Carb heat on Warrior (LYCOMING O-320-D3G)?

[BFPO]

I am taught to do the carb heat checks regardless of temperature if for no other reason than to put you in the habit. If it becomes a routine part of your drills, then you are less likely to forget to use it when you need to!

[DavidHoul52]

apply carb heat on downwind (probably actually as part of the RPM reduction to 2000 or below),

That was what I was taught to do. I see the pre-landing check list says "Check and set". Is there any point in checking it if you are going to set it to hot straight away? What would one do differently if the check showed there was a lot of icing?

[RatherBeFlying]

In the C-172 I simply put on full carb heat on downwind and do my best to remember to turn off carb heat for a go around -- actually the muscle memory has carb heat off with full throttle.

Flight below a ceiling is conducive to carb icing. And I definitely remember the engine stumbles I got after selecting carb heat turning downwind after a descent of a few minutes

[Final 3 Greens]

do my best to remember to turn off carb heat for a go around

Its easy to forget.

I normally return it to cold when taking land flap at about 300' - that then builds in a trap if I land with less than full flap, so have to remind myself at that stage.

I see the pre-landing check list says "Check and set". Is there any point in checking it if you are going to set it to hot straight away?

That line item reads a little ambiguously to me - I see why you read it one way, I could also read that as "check if HOT, if not set to HOT", or even later in the landing (very short final) "check if HOT, if HOT set to COLD."

In my opinion, on the 152, you need to achieve 2 things. One, don't have your engine quit through carb icing before you can make the runaway, so use carb heat during the descent and then (two) have full power available for any go around, since you'll need this, as she is adequately, rather than generously, powered.

The ability to make the runway is dependent on energy in the airframe, I've always liked to approach a little steeply so I'm less engine dependent, but that is a different discussion altogether.

[BeechNut]

If have no experience in the PA28

With all due respect, that pretty much invalidates your response as the query was specifically directed to the PA28, which IS very much different from a Cessna in this important aspect.

There are some key elements to keep in mind here:

1) the hot air circuit is unfiltered, so use of carb heat should be minimized to the extent necessary;
2) the O320 can detonate under full throttle with hot air;
3) the PA28 with the O320 is not exactly overpowered;
4) the design of the carb system on the O320 in the specific PA28 installation (does not apply to Cessna), makes carb ice very unlikely, though not impossible.

I have about 250 hours in my own PA28, operated summer and winter; in rain, snow, cool temperatures and hot temperatures, and freezing temperatures. Never once encountered carb icing, even once when inadvertently flying into unexpected icing conditions (alive to tell the tale: descended to a warmer altitude). I now operate a Beech C23 with the Lyc O360 and the POH states that carb heat should only be used on approach if required, not systematically, and with the Beech, again I have never encountered carb icing.

That said, that's not to say it's impossible, hence the reason for carb heat. I therefore do a brief check of the system during runup (as per checklist) and in the downwind leg to ensure it is functional, but would not fly the approach with carb heat unless called for by conditions.

My current bird has a carb temp gauge though, which is a real help and should be standard on C150s...

[Final 3 Greens]

Not just the Cessna 150

PA28, which IS very much different from a Cessna in this important aspect.

I completely agree with your point Beechnut.

Having flown other aircraft with the Continental 0-100, I found that they needed constant checking for carb ice (i.e. regular additions of hot air in the cruise), whereas PA28s (O320 and 0360), as you say, are highly resistant to carb ice.

This doesn't make the 0-100 a bad engine, it just requires a different approach to engine management.

Thought I'd share that for any newbies/low hours on Pup series 1 or similar.

[Contacttower]

All good stuff guys....

I have occasionally run the engine at full power with the carb heat on for brief periods....classic example being after a stall recovery forgetting to take it off immediately. I know this carries the risk of detonation and should be avoided at all times.

However is one going to do the engine any damage by having the heat on for 15-30 seconds periodically during a flight in the 2200-2400RPM range?

I've always assumed that the answer is no....with the only danger being from foreign objects entering through the unfiltered entry (which I've always assumed is unlikely at altitude).

[robin]

I suppose the only comment I'd make is to avoid the ' I've never had that problem' attitude.

There is a real risk of getting casual with icing checks because you fly a 'resistant' machine. Over the past couple of years it does seem as though there have been a fair number of incidents leading to forced landings and worse which can be attributed to poor recognition and handling of icing conditions.

Having flown behind VWs and Continental 0-200s and having had the engine stop on occasion, I can testify to the way icing can creep up on you.....

Oh, and a friend told me that he was at full power in a Warrior on Saturday and experienced a marked power loss through icing.

[BeechNut]

Agree, doesn't mean it can't happen, hence the reason carb heat exists even on these fairly resistant engines.

My checklist calls for a carb heat check at runup, and I do one on downwind, and occasionally in cruise, but mainly to see if the system is working. I have a carb temp. gauge so I rely on that to see if there's a potential for icing. The test also verifies the functioning of the carb temp. gauge as application of heat should cause it to rise out of the danger zone.

The POH does say use it on approach if necessary. But only if necessary.

[DavidHoul52]

Perhaps I'm just stating the obvious but (according to this AAIB report) the standard 10 second setting to hot which we are taught is not necessarily enough in some conditions.


http://www.aaib.dft.gov.uk/cms_resou...ZT%2003-08.pdf

[bArt2]

With all due respect, that pretty much invalidates your response as the query was specifically directed to the PA28, which IS very much different from a Cessna in this important aspect.

I wrote about 13 lines.

Most of it was general information about using carbu heat and there was something about the Lycoming 540.

There was only 1 line about the C152, so I do not really understand why you interpret this post as being C152 specific.

completely agree with your point Beechnut.

Having flown other aircraft with the Continental 0-100,

By the way the C152 over here have a Lycoming 235, not a continental.

Bart

[Final 3 Greens]

bArt2

Please re-read the sub heading of my post, I wrote it for a reason

[dont overfil]

We had an odd situation a few years ago with a C152 being flown in extremely cold winter weather, around -15 at 4000ft. When carb heat was applied the engine gradually began to lose power. The aircraft managed to limp back to the field and no fault was found. The theory given was due to the abnormally low temperature carb heat brought the temperature in the carb UP to the icing band.
I wouldn't have thought enough moisture would have existed in the air at that temperature.
Any thoughts?
DO.

[bArt2]

around -15 at 4000ft. When carb heat was applied the engine gradually began to lose power

That is why in my first reply in this thread I mentioned that you should use it if the temperature is between -5ºC and +20ºC. If you use it below -5ºC you would create the problem that you just brought up. Having rather low visibility due to moist air could be enough moisture.

I hope this doe not turn into a Cessna discussion just because I mentioned the C152 in one sentence.

@Final 3 greens

I am not shure what you mean with the sub-heading "not just the 150"

Greetings, Bart

[porch monkey]

Would someone mind explaining to me how the use of carb heat can cause detonation?

[barrow]

Would someone mind explaining to me how the use of carb heat can cause detonation?

1, increase in induction air temp.
2, decreasing power output.
3, increasing fuel/air ratio.
4, increase in cylinder temps/pressures for same output (no heat)
5, possible increase for detonation at high power outputs.

[bjornhall]

That is why in my first reply in this thread I mentioned that you should use it if the temperature is between -5ºC and +20ºC.

Do you mean only to use it in that band? According to the various carburettor icing graphs in circulation, such as those repeatedly linked to in this thread, it would appear carburettor icing is possible in the range from -15ºC to +35ºC...

[bArt2]

The rule that I am aware of is to use it when visible moisture is present AND the outside temperature is between -5 and +20ºC.

Now it seems that different rules circulate, such as -5º to +30ºC and -7ºC to +30º.

-15ºC seems a bit on the cold side I think.

So do not use carbu heat if you are above or below this range.
Using it above this range would not be a problem I guess as long as you make sure that you have no detonation and adjust mixture as required.
If you use it below the range however you could actually cause carburetor ice to be formed.

The reason that you should not use carbu heat below -5-ish temperature is that below this waterdroplets would normally be frozen and would just pass through the carburettor. If you would then use carbu heat, the droplets become liquid again and can then re-freeze in the carburetor.

As with most general rules, I guess that it is valid in most but not all cases b.

[SNS3Guppy]

Having flown other aircraft with the Continental 0-100, I found that they needed constant checking for carb ice (i.e. regular additions of hot air in the cruise), whereas PA28s (O320 and 0360), as you say, are highly resistant to carb ice.

This doesn't make the 0-100 a bad engine, it just requires a different approach to engine management.

Continental O-100, you say? Unique engine, don't you think? Did you have it especially installed? Is that possibly a 2 cylinder O-200? Sort of like a half-VW?

1, increase in induction air temp.
2, decreasing power output.
3, increasing fuel/air ratio.
4, increase in cylinder temps/pressures for same output (no heat)
5, possible increase for detonation at high power outputs.

Of the five reasons cited there for causing detonation, only one applies, two are incorrect, and one is a restatement that carb heat causes detonation.

Decreasing power output has nothing to do with causing detonation. Increasing the fuel-air ration, or in other words, enrichening the mixture by applying carburetor heat, does not cause detonation. Enrichening the mixture, unless you were already operating lean of peak, moves the engine farther from the possibility of detonation. By applying carburetor heat and increasing the induction air temperature, one draws less dense air into the carburetor; as you know, with less dense air, you have a richer mixture...and you have just enrichened the mixture by applying carburetor heat.

Detonation occurs at higher power settings, typically close to peak mixture, or stochiometric. If you've leaned your engine manually to a point rich of peak, which is where most typically operate, then by applying carb heat you're moving farther from Stoch, or in other words farther from peak, and decreasing the possibility of detonation.

As for increasing cylinder temperatures and pressures...again, no. If you enrichen the mixture, you decrease the combustion temperatures for a given power setting. Your cylinder pressures aren't increasing, either, and even if they did, you're not going to create a dangerous situation with respect to cylinder pressure in a normally aspirated engine, using carburetor heat. It sounds good, but it's not true. Additionally, think about when you're actually using the carburetor heat...most often at low power settings. If you apply carb heat at a low power setting, do you think you need to be concerned about cylinder head temperatures or cylinder pressures?

As for robbing performance, yes...you're increasing the effective density altitude of the induction air...it's hotter, less dense, and enrichened to boot...so yes, the engine is producing less power. At a low power setting this is really irrelevant. At a high power setting it's more meaningful...which is why you don't normally apply carburetor heat at high power settings at a critical time, such as on takeoff or a go-around.

Now...during takeoff or on a go-around, if you're operating lean of peak and you do apply carburetor heat, there does exist the possibility of creating a situation conducive to engine damage, and that does include potential detonation issues.

[barrow]

They are not reasons, they are bullet points of what happens when carb heat is on!
This first 4 are EXACTLY what happens with carb heat, which may lend itself to the 5th point of "possible detonation"
To say any are incorrect, shows a basic lack of understanding on the recip powerplant.