Country of origin:

Germany

Description:

Multi-purpose high-altitude surveillance and research aircraft

Power Plant:

One 560 kw (750 shp) Allied Signal TPE331-14F-801L flat-rated turboprop

Specifications:

History:

The Grob G-520 Egrett (a name taken from the three companies which developed the proof-of-concept aircraft, ie E-Systems, Grob and Garrett) was one of a series of high-altitude surveillance and research aircraft planned by E-Systems and built by Grob Aerospace, work commencing in 1986, prototype construction taking place at Mindelheim/Mattsies in West Germany. Other members of the development consortium included Hughes Aircraft Company, MBB, Telefunken Systemtechnik and Elekluft.

Five examples were built, the proof of concept aircraft (D-FGEI/N14ES – c/n 10001) setting a number of world records for its class for time to height, height with payload, and height in level flight. It has been said the type was originally developed for the German military to spy across European borders.

E-Systems Inc of Dallas, Texas was the prime contractor for the Egrett program, commencing a feasibility study in the late 1960s in relation to producing an aircraft capable of carrying a 350 kg (770 lb) payload to a height of 12,000 m (39,500 ft) and, as fuel was burned off, climb to 15,000 m (49,200 ft) and operate at that level for 24 hours. A manned model known as the L450 with a Pratt & Whitney Canada PT6A-34 turboprop engine was built, and a United States Air Force (USAF) contract was awarded to construct an un-manned model known as the XQM-93A Remotely Piloted Vehicle. Two were built and tested at Edwards Air Force Base in California from September 1971 to February 1972, flights up to 22 hours being achieved. In March 1972 the L450 established 16 world records for turboprops, including (in the unlimited weight category) a sustained altitude of 15,456 m (50,708 ft) and a time to 15,000 m (49,200 ft) of 46.5 minutes.

Initial plans were for a ten to fifteen aircraft squadron of the G-520 Egrett to enter service with the German Luftwaffe as a means to patrol the Iron Curtain, its sensors looking deep into enemy territory to provide warning of any impending attack. However, this program was abandoned in early 1993 due to German defence economies following the end of the Cold War.

One example of the D-500 was built and four D-520s D-FGEE (c/n 10002); D-FDEM (c/n 10004); D-FGEO (c/n 10003 – ex D-FSTN); and D-FGRO (c/n 10005), the latter known as the Strato I, which first flew on 5 June 1991. One other airframe was built in the initial batch, the G-520T (D-FDST, later D-FARA – c/n 10200) being a two-seat training variant which first flew on 21 April 1993, which had a lengthened fuselage with plugs forward and aft of the wing.

The G-520 was a single-seat high aspect-ratio mid-wing monoplane of all composite construction fitted with a 559 kw (750 shp) Garrett TPE 331-14F-801L turboprop optimised for high-altitude operation driving a four-blade Hartzell propeller 3.05 m (10 ft) in diameter. It was able to carry a payload up to a max weight of 1,000 kg (2,200 lb) in 12 purpose-designed air-conditioned equipment bays in the fuselage, these being modified to suit the particular mission. The cabin was pressurised but at operations above 7,620 m (25,000 ft) a pressure suit was usually used. It was able to remain at mission altitude for between eight and thirteen hours cruising at up to 463 km/h (288 mph) and, with reserve, had a still-air range of 3,428 km (2,130 miles).

Six members of the Egrett family are known to have been completed. The third built D-FGEO (later D-FSTN) was owned by Germany’s STN Atlas Elektronik, and three of the others (D-FGEE, D-FDEM and D-FGRO) were owned by Raytheon Systems, which took over from E-Systems. One was operated for a time by Aurora Flight Sciences in the USA.

The type had a capacious fuselage and a very high aspect-ratio wing, being capable of manned or unmanned operation, there being 12 bays able to accept various payloads to meet customer requirements. Power plant was the TPE331 turboprop driving a four-blade constant-speed fully-feathering reverse-pitch propeller built by Hartzell, fuel capacity being 1,117 litres (246 Imp gals) as standard.

By 1996 two of the aircraft were flying in the United States and one in Germany (all single-seaters), one had been retired, and the G-520T was obtained by Airborne Research Australia (ARA), Australia’s National Research Aircraft Facility, hosted by an Australian Government funded national research facility at the Flinders University in Adelaide, SA for atmospheric and environmental geophysical research mission applications. While already owned by ARA, but still operated in Germany, it carried the registration D-FARA for a period but in 1998 became VH-ARA (c/n 10200 – ex D-FARA, D-FDST).

Following ARA taking over the G-520T, it took part in many international atmospheric science field campaigns operating in the United Kingdom, Japan and Australia. It carried a large variety of scientific instruments during these campaigns studying turbulence in the jetstream, the exchange of Tarce gases between the troposphere and the stratosphere, the characteristics of cirrus clouds and thunderstorms, as well as for verifying satellite-based remote sensing instruments. The aircraft was based at ARA’s operations base at Parafield airport near Adelaide.

The aircraft was withdrawn from service in 2014 and flown to Germany. At this time the German owner offered the aircraft for charter work, stating the aircraft was capable of most of the work that could be carried out by the Global Hawk series of UAV aircraft and could achieve great coverage at altitude because of its 7.5 hour endurance.

In late 1996 Grob indicated it was considering placing the type back in production as interest was being shown by military and commercial operators in using the aircraft for climate research programs, etc, especially in view of the failure at that time of unmanned aircraft to satisfy performance and flexibility criteria.

Development led to the Grob G-850 Strato 2C (D-CDLR), with the world’s largest single-piece all-composite wing, which made its first flight on 31 March 1995. Five months later, on 4 August, it set a world altitude record for manned piston-engined aircraft of 18,552 m (60,867 ft). It was then developed under a contract from the Deutsche Forschungsanstalt for Luft-und-Raumfahrt aimed at producing a research and observation aircraft capable of flying to 24,000 m (78,740 ft) for up to 48 hours.

At this time Grob had great experience in building light-weight airframes for sailplanes and put this to good effect in the new aircraft. It had bays in the nose and rear fuselage which could accommodate equipment such as sensors, cameras and scanners but eventually this area was taken up with equipment for scientific research for atmospheric, stratospheric and climatic conditions.

Further development lead to the provision of 12 hard-points under the fuselage, four under the wings, and altered wing tips for further equipment installations. Optical windows were also installed for remote sensing instruments.

The Strato 2C was fitted with two Teledyne Continental TSIOL-550 turbocharged piston engines and two PW127 gas generators, driving two 6 m (19 ft 8 in) diameter pusher five-blade propellers which rotated at 636 rpm. However, after some testing, in June 1996 the German Government withdrew funding and Grob took over ownership of the sole aircraft completed at that stage. The aircraft has been mounted on a pole in front of the Grob Aerospace Company Headquarters at Mindelheim/Mattsies in Germany.