Maybe – or maybe not.
If you consider that the A330 is a twin engine version of the 4-engined A340 then you might think it might be feasible.
On the other hand, the A380 was designed in the era of ETOPS and airlines paying very close attention to fuel costs. If it could be twin engined, it WOULD be twin engined.
What follows is rather simplistic, but you’ll get the idea:
Firstly lets consider the engines. The RR Trent 900s used on the A380 have a takeoff thrust of of 310–320kN (31 tons) and are designed to grow to 360kN for the unflown A380–900 and -1000 fuselage stretches (which are unlikely to ever happen.)
There are 4 of them, so the total available thrust is 1240kN. If you’re using a twin you’d need 620kN thrust per engine. The most powerful current RR engine is the Trent XWB and it puts out 370–420kN – so you’re a bit short on thrust
Maybe you could make it a 3 engine craft, but putting a turbofan that big on the tail or at the back wouldn’t exactly be easy and the ducting plus hardware changes add a lot of weight and complexity, plus servicing an engine that high in the air is “difficult”, so lets forget that idea and stick with twins and a theoretical Trent XWB putting out 650kN (purely arbitrary, but a round number to work with.
In order to do that, you’re going to need a bigger core (the actual jet part) and a bigger fan (that’s the part out front).
Let’s say the fan increases in size by 25%. You’ll need to adjust the mounting pylon a tad further forward and have the centre of the engine a little lower down but all is good – until you look down and realise your engine nacelle is now bumping along a couple of inches off the ground. This is not good, things get sucked into engines, but you can solve that by giving it longer legs – except that means redesigning the landing gear bays and giving less space to cargo. Let’s say that’s ok and carry on.
The second part is where it gets a little more complicated:
All aircraft have to be able to take off with “one engine out” – which means that you really only need 930–1000kN of thrust in total – which is almost doable with 2 Trent XWBs and probably achieveable with a redesign, BUT….
If you only have two engines then you need to be able to develop that full 1000kN of thrust from ONE engine if the brown stuff hits the rotating thingie (or a bird flies through your engine).
That means you’re going to need an even BIGGER engine and an even bigger fan and even longer legs, with even less cargo space – and one of the things to bear in mind about the A380 is that being a double deck aircraft, passenger bags take up a LOT of space in the cargo hold – So much so that if fully loaded there would only be 8–10 cargo pod spaces left. The longer landing gear just ate all that cargo space even though you’ve increased the lifting capacity by the weight of the 2 engines just removed. Cargo revenue is crucial for airlines, so if you have a passenger-only aircraft, noone will touch it.
And here’s an added twist:
The A380 in its current guise, whilst carrying a full passenger load can carry twice the cargo mass that’s available in a fully passenger-loaded 777, but the 777 can carry 3 times as many cargo containers. However when fully laden, the 777’s range is 3000 miles less than the A380. This is why airlines tend to be more stringent about bag weights on 777 flights than A380 flights (I’ve been waved through many times with an extra 10–15kg on A380s vs having to get rid of everything above the 20kg allowance on 777s)
Air cargo is more profitable than passengers, so airlines like to ensure they carry as much as possible. That’s one of the reasons that A380s are usually setup with only 500 passengers – it gives more sellable cargo space below decks. The resulting extra space per passenger above decks translates into roomier seats and “halo” class accomodation that can be sold for a premium or given to some lucky stiff if it’s not sold for that leg – fantastic advertising and the space is already paid for by what’s below decks, so there’s no loss.
The thing to bear in mind is that passenger aircraft are designed for specific tasks and address different market requirements. The A380 was built to run full loads of passengers and freight between extremely busy high capacity airports in order to keep the number of traffic movements down (the Hub and spoke model). You’d be crazy to run it less than half full or on flight legs less than 3 hours. You’d also be crazy to run it into smaller airports where there aren’t enough immigration desks to handle the influx of passengers in a reasonable period.
The 787 and A350 are designed to haul moderate numbers of passengers on very long haul direct flights between smaller airports (or long thin routes) (9–14 hour flights or longer)
The A330 and 777 are designed for medium haul flights in general and were pushing their limits to get into longhaul operations. Now that better-suited aircraft are available you’re likely to see them being taken off 8+ hour legs as they are not as cost-effective on these kinds of flights. On the other hand the 787 and A350 will never be cost effective on 2–3 hour flights as all their optimisation is for long flight legs.
Something to bear in mind is that making and selling a new aircraft model is a calculated risk based on projecting trends 20–30 years into the future. If you get it wrong, you could end up out of business (Convair, Lockheed, McDonell, Douglas, etc), so when you’re making a BIG aircraft with limited sales, you’re going to be very conservative. Back when the A380 was gestating, the market was all about 747s and hub/spoke models. Airbus predicted that it would stay that way.
On the other hand, Boeing didn’t think that the hub/spoke model would continue and stayed out of the race – the 747–8 is a warmed over version of the 747 and there’s nothing groundbreaking in it, but sales are so low that Boeing may not recover those modest development costs before it cancels the line.
None of this affects smaller aircraft. 737s and A320s sell like hotcakes. There’s also a scramble going on for new generation 100–130 seat shorthaul (regional) craft between Bombardier, Comac, Embraer, Sukhoi, Tupolov and in all liklihood a couple more over the next few years.
At the moment, fuel costs are low, so there’s a preference for long-direct flights over the more efficient hub-spoke model. Passengers may change their minds when fuel costs start rising again and the journey cost differences between the models start being more than a couple of hundred dollars.
Time will tell whose predictions were better, but one thing is certain – we are unlikely to ever see a twin-engine A380 variant, simply because no engines are powerful enough and small enough to fit under the existing wing.
Author – Alan Brown
