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G 109 / Vigilant T1
A British-registered G109B.
Role Motor glider
Manufacturer Grob Aerospace
Designed by Burkhart Grob
First flight 14 March 1980
Primary user Royal Air Force
Number built 476

The Grob G 109 is a light aircraft developed by Grob Aerospace of Mindelheim Mattsies in Germany. It first flew in 1980. It is a two-seat self-launching motor glider in which the pilot and passenger or student sit side by side, with good visibility provided by large windows. This aircraft is now used in Volunteer Gliding Squadrons by the Royal Air Force to train Air Cadets through the Gliding Induction and Gliding Scholarship courses. The Grob 109B is known in RAF service as the Vigilant T1.

The G 109 was the first motor glider built using composite construction to be granted Federal Aviation Administration approval.[1]


Design and development


Technical description (G 109B / Vigilant T1)

The aircraft is a low-wing cantilever motor glider, with a T-tail, folding (and detachable) wings, and side-by-side seating with dual controls. It is mainly constructed from glass-reinforced plastic and has a taildragger undercarriage arrangement. Entry and exit from the cockpit is via two perspex doors which open upwards individually – a modification from the original one-piece G 109 canopy. The cockpit can be heated, providing that the engine is running, and the seat backs can be adjusted and cushions of differing thickness inserted to accommodate a range of body sizes.

Total weight is around 1,870 pounds (850 kg) with a load of 506 pounds (230 kg). Cruising speed is in the region of 60–100 knots (110–190 km/h) on the 95 horsepower (71 kW) engine which can give the aircraft a top speed of 130 knots (240 km/h). The engine (based on a Volkswagen car unit) can be shut down in flight with its propeller blades feathered. The aircraft then becomes a pure glider, with a best glide ratio of around 1:28.

Under the current CAA LASORS document, the G 109 can be classed as either a touring motor glider (TMG), or a self-launching motor glider (SLMG).

Royal Air Force Grob G109B motor glider lands at RIAT 2008, England.


The G 109B is powered by a Grob 2500 E1 horizontally-opposed, four-cylinder, air-cooled petrol engine that develops approximately 95 bhp (71 kW) at 2,950 rpm. The propellor is a two-bladed, manually-operated variable pitch type driven directly from the engine. Three pitch settings can be used: Fine for take-off and general flying, Coarse for cruising, and Feathered for gliding with the engine off.

Hot air can be supplied to the twin carburettors when there is a risk of icing. An electric fuel pump is used.


The G 109 uses conventional controls, duplicated for both seats, with the addition of airbrakes. The controls are colour-coded to match those of a glider to aid pilot conversion training. The rudder pedals, which also operate the wheel brakes, are adjustable forward and backward to suit individuals of differing leg length.

The airbrakes are used to increase the rate of descent and are primarily used during the approach to landing.

Operational history (Vigilant T1)

A Grob Vigilant T1 of 637 VGS

The Vigilant T1 variant was introduced into service in 1991 when it replaced a fleet of Slingsby Ventures, and is used by Volunteer Gliding Squadrons (VGS) around the UK. The VGS role is to train air cadets in basic flying instruction with the aim of bringing them to a standard where they are able to fly solo. Tailored courses are available to air cadets including the advanced gliding training course.

The Vigilant is also used by the Air Cadet Central Gliding School at RAF Syerston in Nottinghamshire, where it is used to train the VGS instructors.


G 109

The first two prototype aircraft (constructor's serial numbers 6001 and 6010) were designated G 109. They differed from later production aircraft by having a shorter wing span of 15 metres (49 ft). The first prototype, (registered D-KBGF), flew for the first time on 14 March 1980.[2]

G 109A

The G 109A was fitted with a 2,000 cc 80 horsepower (60 kW) Limbach-Flugmotoren flat four engine (maximum power delivered at 3,400 rpm), and the wing span was increased to 16.6 metres (54 ft).

The spare engine power available was marginal in hot atmospheric conditions or when flying through rain so around 30 G 109A airframes were fitted with a 2,400 cc 90 horsepower (67 kW) Limbach engine and an electrically-controlled variable pitch propeller. At least one aircraft has been approved by the Luftfahrt-Bundesamt to use the Rotax 912 engine.

A total of 151 G 109A motor gliders were produced.

G 109B

Developed out of the Grob G 109A; the wingspan was further increased to 17.4 metres (57 ft), the one-piece canopy of the earlier versions was replaced with opening doors, and the main landing gear was moved rearwards to ease weight on the tail wheel.[3] The engine was replaced with a Grob-built 2,500 cc unit of 95 horsepower (71 kW).

Some aircraft in Germany have been fitted with a turbocharged engine, and with structural strengthening of the fuselage have been adapted for aero-towing of gliders.

Vigilant T1

The Vigilant T1 is the designation of the adapted Grob 109B used by the Royal Air Force for use on Volunteer Gliding Squadrons. The Vigilant T1 has a landing light fitted, a higher maximum all up mass (AUM) of 908kg and a throttle for use in the left hand seat. 53 were originally built, while several more have been acquired for the RAF on the second-hand market.


 United Kingdom

Specifications (Vigilant T1)


General characteristics

  • Crew: Two (student and instructor)
  • Length: 8.10 m (26.57 ft)
  • Wingspan: 17.4 m (57.09 ft)
  • Height: 1.7m (5.58 ft)
  • Wing area: 19.0 m² (204.5 ft²)
  • Empty weight: 620 kg (1,364 lb)
  • Loaded weight: 850 kg (1,874 lb)
  • Max takeoff weight: 908 kg (2,001 lb)
  • Powerplant: 1× Grob 2500 4-cylinder air-cooled piston engine, 71 kW (95 hp)


See also

Comparable aircraft

Related lists



  1. ^ Grob website Retrieved 23 August 2008
  2. ^ Hardy 1982, p.155.
  3. ^ Hardy 1992, p.156.
  4. ^ Royal Air Force Equipment Retrieved: 13 December 2009


External links


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