Pkone From Ireland, joined Dec 2003, 25 posts, RR: 0 Posted (11 years 9 months 4 days ago) and read 18825 times:
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?
Tomgib From United States of America, joined Nov 2003, 92 posts, RR: 0
Reply 1, posted (11 years 9 months 4 days ago) and read 18762 times:
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 ...??
KLM777 From Netherlands, joined Dec 2003, 372 posts, RR: 0
Reply 3, posted (11 years 9 months 3 days 23 hours ago) and read 18470 times:
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.
Kilavoud From , joined Dec 1969, posts, RR:
Reply 4, posted (11 years 9 months 3 days 23 hours ago) and read 18392 times:
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.
Sllevin From United States of America, joined Jan 2002, 3376 posts, RR: 5
Reply 8, posted (11 years 9 months 3 days 22 hours ago) and read 17986 times:
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.
Justplanesmart From United States of America, joined Mar 2001, 730 posts, RR: 2
Reply 10, posted (11 years 9 months 3 days 22 hours ago) and read 17906 times:
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.
Dw747400 From United States of America, joined Aug 2001, 1273 posts, RR: 1
Reply 12, posted (11 years 9 months 3 days 20 hours ago) and read 17465 times:
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.
Sandiaman From United States of America, joined Nov 2003, 88 posts, RR: 0
Reply 14, posted (11 years 9 months 3 days 20 hours ago) and read 17373 times:
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.
RayChuang From United States of America, joined Jun 2000, 8212 posts, RR: 4
Reply 15, posted (11 years 9 months 3 days 20 hours ago) and read 17363 times:
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 From Germany, joined Jan 2004, 109 posts, RR: 0
Reply 16, posted (11 years 9 months 3 days 20 hours ago) and read 17272 times:
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.
Buslover From Germany, joined Jan 2004, 109 posts, RR: 0
Reply 22, posted (11 years 9 months 3 days 19 hours ago) and read 16758 times:
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.
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.
Slamclick From United States of America, joined Nov 2003, 10062 posts, RR: 66
Reply 23, posted (11 years 9 months 3 days 19 hours ago) and read 16754 times:
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.