By William E. Dubois · October 19, 2023 · 6 Comments
My wife: What’s TKS? Brass Radiator Mesh
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.
William E. Dubois is a NAFI Master Ground Instructor, commercial pilot, two-time National Champion air racer, a World Speed Record Holder, and a FAASTeam Representative.
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On my desk, as I type this, is an inert MARK III 1 I.C.I 42 chisel nosed cable-cutting bullet/cartridge given to my grandfather by Sir James Martin, whom I had the pleasure of meeting in the 1970s.
Sir Jimmy and my grandfather were not only good friends but my grandfather – Sir Harold Roxbee Cox, later Lord Kings Norton and first chancellor of Cranfield University – was also Deputy Director of Scientific Research at the Ministry of Aircraft Production in 1940 and, by 1943, Director of Special Projects, with special responsibility for working with Frank Whittle on jet engines. In 1944, he became Chairman and Managing Director of Power Jets before becoming Chief Scientist at the Ministry of Fuel and Power in 1948.
He got his elder son, Christopher, my late father, a ‘holiday job’ at the Martin Baker factory where he would have lunch with Sir Jimmy in his office every day. This was at the time that the ejector seat was being put through its early ramp tests.
When, as teenagers, my brother and I were at the Farnborough Airshow with (a by then elderly and very deaf) Sir Jimmy, an endless stream of representatives from various aircraft companies would present their card and tell him how one of their pilots had recently been saved by one of his ejector seats. It was extraordinary to behold.
If you’d like some photos of the MARK III 1 I.C.I 42, please let me know and I’d be happy to take a few and to send them to you.
Really fun read, William. Thank you for putting in the effort to bring this interesting piece of aviation history to the community. I’ve been at CAV Ice Protection for 16 years, so I was aware of the history of the system. It’s just nice to read about when written by someone who knows how to turn a phrase. I will be recommending your article to new employees joining CAV.
As you noted, TKS started as a defense initiative and has grown to be available on over 100 General Aviation model variants. Some installed at the aircraft OEM factory and others installed as retrofits. If anyone cares to continue their TKS education, please have a wander through our website at cav-systems.com
I have collected a few articles from the pre-TKS days of the mid to late 1930’s, which provide some insight into the DNA of the TKS system. Happy to share them if anyone has any interest or just has general TKS questions.
Jeff Holden +1 (913) 738-5396 j.holden@cav-systems.com
Thanks William, I work for CAV and can honestly say I have witnessed firsthand people have the same reaction as you when asked what TKS stands for!
Seriously though, we are incredibly proud of our heritage, and I really enjoyed your article.
Today, TKS is certified for installation on over 100 aircraft variants and available for integration on a wide range of GA aircraft in factory or a retrofit. If anyone would like to learn more about the system, I recommend looking at our website cav-systems.com. There is a great introduction to TKS by our CEO or I would be happy to answer any questions. Just drop me a line.
I don’t know about the “vodka-infused maple syrup” part. I do know it tastes bad: I was pre-flighting a DA-42 on my ATP checkride & accidentally hit the “Windshield” de-ice button with the canopy open & my face above the glare shield…
Thanks for the history. You’ve satisfied wives all over America!
Greg Curtis, CFII, MEI says
And inquisitive student pilots inadvertently stumping the omnipotent IP.
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