Slipstream (oz9953)

About this Plan

Slipstream. Free flight competition power model.

Quote: "Slipstream. An International class power model of 'basic' construction. Designed by Brian Cox.

A high performance power model of very simple construction, Slipstream is capable of putting up times as good as many of the more complicated models which are seen today. During the development of the design two main factors were kept in mind, they were, high performance and simplicity of construction. This latter is of prime importance if you wish to develop a design through a series of models but have only a limited amount of time for building.

Development. The original Mk. I was built in May 1956, and was for an Elfin 1.5 cc. It had a wing of 52 x 6 in., and a 40 per cent. tail on a 2i wing chord moment arm. It flew very well but had a few weak points in the airframe which were duly strengthened when the Mk. II was built. Two of these were built and were flown during the seasons of '56 and '57. One of these models took second place in the '56 Frog Senior with 12.00 + 2.14 and the other took second at the South Midland Rally at Cranfield flying under strong gale conditions. Both had a fairly thin flat bottom wing section which gave a fast stable climb, the large wing area giving a reasonable glide.

The first of the 2.5 cc versions was built in January 1958. This was virtually a scaled up version of the Mk. II with a wing of 6o x 7-1/2 in, and a 35 per cent tail on a three chord moment arm. After seeing Draper's FAI models at the 1956 World Champs. I decided that the flat bottom section could be retained without detriment to the glide! This first Mk. III had an Eifflaender 2.5 fitted, which was soon followed by a second one for an Oliver. This performed much better, having a better climb. This model was flown at the 1958 Nats, putting up over 11 min, and it also took second place at that year's Devon Rally.

As the Team Trials loomed up in the contest calendar the Mk. IV was built. This had a greatly strengthened airframe with LE sheeting on both wing and tail. The aspect ratio of the wing was also reduced for structural reasons. The new wing, using the same section, was 56 x 8 in, also the tailplane was reduced in size a little. This model was a little over area and to suit FAI ruling had to weigh 27.5 oz. Engine fitted was an Oliver, and to aid recovery at the top of the climb an auto-rudder was in-corporated. However, I must have collected some gremlins on the way to Hernswell for an air leak developed in the fuel cut-out which did not help matters when using an auto-rudder! At the second trials with a new cut-out fitted the Mk. IV put up an easy 15 min!

The latest model in the series to be built is the Mk. V. This is geometrically the same as the FAI Mk. IV with lighter construction although the leading edge sheeting was retained because I think this was in some way responsible for the very good glide of the Mk. IV. As an experiment thread turbulators were fitted to both wing and tail but gave poor results, in that the stall was very sharp. Although the thread was of the right diameter for the Reynolds' Number of the wing its position may have been incorrect (2 per cent chord). Due to lack of time, further work with turbulators has not yet been carried out. Because this is a fairly large model I think it is important that a really good motor is fitted, e.g. Oliver, Eifflaender, Frog, Enya 15, Rivers or similar. For open events a 3.5 cc motor could be fitted very easily, the model being very docile to trim.

Construction. To anybody who has built a power model before, the construction is ultra-simple. The fuselage is built flat on the plan with the engine-bearers let into the pylon which is cemented together before fitting in the fuselage..."

Slipstream, Model Aircraft, November 1960.

Direct submission to Outerzone.

Supplementary file notes

Article pages, thanks to RFJ.

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