NEO - Why the Fuss?
 

The world has gone mad recently because Airbus want to stick some slighly more efficent engines on their A32x. It feels like another Crash of 2008 but that's a separate story.

What confuses me is if the new engines are about the same weight, size and thrust, why is it such a big deal?

I can see you've got more issues if you are Boeing. You've not got enough ground clearance so you need a new undercarriage. But even then - why can't aircraft be regularly upgraded just like automobiles? Nowadays surely the flight computers are the most tricky part of flying, so as long as you keep the same flight control behaviour does it really matter if there are slight differences in actual flight responses? Slightly different engines surely can't make much difference compared to the normal variation in loads, weather etc?

I suppose I'm saying this because I wish Boeing would just say "OK we'll stick Leap Xs on when they're available and in the meantime just jack up the undercarriage a tad. No problemmo.

Then we wouldn't have this endless Will-they/Won't-they with regard to a totally new aircraft.

Up to 15% improvement in fuel burn is most certainly worth making a fuss about!!

Yes, but presumably if this is something as simple as a different engine, older A320s could be retrofitted? Or is it far more complicated?

As mentioned above, fuel burn is a HUGE deal today. And in fact if they were not pretty much the same size, weight, thrust they wouldn't be a retrofit candidate, so it's not surprising that AB has gone for keeping those parameters fairly stable.

Firstly, you're assuming that aircraft are all about flight dynamics and response. if it's a very very simple aircraft sure. But engines do a lot more than just a bit of push. They are THE power source on-board, and every other system on the aircraft is dependent, in some fashion, on the engines' behaviour. So if i change the engine, suddenly my bleed air is a different temperature (because its from a different port) or is limited in mass flow 9because my new engine can only spare so much bleed). Now i have to potentially redesign my ECS and AI systems to adjust - or I have to impose some significant constraints on the engine supplier. Similarly for hydraulic power and electrical power - all the ancillaries are affected.

Secondly, the engine/wing integration is not that simple - there's a LOT of work goes into ensuring an efficient design in terms of minimizing interference between the two, while still getting good stalling behaviour despite having that big thing hung in front of the leading edge. A new engine nacelle could have significant design work requirements to make it work.

The 15% fuel savings are cumulative with some other aerodynamic changes as well, such as the new blended winglets or sharklets as they're being called which offer a 3.5% fuel burn reduction.

The sharklets as implemented on the NEO cannot be retrofitted, however Airbus have just announced that they are looking at alternatives for retrofit.

MTOW reduction? Many airlines do that anyway to reduce their fees for ATC, handling etc.

Plug compatibility
 

OK - perhaps I'm asking a different question. Why don't plane companies design their planes to take new engines, new instrumentation etc thoughout the lifespan of the product?

It must have been obvious that, when the A320 and the 737NG were on the drawing boards, new more efficient engines would become available as technology moved on. Similarly with electronics, wings etc.

Every now and again you need to make a fresh start, but it's odd Boeing can't easily respond to the NEO. Their order book is healthy enough to suggest the enormous cost and disruption of a new plane is not necessary.

Because you don't KNOW what you'd be designing for. An aircraft design is already a massive exercise in compromise. If someone came along and said "I want all that lot, plus, if anything changes in the future, I want that too" the designers would just give up.

Bear in mind, however, that Boeing is already on the third iteration of the B737, so it's not as if they designed something that wasn't capable of being upgraded. But to imagine that someone sitting down to sketch the initial layout in the mid 1960s should have somehow tried to anticipate what might be wanted 50 years later ... they'd have been designing anchor points for the shielding for the airborne nuclear reactor that was going to be the power source!