A NEW EXPERIMENTAL MONOPLANE
An Interesting Machine Built on New Principles.
WHEN the Mono-Spar system of wing construction was first made public, on the occasion of the last Aero Show at Olympia, it created a great deal of interest amongst all those technically-minded people who inspected it, since it represented a clear breakaway from existing practices and principles employed in aircraft construction. The interest attached to it was not merely on account of it being something new, however ; for it clearly offered fresh possibilities in the construction of a full cantilever monoplane wing with an extremely low structure weight. The student of aeronautics will have seen clearly that the trend of design during the past few years has been towards better performance—the cruising and top speed of ‘planes of all types are increasing more and more— and since this increase demands the elimination of parasitic drag, the cantilever monoplane with its clean exterior form has come very much into favour. Hitherto the good qualities of the cantilever aerofoil have not been obtained without the disadvantage of a rather high structure weight, and, as has already been said, the big point of the
Mono Spar is that this weight is greatly reduced by the system of construction employed.
The MonoSpar wing was invented about four years ago by Mr. H. J. Stieger, a young Swiss en gineeer. As a result of a theoretical analysis of aeroplane construction in general he came to the conclusion that the pro vision of torsional stiffness in a full-cantilever wing at the minimum expense in weight was the fundamental problem which required solving. In a wing built up in
the ordinary way with two spars, all the material in the two main members is never fully stressed ; when the centre of pressure, for instance, is in its most forward position, the rear spar is only partially stressed, and similarly, with the front spar when the centre of pressure of the wing is in its rearmost position. Obviously, since there is nothing else to take it, in a single-spar wing the whole of the load is taken all the time by the single member, but, contrary to what one might assume, a single spar can be designed to take the place of two spars and yet be 40 per cent. lighter in weight. The trouble met with in using the single-spar system is in making the wing sufficiently rigid in torsion ; the method of overcoming this in the past has been the utilisation of metal or three-ply wood covering in place of fabric, but this means more weight. The Mono-Spar system consists of a single main member, strong in bending but braced against torsion by an arrangement of struts and ties. As can be seen from the sketch, the tie rods are in pyramid formation, being anchored at their apices to the extremities of the tubular struts which pass through the spar, and to plates on the top and bottom face of • the spar at a point where the tie rods intersect. The drag and anti-drag members are fixed to the front and rear ends of
tubular struts. When Mr. Stieger first introduced his wing into this the Air Ministry carried out extensive tests it at the R.A.E., Farnborough, and the results that the claims made by him as regards strength,
stiffness and weight were fully justified. More recently a complete machine has been designed embodying the Mono-Spar system not only in the wing structure, but in. the fuselage as well, and this has now been completed and tested. This experimental craft has been built for the Mono-Spar concern by the Gloster Aircraft Co., Ltd. ; it is the low-wing cabin type, and has two 50 h.p. type 9 AD Salmson engines mounted on the wing. The cabin provides accommodation for the pilot and two passengers. The main plane is built up in three sections, the centre portion being made integrally with the fuselage; this centre section
carries the mountings for the two Salmsons, and an interesting feature is that the main members of these mountings are in one with, and extensions of, the tubular struts which pass through the spar. The latter is a Duralumin I-beam built up of a number of members with lattice-work bracing. The form ribs are also of metal, and the fabric covering is wired to these. The two outer sections of the plane are attached to the centre section by three bolts, and the ailerons are carried on a false spar. This is set at a pronounced angle to the main spat, running from the wing tip to the last bay of internal bracing, which is situated about halfway in the span. The application of the Mono-Spar principle to the fuselage layout has been carried out very cleverly. As with the wing, the main member is a Dural beam, and this is placed at the bottom of the fuselage and anchored to the centre-section by a large tubular ” V” fixing. This main member carries a superstructure of hoops and stringers, which form the framework for the fuselage covering, and, being braced, these also serve to stiffen up the assembly as a whole. The undercarriage of the machine follows modern practice in design, being of the axleless type with the shock absorbing medium enclosed in the main ” legs.” The wheels are fitted with brakes, and an experimental arrangement is being tried out in which their application can be made when the pilot
pulls the stick right back in making a three-point landing. This action can be thrown in or out of engagement at the will of the pilot by a simple release, and an. additional independent control by a centrally placed lever is also provided.
The tail unit of the Mono-Spar is of the usual type, and the framework of the rudder (which is partially balanced), the fin, elevators and tailplane is of metal with a fabric covering. The layout of the cabin is well arranged ; the pilot’s seat is in front, where, owing to the large windows, the view is extremely good. One passenger sits next to the pilot, and the third seat is behind. The controls comprise the usual stick and rudder-bar, and the streamlined nose of the fuselage houses the main fuel tank, which provides a gravity feed to both engines.
This first machine has been built solely as an experiment, and while various modifications will naturally be made before a production model is put in hand, the performance figures are highly satisfactory, and practical tests have shown that the machine has achieved the purposes for which it was produced. The one outstanding point is, perhaps, that in the Mono-Spar monoplane we now have a twin-engined three-seater cabin machine (with a full-cantilever wing) which weighs no more than the average two-seater light aeroplane.
piLoTs flying abroad from this country are reminded that a refund of the duty paid on petrol taken on board at the port of clearance outwards, can be obtained from H.M. Customs and Excise, if application is made on the proper form. A.A. members may obtain these forms with their
other foreign touring documents on application to the Aviation Department, The Automobile Association, Panum House, New Coventry Street, London, W.1.
Members clearing customs outwards at Heston Air Port may apply for the refund through Airwork Limited, who make a nominal charge of 10% for their services.
CONCESSION TO OWNER-PILOTS.
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