C-3605 Schlepp (oz1430)

About this Plan

Farner Werke C-3605 Schlepp. Free flight rubber scale model of the Swiss target tow plane.

Update 18/6/2024: Added article, thanks to PeterIngels.

Quote: "This airplane with the long nose and the strange name is ideal for Rubber Scale. Proof? It won the 1978 Nats. Schlepp, by Don Srull.

Among the most important features one looks for in a rubber-powered scale subject are the length of the fuselage and the nose length. A long fuselage can more easily carry a longer, heavier rubber motor than a short one, and a long nose moment means you can extend the motor farther to the rear of the fuselage without having to add significant nose ballast. It would be difficult to find a subject more ideally suited to rubber scale from these standpoints than the Swiss C-3605 'Schlepp' target tow aircraft. Its layout, except for the low wing, is more like a Wakefield or Unlimited rubber ship than the usual scale model.

I first saw several color photos of the Schlepp in the September 1972 issue of Air Enthusiast magazine. In addition to its fine proportions, the colorful yellow and black paint scheme made it an attractive model subject. One rather aston-ishing feature of the Schlepp, which convinced me it was made to be modeled, is the rear fuselage tow/ballast bar. It happens to be exactly where the rear rubber peg should be, and its scale size matches a diameter aluminum tube. Even the rear rubber support peg is scale!

An authentic three-view could not be found, however, so I filed the Schlepp into the bulging 'future models - maybe' file. Early last year I came across a good three-view and additional photos of the 3605 in a book called The Aircraft of the Swiss Air Force Since 1914 by Jakob Urech. I decided to build a jumbo-size (36 in span) model of the Schlepp for the 1978 Nats. Even though flight trimming was not yet finalized, and flight times were well below its potential, the Schlepp won in Outdoor Rubber Scale at Lake Charles.

The C-3605 is not a perfect rubber scale subject by any means. Among its general configuration drawbacks are the relatively small tail surfaces and the small amount of dihedral. Some scale deviations are required in these two respects to achieve good stable flight in breezy outdoor conditions. Also, for scale rubber events where takeoffs are mandatory, the landing gear legs are a little on the short side, and limit the prop to 11 to 12 inch diameter. You could increase the gear length, but I felt it would detract too much from the model's general scale appearance. For sport flying, or competitions like the Flying Aces Club rubber scale event, hand launching is OK. In this case, consider building the gear retracted, and using a larger (13 to 15 in) prop with more rubber. Be advised though: build in a de-thermalizer!

In some people's view, an additional drawback of the Schlepp is its curved, rounded fuselage lines. It certainly is no simple box, and does require a somewhat heavier bulkhead and stringer construction. Since I enjoy building such structures, I view that particular feature as a plus!

Construction: Flight performance will depend upon airframe weight, so use care in wood selection and do not beef up the structure shown - it's plenty strong enough.

Cut out all fuselage formers and ribs from medium-light balsa. The fuselage is built by the standard half-shell method. Note that the top and bottom keels are laminated from two pieces of 1/16 sq balsa. After one side is completed over the plans, the half shell can be lifted, and the other side formers and stringers added. At this stage, make sure the fuselage remains absolutely straight.

Before cutting out the wing cradle from the fuselage bottom, build the wing and tail surfaces. The wing is a simple, multi-spar design - light and strong. After sanding the wing smooth, cut out the fuselage wing cradle and carve/sand to get a good accurate fit to the wing. Next build the wing fillet of hard 1/16 and 1/32 sheet balsa onto the fuselage. When all this fits well, assemble the wing and fuselage, and add the lower formers and stringers to the wing bottom..."

Supplementary file notes

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