Everyday as I watch aircraft with turboprop engines, a question pops up: Why do aircraft with turboprop engines have black painted anti-icing system?
For instance:
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3 Answers
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These are rubber boot deicing systems. When ice forms on the leading edge of a wing, pressurized air is used to inflate the boot so the ice will pop off. Normally, this inflation is not permanent but the air is pulsed. Activation is done by the pilot, so this system is normally switched off. Operation needs some care because if used too late (with too much ice) the boot may become impossible to be inflated.
Historically, it was believed that activation with too little ice would also render the boot ineffective, with ice building up around the inflated boot (ice bridging). This seems to have been a myth.
Deicer boots in operation (source: Wikipedia)
Other deicing systems use heat or constantly seeping deicing fluid. The first method is normally used on jets with bleed air or electricity as the heat source. The second system was for example used on the Beech Starship which had a titanium leading edge with millions of tiny, laser-cut holes for the application of deicing fluid.
Alternatively, surfaces are designed large enough to still be effective under icing conditions.
Fast jets do not need a deicing system - their stagnation point temperature is sufficient to remove ice. However, ice can still be a problem: When the supersonic B-1A was converted into the more stealthy, but subsonic B-1B, ice buildup inside the intake (which now had obstructions added so the engine compressor would be hidden from radar) would result in large chunks of ice building up, then breaking loose and damaging the compressor blades.
answered Oct 27, 2020 at 7:07
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3$\begingroup$ The theory of ice bridging is now disputed by the FAA, at least for contemporary systems. $\endgroup$ Oct 27, 2020 at 17:57
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2$\begingroup$ Airliners can take some credit for compressibility heating and generally aren't required to have wing anti-ice on above a certain speed, like 230 kt, when in technical icing conditions unless the ice detection system senses an actual accumulation on the probe. On the other hand, cowl anti ice has to be on at all speeds when in visible moisture when close to or below freezing. In any case, military fighter aircraft have to avoid icing, which is kind of odd for those that are considered "all-weather" interceptors.. $\endgroup$– John KOct 27, 2020 at 22:19
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1$\begingroup$ @ROIMaison Air is cycled into and out of the boot so it vibrates. Its is not pumped up like a ballon and left that way - this would harm the aerodynamics. $\endgroup$ Oct 29, 2020 at 10:27
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1$\begingroup$ I'm no pilot myself, so my comment might be of little value, but... saying that you shouldn't activate the deicing boots too early to prevent bridging sounds like dangerous advice. Comair Flight 3272 crashed because the pilots were training to not use deicing boots prematurely, while that advice is outdated and not supported by any factual evidence. The NTSB report of that crash recommends activating the boots at the first sign of icing. The FAA, NTSB and NASA have been saying ice bridging is a myth that should be eradicated asap for a while now. $\endgroup$– OpifexOct 29, 2020 at 16:22
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3$\begingroup$ @Opifex: I have been educated when ice bridging was still part of the syllabus. I guess I should rewrite that part of the answer. $\endgroup$ Oct 29, 2020 at 17:37
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They're not painted black, but a rubber (hence black) device called a de-icing boot.
Upon entering icing conditions, the system once activated will repeatedly inflate and deflate the rubber boots. This will destroy any icing build-up.
Larger jets use a system where the leading edge is heated by bleed air. This requires a lot more bleed air, but has the advantage of not deforming a wing while traveling near the speed of sound.
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$\begingroup$ Why don't turboprops use bleed air for deicing? Is it because they don't have the bleed air available that a turbofan has, or is it because it's bad to deform the wing when transonic? $\endgroup$ Oct 30, 2020 at 10:31
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$\begingroup$ @Wayne I didn't include this in my answer because I'm not an expert, but my guess would be a bit of both. $\endgroup$ Oct 30, 2020 at 11:07
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As the other answers have already pointed out these black areas are not painted, they are rubber surfaces that are inflatable to break off any ice that forms on them.
To produce rubber you need a filler. The main "rubber" producer, tire factories, use carbon black (soot) because it is cheap and tested. It also dyes the rubber black. However there are other options available and rubber can be dyed any way you want.
For the aircraft de-icing boots it is sensible to choose a black rubber material. Think of the cabins, they are mostly painted white to reduce the amount of solar radiation the cabin picks up, reducing the need for air conditioning. For the leading edges of the wings, when they are in danger of icing up, you want them as hot as possible (well, not too hot...), so just make them black.
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3$\begingroup$ Congrats! This is the one answer that addresses why the rubber is black! $\endgroup$– FreeManOct 28, 2020 at 12:54
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4$\begingroup$ Also, carbon black protects against UV degradation. UV intensity increases by approximately 4% per 1000 feet of altitude (ref: An NIH document). $\endgroup$ Oct 28, 2020 at 14:07
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3$\begingroup$ It could also be desirable to see white ice against a black background $\endgroup$– JanOct 28, 2020 at 16:09
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$\begingroup$ I can't imagine the colour would have any noticeable impact on temperature. Forced convection from freezing air and conduction from ice accretion will be much more significant, and at night black will actually be colder than white. $\endgroup$ Oct 28, 2020 at 16:29
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1$\begingroup$ That said, it's useful to point out that not all deicing boots are made from black rubber. $\endgroup$ Oct 28, 2020 at 20:16