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Re: Airframe Life Expected/Hours

Posted by bdk on Wed Sep 03, 2003 06:17:02 PM

In reply top Airframe Life Expected/Hours posted by Andrew on Wed Sep 03, 2003 02:18:28 PM

It depends on the make and model of airplane, and the kind of service it has seen. With enough empirical (fleet) data, assumptions can be made regarding fatigue life from high time airframes to allow prediction for inspection or preventative modifications to lower time airframes.

Doublers can be added to lower local stresses to extend the life beyond that of an unmodified aircraft. If an aircraft type has had extensive ground fatigue testing, the life can be quite long, but on military aircraft the intended missions can change over time which changes the picture quite a bit.

Basically, an aircraft that operates at low stress levels can have nearly an unlimited fatigue life like the DC-3, while others like the C-141 and C-5 require wing replacement partway through their life.

Also, aircraft that fly at low levels are subject to gust frequencies not normally seen at high altitudes.

The effects of fatige are much better understood than they were when the B-52 and C-141 were designed, so modern aircraft have much longer life capability.

Military aircraft are cycled between operating bases and training bases to maximize life, otherwise one aircraft may get timed out due to landing cycles, while another gets timed out due to aerial refueling (turbulence/buffet) cycles, for example. If everything is done right, the airframe is timed out evenly for every critical structure at once. Analytical condition inspections are performed periodically to verify that fatigue damage accumulates at the anticipated rate. This way the life of the aircraft can be maximized.

The C-17 was designed for a life of 30,000 flight hours, and this was demonstrated by a full scale airframe fatigue test to 60,000 hours (a safety factor of two was added). This testing was later continued to demonstrate an even longer airframe life.

: No really a Warbird question specficially but I was wonder
: ing how I might get information regarding the life expecta
: ncy of different airframes. I know it's more of an enginee
: ring kinda question but I was wondering if one had ever co
: me across any info on the subject..For example I have
: seen some airliners run up over 100,000hrs..and others
: have high cycle times..take off and landings..
:
: Any ideas?

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