Grumman Ag Cat (oz4785)

About this Plan

Grumman Ag-Cat. Control line scale model biplane.

Quote: "Bob's 'Ag-Cat' is a work of art. Small, light, offers inspired performance with a .35 engine. Bob Adair's Grumman Ag-Cat.

This model was designed and built with only one contest in mind, the 1965 Air Force World Wide Model Airplane Championships. As I planned on entering about 15 events at this meet, the main criteria of this design was simplicity. The Grumman Ag Cat appeared a natural for my purposes due to the relatively easy access to reliable scale documentation, as the ship is in current production, along with the straight forward lines of the ship and the easily duplicated scale features. Additionally it was felt that the model would be a good flyer for the full size craft is. The only miscalculation concerned the weight of the finished model, it weighs only 38 ounces and has a tendency to float on power-on landings, build yours heavy and it should cure this one problem area.

I would like to say that the Ag Cat lived up to my expectations of winning the scale event at the 1965 Air Force World Wide, but it didn't as it wasn't quite finished; the basic construction and finish was done, but little scale detail was added, so it ended up in second. Later in the year with some more detail added it again place second at the Eastern States Model Championships held at Johnsville NAS. During 1966 with more detail added the contest record improved and the Ag Cat won first at the Air Force World Wide, also it either won or placed at every local contest entered in the New York City area.

After mentioning the Ag Cat's successes I would like to point out that I do not consider myself as a specialist in scale competition and took a flyers point of view in building the model, with all those events to fly at the Air Force meet, I couldn't put up with any unnecessary critical frills. This should make the cat appealing to you sport flyers who want to fly a straight forward biplane with good flying characteristics.

The quickest way to get your Ag Cat Flying is to start on the wings and tail surfaces before getting into the fuselage construction. Wing construction is fairly straight forward, egg crate construction is used on the leading edge and front spar, this method automatically lines up the ribs if you are reasonably careful in notching the leading edge and spar. Don't forget to use 1/16 plywood ribs at the wing strut and cabane locations.

The aileron controls should definitely be installed if you anticipate entering scale competition, a modified Veco bellcrank was used as the heart of the system. The proper moment arms and the height of the pivot anchor may vary slightly from the drawing but with a little experimentation the proper ratios should be found. The sheeting should be applied with white glue to eliminate the shrinking tendency of conventional model cement which causes sagging between wing rib..."

Direct submission to Outerzone.

Update 25/07/2016: article pages, text & pics added, thanks to theshadow.

Supplementary file notes

Article pages, text & pics.

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