Paul Phelan/SYDNEY
AN UNUSUAL, but highly fuel-efficient, lightweight powerplant, all-composite construction, and an airframe design which clearly reveals its sailplane lineage, are among the distinctive features which set the Diamond DV20 Katana aside from more orthodox two-seat trainers. All three contribute to what many flying schools say they are now seeking - the elusive combination of crisp control responses and the vice-free handling preferred in a basic trainer, together with significantly reduced direct operating costs.
The Bombardier/Rotax 912A3 engine must not be confused with the less reliable two-stroke units which power numerous ultralights. Katana dealer Aeromil Australia says that the 60kW (80hp) lightweight, geared, four-stroke 912A3 has now been flown some 250,000h in the USA without a reported failure.
An attractive feature is the engine's low on-board and external noise levels, created partly by its propeller gearing and cooling system - finned cylinders air-cool the barrels, while the cylinder heads are jacketed for liquid cooling, which also offers protection against shock cooling of the kind inherent in primary training with its frequent, and harsh, power changes. Coolant loss would not be a terminal event - Rotax has established that the engine can be run "dry" for up to 2h at or below 56% power, without damage. The 912A3 runs on either motor gasoline or avgas, and the recommended lubricant is regular Mobil automotive oil.
Unusually, for such a small engine, the propeller is hydraulically controlled and constant-speed, with composite blades hardened at the leading edges by metal cuffs. The engine/gearbox design provides a finished shape, permitting an unusually streamlined cowling design.
Flying the aircraft with sales executive Peter Kilby at Sydney's Bankstown airport, I was told that the Katana is now certificated under the European joint airworthiness regulations for very light aircraft (JAR/VLA), a modern certification level which is increasingly becoming the basis of a large range of innovative sports trainers worldwide, many of composite construction. Among limitations on VLA certification are a maximum stall speed of 45kt (85km/h), restriction to day visual-flight rules only, and a 750kg maximum take-off weight. The aircraft, which was originally designed in Austria, is now manufactured in Canada, and certificated both there and in the USA. Production planning is for 40 units a month.
A walkaround inspection reveals an all-over sleek surface-finish, and pointers to the banishment of airframe corrosion or working rivets as maintenance considerations. There is no provision for a nosewheel towbar, but the nose can easily be lifted clear of the ground by downward pressure on the aft fuselage, from which point tarmac manoeuvring is most easily achieved.
The fuselage is one-piece, but the wings can be removed and the aircraft prepared for trailer transportation (or re-assembled) in 90min. Any structural stressing or distortion should easily be revealed by skin discolouration.
There are built-in clear Plexiglass panels under the wings for inspecting control bellcranks and linkages, and a tough glassfibre-reinforced -plastic skid under the tail protects the airframe from over-rotation. The main gear legs are of spring steel and attached directly to the main spar. Elevators and ailerons are push-rod operated, while rudder control is by cable.
The entire airframe is innocent of vortex generators, wing fences or other aerodynamic devices, apart from the winglets, which are integral with the wing structure, and which add significantly to aerodynamic performance, according to Diamond, by providing roll stability, reducing drag, and enhancing aileron effectiveness at low speed. The T-tail configuration is claimed to give minimisation of the adverse effects of propeller slipstream on pitch control, and improved low-speed pitch authority.
Excellent visibility
The one-piece bubble canopy hinges upward at the rear, and steps on either side of the fuselage aid cockpit entry. Visibility, unobstructed by windshield posts, is excellent, and there is provision for taxiing with the canopy cracked open for hot-weather ventilation. A full six-unit instrument panel is on the left, avionics are central, and engine instruments are on the right panel.
Individual "stick" flight controls are provided, with the engine controls on a central pedestal. The seats are fixed, but rudder pedals can be adjusted using a T-grip handle near the control stick, each of which is fitted with a press-to-talk switch. The three-stage flaps - take-off, cruise and landing - are electrically operated.
Comfort for the crew, once they are settled in the well-reclined seating, is good, although a tall instructor may have to work at keeping his feet clear of the pedals to allow students a free rein. A small personal-baggage stowage is provided aft of the seat (where the fuel single tank is also located), but items such as charts and calculators should be placed within reach pre-flight as seating is snug, and in-cockpit movement limited.
A choke assists starting, and the engine idles with unaccustomed smoothness and quietness, attributed to its dual electronic capacitance discharge ignition system. A 40Amp belt-driven alternator and integral crankshaft-driven alternator provide dual-electrical-system redundancy.
Students will need to be reminded to avoid propeller damage when idling over loose gravel surfaces, but the aircraft has a unique clutch which automatically disengages the propeller from the engine in the event of an obstacle strike. The nosewheel is fully castoring, and steering is by differential braking, which the pilot quickly learns to manipulate gently. Taxiing visibility is excellent, with a point on the taxiway visible about 3m (1ft) ahead. A good quality intercom is provided as standard, but the low cabin-noise level offers the alternative, sometimes attractive, option during long hours of instructional flying, of discarding the headsets and using cabin speaker and voice communication.
First-stage flap is used for take-off, and the rudder becomes fully effective almost immediately on initial power application which takes prop RPM to about 2,500. All controls come fully alive early in the take-off run, and the aircraft is eased off the runway at 45-50kt, but can be held in ground effect to reach 65kt before starting the climb flapless at 2,400RPM. The highly audible stall warning is set to at activate 15kt above normal stall, and will readily warn students of any decay in climb speed.
Climb performance could be fairly described as equal to that of a Cessna 150. Again, during climb and subsequent cruise, the low noise level and engine smoothness resulting from the 2.27:1 engine/propeller gear ratio will be appreciated by instructors who fly long days in these small aircraft. Also attractive in the training environment is all-round visibility of a kind not available in most conventional trainers.
At 5,000ft, the Diamond accelerates quickly to 120kt true airspeed at 75% power, showing remarkable aerodynamic efficiency for an aircraft powered by a 60kW engine. The high- cruise speed will make the type attractive for cross-country training, and Kilby points out the fuel consumption of only 16.6litres per hour, which compares with 23litres per hour for a Cessna 150, and reduces in typical training operations to around 7litres per hour. General handling is extremely light, but highly positive, and the aircraft is inherently stable in all axes, returning to level flight from a 10kt phugoid displacement in only two oscillations.
Control forces in all regimes are well-balanced, and so fingertip-light that a pilot may tend to overlook the trim unless a spare hand is needed to operate other controls. Elevator trim is located right behind the throttle. Rolling out of a 60 degree steep turn to 60 degrees in the opposite direction takes about 3s. The clean lines of the Katana made it slow to lose speed when power was reduced, and although stalls in all configurations were relatively innocuous, all primary stall symptoms, including buffet, were sufficiently evident to demonstrate effects of controls to students.
Effective ailerons
Built-in twist causes the wing roots to stall well ahead of the wingtips, so that the ailerons are fully effective well after the primary stall, and down to about 28kt IAS, at which speed the Katana begins to lose height without loss of lateral control. A wing drop was only produced by vigorously excessive elevator application in a powered steep climbing turn, and it was corrected by relaxation of back pressure. High-speed descent is achieved at the never-exceed speed of 161kt with the propeller at 2,400RPM, the throttle closed, and carburettor heat on. The carburettor heat control is conveniently adjacent to the throttle, and Kilby encouraged me to apply it with all large throttle reductions, explaining that the engine is otherwise prone to induction icing, particularly at high relative humidities. This aspect will need to be noted by instructors and students in stall and circuit training sequences.
In the circuit, the low-drag airframe dictates forward planning of power and speed changes, and is therefore a useful training tool in itself. A feature resulting from the Katana's 14:1 glide ratio is that the aircraft is capable of a glide approach back to the field from any point in the circuit, normally including initial climb; a possibility which students training in conventional aircraft are customarily encouraged to ignore in the event of an engine failure. The best glide speed is 65kt.
The manufacturer quotes low fuel and maintenance costs, attributable to engine economy and the high-strength and virtually maintenance-free glass-fibre reinforced plastic airframe. Any operator of conventional trainers may look forward to a new operational cost structure reduced by these fuel and maintenance economies; to improved trainee enjoyment and experience, and to handling qualities which will brighten the lives and secure the loyalty of jaded and hard-to-replace professional instructors.
Source: Flight International
