Question for pilots...


#1

Hello

Apologies if this is the wrong place, if it needs moving please do so.

This is something I’ve wondered about for a while: if the Airbus Beluga can carry huge loads under the power of only 2 engines, how come the super-jumbo passenger jets (B747 and A380) are still using 4 engines? Why would 2 engines not be enough in these cases?

There may be a simple answer, the passengers jets may simply weigh more but as far as I know a fully loaded Airbus beluga would probably weigh the same as a jumbo?

I can’t wait to hear the answer

Regards
JS


#2

Its in the right place dont hurt your head :)


#3

Actually, due to the weight of these aircrafts, they cannot take off with only two engines. Now, mind you, these 4 engines were probably designed before the GE90, so they would not be as powerful.


#4

So potentially with today’s more powerful engines they may be able to fly with 2 engines?


#5

@Jake_Savage Here’s some facts:
The 777’s Maximum takeoff weight is about the same as the Airbus A380’s Zero fuel weight


#6

The Max takeoff weight of the Airbus Beluga is 155 tonnes where as the Max takeoff weight of the B747-400 is 412.76 tonnes thats about 2.6 times the weight.


#7

Well just strap 2 GE9Xs to the 747 and boom


#8

I’m not a pilot but one reason is if you have an engine failure during take off like a bird strike, one engine needs to be powerful enough and last long enough at Max power so you can can still fly and immediately land. One of the reasons why only the CRJ 700 is certified to operate commercial, scheduled flights at KASE due to it’s elevation

On another note on cargo aircraft, unless you’re hauling pallets of gold bricks, more times than not you’re going to cube out before you Max weight out.


#9

Not exactly, many aircraft out there are twin engine. The 777 for example which has a large maximum takeoff weight. As long as the engines can support that weight and powerful enough, it’d be fine.


#10

But if you re engine a current 747 with just 2 engines and if one fails the other is not powerful enough to keep the aircraft flying to land safely.

Maybe if it was empty and light on fuel but probably not for regular commercial flights

Just off the top of my head, I think the 747 glide ratio is like 15:1 whereas the 787 and 777 are somewhere around 18-20.


#11

btw my post was a joke. I know that’s not realistic


#12

It’s all down to ETOPS rules and the ability to have a viable diversion within the relevant ETOPS rule range that can take your aircraft.

The Beluga can take extended, non ETOPS, routes over the globe as cargo isn’t as obsessed with arrival times as passengers are.

4 engined and triples don’t have the same restrictions but carry more weight (4 x engines vs 2 x engines) hence have a fuel penalty.

To summarise some twins carrying the same passenger and freight load as a quad might not have the range capability under, say, ETOPS 180, to complete a route that the quad can do.

However with the introduction of the 350-1000 and the 777x times are changing yet again.