O.Thetford, P.Gray German Aircraft of the First World War (Putnam)
Fokker M 6
Although the wing was raised, this modified M 5 airframe could not be strictly classed as parasol, as rear spar was fastened to the upper longerons. The M 6 was a two-seater which appeared in June 1914, and the single prototype was subsequently destroyed in a fatal crash. Engine, 80 h.p. Oberursel U O rotary.
Fokker M 8
The M 8 was the production version of the unfortunate M 6. The wing was in the same position, although the forward decking was extended up to the front spar. The fuselage sides were cut away at the cockpit area to give improved downward visibility. First built in September 1914, some thirty machines were supplied (military designation A I) and used on artillery spotting duties. Engine remained 80 h.p. Oberursel, although some sources credit the 100 h.p. engine from that factory.
Flight, December 10, 1915.
THE CAPTURED GERMAN FOKKER MONOPLANE
ALTHOUGH not being able to lay any claim to being one of the latest types, such as could the Albatros reconnaissance biplane described recently, the captured Fokker monoplane is interesting, if for no other reason, on account of the example it furnishes of what a German aeroplane constructor can, and does do when laying himself out to incorporate his own ideas of construction into a design which is a palpable "crib" of a successful French design. Let it be said at the outset that, considered as a whole, the Fokker monoplane does not appear to us to be an improvement on the French Morane-Saulnier or on its British version as produced by the Grahame-White Aviation Co. It is true that several of the constructional details are very neatly thought out, but these, we think, are more than counterbalanced by shortcomings in other directions.
Aerodynamically the Fokker monoplane differs from the Morane in its proportions and also in the wing section, which is totally dissimilar to that of the French monoplane, having a much flatter "nose" or leading edge and revealing on inspection an entirely different lower camber with its maximum ordinate much farther back from the leading edge.
When turning to the constructional work of the Fokker monoplane radical departures from the French design are noticed. Chief of these is the building up of the body of steel tubes throughout its entire length. In fact with the exception of the wings, which have spars and ribs of wood, the whole machine is constructed of steel tubing. Whether or not this is an advantage is, perhaps, a debatable point, each of the two forms of construction possessing its own merits and disadvantages. By way of example of the last-mentioned, it may be pointed out that a steel tube, while quite strong in its way, may very easily have its strength dangerously impaired by an in itself trivial cause, such as a slight dent made by the dropping of a tool or even by an accidental knock with the toe of a boot.
In the Fokker monoplane longitudinals as well as struts and cross members of the body are, as we have already pointed out, made of steel tubing wrapped with some material that looks like oil cloth, and the function of which probably is to exclude moisture. In shape the body is of rectangular section tapering like that of the Morane to a horizontal knife-edge at the rear. This horizontal stern post takes the form of a short steel tube which serves as a bearing for the main transverse tube of the elevator. This member, which is exactly similar in form to that of the Morane, is also built up of steel tubes and is partly balanced by the portions of it that are in front of the pivoting line. Of similar construction is the rudder, which, as will be seen from the illustrations, consists, roughly speaking, of two semicircles, of which the smaller is in front of the rudder post, thus serving to bring the centre of pressure and the centre of support closer together than they are in an unbalanced rudder.
Carried partly on an extension of the rudder-post and partly on a pyramid formed by four steel tubes is a short skid, sprung in the usual manner by rubber bands, which prevents the tail planes from coming in contact with the ground.
Pilot and passenger are accommodated in a common cockpit, a seat of the kind generally known as the "bucket" type being provided for the pilot, while the passenger apparently has to be satisfied with just a plain board placed immediately behind the pilot's seat. The controls are of the usual type, a central column for the warp and elevator, and a pivoted footbar for the rudder. At the top the lever is terminated by a double handle grip as shown in one of our sketches. On the central portion of this handle is mounted the cut-out switch for the engine in a position where it is within easy reach of either hand.
Owing to the position of the occupants between the main spars of the wings the view in a downward direction is somewhat restricted. In order to improve it the leading and trailing edges have been cut away near the body as shown in the plan view of the machine, and, probably for purposes of facility in firing downwards, windows have been provided in the upper half of the sides of the body. As the aim of the gunner would be made somewhat more difficult by the rush of air that would find its way inwards and upwards through this opening, a small wind screen has been placed at the forward end of it as shown in the illustrations.
In front the body has been enclosed by aluminium sheeting, a cowl of the same material surrounding the upper half of the engine. This cowl, like so many other parts of the design, is very similar to that of the Morane, being provided at its rearward end with two curved shields, which collect the oil thrown out by the engine and prevent it from being blown back along the sides of the body.
The engine, an 80 h.p. version of the Gnome, known in Germany as the Oberursel, is mounted on overhung bearings a la Morane, and drives an Integral propeller of 8 ft. 4 ins. diameter. The Oberursel does not, as far as one is able to judge from oubward appearances, seem to be nearly as well made as the original Gnome, although in fairness to its makers one should perhaps give them the benefit of the doubt and admit that this may be due to hard usage and long service. Otherwise it does not differ, again as far as can be seen from an external inspection, from the Gnome motor of the same type and h.p. The tanks are placed as in the Morane, i.e., the petrol service tank and the oil tank being mounted in the front portion of the body, while the reserve petrol tank is placed just behind the cockpit. Placed above the top covering of the body in front of the wind shield is a petrol gauge, or, as the Germans call it, Benzin Uhl (petrol clock), not inaptly since it is provided with hands like a clock and calibrated to indicate the number of litres of petrol in the tank.
One of the greatest departures from Morane practice is, perhaps, to be found in the design of the under-carriage. Whether Mr. Fokker's chassis design is an improvement on that of the French machine is, to our way of thinking, a very great question. If properly carried out the German form of under-carriage might be equal to the well-known Morane, but, as exemplified in the specimen captured, it certainly leaves room for great improvements in the detail construction. The general arrangement will be readily followed by reference to our illustrations. A longitudinal member, formed of a steel tube, is carried on two pairs of "Vee" steel tubes secured to the lower longitudinals of the body. Hinged to this tube near the point of attachment to the front "Vee" are the two stub axles, which slope downwards towards the wheels. Two other tubes slope upwards to the sides of the body, where they are linked to short transverse horizontal levers pivoted centrally in the floor of the body. Shock absorbers wound round these levers and a transverse strut in the body provide the springing. A diagrammatic sketch of the arrangement will, supplemented by sketches of the details, explain the action. From the axles radius rods in the form of steel tubes run to the apex of the rear "Vee," the hinge forming the fulcrum for the radius rods as well as those for the stub axles being of a decidedly flimsy character. Again, the attachment of the lift cables to the forward end of the longitudinal member of the chassis looks somewhat amateurish, the cables simply being spliced with an eye sufficiently large to slip over the end of the tube, where it is secured by a washer, which again is held in position by a split pin. Although looking rather unfinished, this form of attachment probably is quite adequate, but it cannot compare in neatness with the Morane method of securing the lift cables.
One very neat fitting we noticed in the bracing system of the wings, i.e., the quick release by means of which the bracing cables are attached to the wing spars. It consists, as will be seen from the accompanying sketch, of a hemispherical hollow socket having cut in its side a T-shaped slot and secured, how we were unable to ascertain, to the sheet steel clip gripping one half of the spar. In the top of the T the flat head of the turn buckle has just room to pass, all that is necessary to detach the cable from the spar being to slacken the cable by giving the turnbuckle a few twists and the head may be pulled out of the cross slot of the T. In a similar way the cable is quickly attached by reversing the process.
In plan form the wings of the Fokker are similar to those of the Morane, having their ends considerably raked so as to increase the effectiveness of the warp. The main spars, which are of I section wood, are fitted at the root with a socket terminating in an eye through which a short bolt passes, thereby securing the spar to the corresponding lug on the side of the body of the machine. On each side of the body and a short distance in front of the chassis struts is a bracket having at its outer end an eye of the same size as that of the spar lug. When it is desired to transport the Fokker by road the wings are detached in the manner described above, and the front spar is placed with its root on this bracket, the same bolt that is used for securing the spar in the flying position being employed to secure it to the bracket for transport. A steel hook bolted to the front spar near its outer end fits into a socket a few inches in front of the tail skid attachment, and when a couple of straps have been taken around the wings the machine is ready for transport.
The top wing cables are attached to a two-legged cabane of steel tubes as in the Morane. From the apex of this cabane two cables are taken to the top of the engine bearer, thus staying it in a forward direction. Being placed in line with the front wing spars the top warp cables, which pass over pulleys, naturally slope backwards to the rear spar, thereby providing the rearward staying of the cabane. The lower warp cables run from the wings to short crank levers on the apex of the rear "Vee" of the undercarriage, these levers being operated through vertical cables by a transverse crank lever on the longitudinal rocking shaft inside the body. The warp cables, it will be noticed, are not in line with the front cables, the reason being that the rear spar is longer than the front, and requires different spacing of cable attachments to preserve the load distribution.