My wife: What’s TKS?
Me: It’s deicing fluid.
Wife: I’m not an idiot. I know that. I mean, what do the letters stand for?
Me (loooooong pause): Gosh, look at the time babe. I’m late, gotta run!
As it turns out, TKS stands for Tecalemit-Kilfrost-Sheepbridge Stokes.
That’s the name of the company that invented the fluid used inside modern “weeping wing” deicing systems, prop slingers, and windshield deicing systems. The company was formed in 1942 by the British Ministry of War to develop ice protection systems for Royal Air Force (RAF) bombers.
If you’re wondering about the very odd (even for the British) chain of words that make up the company name, TKS was a joint venture of Tecalemit Limited, Kilfrost Limited, and Sheepbridge Stokes Limited. Apparently Tecalemit was a manufacturer of oil systems and filters, Kilfrost made anti-ice paste, and Sheepbridge Stokes made iron rotors for aircraft fuel and oil pumps.
At the time, inflatable deicing boots, which are still in use on many airplanes today, were state of the art for airplane deicing, but the RAF had a unique problem caused by another type of inflatable technology: The barrage balloon.
You see, the Royal Air Force was keen on flying low-level missions across occupied Europe to improve bombing accuracy, but the brass was worried about those darn Germans floating barrage balloons above the targets. Of course, a barrage balloon itself is really just a lifting system for the real airplane counter measure: Steel cables intended to shear the wings off of unwelcome aircraft.
The Brits, after much research and experimentation into possible barrage balloon countermeasures, decided to fit their bomber fleets with cable-cutting systems made up of armored leading edge wings designed to deflect cables along the wing to specially-designed notches that were equipped with explosive cable cutters.
Think of it as a bad-ass flying hot knife cutting through butter. Only, you know, with all that scary flak and bullets and combat stuff.
As a side note, this cable-cutting tech was developed by none other than Sir James Martin of the Martin-Baker Aircraft Company, the guy who invented the ejection seat.
But while the balloon-cable cutter is really quite clever — and it did work — it ignored the fact that, while the British were barrage balloon happy themselves, apparently the Germans really didn’t use all that many.
That, combined with the amount of time it took to develop the system and the extra weight the system added to the airplanes (reducing the bomb load), meant that few British aircraft were actually equipped with the cable cutter system in the end.
But long before they got to that end game, the Brits realized that their prototype cable-cutting system had a major problem: The deicing boots on the leading edges of the bomber’s wings created friction, keeping the cables from slipping along the wing to the cutter notch.
Oh, right, and the second problem was the low-level missions were flown in prime icing altitudes, hence the drive to develop an alternate method of keeping ice at bay. There’s no point in escaping enemy barrage balloons only to be brought down by ice.
The combined efforts of the experts from Tecalemit, Kilfrost, and Sheepbridge Stokes resulted in the first generation of the modern weeping wing. It used tubes of porous “sintered” metal — metal formed from powder — that were installed into the leading edges of the new cable-resistant armored wings. The porous tubes, much like modern soaker hoses, let a newly developed fluid seep through the leading edge and then migrate back across the top of the wings.
Simply called TKS fluid, it was a freezing point depressant, a chemical that lowered the freezing temperature of water that mixed with the fluid, much the way that adding salt to water lowers its freezing point. While fresh water freezes at 32° Fahrenheit, salt water’s freezing point is around 28°. They’re both water, but salt is a freezing point depressant.
Of course, salt being corrosive to metal, we don’t want to use that stuff on airplanes!
Plus, TKS’s ethylene glycol-based recipe far out-strips the effectiveness of salt. TKS lowers the freezing point of water it mixes with to a mind-numbing negative 76°F!
All of this said, the weeping wings were only installed on a limited number of Vickers Wellington, Avro Lancaster, and Avro Lincoln bombers.
But in the post-war commercial aviation boom, TKS was to come into its own, and the company that created the fluid and the delivery system still exists today, now under the name CAV Systems.
Of course, there have been some changes to TKS systems over the eight-plus decades since they were invented. Apparently, the original sintered metal was prone to cracking, so it was replaced in later years with multiple layers of stainless steel mesh, and later still — thanks to modern technology — by laser-perforated titanium strips.
And all the while, the company has made its signature deicing fluid. So, is that the same as the stuff they spray on airliners during the winter months? Yes and no.
Although chemically similar, TKS — as it is designed to seep through very small holes — is a thin fluid, while most airport deicing fluids (there are four types) are engineered to be thick so that they stay in place long enough for the airplane to get to the active runway.
I’m OK with you thinking of TKS being like vodka: It’ll melt ice if you pour it over the wing, but then it will run off onto the ground.
Airport deice is more like vodka-infused maple syrup. Only, you know, maple syrup designed to break down when exposed to high wind speeds, so it blows off on the takeoff roll. For instance, Type II fluids lose viscosity at 100 knots, one reason we don’t use the stuff on GA airplanes.
For GA airplanes, the airborne TKS fluid can be used for ground deicing, with the only risk that, as it runs off quickly, it opens you up to re-icing on the ground. But if the weather is really that bad, you should be re-thinking your flight anyway.
So there you have it, born of war, Tecalemit-Kilfrost-Sheepbridge Stokes fluid now lets us battle the elements. And what of the cable cutter that started all of this?
It’s frozen in time.