Peter Henley/NORTH WEALD
Although it shares a similar designation with other family members (the G115A to D inclusive), the Grob G115T is, in fact, a new design. It is intended for the highly competitive light-aeroplane, flying-training market.
Although more conventional than its highly innovative stable-mate, the GF200, the G115T is nevertheless technically interesting and unusual. Its airframe is of glassfibre-reinforced-plastic composite construction, with a laminar-flow wing and a retractable, tricycle undercarriage which includes a steerable nosewheel. In addition, it has a constant-speed propeller and is designed to be fully aerobatic (including flick manoeuvres), as well as to provide a stable platform for the teaching of instrument-flying techniques. To a large extent, therefore, Grob hopes that the aircraft will be universally popular, and appeal to military training organisations and civilian schools alike.
To these ends, the G115T has already been given German civil-aviation-authority certification under European JAR 23 rules, and Grob will be seeking US certification next. The United Emirates air force is Grob's first 115T customer, having placed an order for 12 aircraft, plus 12 options, for delivery starting in 1996.
The G115T will doubtless delight future flying instructors, with lashings of power from its 195kW (260hp) Lycoming AE10-DA45 engines. This endows it with a predicted maximum cruising speed of around 165kt (305km/h) indicated airspeed (IAS) at an altitude of 8,000ft (2,500m), and sufficient energy to tackle sensibly planned aerobatics without having to start somewhere near the stratosphere to cater for height bleeding away as the sequence progresses.
To its students, however, the G115T may prove a somewhat daunting prospect because, in addition to the complexities of retractable undercarriage and variable-pitch propeller, there is a suite of instruments to keep the pilot informed about engine RPM, manifold pressure, fuel flow, oil pressure, fuel quantity, fuel pressure, oil temperature, volts, amps and cylinder-head temperature. That is a significant increase in workload over something like a de Havilland Chipmunk's throttle, mixture, flaps, wheel brakes, basic six flying instruments and RPM, oil pressure and temperature gauges.
The G115T, while being more complex than most earlier generations of training aeroplanes is, of course, less demanding of flying skills than many - and each succeeding generation of pilots does seem to be increasingly able to cope with complexities which would have baffled their forebears. The other side of the coin is that the G115T is arguably too easy to fly, and has no inclination to turn and bite the unwary or the sloppy. On balance, Grob's 115T probably offers a laudable quantum jump in flying-training ethos, bringing it alongside the bigger Embraer Tucano or Pilatus PC-7 in terms of sophistication.
ON THE GROUND
I was able to evaluate this Grob at the Flight International-sponsored North Weald '95 general-aviation exhibition, with Grob chief test pilot Uli Schell to keep me company and show me how it worked. On the ground, the aeroplane impresses through the quality of its build and finish - a characteristically Grob attribute.
The development prototype (D-EMGT) is fitted with a two-bladed propeller (the technical specification also lists a three-bladed Hartzell HC-C3YK-4 propeller as an option), servo tabs fitted to both ailerons, a trim tab fitted to the port side of the elevator, four elevator mass-balances (which, I was told, will be deleted after all flutter tests are completed) and a horn balance and small static trim tab, adjustable by bending, on the rudder.
Access to the spacious cockpit is easy via the wing root. This prototype has two seats, with a large shelf behind them offering space for kit such as a flight bag and cold-weather jackets, in addition to the fire axe and extinguisher stowed on it. Both seats are adjustable fore and aft (but not for height), are fitted with full shoulder, lap and negative-G straps and readily accept parachutes (such as the GQ 350 which Schell and I wore).
IN THE COCKPIT
There is plenty of elbowroom within the generously wide cockpit. A third seat could be fitted, as an option, instead of the existing shelf. The rudder pedals have the neat Grob adjustment for reach, using a wheel mounted laterally in the cockpit floor, forward of the seat. This can be adjusted with one's heel - although, at 1.83m (if I stand up straight), I found I could have used a little more forward travel. The two control columns curve forward from pivot-points under each seat and terminate in pistol grips.
A strong mechanical-spring centring device is fitted to the ailerons and full stick deflection can bring it into light contact with the pilot's thighs before the aileron stops are reached. The field of view is good, with the exception of the unfortunately large canopy-latching handle and housing. This is mounted on the aircraft centre line and forward of the pilot's normal head position - just where one might want to be able to look during a tail-chase. D-EMGT's instrumentation is adapted to development needs, but in production aeroplanes, would be influenced by customer options for navigational fit. The instrument panel is well planned and laid out, however, with essential information clearly displayed for both occupants. It is, as already hinted, a "busy" display because of the relatively complex specification.
The throttle, pitch and mixture control levers are mounted in the centre console and come easily to hand for either pilot, as does the longitudinal trim wheel just behind them and the up-lock release handle for emergency lowering of the undercarriage. Engine starting is straightforward and results in a pleasurable, purposeful, burbling from an obviously and satisfyingly powerful motor. Pre-take-off checks are routine piston-engine/light-aeroplane procedures. The G115T is easy to taxi, responding, equally readily to power or wheel brakes, both wing tips: can be seen by both pilots. For take-off, power is applied rapidly at the beginning of the ground roll. Thereafter, the aeroplane accelerates rapidly and rotates cleanly at about 65kt IAS. Undercarriage and flap retraction, are quick and produce little pitch change.
The stall, both clean and with undercarriage and flaps deployed, is conventional and vice-free, with good aerodynamic stall-warning buffet and a nose-drop to define the stall. Any tendency for a wing to drop can be recovered using rudder. Normal approaches to the static stall produced a nose-drop at about 62kt IAS (clean) and 55kt IAS (landing) with the onset of buffet about 8kt earlier in each case. The G115T is stressed to +6/-4G, and is cleared for spinning and aerobatics. Entry to the spin is clean and positive, with a rapid increase in the rate of turn and a comfortably nose-down attitude in the stabilised spin. Conventional recovery control produces a reassuring quick - in fact, almost instantaneous - recovery with no trace of pre-recovery acceleration or hesitation. Schell demonstrated his aerobatic prowess with manoeuvres, which included a flick-roll and much upside-down activity, which convincingly proved the Grob's inverted-flight capabilities.
My own, rather more pedestrian, aerobatic repertoire showed that the aeroplane is pleasant to manoeuvre, but with rather higher control forces than I had expected, although the harmonisation in pitch and roll is good. I also found the roll acceleration a little disappointing, but, it must be reiterated, the G115T is inevitably something of a compromise, and a good instrument trainer cannot be expected to be as agile as, for example, a Pitts Special. When I discussed my reservations with Schell, he told me that work on the ailerons is not yet complete and that a reduction in the power of the centring spring was being considered.
Flying the aeroplane in the circuit is pleasant and easy, but with the obvious caveat that the workload involved in making sure the undercarriage is in the right place and coping with the generally more demanding check-list associated with the Grob's level of sophistication is going to be a challenge to some inexperienced students.
In short, the Grob G115T is convincingly well designed, and equipped to meet the somewhat disparate requirements of flying training and modern, sophisticated, instrument flying plus aerobatics. The aeroplane is, at the same time, more complex to operate than many of its predecessors in the civilian club and military ab initio schools. It therefore may not appeal to operators whose bread-and-butter operation is training to private-pilots-licence standard, but it should be a good bet for the world's air forces and civilian schools concerned with intermediate training and commercial licence levels.
Source: Flight International