Technical: Grob G-109B Vigilant T.Mk1

1. Summary
2. Airframe
3. Engine
4. Performance
5. Weights & Limitations

Summary

Although looking like a powered aircraft, the Vigilant is actually a self-launching motor glider. This means that the aircraft can climb to height under its own power and then may switch its engine off in order to soar like a conventional glider. (Although we don't operate the aircraft in this way generally.)

A number of features make the Vigilant surprisingly good as a glider including

• ‘Spats’ on the main wheels to reduce drag
• Tail dragger configuration to reduce overall drag from the undercarriage
• Ability of pilot to turn the propeller blades end on to the airflow (known as feathering) to prevent the propeller windmilling when the engine is switched off. This reduces drag caused by the propeller spinning when in the glide.

As a glider, the Vigilant can glide around 5.3 miles (4.6 nautical miles) for every 1000 feet of height so, in theory, could glide around 30 miles from its maximum operating height of 8000 feet. Operationally, the Vigilant is used to allow Air Cadets to be trained in basic flying skills a role which it suits well given its side-by-side cockpit layout and forgiving flight characteristics. These flight characteristics also make the aircraft ideal for training up to first solo standard and 637 VGS prides itself on training around 50 Air Cadets each year to fly the Vigilant alone.

The cockpit is well equipped, spacious and boasts fantastic visibility making the aircraft popular with staff & cadets alike. Instruments-wise, the aircraft is equipped with all of the standard instruments namely an airspeed indicator, altimeter, attitude indicator and variometer. These are placed on the left-hand side as student training is done from this side whilst the instructors seat on the right has a duplicate airspeed indicator and the engine & electrical system instruments & circuit breakers.

Airframe

• Configuration: Single tractor propeller engine, Low wing, T-tail, side-by-side cockpit, tail-dragger undercarriage
• Semi-monoque Glass Reinforced Plastic (GRP) shell with aluminium structure
• Wingspan: 17.4m
• Length: 8.1m
• Height: 1.7m
• Aspect Ratio: 15.9 to 1

Engine

• Type: Grob 2500E1 four stroke piston engine
• Number of Cylinders: 4
• Cylinder Configuration: Horizontally Opposed 4 (also known as Flat-4)
• Maximum Power: 95 brake horsepower (bhp)
• Maximum Continuous Power: 85 brake horsepower (bhp)
• Cooling System: Air-cooled (courtesy of the large ‘fan’ bolted to the front of the engine!)
• Propeller: Laminated propeller blades with three settings, fine (for climbing), coarse (for cruising) & feathered (for gliding)
• Air/Fuel Mixing System: Twin Zenith Carburettors
• Aspiration: Normally aspirated (no supercharger or turbocharger)
• Fuel Tank: 100l (72kg) of aviation gasoline
• Fuel Pumps: One mechanical (engine driven) plus one electrically driven fuel boost pump
• Other features: Cabin heat (for cold weather operations), Carb heat (to prevent carb icing), Choke (for cold-starting), Starter motor (although the engine can be started in flight without the use of the starter)

Performance

• Speed for Best Angle of Climb: 49kts
• Speed for Best Rate of Climb: 60kts (fine pitch) or 75kts (coarse pitch)
• Speed for Noise Abatement Climb: 55kts
• Approach Speed: 65kts (or 70 kts if wind > 15kts)
• Speed for Best Glide Angle: 62kts
• Speed for Minimum Sink: 58kts
• Speed for thermal soaring: 55kts
• Glide ratio: 1:28

Weights & Limitations

• Empty weight: 858kg
• Maximum fuel load: 72kg (100l)
• Maximum luggage load: 17kg
• Maximum Crew Mass: 110kg (each)
• Minimum Crew Mass: 35kg (in order for parachute to operate correctly)
• Maximum All-Up Mass (AUM): 908kg
• Maximum Height: 8000ft
• Maximum Speed for Normal Operation: 117kts (up 850kg) or 107kts (851-908kg)
• Never Exceed Speed: 132kts (up 850kg) or 121kts (851-908kg)
• g-limits: 0 to 3.5g (up 850kg) or 0 to 3g (851-908kg)
• Maximum Wind-speed: 30kts*
• Maximum Crosswind Speed: 11kts*
* These restrictions are reduced for less experienced pilots

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