Sportwing (oz10571)

About this Plan

Sportwing. Control line stunt model for .19 to .36 engines. Wingspan 36 in, wing area 250 sq in.

Quote: "As modern in design as a new car, as easy to fly as any trainer, yet possessing remarkable stuntability. Modelers, here is a model that will make you the envy of the gang at any flying session, it's new, it's different, and above all it's a dream to fly! From its sound aerodynamic design to its new and simple jig construction its a model that you will be proud to own and really will enjoy flying!"

This is an Uncle Willies plan.

Direct submission to Outerzone.

Update 2/6/2025: Added review from Model Aircraft, June 1950, thanks to RFJ.

QUote: "Model Report. Harold de Bolt's Sportwing. By Ron Warring.

We make no apologies for introducing another de Bolt design in this series. Even in America, where the Californian area is regarded as the birth-place of all C/L development, de Bolt is rated as amongst the leaders - despite the fact that he operates from the opposite (East) coast. The various de Bolt designs which have been kitted - the Bipe, Dmeco Senior and junior, Speedwagon and Stuntwagon - have all proved their worth in contests. They are, in fact, the only commercial C/L designs which have really made their mark in the contest world.

But quite apart from the fact that each new design is typified by outstanding performance, every new model is also different. And it takes a lot of ability to be both different and successful these days!

Predecessor of the Sportwing was, of course, the Stuntwagon - a large area mid-wing monoplane with a very short coupled tailplane. Tail moment, in fact, was reduced to almost negligible proportions, making for extreme manoeuvrability without excess elevator power. Large elevators with correspond-ingly large movement do not make for ease of control particularly on a long moment aim., There is a definite danger of stalling the model in sharp pull-outs. Short coupling has produced some really easy-to-fly stunters and this design configuration has, in fact, become the rule rather than the exception. The Sportwing carries this to a logical conclusion in hinging the elevators on the trailing edge of the wing itself and dispensing with the fixed tailplane entirely.

Flying wing control liners have, of course, appeared before the Sportwing. In fact, about a year ago the all-wing stunter enjoyed a considerable vogue in this country, ranging from purely circular or rectangular wings, to the more realistic looking layouts with a definite fuselage and swept-back surfaces.

The Sportwing, however, is not just another flying wing design. It incorporates enough original features to put it in a class of its own and has, at the same time, rather an attractive appearance.

Main point of interest is that the wing is swept forwards. Aerodynamically there are various benefits to be gained by sweeping forward a wing. Sweepforward, in fact, may be better than sweep-back on some flying wing layouts, as applied to free flight. But how far free flight aerodynamics have any bearing on C/L model performance and stability is debatable. Probably so 1, ery little as to be almost ignored, as regards planform shapes, at least.

There is the point, however, that sweeping forward the wing in this manner has the effect of moving the relative CG position forward. The Stuntwagon appeared to be at fault in this respect, for with the type of construction shown it was almost impossible to get the CG in the right place without adding ballast to the nose. It invariably came out well aft, often as far aft as the pivot point, when stability on the line became marginal. In other words, rigged with the CG roughly on the pivot point, the model was always tending to come in all the time, and high altitude manoeuvres were more or less out of the question. The model just had to be ballasted to fly properly.

Design CG position for the Sportwing is on the leading edge of the wing at the centre section, which should be achieved quite readily with a 4 to 5 oz motor. The pivot point is then 1-3/4 in farther aft and it would appear that there might be a possible margin of about 3/4 in aft movement of the CG without running in to much trouble. It should be noticed, however, that the control hook-up is contrary to normal stunt practice. The elevator horn comes above the elevators, so that the front line becomes the up line. De Bolt seems to do this quite frequently.

The other point of note is that the Sportwing is laid out to fly clockwise circuits, again opposite to normal practice. but unlike some other de Bolt designs the layout is symmetrical and so it can be modified to fly normal anti-clockwise circuits without any harm being done. The thrust line is straight - no sidethrust - and only the ballast weight requires shifting to the starboard wing tip and the lines relocating in the port wing.

Use of tip ballast is now very common in all stunt models and it has certainly proved beneficial. Normally one adds just sufficient weight to balance out the weight of the lead wires, etc, in the opposite wing, but the 3/4 oz specified here definitely over-balances the model so that the final CG of the model is actually slightly outboard of the centre line. This in itself is quite useful.

The Sportwing makes no pretence of being a contest model, as such. The whole layout appears to be rigged to give a full range of manoeuvrability with an adequate safety margin. In other words, a model which will perform all the stunts in the book, but at the same time prove reasonably easy to handle. The designer, in fact, himself emphasises this point..."

Supplementary file notes

Review.

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