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737 Power; More ≠ Better

by David Hopwood

If you’ve flown commercially in the last twenty years, it’s almost certain that you’ve flown at least once on a Boeing 737. Until recently the 737 had the corporate edge over its main rival the A320, but the Airbus has drawn level in the last few months; although the Boeing 737 family exceeds A320 deliveries, (10563 vs. 9086) the reverse is true for orders. The A320 series recently reached a milestone; more total orders than the Boeing 737 family: 15 157 vs. 15 136.

Two main reasons for this reversal; Boeing had an annus horribilis 2019 with the tragic Lion Air and Ethiopian crashes, subsequent grounding of the 737 MAX and consequent immense reputational and financial damage; not least a stock loss of $28bn. Boeing has been playing technological catch-up since 1988 when the A320 was launched. With a twenty-year lead, Boeing might have become a little complacent.

So what’s the history behind the rise of the 737?

The story of the aircraft can be divided into four generations, roughly told by its engines. Here we’ll look briefly at the evolution of the 737 power.

The 737 was initially conceived as a 50-60-seater, with twin podded engines at the rear, like a DC-9 or BAC 1-11. This design was dropped for weight and structural strength reasons in favour of the familiar configuration with engines suspended under the wings. This first generation first flew in February 1968 as the 737-100 series by (oddly) Lufthansa. Powered by the Pratt and Whitney JT8D low bypass turbofans originally fitted to the 727, the engine producing 71kN. A low by-pass turbofan is essentially a series of vanes arranged in a multiple series of fans producing thrust from combustion exhausting at the rear. The -100 carried 100 passengers and had a maximum take-off weight (MTOW) of 42 211 kilograms. Just thirty were produced and the -100 series was quickly superseded by the -200 with 109 pax, 78kN and an MTOW of 52 390.

737-200. Image; aeroinside.com

The second generation- the 737 ‘Classic’ had three series; the -300, -400 and -500. The Classics were powered by variants of the high-bypass CFM56 engine, produced by a consortium of the American General Electric and French SAFRAN manufacturers. High bypass turbojets use a core operating conventionally, but additionally driving a large fan producing much of the thrust. The -300 series was launched in 1974 with a maximum of 149 pax, 98kN and a MTOW of 62 822 kg. The -400 was a stretched series with maximum of 188 pax, 105kN and 68 038 kg MTOW and the -500, a slightly curious smaller version with figures of 145 pax, 89kN and 60 554 kg MTOW.

737-500. Image: K von Wedelstaedt

By comparing the -200 and -300 series, the former had an additional 40 passengers, a 20% increase in MTOW and 26% more thrust.

The third generation or Next Generation, ‘NG’ was (unsurprisingly) an upgrade of the Classic and a direct competitor of the A320. Included are the -600, -700, -800 and -900 series and the first NG (a -700) flew in February 1997. The aircraft is powered by uprated CFM56 engines and ranged from a maximum of 149 to 220 passengers, 89 to 120kN and MTOW of 65 544 to 85 139 kg.

The -500 and -600 carry similar maximum passengers; 145 vs. 149, the power increases by 13%, MTOW by 8%, but the range increased substantially by 26% to 5600 km.

737-800. Image; S Hackenberger

The most recent iteration, the 737-MAX, first entered service in May 2017, replacing the NG variants and powered by the new CFM LEAP (Leading Edge Aviation Propulsion) 1B. The baseline -8 series can carry 178 passengers, (while the -8200 accommodates up to 200) has 125kN of thrust, and an MTOW of 82 191kg. The MAX-8 was the variant lost in Indonesia and Ethiopia. The -9 figures are 220 passengers, 130kN thrust and MTOW of 88 314kg.

In comparison between the MAX-8 and older NG-800, the MAX can carry (at most) 21 more passengers at 210, very similar thrust; 125kN vs. 121kN, and a similar MTOW; 82 191 vs. 79 000. The main advantage is range; 21% greater at 6570km vs. 5425km.

737 MAX-8. Image; Ken Fielding

To summarise the development between the MAX-8 and the first generation -200 series; a 55% increase in passenger capacity, 40% increase in MTOW, a 62% increase in thrust and a 56% increase in range.

By any measure the development of the 737-and here we’ve only touched on the engines-in the last 52 years has been astonishing.

So why does Boeing seem to have lost the lead in short/medium-haul aircraft? Were they truly complacent? Or panicking? We’ll look at some of these questions in later articles.

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