Exhaust De/Anti-Icing Question/Idea

[SkunkStripe]

Just curious as to why most smaller twin aircraft have boots, TKS, etc

Could you not theoretically funnel the exhaust out of the engines to the leading edges to constantly have heated leading edges?

Sure you have fuel in the wings but you could keep that a safe distance apart.

Don't be to harsh... I have a feeling someone is going to respond with the most simplistic of answera explaing why.

[CID]

There are all kinds of reasons not to do that. Besides the dirty and corrosive exhaust gasses, the different metals required to deal with the heat, the power fluctuations from changing the exhaust tuning, there would be severe reduction in effectiveness at flight idle and/or during an approach when you arguably need it most.

I don't think there would be enough volume to do it effectively either. Imagine what a backfire may do to your leading edges.

Bleed air is used in larger jets but in those applications there is plenty of relatively clean hot air available.

[pdw]

That's right.

The heated wings are there ... in the large aircraft, where there's no shortage of BTUs; they have systems (the hot wing) that are reliable for what's being suggested.

(Funny, I typed "hot wings" into the search mode of this forum and the first thing came up was Skunkstripe's post )

A lot of heat is needed when it counts in an icing encounter, and smaller aircraft can't produce as much bleed air as is sometimes required; so they don't utilize those systems for that reason. De-icing boots don't have the same problem of capacity; they can just keep bursting off the ice that's on them (by re-inflating them) but eventually there is the problem of a build up around the edges ...

[nine sixteenths]

Several small turbo prop aircraft use exhaust gasses for the engine intake De/anti ice. The biggest difference that I can see is that it needs to heat a couple feet of surface, close to the source. Exhaust gas (particularly on piston engines) isn't really that hot, and I can't see it being hot enough 20 feet from the source to be relied on to keep anything but very light ice off

[Docbrad]

To elaborate on what some other posters said, you have to keep in mind that bleed air is NOT exhaust air. In a jet engine, air is compressed and then fuel is added and then burned. Bleed air is only siphoned from the compression stage. As air is compressed it heats up. And quite dramatically too. Thus being usable to melt significant amount of ice, even before being burned.

I'm not sure if you have looked at the bottom of your flying club's 172, but it is usually filthy with grime from the exhaust. Not something you would want in 20' long tubes on your wings.

[Navajo Flyer]

I understand that a heated leading edge has to be hot enough to vaporize the moisture or water droplets. If the wing isn't hot enough you will run into a "run back" condition, where the moisture will simply run back and freeze.

[niss]

Don't forget that the byproducts of (complete) combustion of a Hydrocarbon is Carbon Dioxide and Water Vapour. The surface area involved for effective heating would cause for quite a bit of condensation. With it you have issues of now corrosive condensate, and ice forming. Along with the ice comes increased weight and restriction of the exhaust. You could potentially have issues with max gross or the COG, as well as lose engine power.

Remember that whenever we are heating something, we are effectively cooling something else, and we may have undesirable effects when we cool that something else.

Now we could mitigate these by using a shroud like the cabin heat in singles, however I would still be concerned with condensing and freezing on the inside of the wing and the problems that could bring. Imagine it getting bad enough that now you have cracks, or separation of components due to expanding water!

[fish4life]

Tks is a very effective system even some aircraft companies like Hawker use it for their corporate jets, it takes fuel and power loss to heat the wings and tail surfaces up.

[Eric Janson]

Tks is a very effective system even some aircraft companies like Hawker use it for their corporate jets, it takes fuel and power loss to heat the wings and tail surfaces up.

All the jets I've flown only had the outboard slats/engine intakes heated by bleed air.

No anti ice/de-ice on the the tail surfaces.

[fish4life]

Tks is a very effective system even some aircraft companies like Hawker use it for their corporate jets, it takes fuel and power loss to heat the wings and tail surfaces up.

All the jets I've flown only had the outboard slats/engine intakes heated by bleed air.

No anti ice/de-ice on the the tail surfaces.

Different philosophies by different manufacturers I guess the hawker 800 is tks.

http://www.aerospace-technology.com/pro ... ker_800xp/

[CpnCrunch]

Now we could mitigate these by using a shroud like the cabin heat in singles, however I would still be concerned with condensing and freezing on the inside of the wing and the problems that could bring. Imagine it getting bad enough that now you have cracks, or separation of components due to expanding water!

I think the main problem is that you just don't get very much heat out of the heatbox on most small spamcans. It's barely hot enough to warm the balls of a brass monkey, never mind melting any ice on the wings.

[Liquid Charlie]

As stated small displacement engines do not have the capacity to heat wings to the point of sublimation and all you would get is severe run back and smoking holes -- The piston Convairs had hot wings with adjustable guide vales in the augmenters to control cylinder head temperatures so as much heat as possible to the wings -- system did not work very well - the Convair 640 with Dart engines mounted a janitrol heater in each wheel well - bad -- very bad - the Darts didn't have enough spare air to tap off the engines -- now getting into turbines -- the Herc had hot wings but at heavy weights it robbed too much power and it was used as an deice system rather than an anti ice -- in my experience hot wings is a great system for aircraft that usually don't need anti-icing except for climbing and descending - while no aircraft is certified for anything but light icing when you can't out climb it breaking it off gives you less grief than run back --

[teacher]

On a side note the PC12 used hot exhaust gases to always heat the engine intake. Worked very well and also very simple. Inlet was opposite the exhaust gas flow in the exhaust stack. The heat didn't have far to go so heat loss was not a factor I guess.

[pdw]

On a side note the PC12 used hot exhaust gases to always heat the engine intake. Worked very well and also very simple. Inlet was opposite the exhaust gas flow in the exhaust stack. The heat didn't have far to go so heat loss was not a factor I guess.

There's a lot of BTUs right there and no effect on engine performance if too much heat were lost out of the stack at that location, so it's a reliable heat source but also never too much, ... no question there's always enough to do the job.

We were talking earlier in this thread, as Niss mentioned it, when heating iced areas with engine heat it means something else is cooled (gives up its heat) in the process. So here's one example of the kind of cooling factor that might have been that kind of an issue:
There was a local icing accident years ago and I called up the leading investigator to ask this question. A cold-soaked turbine single at max-load / max-power is burning significantly more chilled Jet-fuel in early takeoff than in top cruise. Is the fuel preheating system that uses engine-made heat to unchill the jetA as it flows in, able to warm up say 2.5 gallons of this -30C fuel instantly-enough once the system's resorvoir-fuel warmed pre-flight has cleared an older engine's fuel nozzles during/after rotation's heavier fuel-flows; or does it heat up too slowly, staying more viscous, so that an unsatisfactory atomization from the inducted fuel spray pattern results in reduced power available in full power climbout ?

I also asked the same question basically as Skunkstripe has in his opening post, and soon came to realize that chill-factor can be a very powerful thing when not enough heat is available; then bleed air is not a surplus heat, ... until further along in the flight once there's ample excess power available ...
EDIT: for spelling / errors

[Rookie50]

Minor thread jack -- forgive me--- 2 questions for winter ops in a piston single:

What fluids can I carry around for:
In case of frozen brakes (I think gas line antifreeze)
- minor wing de-icing.

Thanks!

[skymarc]

The TBM uses the same system. Works very good.

On a side note the PC12 used hot exhaust gases to always heat the engine intake. Worked very well and also very simple. Inlet was opposite the exhaust gas flow in the exhaust stack. The heat didn't have far to go so heat loss was not a factor I guess.

[pdw]

What fluids can I carry around for:
In case of frozen brakes (I think gas line antifreeze)
- minor wing de-icing.

RV/plumbing antifreeze is safe to carry and available lots of places. Check the label to see if it is useful and how much you may warm it.