Stooooooooopid Question...

[Saracenman]

this has puzzled me for years.......

how come the average age of military helicopters tends to be far higher than fixed-wing aircraft?

the latter clearly are governed by fatigue indices, but what about helos? they must be the same surely but anyone who's flown in a chopper will know how much they shake - surely that can't be good for the longevity of the airframe can it?

most of 'our' RAF/Army/RM Seakings, Pumas etc have been in service since the 70s/80s - what makes them last so much longer than fixed-wing a/c?

anyone know?

sm

[Xplumberlives]

Lack of MOD money to replace them!!!!

New Merlin doesn't vibrate anywhere near as much as the previous generation of ROTARY TRUCKS!

[Saracenman]

so? why not save money by keeping the fixed-wings in service the same length of time too?

there must be a specific reason - a specific difference as to how helos 'use up' FI ???

still perplexed!

sm

[Xplumberlives]

OK let's put it another way;

Rotary Truck = Ford Cortina/Vauxhall Cavalier

Fast Jet = Ferarri/Lamborgini

One built like proverbial BRICK SH*T HOUSE

Other one built like fine tuned temperamental high performance machine

[Saracenman]

aha i see - i think

but wouldn't that increase weight? more of an issue with a rotary than fixed wing surely?

still not COMPLETELY sold XPL

sm

[Xplumberlives]

aha i see - i think

but wouldn't that increase weight? more of an issue with a rotary than fixed wing surely?

still not COMPLETELY sold XPL

sm

Perhaps that's why the MIGHTY CHINOOK has two BLOODY great big jet engines and the MARVELLOUS MERLIN has three!

[Mackrick]

I could write reams for you on FI calculations for fixed wing stuff, Manufacturers FI, Fatigue meter readings, sortie profiles, pressurisation cycles and levels, landings, full / braked / rollers / flap cycles etc. There are magic formulas for each type. Components and airframe parts also have lives both calendar and hours / Flown or run. Aircraft structures are put through structural test to define fatigue life wings flexing / pressurisation cycles etc. Now all modern aircraft have these but things like VC10 had no real backstop so they have had trials and tear down inspections to define their life span. (covers alot of RAF aircraft). Then fighters have wing replacements etc as they grow older, the Herc fleet has had this done.

Now for the next age bit.. In years yes you are right but you can have an old aircraft with a few hour on it. Now as I hinted at above landings and cycles alter the FI. You can have a high Cycles but low hours aircraft.
Now look at the helicopter fleet, Different type of FI. No pressure cycles, no fast heavy landings, engine and gearbox changes, Rotor changes , landing gear changes and all you have left is the fuselage itself. On the helicopter you can get to all the outside and most of the inside to carry out inspections for fatigue damage. On aircraft it is not that easy.

Hope this is a good starter to enable further debate....

[Saracenman]

thanks for that Mackrick - it all makes perfect sense now!

i remember FFM telling us all that "with enough time and money" he could make anything fly forever. the thing that you've now said Mackrick that had never dawned on me before is the ACCESS!

so, yes helo airframes DO suffer (differently) with FI, but the 'fixes' are easier and therefore more cost-effective?

interesting stuff

sm

[Mackrick]

You can then take it a step further to mean time between failures... servicing periodicity ... and then you get a Flying hour per servicing hour rate and it will get to a point where it costs more to fix and service per flying hour than it did when it was new. At this point it becomes non cost effective to carry on.

[Saracenman]

.........periodicity ....

is that a word? is now!

again, that does make a lot of sense. so, just out of interest (and might be impossible to answer) do helos suffer less, from the FI perspective, than fixed-wing - per flight-hour?

I'm ignoring landings etc, but just intrigues as to what's most damaging - flying straight and level, or being shaken to death

sm

[Mackrick]

Depends if its at the hands of MF of Naddy

[Spitfire]

Here's a good example you should remember SM - good old G-BCEB - too and from the Isles Of Scilly since 1964



And here she is in her old British Airways livery



As described above I have it on good authority that the only bit still flying that originally started flying in 1964 is the main chassis - everything else has been changed or updated over the years
And she does spend 2/3rds of her active life being maintained

[Saracenman]

OOOOOOOOOOO

i flew on G-BCEB a few years back to go and see Mousehole's Christmas lights - bloody good value trip too

good point, well made Spitfire

and Mackrick - i think I'll go for Naddy............nope, Mayfly............erm................i treasure my testicles!

sm

[Mayfly]

obviously not well enough SM, not well enough -................SQUEezzzzzzzzzzzzzzzzzzzeeeeeeeeeeeeeee

[Saracenman]

[Mackrick]

Bet that brought tears to your eyes SM