MOTOR SPORT A 17 MONOPLANE AN INTERESTING ATTEMPT AT HOME CONSTRUCTION

A •E 1 7 MONOPLANE AN INTERESTING ATTEMPT AT HOME CONSTRUCTION

N intense desire to own some sort of aircraft, and the fact that the means at my disposal completely

precluded any possibility of purchasing a machine -were the two forces which made me decide to do what many people considered foolhardy,—to build a plane myself. I will not pretend that the machine which has now materialised is an absolutely first class job or that it complies in every way with the modern standards of aircraft design, but that it flies and handles quite well, and that its construction entailed a modest expenditure of £17 is, I think, sufficient to give me no regrets that I set myself something which, from the outset, was regarded by others with doubts and disapproval.

On the score of simplicity I decided that the machine I was to build should be a monoplane, and, since I was not able to work out the involved stress calculations necessary for a full cantilever design, I planned a strut-braced high-wing arrangement. At the time when I was about to embark on the task, a large quantity of obsolete aircraft parts were for sale at a local depot. This made me consider the possibility of obtaining a wing about the right size, from a proper machine, in preference to making one. On making enquiries I learnt that there were Sopwith ” Snipe ” wings to be had, and the size was just what was wanted. Thereupon I fetched about a dozen wings and ailerons, two centre sections, two rudders, two elevators and a tail-plane, all ” Snipe “and free of charge. After carefully examining the wings I selected a top pair and centre section, these being 30′ 10” span by 5′. The remaining wings were broken up for the strainers, bolts and Rafwires, etc. The fuselage was the next item, and two methods of construction presented themselves, one, cross-wire

bracing, like a 504K Avro, and the other, longerons and struts covered with three-ply, as in the “Moth.” The former was chosen for several reasons, one of them being there was a plentiful supply of wire and strainers on hand out of the wings which were broken up, whereas with the latter type the plywood would have to be bought. Also, trammelling is easier and quicker than making jigs. I might mention here that no stress calculations were made at all and my method of arriving at the sizes of the parts required was this I measured the sizes on various machines and added a little. The four longerons were spruce from a D.H.10, and were 16′ 0″ long by 1 f” square, tapering to 1″ square. These were cut down to 1k” by r one end to 1″ by r the other. A further 3″ was spliced on the smaller end giving 19′ overall. The inter-longeron struts were

square of spruce.

With these parts I built up a fuselage rectangular in section, 2′ 6″ deep by 2′ 3″ wide, at the maximum part, the pilot’s cockpit, situated 5′ from the front and tapering to a vertical knife edge l’ high at the rear, and to a rectangular engine bearer at the front. The top longeron, side elevation, was horizontal from front to rear to avoid setting up a datum line for trammelling. The nose, as far as the pilot’s cockpit, was covered with glued and screwed plywood and had cross wire bracing to strengthen it up. The end 3′ of the tail was formed with glued and screwed 3 ply. The engine bearer consisted of a rectangular frame 2′ 6″ by 1′ 6″ made from 1 1.” by 1 i” steel angle. The question of a power unit presented certain difficulties since I required one of medium h.p., low-weight and, of necessity, low cost. After much investigation, however, a 45 h.p. 6 cylinder Anzani was secuied for £4, but it had no magneto, no carburettor, and no ail :,crew. A magneto was obtained easily and a carburettor, which at one time had done duty on an Nrmstrong-Siddeley car was unearthed, and adapted for use on the engine. The propeller left me in a quandary, until by chance, I found in a shed at Brooklands a Gnome which had served at one time on a 1912 Short tractor biplane. Having paid the small sum of Is. for this propeller,

I brought it home and experimented by lopping the blades. The engine was mounted on a test frame and started up, I having first cut 12ins. from each propeller blade. I was sure the carburation was practically right because Messrs. Zenith kindly advised me as to the choke and jet sizes necessary. 950 revs, per minute were all I could coax out of her, so a further 8in, was cut off each blade ; the propeller was now 6′ 6″ diam., and looking vay funny with its square tips. After experimenting with carburation, the revs, crept up to 1300, and, as the normal speed was 1400 I assumed that if the blades were cut to a reasonable shape this would give the extra revs., which it did.

The power plant was next bolted to a circular plate, which, in turn was bolted to the angle iron fuselage front. A tubular strut took the overhanging weight, and two short bracing wires held it at bottom. On running it up it wobbled terribly through the plate being too flimsy. This was substituted by a I” plate and everything was then splendidly rigid.

The undercarriage V came off a Sopwith “Camel,” and though rather heavy, it was extremely strong. It was fitted to the fuselage with fish plates. A false longeron was placed underneath the main longerons to strengthen them, as the internal bracing did not distribute the load properly. Elastic shock absorbers were used. Stirrup bolts running from top to bottom of the fuselage held the tail plane on to a positive incidence of 1 degree, and the rudder post was simply a piece of steel tube bolted to the end of the fuselage. A leaf from a car spring formed the tail skid.

Fabric for covering the wings and fuselage was obtained, and sewn on in the approved manner and a ” joyriding ” firm supplied the dope. At this juncture in the production of my hybrid craft,

I was fortunate in obtaining the help of a pilot friend of mine, Mr. J. S. Tanner.

Now came the task of finding the centre of gravity. This was done by balancing the fuselage (with someone in the pilot’s seat) across a pole. The centre of pressure was next discussed. In one of the text books we had on the subject was a graph showing the relative position in terms of chord length at various angles of incidence. Having decided on 4 degrees incidence, the centre section was mounted accordingly on four stout spruce struts fixed to the longerons by i” plates and braced with Rafwire. A friendly farmer lent us a field to which we took the machine for fitting the wings. Each has two outer and two inner strut sockets and wiring bars, and to each outer one an oval steel tube was fitted ; to each inner one, a cable. The strut and wire attachment underneath the fuselage consists of 11″ by -11″ steel strip sandwiched between two pieces of 11″ by r ash, with the wires running to the steel strip ; the struts are flattened at their ends, and the whole bolted up

together. Two drift wires were fitted, running from the engine plate to the tops of the rear struts to get a large angle. Two more drift wires were taken from the engine plate to the front of the centre section to assist the side panel cross bracing. An Avro centre section tank was fitted, of 4 gallons capacity.

The joystick spent its early days in an Avro, and [is. connected to the elevator via a countershaft and crossed wires. The ailerons are cable operated.

After a careful examination of everything, the machine was taxied fast up and down the field and found to answer her controls effectively. My friend then entered the cockpit, taxied into position, opened out and did a straight of about 300 yards some 10 feet off the ground. After two more straights, circuits were flown, and up to the time of storing for the winter some 31 hours were flown, and nothing at all showed signs of stress. The following are brief particulars :

Span 30′ 10″. Chord 5′ 0″. Length overall 22′ 0. Weight 800 lbs. Wing loading 5i lbs. per square foot. Power loading 171 lbs. per horse power. Stalling speed, according to pilot, 33 m.p.h. The cost was approximately as follows :

Steel tubing, struts and fuselage bracing wire came out of the spare wings.

I would like to say how well my friend, Mr. J. S. Tanner flew the machine, especially as he had not flown for some months and that the machine was untried. Some of his banks were nearly vertical. Without him the machinewould still be untried as I have only recently gone solo.

S. L. BUCKLE.