The 'knurling' on Boeing engines? That's what it's for. And why the 777x doesn't have it
Do you want one more system to distinguish Boeings from Airbuses? If you need this, it means that your [...]
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You want one more system to distinguishing Boeings from Airbuses? If you need this, it means that your knowledge of the planes you fly on is really modest, but, in any case, there you go: Newer generation jets produced by Boeing have the profile of the rear of the engine nacelles jagged, which no Airbus aircraft has. Recall that gondola means the aerodynamic 'body' that surrounds the thrusters.
Starting with the Boeing 747-8 (whose first flight was in 2010) the Everett-based manufacturer introduced this novelty, which was then taken on all series of the 787 and on the 737 MAX, of both Series 8 and Series 9 (Series 7 and 10 also have it, but have not yet been certified).
Some might say that engines with a 'crest' look better than those that don't. But is not for aesthetic purposes That gondola knurling has been introduced. It is needed instead, To make airplanes quieter and thus reduce their noise impact especially when they are near the ground, shortly after takeoff or just before landing.
The 'zig-zag' profile of the rear of the gondola, in fact, according to Boeing's statement, "reduces the noise of the air jet expelled at high speed from the turbine by controlling the way it 'mixes' with the air passing through and around the engine."
Noise abatement (About 15 decibels, in the case of the 787) achieved with this system is such that it has enabled Boeing to Remove hundreds of pounds (just under 300, in the case of the 787) of passenger cabin insulation material (as opposed to the one installed on his jets that don't have that profile of engine nacelles), significantly lightening the airplanes, which in turn resulted in lower fuel consumption.
Someone may have noticed that Boeing's latest 'creature', the 777X, does not have the knurling on the back of the motors. It had it in the renderings that appeared before its realization, but the 'flesh and blood' airplane never had it.
This was possible because General Electric (the builder of the 777X engine, the GE90X) e Boeing have been working on A drawing of the turbine 'exhaust pipe' and to honeycomb bulkheads inserted in 'strategic' areas of the GE90X That make knurling unnecessary.
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