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Most large airplanes flying today are mostly metal, which has a relatively big coefficient of thermal expansion. Cruising altitudes of commercial jets can reach 10 km or more, where the air gets down to about -50 Celsius. Room temperature is more like +25 Celsius, and I would not be surprised if that large fuselage, sitting under the sun, gets up near +50 C.

This is quite a range of temperatures to handle. It would cause some contraction/expansion of metals. The larger the piece of metal, such as a wing spar or long airframe beam, the greater the contraction/expansion.

Is this a major design problem for large aircraft, and how is it handled?

EDIT: only interested in subsonic designs. I'm concerned about the cold high altitude air cooling most of the fuselage and making it contract. The nose and leading wing edges might not suffer from this, but I expect the rest of the aircraft will.

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    $\begingroup$ I won’t answer because this is an anecdotal story, but I once had a gripe that every time this specific aircraft (an Airbus as it happened) ascended through 18,000 feet, a spurious warning light would go off in the cockpit. Long story short, we had a real bear of a time finding it because it operated fine on the ground. Turns out that a wire was chaffing to structure because a clamp was turned the wrong way. The thing is that the structure would shrink so much in flight that it would cause this friction but on the ground the fuselage would expand enough so that it didn’t rub, and worked fine. $\endgroup$
    – Frank
    Commented Nov 9, 2018 at 20:54
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    $\begingroup$ @Frank Uh oh, what kinda warning light? Was it something serious like thrust-reverser unlocked? $\endgroup$
    – DrZ214
    Commented Nov 10, 2018 at 2:34
  • $\begingroup$ I don’t remember which light, exactly. I remember it wasn’t anything that would jeopardize the aircraft, but it had a very lengthy history of intermittent behavior. Naturally, it always worked fine on the ground. By the way, the distance between the clamp and the fuselage on the ground was several inches, which is partly why it was glossed over during inspection. No one thought that there would be that much contraction! $\endgroup$
    – Frank
    Commented Nov 10, 2018 at 10:21

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Not thermal contraction but condensation of vapor is a problem.

Immediately, fuselage pressurization is the far bigger problem that comes with the altitude changes. But if you operate in hot and moist weather, the moisture in all the air carried inside the fuselage will condense when this air cools down at altitude and will collect somewhere. If no proper drains are included (remember, drain valves and fuselage pressurization do not mix well) and maintenance is sloppy, this accumulated water can weigh several tons.

A special case are foam sandwich structures. PVC foam is the standard in composite gliders, but airliners use honeycomb sandwich structures. When fairings made from PVC foam were tried on airliners, it was found that pressure and temperature cycles damaged the sandwich core pretty quickly. The moisture inside the cells would condense, the cells themselves would crack and bacteria would munch up the soggy remains. Only with honeycomb cores could the sandwich be made durable enough for airliner use.

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The temperature range the aicraft is dealing with is actually smaller. Indeed, airliners cruise around Mach 0.85, but the velocity on the fuselage is zero. Hence a part of air kinetic energy is transfered into thermal energy. This is called the ram effect. You can find tables that give you the stagnation temperature as a function of the mach number and the altitude.

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