page_title: Cranwell CLA.4
section_title: Design and development
hierarchical_section_title: Cranwell CLA.4 / Design and development
caption_attribution_description: English: The first Cranwell C.L.A.4A, mid 1926.
context_page_description: The Cranwell CLA.4 was a single-engined two-seat inverted sesquiplane designed and constructed for the 1926 Lympne trials by an amateur group from RAF College Cranwell. Two were entered, though engine problems prevented one from taking part; the other was eliminated with a broken undercarriage. A third aircraft was amateur-built in Canada and flew until 1934.
context_section_description: The Cranwell Light Aeroplane (CLA) club was formed in 1923 by staff and students at the RAF College Cranwell. The students came from No.4 Apprentices Wing and one of their lecturers, Flt-Lt Nicholas Comper became chief designer of the three aircraft produced by the club as well as one, the CLA.1 that was not completed. The last of the series, the CLA.4 was designed to compete in the 1926 Lympne Light Aeroplane Trials. Two were built for this competition, one to be powered by a Bristol Cherub engine and the other by the new Pobjoy P.  Unfortunately, the latter engine failed its own trials not long before the Lympne event and only the Cherub powered aircraft took part. Since the CL.4 had been designed for the 65 hp (48 kW) Pobjoy, the 36 hp (27 kW) Cherub left it seriously underpowered.
  Many sesquiplanes have flown, the great majority of types having a smaller lower wing than upper.  The CLA.4, unusually, was an inverted sesquiplane with a smaller upper wing, joining a small group of aircraft like the Fiat CR.1 of 1924 and the later Caproni Ca.100, Caproni Ca.164 and Levasseur PL.15, all military machines.  There is a small aerodynamic penalty for this arrangement, but the advantages for a club machine are good vision, and ease of escape, from both cockpits. In the case of the CLA.4, the upper wing had a span of 80% of the lower and 83% of its chord. The wings were straight, unswept and of constant chord apart from at the rounded tips, with ailerons on the lower wings only. The CLA.4 was a single bay biplane with inward leaning single wide chord interplane struts with wide, faired roots.  Two pairs of centre section struts held the upper wing well clear of the fuselage; the absence of stagger made wing-folding easy. Like much of the rest of the aircraft, the wings were of fabric covered wood.
  The fuselage was built up on four longerons, spruce at the rear where they were linked into a tapering Warren girder, and ash ahead of the rear cockpit where more traditional wire braced rectangular forms were used. It was topped with a standard rounded decking.  The two open cockpits were placed at the leading and trailing upper wing edges and fitted with dual controls. The flat twin Bristol Cherub III was mounted on a steel plate and smoothly partially cowled to a neatly pointed nose, but with the cylinder heads exposed for cooling. At the rear of the fuselage the fin and tailplane were fabric covered metal structures, though the generous control surfaces were wood framed. Fin and rudder together formed a shape not unlike that of many de Havilland aircraft though more rounded and unbalanced.  The main undercarriage was built from a pair of steel V-shaped tubes bearing a single axle and rubber cord shock absorbers.
caption: The first CLA.4
exif: {}