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Why are the leading edges of the wings, horizontal stabiliser and vertical stabiliser and the engine's inlets made from Aluminium?

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    $\begingroup$ Because those surfaces are usually heated for anti-ice. $\endgroup$ – Ron Beyer Feb 10 '17 at 20:01
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    $\begingroup$ Because gold would be too expensive, too soft, and too heavy? $\endgroup$ – Ralph J Feb 10 '17 at 20:08
  • $\begingroup$ @mins: And, of course, having a metal radome would defeat the purpose of a radome. $\endgroup$ – Michael Seifert Feb 10 '17 at 22:05
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There are probably many factors in choosing aluminum vs. composites.

A big one is bird strikes. The leading edges are at the highest risk for this. Metal tends to absorb the impact better while retaining its strength, while composites would tend to delaminate and become much weaker. Resistance to in-flight hail must also be considered.

enter image description here enter image description here
(Source Left, Right) Comparison of bird strike effect on aluminum and carbon fiber.

Anti ice was also mentioned. These areas are heated with bleed air (or, for the 787, electrical elements) to melt or prevent any ice formation. Metals do much better at high temperatures than composites, which would tend to melt or lose strength. Metals are also able to conduct the anti ice heat better than composites.

Another factor could be manufacturing. These surfaces have a lot of curvature. Composite panels are often reinforced with honeycomb core, which is best on relatively flat surfaces. Of course composites could be made into these shapes, but the shape would limit material and configuration options. Metal is also easier to work with or repair than composites.

As far as choosing aluminum over other metals, it tends to be very light and cheap for its strength, has decent temperature capability for anti-ice, and when properly used is fairly resistant to corrosion or fatigue.

The nose does not have anti ice and must serve as a cover for the weather radar. Composites can be made relatively transparent to radar, but metal would tend to block the waves.

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    $\begingroup$ WRT anti-ice, metals also conduct heat much better than typical composites, making your anti-ice heating more effective. $\endgroup$ – jamesqf Feb 10 '17 at 21:33
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    $\begingroup$ Use overexpanded Nomex cores, and curvature is not such a problem anymore. Don't let that distract you; the answer is absolutely correct. $\endgroup$ – Peter Kämpf Feb 11 '17 at 10:00
  • $\begingroup$ The ease of repairing aluminium is also a lot easier than composites. Composites work best when the whole structure is made from a single piece and you don't want to replace such large sections every time you have a bird strike. $\endgroup$ – Notts90 supports Monica Feb 11 '17 at 12:14
  • $\begingroup$ Curvature isn't an issue when making bicycle frames out of composite materials, and bikes have much tighter curves than the leading edge of a large airliner. $\endgroup$ – David Richerby Feb 13 '17 at 15:07
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    $\begingroup$ @DavidRicherby: But do bicycle frames use sandwich shells? The ones I know are either tubes with a single solid wall, or they use a light wall with a foam core over the full diameter. Curvature is a real problem for sandwich structures, especially when you have curvature in two directions. $\endgroup$ – Peter Kämpf Feb 13 '17 at 20:49
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Aluminum is used for erosion prevention. There is no composite solution which can withstand the erosion caused by water/rain or FOD (sand/grit). In addition, aluminum leading edges transfer heat better than composites, which allows for improved anti-icing.

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