Drifter (oz11705)

About this Plan

Drifter. Radio control thermal soarer model.

Quote: "120 in span Thermal Soarer. Drifter, by John Fletcher.

DRIFTER is the direct descendant of my slightly smaller model, Autalycus which was designed and built at the beginning of the 1970 season and used throughout the year (still is, come to that!). This latter proved to be a very efficient and - probably more important - consistent model. During the course of the year, however, I became convinced that a larger model would be more efficient at thermal holding and so Drifter was designed, to incorporate the best features of the previous model, together with some strengthening, where it had proved necessary.

One feature which was given a lot of thought and attention on Drifter, was the wing section for, although the typical A2 section, thin and highly undercambered, is undoubtedly very efficient, it has a very limited speed range. A search was made therefore, for a section which would combine efficient soaring, with the penetrative ability necessary to fly in a wide range of wind velocities. The section finally chosen G392, has proved to possess most of the points required, one particularly useful feature, when flown in strong winds, being the ability to penetrate - how many thermal soarers have you seen making steady progress backwards?

At the designed wing loading of 8 oz/sq ft the only time this model has been consistently outflown is in absolutely still-air conditions, (and how often do we get these in this country?). However, there are two ways around this problem - build light and ballast as necessary or, do as I do, and build another, larger, pair of wings to lower the loading to around 6 oz/sq ft. The only reason I choose the latter approach is because I am one of those people who 'builds heavy' - I like my models to have a good finish and so I pay for it this way.

CONSTRUCTION: Construction of Drifter is relatively straightforward - there is just a lot of it - but I think the end result is worth the effort. Be very careful over the selection of the wood for the wings and tail - a heavy rear end needs a lot of lead in that short nose to bring the centre of gravity to the indicated position!

Wing: I will start by describing the construction of the wings as these have the most work in them. Also they benefit from being allowed to 'age' before use. A number of jobs are best done early, and then construction becomes more or less an assembly operation. The main spar should be built up and then left to dry on a perfectly flat surface for 12 hours at least. The wing tongue box should be treated in the same way - I make the box as one double unit and saw into two before fitting. The ribs are made by the sandwich method, using ply or aluminium alloy templates, and making sure you use light wood for the tip ribs.

Construction can now be commenced, by pinning down the leading edge, spar, and bottom, part of the trailing edge, packing up where necessary (do not forget the 1/4 in washout at each tip), and then ribs W2-W11 are fitted. These are cut along a line joining the back edge of the main spar slots, and the front portion is then glued into position. Before the back portion is fixed, 1/16 in must be cut off the front to allow for the spar web. Ribs W1 are next fitted, noting that the fourth is a ply-and-balsa sandwich, to give a good support to the end of the box. You will find it easier to mount these ribs on the wing boxes and fit as an assembly. This has the advantage of allowing the alignment of these ribs to be checked before cementing..."

Drifter, Radio Modeller, March 1972.

Direct submission to Outerzone.

Supplementary file notes

Article pages, thanks to RFJ.

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