Key Words- MORE EFFICIENT!!!!!!:beer:ToiletDuck said:My question is what's so great abou the 787? What's the overall design for? I heard that it will be composite so is it basically just a 767 that's a lot more efficient?
mzaharis said:What's interesting is that they started with a minimal modification of the A330, and have had to progressively revise it to have less and less commonality with the A330. They originally estimated 2 billion in development costs, then had to up it to 5 billion, as they reduced A330 commonality. I guess it shows how high the bar was set with the 787.
In other news, some people have claimed that it will be difficult for the bleedless engines to really save that much energy, purely by being bleedless. I'm thinking specifically of an article in AW&ST a few months ago. The engines gain in effeciency by not having to bleed off compressed air, but this is partially offset by the massive amount of power that the auxiliary generator is going to tap.
From the March 28, 2005 AW&ST:
"The comments may apply more to General Electric and Pratt & Whitney engines. The variable stators in their engines go much further up the compression chain. A General Electric official says bleed vs. electric "is a wash relative to the engine performance. It may have differing values to each airframer on how they do the installation and how much they need to extract from the engine." General Electric is selling the GEnx engine for both the 787 and the competing Airbus A350, which uses bleed air, and must be careful not to offend either customer's design."
Rolls Royce claimed that their 3-shaft engines are better equipped for this, because tapping off of the intermediate shaft is more efficient than tapping off the low-pressure or high-pressure shafts on a 2-spooler (GenX). I don't know if this just a manufacturer claim, but most of the sales so far have been RR, if I remember correctly.
But that would make a windmilling start the only option for inflight restart. That's a Part 25 no-no.ToiletDuck said:Anything we say negative will probably have had a billion spent on it to make it better. I'm willing to say they've taken care of all these negtive aspects. It could be possible they could just groundstart each engine so it isn't requiring the planes electrical system to do so.
Two things:ToiletDuck said:Anything we say negative will probably have had a billion spent on it to make it better. I'm willing to say they've taken care of all these negtive aspects. It could be possible they could just groundstart each engine so it isn't requiring the planes electrical system to do so.
The 787's "bleedless". The only thing that bleed air is used for is engine inlet deicing - everything else (cabin pressurization, engine starts, wing deicing) is electric, based on some MASSIVE generators on the engines. Engine starting is via the electric generators on the engines, which double as starter motors, nominally powered by electricity from the APU. The engines have no provision for pneumatic start. Pressurization is driven by electrically-driven air compressors. Deicing/anti-icing is performed with electric heat. From a systems standpoint, the aircraft is a really radical shift from prior, bleed-driven, airliner designs.Pedro said:Will the APU still have bleed air? If so that would be a way to start the engines, no bleeds required in the engine for it to have an air turbine starter...
I haven't read much about the 787, so I'm just asking.
Here's the quote from the AvWeek article:EagleRJ said:It's not that difficult to design a starter-generator that is able to start a turbofan in the 60,000# thrust class. It's just that it hasn't been done before. If there's any problem getting that amount of power, it might be with the batteries. I'd guess that the engines will need to be started with either the APU or a GPU. The batteries alone won't hack it.