The John Travolta owned Qantas liveried 707
The John Travolta owned Qantas liveried 707

It can be argued that a design choice made for the Boeing 707 about 58 years ago is causing Boeing present day grief.

And that choice was to make the 707 sit close to the ground. Too close to it for future changes in engine technology.

A Qantas 707-138 in 1961. No need for more ground clearance for those engines
A Qantas 707-138 in 1961. No need for more ground clearance for those engines

The low profile chosen for the main gear or undercarriage section of the 707 was retained very closely for the Boeing 727 tri-jet, and the Boeing 737 family.

But new engine designs, like the CFM International Leap-X, or new types like the Pratt & Whitney GTF or geared turbo-fan are being respectively developed or proposed for jets the size of today’s 737 series, and its Airbus competitor, the A320 family.

And the problem for Boeing is that they fit under the wing of the A320 but not that of current 737s.

Hence Boeing’s signalling of its enthusiasm for an all new 737 replacement design rather than the very significant change it would have to make to its existing product line to keep it competitive with a revised A320 offering.

But Airbus is playing hard ball. It says it is considering new engines for its A320s, and is signalling a degree of enthusiasm for a total replacement design by 2024, when it sees other technological advances in materials and systems coming together to produce a breakthrough concept it argues would be a generational advance over anything new Boeing can come up with using the technology available to it between 2015-2020.

Boeing has tried a number of arguments during this process of talking to Airbus and the customers of both through the media.

There was the ‘Southwest won’t like it’ line, which inter alia, was that it only wanted more of the same, one assumes until it had its competitive advantages consumed by other airlines with something that uses markedly less fuel and maintenance dollars.

Then there was the ‘adverse impact on resale or residual book values’ argument, which put Boeing in the somewhat perverse position of being the first aircraft manufacturer in history to adopt change resistance as plus for doing business, and one completely contrary to its advocacy of the 787.

Earlier this week it changed tack again according to this Bloomberg report in the Seattle Times which said:

Boeing: Fuel-efficient engines could increase aircraft weight
As airlines pressure aircraft makers Boeing and Airbus to deliver more fuel-efficient jets, Boeing noted on Sunday that the more efficient engines on existing narrow-body models would increase weight and the fees that airlines have to pay at airports. “It’s a very complex algorithm, it really is, and there’s a lot of factors that have to be considered,” said Boeing Commercial Airplanes CEO James Albaugh. “We’re not trying to rush into this thing. Whether it’s a re-engine or a new single- aisle plane, it’s the customer who’ll drive us to do the right airplane.

Note that Boeing is doing most of the talking on this topic, with Airbus choosing not to interrupt while it watches its competitor’s efforts to dig itself out of the dilemma of re-engineering the 737, or replacing it perhaps prematurely.

The issue of ground clearance for the entire product range of Boeing single aisle jets since the 707 arose first when Douglas brought out its competing DC-8. It stood tall on higher wheel struts, which meant that in due course it could be offered in stretched versions, using larger diameter and more powerful CFM International engines while the 707 couldn’t, since its tail would strike the runway while rotating for takeoff if its fuselage was lengthened.

A modern engine crammed into an old space, the CFM 56 on a 737-400
A modern engine crammed into an old space, the CFM 56 on a 737-400

When Boeing moved to the Franco-American CFM56 series engine for its 737s from the –300 upwards the larger diameter of the engines caused it to devise the flat bottomed or oblate shaped engine nacelle (above) to minimise the risk of pod strike, which it achieved by shifting the engine accessory gearbox from the bottom of the engine to one side.

However despite the comment some months ago by Boeing that it could still accommodate the fatter diameter of new engine designs under the 737 wing, the engineering reality is that this will require considerable redesign of the wing and wheels, which would involve big dollars and a certification process.

What will Boeing really do? Boeing clearly hasn’t yet chosen its response, and Airbus is just sitting there on its side of the poker table, deciding when it should play whatever cards it is holding to its chest.

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