delivered. A good hydrofoil therefore needs a good boat propeller, so as not to waste the precious energy of our happy pedaller sailing on the wave while dreaming.

To go further, we can edit the plan of the airfoils and of the blade, export the 3D model in IGS format, or control the incidence and the thickness of the wing with the second tutorial on wing or foil design.

Products | Store | My Mecaflux | My Licences | Key generator | My cart | Contact

Copyright © 2024 Mecaflux. All rights reserved. last update 06 february 2024
Terms of sale| Privacy and cookies