How STRONG is a 757 ?

[Desert185]

doubleu-anker

"Ah the DC 8. They don't make planes like that anymore!"

As much as I like Boeing stuff, the 8 is my favorite. When the US guvmint gets their act together, checkout www.nasa.gov/dc-8. It will probably be the only DC-8 flying in the US sometime next year, and it is really more of a flying science lab than an airliner. Great history, too. Alitalia and Braniff as a -62, then the last Cammacorp kit converting it to a -72 with NASA.

[Smilin_Ed]

DC-8s are Tough

As for going supersonic, they were probably lucky to have got away with it.

About four decades ago I monitored a contract with Douglas to provide aircraft for a project which they fulfilled with B-47 airframes. As the B-47s became unsupportable due to age, we asked Douglas to propose replacement airframes. They proposed used DC-8s. When we asked them to assure us of the structural integrity of the nominated planes they removed the wings from one and subjected the spar and other structural elements to detailed metallurgical analysis. The result: They could not detect that the plane had ever been flown. We accepted the planes as adequate for our purposes.

[DozyWannabe]

Originally Posted by tdracer

I saw flight test data from the 747-8 flutter testing at Mach 0.98 to 0.99.

Really plays havoc with some of the sensors.....

That's when you need some diesel oil and lamp black:
http://www.pprune.org/tech-log/42690...ml#post5937737

Originally Posted by KRviator

Didn't that China Airlines 747SP get close to, or exceed, Mach 1 during its upset, they just didn't have the DFDR data to prove it?

Iv'e got a book somewhere that claims they probably exceeded the speed of sound but the flight recorder wasn't working during the periods it would have - convenient?

They wouldn't have had a DFDR on a 747SP of that vintage, and the lateral loads generated during the spiral dive would likely have rendered the airspeed data somewhat suspect. Said lateral loads would have had far more to contribute to the damage than exceeding Mach 1.

@Desert185/Smilin' Ed : While I'm sure the Diesel 8 was tough, I suspect that the VC-10 and Trident were tougher. The Achilles' heel of Douglas designs was that ergonomically and technologically they were somewhat behind the competition.

[tdracer]

They wouldn't have had a DFDR on a 747SP of that vintage, and the lateral loads generated during the spiral dive would likely have rendered the airspeed data somewhat suspect. Said lateral loads would have had far more to contribute to the damage than exceeding Mach 1.

My understanding of that event was that most of the damage was done by the high g's they pulled when they pulled out of the dive.

Speed indications on any subsonic airplane that goes 'supersonic' would be highly suspect - shocks form around the airspeed probes and as I noted, can really cause havoc with some of the readings. During flight test we have special, dedicated instrumentation to measure things like static and total pressures to very high accuracy - something we wouldn't worry about on an airplane that's never supposed to exceed Mach 0.90

[DozyWannabe]

Originally Posted by tdracer

My understanding of that event was that most of the damage was done by the high g's they pulled when they pulled out of the dive.

Entirely plausible, and not inconsistent with what I was suggesting!

[Desert185]

DozyWannabe

"The Achilles' heel of Douglas designs was that ergonomically and technologically they were somewhat behind the competition."

We're talking a 1958 design. You don't fly, right?

[doubleu-anker]

I opened the NSA website and got this:

"Due to the lapse in federal government funding, this website is not available.
We sincerely regret this inconvenience."

[Desert185]

"When the US guvmint gets their act together..."

NASA, not NSA, BTW.

[DozyWannabe]

Originally Posted by Desert185

"The Achilles' heel of Douglas designs was that ergonomically and technologically they were somewhat behind the competition."

We're talking a 1958 design. You don't fly, right?

I was just stating an opinion drawn from what I know. I'm aware a lot of pilots - especially those of the old school - tend to have a lot of love for Douglas, but from an engineering perspective their designs erred towards the conservative, even by 1958 standards. Perhaps the two factors are related!

[Desert185]

DozyWannabe

I'm aware a lot of pilots - especially those of the old school - tend to have a lot of love for Douglas, but from an engineering perspective their designs erred towards the conservative, even by 1958 standards.

Not to be argumentative, but from a pilot's standpoint the rock solid DC-8 has no airframe life restriction, it will fly without hydraulics (automatic manual reversion), and from a science platform standpoint it will fly 12.5 hours with ~4.0 hours of that being at 1500' AGL/MSL, plus reserves. It will also slow to low speed buffet at optimum altitude or above and then accelerate back to M.80 (sometimes a science requirement).

What also might be interesting for some who don't know about the DC-8, it will dump fuel without electrics, as long as there is gravity, that is.

From a freighter standpoint the -73 delivers what the 707 could only promise. BTW...fly through weather nasty enough to block the pitot tubes? The autopilot doesn't trip off. Only zero airspeed indication for awhile. If anything, the Achilles' heel is that it has no wheelwell fire detection.

Frankly, from an engineering and performance perspective, with four-engine redundancy, there is no better science platform, particularly for surveying the ice low level over Antarctica four plus hours from the nearest airport in South America with 35 scientists and crew onboard. Not bad for a 1958 design. Of course, I'm an admittedly biased pilot who greatly appreciates what the airplane provides and not an engineer. Its an airplane that asks you to be a pilot and gives honest, real-time feedback about your attempts toward that end. Maybe that's what I appreciate about the old-school machine. And remember that it did go supersonic without any structural issues realized. From a pilot's standpoint, all of the above is the kind of conservative, common sense engineering I like.

Apologies for the off-topic, but aircraft robustness and capability is somewhat relevant to the discussion.

[A30yoyo]

My understanding was that Douglas originally selected an aerofoil section for the DC-8 which was too draggy and had to do some leading edge modifications to restore projected performance (the Supersonic dive may have been a planned publicity move related to the mods?) There were more mods to the wings and engine pods/pylons in the -62/-63 models
Early in the 707s career Pan Am had one go into a dive over the Atlantic which may have passed Mach 1 before recovery around 6,000 ft

DC-8 youtubes

You Tube

You Tube

[yrvld]

B737-700

A little thread drift, still about a Boeing though..
I think it has been covered here some years ago, in the meantime the investigation is published:

http://www.aaib.gov.uk/cms_resources...JK%2009-10.pdf

B737-700 @ 447Kts somewhere btw FL100 and 5000 feet, on a manual reversion, company test flight.

The report states:

" He then rolled the wings level and attempted to arrest the rate of descent. This had peaked at 20,000 ft/min with the aircraft pitched 30° nose-down after the aircraft had been rolled to the left. The control forces remained high but the commander considered this to be due to the aircraft’s speed, which he observed at a maximum of 447 kt."

And then:

"The aircraft was inspected after landing for damage or deformation in accordance with AMM task 05-51-04 titled ‘severe or unusual turbulence, stall, or speeds more than design limits – maintenance practices (conditional inspection)’. No evidence of damage or deformation of the structure was found."

Makes for interesting reading.

[frieghtdog2000]

DozyWannabe - VC10 White Waltham

At the 50 year reunion of the VC10 at Brooklands a continuous loop video of this flypast was shown (Capt Tony Smith in Command). Included all the grass cuttings getting airborne as they had manicured the aerodrome previously. Awesome. Wouldn't happen to-day.

[jimjim1]

double amplitude

cockney steve mentioned

Either side of neutral? IE 21.3 * left and the same right, total oscillation excursion =42.6 ?

Ah! So 21.3 degrees half amplitude then. Now I understand. But not the terminology:-)

[bubbers44]

I trusted the B757 more than any other of 8 jets I flew. It had performance, systems were simple, automation was good, you could hand fly it easily and it looked like if you ever had to ditch it it looked like a pontoon boat. If I ditched in the Carribean it looked like it would float for days. Just fire up the APU and wait for the rescue boat. It was just lacking fishing poles and lures.
It would fly with almost everything inop.

[bubbers44]

Flying it into TGU over 600 times with not one problem made me a believer in the B757. Doing it in the B727 as I did was marginal. I loved that airplane. The FA's didn't because of the single isle but we loved it. You had to be really stupid to hurt yourself in the 757. Cali was an example of that. Cali was an easy airport to land at but they screwed up.

I don't want to say anything bad about them but I was flying that night and landing at Panama City and there was no moon so they could not see their error turning east into the hills. The R they pushed sent them to Bogota, not Cali. Neither pilot was aware of the error in navigation. Unfortunately there was a mountain there.

[con-pilot]

Flying it into TGU over 600 times with not one problem made me a believer in the B757. Doing it in the B727 as I did was marginal.

I presume that you were flying -200s? We only flew the -100s there and we always came out empty, except for the cabin guards, less than 20 folks. So we never had a problem.

I could see where you would be marginal with a max load for conditions in a 200.

Always wanted to fly a 757 and at one time it looked like we would get a long range version of the 757, but had an Administration change* and that idea was killed.



* No ideas from a previous Administration is a good idea for the new Administration in Washington when a different Party takes over. Sometimes even when it is the same party.

[er340790]

Didn't that China Airlines 747SP get close to, or exceed, Mach 1 during its upset, they just didn't have the DFDR data to prove it?

Yup... and it never flew straight thereafter ever again.

It pitched up in CYQT a few years ago, fleeing creditors apparently, as a huge Biz-Jet entitled Global Peace Ambassadors, and sat on the apron for months. Then it disappeared suddenly and flew right across the US under VFR (honest!) to somewhere in Mexico for overhaul.

Interesting.

[DaveReidUK]

It pitched up in CYQT a few years ago, fleeing creditors apparently, as a huge Biz-Jet entitled Global Peace Ambassadors, and sat on the apron for months. Then it disappeared suddenly and flew right across the US under VFR (honest!) to somewhere in Mexico for overhaul.

Tijuana, it's still there:

[captplaystation]

yrvld,

scarily gash . . . . . of course, we "British" are best

So many deviations/omissions /general misconceptions that it beggars belief, I can only assume the Commander was selected courtesy of his "hand-shake" rather than his inherent piloting/technical abilities.

Very "easy" / Very "British".