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I am a design engineer on GA aircraft and I had a thought whilst flying in icing conditions the other day. I know there are lots of ways we deal with ice buildup (as per the chart below from this post, many of which are complex in nature and require more attention in design and operation as compared to passive coatings.

Why don't we use hydrophobic (or rather icephobic) coatings instead of using the more common methods like deice boots, TKS or bleed air? I would think a strip of hydrophobic material such as this 3M™ Microfluidic Diagnostic Film or a hydrophobic paint additive that covered the leading edge would work on most general aviation aircraft. I am sure there are downsides that I am not seeing otherwise it would be used much more. Anti-ice methods chart

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    $\begingroup$ A successful hydrophobic material needs to be able to withstand temperatures from -50° (at altitude) to 110° (on a desert ramp in the summer), and be durable against light debris (dust and insects) impacting at over 100 mph, while exposed to corrosive pollution (fuel and oil spills, even just tiny drops). Have you considered these effects? $\endgroup$ – abelenky Dec 2 at 20:09
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    $\begingroup$ @abelenky Good point, but yes I have thought about this. We use a material called speedtape a lot on aircraft and it you just vary the thickness and hardness of the tape to which part of the aircraft it is applied to. A sufficiently thick (~.030-.050") should suffice for the abuse it will take not to mention that you can replace it at given intervals. $\endgroup$ – JoeBo Dec 2 at 20:53
  • $\begingroup$ @abelenky: And it has to last for 50 years or more. (Or be readily replaceable.) Most plastics tend to degrade from prolonged exposure to sunlight. $\endgroup$ – jamesqf Dec 3 at 4:41
  • $\begingroup$ -50 degrees celsius will not be enough. Just flew over Greenland, it was -66 deg C at 11000 ft. $\endgroup$ – Jpe61 Dec 3 at 5:40
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    $\begingroup$ @JoeBo the product you provided a link to is hydrophilic, not -phobic. $\endgroup$ – Jpe61 Dec 3 at 5:48
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I have no doubt that a lot of experimentation has been done using coatings on GA airplanes and to the extent that a coating would work, the main problem that I see is degradation of the coating from UV and erosion. A coating would likely have to be restored regularly and would be likely too expensive for most tightwad GA pilots.

The other thing is that clear ice that forms quickly can tend to sit in place because it's "cupped" around the leading edge and a non-stick surface may not help since the ice shape can be more or less mechanically held in place even if it's unable to actually stick to the surface. Rime ice that tends to build up out in front of the nose of the LE would probably shed from a non-stick coating a lot better.

On a side note, your chart doesn't include "evaporative" anti-ice, which is a sub-type of heated anti-ice. On jets this is often used with hard (non-slatted) leading edges because of the need to avoid "runback ice". A leading edge hot enough to melt ice, but below the boiling point, will allow the water to flow back and re-freeze farther back on the non-anti-iced part of the wing. Anti-ice systems in that case will be evaporative, that is, so hot that water immediately vapourizes when it touches (like a steam iron).

Such anti-ice systems run at 105+ C temperatures. A coating that could prevent adhesion of runback ice behind the LE might be quite useful and could allow those wings to run lower temperature systems (the heat plays havoc with the LE structure over the long run).

Runback ice is tolerable on slatted wings and those anti-ice systems will run a lot cooler, around 50 deg C.

On yet another tangent, I always used to wonder why some jets anti-iced horizontal tails and some didn't. Turns out you don't have to anti-ice the surface if you make it big enough.

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    $\begingroup$ And for many GA pilots, encountering icing conditions is a rare thing. In maybe 40 years of flying, I've encountered ice exactly once. (During instrument training, with my instructor along.) $\endgroup$ – jamesqf Dec 3 at 4:44
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    $\begingroup$ Problem for GA aircraft without cert for fight into known icing is, if you want to travel around IFR, you are pretty much stuck below the freezing level, which means in winter you can only fly in VFR weather anyway, or maybe very thin cloud layers you can get through quickly. $\endgroup$ – John K Dec 3 at 4:48
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the thinnest of oily dirt films atop any such anti-wet coating will render it totally ineffective. There is no way in practice of maintaining that coating in an atomistically clean state.

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