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Airliners Strength  
User currently offlineGc From United Kingdom, joined Feb 2003, 356 posts, RR: 6
Posted (11 years 9 months 4 weeks 5 hours ago) and read 2627 times:

Sorry if this is a basic question but I've always wondered, whilst sitting in a bit of chop on an airliner, how much stress can it take. Not just in turbulence but what kind of rolls and maneuvers can, say a 737, up to a 777 do? Are they really just designed to withstand level flight and minimal turns?

17 replies: All unread, jump to last
 
User currently offlineJhooper From United States of America, joined Dec 2001, 6206 posts, RR: 12
Reply 1, posted (11 years 9 months 4 weeks 5 hours ago) and read 2613 times:

They are designed to withstand FAR greater stresses than they would normally encounter. I think they did a test where they bent the wings of the 727 45 degrees up before it finally snapped.


Last year 1,944 New Yorkers saw something and said something.
User currently offlineEssentialpowr From United States of America, joined Sep 2000, 1820 posts, RR: 2
Reply 2, posted (11 years 9 months 4 weeks 4 hours ago) and read 2591 times:

It should be fairly easy to find the g specification for transport category a/c from numerous sources...but +2.5, -1 g come to mind as nominal figures. On top of that, a safety factor is multiplied in (as in a bridge, building or other structure) of around 2.5, which puts the nominal working load at about +6.25gs and -2.5gs, in which the structure should still not sustain any structural damage (all though things like wing rivets could fail.)

The ultimate failure load for significant structure is probably another factor of 3 or so beyond that, so now we're at +18.75g and -7.5g. The classic wing deflection tests occur in which the spar breaks. I believe an "ultimate" load demo must be done for any part 121 a/c to be certified...


User currently offlineBoeing nut From , joined Dec 1969, posts, RR:
Reply 3, posted (11 years 9 months 3 weeks 5 days 22 hours ago) and read 2492 times:

There is a good story on the 777 during it's certification stage when they do the ultimate static test to a 777. I beleive the numbers are that the wing must sustain 150% of MTOW without failing. It a very dramatic to watch. But the engineers were awesome in that they were only 1% off in thier calculations of the percentage of the wing when it would fail. They predicted the wing wuold fail at 153%, it actually failed at 154%. When a wing fails during these tests it makes one hell of a bang.

User currently offlineIkarus From United Kingdom, joined Jan 2001, 3524 posts, RR: 2
Reply 4, posted (11 years 9 months 3 weeks 5 days 15 hours ago) and read 2443 times:

OK, check out JAR 25 (on www.jaa.nl, click on JARs, JAR 25) p. 30 onwards)

p.33:
Positive load factor at any speed must be between 2.5 and 3.8, negative load factor must not be less than -1.0 (oh dear, that's a bad phrasing! They should phrase it as "the absolute value of the negative load factor must no be less than 1, IMO)

So Essentialpower is right. Except, I cannot confirm the safety factors (2.5 sounds rather generous to me, I'd have thought 1.5 would be the maximum safety factor in aviation, otherwise the structural weight gets excessive). To be honest, I have strong doubts that any airliner could withstand 18 or -7g without complete structural failure (my guess would have been structural damage at loads above 3.75g or below -1.5g, and failure arounf +7g or -3g). Perhaps someone could confirm these values from flight manuals etc? Perhaps the quoted ones are GA values, not civil airliner ones?

Regards

Ikarus


User currently offlineB747skipper From , joined Dec 1969, posts, RR:
Reply 5, posted (11 years 9 months 3 weeks 5 days 15 hours ago) and read 2454 times:

Well, Ikarus, cannot recall, goes back too many years, but since my flight manual says 2.5 g flaps up (2.0 g flaps down), if I remember well, values 50% over these are assumed in the design structural integrity, that would be 2.5 + 1.25 = 3.75 g... Correct, higher values can be sustained, but not in FAR/JAR 25 transport aircraft... acrobatic planes, I believe, go to 6 g for certification as "fully acrobatic".
xxx
(s) Skipper  Smile


User currently offlineGc From United Kingdom, joined Feb 2003, 356 posts, RR: 6
Reply 6, posted (11 years 9 months 3 weeks 5 days 3 hours ago) and read 2383 times:

Thanks for the answers so far. Question for pilots though, what is the most "aerobatic" manouver you've done in a heavy jet?

User currently offlineBrons2 From United States of America, joined Sep 2001, 3017 posts, RR: 4
Reply 7, posted (11 years 9 months 3 weeks 5 days 2 hours ago) and read 2368 times:

Tex Johnston of Boeing did a roll in the 707 prototype, the 367-80. AKA the "dash 80".

I don't think todays airliners could probably take that kind of stress though. They don't make them heavy like they used to.



Firings, if well done, are good for employee morale.
User currently offlinePositive rate From Australia, joined Sep 2001, 2143 posts, RR: 1
Reply 8, posted (11 years 9 months 3 weeks 4 days 21 hours ago) and read 2349 times:

A China Airlines 747SP on a flight from Taipei-LAX in 1985 pulled an incredible +5G and several neagtive G also!!! The 747SP is only rated to +2.5G and -1.0G, luckily though Boeing built in a large safety margin because the aircraft did not break up. The 747 even exceeded it's limiting Mach number of .92 and actually went Supersonic for a short period whilst in a dive!!! Talk about a strong airplane.

User currently offlineDalmd88 From United States of America, joined Jul 2000, 2614 posts, RR: 14
Reply 9, posted (11 years 9 months 3 weeks 4 days 11 hours ago) and read 2319 times:

"Tex Johnston of Boeing did a roll in the 707 prototype, the 367-80. AKA the "dash 80".

I don't think todays airliners could probably take that kind of stress though. They don't make them heavy like they used to."

I believe if done properly this only a one g maneuver. Any jet liner should be able to do it.


User currently offlineAirplay From , joined Dec 1969, posts, RR:
Reply 10, posted (11 years 9 months 3 weeks 4 days 4 hours ago) and read 2291 times:

FAR 121 contains operating rules not design and construction standards. You need to consult FAR 25 for transport category aircraft load factors.

FAR 25.303 states:

[Unless otherwise specified, a factor of safety of 1.5 must be applied to the prescribed limit load which are considered external loads on the structure. When a loading condition is prescribed in terms of ultimate loads, a factor of safety need not be applied unless otherwise specified.]

FAR 25.333 provides a information on the "maneuvering envelope". There are various other FAR 25 standards in the "300" series that involve the calculation of flight and gust loads.

In addition there are loads specified for emergency landing conditions contained in FAR 25.561 and 25.562. The latest amendment requires that seats handle up to 16 Gs while making such an impact survivable. Also that the following loads won't destroy the airplane to a point where an occupant can't get out:

(i) Upward, 3.0g.
(ii) Forward, 9.0g.
(iii) Sideward, 3.0g on the airframe; and 4.0g on the seats and their attachments.
(iv) Downward, 6.0g.
(v) Rearward, 1.5g.


So, it's not exactly a black and white answer.







User currently offlineAloges From Germany, joined Jan 2006, 8763 posts, RR: 42
Reply 11, posted (11 years 9 months 3 weeks 4 days 1 hour ago) and read 2266 times:

Positive rate, here it is::D

http://www.ntsb.gov/ntsb/brief.asp?ev_id=20001214X35672&key=1

WHILE ABV A CLOUD LAYER (TOP AT FL 370) NR THE JET STREAM, AUTOPLT WAS ENGAGED & WAS AT Macedonian Airlines (Greece)">IN THE PERFORMANCE MNGMNT SYS (PMS)MODE. THE PMS PROVIDED PITCH GUIDANCE TO HOLD FL 410, ROLL GUIDANCE TO AILERONS & SPOILERS FOR ROLL CTL & AUTOTHROTTLE TO MAINT .85 MACH (254 KIAS). ACFT ENCOUNTERED CLR AIR TURBC & AIRSPEED BGN TO VARY BTN .84 & .88 MACH. PMS BGN MOVING THROTTLES FORE & AFT TO HOLD .85 MACH. DRG AUTOTHROTTLE ADJUSTMENTS, #4 ENG THRUST DECREASED & 'HUNG' AT APRX 1.0 EPR & AIRSPEED BGN DECREASING. FLT ENGINEER ATMTD TO MANUALLY RCVR THE #4 ENG THRUST, BUT DID NOT CLOSE THE BLEED AIR VLV BFR ADJUSTING THE #4 THROTTLE. THE #4 ENG REMAINED AT APRX 1.0 EPR. AS THE ACFT SLOWED, AUTOPLT TRIMMED TO HOLD ALT & HDG TIL THE PLT DISENGAGED IT. AT THAT TIME, ACFT ROLLED/YAWED RGT & ENTERED AN UNCTLD DSCNT INTO THE CLOUDS. AS IT BROKE OUT OF THE CLOUDS AT 11,000', CREW RCVRD & LVLD AT 9500'. DRG DSCNT/RCVRY, ACFT WAS DMGD BY ACCELLERATION FORCES & HI SPEED. THERE WAS EVIDENCE THE PLT WAS PREOCCUPIED WITH ENG PRBLM, DIDN'T MONITOR INSTRUMENTS & OVER-RELIED ON AUTOPLT.



Walk together, talk together all ye peoples of the earth. Then, and only then, shall ye have peace.
User currently offlineArsenal@LHR From United Kingdom, joined Mar 2001, 7792 posts, RR: 19
Reply 12, posted (11 years 9 months 3 weeks 4 days ago) and read 2254 times:
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You'd be amazed how strong an airliner really is, especially the 777. The 777 wings are heavy duty and extremely solid, designed to withstand forces that are far greater than anything it would encounter in normal service. When testing the 777, Boeing engineers literally "bent" both 777 wings until they were in a semi-circular "U" shape!.

Arsenal@LHR



In Arsene we trust!!
User currently offlineBellerophon From United Kingdom, joined May 2002, 585 posts, RR: 59
Reply 13, posted (11 years 9 months 3 weeks 3 days 22 hours ago) and read 2258 times:

Brons2

Tex Johnston of Boeing did a roll in the 707 prototype…I don't think todays airliners could probably take that kind of stress though.

The manoeuvre that A M (Tex) Johnston, then Chief of Boeing Flight Test, flew in a B707 was a barrel roll.

This is a relatively gentle aerobatic manoeuvre, which does not involve any negative "g" force, and not much extra positive "g" force, when flown properly.

The aircraft stays under positive "g" the whole time, as it describes a helical path around an imaginary horizontal barrel in the sky, hence the name of the manoeuvre.

There is not a lot of extra stress involved in a well flown barrel roll, unlike a slow roll or a hesitation roll, and, in theory at least, all of today’s airliners, should be capable of handling the stress involved.

Regards

Bellerophon


User currently offlineAirplay From , joined Dec 1969, posts, RR:
Reply 14, posted (11 years 9 months 3 weeks 3 days 20 hours ago) and read 2263 times:

The 777 wings aren't necessarily stronger than any other Boeing. They are arguably weaker. The reason is that even though it has to obey the 1.5 load factor just like most Boeings before it, the accuracy of the design tools these days, allowed them to achieve a break down mark of 153% (If memory serves).

If you exceed the 1.5 load saftety factor, theoretically the wing is heavier than it needs to be. Because of the computer design tools, the 777 had unprecedented accuracy in hitting this mark.



User currently offlinePositive rate From Australia, joined Sep 2001, 2143 posts, RR: 1
Reply 15, posted (11 years 9 months 3 weeks 3 days 20 hours ago) and read 2244 times:

Yep there was the case of that China Airlines 747SP mentioned by me above and Aloges, and i also recall a TWA in the 1970's where leading edge slats deployed inflight causing it to go into a flat spin or something- around +7G's and several -G's were pulled, aircraft was badly overstressed but didn't break up!

User currently offlineBuckfifty From Canada, joined Oct 2001, 1316 posts, RR: 19
Reply 16, posted (11 years 9 months 3 weeks 3 days 8 hours ago) and read 2203 times:

A cabin crew I know once told me that in JAL's 747-400SR, sometimes the curtains throughout the whole cabin are open, so you can see the aisle from end to end. And during that time, it is possible to actually see the aircraft flexing when it encounters turbulence.

I suppose that would have been eerie to see...


User currently offlineEssentialPowr From United States of America, joined Sep 2000, 1820 posts, RR: 2
Reply 17, posted (11 years 9 months 3 weeks 2 days 8 hours ago) and read 2226 times:

Ikarus/Airplay,

My post was based on assumptions of nominal/ultimate loads to simply explain the process; I did it w/o a ref, so thanks for providing them...


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