ES Sections (oz16611)

About this Plan

ES Sections (Equiangular Spiral Sections). Set of airfoil templates, particularly suited to producing tapered wings.

Quote: "ES Sections. Devised and described by R Annenberg, B.Sc., F.R.Ae.S.

BUILDING A MODEL of your own design? Odds are that the wing has a parallel planform for the greater part of the span and a constant wing section - the reason being that the average aeromodeller is very loath to draw out ribs for an eliptical wing due to the extra effort and time involved for any slight increase in performance.

It is strange, but nonetheless true, that the boffins have generally been so concerned with improving the theoretical performance of wings that the practical aspect of how easily they may be made and repaired, has been overlooked.

The ES templates are in effect a somewhat refined variation of the idea universal among micro-filmers who cut the ribs to the desired chord width by trimming away the trailing edge.

The refinement lies in the shapes, each of which are such that whatever the chord length, if the trailing edge thickness is zero, a proportional shape is produced. Lest the sceptics assert that this is impossible, let me hasten to add that a truly proportional shape is produced, provided the templates are used correctly.

Mathematically, the basis of these templates is a curve known as the Logarithmic or Equiangular Spiral (ES) which has the unique property that the shape to the left of any radius from the origin is independent of the position of that radius. Despite this definition, ES could equally well refer to Extremely Simple - which describes their use!

These templates are designated by the letters ES, followed by a number, ie ES6 is the template whose maximum camber is 6 per cent and ES6,6 is a symmetrical section 12 per cent thick. Incidently, it is not suggested that there are theoretical aerodynamic reasons behind the ES sections which make them particularly desirable - indeed, there is a possibility that these sections may produce a worse-than-normal performance when compared with similar sections, although usually there is a good reason for such a variation (such as a greatly different nose radius or even a faulty method of comparison). The significant value of the ES curves lies in their permitting consistently controlled variations in wing section designs with exceptional ease of construction.

Constructing the Template: Cut out the paper patterns, with a small margin to spare around the outline, and glue to a piece of dural, plastic or plywood not less than 1/16 thick, preferably with a non-water type of adhesive to avoid paper stretch.

Saw and file carefully to the exact outline. The leading edge notch is exceedingly important. Re-member to be very careful and do not hurry as mistakes or inaccuracies in any master templates are manifest in each and every wing rib produced from it.

The paper patterns are for 10 inch chord ribs or less and the maximum camber goes by intervals of 1 per cent to 12 per cent, giving six templates in the following combinations..."

Direct submission to Outerzone.

Update 9/3/2026: Added further article (in Spanish) from RC Model Feb 1985, thanks to Valeria367.

Quote: "Hi, Steve and Mary. Good morning. Last week, when you published the plan and article about the ES Sections (oz16611), it brought to my mind one article about that subject published on the old Spanish magazine "RC Model", in their issue of February 1985, and titled "Sistema gráfico para realizar perfiles". How I think it's one interesting subject for the Outerzone's readers, I searched for it in my magazine's collection, scanned it, and I send it to you. So people can read, and learn about it in both languages.
Greetings, from your friend.
Valeria367."

Supplementary file notes

Article.
Further article (RC Model, Feb 1985).

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