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Aviation History
1969
1969 - 2115.PDF
838 BRITTEN-NORMAN BN-3 NYMPH . . . interna] structures are then temporarily joined by the master holes, using clips so that the remaining rivet holes may be drilled. Before final assembly the parts are taken apart for cleaning and corrosion protection (if desired) but de-burring the holes is not recommended, as this has been found to cause a tendency to open-out the holes in thin material. Skins are then attached in convenient panels—first by clips while the remaining holes are drilled and then finally Cherry-riveted. The 'tween-spars panels go on first, followed by the wrap around leading edges. The control surfaces are very simple structures with a minimum of internal stiffening, but with skin fluting. The single-piece metal fuel tanks fit between the spars at the inboard section of each wing. The tanks are riveted and welded from a number of pieces, but for production there may be a single base pan and welded-on top. The wing spar and strut root-end attachments can be of an optional kind to permit wing folding on the ground for economical hangarage. The fuselage structure of the prototype is not fully represen tative of the visualised production version. In the interests of rapid construction of the first aircraft this was made along conventional lines, using frame boards and jigging. The antici pated scheme for the kit-built fuselage is for assembly to begin with the riveting together of the central box com prising the single-piece door frame pressing, undercarriage/ strut transverse box. and the two wing-spar carry-through beams. The firewall, front decking and panel/control column support beam' will be located on the centre box in a vertical position. This latter method of assembly is expected to be the easiest way in which to check the correct alignment and relative position of the wing spar pick-ups and engine bearer attachment points. The fuselage back-end will then be attached in cantilever fashion, beginning with the single-piece U-shaped bottom skin complete with stringers and frames, followed by the addition of the two side/top pieces. The tailplane hinge attachments are drilled after ensuring correct plan-alignment of the actual surface relative to the wing. Door assembly and fitting should be simplified by the use of the single frame pressing. The main undercarriage on the prototype is a pair of Cessna 172 spring steel legs, but on production aircraft these may be replaced by a tapered spring rod. Access for all equipment stowage appears to be very good. Without the windscreen in place the back of the instrument panel is laid bare for connecting up wires, pipes and control cables. All cables run back along the outside of the fuselage bottom main skin and are covered by a readily detached fair ing. The further unusual routeing of the aileron cables via the back end of the fuselage, and the positioning of the flap motor in the tail, was chosen for minimum weight and least circuit drag in the absence of sufficient strong points for pul ley mountings in the region of the cabin aft frame. In the wings the aileron and flap control cables pass along the out side of the aft face of the rear spar, and are readily accessible since the flaps may be pulled down by hand without the release of any catches (the mechanism pushes the flaps down while a bungee and air pressure keeps them up). Most of the detail in the engine mounting and cooling has followed the Piper Colt practice—including the bearer design incorporating the nose leg, which on the prototype is a Colt component. The nose cowling (incorporating the landing lights) and the matching spinner have been specially devised. Costs and prices Britten-Norman have estimated that the recommended price for the basic Nymph 115 will be $12,600 (£5,250) ex-works in most countries. This is likely to fall between that of the Cessna 150 and the Cessna 172 in neutral markets and will be about the same as the 172 in North America, but will be considerably less than either type in Britain. The comparing of overall prices is complicated by the many different taxation and import terms applicable in various countries. Some allow the duty-free import of aircraft parts, whereas they charge on complete aircraft; such an arrangement would show a sub stantial advantage to a locally assembled Nymph. FLIGHT International, 22 May 1969 TABLE I: Cost breakdown of Nymph 115 Assembly (provisional) Number assembled per annum Airframe kit, each Equipment kit, each ... ... ... Less the quantity discount Nett cost per complete kit Freight Total, including freight ... ... Labour and overhead ac $5 per hour ... Total cost to the licensee ... 5 4.640 3,340 7,980 200 8,180 2.500 SI 0,680 100 4,640 3,340 1,995 5.985 200 6.185 1,250 $7,435 Calculating the likely cost of assembly from a kit depends on many local factors. The estimates given in Table I are Britten-Norman's considered opinion based on certain assump tions discussed. The number of man hours needed is a funda mental parameter. Statistics on light aircraft production are difficult to obtain, and it is even harder to predict allowances for learning and the productivity of local employees. On their best knowledge of American industry practice. B-N estimate that the Nymph 115 would be assembled in 500 man hours each at a production rate of ten aircraft per year, and that this would reduce to around 250hr per aircraft for a run of 100 per year. B-N believe that the learning pattern is likely to follow very closely the formula that a second aircraft takes only 80 per cent as long as the first, that the fourth takes 80 per cent as long as the second, that the eighth takes 80 per cent of the fourth, and so on. The basic ex-works price of the airframe kit is provisionally £1,930 ($4,640), and the equipment kit (including engine) is quoted at £1,390 ($3,340). Assemblers of more than five kits are to be offered a progressive discount which will reach a maxi mum of 25 per cent if 100 or more are assembled in a year. Freight charges are small, as kits will be shipped in minimum lots of five. Constructing the prototype The BN-3 has an exceptionally simple airframe, but sim plicity does not just happen—it is the product of very careful attention to the most minute detail. The entire credit for this on the BN-3 is due to Mr John Britten to his right-hand man on the project, Mr Dennis Berryman. and to their small but highly experienced team of designers and draughtsmen at Bembridge. Design work began in earnest last autumn. An entirely new method of draughting was devised whereby every component was drawn out only once, this being to full scale ready for copying to form the master reference for pre-kit fabrication jigging and so forth. Various minor but representa tive components such as the tailplane, elevator and flaps were made to prove-out the design and production processes: both John Britten and Desmond Norman took a practical hand in that. The decision to have an aircraft at the Paris Salon was taken late in the autumn, and detail preparations began straight away. A fearsomely tight programme was drawn up for the seemingly impossible task and all critical paths were identified early and put in hand. Agonising weeks passed with little visible progress, and then, towards the end of March, every thing was marshalled ready for the final frantic assembly planned to occupy little more than six weeks. Works manager with overall charge of the prototype con struction was Mr Jack Sullivan, who just' four years ago went through a similar feat of producing the impossible when his team turned out the first Islander. At no time in the assembly of the BN-3 have there ever been more than 25 engineers at work on the aircraft; the average has been nearer twelve men. In immediate charge of this skilled, enthusiastic and capable group has been Mr Arthur Rayner, the experi mental shop foreman. What the BN-3 will mean to Britten-Norman as a company is hard to tell at present with the project still in an early formulative stage. The company has openly disassociated itself from the business of mass production and has recognised that its talents lie in project design and development; it is leaving production to the experts. Kits for the BN-3 may be assembled in the Isle of Wight, and they may not—it all depends on demand and the best quotation for the work.
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