Designed by Burkhart Grob GmbH, the two seat Grob 109 motor glider features side by side seating and fixed tail dragger undercarriage with a steerable tail wheel. The fuselage and wings are made of industrial carbon fibre and glass fibre composites with air brakes. Glass Reinforced Plastic (GRP) is the main structural material with Carbon Fibre for the T-tailplane and rudder. Hard foam sandwiched between fibreglass cloth is used for stringers and formers in the fuselage as well as many other applications.
Grob’s G 109 has the ability to shed its wings, tailplane and elevators to enable it to be neatly packaged for transportation in a suitable road-borne trailer. Each wing has a tapered tongue that extends through the centre section to lock into the opposite wing root rib. The ailerons and air brakes are operated through push-pull control rods. The horizontal tailplane is fitted atop the fin and the quick connect fittings for the elevator and trim tab are fitted.
The Limbach L 2000 EB lA engine is rated at 59kw/80hp at 3,400 rpm. The engine has a single Slick magneto, twin Stromberg carbs with “pancake” sport air filters, Motorola alternator and a Hoffman feathering propeller with START (take-off and climb) and CRUISE pitch settings.
The 17.5 Imp gallon fuel tank is behind the cockpit and filled from above the left wing trailing edge. There are GRP skids/tie down points under each wing tip and the engine cooling air exits from fixed louvers in the bottom cowl.
The glassfibre monocoque fuselage has frames and longerons, while the low wing has a glassfibre roving main spar and a glassfibre/epoxy resin sandwich skin; there are aluminium air brakes in the upper wing surfaces. The fixed undercarriage has Scheibe hydraulic brakes on the spatted main wheels, and the tailwheel is steerable. The pilots sit under a one-piece forward-opening canopy and, after some flight testing, this was fitted with a central frame, while changes made to the undercarriage included moving the main wheels further back so as to unload the tailwheel, the main wheel struts being of steel. Wing span was increased from the original 15m (49ft 2.5in) to 54ft, the empty weight was increased and the motor cowling and wing roots were aerodynamically refined.
The prototype, D-KBGF, made its first flight on 14 March 1980, and the Grob G 109 was certified to JAR 22 in March 1980.
The prototype of the G.109B two-seat, side-by-side motorglider first flew in March 1983 as a version of the original G.109, with increased span. The G109B is a two-seat motor glider with T-type stabilizer, fixed landing gear and airbrakes. It is classified as a TMG (Touring Motor Glider). It was designed by Burkhart Grob GmbH and features side by side seating as well as a classical tail-dragger undercarriage with a steerable tail wheel. The fuselage and wings are made of industrial carbon-fibre and glass-fibre composites. The G109B's engine was made by Grob (GR 2500) and is an aircooled 4-stroke flat engine.