For example, the 787
Sometimes the concept may not be as efficient as it was expected, attractiveness is also a key, and so they go back to the drawing board, tons and tons of times, it doesn’t always work the first time :D
Concepts are just that, a concept. Once actual engineering work and simulations are run, things change.
well, a “concept” is not based on 100% detailed and computed engineering drawings.
Wind channel test, sudden over weight problems leading to performance problems, noise and vibration findings during flight testing, customer demands and many many more aspects may lead to changes in the design.
Just take the APU section of the 787 or the trailing edge of the rudder section. Pretty sure, stability, noise, aerodynamic effects, weight, construction complexity and some other factors played a major role in the redesign.
Do not forget about new developments in the applied materials, new aerodynamic methods over time. Sometimes there are 5-10 years between a concept and the maiden flight, which is a long period of time bearing in mind, the jet ages started in the early 50’s of the last century.
In the early ages of flying this phenomenon was pretty common. Nowadays concepts and final designs come pretty close, thanks to modern computer capabilities, don’t you think?
That concept was terrible. I’m glad it was changed.