Whitney Wasp Junior (there being no suitable engine in the Bristol range), performed the type's maiden flight. In mid-1948, the third prototype, which had been built to the improved Sycamore Mk.2 standard, was completed; this model had been fitted with a Alvis Leonides engine, the Leonides engine would become the standard powerplant for all subsequent Sycamore production. On 25 April 1949, a certificate of airworthiness was granted for the Sycamore, the first such to be granted to a British helicopter. During the flight test programme, Bristol's key development pilots for the Type 171 included Charles "Sox" Hosegood and Col. Robert "Bob" Smith. In 1951, a Bristol-owned Sycamore Mk.2 was used during a series of deck landing trials performed on board the Royal Navy aircraft carrier HMS Triumph. An improved model of the helicopter, designated as the Sycamore Mk.3, was rapidly developed; it featured an increased capacity for five occupants, a wider fuselage and a shortened nose. A total of 23 Sycamore Mk.3s were produced, 15 of these were principally used for joint evaluation purposes by the Royal Air Force (RAF), Army Air Corps (AAC), and British European Airways (BEA). Versions of the Sycamore up to and including the Mk.3A retained the standard two-seat cockpit layout, placing the pilot in the left-hand seat and the co-pilot in the right. However, on the main production model, designated Sycamore Mk.4, this seating arrangement was switched to the American practice of positioning the pilot's seat on the right. There were also a number of other developments that had featured upon the earlier versions, such as a four-door design, which had been standardised upon the Sycamore Mk.4. This version entered RAF service, receiving the military designation of HR.14. Civil versions were not marketed under the Sycamore name, they were instead known simply as the Bristol Type 171. By May 1958, over 150 Sycamores had been manufactured and four units per month were being built. Design The Bristol Sycamore was one of the first production helicopters to be developed. Each Sycamore was manufactured with all of the necessary fixed fittings to enable it to be quickly adapted for any of six major roles: search and rescue, air ambulance, passenger transport, freight transport, aerial crane and dual instruction; it was also used for other specialised roles. The Sycamore seated four-to-five occupants, depending on the model; it was usually fitted with three folding canvas seats as well as