Fournier RF-4 (oz1735)

About this Plan

Fournier RF-4 Scale Control line stunt model, of the powered glider. For .19 power.

Update 7/6/2023 Added article thanks to Geoff Goodworth. This comes thanks to the scanning work done by ilgk48 on the original magazine pages as posted on the HPA site, see https://www.hippocketaeronautics.com/hpa_plans/details.php?image_id=13070

Quote: "I HAVE ALWAYS belived a .20 powered stunter can offer many advantages over the traditionally larger powered alternatives. Less weight; less noise; smaller fuel tank - creating less fuel surging problems when nearly empty; choice of higher aspect ratio could produce same size model as current .35 powered models; less frontal area, drag etc; thinner control lines can be used ie .012in diameter; should fly well on 50-60 ft lines.

Certainly there's a lot to be said for smaller stunters, and with these points in mind I started to design a model based on the Aircraft Described Scale drawings ef the Fournier RF4 presented in the May 79 issue of Aeromodeller. I very quickly realised that a model very close to scale should be possible, which could easily be made exact scale with a little modification by true-scale buffs.

WING: The present trend by Stunt flyers to use foam wings allows the use oof higher aspect ratio wings than are in common use at present without structural weakness. If you have never built a foam wing before, this is a good time to start. There is almost certain to be someone in your club who has built a foam wing before.

The design and construction of the wing is fundamental to the performance of any aeroplane including models. In the case of a model like this one, with its slim high aspect ratio wing with a laminar flow section, the structural and aerodynamic problems can become complex. Cantilever loads at the wing root are high because of the small root and long span, and a long span wing is more vulnerable to damage from handling and flying incidents. An accurate wing section and an absolutely warp-free strutture are also vital if the aerodynamic efficiency is to be maintained and the benefits of the planform realised.

In order to meet these requirements, a modern wing using an Expanded Polystyrene core, skinned with obeche veneer was chosen which proved to be simple to build (and repair!), very strong, light weight, aerodynamically efficient and sufficiently accurate to permit the use of an advanced laminar flow section.

When the wing is being prepared, the following points should be borne in mind:

1. Ensure that the hot wire is well tensioned.
2. Cut the cores from the trailing edge forward.
3. Get someone te help you to cut the cores ensuring that you enter the trailing edge and exit from the leading edge at right angles without allowing the wire to stop at either end. Marking off the chord in 10 increments across the template ribs helps judge speed of cut at each end of wing.
4. Use the lowest wire temperature that will satisfactorily cut the foam.

The safeguards ensure that the wing care is accurate and that the section is ma intained, ensuring laminar flow. This wing is slim enough not to need the wing core hollowed.

The construction is started by cutting root and tip rib template eut of hardboard or thin plywood (1/16 or 1/8 in). Obtain 2 in thick expanded polystyrene sheet from builders' merchants, damaged sheets can often be purchased cheap, mark out wings on sheet with felt tip pen and using right angle card triangles pinned on foam as shown, cut blanks. Mark centre line along each end of blank and pin rib templates on centre line..."

Supplementary file notes

Article.

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