Phiggsbroadband:
Funny you should bring that up! In years of flying in Northern Australia I never had issues with icing but certainly did with vapour locking! :ooh:
We always went carby heat cold before landing to avoid dust through the un filtered carby heat system on the ground.:ouch:

So, you need to modify your techniques to cater for different weather situations.:ok:

I wasn't sure whether Phiggs was being ironic or not! Indeed there is a vast body of literature on vapour lock in aero engines and those of us flying on mogas in hot climates are well advised to be conversant with it.

As far as carb heat goes, I pretty much subscribe to the BPF philosophy, modified for the dusty Australian situations as described by Tankengine. One of the problems we have in much of Australia is getting people to believe that carb ice is possible in what often look like benign conditions. I've noticed that CASA have had a number of campaigns on the topic and one of their more useful charts (which I'm sure has equivalents in other countries) is:

http://www.casa.gov.au/wcmswr/_asset...cing_chart.pdf

It's well worth staring at and explains, for example, why partial application of carb heat is usually a bad idea: it's quite possible to push the temperature UP into a severe icing regime.

Having said that, I think we're all agreed that a working knowledge of the fuel/air induction system in your aircraft is a good thing. While all my carb ice problems have been fairly easily resolved, juggling the mixture and carb heat did once get me out of a wasp-induced induction block.

On a slightly different note, I was surprised to see Vilters' insistence of a fully stabilized approach and decision height of 200' in an SEP. All I can say is that, with the tubulence and crosswinds we often get in these parts (and lots of other places), we might never land on that basis. And, of course, there's always the possibility of livestock intrusion or other runway incursion. It's certainly a good idea to go around early if you know you have to do so but it's a dangerous mindset to assume you're prematurely "committed" in an SEP.

Finally, I smiled when looking at the source of this carb heat "trick" discussion. Step Turn, isn't this "trick" the sort of non-POH procedure you've been deprecating in other contexts?

Ach, I am not persistent. LOL
 

Sloppy landings come from sloppy approaches.

When I write "stabilised at 200 ft", read that as.

On centerline, on speed, X-Wind corrected, in gear and flaps landing configuration.

On every landing, one should feel confident in the ability to land the aircraft from this "stable" position.

( Even when fighting a wind or X-Wind, one should be "here" )

But, a wind gust, a deer on the runway, anything can spoil your day.

That is why a GO-AROUND has to be a single move from here till touchdown:
And that is Throttle forward.

All the rest can come later.

= > Throttle forward
= > Positive VVI ( Vertical Velocity Indication) the question was asked. DO not touch ANYTHING untill you have a positive VVI.

And then as per PoH, gear, flaps and so on.

Fair enough, I knew this would come up at some point :uhoh:. That is the case, and that criticism is fair. This "trick" is on the edge of guidance to operate the aircraft in a manner not described in the Flight Manual. So, a few thoughts as to why I made the post of this edgy topic!...

I do not believe that leaning after carb heat application is counter to any flight manual procedure, and I do believe that it equates to flight manual procedures for higher altitude operation. It is not counter to good airmanship. It is a "touchy feely" thing you can do with a running engine to keep it running. Aside from leaning too much, to power reduction, it can be instantly reversed without affecting the flying characteristics of the aircraft. Retracting flaps on final will affect the flying qualities of most aircraft, and mostly in a negative way, in a low power, approach configuration.

I was inspired to think more about the effectiveness of carb heat systems while assiting a freind with his modification of a C185 to have a carburetted engine. Included in that effort was the requirement to build a carb heat system, which would meet the FAA requirement of:

.

We had a heck of a time providing enough heat to rise the 90F heat rise, as measured in the carb venturi. We succeeded, but during the process, also developed the leaning trick, and we did describe it in the changed flight manual, as we had to do that to pass the test for the approval. As you can see from the data I provided on two aircraft, one certified, one not, the carb air temperature rise is not even close to the required value for FAA approval, yet the 150 is approved. The FAA considered this 90F heat rise important enough to specify it, so I suppose any action a pilot can take to get closer to it when needed is a good thing - at least as viewed for certification!

I wanted people to think about this. If after thinking about it, you don't agree, don't do it! But, you'd have to agree that people are thinking and discussing it, and for this topic, I opine that discussion which promotes systems understanding is good.

Yes, I'm the flight manual proponent, nanny state guy. Pilots seem to not want to read them much, and I guess that the manufacturers know this, so they try and keep them thin (though not so much for brand new Cessnas!). So little gems of knowledge are set aside (like not slamming the throttle closed on a cold day at altitude, and shock cooling the engine).

But after all is said and done, this rather good discussion was worth taking a black eye in my inconsistency with respect to following flight manual procedure :ouch:. But, this does not mean that I have now gone soft on retracting flaps for a continued landing, nor waterskiing landplanes! :=

ST, the POH point has been gracefully acknowledged and I'm not going to labour it since, as I noted elsewhere, I actually believe that judgements are always needed and go hand-in-hand with an understanding of the POH.

I quite understand your resolution to keep up standards and the need to draw the line. It put me in mind of a piece by Garrison Keillor who linked the installation of airconditoning to coming home and finding one's mother in moral turpitude :)

I don't see myself needing to lean routinely while applying carb heat but, while there was no carb ice involved in the wasp incident I mentioned, experiences like that one underline that information sharing is useful in opening our minds to possibilities which may help in unusual circumstances. But I would just comment that an inexperienced pilot managing to stop the engine while in a confused state will certainly change the flying quality of the aircraft.

It's interesting that there is a new generation of LSA aircraft powered by Rotax (and other) engines in which there is no carb heat installation. A common view is that the position of the air intake source and the nature of the carbs mitigate against icing. I'm sure this is largely true but it was sobering for me when I did once clear some ice on run-up (being a certified variant of an LSA, my aircraft has a conventional carb heat arrangement). I have no way of knowing if this would have been a problem at full power (and maximum engine environment heating) but I'm not sure I wanted to find out. Of course, it could be that making the air induction system more 'conventional' for certification has negated some of the advantages of LSA installations.

Re BPF 'This switching off of Carb heat on short final seems to be a unique to British flight training practice that seems to have been mindlessly passed down through the generations. :ugh:'

I got my licence on the Australian syllabus and was taught to keep carb heat on until on the ground. When I converted my licence to a UK one, I was told to switch carb hear off at 200'. I've since seen this requirement documented in the order book of a flying club.

I've been following this rule, however a few months ago, climbing out in a Cub behind a C90, I got carb ice at around 300'. I pulled carb heat and recovered power without incident but with a lesson being learned: leave carb heat on until on the ground.

This practice was used for some aeroplanes that would struggle to climb in a go-around with carb heat on!

Which is why you select if off after applying full power when you start the go around. If you are incapable of pushing the card heat knob/lever while flying the aircraft in the go around maneuver, then I would suggest there is a flying skill deficit that needs to get addressed.

Can anyone quote me the power loss for full power with carb. heat on?

BTW, a C172N POH I have quotes for inadvertent icing encounter, to lean the mixture to improve carb. heat efficiency, IF used continuously. No real surprise there.

Same POH says to keep carb. heat on, till go-around (turning off after full power is applied) or after landing therefore.

Wallace

Quote... Can anyone quote me the power loss for full power with carb. heat on?
Well maybe not in terms of BHP, but on the Power Check, done at 1700 rpm it gives an rpm drop of 75rpm.
So my guess would be a drop of 100 rpm at full throttle, say 2500 down to 2400rpm. ( -4%.)


btw... Why are you using full power, are you in the climb?

It could be a long wait on an older Cessna with 40 degrees of flap extended!

The power needed to spin a propeller goes up roughly with the cube of the RPM, so that 4% drop equates to a much greater loss in output - about 12%.

There's also a risk of overheating the engine if you forget to turn the carb heat off.

That is why you select carb heat off after you have applied full power if you have to go around !

As for the power loss why is there such a huge issue about the potential power loss for the brief time the engine is at full power but before you have selected carb heat off, but no thought given about the power loss you will get if you apply full power to an engine that has already started to develop carb ice because it was selected off on final:confused:.

This is the exact scenario you setting your self up for following the stupid, and apparently universal to UK flight training, practice of selecting carb heat off on final. :ugh:

Under the right conditions carb ice can develop in seconds, certainly in the time the aircraft went from 200 feet on final to the start of the landing flare at a very low power setting.

If you are taught to do that why apply carb heat in the first place?

If it ices up during the approach you will at least have a chance of getting power back before you hit the ground.

But carb heat off at 200 feet is beyond stupid.

So you are going to get carby ice between 200' and the ground after not having it at 200' due carby heat on?:confused::hmm:

I think the turning off the carby heat at 200' is to cater for a possible go around and also so the engine does not injest dust from the dirt strip you are landing on, (perhaps not a problem in green countries like Canada), most carby heat systems bypass the air filters.

Tankengine,
I've flown off several quite dusty strips in Canada and that's just in the south. I've never been anywhere near the gravel strips in the north, which can be very dusty in the summer:

http://cdn-www.airliners.net/aviatio.../5/2456567.jpg

This 737 has the "unpaved strip kit" - the most visible parts of which are the gravel deflectors on the nose and main gear, and the vortex dissipator probes under the nacelle leading edges.

Steady on posters....

Carb heat is both preventative, and curative, and should be used as required, by an informed pilot. The affect on engine power resulting from the use of carb heat, has the same variabilities as those induced by atmospheric change on the engine, because it is an atmospheric change, as the engine sees it!

If you're relying on the exact effect of the application of carb heat, both in temperature change in the carb, and affect on power produced, you may be disappointed. It's just not that precise. How much power does your engine make anyway? We really don't know... The design will have a rated power, but many factors, most certainly condition, will affect that. Even a newly overhauled engine is rarely dynomometer checked for actual power output.

Carb heat is always unfiltered, as it also serves as the "alternate air" which must not been drawn through the air filter. I have once used it, when I encountered freezing rain, the air filter instantly iced over, and the engine stopped. "alternate air" got it running again, for my retreat from those conditions. It had not been a carb ice event, but rather obstructed induction system.

I share the opinion that the pilot should manage power as required, and if this means moving carb heat from hot to cold for a go around, than that should be done. If the go around decision is so short that you just can't get to it, then fly the plane, and check configuration as soon as you can as you begin the climb away.

Read CAA safety sense leaflet 14 on Piston Engine Icing, and note their comments on 200ft Carb. heat off.......

CAA of which country? perhaps you could post it here.

The referenced Leaflet 14 can be found here:

http://www.caa.co.uk/docs/33/20130121SSL14.pdf