pkone
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Why Is 747 Fastest Commercial Jet?

Thu Jan 08, 2004 8:42 pm

If this has been answered separately I couldn't find it. Just curious as to why the 747 is faster than any other commerical airliner...thought that 777 or newer jets should be...as they are not, why not?

Tks.
 
tomgib
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RE: Why Is 747 Fastest Commercial Jet?

Thu Jan 08, 2004 8:46 pm

good question... I´ve always been wondering about the same thing. I guess it all comes down to shear engine power. Or is it the same with airplanes as it is with boats. The longer it is the faster it will go ...??

Can´t wait to hear some good answers !
 
fritzi
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RE: Why Is 747 Fastest Commercial Jet?

Thu Jan 08, 2004 9:18 pm

It definetly doesnt have anything to do with the engine power. The 777 would win there!

I am thinking it has to do with the aerodynamics of the wing.

You usually fly at the speed that is the most efficient for the current altitude.

Edit: IIRC, then one of the convair jets (990?) could cruise at M0.90 or above.

PS, the Concorde and TU 144 were a wee bit faster than the 747. Big grin

[Edited 2004-01-08 13:20:08]
 
KLM777
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RE: Why Is 747 Fastest Commercial Jet?

Thu Jan 08, 2004 9:25 pm

Hi guys,

It has to do with the upper deck of the 747 (as you probably expected). When flying closer to Mach 1, the smoother cross-section (wing and fuselage) results in less shock waves over the surface of the aircraft (because there is less possibility of small local flows of air reaching speeds of Mach 1 and above).

Because these shock waves create drag, you want to have the least possible amount of shockwaves at your cruise speed. The 747's has less shockwaves at a certain speed than any other airliner, and thus it can cruise faster while not being less economical.

For some more information, see this link:

http://www.aerospaceweb.org/question/performance/q0150a.shtml

Kind regards,

Jeroen

[Edited 2004-01-08 13:32:09]
Every landing is a controlled crash
 
kilavoud
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RE: Why Is 747 Fastest Commercial Jet?

Thu Jan 08, 2004 9:31 pm

Tail or head winds are playing a big part in the speed of 747. When I flew Singapore-Zurich end of December, it took this time about 13 hours to cover approx. 10350 km. Over Iran and Turkey we had stron head winds at about 200 km/hour. The speed of our SQ 747-400 was during a while not exceeding 720-740 km/hour.

Cheers. Kilavoud.
 
UTA_flyinghigh
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RE: Why Is 747 Fastest Commercial Jet?

Thu Jan 08, 2004 9:32 pm

IMHO the fastest subsonic commercial jet is not the 747 but the Tupolev TU-154, due to its military aircraft wing design :

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KLM777
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RE: Why Is 747 Fastest Commercial Jet?

Thu Jan 08, 2004 9:37 pm

Tail or head winds are playing a big part in the speed of 747.

This is not something unique to the 747 I think. You can add or extract the winds from the airspeed. The 777 will generally fly slower in the same circumstances.

Kind regards,

Jeroen
Every landing is a controlled crash
 
cedarjet
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RE: Why Is 747 Fastest Commercial Jet?

Thu Jan 08, 2004 10:07 pm

The 747 actually used to go faster, until the oil shock in 73. Then they worked out the most efficient cruising speed and flight times got a bit longer.

Headwinds make no difference, it's not as though some planes have a connection to the earth that makes them less affected than other planes.
fly Saha Air 707s daily from Tehran's downtown Mehrabad to Mashhad, Kish Island and Ahwaz
 
sllevin
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RE: Why Is 747 Fastest Commercial Jet?

Thu Jan 08, 2004 10:23 pm

The 747 goes fast because it was designed to go fast. Actually, Pan Am wanted a Mach .90 cruise, but Boeing argued them down to a .87 compromise -- which certainly contributed the the 747's longevity as gas suddenly because VERY expensive in the 1970s!

Flying an aircraft significantly below its design cruise speed can bring problems of its own. The DC-10, for example, now classically flown at M.82 instead or .84, takes a decided nose-up attitude in cruise flight that makes moving service carts much tougher on the flight attendants (the MD-11 was specifically designed with a low angle of incidence to address this problem, and, having ridden in both planes back-to-back, I can tell you, that 3 degrees nose up makes a BIG difference). There's also drag considerations at some point of flying pitched up that negate the slower speed advantages as well.

In short, modern airliners fly slower because it's more fuel efficient. So the standard for cruise speed has hovered around Mach .82-83 these days.

Steve
 
pkone
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RE: Why Is 747 Fastest Commercial Jet?

Thu Jan 08, 2004 10:26 pm

Interesting replies folks...keep'em coming
 
justplanesmart
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RE: Why Is 747 Fastest Commercial Jet?

Thu Jan 08, 2004 10:33 pm

Why is the 747 the fastest (subsonic, or currently in service) commercial jet? Because it was designed to be. The 707 has a wing with 35 degrees sweep back, as does the Convair 880/990, IIRC. The sweep of the 747 wing is 37.5 degrees, and the upper deck creates a bit of area-ruling, as KLM777 explained. In fact, both the 747SP and all 747's with the stretched upper deck have a higher maximum cruising speed than the original due to the area-ruling effect. Of course, none of them fly that fast these days - it's all about fuel economy.
"So many planes; so little time..."
 
POSITIVE RATE
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RE: Why Is 747 Fastest Commercial Jet?

Thu Jan 08, 2004 11:38 pm

The 727 was also a fast cruiser. It cruised a fair bit faster than the 737, probably more due to its extremely efficient wing than the extra engine. I would say the same for the 747.
 
dw747400
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RE: Why Is 747 Fastest Commercial Jet?

Thu Jan 08, 2004 11:54 pm

Remember, when the 747 was coming out, the world was thinking fast. SSTs were in development, and everyone figured that they would represent the future. Though the 747 could never really compete for them with speed, it was figured that a faster aircraft could at least contribute to the longevity of the 747 program.

As fuel economy became a greater concern, the speed of aircraft dropped. The 757 and 767 cruise at mach .80, and most of the Airbus wide-bodies fly in a similar speed envelope. With the 777, the speed went back up to .84 (the -300 can cruise at .85) due in large part to more efficient aerodynamics, particularly in the form of advancements in the supercritical wing. Though I haven't seen much recently, I believe Airbus was aiming for .86 with the A380 (they don't like the fact the 777 is faster than their wide-bodies).

The new 7E7 will cruise around .85, though I've heard speculation Boeing might try to push this up a tad to about .87 (just speculation!).

As for the 727 vs. 737, the main reason for the former being faster is that it was intended for longer stage lengths. Engine number is rarely used to increase the speed of an aircraft, especially today with engines able to produce more thrust then a Mercury-Redstone Rocket.
CFI--Certfied Freakin Idiot
 
Guest

RE: Why Is 747 Fastest Commercial Jet?

Fri Jan 09, 2004 12:03 am

So is the 747 the fastest commercial jet or is it the TU 154.
I know that everything from the US is the biggest, fastest, most beautiful and best, etc. but what about the 154 now?
 
sandiaman
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RE: Why Is 747 Fastest Commercial Jet?

Fri Jan 09, 2004 12:05 am

The use of computational fluid dynamics (CFD) has increased our understanding of airfoil performance. Modern day supercritical airfoils offer reduced drag at optimum speeds. Here are some interesting tidbits I've read over time:

-The 777 wing was designed to be as efficient as the 767 wing, but the 777 wing provides a higher optimum cruising speed (M. 0.84 vs M 0.80 for the 767).
-The A380 wing allows the plane to achieve the same optimum cruising speed as the 747 (M. 0.85), but does so with less sweep.
-The 747X planes were design to offer cruising speeds of M0.86-0.87 with minor modifications to the existing wing (note: modern day supercritical airfoils exhibit significant drag increases if they are pushed beyond their optimum speed. So you couldn't "push" the 777 wing like you can the 747 wing)

The ability to achieve higher economic cruising speeds is not only dependent on the wing, but also on the wing-body combination. For example, as JustPlaneSmart stated in Reply #10, part of the reason that the 747 can cruise at higher speeds is that the aircraft’s total cross-sectional area varies less as you move from the front to the back of the plane. This is due in large part to the hump at the front. If the upper deck were extended over the wing, the aircraft’s drag would increase significantly in the transonic regime. In a way, the 747 has a built-in speed advantage with its distinctive hump.

-M
 
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RayChuang
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RE: Why Is 747 Fastest Commercial Jet?

Fri Jan 09, 2004 12:06 am

I believe that the 747-400 nowadays cruises at around Mach 0.85-0.86 for long range cruise. The 777-200 series cruise at around the same speed on longer flights.

This has caused problems with ATC spacing over the north Atlantic routes, where 744's easily outpace 767's, A330's and A340-200/300's flying these routes at around Mach 0.80-0.81. Is it small wonder why the A340-500/600 cruises at around Mach 0.84, and Airbus wants Mach 0.86 cruise speed for the A380-800? This is also the reason why the upcoming Boeing 7E7 will cruise at around Mach 0.85-0.86.
 
buslover
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RE: Why Is 747 Fastest Commercial Jet?

Fri Jan 09, 2004 12:17 am

DW747400 explained it pretty well!

Whenever an airplane is designed, one also has to define the cruise speed and build the wing etc accordingly. On a 737 with - at that time - pretty many short legs and therefore low cruise time the CRZ speed does not matter as much. Meanwhile it also flies on longer legs and the CRZ SPD is a limiting factor concerning flight crew productivity.
E.g. the 340 and 330 were originally designed for fuel conservation and the resulting CRZ SPD was M 0.83, meanwhile the -600 and -500 models have such a long range capability, that a higher CRZ SPD of M .84 makes it possible to fly distance wise longer legs with a 3 men (women) crew, where the use of M .83 might have caused the neccessity of an additional crew member and higher cost.

Different to the 747 (both 200 and 400) a reduction of CRZ SPD when still able to arrive on time is saving considerable amount of fuel. This is practised by all LH crews and saves on the FRA EZE flight using M.83 iso M .84 approximately 4 to 5 tons of fuel! The same procedure on a 747 saves only a negligible amount of fuel.

Dpon't forget it was designed in the late 60ies and the A340 in the very late 80ies.
The best airplane is the one you fly
 
concordeboac
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RE: Why Is 747 Fastest Commercial Jet?

Fri Jan 09, 2004 12:28 am

Wasn't the VC-10 the fastest, although not commercialy any more, it still flys.
 
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ATA L1011
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RE: Why Is 747 Fastest Commercial Jet?

Fri Jan 09, 2004 12:32 am

Some things I've seen and heard say the DC-8 and L1011 are faster than the 747, who knows.
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tomgib
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RE: Why Is 747 Fastest Commercial Jet?

Fri Jan 09, 2004 12:39 am

This is one of the most interesting threads I´ve read so far...

If the 747 "hump" makes such a difference, then why don´t other planes have it ?
 
tavve
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RE: Why Is 747 Fastest Commercial Jet?

Fri Jan 09, 2004 12:55 am

Or is it the same with airplanes as it is with boats. The longer it is the faster it will go ...??

No one seems to respond to this question. Does anyone know? For boats it's true (yes, yes, under a thousand restrictions and so on). Can it be that the relationship size/air density is out way wrong?
GOT, that's where I live
 
oerk
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RE: Why Is 747 Fastest Commercial Jet?

Fri Jan 09, 2004 1:07 am

Well, just looking at max speeds (not actual speeds) the DC-10 looks pretty nippy!

Tu-154 - Max cruising speed 975km/h, economical cruising speed 900km/h
747-400 - Max cruising speed 939km/h, long range cruising speed 907km/h
DC-10-30 - Max speed 982km/h, cruising speed 908km/h

The terminology and phrases changes here, could someone explain the differences? Especially considering the massively overpowered 757 is slapped down by the lightning like DC-10:

757-200 - Max cruising speed 914km/h, economical cruising speed 850km/h.

I refuse to believe the DC-10 is faster than all these jets - it just doesnt LOOK like a speedy character! Clarification please!
 
buslover
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RE: Why Is 747 Fastest Commercial Jet?

Fri Jan 09, 2004 1:19 am

To Tawe:

Yes it is answered: At the time the 747 was designed speed counted fuel cost was not a factor, every airplane thereafter had to compromise between speed and fuel burn, and therefore was designed for a lower speed.

To Oerk:

Don't take the postcard information, look for the cruise speed published in official documentation, it is always in M - number or IAS, resp. TAS

The 744 is even heavier and if you all remember you aerodynamic lesson right, the heavier an airplane is the faster it has to fly in order to receive the best specific fuel flow.
Also the more headwind --> the faster and vv.
The best airplane is the one you fly
 
SlamClick
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RE: Why Is 747 Fastest Commercial Jet?

Fri Jan 09, 2004 1:19 am

No quarrel regarding the 747 being the fastest currently carrying passengers. And fastest means highest mach number cruise.

But it needs to be mentioned that the DC-8 actually went supersonic in controlled flight. In 1961 a DC-8 achieved mach 1.012 over Edwards AFB, with an F-104 chase plane confirming the data. The actual plane was subsequently sold to a customer and entered passenger service.
Happiness is not seeing another trite Ste. Maarten photo all week long.
 
teva
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RE: Why Is 747 Fastest Commercial Jet?

Fri Jan 09, 2004 1:50 am

Why is 747 fastest commercial jet?
... Because Concorde is not flying anymore....  Big thumbs up

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bahadir
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RE: Why Is 747 Fastest Commercial Jet?

Fri Jan 09, 2004 1:50 am

Correct me if I am wrong but 727 is faster than 747 if we are covering only Western built ones.
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EGGD
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RE: Why Is 747 Fastest Commercial Jet?

Fri Jan 09, 2004 1:52 am

I'm pretty sure with the exception of Supersonic Airliners, the CV990 was the fastest commercial aircraft built..
 
buslover
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RE: Why Is 747 Fastest Commercial Jet?

Fri Jan 09, 2004 2:04 am

To EGGD:

You are right, the CV 990's design CRZ Mach no was .88

To Bahdir:
The 727's speed was .82, the 742 has .84 the 744 has .86
The best airplane is the one you fly
 
Dasheighty
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RE: Why Is 747 Fastest Commercial Jet?

Fri Jan 09, 2004 3:14 am

As of right now 1:12 est the history channel is runnning a program on the 747 if you can see it it may answer your questions.
 
RAAFController
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RE: Why Is 747 Fastest Commercial Jet?

Fri Jan 09, 2004 5:30 am

Hi All,

Putting it simply, design speed is influenced by many factors, one of the most significant being the sweep back angle of the wing. As previously mentioned, the B747 has a sweep back of 37.5 degrees, whereas most other pax jets such as the "original boeing narrow bodies" ie 707, 727, 737, 757 are all 35 degrees. The greater the sweep back the higher the design speed. To illustrate this, look at many prop driven planes, which have wing angles at close to right angles. Aircraft like concorde have a much greater sweep back, due to their higher speed. Some military fighter jets such as the ageing F-111 have variable angles on the wing, a low angle for slow flight which increases as speed increases.

As some history, the concept of sweep back was developed during WWII as part of the Nazi rocket program. Prior to this most aircraft had had largely straight wings. The effect of sweep back was discovered, and shortly after the war, Boeing conducted a number of studies based on this program. This lead to aircraft such as the B707 having a 35 degree sweep as opposed to any other angle. It was flet that this gave a compromise between speed and stability. The B747 was originally supposed to be 40 degrees to have higher speed, but it was found to be too unstable (for the technology of the time). A greater sweep back as a greneral rule requires larger vertical stabs to counter the rolling effect. It also can result in aerodynamic losses due to airflow down the leading edge as opposed to over the wing, resulting in less lift and higher drag.

In short, everything is a compromise. A higher angle means higher speed, less lift, greater required speed, higher drag, more powerful engines for weight, greater fuel consumption, less economy. A lesser angle means slower design speed, but greater lift and lower speed envelope, less powerful engines, and better economy.
There are also many other factors that also effect design speed and wing design.

Hope this helps.
 
AvObserver
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RE: Why Is 747 Fastest Commercial Jet?

Fri Jan 09, 2004 8:04 am

"If the 747 "hump" makes such a difference, then why don´t other planes have it?"

The 747's hump wasn't designed to make it go faster; it's there because the flight deck was raised above the nose to facilitate loading of cargo with a hinged nose in both converted ex-passenger models and new-build freighters. The hump was created when the area aft of the flight deck had to be faired back to meet the main fuselage. At the time the 747 was designed, it was assumed SSTs would take over passenger flights so it was thought that subsonic airliners that could be easily be converted to freighters would have extended lives. Things didn't work out as everyone expected but the hump still served the 747 well, initially providing an area for a 1st class lounge, then later providing extra seating space, especially in the -200B SUD (SUD stood for Stretched Upper Deck), the -300 and the -400. The speed bump it also provides is due partly to the area-ruling around this section.
 
Mir
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RE: Why Is 747 Fastest Commercial Jet?

Fri Jan 09, 2004 8:28 am

Fastest civilian aircarft built these days is Cessna's Citation X, crusies at Mach .92!!!


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MD-90
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RE: Why Is 747 Fastest Commercial Jet?

Fri Jan 09, 2004 8:49 am

I'm surprised no one mention the Citation X before now, just goes to show how airliner-centric this site is.

When I think of area ruling, I think of the "coke bottle effect" which is most often seen nowadays in newer bizjets like Citation X (where the engines are attached to the fuselage, you really can't see it in either of the above pictures). I've never really considered the fact that the 747's hump could be considered area ruling ... I guess so but that's not what immediately pops to my mind when I think of drag reduction.
 
Mir
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RE: Why Is 747 Fastest Commercial Jet?

Fri Jan 09, 2004 9:08 am

Could someone please explain the concept of area ruling? I'm not exactly sure what it is and what effect it has on the plane.
7 billion, one nation, imagination...it's a beautiful day
 
SlamClick
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RE: Why Is 747 Fastest Commercial Jet?

Fri Jan 09, 2004 9:33 am

Mir

Area rule, oversimplified says that the whole thing should not get thick at the same time. If you could pass a plane (geometry plane not airplane) through an airplane from front to rear and see on that plane, what the frontal area was at each "station" from front to rear, you'd see that in early designs they had the most frontal area in the region where the wings are attached to the fuselage. Drag increases with the frontal area.

Not too critical at low speeds but at high mach numbers the drag curve starts going up very steeply. So planes designed for transonic flight (roughly mach 0.75 to mach 1.2) might have the fuselage thin way down in the area of the wing attachment. Look at the Republic F-105 for really obvious example of this.

In response to a couple of posts: Wing sweep is one factor but not the only one. Bear in mind that the plane that first achieved mach one (the Bell X-1) one of the fastest fighter/interceptors ever produced (the Lockheed F-104) and all-time champion high-speed, high mach research aircraft of all time the North American X-15 were all straight-wing airplanes. The latter two had some leading edge sweep but not as much as a DC-3.

Happiness is not seeing another trite Ste. Maarten photo all week long.
 
Mir
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RE: Why Is 747 Fastest Commercial Jet?

Fri Jan 09, 2004 9:46 am

Slamclick, thanks very much for the explanation! So, if I understand correctly, the fact that the drop in fuselage area caused by the hump tapering off offsets the wing-to-fuselage attachments makes the 744 more efficent? In that case, what do almost all other planes do (like the 777 and A330) to minimize drag where the wings meet the fuselage?

7 billion, one nation, imagination...it's a beautiful day
 
MD-90
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RE: Why Is 747 Fastest Commercial Jet?

Fri Jan 09, 2004 9:56 am

Here are some cruise speeds from the reference, The International Directory of Civil Aircraft 2001/2002 edition that airliners.net uses for its own aircraft data.

Max Speed: (not sure what this meant, exactly)
549 - 727-100 and 727-200
545 - 707-120B and 707-320
545 - 720
540 - 747SP
538 - 747-300 (with CF6-80 engines)
530 - 747-200B (with RR engines)
530 - DC-10-30

Max Cruise: (note, this is not the typical cruise speed)
530 - 720
527 - 727-100
527 - Tu-154
526 - L-1011
525 - 707-120B and 707-320
525 - Cessna Citation X*
521 - DC-8-60
518 - L-1011-500
515 - 727-200
513 - Tu-154M
510 - MD-11
507 - 747-300 (with CF6-80 engines)
504 - DC-8-50
500 - MD-81
494 - A340
493 - 767-200
490 - DC-10-30
486 - 767-300
479 - DC-8-70
475 - A330-200/300

*note: I've seen the X listed as having a max cruise of 525 knots. Now, at 51,000 feet, trueing M0.92 could really be 525 knots, but it varies at altitude. The directory has these two listings to ponder

high speed cruise 505 knots Mach 0.88 - Global Express

max cruise at mid cruise weight at Mach 0.91 at 37,000 feet 504 knots. - Cessna Citation

Altitude affects airspeed and mach indicated. Never forget that.
 
Skydrol
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RE: Why Is 747 Fastest Commercial Jet?

Fri Jan 09, 2004 11:15 am

Interesting data, MD-90.

I have heard over and over that Airbus aircraft are 'slow', but never took the time to collect and compare the data as you have provided. Interesting the A340 ends up in 15th place on that list and A330 is close to 20 kts slower than a 767-200. Airbus is beaten by Douglas, Lockheed, Boeing and Tupolev for cruise speed. What's going on with Airbus A/C cruise speed? Inefficient wing designs? Winglets? Undersized V-Stabs causing instability at high speeds? (their V-Stabs do look odd)
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AvObserver
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RE: Why Is 747 Fastest Commercial Jet?

Fri Jan 09, 2004 11:34 am

Airbus's designs are not dramatically slower than Boeing's, only slightly so. In the case of the A340, the fact that it shares a common wing design with the A330 may be the main reason, it's not quite optimized for either a twin or quad engine configuration so there's a small performance tradeoff with both. The economic sense of using the common wing more than offsets this penalty, however. It's worth noting that the A340-500/600 have raised cruise speed from the -300's .82 Mach to .83 Mach, just behind the 777, due to more power and cleaned up aerodynamics in the "NG" series. With the A330, it's probably a similar issue but since airlines are concerned these days with efficiency, not speed, this isn't a liability for Airbus. Just to note, the A380's .85 Mach cruise speed is right up there with the 747 and soon, the 7E7.
 
SlamClick
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RE: Why Is 747 Fastest Commercial Jet?

Fri Jan 09, 2004 12:16 pm

Mir

You are welcome. But as for the hump on the seven-four, I just don't know that. I'd never before heard that the hump had any effect on the speed of the plane.

MD90

Interesting table of speeds, but knots are just not the way to measure airliner speed. Above approximately 27000' all airliners are going to be limited by mach number rather than knots indicated. Every jetliner I've ever heard of had no trouble at all cruising right up to its maximum mach (Mmo) And so we are left only with the question - what is Mmo for each plane?

The speed in knots solves itself for each type with a couple of simple calculations, if you'd like.

Mach number over 1 equals True Airspeed over the Speed of Sound


and

The speed of sound is 39 times the square root of the air temperature in degrees Kelvin. A degree K equals a degree Centigrade but zero K is -273C

Bottom line though, is that mach number is the limiter up where we cruise.

It might be noted that the long-haul planes all tend to get stuck at the same mach number as they motor across the oceans nose-to-tail on organized airways. At the moment a fuel efficient cruise at .80 is probably to be preferred over a cruise speed of .95








Happiness is not seeing another trite Ste. Maarten photo all week long.
 
MD-90
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RE: Why Is 747 Fastest Commercial Jet?

Fri Jan 09, 2004 12:41 pm

The data for older airplanes tends to emphasize knots, while the newer ones show Mach percentages. I know what you mean about mach being the limiting factor, since both temperature and altitude affect the indicated (and true) airspeed.

Here's what the directory shows in Mmo (or as otherwise noted):

0.88 - A380 (long range cruise 0.85)
0.88 - Global Express (0.85 normal and 0.80 long range cruise)
0.84 - Dassault Falcon 2000 (0.80 is both normal and long range cruise)
0.83 - A340-500 and -600 (typical cruise)
0.82 - BBJ (0.80 normal and 0.79 long range cruise)
0.80 - Embraer 170 and 190
0.785 - all 737NG (typical cruise)
0.73 - RJ100 and BAe 146-300
0.70 - Avro RJX
 
Mir
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RE: Why Is 747 Fastest Commercial Jet?

Fri Jan 09, 2004 2:22 pm

As far as I know, there are the typical cruise speeds:

0.92 Citation X (test-flown to .98! WOW!)
0.85 744
0.84 777
0.82 A330/340
0.80 767/757 (sometimes .81)
0.79 A32X and 737NG (can go up to .81 or .82, but not that efficiently)
0.77 older 737s (anywhere from .74 to .79)

and of course, 2.02 for Concorde (sigh...)

I believe these are the most efficient speeds. Planes can fly faster, but it costs fuel, and also if they fly slower, it costs fuel.
7 billion, one nation, imagination...it's a beautiful day
 
L-188
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Joined: Wed Jul 07, 1999 11:27 am

RE: Why Is 747 Fastest Commercial Jet?

Fri Jan 09, 2004 2:34 pm

To get a true answer you would have to find the guy that designed the wing.

I suspect that is is the combination of a lot of power and the fact that it has a 45 degree wing sweep, which I believe is the steepest sweep of any commecial airliner.(Only the Citiation X is as steep in civilian life)


Aslo bear in mind that while the 747-400 may be fast, the DC-8 is faster, It managed to break the sound barrier in a dive.
OBAMA-WORST PRESIDENT EVER....Even SKOORB would be better.
 
sandiaman
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RE: Why Is 747 Fastest Commercial Jet?

Fri Jan 09, 2004 2:59 pm

There should be a distinction made between maximum speed and the cruise speed at which the plane can fly most efficiently. The use of area ruling and supercritical airfoils tends to reduce drag at higher speeds. But it doesn't mean that other planes without such features can't go faster...they just encounter more drag.

Part of the reason the Sonic Cruiser configuration was considered a breakthrough was that it allowed for better area ruling without the need for a coke bottle fuselage at the wing root (a coke bottle fuselage would have been expensive and difficult to stretch). This allowed the sonic cruiser to fly at M 0.90 without encountering the huge drag rise that conventional planes do when approaching such speeds (there were other features as well, such as a thin wing)

Thus, the Sonic Cruiser was to have flown efficiently even at transonic speeds

-M

[Edited 2004-01-09 07:01:07]
 
BOEING747400
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RE: Why Is 747 Fastest Commercial Jet?

Fri Jan 09, 2004 6:25 pm

Is the max. speed the same for 744 regardless of engine type or it may vary depending on what engine it has (GE or PW or RR)?

What about the 744ER (GE B5F vs PW 4062) max. speed comparison? Same or different?
 
GE
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RE: Why Is 747 Fastest Commercial Jet?

Fri Jan 09, 2004 11:55 pm

BOEING747400:
The max speed of an airliner is the same regardless of engine type (as the wing remains the same).

Russell
 
dw747400
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RE: Why Is 747 Fastest Commercial Jet?

Sat Jan 10, 2004 2:23 am

the fact that it has a 45 degree wing sweep

If your talking about the 747, then the sweep at the quarter-chord is actually 37.5 degrees.
CFI--Certfied Freakin Idiot
 
ramme
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RE: Why Is 747 Fastest Commercial Jet?

Sat Jan 10, 2004 5:11 am

Slamclick: you're correct, the DC8 went past Mach1. Keep in mind that this was reached while the airplane was in a shallow dive.
 
RAAFController
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RE: Why Is 747 Fastest Commercial Jet?

Sat Jan 10, 2004 5:46 am

Some further info in response to some posts:

Engine power: Remember that one of the basic laws of flight is that thrust = drag, lift equals weight for steady level flight. Thus, for the same aircraft type (hence same drag), thrust must also remain constant regardless of engine type. This gets complicated as their are different types of drag which are not linearly proportional to speed. Hence by increasing or decreasing speed there can be a disproportionate change in drag, and hence thrust required. Thus, while engine type fitted to an aircraft will not change its design speed (ie, a 747 design speed is a factor of its drag, and wing design, regardless of PW, GE or RR engines), its economical cruising speed may vary. This will be to do with the most economical thrust output of the engines fitted. This is however, an operator function and not to do with aircraft design.

As an aside, different airlines operate not only different engines on the 747, but also prefer to fly at different speeds suject to ATC requirements. For example, SIA try to fly a 747 at between M0.84-85, while in the same airspace, BA will fly M0.83-84. This is because the higher speed of SIA burns more fuel, but over time (years etc) allows higher utilisation of the airframe and less hours. BA bean counters conversly have decided that fuel is proportionately more expensive than airframe hours/utilisation, so choose to fly slower where possible. It may also be a function of the engines fitted. I have witnessed this first had from the flight deck of a QF 744, flying SIN-SYD. We were vertically separeated from a SIA and BA 744. The SIA plane flew faster than QF, and the BA slower. It is just the policy of the airline, and all calculations are worked out as "programs" for the pilots in the FMC. Obviosuly speed subject to other operational constraints such as ATC, weather etc.

Tavve: Regarding your question about aircraft length as a function of speed. Speed (Drag) is more a function of width. Simply put the greater the width of an aircraft the greater the drag, and hence the more powerful the engines required and less economical; resulting in a efficiency/practicality driven lowering in speed. To illustrate: The B767 and 757 are a common type, yet the 767 is wider than the 757. The reason that Beoing did not just shorten the 767 to reduce capacity is more to do with the fact that a narrow body (and hence lower capacity) was more efficient. This is why most aircraft manufactuers when developing new a/c prefer to lenghten the aircraft rather than widen it.

Hope this helps everyone.
 
Thrust
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RE: Why Is 747 Fastest Commercial Jet?

Sat Jan 10, 2004 6:13 am

Engine thrust is obviously not a factor, because the 747-100 uses less overall thrust than a 777-300ER, yet was still faster. I will tell you exactly the reason why. The 747 has a sharply-swept wing like the 727 and the 707. The DC-8 also had sharply-swept back wings. It was the angle curve of the wings that make the 747 a faster aircraft than the 777. To tell you the truth, when I flew BOS-LHR on an AA 777, I saw the aircraft exceed 575 mph. We cruised as high as 625 miles per hour on the aircraft. No, really, we did. Mach 1! But I bet the aircraft wasn't fully loaded. However, I do offer these guesses as a factor in the speed difference. Can anyone please help me confirm whether these are really facts in order to help answer Pkone's question?



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