TKS v De-ice boots v Heated leading edge
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TKS v De-ice boots v Heated leading edge
Not being an expert on this, I thought both systems appear to have their limitations - TKS being the proactive system and boots being effectively, the reactive system.
It occurred to me that a heated leading edge element would be both proactive and reactive - and substantially cheaper (in theory) than both systems but there seems to be little information available on such systems. Is this because no-one has invented such a system, or can't get one certified, or the TKS / boots manufacturers are monopolising the market and realise that a heated leading edge element would out-do both their systems?
Surely, if a pitot can be heated then a thin metal strip along the leading edge can also be heated easily - and it could be sold as a retro fit too?
It occurred to me that a heated leading edge element would be both proactive and reactive - and substantially cheaper (in theory) than both systems but there seems to be little information available on such systems. Is this because no-one has invented such a system, or can't get one certified, or the TKS / boots manufacturers are monopolising the market and realise that a heated leading edge element would out-do both their systems?
Surely, if a pitot can be heated then a thin metal strip along the leading edge can also be heated easily - and it could be sold as a retro fit too?
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But the melted ice would run back to the cold section of wing just behind the leading edge and freeze there instead.
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But the melted ice would run back to the cold section of wing just behind the leading edge and freeze there instead.
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To heat the leading edge of the wing electricly you would need a power station, I have yet to see a light aircraft that can lift one of these.
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Would it? Is that what happens in a non de-iced aircraft when it flies into icing conditions now or does it build up just on the leading edge?
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I understand that non de-iced aircraft shouldn't fly into icing conditions.
So, under what conditions would ice form behind the leading edge - and if ice behind the leading edge is a problem then why do de-icing boots only cover the leading edge?
So, under what conditions would ice form behind the leading edge - and if ice behind the leading edge is a problem then why do de-icing boots only cover the leading edge?
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Look up the term run-back icing. Here's one link: http://www.tc.faa.gov/its/worldpac/techrpt/ar0716.pdf
Deicing boots allow a build up then pulse so the solid ice is forced to fall off. Water doesn't run back because it doesn't melt.
Deicing boots allow a build up then pulse so the solid ice is forced to fall off. Water doesn't run back because it doesn't melt.
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Looking at the size of a heated pitot just to de-ice a small hole, I think heating up the leading edge of 2 wings would require quite some power.
Still i dont have an answer
Still i dont have an answer
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ok like i said, I'm not an expert but perhaps some heat could be diverted from the engine exhaust or something like that? If that were the case ie. if the de-icing system were permanently on, then melt water re-freezing further back wouldn't be an issue?
You may have to heat most of the wing area to prevent runback from refreezing if you rely on a heated leading edge. Think of a plane flying is sub-zero temperatures. Eventually parts of the airframe & wings cool, often reaching freezing temps. That's a huge area to warm. TKS shouldn't have runback problems because the fluid flows back over the wing. Boots don't have the problem either because the ice that gets cracked off remains frozen & gets blown away in the slipstream.
The single engine Cessna 400 Corvalis has an electrically heated wing option.
The problem with boots on light aircraft is they do not go fast enough so that the slipstream peels the ice off as soon as it is cracked. TKS is IMO the best system for light aircraft
The problem with boots on light aircraft is they do not go fast enough so that the slipstream peels the ice off as soon as it is cracked. TKS is IMO the best system for light aircraft
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Is this because no-one has invented such a system, or can't get one certified, or the TKS / boots manufacturers are monopolising the market and realise that a heated leading edge element would out-do both their systems?
Electric are often used on propeller blades.
Electrically heated windscreens are common.
Currently, a good example of a light twin that uses multiple types of anti-ice is the Piaggio Avanti. The forward wing is electrically heated. The windscreen and pitot tube use electric heating. The main wing uses bleed air to heat the leading edge. The engine nacelles use inflatable boots. The horizontal stabilizer is heated by exhaust gasses distributed by the propeller disc.
TKS is fine so long as the fluid holds out and so long as ice isn't allowed to form. Boots are fine so long as the ice doesn't bridge (and that does happen, contrary to popular opinion). Heated leading edges can cause runback that freezes aft of the leading edge. Electric elements can fail.
Heated leading edges are primarily an anti-ice tool, not a de-ice tool. Causing runback is typically only an issue with a de-icing operation, where there's something to run back and freeze. By preventing the formation of ice in the first place, that problem is largely eliminated. Most ice protection falls into the anti-ice category. Boots are the primary exception, and these work primarily once ice has formed. How soon after formation, and how much ice must form before use, is debated. I can tell you from experience that ice briding, in which the ice forms a shell over the inflated boot and then can't be broken by subsequent boot inflations, is a quite real phenomenon, and an inherent possible drawback of boots.
In most cases, one shouldn't be in ice in a light airplane, anyway, whether one is using ice protection, nor not.
The early Citations used electrical heating in an anti-ice mode--huge power drain, the largest on the plane and it only consisted of 3 feet per side. As soon as they had enough bleed air from newer engines, it was gone. The problem is, compared to a car windshield, there is a huge wind problem and need for heat. Heated wings work on temps in the 90C range, it just isn't possible with an engine alternator fitted to a small plane.
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On turbines this is much easier to accomplish as all you need to do is take some bleed air from the compression stage and duct it to the leading edges. The compressors last stage has high temperature, but since it's before the combustion stage it's still uncontaminated with fumes, soot and exhausts.
This is the problem with ducting exhausts from a piston engine; the heat would probably be sufficient enough to do the job, but it's too corrosive.
This is the problem with ducting exhausts from a piston engine; the heat would probably be sufficient enough to do the job, but it's too corrosive.
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No, it's not. Heat from superchargers and turbochargers has been in use for wing anti-ice for over half a century. I used to fly a few of them.
Electric leading edges are viable, as are boots and weeping wings, especially for light aircraft where weight and cost are critical issues.
A big problem with leading edges and surfaces heated by bleed air or hot airflow is that the heat source must be reliable, even at low power settings.
The airplane I operate presently has a massive source of hot bleed air, but also has operating restrictions that require a fairly high minimum power setting in order to meet the anti-ice requirements, and that's just for the engines.
In a light airplane, while one could certainly arrange to have hot air available (combustion heater, turbo air, exhaust, etc), it's less practical than other commonly used sources. Boots use vacuum pumps and work well, but the trick in a light airplane isn't protecting surfaces; it's staying out of the ice in the first place.
Electric leading edges are viable, as are boots and weeping wings, especially for light aircraft where weight and cost are critical issues.
A big problem with leading edges and surfaces heated by bleed air or hot airflow is that the heat source must be reliable, even at low power settings.
The airplane I operate presently has a massive source of hot bleed air, but also has operating restrictions that require a fairly high minimum power setting in order to meet the anti-ice requirements, and that's just for the engines.
In a light airplane, while one could certainly arrange to have hot air available (combustion heater, turbo air, exhaust, etc), it's less practical than other commonly used sources. Boots use vacuum pumps and work well, but the trick in a light airplane isn't protecting surfaces; it's staying out of the ice in the first place.
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The new Boeing airliner uses electrical heating instead of bypass air. It seems obvious that keeping the bypass air inside the engine and using a similar amount of power to drive a big alternator should produce a similar result, and Boeing claim it is actually more efficient.
One can't compare with car windscreens because the airliner heated wing is hot enough to vapourise the droplets upon contact, so there is no runback. This needs a lot of power - to maintain the leading edge at +100C or whatever, against a 400kt wind.
One probably could use piston engine exhaust gases to do it but the plumbing issue would be considerable. It's an interesting idea... Yes the gases are corrosive but if you cooled them down a bit, stainless steel should last a very long time. Inconel exhausts last many years anyway.
The Cessna 400 system uses a large alternator - about 40kW IIRC which is about 50HP of engine loading.
The most effective system for GA is definitely TKS. Sadly the fluid is very expensive and the fill is good for only 1-2hrs of protection at max flow. It makes sense only for transiting icing conditions, which tends to mean a turbocharged aircraft.
One can't compare with car windscreens because the airliner heated wing is hot enough to vapourise the droplets upon contact, so there is no runback. This needs a lot of power - to maintain the leading edge at +100C or whatever, against a 400kt wind.
One probably could use piston engine exhaust gases to do it but the plumbing issue would be considerable. It's an interesting idea... Yes the gases are corrosive but if you cooled them down a bit, stainless steel should last a very long time. Inconel exhausts last many years anyway.
The Cessna 400 system uses a large alternator - about 40kW IIRC which is about 50HP of engine loading.
The most effective system for GA is definitely TKS. Sadly the fluid is very expensive and the fill is good for only 1-2hrs of protection at max flow. It makes sense only for transiting icing conditions, which tends to mean a turbocharged aircraft.
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Bear in mind that wing anti-ice isn't used much on large airline aircraft. Setting aside the fact that it cant' be used for some of the flight (when leading edge devices are deployed), and that much of the flight is conducted in conditions too cold for icing, one needs to remember that the wings are thick enough that icing is seldom a problem, and ram air rise causes a total air temperature at the wing that's considerably colder than the free airstream. What this means is that icing is seldom a problem, especially above 300 knots.
Runback is one of the chief drawbacks to a heated leading edge.
One can't compare with car windscreens because the airliner heated wing is hot enough to vapourise the droplets upon contact, so there is no runback.
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This looks quite interesting:
Aircraft Deicing - Kelly Aerospace ThermaWing™
Goodness knows how much power it requires to work effectively.
Aircraft Deicing - Kelly Aerospace ThermaWing™
Goodness knows how much power it requires to work effectively.
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Goodness knows how much power it requires to work effectively.
On the Cessna 350 and 400, The ThermaWing™ System (formerly EVADE) utilizes 6 heaters, 3 heater control modules, one main electronic controller, and one 7500 watt alternator to deice the aircraft.
Q: How much does the system weigh?
46 pounds with the 16 pound alternator, 30 pounds when the ACU becomes available
Q: How is the system powered?
7500 Watt Alternator
Q: What about run back?
Run back is minimized by the pulsed power method of operation. The bond between the surface of the wing and the ice is broken and the ice flies off aerodynamically. The ice is not melted completely thereby minimizing runback.
46 pounds with the 16 pound alternator, 30 pounds when the ACU becomes available
Q: How is the system powered?
7500 Watt Alternator
Q: What about run back?
Run back is minimized by the pulsed power method of operation. The bond between the surface of the wing and the ice is broken and the ice flies off aerodynamically. The ice is not melted completely thereby minimizing runback.
It's also not certified for flight into known ice.