Handley Page H.P.31 Harrow
Encyclopedia
The Handley Page H.P.31 was a two-seat single-engined biplane
Biplane
A biplane is a fixed-wing aircraft with two superimposed main wings. The Wright brothers' Wright Flyer used a biplane design, as did most aircraft in the early years of aviation. While a biplane wing structure has a structural advantage, it produces more drag than a similar monoplane wing...
built to a British specification for a carrier based torpedo bomber
Torpedo bomber
A torpedo bomber is a bomber aircraft designed primarily to attack ships with aerial torpedoes which could also carry out conventional bombings. Torpedo bombers existed almost exclusively prior to and during World War II when they were an important element in many famous battles, notably the...
and reconnaissance aircraft
Reconnaissance aircraft
A reconnaissance aircraft is a manned military aircraft designed, or adapted, to carry out aerial reconnaissance.-History:The majority of World War I aircraft were reconnaissance designs...
. After trials the Blackburn Ripon
Blackburn Ripon
-See also:-External links:* in Flight...
was preferred, though the Harrow played a significant role in the development of automatic slots.
Development
In early 1924 the Air Ministry specification 21/23 was issued, calling for a two-seat replacement for the Blackburn DartBlackburn Dart
-See also:-Bibliography:* Jackson, A.J. Blackburn Aircraft since 1909. London:Putnam, 1968. ISBN 0-370-00053-6.* Mason, Francis K. The British Bomber since 1914. London:Putnam, 1994. ISBN 0-85177-861-5....
capable of acting as a torpedo or conventional bomber over short ranges as well as having 12 hour reconnaissance capability. The Harrow, initially known as the Type E but retrospectively as the H.P.31 when the company introduced numerical designations in 1924, was Handley Page's tender. They were successful, receiving an order to build two prototypes.
The Harrow was essentially a single bay biplane, though there was an additional pair of interplane struts at the extremities of the centre section. The wings had the same span and constant chord and neither sweep nor stagger. Both upper and lower wings had outboard ailerons and inboard flaps, the latter ending at the centre section. Both wings also had leading edge slots
Leading edge slot
A leading edge slot is an aerodynamic feature of the wing of some aircraft to reduce the stall speed and promote good low-speed handling qualities. A leading edge slot is a span-wise gap in each wing, allowing air to flow from below the wing to its upper surface...
along their full length. The outer sections of these were linked to downward movement of the ailerons and the inner sections to the flaps. The lower wing was flat but the upper carried 4.5o of dihedral so the gap increased quite noticeably along the span. As usual with carrier-borne aircraft, the wings folded at the centre section. The wings were fabric covered; one difference between the two prototypes was that the second had metal wing spars, another that its slots could be operated independently.
It was powered by a single water-cooled Napier Lion
Napier Lion
The Napier Lion was a 12-cylinder broad arrow configuration aircraft engine built by Napier & Son starting in 1917, and ending in the 1930s. A number of advanced features made it the most powerful engine of its day, and kept it in production long after contemporary designs had stopped production...
engine, initially a 470 hp (350 kW) mark V, mounted as low in the nose as airscrew ground clearance allowed so that the top of the fuselage could fall away in front of the cockpit for the best views during high-incidence carrier landings. There was a front-mounted radiator immediately beneath the propeller shaft. The pilot sat below the upper wing just behind the rear spar and with a cut-out for visibility. The observer/gunner's position was close behind the pilot for ease of communication, for he had to do the work of navigation on long flights away from the carrier that had been traditionally assigned to a third crew member. Behind them the fabric-covered fuselage carried a conventional tail with horn balanced control surfaces, though the incidence of the whole tailplane could also be adjusted.
The Harrow had to have a clear space below the fuselage to allow torpedo dropping. The main legs were attached to the front spar at the ends of the centre section, and pairs of bracing struts ran from the stub axles to the lower fuselage longerons. Snap link hooks were fitted to the inner ends of the axles to engage with the longitudinal arrester wires of the time. The specification required that the land
undercarriage could be replaced rapidly with floats. These were long, single stepped and fitted with water rudders, built by Short Brothers
Short Brothers
Short Brothers plc is a British aerospace company, usually referred to simply as Shorts, that is now based in Belfast, Northern Ireland. Founded in 1908, Shorts was the first company in the world to make production aircraft and was a manufacturer of flying boats during the 1920s, 1930s, and 1940s...
.
The first flight of the Harrow was made by Hubert Broad
Hubert Broad
Captain Hubert Standford Broad MBE AFC was an English First World War aviator and notable sports and test pilot.-Early life:Broad was born in Watford on 18 May 1897 the son of Thomas and Amelia Broad. In 1901 when Broad was three the family were living at Aston Lodge, St Johns Road in Watford his...
on 24 April 1926. A number of minor issues emerged from the early flying programme, but one consistent theme was that of engine overheating. By the end of May the Harrow was taking off and landing on HMS Furious
HMS Furious (47)
HMS Furious was a modified cruiser built for the Royal Navy during the First World War. Designed to support the Baltic Project championed by the First Sea Lord of the Admiralty, Lord John Fisher, they were very lightly armoured and armed with only a few heavy guns. Furious was modified while...
as part of the specification competition. It went to RAF Martlesham Heath
RAF Martlesham Heath
RAF Martlesham Heath is a former Royal Air Force airfield in England. The field is located 1½ miles SW of Woodbridge, Suffolk.- RFC/RAF prewar use:Martlesham Heath was first used as a Royal Flying Corps airfield during World War I...
for further Air Ministry
Air Ministry
The Air Ministry was a department of the British Government with the responsibility of managing the affairs of the Royal Air Force, that existed from 1918 to 1964...
specification tests late
in August. In December it was replaced there by the second prototype which had first flown on 30 October 1924. By the spring of 1927 it was clear that the Blackburn Ripon
Blackburn Ripon
-See also:-External links:* in Flight...
was preferred, and in June the second prototype was returned to Handley Page rather than going forward to the seaplane trials, chiefly because of its persistent overheating. Nonetheless Handley Page gained funding for a Harrow Mk II using a more
powerful Napier Lion XI engine producing 530 hp (395 kW) in the first prototype airframe. This engine was housed in a slimmer, more pointed cowling with a semi-circular cross section radiator under the nose. At the same time drag was reduced and rudder and elevator lightness improved by lowering the rear fuselage decking and with it the gunner's position. Later in the Summer a Lion XA was fitted, together with a larger, square radiator. Further modifications to the Mk II followed with the addition of dihedral to both wings, a slimmer nose and retractable side radiators like those on its competitor, the Ripon II. There were further modifications to flaps and slots before the aircraft went back to Martlesham to compete against the Ripon II and the Avro Buffalo II
Avro Buffalo
|-See also:...
, performing torpedo dropping trials before going to Felixstowe as a floatplane. Here it proved unsatisfactory, suffering water spray damage, and was written off charge in August 1928.
During the late summer of 1927 the second prototype had been involved in continuing the series of Air Ministry tests of slots previously conducted on the Hendon III
Handley Page Hendon
|-See also:-Bibliography:*Barnes, C.H. Handley Page Aircraft since 1907. London:Putnam, 1976. ISBN 0 370 00030 7.*Mason, Francis K. The British Bomber since 1914. London:Putnam, 1994. ISBN 0 85177 861 5....
. It used the latest version of automatic wing tip slots and was hailed as a great success and a sure defence against the inadvertent spin. It was retired at the end of September.