|Role||Reconnaissance aircraft/passenger aircraft|
|Manufacturer||NAVO Nederlandse Automobiel en-Vleegtuig Onderneming (Dutch Motorcar and Aircraft Co.)|
|Designer||Walter Rethel and Keidel|
|First flight||29 November 1920|
|Retired||c. March 1921|
The NAVO RK-4/220 was a Dutch aircraft originally designed for unofficial crowd observation but which was completed as an airliner. Only one was built; it flew, but was never certified.
Design and development
NAVO and its only design were result of social conditions immediately after World War I, during which the Netherlands had remained neutral. Some parts of Dutch society were deeply concerned that the popular appeal of left wing movements in Germany might spread to the Netherlands and formed vigilante groups to oppose them but found that the Treaty of Versailles limited their ability to import aircraft to enforce their cause. After a bid for Luchtvaartafdeling (LVA) reconnaissance aircraft was rejected, the group in Cuijk contacted Kondor Flugzeugwerke of Gelsenkirchen and their designer Walther Rethel. They set up a company called the Nederlandse Automobiel en- Vleegtuig Onderneming, funded by a Cuijk export butcher called J. van der Eyken, to provide a Dutch base for the German engineers and the two Kondor E.III fighter aircraft they brought with them. Meanwhile the fear of a Dutch revolution had subsided and NAVO decided to develop the reconnaissance aircraft into a small airliner.
The RK-4/220 was probably named after the two designers' initials, the number of passengers and the 220 hp (164 kW) of its Benz Bz.IV six cylinder water-cooled upright inline engine. It had an aerodynamically thick parasol wing with a constant chord centre section, straight tapered outer panels and square tips. The wings were constructed using a method patented by Kondor and first used on the Kondor E.III which had slightly protuberant, close spaced ribs with narrow veneer panels, their edges secured with L-shaped strips, between them forming the skin. Kondor claimed the raised ribs improved the aerodynamics. Quite small ailerons were fitted, reaching to the tips. On each side a pair of parallel struts joined the ends of the centre section to the lower fuselage longerons, assisted by a lighter strut from the top of the forward main support to the engine mounting. Four very short vertical struts formed a cabane holding the wing immediately above the fuselage.
The fuselage was rectangular in cross-section, the underside bellying out below the wings and cabin. The Benz engine was completely enclosed and cooled by a radiator on the central leading edge of the wing. Entry to the cabin was by a tapered door in both sides; aft of the door two square windows lit the cabin, the rear ones slightly lower than the others. Despite the name the RK-4/220 could carry up to six passengers. The pilot sat in an open cockpit behind the cabin at the trailing edge. At the rear the horizontal and vertical tail leading edges were almost circular, both carrying horn balanced control surfaces; the rudder was a broad, deep oval and the elevators were cropped and with a large V cut-out for rudder movement. The RK-4/220 had a fixed conventional undercarriage of narrow track, single axle type attached by V-struts to the lower fuselage and transversely cross-braced with wires. There was a sprung tailskid.
The NAVO made its first flight from the company's field at Maldense Heath between Cuijk and Nijmegen on 29 November 1920. After further test flights it flew to Soesterberg for certification. There were delays to the tests caused by engine problems, then in March NAVO decided to remove it, uncertified, before Van der Eyken's money ran out and it is believed the RK-4/220 was broken up soon after.
Data from Wesselink
- Crew: One
- Capacity: Four passengers
- Length: 9.50 m (31 ft 2 in)
- Wingspan: 13.80 m (45 ft 3 in)
- Gross weight: 1,750 kg (3,858 lb)
- Powerplant: 1 × Benz Bz.IV 6-cylinder water-cooled upright inline engine, 160 kW (220 hp)
- Propellers: 2-bladed
- Maximum speed: 170 km/h (106 mph; 92 kn) at 1000 m (3,280 ft)