hypersonic
Posts: 55
Joined: Tue Oct 04, 2005 12:36 am

Are Airliners Capable Of Going Supersonic In Dive?

Thu Nov 20, 2008 6:36 pm

Hi,
Considering that a lot of current airliners have cruise speeds between 80% - 85% of the speed of sound, & some of the larger ones & even the fastest biz jets can exceed 90% of the speed of sound in level flight..
Given that, if you were raking along.. then went full throttle, & put the aircraft into a steepish dive, would you most probably go supersonic & by how much?

I've read rumours that VC-10s' in RAF service, have been occasionally (accidentally on purpose  Wink ) pushed to just over mach 1 in level flight (or slight dive?) ?

Just curious
Hyper
 
OPNLguy
Posts: 11191
Joined: Tue Jun 15, 1999 11:29 am

RE: Are Airliners Capable Of Going Supersonic In Dive?

Thu Nov 20, 2008 6:45 pm

IIRC, Hoot Gibson's 727-100 sure did during it's dive some years ago...
ALL views, opinions expressed are mine ONLY and are NOT representative of those shared by Southwest Airlines Co.
 
A10WARTHOG
Posts: 200
Joined: Mon Jul 12, 2004 7:32 am

RE: Are Airliners Capable Of Going Supersonic In Dive?

Thu Nov 20, 2008 7:07 pm

Heard a rumor a Air China 747 did it.
 
EMBQA
Posts: 7795
Joined: Sat Oct 25, 2003 3:52 am

RE: Are Airliners Capable Of Going Supersonic In Dive?

Thu Nov 20, 2008 7:21 pm

A DC-8 did it too..... but keep in mind a commercial jet is not designed to fly supersonic and doing so is a very-very risky undertaking.
"It's not the size of the dog in the fight, but the size of the fight in the dog"
 
Malmi18
Posts: 11
Joined: Sat Oct 27, 2007 6:20 pm

RE: Are Airliners Capable Of Going Supersonic In Dive?

Thu Nov 20, 2008 7:25 pm

Hi !

When I read this thread I remembered my young days and had to go and dig out a book from my youth (o those times!). "The Flier's Handbook" from 1978 says that "DC8-40 became the first airliner to exceed the speed of sound when, in 1961, it reached Mach 1.012 (667 mph) in a shallow dive". Sounds to me like it was intentional then.

And a bit of off-topic newsflash, the evening news said just now that the number of passengers on Finnair MD-11 increased by one in flight today, when a Swedish woman had a baby over Kazakstan. The plane was on the way from Bangkok to Helsinki. According to the news, the mother and the baby were ok so they continued all the way to Helsinki and didn't deviate to Moscow which was under consideration at some point.

Cheers and many more happy landings for both of them.

Malmi18
 
typhaerion
Posts: 425
Joined: Tue Jun 14, 2005 11:27 pm

RE: Are Airliners Capable Of Going Supersonic In Dive?

Thu Nov 20, 2008 7:33 pm

The answer to your question is yes, it can happen, though the adverse affects that it can have on the aircraft structure and the engines need to be mentioned. When the flow goes to supersonic, it causes all sorts of pressure, temperature, and lift changes and all of these play havoc in a tight tolerace environment like the modern airliner.

Locally, with very little variance in the aircraft AOA or airspeed you can have areas that exceed Mach 1 dependant on the situation. Even within the engine, these local areas exceeding Mach 1 are possible, and sometimes are even designed to occur. Most of these are not good for the aircraft, but they do happen. For the entire aircraft to go supersonic, it would require even more deviation from the normal flight envelope, and the affects on the airframe would be worse.

But like everything else, it can happen, both by accident and on purpose. Though anyone who would put a 737 above Mach 1 on purpose has both reckless and stupid streaks in him as this is a very dangerous proposition. I have heard rumors from my former life, but none I will lead any credence too.
For some, the sky is the limit. For us, it is only the beginning... -- Jack Hunt
 
ajd1992
Posts: 2390
Joined: Mon Jul 24, 2006 7:11 am

RE: Are Airliners Capable Of Going Supersonic In Dive?

Thu Nov 20, 2008 7:46 pm

Technically, if you fall from high enough, any aircraft can. Or, if you're high enough, the speed of sound becomes low enough it's easy enough to do, granted you have the power (which would be severely diminished at altitudes due to the thin atmosphere, I'm talking for a normal jet engine would run out of go at about FL550, even at the lightest of weights)

If, however, you are able to talk about it afterwards is a different matter  Wink
 
vikkyvik
Posts: 11768
Joined: Thu Jul 31, 2003 1:58 pm

RE: Are Airliners Capable Of Going Supersonic In Dive?

Thu Nov 20, 2008 9:36 pm



Quoting Ajd1992 (Reply 6):
Technically, if you fall from high enough, any aircraft can. Or, if you're high enough, the speed of sound becomes low enough it's easy enough to do, granted you have the power (which would be severely diminished at altitudes due to the thin atmosphere, I'm talking for a normal jet engine would run out of go at about FL550, even at the lightest of weights)

Well, once you hit the stratosphere, the speed of sound will start going up again, as the temp rises with increasing altitude in the stratosphere.

But airliners will only reach the lower reaches of the stratosphere now and then.
I'm watching Jeopardy. The category is worst Madonna songs. "This one from 1987 is terrible".
 
KELPkid
Posts: 5247
Joined: Wed Nov 02, 2005 5:33 am

RE: Are Airliners Capable Of Going Supersonic In Dive?

Thu Nov 20, 2008 10:51 pm



Quoting OPNLguy (Reply 1):
IIRC, Hoot Gibson's 727-100 sure did during it's dive some years ago...

Hate to delve off topic here (and I've been trying to get an answer to this, but to no avail): This isn't the same Hoot Gibson that was a shuttle astronaut during the 1980's?

IIRC, the "Hoot" Gibson that OPNLguy is referencing was the one that is suspected of experimenting with in cruise slat deployment on a scheduled flight while the flight engineer was off in the can...the flight engineer fixed a few things (like pushed in circuit breakers which the captain and F/O had pulled) when he got back which sent the plane out of control...  Wow!
Celebrating the birth of KELPkidJR on August 5, 2009 :-)
 
SEPilot
Posts: 4919
Joined: Sat Dec 30, 2006 10:21 pm

RE: Are Airliners Capable Of Going Supersonic In Dive?

Thu Nov 20, 2008 11:23 pm



Quoting Vikkyvik (Reply 7):
Well, once you hit the stratosphere, the speed of sound will start going up again, as the temp rises with increasing altitude in the stratosphere.

But the increased temperature is more than counterbalanced by the decreased density. The speed of sound depends on both.
The problem with making things foolproof is that fools are so doggone ingenious...Dan Keebler
 
User avatar
Starlionblue
Posts: 17058
Joined: Fri Feb 27, 2004 9:54 pm

RE: Are Airliners Capable Of Going Supersonic In Dive?

Thu Nov 20, 2008 11:35 pm



Quoting A10WARTHOG (Reply 2):
Heard a rumor a Air China 747 did it.

IIRC this was the one with an engine that flamed out. During the subsequent dive it went supersonic. The pilots recovered the aircraft and landed it. It was missing quite a few parts. It was repaired and put back into service. I heard that it was never quite straight again.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
DeltaGuy
Posts: 3965
Joined: Wed Sep 12, 2001 5:25 am

RE: Are Airliners Capable Of Going Supersonic In Dive?

Fri Nov 21, 2008 12:14 am



Quoting Hypersonic (Thread starter):
& even the fastest biz jets can exceed 90% of the speed of sound in level flight

I know a few test pilots who have taken the G550 to about 1.02 or so. A plane with some huge engines and already high cruise speed can tend to do that.

DeltaGuy
"The cockpit, what is it?" "It's the little room in the front of the plane where the pilot sits, but that's not importan
 
SlamClick
Posts: 9576
Joined: Sun Nov 23, 2003 7:09 am

RE: Are Airliners Capable Of Going Supersonic In Dive?

Fri Nov 21, 2008 1:02 am

Some misconceptions above.

The simple answer is yes, but the trick is recovering from supersonic flight and not damaging anything on your way through the number and back again.

For most types:

It would not take any dramatic nosedive to do it. In fact if you pitched down, say ten degrees or so from cruise you might well end up in Mach tuck and probably not recover.

It would not take any ungodly amount of power. Fact is we are throttled well back to keep it under .8 Mach, or so.

Troposphere/Stratosphere - probably not going to make much difference. The strat starts nominally at 36200' in standard atmosphere. Higher toward the equator, lower toward the poles etc. Below that, temperature (which determines the speed of sound) increases roughly 2°C per thousand feet of altittude loss. In the stratosphere up to any altitude the current crop of A or B airliners is likely to see, the temperature is isothermal. Eventually it may start rising again but that is all so theoretical in our discussion.

The way to go supersonic and recover is pretty much exactly the way the DC-8 did it in flight testing. A moderate push-over to unweight the wings and accelerate in a shallow dive, leaving you not too far below the horizon when you start to rein it all back in.

Here's that story:
http://www.dc-8jet.com/0-dc8-sst-flight.htm

My wife and I had dinner with Paul Patten one night and I did not know at the time that he was the man behind this. Too bad. I'd like to have talked about it. In fact I'd much rather talk about it than actually do it!
Happiness is not seeing another trite Ste. Maarten photo all week long.
 
OPNLguy
Posts: 11191
Joined: Tue Jun 15, 1999 11:29 am

RE: Are Airliners Capable Of Going Supersonic In Dive?

Fri Nov 21, 2008 1:05 am



Quoting KELPkid (Reply 8):
Hate to delve off topic here (and I've been trying to get an answer to this, but to no avail): This isn't the same Hoot Gibson that was a shuttle astronaut during the 1980's?

IIRC, the "Hoot" Gibson that OPNLguy is referencing was the one that is suspected of experimenting with in cruise slat deployment on a scheduled flight while the flight engineer was off in the can...the flight engineer fixed a few things (like pushed in circuit breakers which the captain and F/O had pulled) when he got back which sent the plane out of control... Wow!

Yes, that's something I should have clarified rather than assume folks knew that there were two different Hoots. The one on the 727-100 dive was a TWA guy. The NASA/Shuttle guy was a SWA guy.

Quoting Starlionblue (Reply 10):
IIRC this was the one with an engine that flamed out. During the subsequent dive it went supersonic. The pilots recovered the aircraft and landed it. It was missing quite a few parts. It was repaired and put back into service. I heard that it was never quite straight again.

I saw some photos of the 747 after they landed, and I recall that the main landing gear doors (upon departing the airframe during the dive) also took out the outboard 4-5 feet of each horizontal stabilizer...
ALL views, opinions expressed are mine ONLY and are NOT representative of those shared by Southwest Airlines Co.
 
Viscount724
Posts: 18859
Joined: Thu Oct 12, 2006 7:32 pm

RE: Are Airliners Capable Of Going Supersonic In Dive?

Fri Nov 21, 2008 1:46 am

This is the Canadian Pacific DC-8-43 that went supersonic (Mach 1,012) in a dive from 52,000 ft. on a pre-delivery test flight in 1961. As a sidenote, in the 2nd photo it's carrying a spare R-R Conway in a 5th pod inboard of the #2 engine.


View Large View Medium
Click here for bigger photo!

Photo © Frank C. Duarte Jr.
View Large View Medium
Click here for bigger photo!

Photo © Gary Vincent

 
User avatar
Jetlagged
Posts: 2562
Joined: Sun Jan 23, 2005 3:00 pm

RE: Are Airliners Capable Of Going Supersonic In Dive?

Fri Nov 21, 2008 3:12 am



Quoting Starlionblue (Reply 10):
IIRC this was the one with an engine that flamed out. During the subsequent dive it went supersonic. The pilots recovered the aircraft and landed it. It was missing quite a few parts. It was repaired and put back into service. I heard that it was never quite straight again.

It was rumoured to have gone supersonic, but according to the incident report it didn't even exceed MMO. The engine had a bleed valve fault causing asymmetry, but didn't flame out.

The TWA 727-100, though it was in a vertical dive, peaked at about 0.96 Mach according to the NTSB report.

http://www.airdisaster.com/reports/ntsb/AAR81-08.pdf
The glass isn't half empty, or half full, it's twice as big as it needs to be.
 
Max Q
Posts: 5629
Joined: Wed May 09, 2001 12:40 pm

RE: Are Airliners Capable Of Going Supersonic In Dive?

Fri Nov 21, 2008 5:28 am

Well, MMO on all the 727's I flew (In the less restrictive 'A' mode) was .92 Mach, so .96 is a fairly significant exceedance.

Having said that, the 727, like the 747 and other Boeing aircraft has superb high Mach characteristics and I think an excursion above Mach One would not cause an irrecoverable pitch down.

It is important to remember at these high Mach, albeit subsonic numbers there is already significant supersonic flow over considerable parts of the aircraft.
The best contribution to safety is a competent Pilot.
 
tdscanuck
Posts: 8572
Joined: Wed Jan 11, 2006 7:25 am

RE: Are Airliners Capable Of Going Supersonic In Dive?

Fri Nov 21, 2008 5:51 am



Quoting Hypersonic (Thread starter):
Given that, if you were raking along.. then went full throttle, & put the aircraft into a steepish dive, would you most probably go supersonic & by how much?

Yep. But you won't get much over Mach 1 before something either fails or the drag gets so high that you stop accelerating.

Quoting SEPilot (Reply 9):
But the increased temperature is more than counterbalanced by the decreased density. The speed of sound depends on both.

No, it just depends on temperature. a = sqrt(gamma * R * T).

a = speed of sound
T = temperature (in K or F)
gamma = ratio of specific heats (1.4 for air at all but extreme temperatures)
R = gas constant

Tom.
 
SlamClick
Posts: 9576
Joined: Sun Nov 23, 2003 7:09 am

RE: Are Airliners Capable Of Going Supersonic In Dive?

Fri Nov 21, 2008 3:34 pm



Quoting Tdscanuck (Reply 17):
No, it just depends on temperature.

The simple version any pilot could use: The speed of sound is 39 times the square root of the air temperature in degrees Kelvin. No adujustment for "density" or "altitude" necessary.

Quoting Max Q (Reply 16):
.96 is a fairly significant exceedance

You sir are aptly yclept for this discussion.

M.96 is for sure something to approach with caution. Anything past MMO is test pilot-and-engineer country! For starters MachCRIT which is the point at which supersonic airflow will begin over some parts of the airplane is probably down around .74 or .75 so a 727 at .96 would be a crazy quilt of sub - and -super sonic air flow. You can have my share of it!
Happiness is not seeing another trite Ste. Maarten photo all week long.
 
User avatar
Jetlagged
Posts: 2562
Joined: Sun Jan 23, 2005 3:00 pm

RE: Are Airliners Capable Of Going Supersonic In Dive?

Fri Nov 21, 2008 3:36 pm



Quoting Max Q (Reply 16):
Well, MMO on all the 727's I flew (In the less restrictive 'A' mode) was .92 Mach, so .96 is a fairly significant exceedance.

Absolutely, but I felt it was important that urban myth was not posted as fact in Tech/Ops.
The glass isn't half empty, or half full, it's twice as big as it needs to be.
 
User avatar
Jetlagged
Posts: 2562
Joined: Sun Jan 23, 2005 3:00 pm

RE: Are Airliners Capable Of Going Supersonic In Dive?

Fri Nov 21, 2008 3:43 pm

Of course, Concorde was capable of going supersonic in a climb.  up 
The glass isn't half empty, or half full, it's twice as big as it needs to be.
 
typhaerion
Posts: 425
Joined: Tue Jun 14, 2005 11:27 pm

RE: Are Airliners Capable Of Going Supersonic In Dive?

Fri Nov 21, 2008 3:49 pm



Quoting Jetlagged (Reply 20):
Of course, Concorde was capable of going supersonic in a climb.

Just not when painted any other color than white.  biggrin 

If and when they figure out how to play with the Mach wave better to decrease its destructive potential and noise, there will be supersonic airliners again. It isnt the technology to get the aircraft up to speed and keep it there that is the probelm, it is dealing with the affects of the compression wave that we cant handle.

Personally, I believe I will see supersonic jetliners in my lifetime.
For some, the sky is the limit. For us, it is only the beginning... -- Jack Hunt
 
SEPilot
Posts: 4919
Joined: Sat Dec 30, 2006 10:21 pm

RE: Are Airliners Capable Of Going Supersonic In Dive?

Fri Nov 21, 2008 5:34 pm



Quoting SlamClick (Reply 12):
Here's that story:
http://www.dc-8jet.com/0-dc8-sst-fli...t.htm

There was distinctly some company propaganda in this article about the high speed characteristics of the DC-8. From what I have read the 707 flew faster and had better high speed handling; which is not surprising has Boeing had considerable jet experience with the B-47 and B-52 before the 707, and had their own high speed wind tunnel, while Douglas had to use the NACA tunnel. Besides, Boeing worked on the 367-80 for quite a while before Douglas committed to building the DC-8

Quoting Tdscanuck (Reply 17):
No, it just depends on temperature. a = sqrt(gamma * R * T).

I checked up on this and you are right. It turns out that density and pressure counteract each other, and so the only variable left is temperature.
The problem with making things foolproof is that fools are so doggone ingenious...Dan Keebler
 
SlamClick
Posts: 9576
Joined: Sun Nov 23, 2003 7:09 am

RE: Are Airliners Capable Of Going Supersonic In Dive?

Sat Nov 22, 2008 6:13 pm



Quoting SEPilot (Reply 22):
distinctly some company propaganda in this article

Well, it was written on Company time, on Company letterhead. I guess that should not surprise either of us.

Quoting SEPilot (Reply 22):
From what I have read the 707 flew faster

That is a statement that can have lots of meanings. I don't know much about either type but it certainly could be true for VMO and/or MMO and even higher cruise speeds in any corner of the charts, I don't know. I do know they occupied the same airspace system with a high degree of compatibility so I don't think the difference would have been too great. In absolute terms, however, the DC-8 did go faster. It was taken to a freestream mach number exceeding 1 and brought back, all intentionally and verified by an ubiased third party at Edwards AFB and the same is not true for the Boeing and that is that.

Quoting SEPilot (Reply 22):
had better high speed handling

Is that a quantifiable characteristic or someone's subjective observation?

Quoting SEPilot (Reply 22):
Boeing had considerable jet experience with the B-47 and B-52 before the 707, and had their own high speed wind tunnel, while Douglas had to use the NACA tunnel. Besides, Boeing worked on the 367-80 for quite a while before Douglas committed to building the DC-8

I wouldn't be too quick to dismiss Douglas' expertise in the area of high-speed flight:
World's fastest airplane for a time.


First airplane to exceed Mach 2 and thank you Scott Crossfield.


Okay, bad example. But if it had more powerful engines it might have set some records other than the highest liftoff speed (256 mph) and wickedest-looking design.
Happiness is not seeing another trite Ste. Maarten photo all week long.
 
OPNLguy
Posts: 11191
Joined: Tue Jun 15, 1999 11:29 am

RE: Are Airliners Capable Of Going Supersonic In Dive?

Sat Nov 22, 2008 7:23 pm



Quoting A10WARTHOG (Reply 2):
Heard a rumor a Air China 747 did it.



Quoting Starlionblue (Reply 10):
IIRC this was the one with an engine that flamed out. During the subsequent dive it went supersonic. The pilots recovered the aircraft and landed it. It was missing quite a few parts. It was repaired and put back into service. I heard that it was never quite straight again.



Quoting OPNLguy (Reply 13):
I saw some photos of the 747 after they landed, and I recall that the main landing gear doors (upon departing the airframe during the dive) also took out the outboard 4-5 feet of each horizontal stabilizer...

Yeek!

http://en.wikipedia.org/wiki/Image:D...ina_Airlines_Flight_006-N4522V.JPG
ALL views, opinions expressed are mine ONLY and are NOT representative of those shared by Southwest Airlines Co.
 
MarkC
Posts: 238
Joined: Tue Apr 25, 2006 8:10 am

RE: Are Airliners Capable Of Going Supersonic In Dive?

Sat Nov 22, 2008 7:30 pm

One thing I do not understand. If a DC8 can do it, why would an F15C not go into a shallow dive at full non-afterburner power, go through the mach all the way to say, mach 1.2, level out, and continue to supercruise? An F15C has much better power to weight at altitude than an aniliner, and it has no trouble coping with supersonic speeds.
 
User avatar
Jetlagged
Posts: 2562
Joined: Sun Jan 23, 2005 3:00 pm

RE: Are Airliners Capable Of Going Supersonic In Dive?

Sat Nov 22, 2008 8:04 pm



Quoting MarkC (Reply 25):
One thing I do not understand. If a DC8 can do it, why would an F15C not go into a shallow dive at full non-afterburner power, go through the mach all the way to say, mach 1.2, level out, and continue to supercruise? An F15C has much better power to weight at altitude than an aniliner, and it has no trouble coping with supersonic speeds.

Supercruise is about sustaining supersonic speed without afterburner, not passing Mach 1 without it. Concorde could supercruise across the Atlantic, but most military aircraft have less slippery aerodynamics and rely on brute force to achieve supersonic speed.
The glass isn't half empty, or half full, it's twice as big as it needs to be.
 
MarkC
Posts: 238
Joined: Tue Apr 25, 2006 8:10 am

RE: Are Airliners Capable Of Going Supersonic In Dive?

Sat Nov 22, 2008 10:34 pm

I mean, I don't know, but you are saying that the F15C could not sustain supersonic speed after reaching it in a dive under non afterburning power? Or that the F15C can not attain supersonic speed in a dive under non afterburning power?

Not calling you out. Just curious.
 
Northwest727
Posts: 379
Joined: Sat Jul 30, 2005 10:38 am

RE: Are Airliners Capable Of Going Supersonic In Dive?

Sat Nov 22, 2008 11:53 pm

I think the 747-400 prototype may have broken the sound barrier, or at least approached it. I recall reading about how its wings were severely buffeting during the dive.
 
DashTrash
Posts: 1266
Joined: Mon Aug 21, 2006 8:44 am

RE: Are Airliners Capable Of Going Supersonic In Dive?

Sun Nov 23, 2008 1:25 am



Quoting Max Q (Reply 16):
Well, MMO on all the 727's I flew (In the less restrictive 'A' mode) was .92 Mach

I thought the X was the only thing that went that fast without an ejection seat. I'm crushed.  Wink
 
tdscanuck
Posts: 8572
Joined: Wed Jan 11, 2006 7:25 am

RE: Are Airliners Capable Of Going Supersonic In Dive?

Sun Nov 23, 2008 3:15 am



Quoting MarkC (Reply 27):
I mean, I don't know, but you are saying that the F15C could not sustain supersonic speed after reaching it in a dive under non afterburning power? Or that the F15C can not attain supersonic speed in a dive under non afterburning power?

Fighters are, typically, aerodynamic messes. They're massively overpowered in order to have acceptable dogfight performance, so they can get away with a lousy L/D. Part of that is all the crap hanging from the underside of the wing and fuselage (drop tanks, armaments, pylons, etc.). They also have very low aspect ratios, so very high induced drag.

Tom.
 
Max Q
Posts: 5629
Joined: Wed May 09, 2001 12:40 pm

RE: Are Airliners Capable Of Going Supersonic In Dive?

Sun Nov 23, 2008 6:27 am

No, DashT, the 727 is a very fast aircraft, not a great climber but VMO was close to 400 knots and MMO .92 which I have done just for grins.

Of course, you could not cruise economically at these speeds, you would be 'pouring' the fuel out the back end, even at an 'economical' .8 cruise you would be burning around 10,000 pounds an hour (around the same as a 767)

Back when fuel was cheap though it was very common to cruise around at .86 - .88 mach.

Incidentally, I believe Boeing tested the 727 to .96 Mach with no problems.

More impressively, the 747 was tested to .99 Mach.
The best contribution to safety is a competent Pilot.
 
DashTrash
Posts: 1266
Joined: Mon Aug 21, 2006 8:44 am

RE: Are Airliners Capable Of Going Supersonic In Dive?

Sun Nov 23, 2008 10:45 am



Quoting Max Q (Reply 31):
No, DashT, the 727 is a very fast aircraft, not a great climber but VMO was close to 400 knots and MMO .92 which I have done just for grins.

The X is the same way. When it's light and cold, it climbs well. Heavy and warm, it's a pig until you find cooler air up high. It will haul once you level off though.

Quoting Max Q (Reply 31):
Incidentally, I believe Boeing tested the 727 to .96 Mach with no problems.

More impressively, the 747 was tested to .99 Mach.

The 74 is about the only thing we don't pass rapidly. Especially with all the fuel saving initiatives out there these days.
 
User avatar
Jetlagged
Posts: 2562
Joined: Sun Jan 23, 2005 3:00 pm

RE: Are Airliners Capable Of Going Supersonic In Dive?

Sun Nov 23, 2008 4:35 pm



Quoting MarkC (Reply 27):
I mean, I don't know, but you are saying that the F15C could not sustain supersonic speed after reaching it in a dive under non afterburning power? Or that the F15C can not attain supersonic speed in a dive under non afterburning power?

Not calling you out. Just curious.

The F-15 (C version or any other for that matter) could probably go supersonic in a dive without external stores, but it can't sustain it without afterburner. One of the key requirements for its replacement, the F-22, was that it could do so.
The glass isn't half empty, or half full, it's twice as big as it needs to be.
 
SEPilot
Posts: 4919
Joined: Sat Dec 30, 2006 10:21 pm

RE: Are Airliners Capable Of Going Supersonic In Dive?

Sun Nov 23, 2008 4:40 pm



Quoting SlamClick (Reply 23):
In absolute terms, however, the DC-8 did go faster.

It did in that one flight; all that I have read (including the stats for both on the aircraft data section) say that the 707 was faster. It has more wing sweep, for one thing, and with the aerodynamics of that era that was a pretty good indication of its maximum effective speed. The 707 never went supersonic because nobody ever did it; I suspect that it could have done exactly what the DC-8 did and probably do it a bit better. For that matter, to my knowledge nobody ever barrel rolled a DC-8. I can just as surely assert that the DC-8 is incapable of it.

Quoting SlamClick (Reply 23):

Is that a quantifiable characteristic or someone's subjective observation?

That was the assertion of pilots who had flown both types. In the early days Pan Am was the only airline that ordered both; they bought many, many more 707's but dumped the DC-8's as quickly as they could. The reason is that they did not perform as well as the 707's, and this was one of the factors.
The problem with making things foolproof is that fools are so doggone ingenious...Dan Keebler
 
A342
Posts: 4017
Joined: Sun Jul 31, 2005 11:05 pm

RE: Are Airliners Capable Of Going Supersonic In Dive?

Sun Nov 23, 2008 5:26 pm

While we're at it, what does the design dive speed of airliners say? It is higher than Mmo.
Exceptions confirm the rule.
 
tdscanuck
Posts: 8572
Joined: Wed Jan 11, 2006 7:25 am

RE: Are Airliners Capable Of Going Supersonic In Dive?

Sun Nov 23, 2008 7:05 pm



Quoting SEPilot (Reply 34):
For that matter, to my knowledge nobody ever barrel rolled a DC-8. I can just as surely assert that the DC-8 is incapable of it.

Why couldn't the DC-8 do it? It's a 1 g maneuver...with enough altitude it shouldn't have a problem.

Quoting A342 (Reply 35):
While we're at it, what does the design dive speed of airliners say? It is higher than Mmo.

I took a look at the AFM for a 747...it doesn't list Md, so I suspect that's not a certified number. The AFM maxes out at Mmo (0.92). I'm not sure if Md is a design value or a tested one.

Tom.
 
SlamClick
Posts: 9576
Joined: Sun Nov 23, 2003 7:09 am

RE: Are Airliners Capable Of Going Supersonic In Dive?

Sun Nov 23, 2008 7:35 pm



Quoting SEPilot (Reply 34):
in that one flight

You seem to be responding to something I never said or implied and using subjective hearsay in a technical discussion. I conceded that the 707 may have had a higher VMO and/or MMO and higher cruise speeds everywhere in the charts than the DC-8. I don't know. Apparently neither do you.

"Maximum speed" in a database prepared for laymen is completely useless as it rarely defines the conditions of the speed reading. As an engineer YOU should be the one making that argument. Instead you are dropping phrases like

Quoting SEPilot (Reply 22):
From what I have read

and

Quoting SEPilot (Reply 34):
all that I have read

and

Quoting SEPilot (Reply 34):
the aerodynamics of that era that was a pretty good indication of its maximum effective speed

and

Quoting SEPilot (Reply 34):
was the assertion of pilots who had flown both types

These are utterly and completely non-specific and therefore non-technical. In other words they are more at home in the civil aviation forum than this one. There are a limited number of ways one may define the top speed of an airplane such as these.

VMO or highest permissible indicated airspeed.
MMO or highest permissible indicated Mach number. (which should result in a greater absolute speed)

As an absolute, one might add the highest speed ever attained in controlled flight. It is in that number that the DC-8 outperformed the Boeing 707 for whatever reason. The comparison of the famous 707 roll is not particularly valid since the DC-8 supersonic flight was conducted as part of its certification flight testing for the purpose of gathering data where Johnston rolled the 707 as more or less a stunt and was invited never to repeat the maneuver.

As a practical matter one might take a look at cruise performance charts and find comparable values for MRC, HSC and LRC at weights and altitudes and ISA deviations that would result in numbers that are apples-to-apples comparable. I'm prepared to discover that in every value on such charts the 707 may have been "faster" than the DC-8. I don't know and, frankly, don't care enough to go out to my garage and dig up the manuals for each that I'm pretty sure I have.

The original post was about whether or not "airliners" are capable of "going supersonic" in a dive and my post about the DC-8 flight was in response to that question. Your post also seems intended to invalidate Douglas as a manufacturer of high-speed airplanes. In point of fact I can think of more high-speed Douglas models than I can Boeing. In fact, I cannot off the top of my head think of a single supersonic Boeing product that predates the McDonnell-Douglas acquisition. Perhaps "their own wind tunnel" wasn't as big a factor as it might have been. In any event here is a sampling of Douglas products that flew in the transsonic regime of .75 to 1.2









Some of these aircraft had significant production runs, modification histories and service lives. I just don't think one can safely imply any lack of technical expertise around the Long Beach shops.

I say these things from a point devoid of any prejudice. I have two Boeing type ratings and two Douglas type ratings. (and two Airbus type ratings) and I think both outfits built wonderful airplanes and the history and lore of flight are greatly enriched by products from both houses. Don't think of this as a salvo in an B vs D war, but an explanation for my post that you responded to.
Happiness is not seeing another trite Ste. Maarten photo all week long.
 
SEPilot
Posts: 4919
Joined: Sat Dec 30, 2006 10:21 pm

RE: Are Airliners Capable Of Going Supersonic In Dive?

Sun Nov 23, 2008 8:02 pm



Quoting Tdscanuck (Reply 36):

Why couldn't the DC-8 do it? It's a 1 g maneuver...with enough altitude it shouldn't have a problem.

That is my point; of course it could. Just because nobody on record has does not mean that it can't. Just the same as the 707 going supersonic.

Quoting SlamClick (Reply 37):
These are utterly and completely non-specific and therefore non-technical. In other words they are more at home in the civil aviation forum than this one. There are a limited number of ways one may define the top speed of an airplane such as these.

VMO or highest permissible indicated airspeed.
MMO or highest permissible indicated Mach number. (which should result in a greater absolute speed)

Well, I do not have firsthand experience or knowledge of transport category jet aircraft, as you do, but I have a lot of interest and have read just about everything I could get my hands on. Of course if I had precise engineering information I would happily give it, but I do not. But I have come to the conclusion, based on a number of different sources, that the high speed high altitude characteristics of the 707 were superior to the DC-8. You state that the DC-8 "proved" its supersonic ability in its flight tests; from what I have deduced this was just as much a "stunt" as the 707 barrel roll, albeit an officially sanctioned one. I suspect it was done because Douglas already knew that the 707 had better high speed characteristics, and were trying to steal some thunder. The tone of the report posted here confirms this in my opinion. But honestly, I am not trying to put down the DC-8; there is no question that it was a much more durable plane than the 707, and undoubtedly was at least its equal in most respects. They were both great planes, but saying that the 707 was a better high speed performer is a statement of my opinion based on a lot of diversified evidence. And while Douglas had built a number of high speed jet aircraft before the DC-8, they were all much smaller and not anything near the scope of a transport, while the B-47 and B-52 both were much better experience for building a jet transport. And in fact a number of Boeing engineers have gone on record as stating that having their own high speed wind tunnel and having the experience with the two bombers was absolutely invaluable in building the 707.
The problem with making things foolproof is that fools are so doggone ingenious...Dan Keebler
 
SlamClick
Posts: 9576
Joined: Sun Nov 23, 2003 7:09 am

RE: Are Airliners Capable Of Going Supersonic In Dive?

Sun Nov 23, 2008 8:27 pm



Quoting SEPilot (Reply 38):
You state that the DC-8 "proved" its supersonic ability

I don't think that is what I said at all. Perhaps you would like to copy and paste a direct quote from one of my four posts, above to explain what you mean.

Quoting SEPilot (Reply 38):
this was just as much a "stunt" as the 707 barrel roll

Insofar as each event involved a procedure well outside the normal operating regimes planned for customers of both types, they could both be called a stunt. However, it must be noted that in the case of the DC-8 supersonic excursion:

1. It was planned in advance by the company.
2. Predictions were made in advance, regarding the data to be gleaned.
3. Responsible agencies outside the flight test department were involved.
4. State-of-the-art equipment was used by an outside agency to verify results.
5. The crew was not reprimanded for deviating from a test profile.
6. Data gathered was used by the company for further analysis.

None of those things can be said about the 707 roll.

Quoting SEPilot (Reply 38):
the 707 was a better high speed performer is a statement of my opinion

As a statement of your opinion, I have no quarrel with this at all. It is this...

Quoting SEPilot (Reply 22):
the 707 flew faster

...which has the applearance of an incorrect declarative statement that I am responding to. In absolute terms, the 707 did not "fly faster" than the DC-8, in that the DC-8 was taken under full control, to a Mach number exceeding 1, and recovered. The same is not true for the 707.

Quoting SEPilot (Reply 38):
a number of Boeing engineers have gone on record as stating that having their own high speed wind tunnel and having the experience with the two bombers was absolutely invaluable in building the 707

And unlike the report from Douglas their declarations are completely unbiased?

Do you think these engineers are stating an opinion that Douglas' data was invalid because they didn't actually own their wind tunnel? It might, indeed be more convenient to drive down the street to the wind tunnel but the data is the data, no matter where one must go to obtain it.

BTW, to your knowledge did Boeing have a transsonic wind tunnel at that time?
Happiness is not seeing another trite Ste. Maarten photo all week long.
 
A342
Posts: 4017
Joined: Sun Jul 31, 2005 11:05 pm

RE: Are Airliners Capable Of Going Supersonic In Dive?

Sun Nov 23, 2008 9:10 pm



Quoting Tdscanuck (Reply 36):
I took a look at the AFM for a 747...it doesn't list Md, so I suspect that's not a certified number. The AFM maxes out at Mmo (0.92). I'm not sure if Md is a design value or a tested one.

Have a look at the A330 TCDS (page 12):

http://rgl.faa.gov/Regulatory_and_Gu...c986257504005a9026/$FILE/A46NM.pdf

"Maximum Operating Limit Speed/Mach, VMO/MMO 330 KIAS / .86
Design Diving Speed, VD 365 KIAS / .93"
Exceptions confirm the rule.
 
tdscanuck
Posts: 8572
Joined: Wed Jan 11, 2006 7:25 am

RE: Are Airliners Capable Of Going Supersonic In Dive?

Sun Nov 23, 2008 10:50 pm



Quoting SlamClick (Reply 37):

VMO or highest permissible indicated airspeed.
MMO or highest permissible indicated Mach number. (which should result in a greater absolute speed)

I think that's reversed. Vmo and Mmo meet at the transition altitude and, from there up, constant Mach number is decreasing absolute speed (since the speed of sound is dropping due to the temperature drop). So the largest absolute speed at Mmo is right at the point when Mmo = Vmo.

Quoting A342 (Reply 40):
Have a look at the A330 TCDS (page 12):

http://rgl.faa.gov/Regulatory_and_Gu...c986257504005a9026/$FILE/A46NM.pdf

"Maximum Operating Limit Speed/Mach, VMO/MMO 330 KIAS / .86
Design Diving Speed, VD 365 KIAS / .93"

That's funky. The 747 TCDS lists Vmo/Mmo only, then refers to the AFM for all other speeds, and I couldn't find Vd/Md in the AFM...maybe I just looked in the wrong place. If somebody finds it, please let me know!

Tom.
 
OldAeroGuy
Posts: 3185
Joined: Sun Dec 05, 2004 6:50 am

RE: Are Airliners Capable Of Going Supersonic In Dive?

Mon Nov 24, 2008 4:27 am



Quoting Tdscanuck (Reply 36):
I took a look at the AFM for a 747...it doesn't list Md, so I suspect that's not a certified number. The AFM maxes out at Mmo (0.92). I'm not sure if Md is a design value or a tested one.

Vd/Md are certified numbers.

See FAR 25.335 for the relationship between Vmo/Mmo and Vd/Md.

In the past, Vd/Md were demonstrated numbers. With today's simulators/FBW systems, Vd/Md can be determined by analysis and/or FBW programming.
Airplane design is easy, the difficulty is getting them to fly - Barnes Wallis
 
Viscount724
Posts: 18859
Joined: Thu Oct 12, 2006 7:32 pm

RE: Are Airliners Capable Of Going Supersonic In Dive?

Tue Nov 25, 2008 3:40 am



Quoting SEPilot (Reply 34):
In the early days Pan Am was the only airline that ordered both; they bought many, many more 707's but dumped the DC-8's as quickly as they could. The reason is that they did not perform as well as the 707's, and this was one of the factors.

I expect part of the reason for Pan Am ordering both the 707 and DC-8 initially was that both aircraft existed only on paper at the time (apart from the Dash 80 prototype). There was probably an element of "insurance" in case one of the projects was cancelled.

Another reason for selling the DC-8s was no doubt benefit from synergies and possibly preferential pricing from Boeing since by the time the DC-8s were sold in the late 1960s Pan Am had already taken delivery of their first 25 727s and had become the launch customer for the 747.
 
SEPilot
Posts: 4919
Joined: Sat Dec 30, 2006 10:21 pm

RE: Are Airliners Capable Of Going Supersonic In Dive?

Tue Nov 25, 2008 12:12 pm



Quoting SlamClick (Reply 39):
1. It was planned in advance by the company.
2. Predictions were made in advance, regarding the data to be gleaned.
3. Responsible agencies outside the flight test department were involved.
4. State-of-the-art equipment was used by an outside agency to verify results.
5. The crew was not reprimanded for deviating from a test profile.
6. Data gathered was used by the company for further analysis.

None of those things can be said about the 707 roll.

Quite true; however it does not change my opinion that the "supersonic excursion" was no less a stunt than the barrel roll. A whole company can collaborate on a stunt, as is the case here, or it can be done by one individual, as was the case with the barrel roll. Note that no other airliner has done a supersonic excursion as part of its flight tests; this reinforces my opinion that the data gained from it was of negligible importance and reinforces my belief that it was a stunt.

Quoting SlamClick (Reply 39):

As a statement of your opinion, I have no quarrel with this at all. It is this...

Quoting SEPilot (Reply 22):
the 707 flew faster

I will concede that this was poorly worded. What I meant to say was that in normal operations the 707 was faster. I have no firsthand knowledge of this; my conclusion comes from my reading.

Quoting SlamClick (Reply 39):
And unlike the report from Douglas their declarations are completely unbiased?

Of course! Big grin But in fact those statements I referred to were made long after the event, and mostly after the individuals involved had retired, and were not official company statements, as was the report about the DC-8 supersonic excursion. Therefore I believe they have a greater chance of being impartial.

Quoting SlamClick (Reply 39):

Do you think these engineers are stating an opinion that Douglas' data was invalid because they didn't actually own their wind tunnel? It might, indeed be more convenient to drive down the street to the wind tunnel but the data is the data, no matter where one must go to obtain it.

BTW, to your knowledge did Boeing have a transsonic wind tunnel at that time?

Yes, Boeing had their own transonic tunnel; it was built during the war. This was a particularly far sighted move by Boeing, as they had all kinds of money during the war and figured that when it ended things might be difficult, and they also foresaw that speeds were likely to increase in the future (they probably were aware of Whipple's jet, if not of the German jet program.) So they decided to get a jump on the future and build their own transsonic tunnel; the engineer in charge of it was William Cook, who wrote "The Road to the 707", which is an excellent account of the 707's development. The point I was making was not that the Douglas engineers' data was invalid, but they had a much harder time getting their data because they had to schedule time well in advance on the NACA tunnel, and were competing for time with a lot of other companies, while Boeing engineers could just go down the hall, so to speak, and were able to do tests on short notice, as the 707 program was top priority at the time. Under these circumstances I would expect, but it is not a guarantee, that the Boeing engineers would be able to more thoroughly explore the high speed aerodynamics of their plane, and refine them further. Add to that that the Douglas engineers were playing catch up, as the 707 had a huge head start.

Quoting Viscount724 (Reply 43):
I expect part of the reason for Pan Am ordering both the 707 and DC-8 initially was that both aircraft existed only on paper at the time (apart from the Dash 80 prototype). There was probably an element of "insurance" in case one of the projects was cancelled.

Another reason for selling the DC-8s was no doubt benefit from synergies and possibly preferential pricing from Boeing since by the time the DC-8s were sold in the late 1960s Pan Am had already taken delivery of their first 25 727s and had become the launch customer for the 747.

Juan Trippe was a very shrewd operator, and he wanted to be on top of the game no matter who built his airplanes. He led both Douglas and Boeing to believe that they had an exclusive contract; when they were both announced on the same day Boeing and Douglas were both shocked. You are probably correct in your assessment of the reason, but there was more to it than that. Douglas had proved to be a provider of top quality and excellent performing aircraft, while the only recent aircraft Boeing had built was the Stratocruiser, which, while being the fastest, highest flying, and longest range plane of its time, proved to be a mechanic's (and sometimes a pilot's) worst nightmare. It certainly amassed one of the all-time worst safety records, with 13 out of 56 crashing. So I believe that Trippe's thinking was more along the lines of not fully trusting Boeing's promises and wanting a backup rather than an evenhanded covering of all possible outcomes. The fact he ordered 25 DC-8's and only 20 707's speaks to this. So I believe that he was biased towards the DC-8 from the beginning, and the fact that he settled on the 707 quite early in the game speaks volumes. And while the last DC-8 left Pan Am's fleet in 1969 the process had started much earlier; they only took delivery of 19 of the 25 originally ordered and one at least left the fleet in 1962 (which had been delivered in 1961.) It was very clear that Pan Am decisively preferred the 707.
The problem with making things foolproof is that fools are so doggone ingenious...Dan Keebler
 
SXDFC
Posts: 1657
Joined: Sun Dec 09, 2007 6:07 pm

RE: Are Airliners Capable Of Going Supersonic In Dive?

Wed Nov 26, 2008 3:30 am

When I saw this topic, I could not help but think of UA 175, when it was on its collision course on 9-11, wasn't that plane passing the "red line" on the 76? So pretty much that can mean close to supersonic speeds right?
ALL views, opinions expressed are mine ONLY and are NOT representative of those shared by Southwest Airlines Co.
 
tdscanuck
Posts: 8572
Joined: Wed Jan 11, 2006 7:25 am

RE: Are Airliners Capable Of Going Supersonic In Dive?

Wed Nov 26, 2008 6:08 am



Quoting SXDFC (Reply 45):
When I saw this topic, I could not help but think of UA 175, when it was on its collision course on 9-11, wasn't that plane passing the "red line" on the 76? So pretty much that can mean close to supersonic speeds right?

At those altitudes, you'd be speed limited, not Mach limited. You'd run out of speed before you went supersonic.

Tom.
 
User avatar
Starlionblue
Posts: 17058
Joined: Fri Feb 27, 2004 9:54 pm

RE: Are Airliners Capable Of Going Supersonic In Dive?

Wed Nov 26, 2008 10:44 am



Quoting Tdscanuck (Reply 46):

Quoting SXDFC (Reply 45):
When I saw this topic, I could not help but think of UA 175, when it was on its collision course on 9-11, wasn't that plane passing the "red line" on the 76? So pretty much that can mean close to supersonic speeds right?

At those altitudes, you'd be speed limited, not Mach limited. You'd run out of speed before you went supersonic.

Indeedy. IIRC they were flying fast enough to potentially damage the aircraft, but nowhere near the speed of sound.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
Viscount724
Posts: 18859
Joined: Thu Oct 12, 2006 7:32 pm

RE: Are Airliners Capable Of Going Supersonic In Dive?

Wed Nov 26, 2008 8:28 pm



Quoting SEPilot (Reply 44):
And while the last DC-8 left Pan Am's fleet in 1969 the process had started much earlier; they only took delivery of 19 of the 25 originally ordered

Of the 25 DC-8s ordered by Pan Am I believe 4 were assigned to Panagra and 2 to Panair do Brasil, then both partly-owned by Pan Am (50% in the case of Panagra). Panair do Brasil was then the longhaul international carrier in Brazil, forced to suspend service in 1965 by the new military dictatorship and their route authorities were transferred to Varig.
 
SEPilot
Posts: 4919
Joined: Sat Dec 30, 2006 10:21 pm

RE: Are Airliners Capable Of Going Supersonic In Dive?

Thu Nov 27, 2008 3:22 pm



Quoting Viscount724 (Reply 48):
Of the 25 DC-8s ordered by Pan Am I believe 4 were assigned to Panagra and 2 to Panair do Brasil, then both partly-owned by Pan Am (50% in the case of Panagra).

That makes sense; and the one I referred to earlier that left the fleet in 1962 went to one of those (I forgot which.) But the bottom line of it was that Pan Am didn't want them, but they couldn't just dump them because of the huge amount of money involved. I suspect that Juan Trippe also did not want them to go to a rival carrier; at that time there was more demand for jetliners than there was supply, but Trippe was still a shrewd businessman and didn't want to help any of his rivals.
The problem with making things foolproof is that fools are so doggone ingenious...Dan Keebler

Who is online

Users browsing this forum: No registered users and 14 guests