Трехмоторный FK 33 на девять пассажиров (использовался в компаниях "Lufthansa" и "German Aero")
Flight, December 1924
The Paris Aero Show 1924
THE KOOLHOVEN MONOPLANE
Mr. Koolhoven is also exhibiting a large scale model of a very interesting three-engined monoplane which is now being built at his works to the order of the K.L.M. This will be a large monoplane fitted with three Siddeley "Puma" engines, of which two are placed some distance out from the sides of the fuselage, while the third is to be mounted above the trailing edge of the wing. The placing of the three engines is such that with any one of them stopped the centre of thrust will not alter to any very serious extent, and it is thought that the machine will be able to fly comfortably on any two of the three engines. According to the scale model there will be seating accommodation for nine passengers, so that on this basis the power expenditure will be somewhat high - i.e., about 80 h.p. per passenger. However, the three-engined arrangement has been chosen to give immunity from forced landings, and we believe that in addition to the passengers there is lifting capacity for a fair amount of luggage and/or goods, so that actually the machine will probably be more economical than might be thought from the horsepower per passenger basis. It will certainly be interesting, and when the machine is completed we hope to be in a position to give a detailed description.
Koolhoven FK-33 with Dutch registration H-NADD. Note third engine mounted on aircraft's back
One of the novelties of the Paris Aero Show: Model of the Koolhoven three-engined commercial sesquiplan. Two of the three Siddeley "Puma" engines are mounted on the short lower plane stumps and drive tractor air-screws, while the third engine, driving a propeller, is mounted on the top plane above the fuselage.