Grob G109B

Unfortunately, exceptional soaring pilots are just that – the exception – so the 10 litre consumption of an aero-tow is the more usual way to embark on a serious soaring flight. And on a good thermic day, that usually begins with a long queue of like-minded ‘fast glass’ pilots at the launch point.

But nowadays there is a common practical alternative. Older soaring purists may scoff, but the self-launching motor glider (SLMG) has become an increasingly common sight, not just at gliding fields, but also at ordinary airfields and airports all around the world.

Today’s powered gliders take a variety of forms, ranging from the established competition soaring tadpole equipped with a tiny retractable auxiliary motor in the fuselage behind its pilot’s head, to the Teutonic complexity of a Stemme S-10’s buried Limbach, with that

“ We chose to keep the engine ticking over gently at 1500rpm to give us a minimal sink rate, mimicking a high performance sailplane, while we turned and twisted.

” long, tubular prop shaft extending forward between its occupants, and the ingenious ‘flick-knife’ folding propeller hidden beneath its nose-cone.

Bang in the middle of this broad spectrum of motor gliders comes the two-seat Grob G109B. Its all-composite airframe is sleek and clean, while its wings are long, slim, tapered and low-drag, but its 110cm wide cockpit is roomy enough to accommodate a pair of the biggest, sturdiest Germans. Its engine may derive from the humble Volkswagen Beetle’s air-cooled motor, but it puts out a useful 90hp and drives an efficient, two-position, variablepitch propeller which can also be feathered for soaring flight to give it a handy 28 to one glide ratio.

Not only glider pilots buy these aeroplanes, for a Grob 109B makes a fine and economical long distance cruiser. Flying for nearly eight hours at almost 100kt, full tanks give it a tremendous 800nm range, even if you keep the engine running all the time. And it burns very little fuel – 12 litres per hour being the norm.

The Grob’s spacious cockpit is comfortable enough to make that a pleasure, not an ordeal, and its in-flight visibility is excellent. Even more surprising for a powered aircraft derived from a family of sailplanes, it has excellent handling, with good ailerons and comparatively well harmonised controls.

Everything about this aeroplane whispers efficiency; from that aerodynamically superior tapering fuselage, through the carefully sculpted wing- and tail-to-fuselage fillets and impeccable surface finish, to its long, slender, glider-like, low-induced drag wings. The long ailerons have efficient Mylar gap seals, and both have upward deflected fixed tabs at their inboard ends, to offset their tendency to ride up under air loads at higher speeds, which would unnecessarily increase control forces.

The wings can be folded back to the tail to minimise hangar occupancy by raising a couple of levers at the wing roots.

Twin doors open upwards, and the central, fixed roof is wide enough for them both to be opened without touching in the middle. After climbing from the trailing edge onto either of the non-slip walkways and lifting the gull-wing doors, the cockpit is actually a little difficult to get into without standing on the pristine upholstery. The best way seemed to be to hold the sill with your left hand, and the right seat’s back with your right, while sliding your legs forward into the footwell.

The seats are slightly reclined, comfortably upholstered and equipped with four-point harnesses, while the sidewalls are lined with light grey fabric. The result is a pleasant interior, of higher quality than usual. Each occupant has a short control column with a comfortable grip between his legs and rudder pedals with toe brakes. There are blue-handled airbrake levers on each sidewall, which require a mighty heave to unstow. For a powered approach, the left one can be locked half open with a shaped nylon block operated by a small, awkwardly placed rotating lever below it, but this Grob’s owner, Angus Buchanan, assured me he never uses this system. A shared throttle and a trim lever sit ahead of the on/off fuel cock between the seats, a single 100 litre tank occupying the fuselage behind the cabin.

The broad but shallow instrument panel is mounted low enough not to intrude into the forward view, which is already good for a tailwheeler. The pilot’s ‘standard six’ instruments have been expanded to eight, including a fixed-card ADF display and dual variometers (a glider pilot’s more accurate VSI) one of which has an audio device. A central radio stack incorporates VHF, VOR, ADF and a mode C transponder. Over on the right are the engine gauges and a second slip ball. With the glider pilot’s trusty wool tuft outside on the windscreen as well, there is no excuse for not flying in balance. Below these instruments are the master and ignition/starter switches, plus two further rows of switches for the electrical services.

A central vertical sub-panel contains knobs for the parking brake, choke and cabin and carburettor heat. Also, here are the smaller toggle for manually changing the propeller’s pitch and a big ‘umbrella-handle’ one at the top for feathering it. Finally, there is a compass on the windscreen arch, while over on the left a removable GPS is fitted.

With an empty weight of 665kg and a maximum of 905kg, our 50 litre fuel load (half a tank, but enough for four hours flying or a 400nm range) allowed us a useful 204kg payload.

Being derived from an old fashioned Volkswagen Beetle car engine, the Grob’s start-up is similar. Checking that the fuel valve, master switch and fuel pump are on and the throttle is cracked open, you pull out the choke and twist the magneto switch through to start, whereupon the engine does as bidden, quickly settling to an easy 1200rpm idle.

Releasing the parking brake valve and opening the throttle results in instant motion, while steering is easy. The forward view is superior,While having the engine running at low rpm enables it to perform ‘like a proper glider’, they particularly enjoy the ability of using its motor as a safety feature.

”better than from many nose-wheelers, and the steering works well to turn this long-winged bird around its semi-span.

To pivot around a mainwheel, you simply dab the appropriate brake, and round she goes, tight as you like. The springy fibreglass undercarriage legs are quite close-set, so when traversing rough or undulating ground it is important to stay slow, or the normal slight wing rocking can develop to tip-scraping proportions.

Although there is a little bumper under each tip, it is probably not a good idea to rely on them to protect the wings.

Pre-flight checks are minimal, and advancing the throttle produces a gentle increase in speed rather than blistering acceleration, but since it lifts off at 50kt, the Grob doesn’t run far (maybe 200 metres) before floating gently into the air. Gradually accelerating in ground effect to 60kt takes perhaps another 150m, after which we gently climbed away at around 500ft/min in the 19°C air.

Volkswagens turn rather faster than the bigger, heavier certified engines, so this is at 3000rpm, and we allowed the speed to increase further to 65kt to ensure adequate cooling.

There are no flaps to retract, the landing gear is fixed, and the Grob doesn’t have cowl flaps, so there is nothing to do but relax until 1000ft, when Angus changes his propeller to the coarse pitch setting. A 70kt full throttle cruise climb can then be continued indefinitely, although on the day we flew a low cloudbase forced us to level off at 1800ft, where leaving the throttle wide open crept the airspeed up to 110kt. A reasonable high cruise speed is 105kt, but Angus prefers a more comfortable 2500rpm, which gives a useful 95kt cruise, burning around 12 litres per hour.

The cockpit is comfortable, although with such a low wing loading the aeroplane inevitably reacts to every gust, so it is advisable to fly more slowly on a bumpy day. The published maximum rough air and manoeuvring speed is 92kt, although Vne is a generous 130kt. Glider pilots know these vertical gusts as ‘lift’ and so are not perturbed, slowing down in the rising air and accelerating through the sink, seeking out cloud streets and into wind escarpments, and generally making full use of nature’s abundant energy to eke out their fuel.

You sit right over the Grob’s wing, but visibility is still good in all directions, although the unusual transparent side panels down by your feet are not actually very useful, because your view through them is at such an acute angle.

Control in all axes is light and effective, and to my surprise with such a very long wing, there is remarkably little adverse aileron drag. Indeed, at cruise speeds it is possible to roll into and out of turns without using the rudder at all. Best glide ratio (28 to one) comes at 62kt, with minimum sink at 57kt.

Throttling back and reducing speed to below 50kt, control was still good in all axes, and with a one knot per second speed reduction the stall eventually came at 42kt, with a tiny shudder of buffet preceding it by one or two knots and a slight wing drop at the gentle break. Pitching up a little more quickly depressed the stall speed to 40kt, but still with the same benign behaviour. Circling with 45 degrees of bank between 45 and 50kt was easy, with good control and no sign of misconduct.

Since there was extensive stratocumulus with a comparatively low base around 1800ft and a gentle southwesterly breeze, it was difficult to find any significant lift in the weak thermals. That didn’t stop us trying though. Rather than shutting down the engine completely and feathering the propeller, we chose to keep it ticking over gently at 1500rpm to give us a minimal sink rate, mimicking a high performance sailplane, while we turned and twisted, trying to centre in the narrow cores of what thermals there were. Angus was of course much better at this than me, and showed me just how tightly it was necessary to circle below 1000ft, where the thermals were very slim indeed. In the end, we had a challenging but enjoyable half an hour of simulated soaring.

Visibility and handling in the circuit are excellent, and like most Grob pilotsfound it easiest to fly the approach the glider pilot’s way, by closing the throttle and modulating our descent angle with the powerful airbrakes. A sideslip can be employed for a steeper approach, although I suspect that would seldom be necessary, given these airbrakes’ effectiveness. A comfortable approach speed is between 55 and 60kt, lowering the nose and increasing speed for any turns, glider-style.

Nearing the threshold, Angus recommended I reduce airbrake deflection to half, to decrease the sink rate and give time for a flare and proper hold-off.

Just raising the nose to the three-point attitude (which is significantly less than the stalling attitude) is all that’s required, after which the aeroplane settles gently on to the turf. Then you can fully open the airbrakes again to pin it on the ground and increase the drag. The tail is quite heavy, so moderate braking can be used to slow down, and the landing roll is over in fewer than 200m. Angus says the aeroplane easily copes with crosswinds up to 15kt.

This delightful aeroplane has only one, rare, handling ‘gotcha’, but it’s an important one. If you normally fly from the left seat, but for once are in the right seat (perhaps demonstrating the aeroplane to somebody else), your left hand is on the stick with your right on the half-open airbrakes. During the approach when the throttle is closed it is eminently possible to find yourself instinctively ‘flaring’ with your right hand.

If the sudden increase in descent rate then prompts you to ‘open the throttle’ or ‘stow the airbrakes’ by pushing your left hand forwards, the problem is seriously compounded. This does nothing to assist the hold-off, and can result in a nasty crunch, something a few Grob pilots have learned to their cost.

Afterwards, Angus showed me the easiest way to exit the aeroplane. You merely

Grob Variants

GROB G109B
(Technical specs)
Powerplant
One Grob 2500 producing
90hp (67kW)
at 3600rpm. TBO
1600hrs. Propeller:
Hoffmann two-bladed,
three-speed, variable
pitch wooden propeller.
Performance
(Manufacturer’s stated)
Sea level Vne 130kt
Max speed 130kt
Max cruise 111kt
Economy cruise 97kt
Stall, full flap 40kt
SL take-off run 196m
SL landing run 200m
SL climb rate 650ft/min
Service ceiling 19,675ft
Max range 809nm
Weights
Equipped empty 620kg
Max takeoff 905kg
Load factors +5.3/-
2.65g
Dimensions
Wing span 17.4m
Wing area 19.00m2
Length 8.1m
Height 1.8m
Seating two
Manufacturer
Burkhart Grob
Flugzeugbau Postfach
150, 8948 Mindelheim,
Germany

The sailplanes and powered gliders for which we know Grob are merely a sideline for what is predominantly an automotive components sub-contractor.

The first Grob 109 flew in March 1980, with series production (eventually totalling 160) following in 1981 and JAR 22 certification coming shortly afterwards. With mostly glass fibre construction, a one-piece, forward-opening, hinged canopy, 80 litre fuel tanks and a 75 (or 80, sources differ) horsepower Limbach L2000 EJ engine driving a two-bladed Hoffmann variable-pitch wooden propeller, this early model suffered from minimal longitudinal stability and poor canopy sealing.

Its long wings spanned 16. 6m for a 13. 5 aspect ratio. With three degrees of dihedral, they had carbon fibre main spars and fibreglass skins, and incorporated an Eppler 572 (modified E 603) aerofoil of unusually high 16. 1 per cent thickness.

Early models had steerable tailwheels with soft springs, while rearward movement of the airbrake lever to its stop simultaneously applied Scheibe hydraulic mainwheel brakes.

The developed G109B model followed in 1983. This had longer, lower drag wings spanning 17. 4m and with an Eppler E 580 section, carbon fibre rudder, greater tailplane span, a fuel capacity increased to 100 litres, and a bigger, more powerful Grob produced (but still VW derived) 90hp, 2500cc engine. The tailwheel steering was replaced by the current differential toe brakes.

Angus’s is a 65-series 1990 model. slither out from the cockpit to sit on the wing walkway, and slide down the leading edge to walk away from this lovely aeroplane with a smile.

Owner Angus and his glider pilot wife Maggie paid £45,000 ($110,000) for their Grob a little more than five years ago. They broadly use it for recreation, encompassing anything from short soaring sorties to long distance touring and visiting other airfields and gliding sites. A major advantage of their Grob’s long range and endurance is the ability to seek out better conditions on an otherwise poor soaring day. For instance, they can motor 100 miles for some ridge soaring, and then return afterwards, all in the same flight.

While having the engine running at low rpm enables it to perform ‘like a proper glider’, they particularly enjoy the ability of using its motor as a safety feature.

Keeping it turning at little more than a tick-over allows them to soar in places where it would be unsafe to do so in a conventional glider.

For instance, this means they can work the seaward side of cliffs in an onshore breeze, well out of gliding range of a safe field for an ordinary glider, then merely open the throttle and fly away home. They use it for touring too, having flown it around much of Britain at one time or another.

These Grobs fulfil most of the roles of an ordinary ‘spam can’ but with much nicer handling, better visibility and far better economy.

Unlike some wooden motorised gliders, they can just be covered and tied down outside airliner which clearly means business. It has long been known as “The Mercedes Benz of twins. ” Although a little costly to maintain, this just adds to its exclusivity in the eyes of its devotees. For me this splendid aeroplane remains `the twin with attitude’.

for most of the year, although it is wise to hangar them (with folded wings, natch) over the worst months. When folded, they are just 3. 66m wide, so four will only take the space of a single conventional aeroplane, thereby attracting only one quarter of the usual hangarage fee.

An acknowledged Grob expert told me the airframe is generally strong and reliable, and reckons they only need around one man-week of inspection and maintenance per year. They have a theoretical 12,000 hour life, but none is anywhere near this yet.

The only big airframe job comes after 3000 hours, when the wing spigots must be changed and inspection windows put in for the aileron bellcranks unless these are already fitted. This can be expensive because it needs the Grob factory jigs, which have to be brought over from Germany (or the aeroplane shipped over there). This makes a 3200 hour airframe a better buy than a 2800 hour one.

Running costs are quite low, since it only uses 11 to 12 litres of fuel per hour and burns a negligible amount of oil. Angus does the biannual inspections himself, since they only comprise tappet adjustment, an oil change and cleaning the spark plugs. He says the aeroplane has been very reliable, and has never let them down.

With carbon credits in the wind and fuel usage coming under the microscope, I predict that sailplane pilots and ultra efficient aircraft like this Grob are going to become increasingly popular in the near future.