Grob G 109
| G109/ Vigilant T1 | |
|---|---|
 |
|
| A British-registered G109B. | |
| Role | Motor glider |
| Manufacturer | Grob Aircraft |
| Designer | Burkhart Grob |
| First flight | 14 March 1980 |
| Primary user | Royal Air Force |
| Number built | 476 |
The Grob G109 is a light aircraft developed by Grob Aircraft AG of Mindelheim Mattsies in Germany. It first flew (G109 prototype and then Production G109A form) in 1980 the G109B followed in 1984. 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. As well as normal civilian use this aircraft is now also used in Volunteer Gliding Squadrons(VGS) 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.
The G109B was developed after series production of the G109A which itself followed a number of early prototypes with differing wing spans, configurations etc. The G109B addressed several issues learnt from operation of the earlier G109A which included improvements to power (95Hp up from 80Hp on the G109A), performance of the wings when wet, crosswind behaviour and limits and cockpit space.
The G109B 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 G109A 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 maximum load of 506 pounds (230 kg) though this depends on mod state and history of the airframe and is rarely above 200 kg on most examples. The Royal Air Force sought and obtained a number of military specific modifications; including a dispensation from Grob for operating the military variant aircraft to a Max AUW of 908 kg providing an extra 59 kg of useful load. The aircraft was not modified to allow this and no changes to the operating procedures were required as the centre of gravity constraints were not exceeded. Grob have applied to EASA for permission to have an exception to the design standard (CS22) for the Grob 109B which would allow it to be certified to a similar 903 kg Max AUW however while the two objections received were rejected by EASA the authority has not yet taken the necessary rulemaking action to allow this. 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 Porsche air-cooled 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. The Porsche-derived horizontally opposed air-cooled engine had the cylinder bore increase by Grob to make the engine 2.5-litre capacity and has had its Time Before Overhaul (TBO) increased by a technote to 1,600 hours after many examples run on condition reached up to or in excess of 4,000 hours in service.
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