Aeroplane Monthly, June 1988

Mr Tinson’s DIY ultralight

BILL BODDY, Editor of Motor Sport, recalls a stillborn project of nearly 60yr ago

  Enthusiasm for light aeroplanes ran high between the two World Wars, and those who sought something less expensive to buy and fly than the D.H.60 Moth were usually eager to discuss and plan new ultralights - as Richard Riding’s splendid recent book Ultralights (Patrick Stephens, 1987) makes plain. One such person was Clifford W. Tinson, a member of the Royal Aeronautical Society.
  At a time when there were some 14 light aeroplane clubs in Britain, with others in process of formation, Tinson directed considerable thought to the kind of machine which would undercut the cost of an Avian or Moth, yet be reasonably effective in private pilots’ ownership. First of all, he compared monoplane with biplane. The conclusion was that the former gained in aerodynamic superiority, whereas the latter scored in respect of structural weight, leaving it with a small advantage when these aspects were combined.
  Tinson pointed out that one should not be biased in favour of the monoplane because many great long-distance flights had been accomplished with aeroplanes of this type. Considerations of fuel carrying came into it, although he conceded that a new form of internal wing bracing might well end the disadvantage of the then-usual external bracing struts needed to stiffen a semi-cantilever monoplane wing, which was lighter than a full cantilever wing as used on Fokker and Junkers monoplanes.
  After this discourse in favour of the monoplane, however, in 1929 Tinson designed a high-wing monoplane as his suggested ideal ultralight. He was heard to remark that although all the Schneider Trophy machines were monoplanes, the Gloster people had only reluctantly deserted the biplane configuration: windtunnel tests had convinced them that, for obtaining maximum cruising speed, a biplane was as good as, if not superior to, a monoplane.
  Tinson still backed the monoplane. He prepared a design for a single-seater powered by an engine weighing not more than 100lb, able to carry 3gal of petrol and |gal of oil. He was aiming for a landing speed of 48 m.p.h., a top speed of at least 94 m.p.h. and a cruising speed of 75 m.p.h. The little machine was to weigh 440lb in flying trim with pilot (150lb) and he estimated the climbing abilities of his design as 600ft/min at sea level. This was an attractive proposition, the 38 h.p. aeroplane giving much the same performance as a Cirrus II Moth. Moreover, Tinson intended it to sell at a fair profit for around £350, assuming that the complete engine cost £65-95.
  The designer even gilded the picture by saying he had estimated the speed of his ultralight on the low side in order to allow for a wide cockpit opening; if this were reduced, 105 m.p.h. or more might be had flat-out.
  Tinson proposed to make his monoplane very largely of three-ply. He was anxious to keep the number of parts of the structure to a minimum. The wings and fuselage would be skinned with 3/32in three-ply, the tail with 1/16in, with a minimum of stiffening applied to the latter. If the wing skin were stabilized against buckling it would take the machine’s weight, using a 6in x 1in spruce plank along the span, to form the spars. To this wing structure the skin would be glued and screwed, any local extra stiffening required being added after testing, as it was not possible to stress the structure by prior calculation. Tinson admitted honestly that it would have to be seen whether his simple wing would be permissible on a weight basis.
  He thought, however, that the wing would come out at 77lb, or 1,375lb/ft2 unless more stiffening was needed, and then could hardly exceed 1,5lb/ft2. The fuselage would be made in the same way, using truncated cones of the heavier three-ply, joined by riveted-on covering strips, laminated hoops uniting the cones. This was estimated to take 70ft2 of wood, weighing barely 18lb. Only for a really small aeroplane, said Tinson, would this method of construction be of any advantage. Good but not necessarily “aircraft” quality materials were specified and the designer broke the cost down as £22 for the wing, £15 for the fuselage, and £8 for the tail unit, inclusive of labour, which came out to as much as the materials, even in 1929. That was for quantity production, looking for a 20 per cent profit per machine on the £350 selling price.
  Tinson expected the undercarriage, wheels and tailskid to cost £19, fuel tank and piping £3, and he costed the 9ft propeller at £2 per foot. The cockpit would be equipped with an airspeed indicator, tachometer and altimeter, which, with the pitot head, came out to £15 7s 6d (£15-38), the control-runs absorbing another £6. The purchase price of a Tinson monoplane was based on erecting, testing and delivery to a railhead, and £80 overheads were expected on the engine, undercarriage and equipment. A suitable engine was seen as a stumbling point, very few 30 h.p. power-units being available for less than £127, so that a “souped-up” car or motorcycle engine might be needed, such as a four-cylinder Henderson or similar motorcycle engine. Development costs would then be confined to dual ignition, the shaft for the propeller and so on. A fuel range of 2hr, or 150 miles, was thought adequate.
  The high-wing single-seater was to have a wing span of 18ft 8in, with a surface area of 56ft2 and a lift coefficient of 0-675. A tapering wing plan would have an average chord of about 3ft, the pilot sitting between the spars; the camber of such a high-lift wing would allow a spar depth of about 6in at the root.
  The total length of the machine would be 14ft 4 1/4in, and a height of 5ft 6in would give adequate prop clearance. From the c.g. to the sternpost 9ft would suffice, said Tinson. The tail unit would have a total area of 16,7ft2 - 12,7ft2 for tail and elevators, 4ft2 for fin and rudder.
  The Tinson monoplane was just one of no doubt many “ideal” ultralights that saw paper, but not grass and petrol, in those fascinating years between the wars. Might it even be practical today?

Span 18ft 8in
Length 14ft 4 1/4in
Height 5ft 6in
Wing area 56ft2
Empty weight 262lb
All-up weight 440lb
Maximum speed 94 m.p.h.
Cruising speed 75 m.p.h.