Short SB.4 Sherpa

https://en.wikipedia.org/wiki/Short_SB.4_Sherpa

The Short SB.4 Sherpa was a British experimental aircraft designed and built
during the 1950s to test the flight characteristics of the aero-isoclinic wing.
It was based upon (and used some components of) the Short SB.1, an earlier
glider design.

The Short SB.4 Sherpa was designed by David Keith-Lucas as a research aircraft
aimed primarily at assisting in the development of wings for faster, very
high-altitude aircraft in general and the company's Preliminary Design (Short
PD.1) in response to the U.K. V-Bomber requirement B35/46 in particular. It was
the first powered aircraft to employ the "aero-isoclinic" wing first proposed in
1951 by Professor Geoffrey T.R. Hill, who had been instrumental in the design of
the Westland-Hill Pterodactyl tail-less experimental aircraft in the mid-1920s.

This radical wing configuration was designed to maintain a constant angle of
incidence regardless of flexing, by placing the torsion box well back in the
wing so that the air loads, acting in the region of the quarter-chord line, have
a considerable moment arm about it. The torsional instability and tip stalling
characteristics of conventional swept wings were recognised at the time,
together with their tendency to aileron-reversal and flutter at high speed. It
was to prevent these effects that the aero-isoclinic wing was designed.

In the Sherpa, the wing, which was used without a tailplane, was fitted with
rotating tips comprising approximately one-fifth of the total wing area. Unlike
pure wingtip ailerons, these surfaces were a bit more like "wingtip elevons", as
they were rotated together (to act as elevators) or in opposition (when they
acted as ailerons). They were hinged at about 30% chord and each carried, on the
trailing edge, a small anti-balance tab, the fulcrum of which could be moved by
means of an electric actuator. It was expected that the rotary wing tip controls
would prove greatly superior to the flap type at transonic speeds and provide
greater manœuvrability at high altitudes.

Construction was largely of spruce with plywood covering and light alloy
components at strategic points. Wing sweep-back on the leading edge was just
over 42° to facilitate low-speed research. Two diminutive engines (Turbomeca
Palas) were buried in the upper fuselage with a NACA flush inlet on the top of
the fuselage and toed-out exhausts located at the wing roots. Blackburn, who
produced the Palas under licence, hoping to market these engines as a new
product line, supplied the powerplants for the Sherpa programme.


Role
Experimental aircraft

Manufacturer
Short Brothers

Designer
David Keith-Lucas

First flight
4 October 1953

Primary users
Short Brothers company experimental project
College of Aeronautics (Cranfield)

Number built
1

Developed from
Short SB.1

The Sherpa's first flight, piloted by Shorts' Chief Test Pilot, Tom
Brooke-Smith, was on 4 October 1953. Brooke-Smith had also piloted the earlier
experimental glider aircraft, the Short SB.1, upon which the Sherpa was based.
Although he had a crash in the SB.1, Brooke-Smith recovered and was able to
undertake the test programme of the redesignated SB.4 (registered as G-14-1)
throughout 1953–54. (Incidentally, the Sherpa was named following the conquest
of Mount Everest but derived its name specifically from its company designation
"Short & Harland Experimental Research Prototype Aircraft.)

The Sherpa flew successfully within a limited flight envelope, achieving a
"flat-out" 170 mph (270 km/h) at 5,000 ft (1,500 m) ), making it one of the
slowest jets ever built. Despite reaching its design goals, the concept was
considered "not fully realised in practice" and eventually the project was wound
up.

The Sherpa was subsequently donated to the College of Aeronautics at Cranfield,
where it was flown until 1958, when an engine problem caused it to be grounded
until replacement engines could be found. In 1960, further engines were made
available and flying then resumed until 1964, when, with engine life expired,
the Sherpa was finally grounded. It was then sent to the Bristol College of
Advanced Technology where it served as a "laboratory specimen". Its fuselage was
on display at the Norfolk and Suffolk Aviation Museum, near Bungay, Suffolk
until 17 July 2008 when it was moved to the Lisburn site of the Ulster Aviation
Society.

Specifications

General characteristics
Crew: 1
Length: 31 ft 10 in (9.7 m)
Wingspan: 38 ft 0 in (11.58 m)
Height: 9 ft 1.12 in (2.77 m)
Wing area: 230 sq ft (21.4 m²)
Empty weight: 3,000 lb (1,400 kg)
Loaded weight: 3,268 lb (1,482 kg)
Powerplant: 2 × Blackburn Turbomeca Palas turbojet, 350 lbf (1.6 kN) each

Performance
Maximum speed: 170 mph (150 kn, 275 km/h)
Cruise speed: 117 mph (102 kn, 188 km/h)
Service ceiling: 5,000 ft (1,500 m)
Endurance: 45-50 min



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