The Grob G 109 is a light aircraft developed by Grob Aerospace of Mindelheim Mattsies in Germany that first flew in 1980. The basic concept is that of 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 primarily 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.
Design and development
Technical description (G 109B / Vigilant T1)
The aircraft is a low-wing cantilever motor glider which features 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 wide range of body sizes.
Total weight is around with a load of . Cruising speed is in the region of 60–100 knots (110–190 km/h) on the engine which can give the aircraft a top speed of . 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).
The G 109B is powered by a Grob 2500 E1 horizontally-opposed, four-cylinder, air-cooled petrol engine that develops approximately 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)
The Vigilant T1 variant was introduced into service in 1991 when it replaced a fleet of Slingsby T.61 Ventures, and is currently used by Volunteer Gliding Squadrons (VGS), located at various sites around the UK. Their 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.
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 . The first prototype, (registered D-KGBF
), flew for the first time on 14 March 1980.
The G 109A was fitted with a 2,000 cc Limbach-Flugmotoren flat four
engine (maximum power delivered at 3,400 rpm), and the wing span was increased to .
It was noted that the spare engine power available was marginal in hot atmospheric conditions or when flying through rain. Around 30 G 109A airframes were fitted with a 2,400 cc 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
A total of 151 G 109A motor gliders were produced.
Developed out of the Grob G 109A; the wingspan was further increased to , 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. The engine was replaced with a Grob-built 2,500 cc unit of .
Some aircraft in Germany have recently been fitted with a turbocharged engine, and with structural strengthening of the fuselage have been successfully adapted for aero-towing of gliders.
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 higher maximum all up mass (AUM) of 908kg and a throttle for use in the left hand seat. 53 built.
Specifications (Vigilant T1)