I'm working on some physics questions for dragon riding, mostly regarding changes in temperatures at different altitudes and how that might endanger dragons and their riders. Recently I started wondering if the 'icing problem' from Iron Man might affect dragons, where ice buildup would become a problem during long flights, especially in winter. I don't have a good background in the relevant branches of physics, though. Can anyone shed any light on this?
I seriously doubt it, for the following reasons.
1) Iron Man's icing was more of a function of Altitude. Something as large as a Dragon isn't going to be able to get up that high. It's a huge creature and that high up, the wings aren't going to be able to generate enough downward force from a flap to sustain flight. Also, at that altitude, the air is so thin that the beast won't be able to breathe. Flapping wings that big is going to take enormous amounts of calories and oxygen. Up there, the oxygen isn't going to be available. We can only fly in planes at the altitudes we do because they are basically sealed cans that maintain the same pressure of a much lower elevation.
2) Aircraft wings have a leading edge that is heated. That reduces icing problems at lower altitudes in foul weather. Dragon wings, traditionally, are bare skin. Birds may lose lift in the cold, but that is from ice forming on the feathers. Bare skin is going to have blood vessels which will provide heat to the surface.
3) Dragons are traditionally Cunning. Sorry, but a Dragon is unlikely to be daft enough to try to fly when it's cold enough to overwhelm the natural de-icing properties. that also applies to going high enough that the temperature would get that low.
4) Low Air pressure means lower boiling point of water. To match it up with human blood, this happens at about 63000 ft. A warm blooded creature would have it's blood literally boiling. That is not a survivable thing to have happen to anything.
5) I imagine that, like penguins, evolution would add hydrophobic oils to the dragon's skin. (Thank you AlexP)
6) Because Magic.
In summary, Dragons won't have the Icing problem because it won't fly high enough, it won't be daft enough to get caught out in the nasty weather, and it will have mechanisms given to it by evolution and magic to prevent the problem.
It's a great thought exercise.
Icy wings don't work
Wings lose lift in icing conditions because the ice changes the properties of the wing, causing it become less capable of producing lift. This is a far more dramatic effect than it sounds at first -- even a sandpaper-like coating of ice will produce a massive drop in lifting ability due to the air hitting the rough patches and separating from the wing in a turbulent fashion.
However, getting the ice on there is harder than it sounds
For ice to form on the wing, though, you need water droplets suspended in air that are cold enough to freeze on contact with the wing surface. If they're not cold enough, they don't freeze. If they're too cold, they've become ice crystals already and just bounce off, doing nothing to the wing. The higher the droplet density and/or the bigger the droplets, the more ice buildup you get.
Countering ice with water
There are three basic approaches to countering the problem of icing while inflight (ground icing would be trivial for a dragon to deal with themselves, so we won't cover that here):
- Heat the wing leading edge (the most critical part) up so that the water droplets can't stick to it -- this requires a fair bit of heat, though, due to water's high specific heat and the fact at low speeds, slipstream cooling of the wing is going to overwhelm any ram rise present. (It's what jets do.)
- Put something on the leading edge that expands and contracts, mechanically breaking the ice off. (This is the "de-icing boot" found on most propeller aircraft that can fly into icing.)
- Have the wing emit a substance that lowers the freezing point of the water. (This is a so-called "weeping wing" system, using an antifreeze-ish fluid.)
Given that most dragons probably would have other problems if their blood could deliver the amount of heat jet engine bleed air does, and a mechanical system would probably be quite exhausting for a dragon that's already in heavy need of energy, I'd suggest a "weeping wing" system.
In this, the dragon would have evolved glands along the wing leading edge that secrete a hydrophobic and/or freezing-depressant fluid that lowers the freezing point of the water droplets to well below the conditions where liquid water droplets can be found in flight. As a result, the water impinging on the wing stays liquid and simply blows/falls off just like any other raindrop.
But, this may be moot anyway
One thing about icing is it requires moisture. Guess what this moisture is in the form of?
It's a cloud, of course (unless it's actually falling from the sky in the form of freezing rain). And flying into a cloud on a summer day with no icing to menace you is already a significant challenge due to the lack of a visual horizon reference. Unless your dragons have highly evolved inner ears that can provide them with reliable 3-D attitude references, they'd have to stay out of the clouds and rain, which automatically keeps them clear of ice.