WALLBRO monoplane (Horace S. and Percy V. Wallis, 12 St. Barnabas Rd., Cambridge)

   The brothers built this tractor monoplane in 1909-1910, testing it in a field at Fulbourn, Cambridgeshire from late May onwards, after the machine had been exhibited in public at Whitsun on 16-17 May. The aircraft left the ground on a number of occasions, including a mishap on 4 July 1910, when the machine turned over without causing injury to PV. Wallis who was at the controls. There is no record of sustained flight and the project ended in October, when the machine was wrecked in its shed during a storm.
   In general layout the aircraft resembled a Bleriot XI, but the type of construction was original. The primary structure was of 1" o/d. x 20swg steel tube from Accles and Pollock, and employed brazed joints using Chater Lea fittings, similar to motor cycle frame construction. This method was used for the construction of the fuselage, and tubing was also used for the wing and tailplane spars and for the rudder hinge post. The balanced elevators pivoted at the ends of the tailplane on a tubular spar passing through the main tailplane spar. Wooden ribs were used for the wings and wood was used for the framework of the control surfaces. The lateral control was by wing warping.
   The undercarriage incorporated twin skids of ash on a separate chassis, sprung by tension springs; the skids, on coming into contact with the ground would tilt the chassis, bringing the wheels into contact. Steel tubing of 16 and 18swg was used for the undercarriage. A large sprung tail wheel was fitted. The fuselage was covered with fabric to the rear of the pilot's seat.
   A replica of the Wallbro monoplane was built in 1974-1976 by the son of H.S. Wallis, Wing Cdr. K.H. Wallis and his cousin, G.V. Wallis. This used brazed instead of Chater Lea fittings, fitted to the tubes with Loctite adhesive, and secured by the eyebolts for the bracing wires. The engine employed was a 72hp McCulloch four-cylinder horizontally opposed, aircooled, two-stroke target-drone engine. The replica aircraft was flown successfully at Swanton Morley, Norfolk.

   Power: 25hp JAP four-cylinder air-cooled vee driving a 6ft 6in diameter Avro adjustable pitch propeller with metal blades.
   Data
   Span 30ft
   Area 180 sq. ft
   Area tailplane 12 sq. ft
   Area elevators 18 sq. ft
   Area rudder 8 sq. ft
   Length 25ft
   Weight 330 lb. with fuel & oil