Airframe testing

[Felipe Garcia]

"¿¡Dónde estará ahora mi sobrino Yogurtu Ngue, quien tuvo que huir precipitadamente de la aldea por culpa de la escasez de rinocerontes!?"

Cuando el jefe Afobutu regreso dos dias antes de su caceria, por culpa de la escacez de rinocerontes!

Gotta love Les Luthiers.

Brian,

Both T-130 and T-123 suffered of wing failures, within a month of each other. And it is believed that T-82, which crashed in 1995 also suffered of a similar failure (although that was revisited after 2002, and that's not what the official report says).

On a sidenote, the Black Irish Band, a California-based band wrote a song called "Last Flight of 123", and it talks about how it crashed.

Computer simulation can get you a very approximate answer. For my senior design project we had to design, build and break a wingbox, and we broke it pretty close to my estimates, obtained using the ANSYS FEA software. I gotta say though, watching those structural tests gets pretty exciting, since you know what to expect, but don't know at what exact moment (you know it's coming for sure once you start getting weird data out of a few strain gauges).

In aerospace you design your structures to 1.5 the ultimate load (150%), anything after that is unintentional but appreciated, and you don't design for more because your structure has to be heavier than it needs to.

For some reason I'm thinking the 787 failed the initial wing test, but I'm not 100% sure.

The Comet's problem was pressurization fatigue, mainly due to stress concentrations, which were not very well understood at that time in history.

[Gabriel]

Cuando el jefe Afobutu regreso dos dias antes de su caceria, por culpa de la escacez de rinocerontes!

Gotta love Les Luthiers.

Right. You did get the link with Evan's post, right?

In aerospace you design your structures to 1.5 the ultimate load (150%), anything after that is unintentional but appreciated, and you don't design for more because your structure has to be heavier than it needs to.

Small correction: You design for the ultimate load, which is 150% of the design load. As a side note, the airplane doesn't need to be re-usable after being exposed to a load between design and ultimate. It is admissible that it suffers permanent deformation as long as that deformation doesn't prevent it from safely completing this (last) flight.

For some reason I'm thinking the 787 failed the initial wing test, but I'm not 100% sure.

Nope. Boeing did a test of a partial wing structure up to destruction to validate their computer models. Then they successfully tested a full wing until 150% of the design load and stopped there, short of destruction, with the requirement complied with.

The one that failed just shy of 150% (148% IIRC) was A380 wing, which was then reinforced.

[Felipe Garcia]

I did, or I think I did.


Right, it's 1.5 the design load (Pretty sure we used the term limit load more often in school, at least when we designed the wingbox that was specifically designed to break).


So it was the A380, I knew it had happened, just didn't recall which plane it was. I thought it was the 787 as it also had the delamination problems.

On a sidenote, I'd like to see a side by side test of the 747-8 wing on the current production standard and on the early models (the slightly heavier wing, which I presume is a tad different, the same wing that caused Al-Baker to throw a hissy fit over the 787 delays)

[brianw999]

I don't know that I'd call turbulence the primary cause as much as pulling hard up with a heavy load...and wasn't aircraft age part of this one too?

A combination of aged aircraft, pulling up with a load and turbulence over a fire area ?

[Evan]

Do you have any source whatsoever to support excessive rudder inputs?

I didn't see any mention of that.

I'm thinking you have just achieved the ultimate level of sit on your ass ignorant judgementalism and a cheap attempt at trolling

Do the words "extreme turbulence" mean anything to you, or do you think a tailless aircraft might enter a flat spin on its own?...never mind, you just read the manuals, type on Jetphotos.net and never make mistakes.

Does the word 'perhaps' mean anything to you? Have I mentioned already that to get the point I am making you have to read ALL of the words:

BOAC flt 911 (call it the other 911). Broke up due to extreme turbulence over Mt Fuji. The fin seperated from the fuselage (yes, it also happens to Boeings), perhaps due to pilot using excessive rudder inputs, causing a flat spin and break up in flight.

Thus, my point is that perhaps BOAC 911 did not break apart due to a sudden gust load but rather due to pilot induced loads in response to that turbulence. We will never know because the FDR evidence was destroyed in the fire. I think, given the integrity of the airframe and the absence of any other incident of fin failure on the 707, that this is a reasonable question to ask. Had it been asked at the time, perhaps AA587 would never have occurred...

[Felipe Garcia]

I don't know that I'd call turbulence the primary cause as much as pulling hard up with a heavy load...and wasn't aircraft age part of this one too?

It was fatigue due to age, and due to the loads it was subjected to. Fire areas have some wicked winds and drafts, which may result on loads on the airframe that are more than what it would on a normal, similar mission. To that, add the crazy maneuvers that they sometimes have to perform. Can you call this turbulence? depends on your definition, but I guess that in this case we could say yes.

The sad reality is that fire aviation is quite dangerous, due to the age of the planes, the conditions that you fly in, the maintenance that can be sketchy sometimes and more. Last year I witnessed about a week or so of operations to contain the Gladiator fire, and I got to see two or three emergency engine-out landings, sometimes with fire truck chases, engine swaps, broken down planes. Tanker 55 was severely damaged about a month later, and another Neptune crashed in Utah (both accidents happened the same day). Unfortunately there is a lot of bureaucracy involved and that has kept companies from being able to fully renew their fleets and phase out the Neptunes (which, as much as I would hate to see them go, have to go pretty soon).