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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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Ralph J
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Roh
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3 Answers3

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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.

Rubber boot deicing system

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.

Peter Kämpf
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    The theory of ice bridging is now disputed by the FAA, at least for contemporary systems. – Sanchises Oct 27 '20 at 17:57
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    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.. – John K Oct 27 '20 at 22:19
  • I don’t believe the Beech Starship used a hot prop as the pusher design allowed the exhaust from the PT6 engines for anti-icing on the blades. Same as the Piaggio P.180 Avanti. – Romeo_4808N Oct 28 '20 at 13:26
  • @CarloFelicione, where do I say that the Starship props had thermal deicing? I talk about the wing and its use of deicing fluid. – Peter Kämpf Oct 28 '20 at 14:41
  • @PeterKämpf why not let the air flow out of the boot after application, so you could inflate it again at a later time during flight? – ROIMaison Oct 29 '20 at 09:31
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    @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. – Peter Kämpf Oct 29 '20 at 10:27
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    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. – Opifex Oct 29 '20 at 16:22
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    @Opifex: I have been educated when ice bridging was still part of the syllabus. I guess I should rewrite that part of the answer. – Peter Kämpf Oct 29 '20 at 17:37
  • I can serve as a second data point. 50% of my time is flying commuter class propeller driven aircraft. I have spent a lot if time in ice. Not once have I seen ice bridge and I've gone out of my way to make it happen. All of my training told me that ice bridging was real. It's not. – acpilot Oct 30 '20 at 01:29
  • @acpilot Thank you, that is very interesting. Now I wonder how the ice bridging myth ever came into existence. Is the current wording of the text fine with you? – Peter Kämpf Oct 30 '20 at 06:38
  • Your answers are always perfect. – acpilot Oct 30 '20 at 19:07
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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.

Sanchises
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  • 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? – Wayne Conrad Oct 30 '20 at 10:31
  • @Wayne I didn't include this in my answer because I'm not an expert, but my guess would be a bit of both. – Sanchises Oct 30 '20 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.

YPOC
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    Congrats! This is the one answer that addresses why the rubber is black! – FreeMan Oct 28 '20 at 12:54
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    Also, carbon black protects against UV degradation. UV intensity increases by approximately 4% per 1000 feet of altitude (ref: An NIH document). – Andrew Morton Oct 28 '20 at 14:07
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    It could also be desirable to see white ice against a black background – Jan Oct 28 '20 at 16:09
  • 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. – Sanchises Oct 28 '20 at 16:29
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    That said, it's useful to point out that not all deicing boots are made from black rubber. – Peter Duniho Oct 28 '20 at 20:16
  • The thermal theory has one slight problem; the sign is wrong. Black materials warm up in the sun, but they also cool down faster in the dark. And icing is more a problem in the latter circumstances (consider the long winter nights near the poles). – MSalters Oct 29 '20 at 14:10
  • @Sanchises Try to quantify those effects. For normal objects around us exposed to the wind the temperature is crucial. Now, the air flow is much faster there, but you still cannot dismiss the radiation so easily. At night it would be cooled indeed, as the infrared emmisivite does not differ from the visible one too much. – Vladimir F Героям слава Oct 30 '20 at 15:03
  • This is the correct answer. Raw rubber is NOT black in color. Natural rubber is light in color and often even transparent, but it is also not a very good material on its own. The boots are black for the same reason vehicle tires are black. Carbon black, a material produced by the incomplete combustion of heavy petroleum products such as FCC tar, coal tar, or ethylene cracking tar, is added to the rubber to improve the rubber's characteristics. The addition of carbon black makes the rubber more heat- and abrasion-resistant, tougher, more resilient and long lasting. – Juan Jimenez Nov 28 '20 at 14:59
  • However, "to produce rubber you need a filler" is incorrect. To produce the material that is used for tires and anti-ice boots, among others, the filler is added. Rubber bands, for example, are not made with carbon black filler. – Juan Jimenez Nov 28 '20 at 15:01