Imitation (oz8495)

About this Plan

Imitation. Control line stunt model.

Quote: "THE Imitation was designed as a flying testbed to explore the soundness of a number of aerodynamic philosophies with which I had been experimenting through my 'Citation' series of competition stunt aircraft. In addition, it was intended to be used to test the suitability for stunt purposes of a variety of the currently available very powerful Schnuerle-ported 40 engines.

The Citation, although it has had an enviable contest record, including a third and a second at the last two National Championships, does have a couple of significant shortcomings which I felt had to be corrected before investing time and effort into a new competition airplane. First and foremost, it is too much of a thoroughbred, that is, although it is capable of outstanding performance, it is entirely too critical to trim adjustments and weather conditions. It is necessary to spend considerable time before a contest trimming and adjusting to the peculiarities of the contest site. For instance, before qualifying at the ‘78 Lake Charles Nats I had to tear out almost a full ounce of nose weight in order to regain the same degree of crispness in corners that I had had in the cool, heavy air of Northern California. In addition, it was necessary to explore a whole series of props to find one which would allow crisp maneuvers and not result in excessive air speeds. The single most perplexing problem, however, is the Citation’s inability to come out of a corner hard and flat every time. It is altogether too sensitive to handle adjustment and center of gravity location, and has to be literally nursed around corners if an occasional bobble is to be avoided.

Because of the need to resolve these problems I decided to design an easily built test ship which would allow me to investigate possible solutions. To be meaningful, such a design would have to combine ease of construction with a truly competitive planform which would, as nearly as possible, display the characteristics of a state of the art competition stunt plane. Such a combination would have to include: An inverted engine with an appropriately located fuel system, ie directly behind the engine and adjustable in the vertical to allow trimming for consistent engine runs. In addition, it should be possible to easily interchange engines to explore potential replacements for the venerable ST 46. The planform, ie wing span, wing area, moment arms, horizontal stab and elevator area, aspect ratios, etc, would have to be identical to a competition plane of the same size. And, although it would be an easy matter to build a simple profile significantly lighter than a competition ship, this temptation had to be avoided as a lighter wing loading would make the results of any tests meaningless in the translation to a heavier ship.

In compliance with these basic parameters the Imitation came off the building board sporting a semi full fuselage on the front end, supporting a Kraft-Hayes KM40 engine mount which is easily removable to accommodate a variety of engines. A cutout was incorporated in the nose to allow the fuel tank to be properly located, and allowance was made for space to shim the tank either up or down.

Aerodynamically, the Imitation features a 59 inch wing span with 631 sq in of area. This results in an aspect ratio of 5.5 to 1. (For those unfamiliar with the term, an aspect ratio is mathematically defined as the length of the wing span squared, divided by the area, or for constant chord or straight tapered wings, the wing area divided by the average chord.) A comparatively long tail was employed along with a large horizontal stab and elevator, 140 sq in, or 22.2% of the wing area. No attempt was made to keep weight down and, as a result, the Imitation came out weighing 50 to 53 ounces, pending on the weight of the engine..."

Direct submission to Outerzone.

Update 18/04/2017: added Part 1 of the Model Aviation Imitation feature (Sept '79), thanks to George Albo.

Supplementary file notes

Article in two parts, thanks to GeorgeAlbo & RFJ.

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