TKS v De-ice boots v Heated leading edge

[VMC-on-top]

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?

[ShyTorque]

But the melted ice would run back to the cold section of wing just behind the leading edge and freeze there instead.

[A and C]

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.

[VMC-on-top]

But the melted ice would run back to the cold section of wing just behind the leading edge and freeze there instead.

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?

[VMC-on-top]

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.

Me either but I've seen plenty of cars with very fine heating elements built into the windscreens which can clear a windscreen of a heavy frost in no time at all - and they don't carry power stations round with them?

[ShyTorque]

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?

Depends on the conditions. But non de-iced aircraft shouldn't be flown in icing conditions in any event.

[VMC-on-top]

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?

[ShyTorque]

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.

[chris-h]

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

[VMC-on-top]

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?

[Tinstaafl]

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.

[Big Pistons Forever]

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

[SNS3Guppy]

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?

Such systems are in use. It's not a matter of not inventing one. Heated leading edges are in use in most turbine equipment, and piston equipment has been using heated leading edges since the second world war.

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.

[galaxy flyer]

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.

GF

[AdamFrisch]

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.

[SNS3Guppy]

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.

[IO540]

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.

[SNS3Guppy]

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.

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.

Runback is one of the chief drawbacks to a heated leading edge.

[wsmempson]

This looks quite interesting:

Aircraft Deicing - Kelly Aerospace ThermaWing™ (http://www.kellyaerospace.com/thermawing.html)

Goodness knows how much power it requires to work effectively.

[SNS3Guppy]

Goodness knows how much power it requires to work effectively.


According to the web site:

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.


Worth noting about this system, however, is that it's only certified for the Colombia 300/Cessna 350-400.

It's also not certified for flight into known ice.

[IO540]

One sheet I read about the C400 system is that the alternator was 50A at 80V (or IIRC 80A at 50V) which is 4kW, not the 40kW I posted earlier :)

There were considerable problems with it, for a long time, which Lancair (and later Cessna) blamed on dealers installing it incorrectly (no idea if that's true).

Rubber boots remain popular, after all these years...

Known ice certification is not as clear as it might appear. Take the TB20: the G-reg version is certified but the N-reg one isn't - because the FAA requires a backup alternator and some other bits, which relate to systems redundancy but don't actually relate to ice protection.

By all accounts, TKS is incredibly effective even in the worst conditions in Europe. I know of pilots who fly in virtually all weather in the most northern bits of Europe and they say the ice just comes right off. Expensive though - 20 litres of TKS fluid is about £150 to £200 delivered and you can blow that away in an hour.

[SNS3Guppy]

The problem is that while an anti-ice system may be very effective, it can fail, and even if it doesn't fail, other things can.

Everybody who does instrument training or has an instrument rating has some modicum of exposure to partial panel work. In a controlled environment, it's not that big a deal. In solid IMC, bouncing around, dealing with ice and ATC, it's a very big deal. Flying light airplanes in IMC, especially airplanes equipped with dry vacuum pumps and single sources of instrument power, are begging for trouble.

Flying a single engine airplane IMC is a questionable act at best, given one engine. Flying a single engine airplane IMC with one generator and one vacuum or instrument source is more questionable. Flyin a single engine airplane in instrument conditions in ice with the deck already stacked against one, is playing roulette (russian, to be exact).

If one has flown airplanes with boots and hasn't had one side fail to inflate, or fail to shed ice, or bridge, then one hasn't flown much with boots.

If one has flown in ice but hasn't seen ice quickly build to overwhelm the capabilities of the ice protectiion in use, one hasn't flown much in ice.

The fact is that one can be in icing conditions in which the preceding aircraft and the following aircraft don't experience ice, but you do; severe ice. It happens.

I experienced an ice build-up in a piston Twin Commander years ago that caused us to go from a cruise speed to minimum controllable with a descent below MEA (in the mountains) in less than a minute. A 50 knot loss in less than a minute, and ice protection wouldn't slow it down. Ice shed from the propellers putting holes in both sides of the airplane, and causing a noise in flight that sounded like 12 gauge shotguns being fired continuously behind our heads. It developed unexpectedly, rapidly, and couldn't be controlled.

We were fortunate due to location and circumstances to be able to drift down to the surface where we stopped descending, and followed car taillights in cloud and snow to an airfield. Ice is very serious stuff.

Boots are popular, but they do fail, and boots do change the flight characteristics of the airplane during inflation, and during the case of assymetrical inflation. Also bear in mind that if one is using the same vacuum pump for instruments as for the boots, lose one, lose both.

[Fuji Abound]

We were fortunate due to location and circumstances to be able to drift down to the surface where we stopped descending, and followed car taillights in cloud and snow to an airfield.


What were you flying - it must have been slow?

[IO540]

Flying a single engine airplane IMC is a questionable act at best, given one engine

I never knew what I have been doing the last 10 years was so dangerous.

I think I am going to give up.

[SNS3Guppy]

I believe I said it was a piston twin commander. It wasn't that slow, but following a line of cars taillights in the cloud on a mountain road doesn't require slow. Just enough cars to light the way. We knew where we were, and the cars were leaving a mill, headed for a small town. We landed at the airport at the small town.

[Fuji Abound]

Ah yes, I see.

IMC in a SEP - well it is impossible to generalise and I am a little surprised you should take your view. No one wants to be bashing through hard IMC for any length of time; transitioning to VMC on top is what it is all about.

Of course IMC introduces new and different risks but when push absolutely comes to shove the difference between a SEP and a mulit is the expectation you might make an unscheduled landing. Save that, some SEPs are likely to be more reliable that some twins I know! Personally I have never been able to balance the risks against rewards of flying a SEP over terrain where I would be very uncomfortable to land or over an under cast that would give me little chance of landing. However to state the obvious the engine doesnt know it is in IMC. If it quits, the aircraft is just another glider and with a reasonable base it is probably not going to end a lot differently that if it quit on you in VMC. Just to distinguish in the simplest way between IMC and VMC seems illogical on the basis that you only have one engine; to distinguish because you only have one electrical power source or one vac pumps makes a great deal more sense.

Obviously whether it is SEP or multi dont go there if the aircraft cant cope with the forecast ice, turbulence or whatever hazards are associated with the IMC in question, but that is a factor of the aircraft not the number of engines it has.

[SNS3Guppy]

Of course IMC introduces new and different risks but when push absolutely comes to shove the difference between a SEP and a mulit is the expectation you might make an unscheduled landing.

That's the common view, but it overlooks critical issues, such as redundancy of operational equipment. Most single engine airplanes don't have a second vacum pump or second generator. Many single engine airplanes don't have the same weather capability, performance, or even ice capability that many light twins have. Further, with a power loss,one generally has a lot more options in a twin than a single; both will eventually land, but the single will tpically be landing a lot sooner than the twin. A number of light twins can stay at altitude or drift down slowly with an engine loss, whereas this isn't going to be happening in the single.

Loss of a vacuum pump in the single can be devastating; in the twin it can be a non-event. The same for loss of the alternator or generator, given one's higher expectations for electricity when flying under IFR.

However to state the obvious the engine doesnt know it is in IMC.

Yes, and no. When flying in precipitation and visible moisture, the engine faces a higher potential for induction ice. That may be inlet ice, it may be carburetor ice, but it has a greater potential for icing. Additionally, reduced power is available where higher humidity is present.

If it quits, the aircraft is just another glider and with a reasonable base it is probably not going to end a lot differently that if it quit on you in VMC.

I don't know if you've ever experienced an engine failure in instrument conditions, but I have, and I'd say the potential to end differently (to say nothing of one's response) is not necessarily the same. It's one thing to lose one's engine in normal VFR operations, but another entirely to lose it while flying in instrument conditions. The same maybe said for instrument, vacuum, and electrical failures.

well it is impossible to generalise and I am a little surprised you should take your view.

You might not be so surprised if you'd shared some of the same experiences with me. Most of what I do, preach, and say isn't based on what I read in a book.

[IO540]

When flying in precipitation and visible moisture, the engine faces a higher potential for induction ice.

and two engines don't, obviously... they must be breathing different kinds of air.

Modern SE planes have backups and some have a total dual system. Look at the Cessna 400 as an example.

[Fuji Abound]

Yes, I was also assuming the SEP in question was designed to operate in IMC and the pilot capable.

Of course dealing with an engine failure in IMC is challenging - dont go there if you think you cant.

Of course some twins have more redundancy of some systems that singles but the engine aside some singles are equally capable.

That is why I was surprised by SNS3's comments - I'd taken these as read amoung the more experienced pilots including a realisation that the way the engine performs in IMC will be different but icing and heavy rain aside there is no more or less reason for an injected engine to fail in IMC than in VMC.

Added to clarrify: dealing with failures in IMC is always going to be more challenging than in VMC, I am not suggesting other wise. However all the failures that can happen on a mulit can equally as well happen on a single so my assumption is that the pilot is capable of delaing with the systems failure. As we have said the chances of that failure may be more, less or the same depending on the aircraft type and unrelated to the number of engines.

[SNS3Guppy]

Few here or elsewhere will be flying the Cessna 400.

While the twin "breathes" the same air, the twin also "knows" it's in IMC. I flew the Piaggio Avanti for a thousand hours or so. It was so sensitive to visible moisture that upon entering a cloud, even a little puffy fair weather cumulus cloud, the airplane lost lift and wanted to pitch forward. On autopilot, it was practically unnoticable, but when hand flying one had to move the control yoke up to two inches aft. Point is, the airplane "knows" when it's IMC, and yes, the powerplants do have an increased potential for difficulty.

Modern SE planes have backups and some have a total dual system.

Modern single engine airplanes do lack that one formality that separates them from the multi's, of course; a second engine.

[Fuji Abound]

While the twin "breathes" the same air, the twin also "knows" it's in IMC.


Come on be serious - I meant in the context that the engine doesnt say to itself oow I am in IMC, I had better quit.

Of course there will be some performance changes but when I fly my SR22 into IMC that is the extent of it; I am no more expecting the engine to quit because I am in cloud than not.

[IO540]

I give up... (again) :)

[SNS3Guppy]

Come on be serious - I meant in the context that the engine doesnt say to itself oow I am in IMC, I had better quit.

I don't know about that. I'm thoroughly convinced about the efficacy of Murphy's law, and equally certain that engines watch and wait with calculated effect to determine the most strategic time to let go.

Of course there will be some performance changes but when I fly my SR22 into IMC that is the extent of it; I am no more expecting the engine to quit because I am in cloud than not.

I surely am. I don't fly a Cirrus (and won't), but while I do anticipate and expect an engine failure at any given moment on any given flight, I have a heightened sense of that awareness when flying over terrain and at night or in instrument conditions. I anticipate such a failure all the time, but more so when the timing is worse.

Ever notice how every little tick and pop and rattle becomes more evident in IMC or at night, and how each tiny nuance of the engine and propeller and airplane become manifest by an order of magnitude in feel and sound? The airplane knows that you experience this phenomenon. Just like a horse can feel it through the reins, the airplane can feel it through your butt, and it knows. IO540 is right to give up, because there's no getting around it. You can fool mother nature, but you can't fool the airplane. It knows.

[24Carrot]

You can fool mother nature, but you can't fool the airplane. It knows. Now that adds a whole new dimension to "Human Performance and Limitations"!:D

[sternone]

I would also vote for TKS being a better solution than boots. Negative points are indeed that usable time is limited, fluid costs money, you have to apply them before you enter the clouds and it's such a mess in the hangar afterwards :-)

[SNS3Guppy]

Now that adds a whole new dimension to "Human Performance and Limitations"!

Of course. Aircraft are tempermental. You've got to know how to talk to them.

[blueandwhite]

I used to work for a company that sprayed heating mats onto surfaces for deicing use. It was mainly used on the inlet for turbo props and the leading edge of rotor blades for helicoptors.

I don't know why it wasn't used on leading edges of wings. I guess that the area on the inlet was small and on the helos you had lots of power to spare. (i'm not going to explain that comment :mad:) Also I would guess it could re-freeze as it ran back over the wing.

But I don't know why it wasn't used on aircraft as I didn't work on heating mats, I was working on the Eurofighter and the Tornado (& gippen & a320 & F100 & F16) As an aside is that the first time someone has admitted NOT knowing something on here? ;)