Making Every Gallon Go Further

Perhaps in no other transport manufacturing industry is the relationship between powerplant and vehicle more critical than in the aircraft business. While a harmonious engine/vehicle combination is a logical requirement of all transport modes, it is a crucial prerequisite to a safe, efficient and reliable aeroplane.

With such an important ‘marriage’ of diverse technology – and with widely varying operational requirements of aircraft operators – one might imagine that the airlines have traditionally enjoyed an almost lavish choice of engine/airframe combinations. They have not.

The post-war civil aircraft of the 40s and 50s were only available with the ‘house’ engine. The airframe manufacturer selected the engine which was best suited to his requirements. In most cases, there was only one engine available.

The piston, turboprop and pure jet gas turbine engines of that era were more or less buried in the airframe and once the airframe/engine combination was designed, it was impractical to fit another type of engine.

The introduction of the pure jet gas turbine engine installed in an external pod gave the airframe manufacturer more freedom to change engine models without a major re-design. However, in the 60s and the 70s, the initial engine chosen usually dictated the pylon design and the placement of the engine on the wing or fuselage which led to some compromise being required in installing another manufacturer’s engine. Except with the Boeing 707 and McDonnell Douglas DC 8 the airline, therefore, had no choice in the engine selection. It is arguable that such a choice was unnecessary in the cheap fuel era.

The crisis of fuel price and availability has since determined otherwise, along with the economic need to operate bigger payload aircraft. The engine manufacturers, notably Rolls Royce, were quick to recognise these factors, particularly that fuel conservation would be a major element in any airline’s equipment selection. It has always been very important to Qantas and was a significant factor in the choice of the Rolls-Royce RB 211 engine for its later Boeing 747s.

Were engine options widely available when fuel was 12c a gallon, a differential of two or three per cent fuel burn efficiency between engines would hardly have been incentive enough for an airline to change engine manufacturers. Today such small margins can represent the difference between profit and loss in the unstable economic environment of the international airline industry.

The Qantas decision to re-evaluate engine requirements was prompted by two basic needs – to increase fuel efficiency and to take full advantage of increased payload and range, with an 833,000 lb airframe structural capability then being offered by the Boeing Company.

At that time – late 1978 – it was realised that the engine used in Qantas’ all-747 fleet, the Pratt & Whitney JT9D-7F, had reached its ultimate take-off thrust limit and further development was not economically feasible.

Since Qantas committed itself to the Boeing 747 in 1967, the airline has constantly looked at ways of increasing the gross weight and hence payload/range capability of the aircraft. However, engine power availability has not always matched the structural capability of the aircraft; the latter was always well in advance of engine thrust availability.

The requirement for engine thrusts of 50,000 lb and more arose, not only on the 747 but also on the Lockheed L-1011, the Douglas DC 10 and the A300 Airbus. It was this requirement that motivated Rolls-Royce, Pratt & Whitney and General Electric to develop the second generation of what are known as ‘high bypass ratio’ jet engines, all of which are capable of operating at thrusts in excess of 50,000 lb.

The designs of all these manufacturer’s engines were based on earlier models but the requirement for improved fuel consumption and greater thrust resulted in major design improvements. The airflow through the engines has been considerably increased, reducing the internal working temperatures and resulting in improved fuel consumption.

These new engines are the Pratt & Whitney JT9D-70 series, the General Electric CF6-50 series and the Rolls-Royce RB 211-524 series.

The CF6 engine entered service in 1972 as the CF6-6 in the DC 10-10 series aircraft. The engine was based on the powerplant of the military aircraft, the Lockheed C5A, with a thrust of 40,000 lb.

To meet the requirements of a larger aircraft, the CF6-50 was developed within the same frame size as the CF6-6. This engine was initially rated at 49,000 lb of thrust and has a growth capability of around 56,000 lb thrust. The engine offered to Qantas was the CF6-50E2 with a thrust rating of 52,500 lb. The CF6-50 series is the basic engine on the DC 10-30 and the A300 Airbus.

The decision to develop the second generation Pratt & Whitney high bypass ratio turbofan engine was taken in 1973. This engine was designated the JT9D-70 for the Boeing 747.

A conventional engine, the ‘Dash 70’ as it was known was ‘sized’ for 56,000 lb thrust and aimed at the aircraft manufacturers’ requirements for engines between 50,000 lb and 60,000 lb of thrust.

The version offered to Qantas was designated the JT9D-7Q at 53,000 lb thrust. It was basically the same engine as the ‘Dash 70′, but installed in the smaller nacelle of the earlier engines.

The RB 211-22B engine was the basic engine for the original Lockheed L-1011 aircraft and entered service in 1972. These first engines were rated at 42,000 lb thrust. To meet the higher thrust requirements of later aircraft, the RB 211-524 series was developed. The first -524 was rated at 48,000 lb of thrust and with existing and proposed variants, now extends to 55,000 lb. The two engines offered to Qantas were the -524B2 as an interim engine at 50,000 lb and the later, improved -524D4 version at 53,000 lb.

Although the -524 series incorporates major design improvements over the -22B version, it has benefited from the in-service experience of the earlier engine.

Qantas evaluated these engines for two years before deciding on the power plant best suited to the airline’s unique operational requirements. (Qantas, for example, flies the longest average passenger sector length in the world and operates up to 10-hour sectors daily on its Kangaroo and Southern Cross routes). The evaluation team visited engine and aircraft manufacturers, and airline operators to gather all available performance data on the engines on offer, the study being one of the most comprehensive technical evaluation programmes in the company’s history.

A major consideration in the ultimate selection of the RB 211 was not only that the -524B2 version of the engine was well beyond its development stage and in service at the time, but also that is successor, the much improved -524D4 version, was soon to be available.

At the time, Qantas was able to monitor closely British Airways’ performance statistics on the RB 211 -524B2 version which powered that airline’s 747s on the Kangaroo Route to Australia. They demonstrated that the -524B2 engines were performing in accordance with the engine manufacturer’s claims. Qantas decided to accept the 50,000 lb thrust -524B2 version of the RB 211 as an interim engine, pending the availability of the 53,000 lb thrust -524D4 in late 1981. Qantas, in fact, was the first airline in the world to have the -524D4 engines operating in service. The airline’s 24th Boeing 747 (it operates the world’s largest all-747 fleet) delivered in November 1981, is fitted with the improved engines. Full certification of the aircraft with D4 engines is expected in March 1982 and, until it is obtained, the engine will be used at -524B2 thrust levels.

The airline’s first four Rolls-Royce-powered aircraft are being retrofitted with the -524D4 engines between November 1981 and March 1982.

The -524D4s will provide Qantas with one of the best payload/range performance capabilities of any commercial aircraft by providing the capacity of an all-up take-off weight of 833,000 lb compared with the present 820,000 lb.

The performance of the existing Rolls-Royce engines has been subjected to the closest scrutiny since they went into service on Qantas’ second 747 Combi in November 1979. The five Rolls-Royce-powered aircraft – two Combis, one SP and two passenger 747s – have performed as predicted. Studies have shown that each of these aircraft is saving Qantas $475,000 per year in fuel consumption.

The company is predicting a further four per cent improvement in fuel consumption with the -524D4 engines. This translates into an average of $1. 4 million per aircraft per year in fuel saved.

Qantas has been closely involved with both Boeing and Rolls-Royce during the -524D4’s development for the purpose of satisfying itself that the engine’s projected performance, maintenance and reliability would be achieved. A team of eight of Qantas’ senior engineering and maintenance personnel has been established to coordinate the complex operation of retrofitting the -524D4s to the Rolls-Royce powered aircraft.

The introduction of the Rolls-Royce engines forms part of a concerted effort by the airline to ‘make every gallon go further’. Other elements of this programme include flying aircraft at optimum altitudes and speeds, improving aerodynamics through modifications and utilising flight simulators instead of aircraft, where possible, for technical crew training. Thorough examination is also made of equipment and supplies to ensure the weight of the aircraft without payload is minimised, without compromising the exacting safety standards for which Qantas is renowned.

The need for maximum fuel efficiency has never been greater in the airline industry than it is today. It affords one of the best opportunities to cushion the effects of spiralling jet fuel prices in recent years. Qantas’ fuel bill, for example, doubled from $104 million in 1978/79 to $208 million in 1979/80, contributing to a loss of $21 million. In 1980/81 the fuel bill approached $300 million.

The airline industry is now in an economic straitjacket with many carriers reporting massive losses, not only because of fuel prices but weakening markets, overcapacity and industrial disruption.

Qantas has placed a good deal of faith and capital in the Rolls-Royce engines. But it does so in the knowledge that only those airlines which have modern, fuel-efficient fleets can confidently meet the challenges in today’s fiercely competitive international airline environment.