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Armadillo1
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Re: 2 vs 4 engines

Fri Dec 25, 2020 9:47 am

Starlionblue wrote:
The A340 engines run at or near full thrust at takeoff, and 80-85% in the cruise. Same as the A330 engines.



quad have 133% power. 80*133= 106.4%
twin have 200% power. 80*200=160%.

this means twins need to fly higher , which difficult by regulations


what about 2 engine-off for quad?
 
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Starlionblue
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Re: 2 vs 4 engines

Fri Dec 25, 2020 10:43 am

Armadillo1 wrote:
Starlionblue wrote:
The A340 engines run at or near full thrust at takeoff, and 80-85% in the cruise. Same as the A330 engines.



quad have 133% power. 80*133= 106.4%
twin have 200% power. 80*200=160%.

this means twins need to fly higher , which difficult by regulations


what about 2 engine-off for quad?


Sorry I was unclear. The 80-85% number is N1, not a percentage of max thrust. The relationship between % N1 and % thrust isn't linear. Most of the thrust range is in the top third of the N1 range. And it will be different for different engines.

Two engines out on take-off for a quad is not catered for.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
WayexTDI
Posts: 2293
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Re: 2 vs 4 engines

Fri Dec 25, 2020 3:09 pm

Starlionblue wrote:
WayexTDI wrote:
Junglejames wrote:
The quietest airliners have 4 engines.
Is that just coincidence?

Sent from my SM-G930F using Tapatalk

Of course not, since each engine in a 4-engine plane runs at 1/2 the thrust than what would be needed in the same 2-engine plane (think A340 vs A330).


That makes no sense. No manufacturer would mount engines that ran at half thrust at takeoff, or in the cruise. If nothing else, the engines would very inefficient at half thrust.

The A340 engines run at or near full thrust at takeoff, and 80-85% in the cruise. Same as the A330 engines.

Quads and twins in the same weight range do not use engines in the same thrust range. Compare A340 and 777.

Side note: Noise on approach is mostly due to high lift devices.

You didn't get it.
Hypothetical numbers: if the A330-300 needs a total thrust of 50,000 lbs in cruise, that's 25,000 lbs delivered by each engine (#1 & #2). In comparison, the A340-300 would require the same total thrust, but spread over 4 engines, i.e. 12,500 lbs developed per engine (#1 through #4).
Given that the A340 #2 engine is where the A330 #1 engine is, and the A340 #3 engine is where the A330 #2 engine is, you will hear in the cabin the noise related to the thrust of each engine; so, less on an A340 than on an A330.
 
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Starlionblue
Posts: 20698
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Re: 2 vs 4 engines

Fri Dec 25, 2020 3:31 pm

WayexTDI wrote:
Starlionblue wrote:
WayexTDI wrote:
Of course not, since each engine in a 4-engine plane runs at 1/2 the thrust than what would be needed in the same 2-engine plane (think A340 vs A330).


That makes no sense. No manufacturer would mount engines that ran at half thrust at takeoff, or in the cruise. If nothing else, the engines would very inefficient at half thrust.

The A340 engines run at or near full thrust at takeoff, and 80-85% in the cruise. Same as the A330 engines.

Quads and twins in the same weight range do not use engines in the same thrust range. Compare A340 and 777.

Side note: Noise on approach is mostly due to high lift devices.

You didn't get it.
Hypothetical numbers: if the A330-300 needs a total thrust of 50,000 lbs in cruise, that's 25,000 lbs delivered by each engine (#1 & #2). In comparison, the A340-300 would require the same total thrust, but spread over 4 engines, i.e. 12,500 lbs developed per engine (#1 through #4).
Given that the A340 #2 engine is where the A330 #1 engine is, and the A340 #3 engine is where the A330 #2 engine is, you will hear in the cabin the noise related to the thrust of each engine; so, less on an A340 than on an A330.


You're assuming that noise and noise propagation are exactly proportional to thrust, across different engines. They are not.

Either way, I was talking about outside noise, not outside noise. The A340 is noisier than the A330 on that front. Source: EASA Type Certificate Data Sheets for Noise (TCDSN) https://www.easa.europa.eu/document-lib ... =&year_to=
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
Junglejames
Posts: 89
Joined: Sat Jan 05, 2019 4:07 am

Re: 2 vs 4 engines

Fri Dec 25, 2020 3:41 pm

Starlionblue wrote:
WayexTDI wrote:
Junglejames wrote:
The quietest airliners have 4 engines.
Is that just coincidence?

Sent from my SM-G930F using Tapatalk

Of course not, since each engine in a 4-engine plane runs at 1/2 the thrust than what would be needed in the same 2-engine plane (think A340 vs A330).


That makes no sense. No manufacturer would mount engines that ran at half thrust at takeoff, or in the cruise. If nothing else, the engines would very inefficient at half thrust.

The A340 engines run at or near full thrust at takeoff, and 80-85% in the cruise. Same as the A330 engines.

Quads and twins in the same weight range do not use engines in the same thrust range. Compare A340 and 777.

Side note: Noise on approach is mostly due to high lift devices.



Junglejames wrote:
Starlionblue wrote:

IMHO this one is not really valid, as engines on twins are correctly sized for cruise. Thrust is down to maybe 20% of take-off thrust, so they run at 80-85% N1 in the cruise. That's pretty much where they are most efficient.

The total engine frontal area might be larger with a twin, so you get more form drag, but four engines give more skin friction and interference drag. No idea which one wins here.



The A350 and 787 would like a word. ;)
787 doesn't come close. I'm not the only one that can't work out the name given to them. Unless of course the dream was a nightmare.
A350 also noisier.

They can have words all they like. I presume to agree with me.

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C-Series, 787 and A350 are all quieter than the A380, which is by far the quietest quad.

Source: EASA Type Certificate Data Sheets for Noise. https://www.easa.europa.eu/document-lib ... =&year_to=
I have no idea if we are talking about noise in the same location (perhaps you are flying on the outside of the aircraft). But when sitting inside the aircraft, the A380 is quieter than the 3 twins you mention.


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Junglejames
Posts: 89
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Re: 2 vs 4 engines

Fri Dec 25, 2020 3:44 pm

WayexTDI wrote:
Starlionblue wrote:
WayexTDI wrote:
Of course not, since each engine in a 4-engine plane runs at 1/2 the thrust than what would be needed in the same 2-engine plane (think A340 vs A330).


That makes no sense. No manufacturer would mount engines that ran at half thrust at takeoff, or in the cruise. If nothing else, the engines would very inefficient at half thrust.

The A340 engines run at or near full thrust at takeoff, and 80-85% in the cruise. Same as the A330 engines.

Quads and twins in the same weight range do not use engines in the same thrust range. Compare A340 and 777.

Side note: Noise on approach is mostly due to high lift devices.

You didn't get it.
Hypothetical numbers: if the A330-300 needs a total thrust of 50,000 lbs in cruise, that's 25,000 lbs delivered by each engine (#1 & #2). In comparison, the A340-300 would require the same total thrust, but spread over 4 engines, i.e. 12,500 lbs developed per engine (#1 through #4).
Given that the A340 #2 engine is where the A330 #1 engine is, and the A340 #3 engine is where the A330 #2 engine is, you will hear in the cabin the noise related to the thrust of each engine; so, less on an A340 than on an A330.
Don't worry, it made perfect sense!!!

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Junglejames
Posts: 89
Joined: Sat Jan 05, 2019 4:07 am

Re: 2 vs 4 engines

Fri Dec 25, 2020 3:46 pm

Starlionblue wrote:
WayexTDI wrote:
Starlionblue wrote:

That makes no sense. No manufacturer would mount engines that ran at half thrust at takeoff, or in the cruise. If nothing else, the engines would very inefficient at half thrust.

The A340 engines run at or near full thrust at takeoff, and 80-85% in the cruise. Same as the A330 engines.

Quads and twins in the same weight range do not use engines in the same thrust range. Compare A340 and 777.

Side note: Noise on approach is mostly due to high lift devices.

You didn't get it.
Hypothetical numbers: if the A330-300 needs a total thrust of 50,000 lbs in cruise, that's 25,000 lbs delivered by each engine (#1 & #2). In comparison, the A340-300 would require the same total thrust, but spread over 4 engines, i.e. 12,500 lbs developed per engine (#1 through #4).
Given that the A340 #2 engine is where the A330 #1 engine is, and the A340 #3 engine is where the A330 #2 engine is, you will hear in the cabin the noise related to the thrust of each engine; so, less on an A340 than on an A330.


You're assuming that noise and noise propagation are exactly proportional to thrust, across different engines. They are not.

Either way, I was talking about outside noise, not outside noise. The A340 is noisier than the A330 on that front. Source: EASA Type Certificate Data Sheets for Noise (TCDSN) https://www.easa.europa.eu/document-lib ... =&year_to=
When above 30,000 feet, travelling at over 500kts, I prefer to stay inside the aircraft (bit cold outside!)
So I never need to worry about outside noise.

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GalaxyFlyer
Posts: 7813
Joined: Fri Jan 01, 2016 4:44 am

Re: 2 vs 4 engines

Fri Dec 25, 2020 4:31 pm

Junglejames wrote:
Starlionblue wrote:
WayexTDI wrote:
You didn't get it.
Hypothetical numbers: if the A330-300 needs a total thrust of 50,000 lbs in cruise, that's 25,000 lbs delivered by each engine (#1 & #2). In comparison, the A340-300 would require the same total thrust, but spread over 4 engines, i.e. 12,500 lbs developed per engine (#1 through #4).
Given that the A340 #2 engine is where the A330 #1 engine is, and the A340 #3 engine is where the A330 #2 engine is, you will hear in the cabin the noise related to the thrust of each engine; so, less on an A340 than on an A330.


You're assuming that noise and noise propagation are exactly proportional to thrust, across different engines. They are not.

Either way, I was talking about outside noise, not outside noise. The A340 is noisier than the A330 on that front. Source: EASA Type Certificate Data Sheets for Noise (TCDSN) https://www.easa.europa.eu/document-lib ... =&year_to=
When above 30,000 feet, travelling at over 500kts, I prefer to stay inside the aircraft (bit cold outside!)
So I never need to worry about outside noise.

Sent from my SM-G930F using Tapatalk


Interior sound levels have little to do with engine location and much to do with sound insulation design and installation of things like air ducting, paneling, etc. New Globals get interior sound surveys done for the owner. There’s a noticeable difference between wood and soft fabric bulkheads, fabric or leather seating. The windows bulge a tiny bit under pressure load creating small, noisy burbles in the slipstream. The quietest cabin location is the aft section nearest the engine.
 
Junglejames
Posts: 89
Joined: Sat Jan 05, 2019 4:07 am

Re: 2 vs 4 engines

Fri Dec 25, 2020 7:50 pm

GalaxyFlyer wrote:
Junglejames wrote:
Starlionblue wrote:

You're assuming that noise and noise propagation are exactly proportional to thrust, across different engines. They are not.

Either way, I was talking about outside noise, not outside noise. The A340 is noisier than the A330 on that front. Source: EASA Type Certificate Data Sheets for Noise (TCDSN) https://www.easa.europa.eu/document-lib ... =&year_to=
When above 30,000 feet, travelling at over 500kts, I prefer to stay inside the aircraft (bit cold outside!)
So I never need to worry about outside noise.

Sent from my SM-G930F using Tapatalk


Interior sound levels have little to do with engine location and much to do with sound insulation design and installation of things like air ducting, paneling, etc. New Globals get interior sound surveys done for the owner. There’s a noticeable difference between wood and soft fabric bulkheads, fabric or leather seating. The windows bulge a tiny bit under pressure load creating small, noisy burbles in the slipstream. The quietest cabin location is the aft section nearest the engine.


Are you sure? I find the quietest part of the cabin to be forward of the engine. I'm not the only one to say that either.
There can be a large difference in noise level between fwd and aft of the wings.
My quietest journey on an A340 was an Air France model. I was sitting at the front of the economy section. Nearly comparable to an A380.
Whenever I sit aft of the engine, it is always noisier. For obvious reasons.
This is especially obvious on Airbus aircraft. On Boeing's it is less obvious, as they are just noisy full stop.

On A380s the worst of the noise is from the ventilation, but that's because the engines are so quiet, and I suspect it has good sound insulation. Same for A340s.
On 777s and 787s, the engines are just plain noisy.
On A350s the engines again are noisier than a quad, but it is usually obvious how Airbus have fitted better sound insulation compared to Boeing on the 787s.
A330s are similar to A350s in the noise department.

So I agree, it isn't just the engines, but they do play a part, and quads are always quieter than twins.
The obvious exception is the 747s which are noisier than say A350s. No doubt insulation playing it's part. But compare them to a 777, and the quad of a 747 again wins.


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FriscoHeavy
Posts: 1841
Joined: Tue May 27, 2014 4:31 pm

Re: 2 vs 4 engines

Fri Dec 25, 2020 8:36 pm

Junglejames wrote:
GalaxyFlyer wrote:
Junglejames wrote:
When above 30,000 feet, travelling at over 500kts, I prefer to stay inside the aircraft (bit cold outside!)
So I never need to worry about outside noise.

Sent from my SM-G930F using Tapatalk


Interior sound levels have little to do with engine location and much to do with sound insulation design and installation of things like air ducting, paneling, etc. New Globals get interior sound surveys done for the owner. There’s a noticeable difference between wood and soft fabric bulkheads, fabric or leather seating. The windows bulge a tiny bit under pressure load creating small, noisy burbles in the slipstream. The quietest cabin location is the aft section nearest the engine.


Are you sure? I find the quietest part of the cabin to be forward of the engine. I'm not the only one to say that either.
There can be a large difference in noise level between fwd and aft of the wings.
My quietest journey on an A340 was an Air France model. I was sitting at the front of the economy section. Nearly comparable to an A380.
Whenever I sit aft of the engine, it is always noisier. For obvious reasons.
This is especially obvious on Airbus aircraft. On Boeing's it is less obvious, as they are just noisy full stop.

On A380s the worst of the noise is from the ventilation, but that's because the engines are so quiet, and I suspect it has good sound insulation. Same for A340s.
On 777s and 787s, the engines are just plain noisy.
On A350s the engines again are noisier than a quad, but it is usually obvious how Airbus have fitted better sound insulation compared to Boeing on the 787s.
A330s are similar to A350s in the noise department.

So I agree, it isn't just the engines, but they do play a part, and quads are always quieter than twins.
The obvious exception is the 747s which are noisier than say A350s. No doubt insulation playing it's part. But compare them to a 777, and the quad of a 747 again wins.

The 787 is not loud. I’ve been on them numerous times (along with the 350). No real discernible difference.
Whatever
 
johns624
Posts: 3778
Joined: Mon Jul 07, 2008 11:09 pm

Re: 2 vs 4 engines

Fri Dec 25, 2020 8:42 pm

Junglejames wrote:
GalaxyFlyer wrote:
Junglejames wrote:
When above 30,000 feet, travelling at over 500kts, I prefer to stay inside the aircraft (bit cold outside!)
So I never need to worry about outside noise.

Sent from my SM-G930F using Tapatalk


Interior sound levels have little to do with engine location and much to do with sound insulation design and installation of things like air ducting, paneling, etc. New Globals get interior sound surveys done for the owner. There’s a noticeable difference between wood and soft fabric bulkheads, fabric or leather seating. The windows bulge a tiny bit under pressure load creating small, noisy burbles in the slipstream. The quietest cabin location is the aft section nearest the engine.


Are you sure? I find the quietest part of the cabin to be forward of the engine. I'm not the only one to say that either.
There can be a large difference in noise level between fwd and aft of the wings.
My quietest journey on an A340 was an Air France model. I was sitting at the front of the economy section. Nearly comparable to an A380.
Whenever I sit aft of the engine, it is always noisier. For obvious reasons.
This is especially obvious on Airbus aircraft. On Boeing's it is less obvious, as they are just noisy full stop.

On A380s the worst of the noise is from the ventilation, but that's because the engines are so quiet, and I suspect it has good sound insulation. Same for A340s.
On 777s and 787s, the engines are just plain noisy.
On A350s the engines again are noisier than a quad, but it is usually obvious how Airbus have fitted better sound insulation compared to Boeing on the 787s.
A330s are similar to A350s in the noise department.

So I agree, it isn't just the engines, but they do play a part, and quads are always quieter than twins.
The obvious exception is the 747s which are noisier than say A350s. No doubt insulation playing it's part. But compare them to a 777, and the quad of a 747 again wins.


Sent from my SM-G930F using Tapatalk

You missed what plane he was referring to. Reread his whole post.
 
GalaxyFlyer
Posts: 7813
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Re: 2 vs 4 engines

Fri Dec 25, 2020 9:07 pm

True, it’s a Global 6000, tail-mounted engines and the act cabin is closer to the engines, but consistently the quietest area—52-55 dB. Yes, during refueling, on the boom, you can hear the engines, in the A-10, less noticeable in the C-5. The exhaust stream is noisy.

The A380 is notably quieter than nearly everything else I’ve flown, but frankly, I don’t pay much attention. Get on, suffer thru the ride, eat and drink what they give me and happy to arrive.
 
Junglejames
Posts: 89
Joined: Sat Jan 05, 2019 4:07 am

Re: 2 vs 4 engines

Sat Dec 26, 2020 12:41 am

FriscoHeavy wrote:

The 787 is not loud. I’ve been on them numerous times (along with the 350). No real discernible difference.


Perhaps loud was an unfair comment, but it depends what you compare it against. They certainly aren't quiet.

You've got A380 and A340 at the top.
Then an obvious gap.
A350/ A330
787
Then an obvious gap
747
777

I'm off now to see the difference in individual engine sizes between all these aircraft!!

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Junglejames
Posts: 89
Joined: Sat Jan 05, 2019 4:07 am

Re: 2 vs 4 engines

Sat Dec 26, 2020 12:42 am

johns624 wrote:
Junglejames wrote:
GalaxyFlyer wrote:

Interior sound levels have little to do with engine location and much to do with sound insulation design and installation of things like air ducting, paneling, etc. New Globals get interior sound surveys done for the owner. There’s a noticeable difference between wood and soft fabric bulkheads, fabric or leather seating. The windows bulge a tiny bit under pressure load creating small, noisy burbles in the slipstream. The quietest cabin location is the aft section nearest the engine.


Are you sure? I find the quietest part of the cabin to be forward of the engine. I'm not the only one to say that either.
There can be a large difference in noise level between fwd and aft of the wings.
My quietest journey on an A340 was an Air France model. I was sitting at the front of the economy section. Nearly comparable to an A380.
Whenever I sit aft of the engine, it is always noisier. For obvious reasons.
This is especially obvious on Airbus aircraft. On Boeing's it is less obvious, as they are just noisy full stop.

On A380s the worst of the noise is from the ventilation, but that's because the engines are so quiet, and I suspect it has good sound insulation. Same for A340s.
On 777s and 787s, the engines are just plain noisy.
On A350s the engines again are noisier than a quad, but it is usually obvious how Airbus have fitted better sound insulation compared to Boeing on the 787s.
A330s are similar to A350s in the noise department.

So I agree, it isn't just the engines, but they do play a part, and quads are always quieter than twins.
The obvious exception is the 747s which are noisier than say A350s. No doubt insulation playing it's part. But compare them to a 777, and the quad of a 747 again wins.


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You missed what plane he was referring to. Reread his whole post.
That is a fair point. I may have misread his point about quietest section!!

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GalaxyFlyer
Posts: 7813
Joined: Fri Jan 01, 2016 4:44 am

Re: 2 vs 4 engines

Sat Dec 26, 2020 12:47 am

From a pilot/builder point of view, noise levels are about certification of the design outside the plane. Perceived sound levels inside are not certification matters. Heck, most certification testing is done on planes with little or no interior sound insulation. Pilots get violated for sound outside the plane by not making good the track, flying the NADP correctly or overflying a microphone.
 
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Starlionblue
Posts: 20698
Joined: Fri Feb 27, 2004 9:54 pm

Re: 2 vs 4 engines

Sat Dec 26, 2020 1:10 am

GalaxyFlyer wrote:
Interior sound levels have little to do with engine location and much to do with sound insulation design and installation of things like air ducting, paneling, etc. New Globals get interior sound surveys done for the owner. There’s a noticeable difference between wood and soft fabric bulkheads, fabric or leather seating. The windows bulge a tiny bit under pressure load creating small, noisy burbles in the slipstream. The quietest cabin location is the aft section nearest the engine.


I completely agree. Airbus is well known for better cabin noise insulation in its widebodies, hence why the cabins are perceived as quieter. For example, the A350 seems to have a quieter cabin than the 787, even though the A350 is the noisier aircraft. (Yes, on the outside...)

The A380 engines are 78000lbf, which is comparable to the A350-900, at 84000lbf and the 787-10, at 76000lbf. Despite the fact that the engines are pretty close in thrust, the cabin noise level in the A380 is way lower than the other two, and the A350 has a quieter cabin than the 787 despite higher thrust. Since relative thrust levels in cruise are pretty close for all airliners, it would appear that, just as GalaxyFlyer says, engine thrust is not directly correlated to cabin noise.

I've ignored, for this exercise, the fact that the outer engines on the A380 probably also contribute a bit to cabin noise. :)

Junglejames wrote:
]I have no idea if we are talking about noise in the same location (perhaps you are flying on the outside of the aircraft). But when sitting inside the aircraft, the A380 is quieter than the 3 twins you mention.

Sent from my SM-G930F using Tapatalk


I linked to EASA documentation which made it perfectly clear that I was referring to outside noise.

Junglejames wrote:
When above 30,000 feet, travelling at over 500kts, I prefer to stay inside the aircraft (bit cold outside!)
So I never need to worry about outside noise.

Sent from my SM-G930F using Tapatalk


This is tech/ops. When we talk about aircraft noise without specifying, in general we mean the noise the aircraft makes. In this case, it is also a thread about engines, which mostly impact exterior noise.

You're talking about cabin noise, which is another thing, and I did not understand that initially. If you're not specific, the rest of us might not understand what you mean.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
Junglejames
Posts: 89
Joined: Sat Jan 05, 2019 4:07 am

Re: 2 vs 4 engines

Sat Dec 26, 2020 1:18 am

GalaxyFlyer wrote:
From a pilot/builder point of view, noise levels are about certification of the design outside the plane. Perceived sound levels inside are not certification matters. Heck, most certification testing is done on planes with little or no interior sound insulation. Pilots get violated for sound outside the plane by not making good the track, flying the NADP correctly or overflying a microphone.
That may be so. I'm more worried about noise inside though! I may need to sleep!!


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Junglejames
Posts: 89
Joined: Sat Jan 05, 2019 4:07 am

Re: 2 vs 4 engines

Sat Dec 26, 2020 1:44 am

Starlionblue wrote:
GalaxyFlyer wrote:
Interior sound levels have little to do with engine location and much to do with sound insulation design and installation of things like air ducting, paneling, etc. New Globals get interior sound surveys done for the owner. There’s a noticeable difference between wood and soft fabric bulkheads, fabric or leather seating. The windows bulge a tiny bit under pressure load creating small, noisy burbles in the slipstream. The quietest cabin location is the aft section nearest the engine.


I completely agree. Airbus is well known for better cabin noise insulation in its widebodies, hence why the cabins are perceived as quieter. For example, the A350 seems to have a quieter cabin than the 787, even though the A350 is the noisier aircraft. (Yes, on the outside...)

The A380 engines are 78000lbf, which is comparable to the A350-900, at 84000lbf and the 787-10, at 76000lbf. Despite the fact that the engines are pretty close in thrust, the cabin noise level in the A380 is way lower than the other two, and the A350 has a quieter cabin than the 787 despite higher thrust. Since relative thrust levels in cruise are pretty close for all airliners, it would appear that, just as GalaxyFlyer says, engine thrust is not directly correlated to cabin noise.

I've ignored, for this exercise, the fact that the outer engines on the A380 probably also contribute a bit to cabin noise. :)

Junglejames wrote:
]I have no idea if we are talking about noise in the same location (perhaps you are flying on the outside of the aircraft). But when sitting inside the aircraft, the A380 is quieter than the 3 twins you mention.

Sent from my SM-G930F using Tapatalk


I linked to EASA documentation which made it perfectly clear that I was referring to outside noise.

Junglejames wrote:
When above 30,000 feet, travelling at over 500kts, I prefer to stay inside the aircraft (bit cold outside!)
So I never need to worry about outside noise.

Sent from my SM-G930F using Tapatalk


This is tech/ops. When we talk about aircraft noise without specifying, in general we mean the noise the aircraft makes. In this case, it is also a thread about engines, which mostly impact exterior noise.

You're talking about cabin noise, which is another thing, and I did not understand that initially. If you're not specific, the rest of us might not understand what you mean.
Easily misunderstood!
I haven't actually opened your link yet. Although I'm sure it is an interesting read.

Going through everything though, it is interesting to see what may be effecting different aircraft.
Comparing Airbus and Boeing is, as you say, probably not a good comparison, apart from seeing just how much more effort Airbus put into passenger comfort.

I suppose if any 2 aircraft make my point of 4v2 obvious though, it has to be the A340 and A330.
I was amazed to see just how much larger the engines are on an A330-300 compared to an A340-300. About twice the thrust if what I have seen is correct. Which goes along with the fact the A340 is quite a bit quieter.

Moving onto another point mentioned, and which was argued upon.
The engines on the A330 must be massively overpowered for normal cruise.
Which, whilst I suspect the engines on the A330 are slightly more efficient at full power, I would suspect the A340s engines are running more efficiently during normal cruise operation.

Obviously engine efficiency is different to the amount of fuel an aircraft sips, but it would be interesting to see an SFOC graph for the 2 types of engine, as well as fuel consumption info for the 2 types of aircraft.

Overall an interesting topic with many points to consider.

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GalaxyFlyer
Posts: 7813
Joined: Fri Jan 01, 2016 4:44 am

Re: 2 vs 4 engines

Sat Dec 26, 2020 3:03 am

Actually, the twin is somewhat over-powered at cruise due to the take-off performance requirements of the OEI case. Perhaps, strangely, but it’s a benefit at cruise. At most optimum levels for the wing, the twin must operate at at lower percentage of maximum available thrust, this is around 85% N1 which is right around the low point of the TSFC curve. Also, known as the “thrust bucket”. Where a quad, in most cases, requires a higher thrust setting at cruise and farther up the TSFC curve.

Here’s a high level quote from a retired Boeing propulsion engineer,

If you look at a plot of TSFC for a typical turbofan engine (specific fuel consumption on the vertical scale, thrust on the horizontal) it looks rather like a stretched out 'U'. At very low power and very high power, the efficiency is fairly poor, but it's really good in the middle. This is 'OK' because you're still not burning much fuel at idle, and you don't spend more than a few minutes per flight at takeoff. The efficiency at idle is so poor that for some engine types, as you accelerate from minimum ground idle to flight or approach idle, the EGT actually drops. Now this 'U' curve moves around with altitude, airspeed, and total temp (it's mainly a function of inlet total pressure) but the basic shape remains.

Now this is a broad generalization, but because twins are overpowered relative to quads they tend to cruise closer to the bottom of that 'U' shaped TSFC curve while a quad tends to move more up the increasing TSFC slope due to the higher relative thrust demand.

As an extreme example, think of the case of a 747 with an engine out. Now, a 747-400 or -8 will happily cruise on 3 engines at 35k or above provided it's not really heavy. But the fuel consumption skyrockets relative to 4 engine cruise because now you're way up on the high power side of that U curve.





Again, thrust isn’t necessarily, noise, inside or out.
 
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Starlionblue
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Re: 2 vs 4 engines

Sat Dec 26, 2020 7:59 am

Junglejames wrote:
Starlionblue wrote:
GalaxyFlyer wrote:
Interior sound levels have little to do with engine location and much to do with sound insulation design and installation of things like air ducting, paneling, etc. New Globals get interior sound surveys done for the owner. There’s a noticeable difference between wood and soft fabric bulkheads, fabric or leather seating. The windows bulge a tiny bit under pressure load creating small, noisy burbles in the slipstream. The quietest cabin location is the aft section nearest the engine.


I completely agree. Airbus is well known for better cabin noise insulation in its widebodies, hence why the cabins are perceived as quieter. For example, the A350 seems to have a quieter cabin than the 787, even though the A350 is the noisier aircraft. (Yes, on the outside...)

The A380 engines are 78000lbf, which is comparable to the A350-900, at 84000lbf and the 787-10, at 76000lbf. Despite the fact that the engines are pretty close in thrust, the cabin noise level in the A380 is way lower than the other two, and the A350 has a quieter cabin than the 787 despite higher thrust. Since relative thrust levels in cruise are pretty close for all airliners, it would appear that, just as GalaxyFlyer says, engine thrust is not directly correlated to cabin noise.

I've ignored, for this exercise, the fact that the outer engines on the A380 probably also contribute a bit to cabin noise. :)

Junglejames wrote:
]I have no idea if we are talking about noise in the same location (perhaps you are flying on the outside of the aircraft). But when sitting inside the aircraft, the A380 is quieter than the 3 twins you mention.

Sent from my SM-G930F using Tapatalk


I linked to EASA documentation which made it perfectly clear that I was referring to outside noise.

Junglejames wrote:
When above 30,000 feet, travelling at over 500kts, I prefer to stay inside the aircraft (bit cold outside!)
So I never need to worry about outside noise.

Sent from my SM-G930F using Tapatalk


This is tech/ops. When we talk about aircraft noise without specifying, in general we mean the noise the aircraft makes. In this case, it is also a thread about engines, which mostly impact exterior noise.

You're talking about cabin noise, which is another thing, and I did not understand that initially. If you're not specific, the rest of us might not understand what you mean.
Easily misunderstood!
I haven't actually opened your link yet. Although I'm sure it is an interesting read.

Going through everything though, it is interesting to see what may be effecting different aircraft.
Comparing Airbus and Boeing is, as you say, probably not a good comparison, apart from seeing just how much more effort Airbus put into passenger comfort.

I suppose if any 2 aircraft make my point of 4v2 obvious though, it has to be the A340 and A330.
I was amazed to see just how much larger the engines are on an A330-300 compared to an A340-300. About twice the thrust if what I have seen is correct. Which goes along with the fact the A340 is quite a bit quieter.

Moving onto another point mentioned, and which was argued upon.
The engines on the A330 must be massively overpowered for normal cruise.
Which, whilst I suspect the engines on the A330 are slightly more efficient at full power, I would suspect the A340s engines are running more efficiently during normal cruise operation.

Obviously engine efficiency is different to the amount of fuel an aircraft sips, but it would be interesting to see an SFOC graph for the 2 types of engine, as well as fuel consumption info for the 2 types of aircraft.

Overall an interesting topic with many points to consider.

Sent from my SM-G930F using Tapatalk


Adding to what GalaxyFlyer posted, if you have lots of excess thrust, and are not wing limited, the optimum FL is higher than if you don't have excess thrust. So you might simply cruise higher than the A340 given the same conditions because there's more oomph left.

It's much more complicated than that of course. Different wings mean different things.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
Junglejames
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Re: 2 vs 4 engines

Sat Dec 26, 2020 11:18 am

GalaxyFlyer wrote:
Actually, the twin is somewhat over-powered at cruise due to the take-off performance requirements of the OEI case. Perhaps, strangely, but it’s a benefit at cruise. At most optimum levels for the wing, the twin must operate at at lower percentage of maximum available thrust, this is around 85% N1 which is right around the low point of the TSFC curve. Also, known as the “thrust bucket”. Where a quad, in most cases, requires a higher thrust setting at cruise and farther up the TSFC curve.

Here’s a high level quote from a retired Boeing propulsion engineer,

If you look at a plot of TSFC for a typical turbofan engine (specific fuel consumption on the vertical scale, thrust on the horizontal) it looks rather like a stretched out 'U'. At very low power and very high power, the efficiency is fairly poor, but it's really good in the middle. This is 'OK' because you're still not burning much fuel at idle, and you don't spend more than a few minutes per flight at takeoff. The efficiency at idle is so poor that for some engine types, as you accelerate from minimum ground idle to flight or approach idle, the EGT actually drops. Now this 'U' curve moves around with altitude, airspeed, and total temp (it's mainly a function of inlet total pressure) but the basic shape remains.

Now this is a broad generalization, but because twins are overpowered relative to quads they tend to cruise closer to the bottom of that 'U' shaped TSFC curve while a quad tends to move more up the increasing TSFC slope due to the higher relative thrust demand.

As an extreme example, think of the case of a 747 with an engine out. Now, a 747-400 or -8 will happily cruise on 3 engines at 35k or above provided it's not really heavy. But the fuel consumption skyrockets relative to 4 engine cruise because now you're way up on the high power side of that U curve.





Again, thrust isn’t necessarily, noise, inside or out.


Ah ha, gotcha. I think someone said N1 wasn't maximum thrust?

So by the sounds of it, the low point of the TSFC curve for a jet engine (or turbofan, whatever you call it, they are all jet engines to me!!!) is at a lower percentage of max power than say a diesel engine. Where it is usually around 80 to 85% of max power.
By the sounds of it the sides of the U are steeper on the jet engine as well.

It is interesting about the increased flight level as well. Reduces fuel consumption even more.

Bringing us to engine noise (Which may or may not be best heard outside). This then adds another dimension.
A larger engine operating at its sweet point should be quieter. Unless of course the engine is stupidly large (777-300?). In which case smaller engines usually win.


PS. Quads are still better in every way!!!!!!!

Sent from my SM-G930F using Tapatalk
 
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Starlionblue
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Re: 2 vs 4 engines

Sat Dec 26, 2020 1:10 pm

Junglejames wrote:
GalaxyFlyer wrote:
Actually, the twin is somewhat over-powered at cruise due to the take-off performance requirements of the OEI case. Perhaps, strangely, but it’s a benefit at cruise. At most optimum levels for the wing, the twin must operate at at lower percentage of maximum available thrust, this is around 85% N1 which is right around the low point of the TSFC curve. Also, known as the “thrust bucket”. Where a quad, in most cases, requires a higher thrust setting at cruise and farther up the TSFC curve.

Here’s a high level quote from a retired Boeing propulsion engineer,

If you look at a plot of TSFC for a typical turbofan engine (specific fuel consumption on the vertical scale, thrust on the horizontal) it looks rather like a stretched out 'U'. At very low power and very high power, the efficiency is fairly poor, but it's really good in the middle. This is 'OK' because you're still not burning much fuel at idle, and you don't spend more than a few minutes per flight at takeoff. The efficiency at idle is so poor that for some engine types, as you accelerate from minimum ground idle to flight or approach idle, the EGT actually drops. Now this 'U' curve moves around with altitude, airspeed, and total temp (it's mainly a function of inlet total pressure) but the basic shape remains.

Now this is a broad generalization, but because twins are overpowered relative to quads they tend to cruise closer to the bottom of that 'U' shaped TSFC curve while a quad tends to move more up the increasing TSFC slope due to the higher relative thrust demand.

As an extreme example, think of the case of a 747 with an engine out. Now, a 747-400 or -8 will happily cruise on 3 engines at 35k or above provided it's not really heavy. But the fuel consumption skyrockets relative to 4 engine cruise because now you're way up on the high power side of that U curve.





Again, thrust isn’t necessarily, noise, inside or out.


Ah ha, gotcha. I think someone said N1 wasn't maximum thrust?

So by the sounds of it, the low point of the TSFC curve for a jet engine (or turbofan, whatever you call it, they are all jet engines to me!!!) is at a lower percentage of max power than say a diesel engine. Where it is usually around 80 to 85% of max power.
By the sounds of it the sides of the U are steeper on the jet engine as well.

It is interesting about the increased flight level as well. Reduces fuel consumption even more.

Bringing us to engine noise (Which may or may not be best heard outside). This then adds another dimension.
A larger engine operating at its sweet point should be quieter. Unless of course the engine is stupidly large (777-300?). In which case smaller engines usually win.


PS. Quads are still better in every way!!!!!!!

Sent from my SM-G930F using Tapatalk


N1 is the rotation speed of the low-pressure spool as a percentage of its nominal maximum. Higher N1 gives higher thrust, but it is not a linear relationship as I mentioned earlier.

Quads are not better in every way. So many more bits that need maintenance and can break. But they have their moments. :)
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
Junglejames
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Re: 2 vs 4 engines

Sat Dec 26, 2020 1:37 pm

Starlionblue wrote:
Junglejames wrote:
GalaxyFlyer wrote:
Actually, the twin is somewhat over-powered at cruise due to the take-off performance requirements of the OEI case. Perhaps, strangely, but it’s a benefit at cruise. At most optimum levels for the wing, the twin must operate at at lower percentage of maximum available thrust, this is around 85% N1 which is right around the low point of the TSFC curve. Also, known as the “thrust bucket”. Where a quad, in most cases, requires a higher thrust setting at cruise and farther up the TSFC curve.

Here’s a high level quote from a retired Boeing propulsion engineer,

If you look at a plot of TSFC for a typical turbofan engine (specific fuel consumption on the vertical scale, thrust on the horizontal) it looks rather like a stretched out 'U'. At very low power and very high power, the efficiency is fairly poor, but it's really good in the middle. This is 'OK' because you're still not burning much fuel at idle, and you don't spend more than a few minutes per flight at takeoff. The efficiency at idle is so poor that for some engine types, as you accelerate from minimum ground idle to flight or approach idle, the EGT actually drops. Now this 'U' curve moves around with altitude, airspeed, and total temp (it's mainly a function of inlet total pressure) but the basic shape remains.

Now this is a broad generalization, but because twins are overpowered relative to quads they tend to cruise closer to the bottom of that 'U' shaped TSFC curve while a quad tends to move more up the increasing TSFC slope due to the higher relative thrust demand.

As an extreme example, think of the case of a 747 with an engine out. Now, a 747-400 or -8 will happily cruise on 3 engines at 35k or above provided it's not really heavy. But the fuel consumption skyrockets relative to 4 engine cruise because now you're way up on the high power side of that U curve.





Again, thrust isn’t necessarily, noise, inside or out.


Ah ha, gotcha. I think someone said N1 wasn't maximum thrust?

So by the sounds of it, the low point of the TSFC curve for a jet engine (or turbofan, whatever you call it, they are all jet engines to me!!!) is at a lower percentage of max power than say a diesel engine. Where it is usually around 80 to 85% of max power.
By the sounds of it the sides of the U are steeper on the jet engine as well.

It is interesting about the increased flight level as well. Reduces fuel consumption even more.

Bringing us to engine noise (Which may or may not be best heard outside). This then adds another dimension.
A larger engine operating at its sweet point should be quieter. Unless of course the engine is stupidly large (777-300?). In which case smaller engines usually win.


PS. Quads are still better in every way!!!!!!!

Sent from my SM-G930F using Tapatalk


N1 is the rotation speed of the low-pressure spool as a percentage of its nominal maximum. Higher N1 gives higher thrust, but it is not a linear relationship as I mentioned earlier.

Quads are not better in every way. So many more bits that need maintenance and can break. But they have their moments. :)


I think I get what you are saying!!

Marvellous. More things to break, more work, more employment. Playing into my hands here!!!

Planes always look better with 4 engines.
Especially when you get to 777x size. The engines are so large the planes look stupid.
It's also a better view from the inside, looking out over the wing.

Of course, I have more chance of an engine letting go and a blade flying through the fuselage and chopping my head off, but some would say that could be counted as another benefit of quads!!!!!


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Starlionblue
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Re: 2 vs 4 engines

Sat Dec 26, 2020 2:28 pm

Junglejames wrote:
Starlionblue wrote:
Junglejames wrote:

Ah ha, gotcha. I think someone said N1 wasn't maximum thrust?

So by the sounds of it, the low point of the TSFC curve for a jet engine (or turbofan, whatever you call it, they are all jet engines to me!!!) is at a lower percentage of max power than say a diesel engine. Where it is usually around 80 to 85% of max power.
By the sounds of it the sides of the U are steeper on the jet engine as well.

It is interesting about the increased flight level as well. Reduces fuel consumption even more.

Bringing us to engine noise (Which may or may not be best heard outside). This then adds another dimension.
A larger engine operating at its sweet point should be quieter. Unless of course the engine is stupidly large (777-300?). In which case smaller engines usually win.


PS. Quads are still better in every way!!!!!!!

Sent from my SM-G930F using Tapatalk


N1 is the rotation speed of the low-pressure spool as a percentage of its nominal maximum. Higher N1 gives higher thrust, but it is not a linear relationship as I mentioned earlier.

Quads are not better in every way. So many more bits that need maintenance and can break. But they have their moments. :)


I think I get what you are saying!!

Marvellous. More things to break, more work, more employment. Playing into my hands here!!!

Planes always look better with 4 engines.
Especially when you get to 777x size. The engines are so large the planes look stupid.
It's also a better view from the inside, looking out over the wing.

Of course, I have more chance of an engine letting go and a blade flying through the fuselage and chopping my head off, but some would say that could be counted as another benefit of quads!!!!!


Sent from my SM-G930F using Tapatalk


Now we are getting into subjective stuff. And if we're going to do that, I find the A350-1000 absolutely stunning. And the cockpit is very space age, too. :mrgreen: :stirthepot:
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
Junglejames
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Re: 2 vs 4 engines

Sat Dec 26, 2020 2:44 pm

Starlionblue wrote:
Junglejames wrote:
Starlionblue wrote:

N1 is the rotation speed of the low-pressure spool as a percentage of its nominal maximum. Higher N1 gives higher thrust, but it is not a linear relationship as I mentioned earlier.

Quads are not better in every way. So many more bits that need maintenance and can break. But they have their moments. :)


I think I get what you are saying!!

Marvellous. More things to break, more work, more employment. Playing into my hands here!!!

Planes always look better with 4 engines.
Especially when you get to 777x size. The engines are so large the planes look stupid.
It's also a better view from the inside, looking out over the wing.

Of course, I have more chance of an engine letting go and a blade flying through the fuselage and chopping my head off, but some would say that could be counted as another benefit of quads!!!!!


Sent from my SM-G930F using Tapatalk


Now we are getting into subjective stuff. And if we're going to do that, I find the A350-1000 absolutely stunning. And the cockpit is very space age, too. :mrgreen: :stirthepot:
The A350 is a good looking jet.
Let's say 5th in the all time list behind
A380
A340 (preferably the 600)
A330
B747

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GalaxyFlyer
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Re: 2 vs 4 engines

Sat Dec 26, 2020 3:38 pm

I’ve shutdown precisely ZERO engines on single, twin and tri jets; about a dozen on the one quad I flew, mostly for ancillary problems—engine was fine but indicating problem. Low oil once, a blade failure once, several thrust reverser false indications, couple of fluid leaks, a bleed leak.
 
Strato2
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Re: 2 vs 4 engines

Sun Dec 27, 2020 2:58 pm

MIflyer12 wrote:
lhrnue wrote:
Looks like the industry has answered this question.


More than 20 years ago, really:

777ER vs. A342/343


When the A340 was designed there was no big enough engine to make it a twin. Also it did quite well against the 772 actually and if it had got the superfan the sales numbers could have been the opposite way.

Add, perhaps finally for this generation, 77W vs. A380


The A380 could not have been a twin as it would have needed a powerplant putting out 200000 lbs of thrust.
 
WayexTDI
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Re: 2 vs 4 engines

Mon Dec 28, 2020 6:41 pm

Strato2 wrote:
MIflyer12 wrote:
lhrnue wrote:
Looks like the industry has answered this question.


More than 20 years ago, really:

777ER vs. A342/343


When the A340 was designed there was no big enough engine to make it a twin. Also it did quite well against the 772 actually and if it had got the superfan the sales numbers could have been the opposite way.

The A330 would like to have a word with you...
Maybe you're missing some premises to your assertion (such as, enough fuel/weight for longer range and the such); but there definitely was an engine big enough to make the A340 a twin since the A330 was developed in parallel to the A340 and used most of everything from the A340 (minus the center main landing gear).
 
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Starlionblue
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Re: 2 vs 4 engines

Tue Dec 29, 2020 12:21 am

WayexTDI wrote:
Strato2 wrote:
MIflyer12 wrote:

More than 20 years ago, really:

777ER vs. A342/343


When the A340 was designed there was no big enough engine to make it a twin. Also it did quite well against the 772 actually and if it had got the superfan the sales numbers could have been the opposite way.

The A330 would like to have a word with you...
Maybe you're missing some premises to your assertion (such as, enough fuel/weight for longer range and the such); but there definitely was an engine big enough to make the A340 a twin since the A330 was developed in parallel to the A340 and used most of everything from the A340 (minus the center main landing gear).


Of course the A330 is a twin and thus the A340 had a twin "version". But the twin version could not have performed the A340 mission. The A330 had a 40-ish tonne lower MTOW compared to the A340, with consequently much shorter range.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
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zeke
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Re: 2 vs 4 engines

Tue Dec 29, 2020 7:08 am

There is a lot of misconceptions on this thread regarding the A330/A340, the bulletin below from Airbus may help educate users on how the A340 was very effective in its design mission. However the A340 design mission did not suit many operators, most operators had requirements for shorter stage lengths which the A340 was not optimal for. In this area the A330 excelled.

1 Image
2 Image
3 Image
4 Image
5 Image
6 Image
7 Image
8 Image
9 Image
“Don't be a show-off. Never be too proud to turn back. There are old pilots and bold pilots, but no old, bold pilots.” E. Hamilton Lee, 1949
 
LH707330
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Re: 2 vs 4 engines

Tue Dec 29, 2020 5:36 pm

zeke wrote:
There is a lot of misconceptions on this thread regarding the A330/A340, the bulletin below from Airbus may help educate users on how the A340 was very effective in its design mission. However the A340 design mission did not suit many operators, most operators had requirements for shorter stage lengths which the A340 was not optimal for. In this area the A330 excelled.

Thanks for posting this, the comparisons are good to see. One claim I'm having a hard time with, however, is that fuel burn per seat for the 343 vs a 744 is 14% better. From your experience on the 343, does that number for the burn on 4000 nm make sense?

I'm curious to know if they juiced the pax numbers or made other assumptions, or if that's a typo, because I'd have a hard time believing that Boeing would have sold as many 744s in the late 90s if that was right.
 
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dennypayne
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Re: 2 vs 4 engines

Tue Dec 29, 2020 6:04 pm

LH707330 wrote:
One claim I'm having a hard time with, however, is that fuel burn per seat for the 343 vs a 744 is 14% better. From your experience on the 343, does that number for the burn on 4000 nm make sense?

I'm curious to know if they juiced the pax numbers or made other assumptions, or if that's a typo, because I'd have a hard time believing that Boeing would have sold as many 744s in the late 90s if that was right.


What if your airline needs to fly 400 passengers a day on a route? You'd have to buy two 343's to service that route versus one 744. You can't just look at one stat in a vacuum.
A300/310/319/320/321/332/333/343/380 AN24/28/38/148 ARJ AT6/7 B190
B717/722/732/3/4/5/7/8/9 741/744/752/753/762/763/764/772/773/788/789
CR1/2/7/9 D8S D93/4/5 DHC2/3/7/8 D28/38 EMB/EM2/ER3/D/4/E70/75/90
F50/100 J31 L10 L4T M11/80/87/90 SF3 SU9 TU3/TU5 YK2
 
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zeke
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Re: 2 vs 4 engines

Tue Dec 29, 2020 6:35 pm

LH707330 wrote:
Thanks for posting this, the comparisons are good to see. One claim I'm having a hard time with, however, is that fuel burn per seat for the 343 vs a 744 is 14% better. From your experience on the 343, does that number for the burn on 4000 nm make sense?


It was in the order of 4-5 tonnes per hour different, so 14% would not be unreasonable depending as you mentioned how it was configured.


dennypayne wrote:

What if your airline needs to fly 400 passengers a day on a route? You'd have to buy two 343's to service that route versus one 744. You can't just look at one stat in a vacuum.


No hard and fast answer to that, do all 400 people want to travel at the same time of day ? Sometimes frequency can be better, sometimes more seats at once and better connections is the answer.
“Don't be a show-off. Never be too proud to turn back. There are old pilots and bold pilots, but no old, bold pilots.” E. Hamilton Lee, 1949
 
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dennypayne
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Re: 2 vs 4 engines

Tue Dec 29, 2020 9:19 pm

zeke wrote:
No hard and fast answer to that, do all 400 people want to travel at the same time of day ? Sometimes frequency can be better, sometimes more seats at once and better connections is the answer.


Precisely my point. So many people on this forum seem to want to proclaim a particular aircraft as "better" because of one statistic (or doubting that statistic) without taking all the other potential variables into consideration.
A300/310/319/320/321/332/333/343/380 AN24/28/38/148 ARJ AT6/7 B190
B717/722/732/3/4/5/7/8/9 741/744/752/753/762/763/764/772/773/788/789
CR1/2/7/9 D8S D93/4/5 DHC2/3/7/8 D28/38 EMB/EM2/ER3/D/4/E70/75/90
F50/100 J31 L10 L4T M11/80/87/90 SF3 SU9 TU3/TU5 YK2
 
WayexTDI
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Re: 2 vs 4 engines

Wed Dec 30, 2020 1:54 pm

dennypayne wrote:
zeke wrote:
No hard and fast answer to that, do all 400 people want to travel at the same time of day ? Sometimes frequency can be better, sometimes more seats at once and better connections is the answer.


Precisely my point. So many people on this forum seem to want to proclaim a particular aircraft as "better" because of one statistic (or doubting that statistic) without taking all the other potential variables into consideration.

The "success" of the A380 just proves that.
 
LH707330
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Re: 2 vs 4 engines

Sat Jan 02, 2021 9:44 pm

zeke wrote:
LH707330 wrote:
Thanks for posting this, the comparisons are good to see. One claim I'm having a hard time with, however, is that fuel burn per seat for the 343 vs a 744 is 14% better. From your experience on the 343, does that number for the burn on 4000 nm make sense?


It was in the order of 4-5 tonnes per hour different, so 14% would not be unreasonable depending as you mentioned how it was configured.


One thing I noticed on the passenger breakouts there is that the assumed pax counts for the 744 are off, 22+66+304=392, not 402. The ratios as a function of the total are pretty fair though, both roughly 6%, 17%, and 77% of the total for F/C/Y. Would 6.5t/h for the 343 and 10.2t/h on the 744 sound like reasonable fuel burn numbers over 4,000 nm? Using those burns and 295 and 392 as pax counts would give the 343 an 18% advantage, which seems too high. viewtopic.php?t=1355819

dennypayne wrote:
LH707330 wrote:
One claim I'm having a hard time with, however, is that fuel burn per seat for the 343 vs a 744 is 14% better. From your experience on the 343, does that number for the burn on 4000 nm make sense?

I'm curious to know if they juiced the pax numbers or made other assumptions, or if that's a typo, because I'd have a hard time believing that Boeing would have sold as many 744s in the late 90s if that was right.


What if your airline needs to fly 400 passengers a day on a route? You'd have to buy two 343's to service that route versus one 744. You can't just look at one stat in a vacuum.


I could also scoop up the higher-margin 300 pax and leave the lowest-paying 100 passengers behind. In general, larger planes don't sell unless they have significantly better seat-mile costs to cover the fact that the marginal passengers tend to be lower paying. This is why the A380 didn't sell well: although it had the best CASM, it wasn't better enough to make it worthwhile.

If the 343 is really that much more efficient than the 744 with 100 fewer passengers, then no 744 should have been sold after 1996ish when the 276t 343 came out. Something doesn't add up in that Airbus brochure....
 
Armadillo1
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Re: 2 vs 4 engines

Sat Jan 02, 2021 10:02 pm

fuel price played different role in those times.
 
VierBe
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Re: 2 vs 4 engines

Mon Jan 04, 2021 7:15 am

Hello all,

I have been reading here a lot, and i am very thankful for all the great information here.
And for me it is clear, that comparing the last four holer that is really on pair with a two holer fuelwise ,sizewise and mission profile like (A343 vs. B772) there are doubletimes engines that needs overhaul and maintenance.
Also i am aware that the projected engines for the A340 the Superfans didnt happen and that bigger engines have efficency gaines because of the size, which is why the 4 holers are dying (And because of ETOPS of couse).

But now there comes my but, which i dont understand.
Now there are extreme efficient engines available that have the Thrust the PW1133G. If i put that thing under a A343 and Project a fuel efficiency gain of a mild 15% on a TATL Run of 4000nm, this leaves me with (comparing with the ICAO document page 16 of this post viewtopic.php?f=5&t=1355819).

Fuel Consumption KG

A330-300: 54788
A340-300: 58678
B777-200ER: 62861
B787-8: 45093
A340-300NEO: 49876 (58678x0,85)

There are no numbers but i think that aircarft would be on pair with the A330Neo if not slightly better.
You may argue, there are still two engines more that need the maintenance. But then you have A320neos in the fleet and the A220 which do all have the PWs, You only have one engine family in your whole fleet and i think there kicks the economy of scale in . You could run a huge Overhaul facility and not 5 smaller ones and suddendly the issues with the more engines vanish. You dont need 5000 different technicans that are looking at the different engines types and so on. So why did Airbus do the A330Neo instead of the A343Neo? Because two engines are in or what? Nobody in the managment had the guts? No Airline had the thought of this? Is the A330Neo Wing still the same as the normal A330, i Mean is it reinforced to hold the other two engines (They are not heavier than the CFM hairdryes)?

Imaging a Fleet of A220-300s, A321Neo (Normal and XLR) and the A343Neo that has the Legs and capacity if need. You could do everything with these 3 Types and one Engine.

Any thoughts, did i miss something?
 
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Starlionblue
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Re: 2 vs 4 engines

Mon Jan 04, 2021 7:35 am

VierBe wrote:
Hello all,

I have been reading here a lot, and i am very thankful for all the great information here.
And for me it is clear, that comparing the last four holer that is really on pair with a two holer fuelwise ,sizewise and mission profile like (A343 vs. B772) there are doubletimes engines that needs overhaul and maintenance.
Also i am aware that the projected engines for the A340 the Superfans didnt happen and that bigger engines have efficency gaines because of the size, which is why the 4 holers are dying (And because of ETOPS of couse).

But now there comes my but, which i dont understand.
Now there are extreme efficient engines available that have the Thrust the PW1133G. If i put that thing under a A343 and Project a fuel efficiency gain of a mild 15% on a TATL Run of 4000nm, this leaves me with (comparing with the ICAO document page 16 of this post viewtopic.php?f=5&t=1355819).

Fuel Consumption KG

A330-300: 54788
A340-300: 58678
B777-200ER: 62861
B787-8: 45093
A340-300NEO: 49876 (58678x0,85)

There are no numbers but i think that aircarft would be on pair with the A330Neo if not slightly better.
You may argue, there are still two engines more that need the maintenance. But then you have A320neos in the fleet and the A220 which do all have the PWs, You only have one engine family in your whole fleet and i think there kicks the economy of scale in . You could run a huge Overhaul facility and not 5 smaller ones and suddendly the issues with the more engines vanish. You dont need 5000 different technicans that are looking at the different engines types and so on. So why did Airbus do the A330Neo instead of the A343Neo? Because two engines are in or what? Nobody in the managment had the guts? No Airline had the thought of this? Is the A330Neo Wing still the same as the normal A330, i Mean is it reinforced to hold the other two engines (They are not heavier than the CFM hairdryes)?

Imaging a Fleet of A220-300s, A321Neo (Normal and XLR) and the A343Neo that has the Legs and capacity if need. You could do everything with these 3 Types and one Engine.

Any thoughts, did i miss something?


Even if your A220s, the A32xs and the A343NEOs have engines from the same manufacturer, that doesn't necessarily make them so alike you get massive economies of scale. Your staff still needs to be trained on all the types, have parts available for different engines, and so on.

Either way, the cost of engine maintenance is way more complex than that. For example, from RR you can get "power by the hour". Simply pay x per unit of time. As an airline, you're then not concerned with the cost of maintenance.



Why did Airbus do the A330NEO instead of the A340NEO?

Airbus already makes an "A340NEO". It's called the A350. It can perform all the A340 missions at a lower cost, and it flies faster.

The A330NEO is not an A340 replacement, and an actual A340NEO would not be nearly as good as an A350.

Is the A330Neo Wing still the same as the normal A330, i Mean is it reinforced to hold the other two engines (They are not heavier than the CFM hairdryes)?

The weight of the engines is trivial compared to the lift produced in the other direction. Heavier engines could well mean a lighter wing. The engines pull the wing down in flight, mitigating the bending force of lift production. Four engines even have an advantage over two when it comes to wing structure, as the downward force is more evenly distributed and further outboard on average.



So why did Airbus do the A330Neo instead of the A343Neo? Because two engines are in or what?

Because two engines make better economic sense for all aircraft until you reach A380 size.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
VierBe
Posts: 7
Joined: Wed Dec 23, 2020 3:19 pm

Re: 2 vs 4 engines

Mon Jan 04, 2021 8:39 am

Thanks for the fast answer,

I didnt know there where Engine Maintenance Flatrates, thanks for the info.

I am not arguing about the a350, that bird is aerodynamically in another league and it hauls more freight. But the PW Powerplants are in another league enginewise. Here the argument 4 engines do only make sense from a380 size onward would only work if the two engines would have a geared fan. When will a 350kN Geared Turbofan exist?

You would at least have the A321 and the A340 with the exact same engines. You can reduce spares because the fleets would help each other. Instead having two Narrowbody engines and a widebody Engine as spare, you would only need two common, etc... Would make it more simple and more productive.

I wouldnt say, that an a350 could make a mission at lower cost. You could possible earn more with a flight, but comparing the seatmaps of the a343 at Lufthansa with the A359, you have (30b/28e+/221e vs 48b/21e+/224e), and you could do a 3-3-3 if you had to on the a340 (Ouch i know, just saying) so if you cant fill Business and dont have a full freight belly i think espacially for a smaller carrier an a343neo would be the better option. And i also think that the captial costs, which are not a small portion having brand new planes to finance or lease.

Still think that would be a tremendous fleet concept and plane.
 
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Starlionblue
Posts: 20698
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Re: 2 vs 4 engines

Mon Jan 04, 2021 9:42 am

VierBe wrote:
Thanks for the fast answer,

I didnt know there where Engine Maintenance Flatrates, thanks for the info.

I am not arguing about the a350, that bird is aerodynamically in another league and it hauls more freight. But the PW Powerplants are in another league enginewise. Here the argument 4 engines do only make sense from a380 size onward would only work if the two engines would have a geared fan. When will a 350kN Geared Turbofan exist?

You would at least have the A321 and the A340 with the exact same engines. You can reduce spares because the fleets would help each other. Instead having two Narrowbody engines and a widebody Engine as spare, you would only need two common, etc... Would make it more simple and more productive.

I wouldnt say, that an a350 could make a mission at lower cost. You could possible earn more with a flight, but comparing the seatmaps of the a343 at Lufthansa with the A359, you have (30b/28e+/221e vs 48b/21e+/224e), and you could do a 3-3-3 if you had to on the a340 (Ouch i know, just saying) so if you cant fill Business and dont have a full freight belly i think espacially for a smaller carrier an a343neo would be the better option. And i also think that the captial costs, which are not a small portion having brand new planes to finance or lease.

Still think that would be a tremendous fleet concept and plane.


The market seems to disagree. Quads have been slowly dying since the early 90s.

If you can't fill business and don't have a full freight belly you might not want to go in the first place. Those are the bits with the good margins.

Having an A321 and an A340 with the same engine would indeed save some money. But you'd still need two extra engines on each widebody. At a guess, all your savings would evaporate, and more, right there.

It isn't just the engines. Lots of systems become more complex with more engines. Case in point: the fuel system in the A380. The A350 systems are also a marvel of simplicity compared to A330/A340.

It may be true that a 350kN geared fan would be more efficient than a 350kN three spool turbofan. However, such an engine does not exist today. As things stand, 2x turbofans seem to beat 4x less powerful geared fans on the same frame.

If you really wanted to make an A340NEO, I think you'd be better off plonking more powerful engines and more tankage on the A330NEO, and making the required structural modifications. But again, then you might as well sell the customer an A350 instead of going through a whole development program.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
VierBe
Posts: 7
Joined: Wed Dec 23, 2020 3:19 pm

Re: 2 vs 4 engines

Mon Jan 04, 2021 10:06 am

Starlionblue wrote:
The market seems to disagree. Quads have been slowly dying since the early 90s.


Yes, and i do understand, 2 engines with comparable technology level will always prevail against 4 (Thanks to all the things lightsaber explained). But as long as the smaller is far more advanced + you can use it on more aircraft this is not an argument.

Starlionblue wrote:
If you can't fill business and don't have a full freight belly you might not want to go in the first place. Those are the bits with the good margins.


Exactly, thats why the planes are getting smaller, because you can fill them up more easily and the trip cost are lower, so if you cant fill them the loss is not hurting so much :) (A321XLR)
Thats more a pro for the a340 which is the smaller plane.

Starlionblue wrote:
Having an A321 and an A340 with the same engine would indeed save some money. But you'd still need two extra engines on each widebody. At a guess, all your savings would evaporate, and more, right there.


But the Engines can be bought a lot cheaper, because of the number you buy them, and also you only have to service one typ, which make it easier and thus cheaper, too.

Starlionblue wrote:
It isn't just the engines. Lots of systems become more complex with more engines. Case in point: the fuel system in the A380. The A350 systems are also a marvel of simplicity compared to A330/A340.


A330Neo is still a lot cheaper than a A350 and the systems exist. I dont know if the system of the A340 is more complex compared to the A330. If so, just use the one of the A330, as the A340Neo would need to carry a lot less fuel to have the Range of an A340ceo.

Starlionblue wrote:
It may be true that a 350kN geared fan would be more efficient than a 350kN three spool turbofan. However, such an engine does not exist today. As things stand, 2x turbofans seem to beat 4x less powerful geared fans on the same frame.


I would love to have numbers for that. From what i see here in the Forum an A343 burns a little less than a B772ER. The only problem is, that it doesnt have engines that can be used on the A321ceo :)


Starlionblue wrote:
If you really wanted to make an A340NEO, I think you'd be better off plonking more powerful engines and more tankage on the A330NEO, and making the required structural modifications. But again, then you might as well sell the customer an A350 instead of going through a whole development program.


I dont think a A330Neo would be as efficient as an PW powered A343Neo. I just dont think so. But i guess we will never know. :) And i think that is a fault by Airbus. Maybe they thought the PW Engines wouldnt be that good 10 years ago, or that Geared Turbofans in that Thrust class would come earlier.

Edit for Typos
 
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Starlionblue
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Re: 2 vs 4 engines

Mon Jan 04, 2021 10:53 am

I think you're vastly overestimating the savings from having only one engine type in the fleet. Most airlines don't even service their own engines. They buy engine servicing from an outside contractor, or from a company in the same group. The pricing there is typically tied to usage, and will not significantly if you need two engine types serviced or one. It will definitely vary by number of engines in total.

The outside provider will typically be large enough to handle multiple engine types, plus often do other stuff, and derive economies of scale from their size. These needed economies of scale are why most airlines don't service their own engines. They pay Lufthansa Technik or the like to do it.


I think we do know which is more efficient between an A330NEO and a PW powered A343NEO. If a A343NEO was a significantly more efficient proposition, it would have been in production.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
VierBe
Posts: 7
Joined: Wed Dec 23, 2020 3:19 pm

Re: 2 vs 4 engines

Mon Jan 04, 2021 11:41 am

So,

If i compare the A339 with the PW powered A343. I found out two things that favor the A340 Platform.

The PW1133G dry weight is 2857.6kg. In the Type certificate this is the weight for all variants of the family, which tells me, its the exact same Engine only derated, which allows even more communality with the A32xNeos.

I am working in the automotive industry and commonality is the key to win actual. I did some research and found out (Had too much tabs open and lost the overview), But IIRC there are about 200 facilities to service the CFM56, but only 10 for the GE90. A lot more competition that lower the price for maintenance.

Also these are list prices, i know, but still point into a direction. A PW1100G has a list Price of 10m$ whereas the RR Trent 7000 is 38m$. I know there a lot of different pricing models and discounts etc., but still.

Also found this one:

http://www.aircraftmonitor.com/uploads/ ... ers_v1.pdf
From Page 147 there are maintenance price comparisons between the most Narrowbody and Widebody Engines. Looking at this 4x smaller engines are not more expensive.

Also the Time on Wing of the PWG1100G should be higher than that the Trent 7000.


This can only mean Airbus did something wrong, or the airlines didnt ask for it,
Or the A330 NEO is far better then thought and is a real gem that will start to sell after Corona more and preasure the B787.
 
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Starlionblue
Posts: 20698
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Re: 2 vs 4 engines

Mon Jan 04, 2021 1:05 pm

VierBe wrote:
This can only mean Airbus did something wrong, or the airlines didnt ask for it,
Or the A330 NEO is far better then thought and is a real gem that will start to sell after Corona more and preasure the B787.


I'm not saying Airbus is infallible, but I don't think Airbus did something wrong in their market analysis in this case. If they had, wouldn't Boeing also be looking at a new quad instead of building the largest twin in history?

What do you know, beyond assumptions about cost that you've made from searching incomplete publicly available documentation, that Airbus and the airlines don't?

The A330NEO doesn't need to sell amazingly well. It is a development of an airliner programme that repaid the initial investment decades ago. It only needs to recoup the relatively low costs of the development itself.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
VierBe
Posts: 7
Joined: Wed Dec 23, 2020 3:19 pm

Re: 2 vs 4 engines

Mon Jan 04, 2021 1:46 pm

Starlionblue wrote:

I'm not saying Airbus is infallible, but I don't think Airbus did something wrong in their market analysis in this case. If they had, wouldn't Boeing also be looking at a new quad instead of building the largest twin in history?itself.


Because there is no geared Engine in that size available, not even 4x geared ones that are on the market.

Starlionblue wrote:
What do you know, beyond assumptions about cost that you've made from searching incomplete publicly available documentation, that Airbus and the airlines don't?


I really dont know, would love to know. In a very short analysis it just makes perfect sense. The engineering cost would be very very small even smaller compared to the a330neo! You could have saved the whole enginerring for the Trent 7000 and have communality with a whole different jet family and i cant think that the Trent would be better than the PWs, because the geared Fan is just that superior and the rest of the Engine is pretty low tech and easy to maintenance IIRC. You could also save costs that are coming with ETOPS certification and running costs for that subfleet, allowing smaller airlines and charters to have easier access to longhaul operations.
Maybe it was about availability for the Pratts. Or the assumption that quads are outdated and old from a marketing perspective. Technically i dont think the geard Turbofans can be beaten.

Starlionblue wrote:
The A330NEO doesn't need to sell amazingly well. It is a development of an airliner programme that repaid the initial investment decades ago. It only needs to recoup the relatively low costs of the development itself.


A340NEO even less

But if the A330Neo is even better, then i dont get what Boeing did with the 787. Of course it has a little more range, but come on. The A339 design is 20 Years older with same tech engines and can have another life holding beverages.
 
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zeke
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Re: 2 vs 4 engines

Mon Jan 04, 2021 2:30 pm

VierBe wrote:
Any thoughts, did i miss something?


It goes back to the initial sizing of the aircraft and what they call matching charts. The wing on the A340 is essentially too heavy as it was designed to carry the load of the higher fuel mass fraction the aircraft needed with the CFM56. To put the newer narrow body engines onto the A340 and to give it justice they would need to do what Boeing had to do with the 777 and put a new wing on it. The cost/benefit of such a large investment are not there as it just doesn’t add anything that Airbus does not already provide.

If Airbus were to put any more money into the A330/340 I would wager it would to make the fuselage longer as a medium haul package freighter.
“Don't be a show-off. Never be too proud to turn back. There are old pilots and bold pilots, but no old, bold pilots.” E. Hamilton Lee, 1949
 
VierBe
Posts: 7
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Re: 2 vs 4 engines

Mon Jan 04, 2021 6:16 pm

Hi, thank you for your answer.

From the lot a330 vs a340 wings threads this one is the best in my opinion.

viewtopic.php?t=766009#p11056683

Somewhere else I read that a slat is different and some smaller tweaks but essentially it's the same wing that was also supposed to hold the Superfan, which is basically the PW1133g. Sorry I don't see, why there needes to be a new wing.

Needs to be something else. Oh guys, that would be a superb looking airliner. :)
 
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zeke
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Re: 2 vs 4 engines

Tue Jan 05, 2021 5:29 am

VierBe wrote:
Somewhere else I read that a slat is different and some smaller tweaks but essentially it's the same wing that was also supposed to hold the Superfan, which is basically the PW1133g. Sorry I don't see, why there needes to be a new wing.

Needs to be something else. Oh guys, that would be a superb looking airliner. :)


That is correct, the wings are essentially the same, the deflections on flaps etc are slightly different between the the A330/340.

As for the wing itself, it was sized around the CFM56 engines, so it is designed not only to be able to takeoff with the fuel onboard for 12-14 hours, that increases the TOW, which the wing needs to be strong enough to hold, also the weight of those engines.

Countering the wing lift if the weight of the fuel and the weight of the engines. Changing to the new A320 engine would reduce fuel burn back closer to around 1-1.5 tonne per engine per hour, that means the fuel mass that is in the wing will be a lot lower as well as the reduced weight of the engine. The wing then would be significantly oversized resulting in the empty weight being much higher than it needs to be. It would still not be as capable as the A350-900 in range or payload.
“Don't be a show-off. Never be too proud to turn back. There are old pilots and bold pilots, but no old, bold pilots.” E. Hamilton Lee, 1949
 
VierBe
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Joined: Wed Dec 23, 2020 3:19 pm

Re: 2 vs 4 engines

Tue Jan 05, 2021 6:17 am

Thank you Zeke,

Of course to have a perfect fit, the wings needed to be made smaller, because the tank volume isnt needed. And its clear, that that would be a too high investment. Still that would also apply for the A330Neo. If you need the legs, just buy the A350. But it would still be a very efficient airliner. But i wont let the engine weight count as a no go , as the CFM56-5C weights 2572kg and the PW1133G is at 2857.6kg.

Of the thump with the known tankage if you say you have a mild 15% Efficency gain, the a 340Neo would have 20% more range, we have a 9000nm plane (Which noone really needs, but still), that is also very competitive on shorter hops. So why make the A330Neo instead the A340Neo, still no real answer.

This all makes me think, Airbus put a smaller wing under the A330/A340 invest the 6-8 Billion and have a real TATL and intra-Asia Workhorse designed for 4500-5000nm. The A330Neo is to close rangewise to the A350. That would close the Gap that there is betweeen A321XLR with 4200nm and A330-900 with 7200nm.

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