STOL Is Their Specialty

During the last year, however, the company’s products have had a substantial boost in Australia and the surrounding region.

The company’s main current development program, for the 36-passenger Dash 8, received support from local operators recently following a visit here by Dash 8 program manager John Shaw.

Bush Pilots doubled their firm order for three of the aircraft to six. Similarly, Talair doubled its order from two to four. And later East-West took out options on two.

Worldwide the company holds orders for more than 115 Dash 8s and expects to achieve a 50 per cent market share in the 30-40 passenger category by the year 1995. The $A3. 5 million Dash 8 will fly in mid-1983 and deliveries to Australia will begin in 1985.

The company has three aircraft currently in production – the Twin Otter, Dash 7 and Buffalo/Transporter – and local interest in at least two of these has heightened noticeably.

Last year, DHC with local representatives Australian Aerospace achieved the first sale of Dash 7s in the region, with three of the 50-passenger aircraft being bought by Air Niugini, for delivery later this year.

The airline chose the aircraft expressly because of its ability to couple the airline’s standard size, safety and comfort with low runway requirements, thus extending the effective network of Air Niugini to areas previously served only by General Aviation category aircraft.

However, the Air Niugini purchase has implications for Australia.

Recent moves by the Ansett-TNT group back into areas served traditionally by commuter airlines and their takeover of the Masling-Aeropelican operation point to a return by major airlines to these networks surrendered to commuter operators years ago.

Particularly on the Pelican-Sydney run, where services using 20-passenger Twin Otter aircraft are restricted to no more than 16 a day, any operator would be looking closely at a larger capacity aircraft which could increase passenger turnover without increasing frequency and yet still operate from the 3000ft (1000m) runway at Pelican.

It is in this role that the Dash 7 has proven to be the most popular turboprop of its size among operators worldwide.

According to DHC, over the last three years, the Dash 7 has secured 46 per cent of this market compared to the 30 per cent of the Fokker F-27 and BAe 748 combined.

And in the first nine months of DHC’s current financial year, says Australian Aerospace’s Don Newson, the Dash 7 has captured 63 per cent of new aircraft sales in this category.

One of the most sensitive issues confronting any manufacturer attempting to sell aircraft to Australian domestic operators is airport noise, especially at Sydney’s Kingsford Smith Airport.

Turboprop aircraft operated by domestic airlines currently account for some 20 per cent of all aircraft movements at KSA and, apart from adding to congestion problems, contribute substantially to the total noise level experienced by surrounding residents.

The Dash 7, says DHC, quoting the US FAA, is the quietest airliner ever manufactured, by virtue of noise suppressant features of its design and engineering and also its ability to make steep approaches and take-offs.

Last month, Transport Australia supported these claims convincingly.

A Dash 7 demonstrator aircraft in April 1979 conducted a series of tests at KSA using the then Department of Transport’s 10 noise monitoring stations located within the airport perimeter and at key points in surrounding suburbs and the central business area of Sydney.

Quite simply, the Dash 7 failed to register any noise whatsoever at any of the stations in the noise monitoring system operated by Transport Australia.

Of the 1 0 stations, those set close to the airport were set to between 80 and 85dB and those more distant were set to a very low threshold of 65 dB.

The implications for any airline operating Dash 7s into KSA are obvious. In terms of current noise levels created by existing aircraft, jet and turboprops, the Dash 7 adds nothing to the total noise exposure. Given a replacement of existing turboprops by Dash 7s, a very substantial reduction in total noise would be effected. DHC says.

The Dash 8, DHC points out, has a noise footprint nearly identical to the Dash 7 and also has a relatively high approach angle.

Conventional turboprop airliners in service have approach angles in the region of 2-3 degrees, enforcing long, flat approaches and increasing the potential for exposing sensitive areas to aircraft noise.

The Dash 7 is currently licensed for approaches at 7 Degrees and the Dash 8 will be for 6 degrees.

The full potential of this capability may only be achieved by greater utilisation of existing runways at KSA as well as other airports with significant congestion problems.

While a steep conventional approach to a runway in use by all traffic will reduce noise, it will do little to reduce the congestion caused by the need to stream all aircraft, regardless of speed, approach angle and ability to execute tight turns, into a single approach pattern for the one runway.

Recent developments by DHC in conjunction with avionics manufacturers and US commuter airlines have produced an approach pattern for DHC aircraft – Dash 7, Dash 8 and Twin Otter – whereby their low runway requirement allows them to land on a section, or stub, of a runway not in use by the mainstream of traffic.

The critical innovation in this system is the use of area navigation, or RNAV, to replace the usual approach pattern imposed on conventional aircraft with less capability than the DHC machines.

With RNAV, the aircraft does not have to navigate to and from a conventional vortex. Instead, an RNAV waypoint can be located anywhere in space relative to a particular vortac ground station.

Operationally, this frees an aircraft so equipped from reliance on conventional approach ground stations. A totally independent and individual set of waypoints relative to conventional aids can be set up for each aircraft so as to clear it from the bulk of conventional traffic.

The American FAA has certified this system for use at Washington National and more recently Philadelphia Airport. The US carrier Ransome reports fuel savings of the order of 675,000lb per year directly attributable to the RNAV system.

The practicability of the system has not yet been accepted by Transport Australia although senior officials have inspected it in operation.

The applications of it to KSA would have great significance in reducing both noise and congestion, says DHC, and their point most affected traffic restrictions at KSA – Aeropelican.

Ironically, the issue has become public since the delivery of three DHC Twin Otters, the company’s oldest aircraft in production, to Aeropelican in July this year.

The Twin Otter, in its current Series 300 form, continues to log substantial sales with more than 800 ordered since the first aircraft off the production line was accepted by TAA in 1966.

The population of Twin Otters in Australia and the surrounding region now stands at 20.

A Solution to KSA Traffic Problems?

The saturation of Sydney’s KSA Airport Is already resulting In restrictions being imposed on commuters and other operators and while the problem can be seen as stemming from the inability of governments to agree on expanding capacity, It Is far from novel.

According to the American FAA, airports in Boston, Philadelphia, Los Angeles, Pittsburgh, Denver, Chicago New York (La Guardia), Houston and Washington DC will all be saturated by 1990.

Frankfurt, Copenhagen and London (Heathrow) face similar problems.

One obvious source of the extra traffic is the commuter-GA sector which has been growing steadily in terms of aircraft movements in recent years.

General Aviation in this country in July won a significant victory in successfully opposing the implementation of aircraft movement charges by Transport Australia. However beneficial to GA, pressure on operators to reduce movements can be expected to mount steadily.

The experience of an American commuter operator is worthy of note because of its achievement in reducing runway requirements at airports it serves.

Its eventual application at KSA and other Australian airports would, it is argued by de Havilland Canada, substantially lighten the burden of the ATC system and reduce the need to limit frequencies.

Ransome Airlines of Philadelphia, in conjunction with DHC, conceived a system that added area navigation (RNAV) to a suitably capable aircraft for use in the US northeastern corridor.

Ransome uses Dash 7s equipped with the JET Electronics and Technology DAC-7000 three-dimensional area navigational system. The 30 RNAV is integrated with the standard Sperry SPZ-700 automatic flight control system to give automatic control of the aircraft’s flight path through the terminal area.

The RNAV track is displayed on an RCA Primus colour radar, on which pilots can observe their progress along the pre-determined approach route and watch for adverse weather.

Should air traffic or weather conditions require a change in track, any of the approach-path waypoints (up to nine) that have been selected can be displaced by using a slewing switch on the control console to enter automatically updated waypoint coordinates into the RNAV computer.

Although it was intended as a non-precision approach aid, the DAC-7000 system provides lateral guidance and a projected guide path similar to the glideslope/localiser information of a conventional ILS approach.

The computer has pre-programmed routes inserted so that it establishes a series of waypoints on an approach route and navigates from one waypoint to the next.

Vertical deviation information is computed along the desired descending or ascending flight paths to satisfy altitude requirements at each waypoint. Programming a final waypoint at the runway threshold ends the approach in a conventional manner.

In the Dash 7, Twin Otter and later the Dash 8, this system becomes of inestimable value when seen in terms of aircraft performance.

According to DHC, placing a Dash 7, which doesn’t need long, shallow approaches or miles of runway on the ground, in the same operating environment as a Boeing 727 doesn’t make a lot of sense.

The Dash 7 at 100 has about one-third the turning radius of a conventional jet transport (at its normal approach speed-175 kt) when both aircraft are banking at 20 degrees. This characteristic allows the Dash 7 to manoeuvre safely in tightly defined parcels of airspace well inside the initial approach turn area required by conventional jets, and still maintain separation.

The large volumes of airspace that are effectively wasted by conventional jets can be put to use by manoeuvrable aircraft such as the Dash 7, providing that accurate position information can be obtained to prevent encroachment on airspace used for operations by conventional aircraft.

And this is what RNAV does.

Using the system as outlined earlier, a flight planner can straighten out the dog-legged path of many route IFR segments. The RNAV system in operation with Ransome is based on microprocessor technology and digital signal handling techniques which make waypoint updating easy and protect the flight from using inadequate signals.

Obviously, such a system has advantages for the conventional jet. However, it is only with the flying characteristics of the Dash 7, Dash 8 and Twin Otter that the main advantage – in approach manoeuvring – can be secured.

Agile in the air, these aircraft need only short runways. The Dash 7’s FAR 25 factored landing distance is 1,950 ft, far less than that of conventional jets or turboprops. As a result, the aircraft is quite capable of using runway stubs, or segments not in use for conventional arrivals.

The 7 degree approach the aircraft is capable of makes this doubly feasible.

Ransome pioneered this technique at Washington National Airport, flying commercial RNAV/STOL approaches to runway 33 while conventional traffic flies to ILS to runway 36.

The FAA is satisfied that each landing operation will be confined to the stub of runway 33 and will not interfere with primary approaches on 36 under any circumstances, including missed approaches and baulked landings.

This means Washington tower clears RNAV/STOL traffic without sequencing conventional traffic and the resultant converging approaches and landings are carried out routinely using the 2300 ft of clear space on 33 before its intersection with 36.

The RNAV/STOL approach saves Ransome 40 miles per approach, or about 675,000lb of fuel a year. It does not appear in the stream of conventional traffic and its vacant slot is allocated to the aircraft incapable of an RNAV/STOL approach and landing.

DHC points to the fact that this has given the airport a quantum increase in capacity with no compromise of controller workload, air safety or noise exposure – and no additional navigation or runway facilities.

Aeropelican previously operated a fleet of three Twin Otters, a Series 200 and two Series 100s, one of which had logged more than 22,700 hours.

Aeropelican’s chief pilot, Michael Hunt, gave an indication of the reliability of the Twin Otter in Australia’s highest-density commuter operation.

“Last year we flew more than 100,000 passengers,” he said.

“Even with the KSA limitations, our Twin Otters each fly 1500 hours a year on the 60-minute Newcastle-Sydney round trip. As a guide to the reliability of these aircraft, 97 per cent of departures over five years have been within five minutes of advertised time and in-flight delays have been less than one per cent – and most of these have been due to ATC or other factors. ”

DHC points to the fact that Twin Otter production was recently doubled to five per month to accommodate greatly increased demand worldwide and Australian Aerospace said further orders by undisclosed customers in this region were imminent.

Mr Hunt said, pointedly, that the RNAV-stub runway system in use at Washington National and Philadelphia could provide immediate relief to crippling congestion at KSA if local authorities would permit its use.

“Stub runway landings would do a great deal to improve the lot of the country passengers who now have to book days ahead for a peak hour flight to Sydney from Pelican,” he said.

Twin Otters are flying in more than 80 countries and DHC says the “secret” of its success over the years has been simplicity of design and the use of unusually reliable Pratt & Whitney PT6 engines.

DHC has relied heavily on the PT6, using it both on the Twin Otter and Dash 7 while employing a new engine, the PW100, for the upcoming Dash 8.

The company says it is committed to turboprops as the power plant of the future.

Despite their undeniable efficiency, turboprops have still been notable for their absence from the airline scene since the days of the medium-range Viscount, Electra Vanguard and the long-range Britannia.

Only in the short haul field have the Fokker F-27 and the BAe 748 prevailed over jets, not only in Australia but throughout the world.

DHC, after major studies into fuel economics and the development of new technology design and materials, has concluded that there is underway a definite return to new-generation turboprops at the expense of older vintage turboprops and turbojet-turbofans on short and medium-haul routes.

There are many reasons for this, according to the company.

Gas turbines, propellers, aircraft aerodynamics and materials technology have made important advances which are now coming together in the form of a new generation of turboprop aircraft.

These are and will be significantly more fuel efficient than even the best older aircraft powered by the most efficient turbofans, DHC maintains.

The move will take time, but it has begun and is irreversible.

Initial turboprop development took place after the war with the development of the Rolls-Royce Dart for the Viscount, then the F-27 and the (then) Avro 748.

Their widespread use, especially in long-range aircraft, was short-lived with the development of the turbojet, its application to civil transport designs and the availability of cheap fuel. The extra speed available was quite affordable in terms of extra fuel consumption.

While the development of the high bypass ratio commercial turbofan achieved more power and better economy, since the evolution of the Pratt & Whitney JT9D, the General Electric CF6 and the Rolls-Royce RB. 211, only two new large engines have appeared since – the GE/SNECMA CFM56 and the Pratt & Whitney PW2000.

The latest development in power plant design, says DHC, is the NASA-Lewis/Hamilton Standard 10-blade propeller to operate at aircraft cruise speeds of Mach 0. 8 at altitudes of 35,000ft.

At the same time, Lockheed has undertaken design studies for an aircraft using four advanced turboprop engines with similar propellers.

The crux of the shift in priorities lies in the fact that engine-specific fuel consumption was improved by about 20 per cent following the move from turbojets to low bypass turbofans and another 20 per cent following the development of high bypass engines.

The next stage of refinement here, according to DHC, is not expected to improve SFCs by more than 5 per cent.

For this reason, the overall direction to be taken with engine development appears to be the combination of a new engine, typified by the NASA energy-efficient engine (E3) program and the advanced turboprop program. By the end of the 1980s, this trend should be well defined, with a possible further improvement over existing SFCs of 30 per cent.

At the other end of the spectrum, however, development has continued, especially with the Pratt & Whitney PT6 that first ran late in 1959 and which was certificated in 1963.

This engine has undergone continuous refinement in the face of new designs meeting requirements in short-haul route structures. From an initial rating of 550shp in 1963, the PT6A-50 used on the Dash 7 is rated at 1120shp.

A later model, the PT6A-65, is available with an output of 1473shp.

While the development of large turboprops, then, is only recently undergoing a resurgence after years of lying dormant, the development of the technology of the smaller engines has continued unabated.

The latest development, the 1800shp PW1oo (formerly the Pratt & Whitney PT?) to be used on the Dash 8 has a cruise SFC of 0. 45. This engine ran first in March of this year and deliveries of certificated engines are due to begin in 1984.

According to DHC, a comparison with the 2080shp Dart Mk. 535-2, which powers the BAe 748, and the Dart Mk. 536-?R, which powers the Fokker F27, shows the older engine to have a cruise SFC of 0. 58.

This is interesting in light of the fact that both Dart and PW100 have two-stage centrifugal compressors but the PW100 is a three-shaft engine with a free power turbine while the Dart is a single-shaft engine.

Its vintage is borne out by a weight comparison – 919Ib for the PW100 and 1409Ib for the Dart.