We heard you the first time, Robert.

😉

Even FI is imperfect – partly as a result of the factors listed.

Nor is it ‘counted in units’ exactly. Units of FI are a percentile of the planned fatigue life – thus:

100 FI = Planned fatigue life.

You might consume a tiny fraction of an FI unit in one sortie, or a whole unit (Lightning air combat sorties consumed 1 FI at the end).

This can be extended by structural programmes (so that some RAF aircraft have gone on to 125 FI) or an aircraft can fall short, requiring re-lifing long before reaching the end of its planned life (thus the 25 FI upgrade to RAF Tornado F3s).

Indeed as you rightly point out it is still a calculation based on some form of Guesstimation within the equation. That is probably why the Valiants were so abruptly taken out of service, why the Victor stress frame failed at 127 FI and some airframes actually managed more than 130 FI. As for the Lightnings consuming 1 FI at the end of their career, that is more indicative of the pilots pushing that little further because they were going out of service. One airframe (F6) did pull an estimated 10-14 g during a dive once and carried on in service for some years after.

There’s a great deal of bol.locks being spouted here.

The accurate prediction of structural life remains a black art even now – which is why a ‘scatter factor’ is applied when life is calculated.

And unpleasant surprises happen all the time – when the Buccaneer switched from over-water to overland, for example….. or the effect of taxying on rough ground on Hercules fatigue life (and the Herc fatigue meters are in the wrong place, and are inhibited when the aircraft is on the ground).

Whether the accident aircraft was 25 years old or 30 years old is completely irrelevant. The number of flying hours is a better guide, though one hundred hours of CAP will usually impose less stress and strain than ten minutes of air combat, so a low-houred aircraft may have had more fatigue consumption than a high-houred one, depending on the profiles flown. Nor is it just about the application of g – a rapid pull to 9 g will impose more damage than a gradual application.

Which is why you have fatugue meters on the jet – and don’t simply count the years in service or the hours flown.

And then you have the ‘mission-external’ factors – of which corrosion, faulty maintenance, manufacturing and materials defects/problems are just the tip of the iceberg, and all of these factors can be applicable across a fleet, or just to a sub-set of aircraft, or even just to a single airframe.

Which is why the life tends to be measured in FI (fatigue index) units.

From this week’s AvWeek:

“Aerospace industry and USAF officials say the fuselage broke in two immediately behind the cockpit during a 2.5-3.5g maneuver. The aircraft had been delivered to USAF in 1982.”

Makes you wonder how it even got in the air in one piece. also makes you wonder how an inspection could miss something that you’d think would be apparent. Guess we’ll find out.

Ouch.

I agree that miliary aircraft are hardly comparable to civil aircraft in that matter. But in this particular case I would ask for an exception. The B-52 bascially flew the profile of a civil airliner, at least it was designed for it. The majority of flight time was spent at cruise speed and high altitudes.
Of course, the whole issue changed when B-52s started to fly low level missions at max VMO. That would tear apart any Airbus or Boeing after a short time, too.

Please understand my statement “underengineered” as a statement of 2007. For 195x it was state-of-the-art. First civil aircraft with comparable weights appeared over 15 years later (the B747 was the first civil aircraft to exceed the MTOW of the B-52).

I’m sorry but your statement still doesn’t hold water. Misiions can be flown in a number of configurations of lo-hi depending on the circumstances. Then there is such things as toss-bombing (even the Vulcan used to do that).
The rigours of military life are much more extreme. You only have to look at the low engine life between servicings on mil a/c to understand that.

Thanks Phillip, I’ve scanned through and will read it fully soon.
I live close to RAF Laarbruch (where I served) so I can relate to your feelings.

Hi all,

After the war the French took the two squadrons of Halifaxes with them (they flew from Elvington). These were mainly Mk III and Mk VI’s. They were used until the early fifties.

Does anyone know what happened to them, were they scrapped locally, burned etc. And is there anythting left such as wheels etc. Is there in fact anything left apart from photographs?

Cheers

Cees
__________________
The Dutchman formerly known as HP57

Knowing the French they’re still parked in the field next to the house.

The Hunter famously suffered from Avon surging when the guns were fired, where as the Swift didn’t, air inlet design has alot to do with engine surging and performance.
The Javelins Sapphires went on to have problems with blade expansion but you don’t hear of the same problem with Victor B.1s.

I heard tell that the “hockey sticks” vaporiser burners tended to break off in the Victor Sapphires.