|Quoting PPVRA (Reply 5):|
Would it be viable to design an aircraft, from scratch, that has the flexibility to switch engine makers/models?
That would be wonderful for the customer, no doubt! Can you imagine if all the 767 operators could just switch to GEnx engines and instantly gain 10-15% efficiency? That would be an incredible capability.
Unfortunately it is also not viable for a series of reasons, some of which are:
1. Airworthiness Regulation: This is the big one really. When an aircraft is certified, it is certified with a specific engine - extensive testing is performed that is extremely dependent on the particular characteristics of a given engine. Aside from performance (TO field length, climb, go around, range, landing field length) many other certification issues are hugely dependent on the engine (VMC, VMCg, internal noise, external noise, icing susceptibility, pressurization performance in case of bleed operated systems etc.). Approving a new engine requires showing compliance to all applicable regulation when using the new engine, which is expensive.
2. System integration: In most aircraft, the engines provide thrust, provide electrical power, provide hydraulic power and provide bleed air to systems. Integrating multiple different powerplants into all the systems that depend on them is a very tough task. Different engines will have different, spool up/down times, N2
, will have different parameter thresholds (ITT, N1, N2
, oil pressure), will probably communicate different data using different formats (they have, presumably, different FADECs). It is possible to provide a "standard engine interface", no doubt, but it is a huge task. Also, you depend on the engine makers actually building future engines to fit your interface (which may not be even possible, such as when the new engine is bleed-less and your standard interface uses bleed air).
3. Type rating: Assuming the manufacturer could approve several engines for use with the airframe and design a plane that could use them interchangeably, there remains the issue of type rating. There could come a point where different engines are so different in performance or in operating procedures that the different installations could not share a type rating.
I'm sure that there are many other factors that affect this issue. Keeping all that in mind, the 787's capability to interchangeably use two engine types is quite an accomplishment.