Next aircraft

F.XX 20
Type of aircraft
The Netherlands
Date first flight
25.7 m
16.5 m
4.5 m
Wing area
96.0 sq. m
number of passengers
3xWright Cyclone R-1820-F 3xWright Cyclone R-1820-F2
650 hp/690 hp each
Max. take-off weight
8850 kg
Empty weight
5350 kg
Max. speed
325 km/h
Cruise speed
250 km/h
Landing speed
110 km/h
Climb rate
5.0 m/s
6200 m
1660 km
KLM, Lufthansa, Air Tropic.
Fokker F.XX

The new Fokker FXX would fly this superfast Christmas postservice. However, on the moment of departure a enginefailure occured. Plesman then decided to choose for the slower but reliable FXVIII Pelican (Pelikaan)

Building the F.XX

Fokker F.XX cockpit

Anthony Fokker and ir. Beeling in the cockpit of a Fokker F.XX

Fokker F.XX



An elegant but unlucky bird

At 3 o'clock on the morning of 18 December 1933, several hundred well-wishers gathered on a cold and dark Schiphol airport to see off KLM's latest F.XX, the 'Zilvermeeuw' (Herring Gull) on a special Christmas mail flight to the East Indies.

The objective was to fly as fast as possible to the Dutch colony in competition with another contender, the Pander Postjager, to inaugurate a special mail service via the Indies route.

The Pander Postjager had already departed in early December, but because of an engine failure had got no further than Italy. So at this moment KLM seemed to have the advantage. However, during warm-up of the Zilvermeeuw at Schiphol, its two engines stopped one after the other because of gear failures.

Repair work would take too much time and so the F.XVIII Pelican was quickly made ready for departure to Batavia. The F.XX could not have had a worse start to its career and because of this the aircraft always had a bad name.

However, the F.XX was certainly not a bad design (and neither was the Postjager), although teething troubles during tests in the month before the ill-fated departure attempt, made the crew none too happy about the change of the aircraft.

Their trust in the proven F.XVIII was certainly greater at that moment. Aesthetically, the F.XX was one of Fokker's finest designs. its graceful lines however, could not help it succeed.

In addition to the bad luck with the intended Christmas flight, the advent of metal aircraft also played a part in the story. And so the Zilvermeeuw remained the only F.XX to be built.

The F.XX was designed at the request of KLM who wanted an aircraft for its Indies route that could fly some 30 mph faster than the Fokker F.XVIII.

Fokker F.20 Zilvermeeuw C Thijs Postma

The cabin of the Fokker F.20


With faster aircraft, KLM wanted to prove that it was not necessary to put on special 'mail' aircraft to the Indies.


Plesman was convinced that normal commercial aircraft could do the job just as well as purpose-built mail planes. Even if the F.XX failed to prove Plesman's point, the Douglas DC-2 and DC-3 showed later, during special record flights, that passenger aircraft could also perform perfectly well as mail aircraft.

Although KLM originally asked for the F.XX, the airline was not really interested in it any more. It was even difficult to persuade Plesman to take over the aircraft already built, despite it being at a giveaway price. The increase in cruise speed was largely achieved by the F.XX and subsequent Fokker types by virtue of reducing the fuselage drag.
The shape of the fuselage, which with the F.XVIII had already been rounded along the topside, was made completely eliptical on the F.XX. Fokker had previously used a pyramid-shaped frame construction for the fuselage. With the change to an elipse, model tests showed that the fuselage drag of the F.XX was only 58 per cent of that of the F.XVIII.

Retractable gear

The improved fuselage was only one of many changes compared with earlier types. An interesting addition for a Fokker commercial aircraft was a retractable main undercarriage.

This of course made an important contribution to the drag reduction. Operation of the undercarriage was performed by turning a crank handle behind the second pilot's seat to raise or lower the gear. This was one of the responsibilities of the flight engineer and was definitely not the lightest of his duties. The tail wheel was also retractable using a similar mechanism.

A further improvement in streamlining the aircraft was the NACA cowl around each engine.

The F.XX made its first flight on 3 June 1933 but without these cowls and without the undercarriage being retracted.


A large door hinged forward in front of each main wheel as the undercarriage was lowered. It was soon found that these doors caused turbulence and made the tail assembly vibrate severely.

The effect was not so much dangerous as annoying, and the turbulence disappeared once the wheels were retracted. However, as reducing the doors in size did not solve the problem, it was finally decided to remove them altogether. Later, more refinements were made to reduce the drag. For example, after studying the airflow around the nacelles, it was decided to lengthen them. Investigation of the airflow in those days was performed by means of wool tufts.

Thin tufts were attached to the area to be studied, and the direction taken up by the tufts in flight gave an indication of the local flow.

Wing flaps

The F.XX was also provided with balanced wing flaps that the pilot could adjust using a hand wheel.

The rudder was likewise balanced. For the first time, the windows of the passenger cabin could not be opened. And on both sides of the cabin, there was a window with glass that could be smashed to act as an emergency exit.

An innovation in the cockpit was the introduction of what today is a typical aircraft control column. Until then, control columns had a circular handgrip but, with the F.XX, a section was removed at the top to allow the pilot a better view of the instrument panel. It is surprising that to begin with most pilots had difficulty in using the new column: they were worried that the missing section might cause them to lose their hold.

The plywood skin of the wing section above the cabin was omitted so that more headroom was available for the passengers. Within the wing, in the part adjacent to the fuselage, luggage space was provided which could be reached from inside the cabin.

In the F.XX more Bakelite Triplex was used than on earlier Fokker designs. The F.XX had accommodation for twelve passengers and three crew members. The aircraft was fitted with three 650 hp nine-cylinder air-cooled Wright Cyclone R1820-F engines. Later, KLM replaced these with more powerful Cyclone R1820-F.2 engines of 690 hp.


The propellers were initially two-bladed and adjustable in pitch on the ground. When changing to the more powerful engines, Hamilton Standard metal propellers were fitted which were adjustable in flight. During a test on 29 June 1933 it was found that as speed was increased, heavy aileron vibration occurred. To solve this problem, the ailerons were fitted with balance weights over their full length, amounting to a total of 70 lb extra weight.

Flight testing was resumed on 11 August and it was found that the vibration and certain other adverse symptoms had disappeared. The F.XX became the first Fokker commercial aircraft to reach a speed of185mph. The flight test program, the airworthiness trials and the acceptance flights together occupied about four months.

During that period, 62 flights were made amounting to a total airborn time of 37 hours. KLM pilots also flew the aircraft and the test reports show such famous names as Aler, Beekman, Duirnelaar, Frijns, Geijsendorffer, Hondong, Parmentier, Scholte, Soer and Grosfeld.

Anthony Fokker, who had long been a keen film and photography enthusiast, had installed a cine-camera in the starboard horizontal stabilizer. This was to film the undercarriage during take-off. Ir. Marius Beeling, who was Head of the Design Department at the time, acted as camera operator.


Failure of the F.XX Christmas mail flight, as already mentioned, brought unwarranted discredit to the aircraft. Later, its reputation was largely restored when KLM opened a fast London-Amsterdam-Berlin service on 1 March 1934: average speed on the Amsterdam-Berlin leg was 157 mph.

In that same year, the F.XX flew 1,535 hours which was a record for those days, being almost double KLM's 850 hours' average utilization with the F.XVIII.

Some of the daily press drew attention to this and it was noted that "the machine has re-established itself quite successfully after its failure at the start of the Christmas mail flight".


The F.XX was in service with KLM for only a few years. In October 1936, the airline sold the aircraft to the French airline Air Tropique which actually was a cover for a Spanish organisation. Air Tropique 'sold' the F.XX to SFTA (Société Française de Transports Aériens), which was neither French nor an airline but a purchasing agent for the Spanish Nationalists.

SFTA flew the aircraft to Spain where it was used in the war raging there. The F.XX was seen on 1 May 1937 at Le Bourget airport, camouflaged and provided with a French registration.

This unique aircraft was destroyed in a crash in Spain in 1938.