Carb Heat in the Circuit
 

The carb heat comments in the bounce bounce thread reminded me of a question I wanted to ask you guys!

When I did my initial training I was always thought to do a carb heat check on downwind, to clear any ice that might exist. Carb heat would then remain off (cold) for base and final, until next the next downwind check.

Then the club changed ownership, and a checkout with a new instructor took serious issue with this, and insisted that carb heat was applied a couple of seconds before reducing power for base. It would remain on until either on the runway and applying full power, if if I wished I could remove it on short final. Old habits die hard, and it took me a while to get used to this, but I could see the logic and eventually got used to it.

Then more recently, I joined a new club, and their procedure was the same as the first school..ie carb heat as part of down wind checks only, and cold at all other times in the circuit.

I'm just curious as to which is the more common practice.

Thanks,
dp

Carb Heat
 

I first apply carb heat during my downwind checks, then back to off. When I have turned base I then apply carb heat again before reducing power. I keep carb heat on until 300-400 feet when I then turn it off so I have full power available for a go around.

I would guess this is one of those subjects where everyone knows the "correct" way of doing it, and will try to shout down any other methods ;)

Personally, I was taught to apply carb heat as part of the downwind checks, and either remove it on short final, or else either on go-around or when clear of the runway (depending on instructor).

I don't fancy the idea of a quick check on downwind, then leaving it off for base and final - I have flown aircraft which, at the low power settings used on base/final, would certainly get carb icing in this short time without carb heat applied in normal UK weather.

On a related note, it is scary how easy it is to forget habits. Having learnt to fly in a PA28 with carb-heat, then moved to a PA18 with carb heat, and occassionally various other aircraft with carb heat, I now mainly fly two aircraft which don't have carb heat controls (one uses the supercharger to heat the inlet air, and the other is fuel injected). On the rare occassions when I find myself with a carb heat control, it is very easy to forget to use it :eek:

FFF
---------------

G'day Dublin,

I do carb-heat on/off as part of downwind checks. I also then re-apply carb-heat when reducing power to commence descent (i.e. base leg) as I would for any descent! Then, I have to remember (at 200~300') to take carb-heat off in case full power needed for go-around (as per another current thread!).

I am very surprised if people don't use carb-heat on final..! This is one of the most vulnerable phases of flight: you are LOW and you are SLOW... AND the throttle is close to closed, ideal for forming carb-ice in atmospheric conditions which - lets face it - are common in the British Isles and Eire at most times of the year!

Think of the consequences of losing power on short final - when not established for a glide approach: power was planned to be needed to reach the threshold... so you will almost certainly hit the hedge or worse: at Wycombe, where I trained, we have to cross the busy M40 motorway on short final, and dropping in across 6 lanes of traffic would hurt I reckon :ooh: !

But maybe others have a different view: I'd be very interested to learn the rationale behind not using carb-heat during descent through base and final.

Cheers!


Andy :cool: (sunglasses on as I am in Florida at present...)

Good question dp.

When I was first checked out on a PA28 I was taught to use carb heat only while doing down wind checks. I did this during a check out on a C152 and the engine stopped on short final. Fortunately I was able to reach the runway. Since then, I leave CH on until I'm on the ground although, in my forthcoming biennual training flight, I will probably have to remember to change to cold on short final.

I always understood that the Continental engine on the Cessna was much more prone to icing than the Lycoming.

pulse1 - Ouch! You were lucky mate... Leaving carb-heat on until on the rwy is definitely a better idea than having it off after d/wind - as long as you remember to take it off on the go-around. Well done you for making it!

Andy

I was taught to apply Carb Heat when I reduce the RPM in my PA-28 to below 2000 rpm, so when I turn base and have reduced power to 1800 RPM that constitutes carb heat, if you dont reduce power to below 2000 rpm then I guess there is no need?
I would have thought that the more sensible option would be to apply it on final for the reasons Andy stated, there would be nothing worse than to screw up your approach and landing then needing full power if approaching stall etc only to find you have insufficient power due to carb icing, dont think this would go down well with the insurance companies :)

D.

I was taught to apply carb heat during the downwind checks and leave it on until applying full power for the go around or touch and go or until clear of the runway.

However, one day when the wind was 14 knots straight across the runway and pretty gusty, not student solo weather in a 152, instead of scrubbing the lesson I chose to do some circuits with the instructor so as to practise cross wind landings.

I think I might have frightened him slightly on one of the attempts - he managed to go around OK, but made me turn the carb heat off just before landing for the rest of that trip so that he'd have a bit more power if he needed to do it again. So for him killing the carb heat just above the ground was not normal practice but was something you might want to do in bad weather.

The engine does make a difference. In Florida's humidity, a 150 is almost guaranteed to generate ice on descent with no CH. As others have said, I was taught in the Warrior to just give it a quick blast on downwind.

I personally leave CH on until about 100ft agl. You don't want the carb too hot in case you need full throttle a few seconds later. (Or would the extra fuel chucked into the carb just soak up the excess heat anyway?)

It does depend on what a/c you are in. Look at the POH and work from there. In Cessnas the carb control and throttle can be easily used at the same time, so on go arounds that is what I would recommend. Other types PA28's, robins etc. If you have time, carb heat first and then power. But I must stress that ONLY if you are initiating a g/a before getting any where near the runway.
Usually if you have forgotten to put the carb heat away on finals (can't believe that ever happens!!:rolleyes: ) Apply full power and then immediately check if the carb heat is cold or not.

I always (try to) get my students into the habit of thinking about the carb heat whenever they consider power. As stated on another thread, carb heat is a large chunk of power missing especially on C150's with a knackered old Lycoming!

As most others have said,

Flying Cessna 152 / 150, I was taught 10 seconds burst of carb heat on downwind checks (unless evidence of icing, in which case leave it on) and then carb heat on when setting up for descent before reducing the throttle. Carb heat to cold at 300' on short final in case full power was required for a go-around.

I was also taught that carb heat should always be on when the engine RPM is below the green or if it is drizzling or raining.

On top of this the engine should be warmed during glide approaches or PFLs. Just my 2ps worth.

F - Wyg

Much like many others have said, I give ten seconds of carb heat during my downwind checks as I'm in cruise power, then turn it back off.

As soon as I turn base, I begin my descent and the carb heat goes in then to guard against potential icing while I'm only at 1700rpm. Carb heat then comes back off at 300 feet in case I need to go around.

Carb heat on during the downwind leg until on the deck.

Just have to bear in mind that some engines completely do not like full throttle (especially if applied to swiftly) with the carb heat out. May give rich cut.

However chances of that are less likely (and unless it stops - easier to cure) than icing up when you go to 'cold' on finals.

Depends on what you are happiest with for your particular mount.

Injection takes the guesswork out of the equation.

FD

I stand to be corrected but here's my theory.

Carb heat is only properly effective when the engine is hot. Therefore it is not as effective to apply the heat once the power has been reduced as the amount of heat given off to combat ice is less than if cruise power has been applied for several minutes before its introduction.

There are some days when icing is very prevalent, there are others when it is not.

The facts are clear and proven though. If carb ice HAS built up it takes a lot longer than most people think to clear it. Up to 40 seconds in fact. I don't believe that one would wish to find carb icing on base leg and have to wait 40 seconds for it to clear whilst in the latter stages of the final approach.

Basically, I perform the check downwind and if there is signs of icing, redo the check just before pulling power back on base.

If the revs did not rise after applying downwind then I consider it safe to slide from base to finals without another application.

I remember learning to fly 14 years ago and performing the carb ice check "just because I thought it was right to do so". Since then I have found myself in numerous situations where applying the carb heat has given a 300 rpm rise in power with some serious coughing and spluttering of the engine to boot.

As far as I'm concerned, keep applying it even if it's habitual or seems unecessary at the time.



:ok:

I have just done a GFT to re-validate my PPL after 2 years absence, and was told to put the carb heat on when descending on the dead side (PA28), and keep it on till 300 feet.
When I queried this the examiner said it was an engine manufactures directive. :confused:

Just as a practical aside, if a steep approach is made (say 5-6 degrees), then if the engine does stop, there should be enough energy left inf the airframe to make the runway.

I like to arrive at a 1 mile final around 700' agl for this reason.

Gulp! I was never taught to apply carb heat on the downwind leg at all. As part of the field approach checks, yes, but not in the circuit until base leg, just before reducing power. And then off at about 300ft agl. (I was very bad at remembering to do this until my instructor said I owed him a pint for every time I forgot - an amazingly effective strategy! ;) )

I don't quite understand why people are so reluctant to use carb heat. In this country, carb icing is likely at almost any time of year, in almost any weather. Apart from when you need full power, for example for a go-around, to my knowledge it can't do any harm when used for short periods. And at low power settings carb icing is more likely. So why not use it, just in case? If in doubt, why not use it? What's wrong with putting it on on downwind, and leaving it till 200ft or so on final? Am I missing something here?

I know what you mean Whirly. It may come from a belief that using carb heat would damage an engine due to over heating! I've heard this more than once.
I wouldn't recommend that you use it all the time though (unlike in an R22 where you could and can also use partial carb ht) simply due to the fact that the carb air is usually unfiltered and in straight and level flight light aircraft engines need quite a bit of power, again unlike an R22 which has a derated engine, so has an excess of power compared to it's fixed wing brothers.

Hi peeps
i think you are all a bit right but know your engines ! The carb of lycoming engines is recessed in to the sump so gets heat from the engine oil , a conti is stuck out in the elements below the sump very prone to carb ice , not saying any 1 is wrong just passing on info lol