31–40 of 80 posts
Could some knowledgable aircraft people answer these questions for me? 1. Can/are jet engines ever swapped out after a plane as been put into service? Or will these only ever be sold attached to new aircraft orders. 2. Any idea on what the engine costs? And what percentage of the overall airline cost is engine? I didn't see any references to costs of this engine vs existing models.
Could some knowledgable aircraft people answer these questions for me? 1. Can/are jet engines ever swapped out after a plane as been put into service? Or will these only ever be sold attached to new aircraft orders. 2. Any idea on what the engine costs? And what percentage of the overall airline cost is engine? I didn't see any references to costs of this engine vs existing models.
I wonder if instead of gearing a single large fan, you could just remove the fan from the turbine altogether, add a much larger alternator, and power several large electric external fans from each turbine? That would give you more fan area than you can get with a geared turbofan, optimal fan speed for efficiency, redundancy in case one of the fans suffered damage, allow cross-routing of power between turbines if one…
just remove the fan from the turbine altogether I don't think you can. The large volume of airflow surrounding the turbine is what makes it a turbofan[1]. Without, it is a turbojet[2]. The airflow from the turbofan surrounds the hot exhaust gas and it is much quieter than the turbojet. But, other than noise, the rest of your comment makes a lot of sense to me. But I know very little about this stuff. [1] https://en.w…
Turbojets derive all of their thrust from the turbine exhaust. It's a small, compact engine, which means high power-to-weight ratio, and it's great for small jet fighters. Unfortunately, it also consumes a lot of fuel. Turboprops are at the other end, where the turbine drives the propeller at much faster speeds than a regular 4-stroke engine would. But the exhaust provides next to no thrust.
Turbofans sit in the middle. They provided much better fuel efficiency than a turbojet but greater power than a turbofan. It was very much a "we need a middle solution" type of engine.
As turbines became more efficient and compact, the turbofan became smaller as well. To the point that they could be places on a fighter, but with a smaller bypass ratio. This gives much better fuel efficiency (range), while still retaining high power.
For jetliners, it's all about efficiency, but still retaining a degree of speed. But for a really high-bypass turbofan (50% or more), it's going to be a huge engine. Fighters are between 15-20% now, but you won't see much more than that.
https://en.wikipedia.org/wiki/Bypass_ratio
Tom Clancy wrote a book many years ago in which he discusses this in laymans terms really well: http://www.amazon.com/Fighter-Wing-Clancys-Military-Referenc...
> what may be most remarkable about the engines is that they took almost 30 years to develop. That’s about 15 times as long as the gestation period of an elephant Who the hell is running their analogy department?!? "Thirty years! That's a big number! We need some kind of comparison that will instantly give the reader perspective. Of course, in this, as in so many other things, the answer lies in pachydermian pregnanc…
~ 0.36 x orbital period of Uranus
~ 1.02 x orbital period of Saturn
~ 5.7 x half-life of colbalt-60
source:
So basically this seems to be a extra-high-bypass turbofan achieved by gearing down the fan. But delayed hugely because giant megacorps move very very slowly.
> what may be most remarkable about the engines is that they took almost 30 years to develop. That’s about 15 times as long as the gestation period of an elephant Who the hell is running their analogy department?!? "Thirty years! That's a big number! We need some kind of comparison that will instantly give the reader perspective. Of course, in this, as in so many other things, the answer lies in pachydermian pregnanc…
Earlier quoted context omitted.
This idea would unfortunately negate one of the top benefits of a high-bypass turbofan. Noise reduction.
Yes, but why is a high bypass turbofan quieter? If I understood correctly, it's because most of the thrust comes from the large slow moving fan, so you don't need to blast nearly so much air through the turbine as a turbojet to get the same thrust. The whole purpose of decoupling the fans is to give you an even higher bypass ratio - two or three large electric fans driven from one turbine can have a larger swept area…
The noise comes from high speed air alongside slow moving air. A high bypass fan moves more air at slower speed to get the same push. The slower speed means less noise.
Could some knowledgable aircraft people answer these questions for me? 1. Can/are jet engines ever swapped out after a plane as been put into service? Or will these only ever be sold attached to new aircraft orders. 2. Any idea on what the engine costs? And what percentage of the overall airline cost is engine? I didn't see any references to costs of this engine vs existing models.
So basically this seems to be a extra-high-bypass turbofan achieved by gearing down the fan. But delayed hugely because giant megacorps move very very slowly.
Move to short and fatal flaw kills people? ZOMG KKKORPORTATION$!!!
Can't win for losing...
Could some knowledgable aircraft people answer these questions for me? 1. Can/are jet engines ever swapped out after a plane as been put into service? Or will these only ever be sold attached to new aircraft orders. 2. Any idea on what the engine costs? And what percentage of the overall airline cost is engine? I didn't see any references to costs of this engine vs existing models.