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{|{{Infobox aircraft begin
 |name= Grob G 520
 |image= File:G520 EGRETT.jpg
 |caption= Grob G 520T
}}{{Infobox aircraft type
 |type= High-altitude and reconnaissance aircraft
 |manufacturer= [[Grob Aircraft]]
 |designer=
 |first flight= 24 June 1987
 |introduced= 1991
 |retired=
 |status=
 |primary user=
 |more users=
 |produced=
 |number built= 6
 |variants with their own articles=
}}
|}

The '''Grob G 520 ‘EGRETT’''' is a [[turboprop]]-powered long-endurance, high-altitude reconnaissance and surveillance aircraft designed and produced by the German aircraft manufacturer [[Grob Aircraft]]. Since September 1988, it has been the holder of several world records relating to altitude and time to climb.

The G 520 was developed during the 1980s to fulfil a joint [[German Air Force]] – [[USAF|United States Air Force]] requirement for a high-altitude, long-duration surveillance platform. The resulting aircraft is one of the world's largest fully [[composite material|composite]] manned aircraft;  it possesses full approval for all-weather IFR/icing operations according to LBA/FAA Part 23 regulations along with short runway capabilities. While designing the G 520, Grob Aircraft closely collaborated with two other companies: [[E-Systems]] and [[Garrett AiResearch|Garrett]]; the name ‘Egrett’ was derived from the three companies involved in its design.<ref name = "bornspy 2020"/> The ''D-450 EGRETT I'' development aircraft performed its [[maiden flight]] on 24 June 1987.

During 1991, the G 520 received [[Airworthiness certificate|certification]]; one year later, an order was placed by the [[German Air Force]] for production of nine EGRETT IIs, however, this was cancelled in 1993. Several single-seat aircraft, as well the sole twin-seat trainer ''G 520T'', were completed during the early 1990s. The type has been used by various agencies, including the [[German Aerospace Center]] (DLR), to undertake scientific research and other niche high-altitude roles, including the highest known glider tow for the [[Windward Performance Perlan II]] in 2018. During the mid 2010s, Grob Aircraft announced their intention to resume quantity production of a modernised version of the aircraft, designated ''G 520NG''; new abilities include its potential use as an [[optionally piloted vehicle]].

== Development ==
The G. 520 originated during the 1980s as a purpose-built surveillance aircraft developed under an international partnership comprising three companies: [[E-Systems]], [[Garrett AiResearch|Garrett]], and [[Grob Aircraft]].<ref name="Brasseys96 p172">Taylor 1996, p. 172.</ref><ref name = "bornspy 2020">{{cite web |url = https://aerospace.aerosociety.com/aerospace/aerospace-september-2020/features/born-to-spy |title = Germany’s U-2: Born to Spy |publisher = aerospace.aerosociety.com |first = Alan |last = Warnes |date = September 2020}}</ref> It was intended to fill a joint [[German Air Force]] – [[USAF|United States Air Force]] requirement for a high-altitude, long-duration surveillance platform for treaty verification and [[environmental monitoring]]. Known as "LAPAS" (''Luftgestütztes, abstandsfähiges Primär-Aufklärungssystem'', engl: airborne, long distance primary reconnaissance system) in Germany and "Senior Guardian" in the US, the program initially attempted to acquire the [[Lockheed TR-1]] (U-2) for this role, but when this did not succeed, a new aircraft was sought.<ref name = "bornspy 2020"/>

Under the partnership framework, the airframe was developed by Grob, the avionics were provided by E-Systems, and the [[Honeywell TPE331|TPE 331-14F]] turboprop engine was supplied by Garrett.<ref name = "bornspy 2020"/> During the design phase, the programme was viewed by E-Systems as a major opportunity to increase its prominence in the international markets and grow the business, which offset the difficulties associated with the export of technologies that were considered to be highly sensitive at that time.<ref name = "bornspy 2020"/>

On 24 June 1987, the initial ''D-450 EGRETT I'' development aircraft conducted its [[maiden flight]], piloted by Einar Enevoldson. Considerable emphasis was placed on demonstrating the aircraft’s high altitude capabilities.<ref name = "bornspy 2020"/> According, during September 1988, the D-450 established three separate world records related to altitude and time to climb; specifically: 
* Time to climb to {{convert|15,000|m|ft|0}}: 40 minutes 47 seconds<ref>{{cite web |url= https://www.fai.org/record/1392 |title=Class C-1e (Landplanes: take off weight 3 000 to 6 000 kg) - Time to climb to a height of 15 000 m |publisher= [[Fédération Aéronautique Internationale]] |date=1 September 1988}}</ref>
* Altitude in horizontal flight: {{convert|16,239|m|ft|0}}<ref>{{cite web |url= https://www.fai.org/record/1390 |title= Class C-1e (Landplanes: take off weight 3 000 to 6 000 kg) - Altitude in horizontal flight |publisher=[[Fédération Aéronautique Internationale]] |date=1 September 1988 }}</ref>
* Altitude without payload: {{convert|16,329|m|ft|0}}<ref>{{cite web |url= https://www.fai.org/record/1388 |title=Class C-1e (Landplanes: take off weight 3 000 to 6 000 kg) - Altitude |publisher=[[Fédération Aéronautique Internationale]] |date=1 September 1988 }}</ref>

[[File:Egrett.jpg|thumb|left|G 520 during a test flight, 1991]]
During 1989 and 1990, a pair of pre-production aircraft, referred to as the ''D-500 EGRETT II'', were completed. On 13 September 1991, the aircraft received [[Airworthiness certificate|airworthiness certification]].<ref name = "bornspy 2020"/> That same year, the two pre-production aircraft were fitted out to the finalized G 520 configuration; owned by E-Systems and Grob respectively, both aircraft were typically used for promotional purposes. While E-Systems' aircraft was focused on demonstrating its various sensor packages, Grob's aircraft (renamed the ''Strato 1'') was commonly used to market the aircraft towards civil authorities as a resource management platform.<ref name = "bornspy 2020"/><ref name = "warzone 2020"/>

In 1992, the [[German Air Force]] placed an order for production of nine EGRETT IIs; these were intended to be supplemented by at least one G 520T twin seat trainer and one of the demonstrator aircraft.<ref name="JAWA93p138-0">Lambert 1993, pp. 138–140.</ref> The estimated value of this contact was between $600 million and $1 billion.<ref name = "bornspy 2020"/><ref name = "warzone 2020"/>

However, during February 1993, before much of the manufacturing work had taken place, the procurement process came under intense scrutiny when accusations of [[corruption]] (''Amigo Affair'') surrounding the former [[Bavaria]]n [[Minister President]] [[Max Streibl]] became public. A further factor was the end of the [[Cold War]] and the subsequent defence budget reductions that impacted the [[German Air Force]].<ref name = "bornspy 2020"/> The program was formally cancelled as the threat from [[Eastern Europe]] was perceived to be no longer present.<ref name="JAWA93p138-0"/><ref>{{cite web |first = Gerhard |last = Hegmann |url = https://www.welt.de/wirtschaft/article128950948/Grob-baut-deutschen-Aufklaerer-auch-als-Drohne.html |title = Grob baut deutschen Aufklärer – auch als Drohne |publisher = [[Die Welt]] |date = 11 June 2014 |access-date = 19 September 2021}}</ref><ref>{{cite web |first = Sebastian |last = Steinke |url = https://www.aerokurier.de/motorflug/rekord-schlepp-mit-der-grob-egrett-in-die-stratosphaere/ |title = Rekord-Schlepp: Mit der Grob Egrett in die Stratosphäre |publisher = [[Aerokurier]] |date = 22 August 2018}}</ref> A total of five single-seat aircraft had been completed by the time of the termination. During 1993, E-Systems decided to pull out of the G 520 programme entirely.<ref name = "bornspy 2020"/>

In the early 1990s, a single twin-seat trainer G 520T was completed by Grob and was initially acquired to the [[German Aerospace Center]] (DLR).<ref name = "bornspy 2020"/> During 1997, the DLR sold it on to [[Airborne Research Australia]] in [[Adelaide]], which performed numerous scientific programmes using the aircraft. The G 520T was grounded in 2007 due to a lack of funds and was repurchased by Grob Aircraft during 2013,<ref name = "bornspy 2020"/> after which it was upgraded, returned to flightworthy condition, and flown back to Germany.<ref>{{cite web |title = TV documentation: Return of the G 520T |url = http://www.br.de/mediathek/video/sendungen/abendschau-der-sueden/grob-flugzeug-mindelheim-100.html |website = br.de |archive-url = https://web.archive.org/web/20140617043901/http://www.br.de/mediathek/video/sendungen/abendschau-der-sueden/grob-flugzeug-mindelheim-100.html |archive-date = 17 June 2014 }}</ref> Following repainting, it was presented to the public during the 2014 [[Farnborough Airshow]] as part of the firm’s promotion of its plans to resume production of the G 520.<ref name="flugrevue.de">{{cite web |title = Farnborough: Return of the Grob Egrett |url = http://www.flugrevue.de/militaerluftfahrt/kampfflugzeuge-helikopter/grob-egrett-kehrt-zurueck/581998 |website = flugrevue.de |archive-url = https://web.archive.org/web/20140726052621/http://www.flugrevue.de/militaerluftfahrt/kampfflugzeuge-helikopter/grob-egrett-kehrt-zurueck/581998 |archive-date = 26 July 2014 }}</ref>

During the late 2010s, the sole G 520T has been upgraded with many of the innovations intended for the new generation G 520NG.<ref name = "bornspy 2020"/> These include the adoption of a [[Pratt & Whitney PT-6]], a total-authority autopilot, and other fittings to turn it into an [[optionally piloted vehicle]] that can be flown remotely from a ground station. The prospective G 520NG has been promoted as being a more affordable alternative to [[unmanned surveillance and reconnaissance aerial vehicle]]s such as the [[Northrop Grumman RQ-4 Global Hawk]] as well as the aircraft not falling under [[International Traffic in Arms Regulations]] (ITAR) restrictions.<ref name = "bornspy 2020"/>

During the latter half of 2018, a G 520 was outfitted with a new towing system and used to perform the highest altitude glider tow in history while conveying the [[Windward Performance Perlan II]] (a pressurised space capsule intended to fly by riding stratrospheric mountain waves to heights of up to 90,000ft) to altitude.<ref name = "bornspy 2020"/>

== Design ==
[[File:N520DM (8484060648).jpg|thumb|right|inflight, showing the high [[wing aspect ratio]]]]
The G 520 is a fully composite conventional mid-wing monoplane with extremely [[high aspect ratio]] wings. These wings flex considerably during flight, especially when encountering [[turbulence]].<ref name = "bornspy 2020"/> It was the first composite aircraft specifically designed for stratospheric research.{{citation needed|date=October 2024}}

Power is typically provided by a single turboprop [[Honeywell TPE331|Honeywell TPE 331-14F]] that drives a four-blade [[Hartzell Propeller|Hartzell]] propeller. This engine is fitted with large exhaust [[muffler]]s that are intended to reduce both the [[Acoustic signature|acoustic]] and [[infrared]] signatures produced.<ref name = "warzone 2020"/> It is equipped with a [[tricycle undercarriage]], whose main units retract into fairings on the wings. Differential braking is used to control the aircraft while taxiing, except on the twin-seat G 520T, which can be steered using the nose wheel instead.<ref name = "bornspy 2020"/> Up to 100kg of [[ballast]] can be installed within the tail unit to offset balance and weight issues posed by the payloads that can be carried.<ref name = "bornspy 2020"/>

The slender fuselage of the G 520 is [[modular design|modular]], the whole lower section not forming a part of the aircraft’s structure.<ref name = "bornspy 2020"/> This approach is uncommon and made the aircraft easily adaptable to suit a wide variety of surveillance missions. In the center of the lower fuselage is a flexible payload compartment (sometimes referred to as Bay 13) that was entirely detachable, allowing preconfigured payloads to be rapidly interchanged.<ref name = "bornspy 2020"/> The G 520 can accommodate multiple mission systems for both civilian and military applications, a total of 12 payload compartments for the carriage of up to 850&nbsp;kg of mission equipment are provisioned. These compartments can be adapted to accept various customer-specified payloads, including electro-optical sensors, [[LIDAR]], [[sigint]], and scientific packages. When functioning as a [[maritime patrol aircraft]], it can be furnished with a suitable [[radar]], or be used as a satellite relay system to bolster ground communications via [[communications satellite|satcom]] apparatus.<ref name = "bornspy 2020"/> An optional [[radome]] can be present on the underside of the fuselage.<ref name = "warzone 2020">{{cite web |url = https://www.twz.com/12569/unusual-high-altitude-spy-plane-appears-at-special-operations-exercise |title = Unusual High-Altitude Spy Plane Appears at Special Operations Exercise |publisher = The Warzone |first = Joseph |last = Trevithick |date = 5 July 2020}}</ref>

The cockpit of the G 520T provides room for a pilot and a sensor operator as well as for equipment which has to be placed inside the pressurized cabin. The instrument panel can be optionally equipped with a digital glass cockpit IDU-680 EFIS by [[Genesys Aerosystems]].<ref name = "bornspy 2020"/> An optional operator console can be installed in the rear cockpit of twin seat aircraft; these furnishing include a full keyboard, hand controller units, and a camera grip. The rear cockpit can also be configured for training duties.<ref name = "bornspy 2020"/> Refit aircraft are commonly equipped with a dual-[[GPS]] system and have been outfitted for all-weather operations.<ref name = "bornspy 2020"/>

==Variants==
;D-450 EGRETT I
:Initial prototype. One built.
;D-500 EGRETT II
:Pre-production aircraft. Two built.
;G 520
:Original single-seat production standard aircraft. Five built.
;G 520T
:Twin-seat version of the G 520. One built.
;G 520NG
:Modernised version of the G 520T. Production of the type was envisioned to commence during the 2010s.<ref name="flugrevue.de"/>{{update|date=October 2024}}


==Operators==
;{{AUS}}
:[[Airborne Research Australia]]
;{{GER}}
:[[German Aerospace Center]] (DLR)
;{{USA}}{{ARG}}
:[[Perlan Project]] High altitude glider towing <ref>{{cite web |url=http://www.perlanproject.org/blog/tow-42800-feet |title=Tow to 42,000 feet |website=pelanproject.org |date=23 August 2018 |access-date=19 September 2021 }}</ref>

== Specifications ==

{{Aircraft specs
|ref= Grob<ref name="Specs">{{cite web |url = http://www.grob-aircraft.com/index.php/technical-specification-23.html |title = Grob G 520 Technical Specifications |access-date = 15 July 2014 |last = Grob Aircraft |author-link = Grob Aircraft |date = n.d.}}</ref>
|prime units?= met<!-- imp or kts first for US aircraft, and UK aircraft pre-metrification, 
met(ric) first for all others. You MUST choose a format, or no specifications will show -->
<!--
        General characteristics

-->
|genhide=

|crew= one
|capacity= one passenger / {{convert|850|kg|abbr=on}} payload
|length m= 13.82
|span m= 33.0
|height m= 5.66
|wing area sqm= 39.67
|aspect ratio=<!-- sailplanes -->
|airfoil=
|empty weight kg= 3,300
|gross weight kg=
|gross weight lb=
|gross weight note=
|max takeoff weight kg= 4,700
|fuel capacity= {{convert|1070|kg|abbr=on}}
|more general=
<!--
        Powerplant
-->
|eng1 number= 1
|eng1 name= [[Honeywell TPE331-14F]]
|eng1 type= Turboprop [[aircraft engine]]
|eng1 hp= 750

|prop blade number= 4<!-- propeller aircraft -->
|prop name= [[Hartzell Propeller|Hartzell]]
|prop dia m= 3.04<!-- propeller aircraft -->
|prop dia ft= 10<!-- propeller aircraft -->
|prop dia in=<!-- propeller aircraft -->
|prop dia note= constant-speed propeller

<!--
        Performance
-->
|max speed kts= 253
|max speed note= maximum operating weight, MSL
|cruise speed kts= 153
|cruise speed note= at {{convert|35000|ft|abbr=on|order=flip}} ISA, MTOW
|stall speed kts= 58
|stall speed note= (MLW, landing configuration)
|never exceed speed kmh=
|never exceed speed mph=
|never exceed speed kts=
|never exceed speed note=
|range km= 3,670
|range note= at {{convert|50000|ft|abbr=on|order=flip}} ISA, MTOW, 45 minutes of reserve fuel, {{convert|500|kg|abbr=on}} payload
|endurance= 7.5 hours at {{convert|50000|ft|abbr=on|order=flip}} ISA, MTOW, 45 minutes of reserve fuel, {{convert|500|kg|abbr=on}} payload
|ceiling m= 15,240
|ceiling note= (max. certified operating altitude)
|g limits=
|climb rate ms= 7.3
|time to altitude= 50 minutes to {{convert|45000|ft|abbr=on|order=flip}}
|lift to drag=
|wing loading kg/m2=
|wing loading lb/sqft=
|wing loading note=
|fuel consumption kg/km=
|fuel consumption lb/mi=
|power/mass=
|thrust/weight=
|more performance=
* '''Take off distance over {{convert|50|ft|abbr=on|order=flip}}:''' {{convert|670|m|abbr=on}} (MSL, ISA, MTOW, no wind, no slope)
* '''Landing distance over {{convert|50|ft|abbr=on|order=flip}}:''' {{convert|685|m|abbr=on}} (MSL, ISA, MTOW, no wind, no slope)
|avionics=
}}

<!-- ==See also== -->
{{aircontent
<!-- include as many lines are appropriate. additional lines/entries with carriage return. -->
|see also=
|related=<!-- related developments -->
|similar aircraft=<!-- similar or comparable aircraft -->
|lists=<!-- related lists -->
}}

==References==

===Citations===
{{Reflist}}

===Bibliography===
* {{cite book |last=Lambert |first=Mark |title=Jane's All The Worlds Aircraft 1993–94 |publisher=Janes's Data Division |location=Coudsdon, UK |year=1993 |isbn=0-7106-1066-1}}
* {{cite book |last= Taylor |first= Michael J. H. |title=Jane's Encyclopedia of Aviation |year=1989 |publisher=Studio Editions |location=London, UK |pages=924 }}
* {{cite book |last=Taylor |first=Michael |title=Brassey's World Aircraft & Systems Directory 1996/97 |year=1996 |publisher=Brassey's |location=London, UK |isbn=1-85753-198-1 |url-access=registration |url=https://archive.org/details/brasseysworldair0000unse }}
* {{cite book |title=World Aircraft Information Files |publisher=Bright Star Publishing |location=London, UK |pages=File 895 Sheet 14 }}

==External links==
{{commons category|Grob G 520}}
* [https://grob-aircraft.com/en/g-520ng.html G 520 official website]
* [http://www.grob-aircraft.com/ Grob Aircraft official website]

{{Grob aircraft}}

{{DEFAULTSORT:Grob E-Systems AlliedSignal Egrett}}
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