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Fastest Normal Cruise Speed  
User currently offlineKuja From Bermuda, joined Aug 2013, 80 posts, RR: 0
Posted (1 year 2 months 3 weeks 3 days 8 hours ago) and read 7816 times:

A topic that has fascinated me for a long time - excluding the supersonic superlatives (Concorde and the Tu-144), which airliner had the fastest in-service cruise speed? There have been various threads in the past about this, but all of them seemed to be largely anecdotal and focused on the Vmo / Mmo.

From previous topics, some seemed to suggest that the first and second generation jets cruised rather quicker than the modern day models, but from what I can find, the DC-8 and 707 seemed to top out at around Mach 0.88 and cruised around 0.85 - very similar to modern jets like the 777. It seems that the 727 could reach 0.90, but fuel burn at that speed was apparently prohibitive even in the early days.

The 747 has always been fast; it seems that the 747SP and, from past comments, the Rolls-Royce powered -200B were the quickest of them, and the SP was designed for a high cruise speed - apparently it cruised at 0.88 and could go up to its 0.92 limit without too much difficulty? The TriStar was also known as a quick ship, but, again, I don't know how fast they normally operated.

The Convair 880 and particularly the 990 seem to be likely candidates here, but I can't find reliable figures for how fast they actually operated.

I know that the VC10 still holds a few speed records as well, but, again, I can't find reliable figures for it. Depending on source, the Mmo is given as high as 0.94 or as low as 0.88, with cruise varying between 0.90 and 0.86.

So, what subsonic airliner had the fastest cruise speed in service? 747SP? CV-990? VC10? Or something completely different?

Thank you for any replies.

35 replies: All unread, showing first 25:
 
User currently offlinetimz From United States of America, joined Sep 1999, 6895 posts, RR: 7
Reply 1, posted (1 year 2 months 3 weeks 2 days 13 hours ago) and read 7585 times:

Quoting Kuja (Thread starter):
The Convair 880 and particularly the 990 seem to be likely candidates here, but I can't find reliable figures for how fast they actually operated.

Bet you never find any. People like to think Convairs were fast, but no one has actual data.

Mach is all you care about? If you want the fastest airspeed you'll need to stay below 25000 ft.


User currently onlineStarlionblue From Greenland, joined Feb 2004, 17108 posts, RR: 66
Reply 2, posted (1 year 2 months 3 weeks 2 days 12 hours ago) and read 7538 times:

Quoting timz (Reply 1):
If you want the fastest airspeed you'll need to stay below 25000 ft.

Quite. When Mike Lithgow broke the world speed record in a Supermarine Swift, he did it at low level in Lybia, flying along an oil road. High temperatures mean a but of an edge.



"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlineKuja From Bermuda, joined Aug 2013, 80 posts, RR: 0
Reply 3, posted (1 year 2 months 3 weeks 2 days 11 hours ago) and read 7528 times:

Quoting timz (Reply 1):
Mach is all you care about? If you want the fastest airspeed you'll need to stay below 25000 ft.

No, not at all. I know that below 25000 ft speed is measured in knots; in my initial post I used Mach because it seemed to be easier to find approximate figures in Mach for the sake of comparison. Apologies for the poor original post.   

Quoting timz (Reply 1):
Bet you never find any. People like to think Convairs were fast, but no one has actual data.

I suspect that you are right, but I thought that it wouldn't hurt to ask. I assume a large part of the reason for their city pair records was the lack of the 250 kts restriction under 10000 ft when they operated?


User currently offlinetimz From United States of America, joined Sep 1999, 6895 posts, RR: 7
Reply 4, posted (1 year 2 months 3 weeks 2 days 9 hours ago) and read 7450 times:

Quoting Kuja (Reply 3):
I assume a large part of the reason for their city pair records

Offhand guess: 707/720s have more records than Convairs.


User currently offlineMrBuzzcut From United States of America, joined Jan 2008, 64 posts, RR: 0
Reply 5, posted (1 year 2 months 3 weeks 2 days 6 hours ago) and read 7379 times:

It wasn't normal cruise by any means, but the DC-8 is the only airliner I know of that has gone over Mach 1 and lived to tell the tale. Sure, it was a test flight, and they were in a dive, but cool nonetheless.

Read more: http://www.airspacemag.com/history-o...-Will-Never-Try-It.html?c=y&page=1


User currently onlineStarlionblue From Greenland, joined Feb 2004, 17108 posts, RR: 66
Reply 6, posted (1 year 2 months 3 weeks 2 days 3 hours ago) and read 7312 times:

Quoting Kuja (Reply 3):
I know that below 25000 ft speed is measured in knots;

That's just a convention for practicality. Speed can always be measured in knots. Above the crossover altitude the convention (and regulation) is Mach number, but there certainly is a Mach number under the crossover altitude.



"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlineFlyboyOz From Australia, joined Nov 2000, 1987 posts, RR: 25
Reply 7, posted (1 year 2 months 3 weeks 2 days 1 hour ago) and read 7274 times:

Aircraft Specifications
The CV-990 was built by the Convair Division of General Dynamics Corp., Ft. Worth, Tex., in 1962.

The aircraft was used for commercial passenger service by American Airlines and Modern Air Transport until acquired by NASA in 1975 for use as a research aircraft at the Ames Research Center, Moffett Field, Calif.

The aircraft, which has a cruise speed of 432 kph (496 mph), is 139 feet long and has a wing span of 120 feet. Landing speeds of the CV-990 duplicate those of the space shuttle orbiters - about 230 kph (256 mph).

It is powered by four General Electric CJ805-23 engines, each producing 16,000 pounds of thrust.

From the website:
http://www.nasa.gov/centers/dryden/news/FactSheets/FS-027-DFRC.html



The Spirit of AustraliAN - Longreach
User currently offlineflyingturtle From Switzerland, joined Oct 2011, 2451 posts, RR: 14
Reply 8, posted (1 year 2 months 3 weeks 2 days ago) and read 7263 times:

If operated commercially and called "airliners", would the Cessna Citation X or the Gulfstream G650 take the cake?


David



Keeping calm is terrorism against those who want to live in fear.
User currently offlineKuja From Bermuda, joined Aug 2013, 80 posts, RR: 0
Reply 9, posted (1 year 2 months 3 weeks 1 day 15 hours ago) and read 7116 times:

Quoting FlyboyOz (Reply 7):

Interesting, thanks for that.

Some figures I came across in a scan of an old 'book of airliners' from the '60s gives some speeds for the Convair jets:
CV-880-22
  Max Cruise: 535 kts at 22,500 ft (Mach 0.88)
CV-990A-30
  Max Cruise: 540 kts at 21,200 ft (Mach 0.88)
  Normal Cruise: 485 at 35,000 ft (Mach 0.84)

So if that is to be trusted, it seems that the Convairs were fast, but not as blisteringly quick as some had said. As to how fast they were operated in service, I guess unless a former Convair pilot with a good memory pops up, we won't know.

Some speeds given for the VC10:
Standard VC10
  Max Cruise: 502 kts at 25,000 ft (Mach 0.833)
  Regular Cruise: 480 kts at 25,000 ft (Mach 0.797)
Super VC10
  Max Cruise: 505 kts at 31,000 ft (Mach 0.859)
  Regular Cruise: 478 kts at 38,000 ft (Mach 0.832)

Quoting flyingturtle (Reply 8):
If operated commercially and called "airliners", would the Cessna Citation X or the Gulfstream G650 take the cake?

Yes, that was one of the things that sparked my curiosity on this subject - whether any airliners from the past could match the fastest business jets of today. It seems quite possibly not.


User currently offlinetimz From United States of America, joined Sep 1999, 6895 posts, RR: 7
Reply 10, posted (1 year 2 months 3 weeks 1 day 10 hours ago) and read 6930 times:

Quoting FlyboyOz (Reply 7):
From the website:
http://www.nasa.gov/centers/dryden/n....html

Sure nuff, you quoted it correctly. That site needs work.


User currently offlineViscount724 From Switzerland, joined Oct 2006, 25838 posts, RR: 22
Reply 11, posted (1 year 2 months 3 weeks 1 day 8 hours ago) and read 6901 times:

Quoting FlyboyOz (Reply 7):
Landing speeds of the CV-990 duplicate those of the space shuttle orbiters - about 230 kph (256 mph).

That's only when it was used to simulate the space shuttle. The standard landing speed in airline use was in the same range as other competitive types.


User currently offlineMax Q From United States of America, joined May 2001, 4737 posts, RR: 18
Reply 12, posted (1 year 2 months 3 weeks 1 day 4 hours ago) and read 6832 times:

The question was 'normal cruise speed' not maximum.


In other words a cruise mach number that provides for the most economical operation, in that respect I think the B747 in all of its fantastic versions has to be the fastest.


.84 to .86 Mach is quite normal on the queen of the skies and economical, it can also go considerably faster if it needs to, up to .92 Mach.



The best contribution to safety is a competent Pilot.
User currently offlineC680 From United States of America, joined Apr 2005, 588 posts, RR: 0
Reply 13, posted (1 year 2 months 3 weeks 21 hours ago) and read 6716 times:

As of today, fastest certified, sub sonic, civil aircraft made is Cessna Citation X with a Mmo of 0.935

The gulfstream 650 Mmo is 0.93

All models of 747 Mmo is 0.92

787 Mmo is 0.90

L-1011 Mmo is 0.90

777 Mmo is 0.89

A380 Mmo is 0.89

DC-10 Mmo is 0.88

767 Mmo is 0.86

A330 Mmo is 0.86

A320 Mmo is 0.82



My happy place is FL470 - what's yours?
User currently offlineflylku From United States of America, joined Apr 2006, 825 posts, RR: 0
Reply 14, posted (1 year 2 months 3 weeks 20 hours ago) and read 6714 times:

Quoting Kuja (Reply 3):
It wasn't normal cruise by any means, but the DC-8 is the only airliner I know of that has gone over Mach 1 and lived to tell the tale. Sure, it was a test flight, and they were in a dive, but cool nonetheless.



It is all heresay but I have it on good authority (or maybe just an aviation legend) that the 747 has done it in level flight

1) A friend and Naval Aviator knew a guy who was a test pilot on the 747 and claims they did it. If you think about the shape of the fuselage conforms to he area rule. So then the big worry is flutter and control lock on he control surfaces.

... so I thought I would ask around.

2) An collegue was the FE on Air Force One when they transitioned to the 747 and flew some of the acceptance test flights. I told him the story and he said he had not heard it but believed it was plausible.

3) I was killing time during a delay and shooting the bull with a 737 captain who had been a 747 FO and told him the story and he said he believed it was possible. He said one night they had lots of extra pull and started bumping up the speed in the FMS. He said they got the airplane to mach .90 or .95 (I forget which but I really think he said .95) and he was confident the airplane easily could have gone faster but the computer would not accept anything higher.

I think a BA 747 captain told me their normal cruise is .83 and high speed cruise is .85 ... somehting like that? Its just fuel.



...are we there yet?
User currently offlineflyingturtle From Switzerland, joined Oct 2011, 2451 posts, RR: 14
Reply 15, posted (1 year 2 months 3 weeks 19 hours ago) and read 6679 times:

Quoting flylku (Reply 14):

And there is also a story about a supersonic CV 990 somewhere in the US. The pilots were sacked after that revenue flight. But I do not know when and where this happened...




David



Keeping calm is terrorism against those who want to live in fear.
User currently onlineStarlionblue From Greenland, joined Feb 2004, 17108 posts, RR: 66
Reply 16, posted (1 year 2 months 3 weeks 17 hours ago) and read 6645 times:

Quoting flylku (Reply 14):
1) A friend and Naval Aviator knew a guy who was a test pilot on the 747 and claims they did it. If you think about the shape of the fuselage conforms to he area rule. So then the big worry is flutter and control lock on he control surfaces.

All modern aircraft conform to the area rule to some extent.

If memory serves when an Isreali cargo conversion firm tested their 747, they dove it at M0.97.



"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlineMax Q From United States of America, joined May 2001, 4737 posts, RR: 18
Reply 17, posted (1 year 2 months 3 weeks 13 hours ago) and read 6577 times:

During flight test the B747 was taken up to .99 Mach.


Bear in mind that at that speed the airflow over much of the airframe was already supersonic.


China Airlines did take their -SP supersonic when they did their inadvertent 'Air Display' over the Pacific.



The best contribution to safety is a competent Pilot.
User currently offlineKuja From Bermuda, joined Aug 2013, 80 posts, RR: 0
Reply 18, posted (1 year 2 months 3 weeks 12 hours ago) and read 6555 times:

Quoting Max Q (Reply 12):

  

Quoting flylku (Reply 14):
I think a BA 747 captain told me their normal cruise is .83 and high speed cruise is .85 ... somehting like that? Its just fuel.

The flight crew of a VS 744 told me that their regular cruise was 0.84 to save fuel, sometimes 0.83. Interestingly, they mentioned that the BA 747 flight from LHR to JNB was known as 'the bullet' and cruised at 0.86 most of the way. This may have since been slowed down to save fuel, of course.


So, as far as airliners are concerned, it seems that the fastest regular cruise was the 'hot rod' 747, the SP? That would apprently cruise at 0.88 regularly because of its lighter weight and the beneficial aerodynamic effect of the upper deck ending above the wing as opposed to ahead of it as on the Classics up to that point.
Judging from reports from Iran Air flights on the type, though, the ones still flying likely cruise closer to 0.84 now for economy.

A couple of wildcards would be the HS Trident (not quick to get off the ground but apparently plenty quick in flight) and the Tu-154B (which certainly was faster than the later -154M, but at the expense of what was described as 'alarming' fuel economy even in the days of cheap fuel    )


User currently offlineViscount724 From Switzerland, joined Oct 2006, 25838 posts, RR: 22
Reply 19, posted (1 year 2 months 3 weeks 10 hours ago) and read 6519 times:

Quoting Max Q (Reply 17):
China Airlines did take their -SP supersonic when they did their inadvertent 'Air Display' over the Pacific.

Isn't that just speculation? If memory correct the accident report only refers to "high speed" but doesn't specifically say it exceeded Mach 1.


User currently offlinePellegrine From France, joined Mar 2007, 2472 posts, RR: 8
Reply 20, posted (1 year 2 months 3 weeks 5 hours ago) and read 6474 times:

I've read that the CV-990 cruised at M0.90-M0.92. I've also read that a lot of airlines slowed them down to save fuel.

I'd love to bring a CV-990 back in the air if a serviceable one existed anymore...too bad they've all been chopped to hell.



oh boy!!!
User currently offlineBoeingGuy From United States of America, joined Dec 2010, 3208 posts, RR: 7
Reply 21, posted (1 year 2 months 2 weeks 6 days 13 hours ago) and read 6304 times:

Quoting MrBuzzcut (Reply 5):
It wasn't normal cruise by any means, but the DC-8 is the only airliner I know of that has gone over Mach 1 and lived to tell the tale. Sure, it was a test flight, and they were in a dive, but cool nonetheless.

Didn't the TWA 727 that rolled over Michigan exceed Mach 1?

Tragically PSA 1771 broke the sound barrier also.

For mainline commercial jets today, the 747-8 is the fastest.


User currently offlineViscount724 From Switzerland, joined Oct 2006, 25838 posts, RR: 22
Reply 22, posted (1 year 2 months 2 weeks 6 days 7 hours ago) and read 6227 times:

Quoting BoeingGuy (Reply 21):
Tragically PSA 1771 broke the sound barrier also.

Do you have a source for that? I can't find any official reference to that (NTSB etc.)


User currently offlineMax Q From United States of America, joined May 2001, 4737 posts, RR: 18
Reply 23, posted (1 year 2 months 2 weeks 6 days 5 hours ago) and read 6178 times:

Quoting Kuja (Reply 18):

Judging from reports from Iran Air flights on the type, though, the ones still flying likely cruise closer to 0.84 now for economy.

There's a common misconception that slower always saves fuel and / or is more economical.
Quite often you can save fuel by flying faster into a headwind (less time spent flying into the wind means less fuel burnt)


Not to mention, less time in the air is less time wearing out all Aircraft components, less pay for crews, etc..


It's just not that simple and many Aircraft are designed to be most economical at higher Mach, flying slower can actually increase drag.



The best contribution to safety is a competent Pilot.
User currently offlinegeorgiaame From United States of America, joined Aug 2005, 994 posts, RR: 6
Reply 24, posted (1 year 2 months 2 weeks 5 days 18 hours ago) and read 6101 times:

Quoting Starlionblue (Reply 6):
Above the crossover altitude the convention (and regulation) is Mach numbe

For a non pilot and a non engineer, my question is why?



"Trust, but verify!" An old Russian proverb, quoted often by a modern American hero
User currently onlineStarlionblue From Greenland, joined Feb 2004, 17108 posts, RR: 66
Reply 25, posted (1 year 2 months 2 weeks 5 days 17 hours ago) and read 6340 times:

Quoting georgiaame (Reply 24):
Quoting Starlionblue (Reply 6):
Above the crossover altitude the convention (and regulation) is Mach numbe

For a non pilot and a non engineer, my question is why?

I'll try to explain it simply but this will take a while. I also may make some mistakes which no doubt the experts will jump on.


Down here on the surface and in the lowish end of the troposphere, up to about 25000-30000 feet, flying at an indicated airspeed (IAS) is fine.

As you climb at a constant IAS, mach number increases. This is because the Local Speed of Sound (LSS) is dependent on temperature. Temperature goes down with altitude, LSS goes down and thus mach number goes up. Note: Mach = Airspeed / LSS.

At a certain Mach, you reach Mcrit (the critical Mach number), the air molecules can't get out of the way fast enough. Shockwaves start to form over the wing and you are now in the transonic range.

A while after that (if you're in a subsonic airplane) it is inadvisable to accelerate any more because those shockwaves start doing bad things to lift and drag (mach buffet). You have reached Mmo, the maximum operating mach. You can't keep climbing at constant indicated airspeed because you would exceed Mmo.

Note that typically you wouldn't go all the way to Mmo, but to some mach number below Mmo.

Anyway at this point in your climb you switch over to a constant Mach number. Since temperature is still decreasing, LSS is also still decreasing. Thus IAS starts to decrease. You keep climbing at constant mach. If you exceed Mmo you go into mach buffet (bad). At a certain point you can't climb anymore because your IAS would decrease below your stall speed. This altitude is known as coffin corner. Airliners stay well below coffin corner since any maneuver increases load factor and thus stall speed but that's another story.

You could of course keep using IAS but it would really mean very much, as speeds would be lower than at lower altitude. Thus Mach number is used for separation, and by autopilots.



"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlineYQBexYHZBGM From Canada, joined May 2009, 204 posts, RR: 1
Reply 26, posted (1 year 2 months 2 weeks 4 days 13 hours ago) and read 6100 times:

I've read through this thread, and read about speed in dives and at maximum thrust. But, in answer to the original question, I have always been led to believe that the Convair 990 did indeed have the fastest normal cruise speed. Too bad the era of cheap fuel didn't last longer.

-Al YQBexYHZBGM


User currently offlinegeorgiaame From United States of America, joined Aug 2005, 994 posts, RR: 6
Reply 27, posted (1 year 2 months 2 weeks 3 days 17 hours ago) and read 6035 times:

Starlionblue, thank you very much! As a non engineer, supersonic has fascinated me, especially bad things that begin t ohappen in the transonic range. (I have, in fact, looked for, and seen supersonic shock waves forming on an aircraft wing, after learning about them on this BB). So I guess to sum it up, because of the drop in air density with altitude, (not temperature), IAS drops because that is what the airspeed sensor is feeling. But as temperature drops, and the air becomes more rarefied, it takes "longer" for one air molecule to bump the next, and that "slows" the local speed of sound. But that in turn alters the mathematics of the mach number, which goes up. Indicated airspeed drops for sensor reasons, Mach number increases for arithmetical reasons, and can be displayed as a better indicator of what the wing is actually "feeling". Makes sense to me, I'm just a bit surprised that you you can actually "wait" until you hit 25,000 feet before actually needing to switch over. I wouldn't want to stick my head out of the window at that altitude and try breathing. And back on topic, it's my understanding that with the "pods" put on the wings of the Convair 990, the design conformed more to the area rule, 4 humongous jet fighter engines put out a lot of power, and it was the fastest of the commercial jetliners. But not a challenge with 5 abreast seating to the 707/DC8 6 across. The 707s were touted to cruise at 600mph, 6 miles every 10 seconds, when the first arrived on the scene. (Learned about that in my Weekly Reader, in the 3rd grade). Cruise speeds gradually dropped, until the area-rule conforming 747 came along, when it became the speed queen. Therein ends my knowledge of jetliner speed, area rules, and supersonic/transonic flight. Thanks for the forbearance.


"Trust, but verify!" An old Russian proverb, quoted often by a modern American hero
User currently offlinevikkyvik From United States of America, joined Jul 2003, 10239 posts, RR: 26
Reply 28, posted (1 year 2 months 2 weeks 3 days 13 hours ago) and read 5957 times:
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Quoting Starlionblue (Reply 25):
Note: Mach = Airspeed / LSS.

To be perfectly clear, since you mentioned IAS a lot in your post, Mach = TAS (true airspeed) / LSS.  
Quoting Starlionblue (Reply 25):
At a certain point you can't climb anymore because your IAS would decrease below your stall speed. This altitude is known as coffin corner.

I would assume (and correct me if I'm wrong), that a fair number of airplanes can't even get to that point, due to hitting Absolute Ceiling prior to hitting Coffin Corner (Absolute Ceiling being where the thrust required to maintain level flight equals the max thrust your engines can provide, and therefore you can't climb any higher).



How can I be an admiral without my cap??!
User currently onlineStarlionblue From Greenland, joined Feb 2004, 17108 posts, RR: 66
Reply 29, posted (1 year 2 months 2 weeks 3 days 8 hours ago) and read 5880 times:

Quoting vikkyvik (Reply 28):
Quoting Starlionblue (Reply 25):
Note: Mach = Airspeed / LSS.

To be perfectly clear, since you mentioned IAS a lot in your post, Mach = TAS (true airspeed) / LSS.

Indeed. I just didn't want to overcomplicate things. 

Here is an ECTM graph. The easiest way to visualize the relationship between Equivalent Airspeed, Calibrated Airspeed (IAS), True Airspeed and Mach number with changing altitude. Each graph assumes one parameter is constant and shows how the others change in relation.

Quoting vikkyvik (Reply 28):
Quoting Starlionblue (Reply 25):
At a certain point you can't climb anymore because your IAS would decrease below your stall speed. This altitude is known as coffin corner.

I would assume (and correct me if I'm wrong), that a fair number of airplanes can't even get to that point, due to hitting Absolute Ceiling prior to hitting Coffin Corner (Absolute Ceiling being where the thrust required to maintain level flight equals the max thrust your engines can provide, and therefore you can't climb any higher).

Not sure. I imagine most modern jet airliners have no problem getting right up to coffin corner.

Quoting georgiaame (Reply 27):
So I guess to sum it up, because of the drop in air density with altitude, (not temperature), IAS drops because that is what the airspeed sensor is feeling. But as temperature drops, and the air becomes more rarefied, it takes "longer" for one air molecule to bump the next, and that "slows" the local speed of sound. But that in turn alters the mathematics of the mach number, which goes up. Indicated airspeed drops for sensor reasons, Mach number increases for arithmetical reasons, and can be displayed as a better indicator of what the wing is actually "feeling".

Indeed. IAS is pretty much a measurement of dynamic pressure, which is the "half rho v squared" part of the lift equation. Rho is air density and V is True airspeed. Cl is lift coefficient (comprising angle of attack, Reynolds number and some other stuff I can't remember) and A is the wing area.

Quoting georgiaame (Reply 27):
makes sense to me, I'm just a bit surprised that you you can actually "wait" until you hit 25,000 feet before actually needing to switch over.

The reason you're still getting quite a bit of dynamic pressure at 25000 feet in an airliner is that dynamic pressure increases with the square of speed but only linearly with density. So even if density is decreasing with altitude this is not affecting dynamic pressure nearly as much as the increase in speed.

Quoting georgiaame (Reply 27):
And back on topic, it's my understanding that with the "pods" put on the wings of the Convair 990, the design conformed more to the area rule,

Yes they were. Nowadays the area rule is still very much applied, but instead of dedicated pods the function is incorporated in flap track fairings and wing/body fairings. The effect is particularly apparent on the 380. Check out how the wing body fairing expands after the wing to give a smooth area ruled transition.


View Large View Medium
Click here for bigger photo!

Photo © CL Kwek

Quoting georgiaame (Reply 27):
herein ends my knowledge of jetliner speed, area rules, and supersonic/transonic flight. Thanks for the forbearance.

This here forum is a great place to learn. If you don't delve too deeply into the maths, transonic flight is not that hard to understand actually. All about shockwaves moving along the wing and how they affect lift and drag. Davies's classic "Handling the Big Jets" is a good place to start despite the somewhat dated language.



[Edited 2013-09-06 18:29:30]


"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlinetimz From United States of America, joined Sep 1999, 6895 posts, RR: 7
Reply 30, posted (1 year 2 months 2 weeks 2 days 16 hours ago) and read 5752 times:

Quoting georgiaame (Reply 27):
The 707s were touted to cruise at 600mph

A 707 could perhaps maintain 600 mph at 22000? ft altitude, burning 50%? more fuel per mile than it would at Mach 0.82 at 35000 ft. So if a 707-120 is flying nonstop across the US, 600 mph airspeed was out of the question, if it had a payload.

Quoting georgiaame (Reply 27):
[The CV990] was the fastest of the commercial jetliners.

That's what everyone thinks-- no one knows where they got that idea.


User currently offlineTrijetsonly From Germany, joined Jul 2009, 232 posts, RR: 0
Reply 31, posted (1 year 2 months ago) and read 4184 times:

I was always tought that the second fastest commercial jetliner in service during the 1990s was the Tupolev Tu-154.

Unfortunately I have no data to rely on but I think it's important to look at these soviet birds, too, regarding this topic.


User currently offlineKuja From Bermuda, joined Aug 2013, 80 posts, RR: 0
Reply 32, posted (1 year 1 month 4 weeks 1 day 18 hours ago) and read 4071 times:

Quoting Trijetsonly (Reply 31):
I was always tought that the second fastest commercial jetliner in service during the 1990s was the Tupolev Tu-154.

Unfortunately I have no data to rely on but I think it's important to look at these soviet birds, too, regarding this topic.

Indeed, I did consider the Soviet jets. The Il-62, Il-86 and Il-96 were not particularly quick planes, from what I can tell; the Tu-134 appears to have been faster than the equivalent Western models (DC-9 and 1-11), but not near the level of the fastest.
The Tu-154 does seem possible, though, as I mentioned earlier:

Quoting Kuja (Reply 18):
the Tu-154B (which certainly was faster than the later -154M, but at the expense of what was described as 'alarming' fuel economy even in the days of cheap fuel  )

Like you, though, I can't find reliable data, so I can only go with hearsay.

Considering everything said in this thread, it seems that the answer to my original question is that the title of fastest regular cruise speed belongs to the 747SP, which could cruise at 0.88 and, indeed, it seems that it did so, at least in its early days.
Equally interestingly, though, it would appear that no subsonic airliner was quicker than the G650 and Citation X are today, which makes their achievements all the more impressive.


User currently offlineTrijetsonly From Germany, joined Jul 2009, 232 posts, RR: 0
Reply 33, posted (1 year 1 month 3 weeks 6 days 14 hours ago) and read 3628 times:

Quoting Kuja (Reply 32):
Like you, though, I can't find reliable data, so I can only go with hearsay.

Considering everything said in this thread, it seems that the answer to my original question is that the title of fastest regular cruise speed belongs to the 747SP, which could cruise at 0.88 and, indeed, it seems that it did so, at least in its early days.

In my bookshelf I've just found a German ATC (DFS) training book by the "DFS Air Navigation Services Academy" with technical data of many aircraft, that I've bought like 15 years ago on a second hand fair.
It lists as Max. Cruise Speed and Long Range Cruise Speed for several aircraft on their typical cruise flight level:

(kts/Mach) Max_______LR

A330-300:_500/0.86_____465/0.805
B 52:_____546/0.94_____453/0.79
B707:_____525/0.90_____470/0.81
B727:_____530/0.88_____467/0.805
B747 SP:__505/0.88_____488/0.84
C750 X:____516/0.90_____473/0.82
DC10:_____510/0.87_____470/0.81
G5:_______499/0.87_____462/0.80
IL86:______512/0.87_____484/0.825
L1011-500:_518/0.885____486/0.835
Tu154:_____514/0.88_____459/0.79
VC10:_____493/0.875____425/0.725


User currently offlineMax Q From United States of America, joined May 2001, 4737 posts, RR: 18
Reply 34, posted (1 year 1 month 3 weeks 6 days 7 hours ago) and read 3496 times:

Those numbers are inaccurate,


B727 Max Mach is .9


B747 Max Mach is .92



The best contribution to safety is a competent Pilot.
User currently offlineFabo From Slovakia, joined Aug 2005, 1219 posts, RR: 1
Reply 35, posted (1 year 1 month 3 weeks 5 days 18 hours ago) and read 3413 times:

There is one thing to consider when discussing this - older aircraft usually flew lower than their current counterparts...

and that means flying faster for the same Mach number.

Anyway, for Tu-154M - from my manuals. The operative maximum Mach number was .86, and typical cruise in late years of operation would be somewhere in region of .80-.82. However the actual limit (listed as M max max in the manual) was .95, and, anecdotally, the 154 was taken over .90 on occasion when needed.

(the 0.95M limit is valid above 10300m, under that the limit is 625 or 650km/h, by altitude. Operating limit is 600/575 under normal W&B situation)



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