Rc model of the Koolhoven F.K.49

Rc model built to take part in the FAI (world) championships, in scale 1:6. First flight March 2, 2001.
Modeller: Bert Hazeborg, Lelystad.

This scale project started 1995. Bert Hazeborg was looking for a unique model to take part in the FAI scale championships. It had to be multi engined and he would like very much to build a Dutch plane. In the book on Koolhoven by Thijs Postma and Theo Wesselink, he found the F.K.49, a twin engined aircraft from 1935, with a very characteristic appearance. The first F.K.49 produced was operated by the LVA (the pre-war Dutch Airforce) for aerial photography and cartography. Being a cartographic surveyor by profession, Bert had another reason to choose this plane.

Bert used the three view from the book as a base for his scale plan, but the illustration was far from accurate and soon the work got stuck. The Foundation helped him out with copies of photographs and one remaining drawing of the tail planes. (Further drawings of the F.K.49 do not exist anymore.) More information would perhaps follow since the Foundation was in the process of tracing former Koolhoven employees who might still have Koolhoven material in their possession.

In the years following, information slowly gathered. Bert kept working on his drawings which were regular send to the Foundation for approval and received back with remarks in red. Finally, in 1997, Bert could be certain about the outlines of the F.K.49 and made his start building.

While building, the research continued and details were drawn out with help from further received material such as photographs, sketches, technical descriptions and original correspondence concerning the building of the F.K.49.
The LVA color's turned out to be old color numbers of the paint factory Sikkens. The colors to these numbers could not be traced anymore. Bert suspected them to be only slightly different from RAL colors. This could be checked with a factory model of an LVA F.K.51 in possession of the Foundation. These wooden models were painted with the paint used for the production planes. Eventually all the F.K.49's colors were found in the RAL color system.
Documentation on the engines, cowlings and exhausts was easy to get since the F.K.49 was engined with Gipsy Major's I (as used for the well known Tiger Moth).

In 1998 the Foundation had gathered enough material to publish a profile on the F.K.49 (see "publications"). Having worked on the aircraft for so long, Bert was able to contribute to the information, plus he would produce the official three view for the profile.

Construction of the model

The fuselage of the model is a traditional spruce and balsa construction except for the cabin area which had to show the original welded frame. This steel frame is imitated by carbon tube from a kite shop. Carbon tube has great push and pull strength so it could be used as an actual part of the construction.

Solartex is used to cover the fuselage because its structure matches the scale structure. Stitchings were imitated with strings of white glue and covered with Solartex strips.

The wing is divided in three parts, the centerpiece with engines and landing gear built to the fuselage. All three parts are cut from tempex, covered with balsa sheets and finished with glass cloth and poly-urethane lacquer. The original wooden plating is imitated making use of drawing film and thin cardboard with 'panel lines' and 'sunk nails' pressed into it.

The tail planes are built from ribs and box shaped longerons laminated from plywood and balsa. Hinges were built similar to the original, making use of aluminum tube, collars of pvc tube and steel band.

Metal parts, such as scale exhausts, oleo struts, tail gear and hubs for the wheels, have been fabricated by a friend with a real talent for metal working. Springs are used for the oleo struts which have scale deflection. The hubs consist of two aluminum halves with built in brakes. Hub covers could be made from gas can bottoms. The tyres come from standard model wheels and have been made realistic by light sanding.

Because of the many cabin windows, cockpit detail was very important. Everything is built into it, up to the backside of the instrument panels. The pilot dolls could be modelled after a photograph of the crew, which is done in latex by 'Pete's Pilots' in Stafford, England.

In the back of the cabin the cartography camera is standing; a very intriguing feature.

To avoid wires in the cabin, the model is equipped with two receivers. One is stored in the wing's centerpiece together with the servo's for the controls. The second receiver for brakes and lights, could be placed in the box under the seat of the second pilot where originally the batteries were stored.

A lot of scale details. (The dent in the nose is scale too.)

Flying the model
First flight March 2, 2001

After thoroughly adjusting the engines, a carefull first run and a little hop on which the controls felt right, there was no more excuse for Bert to fly. At half throttle the F.K.49 majestically lifted itself up in the air for what would become a very nervous experience. The model turned out to be extremely sensitive at its controls.
After having programmed quite some exponential into the elevator and ailerons, the next flights were far more enjoyable. Even though the model is a bit tail heavy in flight and nose heavy at low speed, which is caused by a somewhat small stabilizer.

The F.K.49 is not easy, but very rewarding to fly. Its cruising speed is realistic. A beautiful sight! And the sound of two four strokes running synchronous at one third throttle! ... like the real thing, perhaps even better.

The Koolhoven F.K.49 model at the World Scale Championships
July 12 to July 21, 2002

In 2002 Bert and his model took part in the World Scale Championships, which were held in Canada that year. Unfortunately he was not very lucky at his first world championship. Engine failure at he start of his third flight made him lose his last change to score. He ended somewhere at the bottom of the list. Better luck next time!
Nevertheless his model received quite some attention. Bert had to answer a lot of questions about this "strange Fokker".

Specifications

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