Fatigue life in Aircraft (particularly Fins)

[petermcleland]

I was always interested in the wing flex aspect of these things, on the aircraft that I flew...I remember distinctly with the Venom that the wing flexed quite a bit. I remember a flight with tip tanks fitted, when I noticed that it gradually became one wing heavy (there is no trim control for ailerons)...It got a bit tiring to hold the left wing up and I was wondering what was causing it...Checking fuel gauge contents and doll's eyes made me realise that the left wingtip tank was still full of fuel and the right wingtip tank was empty...There were no fuel gauges for the tip tanks but the situation was obvious when you looked out at the wingtip tanks...There was mild turbulence at the time and when I looked at the right wingtip, it was bouncing up and down at high frequence over a short distance...Gerding!..Gerding!..Gerding! But when I looked at the left wingtip it was flexing up and down in the turbulence more slowly and over a greater distance...GERDONG!......GERDONG!.......GERDONG! The fuel transfer system had failed on the left side and no fuel had fed to the main tank from it. I just had to put up with it and land a bit earlier...Looked a bit funny taxying in all lopsided.

On the same subject we used to hang a lot of fuel under our Hunter wings for long trips...Two Hundred and Thirty gallons in the inboard drop tanks and One Hundred gallons in the outboard drop tanks...It was amazing to screw your head round far enough to see them in turbulence and note that the Hunter wing did not seem to flex at all! :flying:

[forthbridge]

:o :o

Whenever I fly 'Easy' - I always pick a window seat just in front or behind of the wing, so I can look out at the control surfaces etc - however I am always amazed (and If I am honest a wee bit un-nerved) when I see the engine pod move around in turbulence, especially since at times I cannot see the wing move in unison! As I am a distinct take-off buff, I always closely watch the wing for changes in 'flex' on the takeoff roll.

Nothing more reassuring than the spoilers popping up when the wheels are down mind you.... I am certainly a 'Sim preferred' air passenger (particularly given the usual bumpy air around my local airport, EGPH)!

Strangely on flights I can't get a window seat, it never crosses my mind....... :flying:

[Garry Russell]

It's as well it all does flex as that absorbs bumps and helps stop it breaking

Viscounts were good as you could sit between the wing and watch both wings bending in turbulence through the huge windows.

Infact the impression was not so much the wingtips bending but the fuse bucking......all exciting stuff

Garry

[Garry Russell]

What you don't know won't hurt you.........

Take a look at a slow motion vid of a Helicopter rotor blade :o

Click on the pic

http://www.rapp.org/archives/2004/12/rotor/

Garry

[forthbridge]

:o :o

Thats' just about enough to stop me ever going for a spin in a chopper :o

[jonesey2k]

Talking about wing flex. Does anybody else think that the "artists impression" of a 787 looks a bit stupid? Surely if the wing was that flexible ailerons would be useless due to control reversal?

Sitting at the back of s stretched DC9 in turbulence is always fun

[Garry Russell]

That used to be said of the DC 8 61/63 too, with quite a marked fuse flex

Garry

[John R]

quite a lot of the display is flown with the airbrake extended.

I work on Hawk U/C & hydraulics, we keep an close eye on the log cards to spot if it's an ex RAFAT airbrake jack, ( the usual big clue for us is the colour ;-) ) They are lifed a lot lower than the standard or export fleet.
They have also gone though a life extension exercise, nearly but not quite doubling the life.

John

[auster]

Peter,

I remember one Hunter when the wings flexed. It was during my time at Hawkers and the Hunter was just going into service. It was being evaluated by, I believe, the first unit to get them. A squadron leader was diving through cloud over the North Sea and when he broke out, he was a lot closer to the water than he anticipated!

I saw the damage report. The wings were permanently bent upwards, the top skins at the root, no less than an eighth of an inch thick, were badly buckled in compression and a lot of the large solid ¼ inch dia. rivets in the root areas had popped. The maximum expected design load in the symmetric diving case was 7.5g to give an ultimate design load of 11.25g. The 7.5g was the maximum load that a pilot was expected to apply before blacking out. The g-meter read 10g!

Jonesey2k,

Simplifying things, wing flexing or bending results from the ‘vertical’ aerodynamic loads being applied to the wing. Other loads are trying to twist the wing and aileron reversal can occur when the wing does not have sufficient torsional stiffness.

HTH

Ralph

[petermcleland]

Talking about wing flex. Does anybody else think that the "artists impression" of a 787 looks a bit stupid? Surely if the wing was that flexible ailerons would be useless due to control reversal?

Jonesey,

On a lot of Boeing wings the outboard ailerons are locked in the neutral position just after take-off when the last notch of flap is brought in. For the rest of the flight, till flaps are lowered again, the only ailerons are very small in span and very inboard...Not very far out from the root in fact. These are the only ones you will see moving in the cruise.