Flight, September 1922
THE BELLANCA CF FIVE-SEATER COMMERCIAL "SESQUIPLAN"
ON the occasion of the flying meeting held at Monmouth, Ill., U.S.A., last June, some considerable stir was caused in aviation circles by the appearance of a new American-built machine,
which carried off the first prizes in the four competitions in which it took part. This machine was the Bellanca CF five-seater cabin-type "Sesquiplan," or "one-and-a-half-plane." It has been designed by G. M. Bellanca - who was responsible for the successful small, low-powered biplanes bearing his name of 1918 - with the financial assistance of Victor H. Roos and others of Omaha, Nebr.
The Bellanca CF embodies several noteworthy features, such as, apart from general design, low landing speed and quick take-off, high speed with high pay load, simplicity of design, low head resistance - although not of the cantilever or internally-braced type, external bracing wires are conspicuous for their absence - and economy. The primary object before the designer was to produce a machine with an increased carrying capacity per h.p. of useful load, which at the same time had a low cost of manufacture and low cost of maintenance.
Actual flights have demonstrated that the above characteristics have been successfully fulfilled, and a remarkably efficient machine produced. With a 90 h.p. Anzani engine and pilot and four passengers, the Bellanca CF accomplished a speed of 109-8 m.p.h., over the measured course (six half-mile flights, three each direction) at the Fort Crook Army Field. The landing speed is claimed to be as low as 30 m.p.h.
In the trial flights the machine handled remarkably well, and showed a remarkable degree of inherent stability - flying several complete circles with only the rudder control in action. It also carried out all the usual "stunts" (loops, spins, etc.) in a satisfactory manner.
Before passing on to a brief description of this machine, it may be of interest to refer to the events won by this machine at the Monmouth meeting - previously mentioned. In a speed contest, it covered the 15-mile triangular course in 9 mins. 15 secs., as against 11 mins. 30 secs, put up by the second machine, fitted with a 150 h.p. engine. In the gliding contest it took 4 mins. 43 secs, to descend (engine off) from 2,000, covering a distance of 4 1/2 miles, equivalent to a gliding angle of 1 in 12. Such a performance indicates a valuable feature in the event of an engine failure when on a cross-country flight, enabling the pilot to look around for a suitable landing ground. Another event was the climbing contest, in which this machine, reached an altitude of 7,000 ft. in 11 mins.
As will be seen from the accompanying illustrations, the Bellanca CF is a monoplane with comparatively small auxiliary planes, set at a fairly pronounced dihedral angle, underneath the main planes, and serving as braces for the latter. The fuselage, which is of good streamline form, is of the composite type, and is of box-veneer construction with internal reinforcing of Port Orford cedar, forming a stiff frame of triangles and box-girder construction with cables and wires. The forward portion, just behind the engine, is formed into a roomy cabin at the top of which are the main plane attachments. The position of the cabin is such that the weight of the passengers coincides, at all times, with the centre of gravity of the machine. Thus the machine is always well-balanced, whether with full or light load. The cabin is of veneer construction, and accommodates four passengers, with comfort, the rear passengers facing forward, whilst those in front can face either forward or backward. Should occasion arise, six passengers can easily be taken in the cabin. On each side of the cabin are three windows, and in front a large window gives a good view ahead, looking over the engine. Air intakes provide for the ventilation of the cabin, and if necessary the front window can be opened as widely as desired. As the engine compartment is completely separated from the cabin, it is possible to smoke in the latter, whilst the noise from the engine is reduced to a minimum.
At the rear of the cabin is the pilot's cockpit, aft of which the fuselage tapers sharply to a vertical knife-edge. The pilot's view forward is, we should say, somewhat restricted by the top of the cabin, but by looking over the sides he has a fairly clear view forward under the main planes.
The main characteristic of the wing construction is extreme simplicity. The spars are of Port Orford cedar I-beam cross-section, and the ribs are a combination of bass wood, ash and fabric. The average strength of these ribs, which weigh about 9 ozs. each, is stated to be 700 lbs.
The wing spars extend beyond the wing roots, and pass through the top of the cabin to the attachment within, so that port and starboard spars abutt, forming thereby what is practically a continuous beam. Thus, the main stresses of the wings are not transfered to the fuselage. Extending from the lower longerons of the fuselage up to a point on the main wings about midway out from the roots are the auxiliary planes, the spars of which are splayed out near the extremities, so as to attach to the front and rear spars of the main wings; they are left uncovered at this portion, and practically speaking take the form of struts. These auxiliary wings thus take the landing and flying stresses, thereby eliminating the usual bracings, streamline struts and wires, and so considerably decreasing the weight and head resistance whilst at the same time adding to the lift. They have the further advantage of improving the lateral stability of the machine, by virtue of their pronounced dihedral angle.
The load factor for the lifting stresses is 14, the lift being taken by 1/4 in. cables attached to the spars of the main wings at the cantilever points, and passing through the auxiliary wings and through the fuselage. The load factor at the cantilever point of the rear main spar is 9 - this being the weakest point in the machine - and for the front spar 10 1/2. The safety factor for the reverse air load is 5 1/2, which is claimed to be more than sufficient. While on the subject of safety factors, it may be mentioned that the fuselage is capable of withstanding a load of 70 lbs. per sq. ft. applied at the tail, the f.s. of the various members having been figured at 2. The stabiliser and elevators are made to withstand a load of 50 lbs. per sq. ft., and the rudder a load of 35 lbs. per sq. ft. The f.s. of the landing gear is 8.
The main wings are of fairly thick section, and have an L/D of 20, the centre of pressure displacement being 10 per cent, of the chord; the drift at low angle is very small, making the wing well adapted for high speed. The cross-section of the lower wing - the thickness of which is 16 per cent, of the chord - is such that its L/D is 16-4; the combined L/D of the complete supporting unit (main wings, auxiliary planes, and resistance of short wires and struts) is 18, which compares very favourably with the internally braced wing, in that it gives lighter construction, higher L/D, and smaller drift at low lift coefficient.
The tail group is composed of a non-lifting fixed stabiliser, with divided elevators and rudder. The attachment of the stabiliser is such that it can easily be detached by removing four cotter pins. Control cables pass within the fuselage.
A 90 h.p. 10-cylindered air-cooled Anzani engine is fitted within a neat streamlined nose piece, only the cylinder heads being exposed to the open. The tractor screw, designed by Prof. Bellanca, is 8 ft. diameter by 8 ft. pitch, and is fitted with an aluminium spinner having air vents which cool the covered part of the engine. Two magnetos are fitted, and a double oil pump assures ample lubrication under all conditions.
The landing gear is of the conventional V-type, consisting of stout ash streamline struts - glued together with birch veneer - and rubber sprung axle enclosed by a fairing having a lifting cross-section.
The principal characteristics of the Bellanca CF are :-
Span (main) 40 ft.
Span (auxiliary) 22 ft.
Chord (main) 6 ft. 6 ins.
Chord (auxiliary) 2 ft. 6 ins.
Overall length 23 ft. 10 ins.
Total wing area 290 sq. ft.
Weight empty 950 lbs.
Weight loaded 1,990 lbs.
Weight/sq. ft 6-85 lbs.
Weight/h.p 22-1 lbs.
Useful pay-load 680 lbs.
Speed range (full load) 40-108 m.p.h.
Climb in 10 mins. (full load) 5,000 ft.
Range (full speed) 440 miles.
Miles per gall, of fuel 16 miles.