Wing sweep on the Boeing 747 is 37.5 degrees at quarter chord. This allows it a higher Mach cruise speed. I am curious why Airbus didn't adopt such a highly swept wing for its A-380 and other long range aircraft? [Apparently the A380 has a double swept wing.]

For that matter, why didn't Boeing adopt it for the 777 and other long range aircraft. Are highly swept wings a thing of the past?

Wing sweep is used to delay the transonic shockwave. Essentially it allows you to fly at higher speeds than otherwise by decreasing wave drag. Higher Mach cruise speed as you say.

However, for a given speed, a swept wing has less lift than an unswept one. It also requires a more beefy structure, and has nastier stall characteristics.

Enter supercritical wing profiles in the 70s and 80s. These also delay the transonic shockwave, but with fewer negative consequences. Hence high mach numbers can be achieved without as sharp a wing sweep as back in the day.

Modern CFD allows designs with less sweep to perform well at Mach numbers below .85-ish. The new G7500 has 35 degrees of sweep at cruises at M.88. The Citation X has 37.5 degrees, again very high Mach design.

Is the Boeing 747 the fastest non-supersonic jetliner? And if so, does the wing sweep have something to do with that. Are there airliners with the newer supercritical wings that can match the 747 for speed? Not sure speed is a big deal anymore since crowded airports and other delays eat up any speed gains? Does the A-380 fly as fast at the B747? Seems like if speed does matter, it would matter most on long haul flights. Thanks for all your responses and past responses.

convair880mfan wrote:

Is the Boeing 747 the fastest non-supersonic jetliner? And if so, does the wing sweep have something to do with that. Are there airliners with the newer supercritical wings that can match the 747 for speed? Not sure speed is a big deal anymore since crowded airports and other delays eat up any speed gains? Does the A-380 fly as fast at the B747? Seems like if speed does matter, it would matter most on long haul flights. Thanks for all your responses and past responses.

Wing sweep and high cruise speed are related, yes. The 747-8 is currently the fastest jetliner. The speed gains are not the issue - fuel burn is. The difference between mach .86 and .84 cruise is not much in terms of time gain, but to airline bean counters is huge. Also, modern dispatching and weather forecasting allow flight plans to take maximum advantage of winds on most long haul routes that don't have airspace or regulatory limitations.

Just a reminder some of these questions are easily referenced via Google search - use it liberally Also there are follow-up questions for you in threads you started still unanswered...

convair880mfan wrote:

Is the Boeing 747 the fastest non-supersonic jetliner? And if so, does the wing sweep have something to do with that. Are there airliners with the newer supercritical wings that can match the 747 for speed?

Even surpass it. On average, you'll often see 747 and 777 cruising at around .84 while 380/350/787 cruise at .85. That said I don't know about the actual MMO of the different models.

Remember a hundredth of a Mach is only about 6 knots or 1 minute every 600 nautical miles.

Aaron747 wrote:

The 747-8 is currently the fastest jetliner. The speed gains are not the issue - fuel burn is. The difference between mach .86 and .84 cruise is not much in terms of time gain, but to airline bean counters is huge.

The 747-8 is not the fastest, there are numerous aircraft flying around today with Econ cruise of 0.85 or greater. Some business jets cruise closer to M0.90.

Simple fact is with a supercritical section the A380 can achieve normal cruise speeds in excess of M0.85 without the need for greater sweep. This results in a lighter wing, the greater the seep, the heavier the wing. That is why the 787/A350 have less sweep and yet can fly faster than the 747-8.

zeke wrote:

Aaron747 wrote:

The 747-8 is currently the fastest jetliner. The speed gains are not the issue - fuel burn is. The difference between mach .86 and .84 cruise is not much in terms of time gain, but to airline bean counters is huge.

The 747-8 is not the fastest, there are numerous aircraft flying around today with Econ cruise of 0.85 or greater. Some business jets cruise closer to M0.90.

Simple fact is with a supercritical section the A380 can achieve normal cruise speeds in excess of M0.85 without the need for greater sweep. This results in a lighter wing, the greater the seep, the heavier the wing. That is why the 787/A350 have less sweep and yet can fly faster than the 747-8.

Several sources including the (in)famous John Cox have claimed in articles that the 747-8 is still fastest.

https://www.telegraph.co.uk/travel/trav ... e-fastest/

https://amp.usatoday.com/amp/80946366

Well aware of bizjet performance, I think the distinction here is jetliner refers to larger aircraft. I don’t really have a dog in this though, speed wars are
for A vs B fanboys to fight over

Aaron747 wrote:

I don’t really have a dog in this though, speed wars are for A vs B fanboys to fight over

You were the one who raised it, I cannot read your first link as its behind a paywall, the second link states

"Question: What is the fastest airliner and how fast does it fly?

— submitted by reader James Kriplean, Knoxville, Tenn.

Answer: The Boeing 747 can cruise at 92% of the speed of sound, Mach .92. It is very rarely flown at this speed due to the increased fuel burn required. Most modern jets fly around 80% of the speed of sound, Mach .8."

This is clearly false, the 744/748 typical econ cruise is in the 0.84/0.85 range. No one flies around at Mmo. No idea who John Cox is and what makes them an authority on the 748.

zeke wrote:

Aaron747 wrote:

I don’t really have a dog in this though, speed wars are for A vs B fanboys to fight over

You were the one who raised it, I cannot read your first link as its behind a paywall, the second link states

"Question: What is the fastest airliner and how fast does it fly?

— submitted by reader James Kriplean, Knoxville, Tenn.

Answer: The Boeing 747 can cruise at 92% of the speed of sound, Mach .92. It is very rarely flown at this speed due to the increased fuel burn required. Most modern jets fly around 80% of the speed of sound, Mach .8."

This is clearly false, the 744/748 typical econ cruise is in the 0.84/0.85 range. No one flies around at Mmo. No idea who John Cox is and what makes them an authority on the 748.

The Telegraph article reports on standard cruise speeds compared to Concorde, and claims the following:

747-8 M0.86
A380 M0.855
A350 M0.85
787 M0.85
777 M0.84

John Cox, on the other hand, is a well-known retired captain personality in the US who frequently appears on major news networks to comment on aviation incidents and developments. He is somewhat infamous because his predictions of outcomes of accident investigations have often been wrong.

Technically the 747SP is the commercial airliner with the highest "econ" cruise speed at M.86 to M.88 IIRC. Definitely faster than the 787, A350 or A380. Mmo is still M.92

744SPX wrote:

Technically the 747SP is the commercial airliner with the highest "econ" cruise speed at M.86 to M.88 IIRC. Definitely faster than the 787, A350 or A380. Mmo is still M.92

Technically yes but with specialty operators like NASA and PWCanada, who knows if those speeds are still utilized?

Aaron747 wrote:

The Telegraph article reports on standard cruise speeds compared to Concorde, and claims the following:

747-8 M0.86
A380 M0.855
A350 M0.85
787 M0.85
777 M0.84

John Cox, on the other hand, is a well-known retired captain personality in the US who frequently appears on major news networks to comment on aviation incidents and developments. He is somewhat infamous because his predictions of outcomes of accident investigations have often been wrong.

I am not able to read the telegraph article, cruise speeds will vary typically by M0.05 during a long flight depending on levels and winds. We operate the 744 and 748, the 748 does the same city pairs in the same time a 744 does. The 748 engines are essentially 787 engines, the 748 optimum cruise speed for its engines is the same as the 787.

The A350 will happily sit at M0.83 with a strong tailwind, and 0.865 into a strong headwind, indicated mach numbers are always changing, they are not constant for a cruise. Turbulence penetration speed is M0.85.

Looking at the biography of John Cox on https://aviationsafety.usc.edu/about/in ... /john-cox/ it says he has flown the king air, 737-200/300/400, A319/20/21. Dont see how he has any relevant experience with the topic at hand.

zeke wrote:

Aaron747 wrote:

The Telegraph article reports on standard cruise speeds compared to Concorde, and claims the following:

747-8 M0.86
A380 M0.855
A350 M0.85
787 M0.85
777 M0.84

John Cox, on the other hand, is a well-known retired captain personality in the US who frequently appears on major news networks to comment on aviation incidents and developments. He is somewhat infamous because his predictions of outcomes of accident investigations have often been wrong.

I am not able to read the telegraph article, cruise speeds will vary typically by M0.05 during a long flight depending on levels and winds. We operate the 744 and 748, the 748 does the same city pairs in the same time a 744 does. The 748 engines are essentially 787 engines, the 748 optimum cruise speed for its engines is the same as the 787.

The A350 will happily sit at M0.83 with a strong tailwind, and 0.865 into a strong headwind, indicated mach numbers are always changing, they are not constant for a cruise. Turbulence penetration speed is M0.85.

Looking at the biography of John Cox on https://aviationsafety.usc.edu/about/in ... /john-cox/ it says he has flown the king air, 737-200/300/400, A319/20/21. Dont see how he has any relevant experience with the topic at hand.

I didn't say he did - my first comment was to poke a little fun at his claims in the article.