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{{Short description|Experimental aircraft in the UK}}
{{about|the experimental research aircraft|cargo aircraft|Short C-23 Sherpa}}
{{for|the cargo aircraft|Short C-23 Sherpa}}

<!-- This article is a part of [[Wikipedia:WikiProject Aircraft]]. Please see [[Wikipedia:WikiProject Aircraft/page content]] for recommended layout. -->
{{Use dmy dates|date=January 2017}}
{{Use dmy dates|date=January 2017}}
{{Use British English|date=January 2017}}
{{Use British English|date=January 2017}}
{|{{Infobox Aircraft Begin
{{Infobox aircraft
|name=SB.4 Sherpa
|name=SB.4 Sherpa
|image=Short Sherpa Farnborough 1954.jpg
|image= File:Short Sherpa Farnborough 1954.jpg
|caption=Short Sherpa demonstrating at the Farnborough SBAC Show in September 1954
|caption= Short Sherpa demonstrating at the [[Farnborough Airshow|Farnborough SBAC Show]] in September 1954
⚫
|type = [[Experimental aircraft]]
}}{{Infobox Aircraft Type
|national_origin= United Kingdom
⚫
|type=[[Experimental aircraft]]
|manufacturer=[[Short Brothers]]
|manufacturer = [[Short Brothers]]
|designer= [[David Keith-Lucas]]
|designer = [[David Keith-Lucas]]
|first flight=4 October 1953
|first_flight = 4 October 1953
|introduced=
|introduction =
|retired=
|retired =
|status=
|status =
|primary_user =
|primary user=[[Short Brothers]] company experimental project
|more users=College of Aeronautics (Cranfield)
|more_users = College of Aeronautics (Cranfield)
|produced=<!--years in production, e.g. 1970-1999, if still in active use but no longer built-->
|produced =<!--years in production, e.g. 1970-1999, if still in active use but no longer built-->
|number built=1
|number_built = 1
⚫
|developed_from = [[Short SB.1]]
|unit cost=
|variants=
⚫
|developed from=[[Short SB.1]]
|variants with their own articles=
}}
}}
|}
The '''Short SB.4 Sherpa''' was a [[united Kingdom|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 an experimental aircraft designed and produced by the British aircraft manufacturer [[Short Brothers]]. Only a single example was ever produced.
==Design and development==
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. [[List of Air Ministry Specifications|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.


The Sherpa was developed during the 1950s for the purpose of testing a novel wing design, referred to as an [[aero-isoclinic wing]]. It was believed that this wing design could possess favourable qualities for producing [[tailless aircraft]], and that the Sherpa would validate the characteristics of the wing for such aircraft to be produced in the future. While such a wing had been flown on the earlier [[Short SB.1]], an unpowered [[Glider (aircraft)|glider]], it was deemed valuable to use a powered aircraft instead. The design of the Sherpa is largely based upon that of the SB.1, to the extent that it incorporated numerous elements of this aircraft.
⚫
[[File:Short SB4 Sherpa headon.jpg|thumb|right|Short SB.4 Sherpa]]


The Sherpa performed its [[maiden flight]] on 4 October 1953, after which it spent several years performing experimental flights and the occasional aerial display. After gathering sufficient data for Shorts' purposes, the company decided that it did not show sufficient potential as to continue its research into the aero-isoclinic wing. The sole Sherpa was donated to the [[Cranfield University|College of Aeronautics]] at [[Cranfield]] during the late 1950s and flown for numerous years. It was eventually grounded and used as a static laboratory specimen at the Bristol College of Advanced Technology, before being preserved and put on display at the [[Norfolk and Suffolk Aviation Museum]].
⚫
This radical wing configuration was designed to maintain a constant [[angle of incidence (aerodynamics)|angle of incidence]] regardless of flexing, by placing the [[Torsion (mechanics)|torsion]] box well back in the wing so that the air loads, acting in the region of the quarter-[[Chord (aircraft)|chord]] line, have a considerable [[Moment (physics)|moment arm]] about it. The torsional instability and tip stalling characteristics of conventional [[swept wing]]s were recognised at the time, together with their tendency to [[Control reversal|aileron-reversal]] and [[Aeroelasticity#Flutter|flutter]] at high speed. It was to prevent these effects that the aero-isoclinic wing was designed.


==Development==
⚫
In the Sherpa, the wing, which was used without a [[tailplane]], was fitted with [[Aileron#Wingtip ailerons|rotating tips]] comprising approximately one-fifth of the total wing area. Unlike pure wingtip ailerons, these surfaces were a bit more like "wingtip [[elevon]]s", as they were rotated together (to act as [[Elevator (aircraft)|elevator]]s) or in opposition (when they acted as [[aileron]]s). 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.
The origins of the Short SB.4 Sherpa can be traced back to the 1920s and the activities of Professor [[Geoffrey T.R. Hill]], who was pivotal in the design of the [[Westland-Hill Pterodactyl]], a pioneering tailless experimental aircraft.<ref name="Barnes 1967, p. 4394.">Barnes 1967, pp. 439-440.</ref> Even prior to the [[First World War]], Shorts had been involved in tailless aircraft research, but interest in the field reached new heights in the years immediately following the [[Second World War]]. During the late 1940s, the company worked on multiple proposals for tailless aircraft in response to specifications issued by the [[Air Ministry]], including [[List of Air Ministry specifications#1940–1949|Specification X.30/46]] and [[List of Air Ministry specifications#1940–1949|Specification B.35/46]], which sought a military assault [[Glider (aircraft)|glider]] and [[strategic bomber]] respectively.<ref name="Barnes 1967, p. 43941.">Barnes 1967, pp. 439-441.</ref>


⚫
[[File:Short SB4 Sherpa headon.jpg|thumb|right|Short SB.4 Sherpa]]
⚫
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 duct|NACA flush inlet]] on the top of the fuselage and toed-out exhausts located at the wing roots. [[Blackburn Aircraft|Blackburn]], who produced the Palas under licence, hoping to market these engines as a new product line, supplied the powerplants for the Sherpa programme.<ref>Gunston 1977, p. 512.</ref>
In particular, one of the company's [[Aerospace engineering|aeronautical engineer]]s, [[David Keith-Lucas]], was keen to eliminate the parasitic drag normally incurred by the presence of a conventional tail and fuselage, and thus was a keen proponent of the tailless approach.<ref name="Barnes 1967, p. 441.">Barnes 1967, p. 441.</ref> He also observed that directional stability was a critical issue without the application of traditional fins and [[rudder]]s; it was identified that the outermost parts of the wing could be rotated and repositioned to function as [[elevon]]s for stability and control purposes. New wing designs that presented a low aspect ratio, such as the [[delta wing]], had been observed to reduce the onset of these issues; Keith-Lucas and Hill, jointly developed what became known as the [[aero-isoclinic wing]].<ref name="Barnes 1967, p. 4412."/>

Having become sufficiently confident in the merits of the aero-isoclinic wing , Shorts opted to produce a new experimental aircraft to incorporate the latest advances and explore its behaviour, thus it constructed the [[Short SB.1]] glider.<ref name="Barnes 1967, p. 4412.">Barnes 1967, pp. 441-442.</ref> This aircraft was designed to be as inexpensive as possible and thus featured extensive wooden construction alongside its innovative wing.<ref name="Barnes 1967, p. 442.">Barnes 1967, p. 442.</ref> After only a few months of flight, the SB.1 suffered damage in a heavy landing at [[Joint Helicopter Command Flying Station Aldergrove|RAF Aldergrove]] on 17 October 1951. Shorts' chief test pilot, Tom Brooke Smith, objected to further flights of the unpowered glider. Accordingly, it was decided that the fuselage, which had been heavily damaged, would be replaced by a modified design that incorporated a pair of [[Turbomeca Palas]] [[turbojet]] engines.<ref name="Barnes 1967, p. 4423.">Barnes 1967, pp. 442-443.</ref>

==Design==
[[File:Short Sherpa wingtip from above.jpg|thumb|Rotated wingtip]]
[[File:Short Sherpa wingtip from above.jpg|thumb|Rotated wingtip]]
[[File:Short Sherpa wingtip from below.jpg|thumb|Rotated wingtip (from below and behind)]]
[[File:Short Sherpa wingtip from below.jpg|thumb|Rotated wingtip (from below and behind)]]
⚫
The Short SB.4 Sherpa was an experimental aircraft, featuring an unusual [[aero-isoclinic wing]].<ref name="Barnes 1967, p. 4423."/> This radical wing configuration was designed to maintain a constant [[angle of incidence (aerodynamics)|angle of incidence]] regardless of flexing, by placing the [[Torsion (mechanics)|torsion]] box well back in the wing so that the air loads, acting in the region of the quarter-[[Chord (aircraft)|chord]] line, have a considerable [[Moment (physics)|moment arm]] about it. The torsional instability and tip stalling characteristics of conventional [[swept wing]]s were recognised at the time, together with their tendency to [[Control reversal|aileron-reversal]] and [[Aeroelasticity#Flutter|flutter]] at high speed; the aero-isoclinic wing was designed to specifically prevent these undesirable effects.<ref name="Barnes 1967, p. 4413.">Barnes 1967, pp. 441-443.</ref>

⚫
In the Sherpa, the wing, which was used without a [[tailplane]], was fitted with [[Aileron#Wingtip ailerons|rotating tips]] comprising approximately one-fifth of the total wing area. Unlike pure wingtip ailerons, these surfaces were a bit more like "wingtip [[elevon]]s", as they were rotated together (to act as [[Elevator (aircraft)|elevator]]s) or in opposition (when they acted as [[aileron]]s). 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 manoeuvrability at high altitudes.<ref name="Barnes 1967, p. 4434.">Barnes 1967, pp. 443-444.</ref>

⚫
In terms of its construction, the Sherpa was primarily composed of light [[alloy]]s and featured a [[monocoque]] arrangement.<ref name="Barnes 1967, p. 4434."/> Wing sweep-back on the leading edge was just over 42° to facilitate low-speed research. The Sherpa was provisioned with a conventional [[tricycle landing gear|tricycle undercarriage]].<ref name="Barnes 1967, p. 4434."/> Two diminutive engines ([[Turbomeca Palas]]) were buried in the upper fuselage with a [[NACA duct|NACA flush inlet]] on the top of the fuselage and toed-out exhausts located at the wing roots. Fuel was housed within the fuselage in two 250 gallon tanks, which were balanced around the aircraft's centre of gravity; electrical power was supplied by a [[ram air turbine]] by the engines.<ref name="Barnes 1967, p. 444.">Barnes 1967, p. 444.</ref> [[Blackburn Aircraft|Blackburn]], who produced the Palas under licence, hoping to market these engines as a new product line, supplied the powerplants for the Sherpa programme.<ref>Gunston 1977, p. 512.</ref>


==Testing==
==Testing==
The Sherpa's first flight, piloted by Shorts' Chief [[Test pilot|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 "'''S'''hort & '''H'''arland '''E'''xperimental '''R'''esearch '''P'''rototype '''A'''ircraft.)
On 4 October 1953, the Sherpa performed its [[maiden flight]], piloted by Shorts' Chief [[Test pilot|Test Pilot]], [[Tom Brooke-Smith]].<ref name="Barnes 1967, p. 444."/> Brooke-Smith had also piloted the earlier experimental glider aircraft, the [[Short SB.1]], upon which the Sherpa was based. Although he sustained injuries in the crash landing of the SB.1, Brooke-Smith had quickly recovered and was able to undertake the test programme of the redesignated SB.4 (registered as ''G-14-1'') throughout 1953–1954. (Incidentally, the Sherpa was named following the conquest of Mount Everest but derived its name specifically from its company designation "'''S'''hort & '''H'''arland '''E'''xperimental '''R'''esearch '''P'''rototype '''A'''ircraft.<ref name="Barnes 1967, p. 444."/>)

[[File:Short SB4 Sherpa crop.JPG|thumb|left|Short Sherpa testing at College of Aeronautics]]
[[File:Short SB4 Sherpa crop.JPG|thumb|left|Short Sherpa testing at College of Aeronautics]]


The Sherpa flew successfully within a limited flight envelope, achieving a "flat-out" {{convert|170|mi/h|km/h|-1|abbr=on}} at {{convert|5000|ft|m|-2|abbr=on}} <ref name="Barnes and James 1989, p. 444.">Barnes and James 1989, p. 444.</ref>), making it one of the slowest jets ever built.<ref name="Barnes and James 1989, p. 444."/><ref name="Gunston 1977, p. 513.">Gunston 1977, p. 513.</ref> Despite reaching its design goals, the concept was considered "not fully realised in practice" and eventually the project was wound up.<ref name="Gunston 1977, p. 513."/>
During the initial series of flying trials of the Sherpa, performed largely by Brooke-Smith, the aircraft had reportedly proved to be quite satisfactory; its docile handling characteristics led to be being described as being 'one of the most graceful aircraft now flying'.<ref>Shorts Quarterly Review, Autumn 1953.</ref><ref name="Barnes 1967, p. 444."/> The aircraft was typically flown within a restricted flight envelope, during which it reportedly achieved a "flat-out" speed of {{convert|170|mi/h|km/h|-1|abbr=on}} at {{convert|5000|ft|m|-2|abbr=on}},<ref name="Barnes and James 1989, p. 444.">Barnes and James 1989, p. 444.</ref> which made it amongst the slowest jet-powered aircraft to have ever flown.<ref name="Barnes and James 1989, p. 444."/><ref name="Gunston 1977, p. 513.">Gunston 1977, p. 513.</ref>


Data from these flights was typically captured by an onboard [[flight data recorder]] and analysed post-flight to build up a model of how a similar full-sized wing would behave under various conditions, including various altitudes and speeds.<ref name="Barnes 1967, p. 444."/> Keith-Lucas had aimed to validated the wing as a low weight solution that behaved well across various speeds, including the [[transonic]] range, but the attained test results did not fully validate his hopes.<ref name="Barnes 1967, p. 4445.">Barnes 1967, pp. 444-445.</ref> Aviation author Bill Gunston notes that, despite the Sherpa having attaining its design goals, the concept was considered to be "not fully realised in practice" and the project was eventually wound up without a direct continuation.<ref name="Gunston 1977, p. 513."/> Shorts did prepare multiple proposals, such as the retrofitting of the [[Supermarine Swift]] fighter with the aero-isoclinic wing, but these were not pursued.<ref name="Barnes 1967, p. 445.">Barnes 1967, p. 445.</ref>
⚫
The Sherpa was subsequently donated to the [[Cranfield University|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".<ref name="Gunston 1977, p. 513."/><ref>Barnes and James 1989, p. 445.</ref> Its fuselage was on display at the [[Norfolk and Suffolk Aviation Museum]], near [[Bungay, Suffolk|Bungay]], [[Suffolk]] until 17 July 2008 when it was moved to the Lisburn site of the [[Ulster Aviation Society]].<ref>[http://www.ulsteraviationsociety.org/#/short-sb4-sherpa/4537302722 Ulster Aviation Society SB4 page]</ref>


⚫
The Sherpa itself was subsequently donated to the [[Cranfield University|College of Aeronautics]] at [[Cranfield]], where it continued to fly up until 1958. At this point, engine issues forced the aircraft to be grounded until replacement powerplants could be organised.<ref name="Barnes 1967, p. 445."/> During 1960, further engines were made available, thus flying of the Sherpa resumed until 1964, when, with its engine life expired, the Sherpa was finally grounded. Following this, it was transported to the Bristol College of Advanced Technology, where the airframe was used as a "laboratory specimen".<ref name="Gunston 1977, p. 513."/><ref>Barnes and James 1989, p. 445.</ref> Its fuselage was on display at the [[Norfolk and Suffolk Aviation Museum]], near [[Bungay, Suffolk|Bungay]], [[Suffolk]],<ref name="Barnes 1967, p. 4456.">Barnes 1967, pp. 445-446.</ref> until 17 July 2008, after which it was moved to the Lisburn site of the [[Ulster Aviation Society]].<ref>[https://www.ulsteraviationsociety.org/sherpa-jet-sb4 Ulster Aviation Society SB4 page]</ref>
===Handling characteristics===
"The Sherpa's first trials, with Shorts' Chief Test Pilot, Tom Brooke-Smith at the controls, proved very satisfactory and the small black and silver plane has been quoted as being 'one of the most graceful aircraft now flying'."<ref>Shorts Quarterly Review, Autumn 1953</ref>


== Aircraft on display ==
== Aircraft on display ==
The SB4 is on display at the Ulster Aviation Collection, Long Kesh Airfield, near Belfast (See [https://www.ulsteraviationsociety.org/ Ulster Aviation Society website] for details of how to visit)
The sole SB.4 is on display at the Ulster Aviation Collection, Long Kesh Airfield, near Belfast<ref>[https://www.ulsteraviationsociety.org/aircraft-collection Ulster Aviation Society website]</ref>


==Specifications==
==Specifications==
[[File:Short SB4 Sherpa.png|right|300px|3-view projection of the Short Sherpa.]]
[[File:Short SB4 Sherpa.png|right|300px|3-view projection of the Short Sherpa.]]
{{Aircraft specs
{{Aircraft specs
|prime units?=imp
|prime units?= imp
|ref=Shorts Aircraft since 1900<ref>Barnes and James 1989, p. 446.</ref>
|ref= ''Shorts Aircraft since 1900.''<ref>Barnes and James 1989, p. 446.</ref>
|crew=1
|crew= 1
|length ft=31
|length ft= 31
|length in=10
|length in= 10
|length m=9.7
|length m= 9.7
|span ft=38
|span ft= 38
|span in=0
|span in= 0
|span m=11.58
|span m= 11.58
|span sweep=42 degrees
|span note= sweepback 42 degrees
|height ft=9
|height ft= 9
|height in=1.12
|height in= 1.12
|height m=2.77
|height m= 2.77
|wing area sqft=230
|wing area sqft= 230
|wing area sqm=21.4
|wing area sqm= 21.4
|empty weight lb=3,000
|empty weight lb= 3,000
|empty weight kg=1,400
|empty weight kg= 1,400
|gross weight lb=3,268
|gross weight lb= 3,268
|gross weight kg=1,482
|gross weight kg= 1,482
|eng1 name=[[Turbomeca Palas|Blackburn Turbomeca Palas]]
|eng1 name= [[Turbomeca Palas|Blackburn Turbomeca Palas]]
|eng1 type=[[turbojet]]
|eng1 type= [[turbojet]]
|eng1 number=2
|eng1 number= 2
|eng1 lbf=350
|eng1 lbf= 350
|eng1 kn=1.6
|eng1 kn= 1.6
|max speed mph=170
|max speed mph= 170
|max speed kts=150
|max speed kts= 150
|max speed kmh=275
|max speed kmh= 275
|cruise speed mph=117
|cruise speed mph= 117
|cruise speed kts= 102
|cruise speed kts= 102
|cruise speed kmh= 188
|cruise speed kmh= 188
Line 104: Line 110:


==References==
==References==
===Citations===
;Notes
{{reflist|2}}
{{reflist}}

;Bibliography
===Bibliography===
{{refbegin}}
* Barnes, C.H. ''Shorts Aircraft since 1900''. London: Putnam, 1967.
* Barnes, C.H. with revisions by Derek N. James. ''Shorts Aircraft since 1900''. London: Putnam, 1989 (revised). {{ISBN|0-85177-819-4}}.
* Barnes, C.H. with revisions by Derek N. James. ''Shorts Aircraft since 1900''. London: Putnam, 1989 (revised). {{ISBN|0-85177-819-4}}.
* {{cite journal |last1=Buttler |first1=Tony |title=Control at the Tips: Aero-isoclinics and Their Influence on Design |journal=Air Enthusiast |date=May–June 1999 |issue=81 |pages=50–55 |issn=0143-5450}}
⚫
* Gunston, Bill. "Short's Experimental Sherpa." ''Aeroplane Monthly,'' Vol. 5, no. 10. October 1977, pp. 508–515.
* Buttler, Tony and Jean-Louis Delezenne. ''X-Planes of Europe: Secret Research Aircraft from the Golden Age 1946-1974''. Manchester, UK: Hikoki Publications, 2012. {{ISBN|978-1-902-10921-3}}
⚫
* Gunston, Bill. "Short's Experimental Sherpa." ''Aeroplane Monthly,'' Vol. 5, no. 10. October 1977, pp.&nbsp;508–515.
* "Sherpa - Fore-runner of High Speed, High Altitude Aircraft." ''Shorts Quarterly Review, Vol. 2, No. 3, Autumn 1953.''
* "Sherpa - Fore-runner of High Speed, High Altitude Aircraft." ''Shorts Quarterly Review, Vol. 2, No. 3, Autumn 1953.''
* {{cite magazine |last=Warner |first=Guy |title=From Bombay to Bombardier: Aircraft Production at Sydenham, Part One |magazine=[[Air Enthusiast]] |date=July–August 2002 |issue=100 |pages=13–24 |issn=0143-5450}}
{{refend}}


==External links==
==External links==
{{Commons category}}
{{Commons category}}
*[http://minijets.org/page_palas.php Turboméca Palas description]
*[http://minijets.org/page_palas.php Turboméca Palas description] {{Webarchive|url=https://web.archive.org/web/20071007005850/https://minijets.org/fr/150-300/turbomeca-palas/short-sb4-sherpa/ |date=7 October 2007 }}
*[http://www.aviationmuseum.net/ Sherpa fuselage exhibited at Norfolk and Suffolk Aviation Museum, Flixton ]
*[http://www.aviationmuseum.net/ Sherpa fuselage exhibited at Norfolk and Suffolk Aviation Museum, Flixton ]


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[[Category:1950s British experimental aircraft]]
[[Category:1950s British experimental aircraft]]
[[Category:Short Brothers aircraft]]
[[Category:Short Brothers aircraft]]
[[Category:High-wing aircraft]]
[[Category:Tailless aircraft]]
[[Category:Twinjets]]

Latest revision as of 04:39, 7 November 2024

For the cargo aircraft, see Short C-23 Sherpa.

SB.4 Sherpa
Short Sherpa demonstrating at the Farnborough SBAC Show in September 1954
General information
TypeExperimental aircraft
National originUnited Kingdom
ManufacturerShort Brothers
Designer
Primary users
College of Aeronautics (Cranfield)
Number built1
History
First flight4 October 1953
Developed fromShort SB.1

The Short SB.4 Sherpa was an experimental aircraft designed and produced by the British aircraft manufacturer Short Brothers. Only a single example was ever produced.

The Sherpa was developed during the 1950s for the purpose of testing a novel wing design, referred to as an aero-isoclinic wing. It was believed that this wing design could possess favourable qualities for producing tailless aircraft, and that the Sherpa would validate the characteristics of the wing for such aircraft to be produced in the future. While such a wing had been flown on the earlier Short SB.1, an unpowered glider, it was deemed valuable to use a powered aircraft instead. The design of the Sherpa is largely based upon that of the SB.1, to the extent that it incorporated numerous elements of this aircraft.

The Sherpa performed its maiden flight on 4 October 1953, after which it spent several years performing experimental flights and the occasional aerial display. After gathering sufficient data for Shorts' purposes, the company decided that it did not show sufficient potential as to continue its research into the aero-isoclinic wing. The sole Sherpa was donated to the College of Aeronautics at Cranfield during the late 1950s and flown for numerous years. It was eventually grounded and used as a static laboratory specimen at the Bristol College of Advanced Technology, before being preserved and put on display at the Norfolk and Suffolk Aviation Museum.

Development

[edit]

The origins of the Short SB.4 Sherpa can be traced back to the 1920s and the activities of Professor Geoffrey T.R. Hill, who was pivotal in the design of the Westland-Hill Pterodactyl, a pioneering tailless experimental aircraft.[1] Even prior to the First World War, Shorts had been involved in tailless aircraft research, but interest in the field reached new heights in the years immediately following the Second World War. During the late 1940s, the company worked on multiple proposals for tailless aircraft in response to specifications issued by the Air Ministry, including Specification X.30/46 and Specification B.35/46, which sought a military assault glider and strategic bomber respectively.[2]

Short SB.4 Sherpa

In particular, one of the company's aeronautical engineers, David Keith-Lucas, was keen to eliminate the parasitic drag normally incurred by the presence of a conventional tail and fuselage, and thus was a keen proponent of the tailless approach.[3] He also observed that directional stability was a critical issue without the application of traditional fins and rudders; it was identified that the outermost parts of the wing could be rotated and repositioned to function as elevons for stability and control purposes. New wing designs that presented a low aspect ratio, such as the delta wing, had been observed to reduce the onset of these issues; Keith-Lucas and Hill, jointly developed what became known as the aero-isoclinic wing.[4]

Having become sufficiently confident in the merits of the aero-isoclinic wing , Shorts opted to produce a new experimental aircraft to incorporate the latest advances and explore its behaviour, thus it constructed the Short SB.1 glider.[4] This aircraft was designed to be as inexpensive as possible and thus featured extensive wooden construction alongside its innovative wing.[5] After only a few months of flight, the SB.1 suffered damage in a heavy landing at RAF Aldergrove on 17 October 1951. Shorts' chief test pilot, Tom Brooke Smith, objected to further flights of the unpowered glider. Accordingly, it was decided that the fuselage, which had been heavily damaged, would be replaced by a modified design that incorporated a pair of Turbomeca Palas turbojet engines.[6]

Design

[edit]
Rotated wingtip
Rotated wingtip (from below and behind)

The Short SB.4 Sherpa was an experimental aircraft, featuring an unusual aero-isoclinic wing.[6] 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; the aero-isoclinic wing was designed to specifically prevent these undesirable effects.[7]

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 manoeuvrability at high altitudes.[8]

In terms of its construction, the Sherpa was primarily composed of light alloys and featured a monocoque arrangement.[8] Wing sweep-back on the leading edge was just over 42° to facilitate low-speed research. The Sherpa was provisioned with a conventional tricycle undercarriage.[8] 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. Fuel was housed within the fuselage in two 250 gallon tanks, which were balanced around the aircraft's centre of gravity; electrical power was supplied by a ram air turbine by the engines.[9] Blackburn, who produced the Palas under licence, hoping to market these engines as a new product line, supplied the powerplants for the Sherpa programme.[10]

Testing

[edit]

On 4 October 1953, the Sherpa performed its maiden flight, piloted by Shorts' Chief Test Pilot, Tom Brooke-Smith.[9] Brooke-Smith had also piloted the earlier experimental glider aircraft, the Short SB.1, upon which the Sherpa was based. Although he sustained injuries in the crash landing of the SB.1, Brooke-Smith had quickly recovered and was able to undertake the test programme of the redesignated SB.4 (registered as G-14-1) throughout 1953–1954. (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.[9])

Short Sherpa testing at College of Aeronautics

During the initial series of flying trials of the Sherpa, performed largely by Brooke-Smith, the aircraft had reportedly proved to be quite satisfactory; its docile handling characteristics led to be being described as being 'one of the most graceful aircraft now flying'.[11][9] The aircraft was typically flown within a restricted flight envelope, during which it reportedly achieved a "flat-out" speed of 170 mph (270 km/h) at 5,000 ft (1,500 m),[12] which made it amongst the slowest jet-powered aircraft to have ever flown.[12][13]

Data from these flights was typically captured by an onboard flight data recorder and analysed post-flight to build up a model of how a similar full-sized wing would behave under various conditions, including various altitudes and speeds.[9] Keith-Lucas had aimed to validated the wing as a low weight solution that behaved well across various speeds, including the transonic range, but the attained test results did not fully validate his hopes.[14] Aviation author Bill Gunston notes that, despite the Sherpa having attaining its design goals, the concept was considered to be "not fully realised in practice" and the project was eventually wound up without a direct continuation.[13] Shorts did prepare multiple proposals, such as the retrofitting of the Supermarine Swift fighter with the aero-isoclinic wing, but these were not pursued.[15]

The Sherpa itself was subsequently donated to the College of Aeronautics at Cranfield, where it continued to fly up until 1958. At this point, engine issues forced the aircraft to be grounded until replacement powerplants could be organised.[15] During 1960, further engines were made available, thus flying of the Sherpa resumed until 1964, when, with its engine life expired, the Sherpa was finally grounded. Following this, it was transported to the Bristol College of Advanced Technology, where the airframe was used as a "laboratory specimen".[13][16] Its fuselage was on display at the Norfolk and Suffolk Aviation Museum, near Bungay, Suffolk,[17] until 17 July 2008, after which it was moved to the Lisburn site of the Ulster Aviation Society.[18]

Aircraft on display

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The sole SB.4 is on display at the Ulster Aviation Collection, Long Kesh Airfield, near Belfast[19]

Specifications

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3-view projection of the Short Sherpa.
3-view projection of the Short Sherpa.

Data from Shorts Aircraft since 1900.[20]

General characteristics

  • Crew: 1
  • Length: 31 ft 10 in (9.7 m)
  • Wingspan: 38 ft 0 in (11.58 m) sweepback 42 degrees
  • 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)
  • Gross weight: 3,268 lb (1,482 kg)
  • Powerplant: 2 × Blackburn Turbomeca Palas turbojet, 350 lbf (1.6 kN) thrust each

Performance

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

See also

[edit]

Related development

References

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Citations

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  1. ^ Barnes 1967, pp. 439-440.
  2. ^ Barnes 1967, pp. 439-441.
  3. ^ Barnes 1967, p. 441.
  4. ^ a b Barnes 1967, pp. 441-442.
  5. ^ Barnes 1967, p. 442.
  6. ^ a b Barnes 1967, pp. 442-443.
  7. ^ Barnes 1967, pp. 441-443.
  8. ^ a b c Barnes 1967, pp. 443-444.
  9. ^ a b c d e Barnes 1967, p. 444.
  10. ^ Gunston 1977, p. 512.
  11. ^ Shorts Quarterly Review, Autumn 1953.
  12. ^ a b Barnes and James 1989, p. 444.
  13. ^ a b c Gunston 1977, p. 513.
  14. ^ Barnes 1967, pp. 444-445.
  15. ^ a b Barnes 1967, p. 445.
  16. ^ Barnes and James 1989, p. 445.
  17. ^ Barnes 1967, pp. 445-446.
  18. ^ Ulster Aviation Society SB4 page
  19. ^ Ulster Aviation Society website
  20. ^ Barnes and James 1989, p. 446.

Bibliography

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  • Barnes, C.H. Shorts Aircraft since 1900. London: Putnam, 1967.
  • Barnes, C.H. with revisions by Derek N. James. Shorts Aircraft since 1900. London: Putnam, 1989 (revised). ISBN 0-85177-819-4.
  • Buttler, Tony (May–June 1999). "Control at the Tips: Aero-isoclinics and Their Influence on Design". Air Enthusiast (81): 50–55. ISSN 0143-5450.
  • Buttler, Tony and Jean-Louis Delezenne. X-Planes of Europe: Secret Research Aircraft from the Golden Age 1946-1974. Manchester, UK: Hikoki Publications, 2012. ISBN 978-1-902-10921-3
  • Gunston, Bill. "Short's Experimental Sherpa." Aeroplane Monthly, Vol. 5, no. 10. October 1977, pp. 508–515.
  • "Sherpa - Fore-runner of High Speed, High Altitude Aircraft." Shorts Quarterly Review, Vol. 2, No. 3, Autumn 1953.
  • Warner, Guy (July–August 2002). "From Bombay to Bombardier: Aircraft Production at Sydenham, Part One". Air Enthusiast. No. 100. pp. 13–24. ISSN 0143-5450.
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