With all the attention on pneumatic de-icing boots from the Colgan 3407 Q400 disaster in Buffalo last week, I was curious to see if any new technologies have been put to use to crack ice off the leading edge of lifting surfaces.
One very promising advance is a low-power "electro-mechanical expulsion deicing system" (EMEDS) built by Cox & Company and already in use on two Hawker Beechcraft models, the Premier 1A and the Hawker 4000, for the horizontal stabilizer. Boeing is also using the technology for the raked wing extensions of its P-8A Multi-Mission Maritime Aircraft, a variant of next generation 737.
Unlike a pneumatic system, which inflates rubber bladders on the leading edge of wings and tail surfaces....
...the EMEDS uses an aluminum or stainless steel leading edge with the guts of the deicing system behind the leading edge, protected from the elements. Actuators, driven by electro-magnetic forces, move at high frequencies, changing the shape of the leading edge such that ice thicker than 0.06in breaks off.
Benefits of having a metal leading edge include less drag and longer life compared to the rubber boots which wear away from abrasion.
Perhaps more beneficial is that EMEDS is immune to ice bridging, a phenomena where pneumatic boots, if activated too early in ice formation stage, can potentially form a "bridge" over the leading edge which cannot be removed by the boots on subsequent cycles.
The video below, provided by Cox, shows how EMEDS works on the horizontal tail of a typical business jet. Note how the de-icing action takes place in sections, with the entire process repeating every 20 seconds.
Though jet powered aircraft use bleed air from the jet engines through piccolo ducts to pump hot air out onto the leading edge to melt ice before it forms (so-called anti-ice), some locations on the airframe are too difficult to reach with the hot air, and sometimes there simply isn't enough hot air left after servicing the main wing and the cabin.
Cox says it is in talks with multiple manufacturers about using the technology on a variety of new aircraft, and not just for the tail.
on March 1, 2009 3:56 PM | Reply
The EMEDS technology is an outstanding piece of work. This may represent the direction the industry needs to aim in, although it remains to be seen how well this technology will work in larger liquid water encounters or with supercooled large droplets. Thats said, the low energy requirements may allow some flexibility in terms of either additional thermal energy or additional surface area coverage to meet those challenges.
I should point out that the ice bridging notion has been pretty well debunked over the last ten years. It retains quite a following in the industry, but there is no documented evidence of it ever being associated with an accident, or, in fact, ever truly occurring. There is a significant issue with intercycle and residual ice associated with pneumatic boots, particularly in cases where the boot material has not been maintained.
on March 2, 2009 5:35 PM | Reply
Thanks for the comment Steve. Regarding ice bridging, I have never seen it myself, but can remember being perplexed by the concept when I used to fly night cargo in a Piper Navajo with my primary flight instructor, Brent Myers, back in the late 1970s. I was perplexed because the process for using the pneumatic deicing boots was very qualitative rather than quantitative -- "Turn the boots on after ice has formed on the leading edge, but not TOO soon" or else risk ice bridging.
An interesting article recently published by Aviation Information Network (AIN), written by friend and fellow GA pilot Matt Thurber (who's spend his share of time avoiding ice while flying IFR is his Grumman American single) discussed one pilot's experience with the beast however:
...AIN has interviewed pilots who claim to have experienced ice bridging. One told AIN that he saw ice build a shell over the inflated dimensions of the boots on a Piper Navajo that he was flying in heavy icing conditions. And NBAA Southeast regional representative Harry Houckes said, “I’ve seen it happen; it’s a fact of life. I’ve seen situations where if you don’t wait for some icing accumulation on the leading edge where the boots are and activate too soon, you push out a slushy mixture and it freezes and you have an icy extension beyond the boots. And you can’t get rid of it. Once it’s formed beyond the boot extension range, you’re [out of luck]. You can cycle the boots as much as you want.”
Houckes’ experience with ice bridging was when flying Beech King Air 200s and 300s, he said. Although the King Air has an automatic mode for de-icer boot actuation, he had a policy of using only the manual mode so ice could accumulate before first deploying the boots. Houckes doesn’t agree that all pilots in all boot-equipped aircraft should follow the advice to inflate boots as soon as icing is encountered. “It seems like the NTSB leaves you some wiggle room by saying ‘follow flight manual procedures,’” he said. “I don’t want to see folks coming into the industry getting lulled into a false sense of security. [Ice bridging] does happen; I’ve seen it.”....