Tutorial: designing an RC aircraft wing with Heliciel

An aeromodeller is designing a high-wing RC trainer and wants to check that its wing will carry the aircraft in cruise with a comfortable stall margin. The data:

Total mass in flight: 1.8 kg → required lift 1.8 × 9.81 = 17.7 N;
Cruise: 15 m/s (54 km/h);
Span: 1.4 m (Heliciel works on the 700 mm half-wing and displays the results of the complete wing), chord 220 mm at the root, 140 mm at the tip;
section of the supplied model's law: NACA 2411 on the root side (maximum lift-to-drag ratio 71 at the Reynolds number of 200,000 met in flight).

A particularity of wings in Heliciel: there is no objective to optimise. A propeller has an rpm the software can search for; a wing has no free variable — you set the geometry and the angle of attack, read the lift, and iterate. That is exactly the approach of this tutorial.

Organisation and design phases:

Load the wing and set the geometry
Iterate the angle of attack towards the target lift
The wing polar: lift-to-drag ratio and stall
Summary and model to download

1: Load the wing and set the geometry: the “wing” model is loaded then brought to our dimensions (half-wing 700 mm, chords 220/140 mm). First computation at 15 m/s, each section left at its angle of attack of maximum lift-to-drag ratio:

lift (complete wing): 14.6 N — not enough for our 17.7 N;
total drag 0.79 N, aspect ratio 7.7;
Heliciel reports “irregular angles of attack” (from 0 to 6° depending on the element): since the polars are tabulated, the maximum lift-to-drag ratio of each segment falls at different angles — a “staircase” wing, unrealistic to build.

RC wing loaded in Heliciel

2: Iterate the angle of attack: we impose a UNIFORM angle of attack over the whole wing (flat wing, no twist — the choice of construction simplicity) and iterate:

Uniform angle of attack	Lift (N)	Drag (N)	L/D
4°	16.38	0.93	17.6
5°	18.54	1.12	16.6

At 5° angle of attack, the 18.5 N of lift covers our 17.7 N with a 5 % margin: adopted. The power to overcome in cruise is only 16.8 W (drag 1.12 N × 15 m/s): that is the wing's share — fuselage and tail surfaces will add to it.

RC wing at 5 degrees angle of attack in Heliciel

An instructive detail: by selecting a wing element in the 3D area, Heliciel displays its two sections with the downwash — the finite-span wing deflects the air downwards, so that at 5° of setting the central element only “sees” 3.6° effective. That is induced drag in a picture, and the reason why a 2D section computation is never enough to predict a wing.

3: The wing polar: the multi-point analysis sweeps the angle of attack (on a wing project, the “rpm” sweep axis becomes the angle of attack). Values for the half-wing, as returned by the analysis table:

RC wing polar: lift, drag and lift-to-drag ratio against angle of attack

Angle of attack	Lift ½ wing (N)	Drag ½ wing (N)	L/D
5°	9.27	0.56	16.6
7°	11.71	0.83	14.1
9°	13.88	1.12	12.4
10°	14.09	1.27	11.1
11°	13.96	1.49	9.4
12°	13.60	2.00	6.8
15°	15.10	3.09	4.9

Reading: lift levels off around 10° — the stall begins (lift stagnates then falls while drag soars; the apparent rise towards 15° goes with a lift-to-drag ratio collapsed to 4.9: the wing “ploughs”). Our cruise flight at 5° therefore keeps 5° of reserve before the stall. The maximum useful lift (~28 N for the complete wing at 10°) also gives the minimum flying speed: v ≈ 15 × √(17.7/28.2) ≈ 11.9 m/s — below that, the aircraft no longer flies (the author's computation from the table values).

4: Summary and model to download

Wing 1.4 m × (220/140 mm), NACA 2411 section, uniform angle of attack 5°, aspect ratio 7.7;
cruise at 15 m/s: lift 18.5 N (5 % margin on the 17.7 N required), drag 1.12 N, L/D 16.6, 16.8 W to overcome;
stall around 10° angle of attack; minimum speed ≈ 12 m/s;
the wing approach: set → read → iterate (no optimiser), and watch the downwash.

The complete project can be downloaded here: aile_rc_1400mm_15ms.hlc (open it with Heliciel). It is also included in the models supplied with the software. To go further: the advanced wings and foils tutorial.

I remain at your disposal for any remarks or further information at contact@heliciel.com

JF Iglesias, Heliciel developer.

To watch the air speed up over the upper surface and read lift and drag on the whole wing, read the case study wing CFD: a wing simulated at three mesh refinements.