Handley Page H.P.20
| H.P.20 | |
|---|---|
 |
|
| Showing open and closed slots and depressed aileron | |
| Role | experimental monoplane |
| National origin | United Kingdom |
| Manufacturer | Handley Page |
| First flight | 24 February 1921 |
| Number built | 1 |
The Handley Page H.P.20 was an experimental monoplane modification of a de Havilland DH.9A, built to study controllable slots and slotted ailerons as high lift devices. It was the first aircraft to fly with controllable slots.
Frederick Handley Page obtained his master patent for controllable slots on the edge of an aircraft wing on 24 October 1919. He knew that the lift coefficient of all wings increased linearly until the stall was approached, then fell away; he argued that if the stall could be delayed, higher lift coefficients could be reached. In Germany Gustav Lachmann had the same idea, though through a wish to avoid the dangers of stalling. Rather than going to litigation an agreement was reached in which Lachmann, working with Prandtl at the advanced Goettingen air tunnel acted as consultant to Handley Page. Lachmann heard about the Handley Page work when they modified a standard DH.9A with fixed slots and demonstrated it dramatically at the Handley Page airfield at Cricklewood on 21 October 1920. That machine was retrospectively designated the H.P.17. The first aircraft with pilot controllable slots, designed by Handley Page and wind tunnel tested by Lachmann was called the X.4B in the company's contemporary notation but became, retrospectively, the H.P.20. The Air Ministry met the cost.
Like the H.P.17 it used a D.H.9A engine, fuselage and empennage, but fitted with an entirely new wing. The H.P.20 was a high-wing monoplane, using a thick wing with a straight leading edge but taper on the trailing edge. It was a semi-cantilever structure bolted to a small cabane on the fuselage and braced to the lower fuselage longerons with a pair of steeply rising struts on each side. The heaviness of early cantilever wing structures is shown by a comparison of the loaded weight of the H.P.20 (6,500 lb) with that of the loaded standard biplane DH.9A (4,645 lb including fuel for over 5 hours of flight and a 460 lb bomb load). The undersurface was flat and the front edge cropped to allow the full span slats, when closed, to form the true leading edge. The slats were hinged ahead of the wing and at their leading edges; their rotation formed the slots. In addition, slots opened in front of the ailerons when they were lowered. This was done via a groove in the wing just in front of the aileron hinge, narrowing towards the top surface.
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