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Typenumber	F.25 Promotor
Type of aircraft	Passengerplane airtaxi
Country	Netherlands
Date	1946
Crew	1
Wingspan	12.01 m
Lenght	8.53 m
Height	2.64 m
number of passengers	3
Enginetype	Lycoming O-435A
Enginepower	190 hp
Max. take-off weight	1425 kg
Empty weight	960 kg
Cruise speed	209 km/h
Range	950 km

Fokker F.25 Promotor

A neat executive plane

The end of the Second World War was also almost the end of Fokker as a manufacturer of aircraft. in late 1944 the Nazi occupying forces had removed all machinery, equipment, materials and stock to Germany, and virtually all the company's factory buildings had been destroyed.

This meant that after Germany's surrender, reconstruction of the buildings and Fokker organization had to start all over again - but needless to say, everyone worked with great enthusiasm.

The majority of Fokker employees were on reduced pay at the time.

They were called back to work in provisional accommodation or even in the open air. Not everyone could resume their old job, at least not initially, but that was the least of problems. People did what had to be done to get Fokker going again.

Then, gradually, they were able to return to their former jobs and departments. It took over a year to rebuild the heavily damaged factory at Amsterdam-North.

Once operational again, one of its first post-war contracts was to convert surplus military Douglas Dakotas for passenger transportation. These aircraft went to airlines all over Europe that were restarting their route networks.

Fokker also built several hundred buses to help meet the urgent need to renew the Dutch public transport service which was almost non-existent after the war. Fokker was of course an aircraft manufacturer and it was aircraft that it most wanted to build. So, even before the end of 1945, the Design Department was working on the first post-war design to take physical shape.

This was the F25 Promotor, an attractive little four-seat business aircraft.

The pilot was located up front to the left, and the three passengers sat on a wide couch behind him.

The layout was twin-boom with a pusher propeller, showing some resemblance to the pre-war Fokker G.1.

Brainchild

The F25 was actually the wartime brainchild of Frits Diepen, a garage owner of Bergen op Zoom in southern Holland. As the war dragged on, Diepen's car business declined, so he turned his attention to his other interest, aircraft.

As hostilities continued, he built - although strictly 'verboten' - a small sports/business plane. This was the Difoga 421, that is Diepen Ford Garage, design 1942 number 1. The actual design work was performed by Ir. H Koekebakker, an aeronautical engineer living in the same town as Diepen. Building the aircraft was not without its difficulties.

With the non-availability of suitable materials, substitutes had to be used which were as unairworthy as the powerplant, a Ford V-8 car engine.

But after the war, the Difoga did fly.

It was not a great success - but nobody really expected it to be. Even so, Diepen still found the basic concept of a short fuselage with twin tail booms and pusher prop, very appealing. He contacted Fokker and the outcome was the F25 Promotor of which Diepen ordered 100. Some of these Diepen intended to use in his airtaxi and charter company, and the others he planned to sell.

The contract with Fokker gave Diepen exclusive sales rights. From a technical point of view, the F25 was clearly not revolutionary. Pre-war construction methods were used. The wing and fuselage were all wood except for the engine mounting and cowling. The tailbooms were of metal however as Fokker, after having stayed with wooden construction for so long, was finally coming to accept that aircraft had to be metal.

First flight

Maiden flight of the Promotor was on 20 October 1946. After only its second flight, the aircraft was disassembled and transported to France for the first post-war Paris Air Show. Back in Holland after the Show, flight testing began in earnest and it soon became apparent that the short stubby fuselage generated more drag than anticipated. This resulted in a speed performance well below design calculations. A number of modifications were embodied, including the addition of small dorsal fins to the vertical stabilizers.

The most critical change however was the lengthening of the rear fuselage, in turn necessitating a longer prop shaft. Rather severe vibration of this shaft when running, ruined the bearings. Ir. Marius Beeling, who was in charge of the F25 program, designed a new layout for the lengthened shaft and its bearings.

This was successfully tested on a rig in mid-1949, but was never tried on the aircraft itself. This was because the sales prospects for the Fokker plane were rapidly collapsing following the offer for sale of thousands of small surplus military aircraft.

These effectively saturated the market for which the F25 was intended.

Further market analysis showed that to continue with the program was no longer viable. In any case, the company had meanwhile been awarded a contract for 100 Fokker S.11 military trainers and to manufacture two types simultaneously was beyond its capabilities at the time. A choice had to be made and as sales prospects for the S.11 were more promising than for the F25, the latter was dropped.

Production of the F25 was terminated in 1949 when aircraft number 21 was under construction. Just prior to termination of the program, two F25s had been sent to Spain for flight testing.
The Spanish climate was normally less capricious than that of Holland, enabling greater continuity of testing. However, no test flights were ever made in Spain. Shortly after the aircraft had arrived in the country, an exceptionally heavy hail storm so damaged the F25s, which were parked outside, that flying was impossible. As local repair was not feasible, the aircraft were stripped down and returned to Holland.

Everyone at Fokker involved in the program regretted its demise. The Promotor was not only Fokker's first post-war aircraft, it was a charming little airplane. Despite this, all F25s were broken up and none was saved for posterity.