Flight, February 1927

A NEW KOOLHOVEN LIGHT 'PLANE
The "Pusher" Up-to-Date

   IT may be recollected that at the Elta exhibition at Amsterdam in 1919 was exhibited a very small monoplane, the Bat "Crow," designed by Mr. Frederick Koolhoven, who was at that time designer to the B.A.T. Company. The "Crow" was never much of a success, but it undoubtedly had in it the germ of something really worth developing. It would be a stretch of the imagination to claim that the Koolhoven machine illustrated herewith is a direct descendant of the "Crow," but just as the latter was, so to speak, the modernised version of the Santos Dumont "Demoiselle," so the latest Koolhoven light 'plane can be said to be the modernised version of the "pusher."
   Mr. Frederick Koolhoven was never the man to be content to follow orthodox lines merely to save himself trouble, and he never minded doing a bit of hard thinking, as some of his very original aeroplanes testify. In this latest machine of his he has once more struck out along original lines, and the result is certainly interesting. As the general arrangement drawings show, the new Koolhoven two-seater touring and sporting machine is a parasol cantilever monoplane fitted with a "pusher" engine. The usual open tail booms associated with the pre-war and war-time "pusher" have given place to a thinned-down fuselage carrying the tail surfaces and tail skid, and the engine (a five-cylinder radial, is shown, but presumably any other suitable radial can be fitted if desired), is supported on the wing structure and placed aft of the wing. The result is a machine giving an exceptionally good view to both occupants, as well as getting them out of the slipstream. The noise from the engine also is far less troublesome in a pusher, while there is no oil or exhaust gases blown back on the pilot and passenger.
   A very interesting feature of the machine is the manner in which the monoplane wing is "folded." The entire wing, complete with engine mounting, engine and propeller, is supported on struts from a form of turntable situated on top of the fuselage and taking its bearing on or in the fuselage. A simple locking arrangement is provided whereby the wing can be locked either in the "natural" position or in the "folded." The operation is carried out in a couple of minutes.
   (It may be recollected that in a series of articles by "Marco Polo," published in FLIGHT in March, 1920, entitled "The Case for the Cantilever Wing," a sketch design was given —March 18, p. 313—of a parasol monoplane in which the wing was "folded" in this manner. As the machine was a tractor, the necessity for the turntable was not, however present.)
   At present it is not known whether the position of the engine is such that direct gravity feed can be employed if the tank is placed in the wing. Normally sufficient head should be available, although possibly difficulty might arise when opening up the engine after a long steep glide. However, that is mainly a question of carburettor position on the particular engine used.
   The undercarriage of the Koolhoven light 'plane is of the oleo type, and as the stroke provided is long (about 1 foot), the machine should be able to withstand rough handling. With the rather long nose of the fuselage, and its very low position over the ground, it should be next to impossible to turn the machine over, especially as the wheel track is wide.
   That this type of machine has a number of advantages cannot be denied. As is usually the case, these are accompanied by a few disadvantages. For instance, the placing of the engine results in a high centre of thrust, but with the relatively small forces in question this is probably not a serious matter. Flying-boats are handled successfully with much greater forces involved. Objection number two is that a broken propeller might damage the fuselage and so imperil the support of the tail. A broken propeller is, however, a rare occurrence nowadays. Objection number three: that with the rear portion of the fuselage of such small cross-sectional area, a somewhat heavier structure may be required to give rigidity than would otherwise be necessary. Again this probably does not amount to a great deal. Altogether the experiment seems to be one very well worth trying.
   It is interesting to learn that Mr. Clifford Harmon, President of the International League of Aviators, has ordered one of these machines for use in visiting sections of the League all over Europe.
   The main data are: Length o.a. with wing "folded," 9-25 m. (30-3 ft.); length o.a., with wing spread, 8 m. (26-3 ft.); wing span, 8-5 m. (27-9 ft.); weight of machine empty, 600 lbs.; weight loaded with two occupants and 5 hrs.' fuel, 1,180 lbs.; cruising speed, 80 m.p.h.; landing speed, 33 m.p.h. The latter figure seems somewhat doubtful.
   Owing to the small size of this machine, Mr. Koolhoven is selling with it a packing case slightly better finished than the ordinary, which can be used as a garage or hangar, as well, so that the owner can "settle" in a convenient field and can change his base very easily when required.

Flight, January 1928

THE NEW KOOLHOVEN LIGHT 'PLANE
The F.K.30 "Toerist" With Siemens Engine

   IN our issue of February 3, 1927, we published general arrangement drawings and a description of a new light monoplane designed by Mr. Frederick Koolhoven of Rijswijk, Holland. At the time, the machine had just been designed, and the work of construction had not been commenced. The machine has now been completed and has, we understand, been put through some of its flying tests. It may be recollected that one of these machines was ordered by Mr. Clifford Harmon, President of the International League of Aviators, who intends to use it for visiting the various European posts of the League.
   The F.K. 30 is of very unusual design, and may be said to represent an attempt to combine the comfort and view of the old pre-war "pusher" type of machine with the aerodynamic efficiency of modern aircraft. Whether or not Mr. Koolhoven has succeeded in this aim cannot be said until complete test results are available, and some practical experience has shown how the machine behaves in regular use. That there will be minor "teething troubles" to get through is to be expected in a type which differs so materially from the normal.
   A comparison between the photograph published this week, which has just been received, and the general arrangement drawings published in our February 3 issue, it will be observed that certain minor changes have been made since the original lay-out of the machine. These, however, are not of a nature to cause any fundamental changes in the design, which remains a parasol "pusher" semi-cantilever monoplane. Apart from the "pusher" arrangement, the Koolhoven F.K. 30 is remarkable on account of the "turntable" mounting of the wing and engine unit. This turntable, secured to the fuselage structure just below the engine, supports the whole superstructure. Normally, the turntable is locked in position with the wing "spread," but by undoing a quick-release the turntable can be rotated, bringing the wing into a fore-and-aft or "folded" position, the engine taking part in this rotation. With the wing "folded," the engine is outboard, and thus throws a load oil that side of the undercarriage, but as the wheel track is wide, there is probably little or no tendency for the machine to tilt over. From the photograph it will be noted that the wheels are somewhat "knock-kneed." At the moment it is not quite clear whether this is due to the shock absorbers not having been in place when the photograph was taken, or to too weak rubbers. At any rate, this position probably represents maximum travel, which in this machine is very large, something like one foot, as against the three or four inches more usually found on small machines.
   The fuselage and wing are both covered with three-ply, so that there should be no question of rigging or keeping in trim the machine during use. In the deep portion of the fuselage, under the engine mounting, is a large luggage compartment. The two seats are arranged in tandem, and dual controls are provided. The view is particularly good forward and down as there is neither engine nor wing in front to obstruct it.
   The high centre of thrust resulting from this unusual arrangement of the machine may be expected to have an effect on the trim according to whether the engine is running or not, but the same applies in large flying-boats, where the forces are much greater, and with proper design there is no reason to believe that this should give rise to any trouble. The slight loss in efficiency due to the down load on the tail probably does not amount to a great deal either, and if the advantages of the "pusher" can be attained without much sacrifice in performance or trim, they would be well worth having. The narrow and shallow rear portion of the fuselage is open to objection on the score that it will require to be comparatively substantially built so as to give the strength necessary to carry a tail mounted high above it, and in the slipstream of, and fairly close to, the propeller. This feature, however, is Mr. Koolhoven's modern manner of getting away from the open tail girders of the old "pushers." To keep the machine small and compact, Mr. Koolhoven has had to use a fairly heavy wing loading, although a wing section of fairly deep camber helps to keep down the landing speed, which is claimed to be only about 40 m.p.h.
   There is no fuel in the fuselage, the petrol being contained in two tanks in the wing, one on each side some little distance out. As the engine is entirely exposed, there should be little or no risk of fire, especially as the pipes from the tank have been so arranged as to reduce to a minimum the consequences of a fractured pipe.
   The Koolhoven F.K. 30 shown in the photograph is fitted with a Siemens engine, but we gather that if desired it can be supplied with a "Genet" or other similar engine of approximately the same power.
   The F.K. 30 weighs 330 kgs. (726 lbs.) empty, and carries a useful load of 300 kgs. (660 lbs.), giving a total loaded weight of 630 kgs. (1,386 lbs.). The useful load can be composed of pilot, passenger, 90 lbs. of luggage, and five hours' fuel, or, of course, any other combination giving the same total, such as more luggage and less fuel, and so forth. The packing case for the machine is constructed to be used as hangar and workshop.