Airtest- Dornier 228-200

The subject of this report is the latest in a line of utility transport aircraft which started in earnest with the Do. 27 single-engined high-winged six to eight seater of 1955. The line progressed through the Do. 28, which featured twin piston engines on a low-mounted auxiliary stub wing, the generally similar but larger Do. 28O Skyservant and the improved Do. 128- 2 Skyservant. Turbine power was introduced on the Do. 128-6 Turbo Skyservant which first flew in 1980. Production of this series of aircraft totalled nearly 1000 units over the 25 year period and although the types were seldom if ever seen in Australia, at least one example of the Do. 27 was in service for a period with the Catholic missions in Papua New Guinea.

The major advance with the Do. 228 was the introduction of a very different wing. This new technology wing, known as TNT (Traflugel Neuer Technogie), resulted from studies conducted by Dornier in 1975-76 with support from the German Federal Ministry of Research and Technology. It was first flown in prototype form on an extensively modified Do. 28O2 in mid-

1979. During this flight test programme, the opportunity was taken to optimise the matching of high technology propellors to the newly wing-mounted Garrett TPE331 engines and to test various combinations of spoilers, ailerons and Fowler flaps to maximise both high lift and roll control.

And what a wing it is! It introduces a new platform, a new wing section and for this class of aircraft, new construction methods. As regards planform, the leading edge out to the engine nacelles is unswept, as is the trailing edge. Outboard of the engines the leading edge adopts a mild sweep out to the tips which are raked back at nearly 45 degrees. This triangular tip is claimed by Dornier to provide similar benefits to the winglets which are becoming so fashionable on other types, whilst still generating a little lift. The wing section, designated Dornier Do. A. 5, has its maximum thickness well aft at nearly 50% M. A. C. This is combined with Fowler flaps over about 60% span and ailerons whose reference position is drooped in proportion to flap extension while retaining the same angular movement about that reference position.

The main component of the wing consists of three box structures, i.e. a centre section including the engine mountings and an outboard section on either side. These are each constructed from an upper and lower skin with integral ribs and spars milled from solid aluminium billets on numerically controlled machines as used by Dornier for the Alpha Jet programme. These skins are then accurately formed to the required wing section and joined together to produce a wing box with a very smooth and accurate outer skin, unmarred by any external rivets. This box also doubles as a wetwing fuel tank system. Whilst respectably light, this structure has proved even more durable than expected. As a result of tests carried out recently, the aircraft has been cleared for a service life of 62,500 flights or 50,000 flying hours under normal conditions, more than doubling the original design objective. Added to this wing box are leading edges of conventional light alloy construction to facilitate easy repair of minor damage in the field and tips and trailing edges of composite construction including kevlar and carbon fibre to save weight.

The rest of the airframe is conventional by comparison and owes a lot to the Skyservant series. The fuselage, stretched from that of the Skyservant, is of conventional unpressurised light-alloy construction with composites at its extremities to provide rounded form. The different fuselage lengths provide 15 cabin seats in the -100 series and 19 cabin seats in the -200. Tail surfaces continue the Skyservant tradition even to the Eonnex fabric covering on the rudder and the after surfaces of the all-moving horizontal tail. The retractable tricycle undercarriage is electrically controlled and hydraulically operated. The twin nosewheels retract forward, while the single-wheel main gear units retract sideways into small sponsons projecting from the lower fuselage – well it is a Dornier. Emergency gear extension is by nitrogen bottle from aircraft number 35, replacing an emergency hand pump on earlier aircraft.

Dornier has standardised on the Garrett TPE 331-5 turboprop engine for the Do. 228 series after considering offering various other engines at customer option. The TPE 331 is a fixed shaft engine with a two-stage centrifugal compressor feeding air to a reverse flow annular combustor thus driving a three stage axial turbine. The centrifugal compressor provides good resistance to foreign object damage and the basically front to rear flow pattern provides some gains in the ram effect. From an engine handling point of view, response to power lever movement is almost instantaneous as with a constant speed engine, no allowance need be made for spool-up time. Engine speed 41000 RPM equals Propellor speed 1591 RPM. Hot and high performance is very good as this basically 840 hp engine is flat rated to 715 shaft horsepower up to ISA © 18 degrees C or 33 degrees C at sea level. A Negative Torque-Sensing system (NTS) provides immediate propellor drag reduction by moving propellor blades towards the feather position in the event of fuel starvation or engine shutdown.

A torque and temperature limiting system and automatic start- ing systems improve power plant longevity by simplifying pilot engine monitoring. The TPE 331 also offers very competitive specific fuel consumption for this class of engine.

The subject of our flight test was the third of six Do. 228-200s ordered by Precision Airlines of Springfield, Vermont and was programmed to enter service with them at the conclusion of the world sales tour. It already bore the purple and tan stripes of that company but still proudly carried its German registration (D. IDBI) and company identification. Parked amongst pools of water on a sodden and windswept Flight Facilities apron with its substantially white upper fuselage contrasted against a decidedly leaden sky, it exuded an air of quality that prevailed throughout the flight test. Everything was clearly designed for function and fit, suggesting a parallel with a well-known marque of quality German motor car and explaining why all the promotional literature for the aircraft carried the slogan ‘Made in Germany’ in a prominent place.

Dominating the external appearance was that wing. In some way the pointed tips reminded me of some of the classic de Havilland products of the early thirties. Yet didn’t they have a problem with tip stall? That question was soon to be answered. Chief Test Pilot Frank Tuytjens, who was to occupy the left-hand seat throughout the flight, lead us through the preflight walk- around, explaining that this was a fairly typically equipped commuter aircraft with the addition of HF radio and VLF/Omega navigation equipment for the calls tour. The cabin was furnished with 19 seats at 30-inch pitch with the two pilots seats ahead of a substantial bulkhead. The cabin has 5 ft. 1 in. headroom in the centre aisle, with a single row of quite comfortable cloth-covered seats down either side. Baggage space is provided in a nose locker (. 89 cubic metres/90 kg) and an aft hold (2. 6 cubic metres/210 kgs).

The cockpit was well laid out and whilst clearly capable of single pilot operation, was obviously well suited to the two-plot crew type operation that commuter flying has become. Both pilot panels featured a full set of conventional flight instruments, including a Horizontal Situation Indicator (HSI) and Radio Magnetic Indicator (RMI). Additionally, the Captain has the benefit of a Radio Altimeter and a Reference Speed Deviation Indicator, of which we shall hear more later. The centre instrument panel featured two vertical stacks of engine instruments reading from top to bottom: Torque, Intermediate Turbine Temperature, Fuel Flow, RPM, Oil Pressure/Oil Temperature. Beside these were an extensive caption light warning panel, fuel quantity gauges and the weather radar. The centre pedestal carried, amongst other things, the Power and Propellor levers, radio selector boxes and the flap lever, well distanced from the panel-mounted gear selector. Small overhead panels catered for lighting, de-icing, fuel, starting and electrical power controls. The cockpit seats were most comfortable with plenty of adjustment, and vision through the cockpit windows was good, especially through the side windows which featured a very low sill height. This proved to be a considerable asset in low-level manoeuvreing.

The aircraft weight and surface conditions for our flight were as follows: Weights: Equipped empty weight Fuel Payload Take off weight 3,600 kgs 1,000 kgs 560 kgs 5,160 kgs Surface conditions “Information Kilo’, Wind 150 degrees/15-20 kts, Temperature 20 degrees C.

Clearance was from Sydney Omni, Radial 090, maintained at 6000 feet. The altitude clearance was later expanded to a block from 6000 to 8000 feet to allow for the artwork.

Engine start proved to be simplicity itself with the automatic starting system. Each engine ITT peaked around 950 degrees C, well below the limitation of 1149 degrees C, then stabilised at 550 degrees C with an idle fuel flow of 145 lbs/hr/engine. With the engine speed levers in low, the underspend governor maintains a minimum of 70% RPM. On receiving our taxi clearance, the engine power levers were advanced slightly, with breakaway occurring at 80% RPM. then retarded to ground idle to maintain a safe taxi speed. Nose wheel steering is through the rudder pedals, which normally provide 8 degrees of nosewheel deflection either side of straight ahead. Whilst this is sufficient for most operations, a switch on the control wheel will supply 45 degrees of authority either side for manoeuvring in confined areas. We were cleared into position and hold on runway 16 at the intersection with taxiway C. Speed levers were moved to high and with receipt of our take-off clearance, the power levers were advanced to max. With 100% RPM and 100% torque, acceleration was brisk. Experiencing just a momentary touch of crosswind, the aircraft was rotated at 90 kts and airborne before the runway intersection after a ground roll of about 150 metres. Holding a V2 of 98 kts, we crossed the General Holmes Drive tunnel at 250 feet, then allowed the aircraft to accelerate to a normal climb speed of 120 kts. Turning further left to intercept the 090 radial, we crossed the coast near Malabar at 5000 feet, still maintaining 2000 ft. /min. rate of climb at 120 kts IAS.

Level at 6000 ft. with an outside air temperature of 10 degrees C, speed built rapidly and a relatively stable cruise was established in light turbulence and moderate rain, in and out of cloud. With speed levers pulled back to cruise and power levers set, a cruising speed of 195-200 kts IAS was achieved with 96. 5% RPM, 83% torque, 805 degrees C ITT, and a fuel flow around 325 lb/hr/engine. Later calculations showed a TAS for these conditions of around 220 kts. At this stage I ventured back into the cabin to sample passenger conditions. There was a little noise, perhaps best described as a low drumming, in the rear cabin, seats in the mid cabin were a little quieter. However at no stage was the sound level obtrusive, but perhaps comparable to in-cabin noise in a wide-bodied airliner in the circuit. Normal conversation proved to be no strain and I would rate the comfort factor better than many other similar class aircraft that I have experienced.

Back to the cockpit for low-speed and single-engine demonstrations, we were getting very much to the point of the demonstration. With all seat belts fastened, the right engine power lever was retarded to flight idle and the propellor feathered. With the aural warning sounding and caption lights for No. 2 engine oil and generator illuminated, 100% torque was established on the No. 1 engine and the speed stabilised at 165 kts IAS. Level turns both ways with 45 degrees bank produced a speed bleed back to 150 kts but the aircraft retained its rock-solid feel. With the nose raised to an almost obscene angle, speed was allowed to bleed back toward the stall. Turns with 60 degrees bank either way at 80 kts showed how much aileron control was left.

Light airframe buffet below 80 kts augmented the stall warning system and the aircraft finally stalled at 68 kts indicated, still with full roll control capability. So much for the theory of pointed wing tips and undesirable stalling characteristics.

Flying the aircraft out of the stall, we established a typical en-route single-engined climb condition. When this condition had stabilised, we were achieving a climb rate of just over 500 ft. / min. at the recommended single-engined climb speed of 105 kts. Levelling off at 7000 ft. , the No. 2 engine was restarted and further low speed manoeuvring was carried out, emphasising the aircraft’s suitability for the low level search role where the good lateral visibility conferred by the low side window sill height was appreciated. Then, after a demonstration that the aircraft had all the roll control that any pilot could ever want, we reluctant- ly received a clearance and returned to Mascot.

Flying a simulated instrument approach back to runway 16, the excellent stability of the Do. 228 came to the fore. Even in the annoyingly rough air. the interception and tracking on the ILS was a delight to handle. Gear and flap extension provided only very small trim changes, and thrust control with the constant-speed engines was instantaneous and precise. At about 1000 ft. we declared visual and Frank Tuytjens took over to demonstrate the use of the reference speed deviation system. The RSD indicator, in the top centre of the pilots instrument panel, features a needle moving over a scale from SLOW through a VREF triangle to FAST. The system derives this speed by feeding angle of attack and flap position information through a small computer. VREF (1. 3Vs) or approach safety speed can be accurately flown by reference to this needle for any combination of aircraft weight or configuration, surely a boon in commuter use when many approaches under differing conditions must be flown each day.

Using just a little STOL technique, a very short landing was achieved into the brisk southerly wind. Using reverse pitch and moderate braking, a ground roll of probably less than 150 metres was achieved. Power was applied to reach the first taxiway and the aircraft was taxied back to the Flight Facilities apron using the 45-degree nosewheel steering feature only for the final parking manoeuvre. Engines were shut down and we repaired to the briefing room for coffee, sandwiches and more talk.

Dornier are delighted with the progress so far on the Do. 228 Programme At the time of the flight, nearly forty aircraft had entered service with many more on order. Applications so far are extremely varied. Commuter operations through Europe from Norway to Greece, high-altitude work for Druk Air of Bhutan, commuting in Taiwan and Japan and support work (on skis) for German teams in Antarctica are all proceeding according to plan. An agreement has been reached with the Indian governmentment for licence production of an initial batch of 150 Do. 228s by Hindustan Aeronautics Ltd. As well as the commuter configuration, the aircraft is offered as a VIP transport, a freighter with 2-tonne capacity, an ambulance, a patrol aircraft with 360 degrees radar or SLAR, or fitted out with geophysical survey equipment. No seaplanes yet, you will notice, but after the Sydney rain, who knows? On a more serious note, I would think Dornier are on to a winner. This is a quality aircraft, very durable with excellent handling qualities. The operating economics have made sense already to quite a few commuter operators. If SFAR 41 certification can be achieved in Australia, it makes even more sense. With an Australian price as tested of A$2. 25m, it must be considered as a serious contender for any local operator who can use its not inconsiderable capabilities.