Flapping Madly
Please explain to me why the 800 or 1000 would not be suitable. They have as much thrust if not more. What makes the 900 the only RR engine for the A380 ?
I think the bottom-line to this question is SFC (specific fuel consumption). When Airbus decided to examine the possibility of building a new long range transport, larger than the B-747-400, Airbus went to work internally on the design. They came up with everything new, especially the wing. As part of this wing development they tested various designs and eventually tested the best candidate with various nacelle designs, before settling on the final nacelle shape and size. Then they went to the engine suppliers with a recipe of ingredients they needed, particularly to achieve the maximum range goal of the aircraft. The engines had to:
- Produce 70K lbs. of thrust with some growth potential
- The engines had to fit inside the designed nacelle
- The engines had to have a SFC capable of delivering the maximum range plus minimum reserves.
- The engines should not weigh more than "X" and it must attach to the pylon at these points.
- And there were many more technical requirements such as noise.
Pratt and GE were unsure of the market size and neither thought they wanted to spend $2B US to develop an engine in a marketplace that could be divided up three ways. No one had an engine that met Airbus' requirements. So Pratt and GE decided to form a new company (Engine Alliance) and take the best of the PW4000 and the GE90 and come up with a design to meet requirements.
Rolls Royce decided to develop the Trent 900 with some technology coming from the previous family of Trents, some new features.
And IMHO, this is how it got started. The biggest challenge was SFC, especially for Rolls Royce. Traditionally, 3 spool engines (Trents) are shorter than two spool engines (GE or PW) and when contained in shorter nacelles, overcome a deficiency in SFC compared to a longer engine that has good SFC. But the Airbus A-380 has longer nacelles aerodynamically matched to the new wing.
So if you look at SFC:
GE90 SFC (SLS) 8.30 mg/N-s (cruise)
Trent 882 SFC (SLS) 15.66 mg/N-s (cruise)
Cruise at altitude is where most of the fuel is burned in long range flights.
The Trent 800 probably wouldn't meet the SFC target.
So the GP7200 uses a GE90 core with a PW fan and LP turbine.
Rolls Royce had a big challenge and needed all the best of the new technology to narrow the gap, and for the most part new technology worked with the Trent 900 to meet the SFC target.
The Trent 1000 came along later specifically designed to meet the Boeing 787
Requirements and as such, may not meet the A-380 requirements.
This represents my best estimations of this and it could be wrong
(disclaimer).