I seem to remember that the regulations concerning evacuation of aircraft say that you have to get everyone off the aircraft in 90 seconds, using only half the exits. This means that you’ve got to get somewhere in the region of 1 person going down the slides every second… roughly speaking! The problem with evacuation of the A380 comes in the top deck… it’s high off the ground… so if you have say an 80 year old frail woman… terrified, because of the emergency…. stood looking out of the door on the top deck of an A380 thinking it’s a bloody long way down to the ground… and just freezing… not moving… this means people are trapped and could make the difference between life or death.

“Boeing also want to run all of their electrical power off of the engine aswell, and not have to carry anything such as batteries on board”

The electrical power for the aircraft comes from a generator connected to the engine gearbox. If there is an engine failure, the APU can be brought online to provide some engine power… On the 777, the APU and the each engine is designed to produce the same amount of elecrical power, so if the engines fail, something is going to have to be switched off! If the APU fails, then there is a RAT, or ram air turbine which produces power like a windmill… this only produces a small amount of power, only enough to maybe power the flight instruments. If that fails, then I think there are smoe batteries somewhere… not sure if the RAT or batteries provide the last of the power! But the chances of all of these failing are very remote, so perhaps Boeing could get rid of the batteries.

“a large amount of the energy is actually created without having to use any fuel at all”

You never get something for nothing in the aviation world!! Most of the air passes through a bypass duct after passing through the fan, the fan, which sends the air backwards is driven by a turbine stage, to turn the turbine you have to use fuel!

With Jet engines, there’s basically 2 ways to get thrust, either you put a large mass of air through the engine at a relatively slow speed (bypass turbofan), or you send a small mass of air through the engine at a high speed (turbojet).

For civil airliners the former is preferred because it increases the propulsive efficiency, which depends on the difference between the velocity of the air coming out of the back of the engine and the aircraft forward velocity, so the closer these two velocities are, the better the propulsive efficiency.

The overall efficiency of an engine is the propulsive efficiency multiplied by the thermal efficiency. The thermal efficiency is the kinetic energy of the air through the engine(useful work out) divided by the work put in by the fuel (energy in). The thermal efficiency gets higher when the temperature is higher, but there are material constraints here, materials can only take temperatures up to… I think 1700K is the standard Turbine entry temperature at the moment.

The down side to the turbofan is that it’s got a large diameter, so produces more drag. The turbojet which produces less drag is noisier, and is more efficient as the airspeed goes up into the supersonic regime.

That OK? Man reading that you can tell I’ve been busy revising for my Turbomachinery exam!!

“Those are essentially newer, moderately larger 777 engines. Why would they be having so many problems with them?”

The fan blades are larger, there’s a contra rotating High pressure system in there which the 777 engine doesn’t have, that’s a new idea which leads to problems.

Back in Year 9 I got 2 weeks work experience working for Multiflight at LBA. Was quite fun… spent a couple of days with the flying school… a couple of days in stores, and a week working with the engineers putting panels back on a twin prop plane they were overhauling. Was great fun!!!

They all run on gas turbines! 🙂 But they’re props!

Without doubt, the best type of intake to have is one where the air flows in a straight line, like that of the Lighting or MiG-21 for a single engined type, or an F-14, or maybe a MiG-29 for a twin. The problems with a single engine, straight through layout, like a lightning is that the nose is often required to house a radar.

Side intakes, while not necessarily bad, have to turn the flow twice, before the air reaches the engine, this means that the air is slowing down in the turns, and if it slows down too much, this can lead to turbulence, and the engine being temporarily starved of air, or the turbulent air causing vibration of the engine.

A chin intake cuts down the amount of turning for the air, while also freeing the nose for a radar.

Also of note… with side and chin intakes… if the air comes into contact with a surface, before reaching the intake, say a fuselage side, then there will be a boundary layer which must be separated as it is slow moving, and will develop rapidly when going through turning in an intake. The solution is a splitter plate, (that big rectangle on the side of a phantom for example, where aces put kill marks sometimes for those who don’t know!).

The Rafale and Ching Kuo and F/A-18, pretty much have straight through air intakes, which is a good thing for designers.. makes calculations so much easier!!!

Just my 2 cents!!