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GRP lifespan
"DSK" wrote in message ... wrote: I fly glassfibre aircraft, sailplanes actually - structure lifespan is a topic of interest when you are at 20 000' above ground level flying at 200 kph plus and the outside air temperature is below -15 degrees Celcius. Hmm. And some airliners fly at 500kts at 40 000' in -40C the test is how well an airplane survives going through a Cumulo Nimbus Cloud - and development around sailplanes ( OSTIV ) recently published a rather reassuring article giving an estimated service lifespan of a glassfibre sailplane of around half a million flying hours. and that was with a safety factor of at least 1 order of magnitude. the requirement for a civil aircraft is not to cause more than 1 death in every 1,000,000 flying hours. And, on average, that's achieved. Although yacht hulls are stressed by rigging and water loads I suspect that the stresses involved ( in a normal cruising boat ) are somewhat less than experienced by an aircraft structure. I disagree. In fact I'd suggest that since yachts experience structural failure more often, they are more highly loaded. Also they experience greater load transients . (AFAIK... it may be that aircraft experience more structural failures that I don't hear about). Think about how your airplane would react if you picked it up & dropped it 10 or 20 feet (3 ~ 6 meters) three times a minute, at varying angles, for several days. Yup. Just like flying through a Cu Nim. Only for an hour or so though. Hundreds of feet. On lots of flights in its lifetime. ..... The wings on my 25m span Nimbus regularly deflect by a metre or so in normal flight. Even using the same figure of half a million hours one gets 47 odd years of 'use', not just sitting in a berth. Watch the wings of your 747 next time you lift off. They flex through nearly 4 metres! More in sever turbulence. I'd be willing to bet that this is well within the range of unrelieved strain (ie does not accumulate fatigue) and the wing is designed for this much deflection. Sailboats have to be a good bit more rigid... I'm guessing that parts of the plane are too, like for example how much does the fuselage flex & deflect when you put on some rudder? Exactly. Airplanes are designed to absorb energy by being incredibly flexible. Yachts are designed rigid. Bad news for yachts, so they have to be overdesigned in strength to reduce failures. But yacht failure isn't so critical anyway; yacht manufacturers get away with the occasional lost keel . . . only affects a few people. Of course if you insist on building a hull only millimetres thick out of Nomex, Kevlar, Carbon and other exotics, sail it in across Biscay in a gale with only one hull of three in the water and driving through 5m high swells then 'all bets are off' and you may well run into mechanical limits of the structure. Some production yachts have failed in lighter circumstances - ask Bavaria about Croatia . . . Could happen in planes too. And parachutes are cheaper than ocean rescues  Doubt it, there's a big industry looking after flight safety . . . JimB |
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