Simviation Forums

Hello, Fellow Carburettor Enthusiast Chums... ....

In the FS 2004 Flight Sim, whilst aboard my trusty Cessna 150 Trainer....

...as a VERY keen advocate of the regular use of Carburettor Heat during what may appear to be adverse Weather conditions, (cold and wet), likely to produce dangerous ice build-up in the Carburettor...(as well as the recommended heat application at times of Power decrease, prior to landing, etc)....

...and there is no disadvantage in the resulting decrease in Engine power output.....

......is keeping the Carburettor Heat permanently in the "ON" position during the flight to prevent a sudden, unexpected, Engine falter and cut-out, (and the electrical system can cope with the extra load), to be advised?

What do you reckon?

(I always keep a regular wary eye on the Carb Heat Knob to check whether it is "In" or "Out")... ...!

Paul..G-BPLF...and FS 2004... 8-)

As a keen Motorcyclist and Motorist of Old/Vintage Vehicles, I have experienced Carburettor Ice build-up many times, with annoying, (but not lethal!), results!......!

Hey Paul...

*Quick note..

Just to add, while the wheels are on the ground, the carb heat should be off as it is unfiltered air that is being drawn into the engine with carb heat on.

As Mobius said, the carb heat uses unfiltered air, so it is much like running the engine without the air filter.  As long as power is in the green arc, I wouldn't use carb heat unless carb ice is suspected.  As a reminder, it need not be cold to have carb ice.  I have seen a twin land dual engine out after developing carb ice on final on a 80 degree day.  

Now in real life, in 150/152/172, I have always been taught to turn on carb heat in the pattern before reducing power below the green arc, and leave it on throughout the landing.  In the Piper aircraft I fly now, I have been told to simply check the carb heat before entering the pattern, then leave it off.  The reasoning is that in Pipers, the carb is surrounded by the oil pan, which keeps the carb de-iced under all but the most extreme circumstances.

Another 2 cents for you, Foz...

All of the above is true, but in RL it would also not be a good idea to leave the carb heat on in a 150/152 (which I know you fly often in the sim) during takeoff! That's when the difference in power output may be critical.  Even more so, of course, with an even smaller engine.
If there's ice in the carb as you begin your takeoff roll, in a 150, you will know right away (low tach reading or no increase in rpm), and you should be able to abort safely. To me, that mindset is more valuable for safety than planning to use carb heat on the takeoff roll and climbout. A 150 or 152 needs all the hp it can generate for takeoff.

If conditions are so bad as to require carb heat just to prevent icing while preparing to take off, you might want to cancel your flight.

That being said, sometimes carb heat can be used while warming up in very cold weather (remembering about the air filter)... not so much to prevent ice as to just help warm up the engine.

A word about conditions that my require carb heat: some days it's obvious, some it's not so obvious. Only time I ever picked up carb ice (in a 172), it was very cold out, but it was a pretty dry day- it took me by surprise. What was most surprising was that I was at a cruise power setting...  it's "not supposed to happen" when you have the tach well within the green arc. I guess in that instance, the cold made up for the relatively low humidity level. But even in warm weather, with no clouds visible, it can get you.

So... what does this actually mean? Takeoff aside, can you leave it on? I never have. Pitot heat, maybe, but not carb heat. My reasoning is that the most dangerous time to get ice is during the approach, when you are getting lower. It takes a few tense moments to clear carb ice... including the brief period when the power drops off even more when you turn on the heat. In cruise, it's alarming but no big deal (I was able to hold my altitude that one time, and it cleared up very quickly), but at pattern altitudes and airspeeds it could be a very bad deal. So the normal method of making carb heat part of the pre-landing checklist ("abeam the numbers" or whatever) is sensible. You might also want to turn it on if you are throttling way back to descend from cruise, as a precaution (it would suck to restore power as you level off from your descent, only to find there is no power).

Also, unfiltered air may not be so good even while aloft... or the carb heat door mechanism may get stuck... etc... I only use it pre-emptively when I think I'll really need it -which is whenever I throttle back to the bottom of the green arc, or beyond. and of course, if I do pick up ice in cruise, I'll leave it on!!

Another 2-cents

...excellent news. Chums...

I'm afraid I'm paranoid about Carburettor Icing, due to my experiences in Ground vehicles....

..so I always apply the same precautions in my Carburettor fitted Sim Aero Engines...(like my little Cessna 150/152).... ..!

Run the engine up to max revs on the runway with the brakes on, to test for any problems, apply Carb heat and watch/listen for rev drops, (around 100/150 RPM if all is working fine).

Then make sure the Carb heat is OFF for a full power take-off.

Apply Carb heat prior to reducing or closing the throttle opening, (maximum Carb Venturi Suction, chilling the Carb body), especilly when on the approach to land.....Then shut it off prior to landing, in case a full power aborted landing/go-around/ touch-and-go is required!

All the time listening for gradual changes in the engine revs, and watching the gauges, which may be heralding a build up of Ice in the Venturi Tube!

There you go Chums.....Its just a shame the the MS Flight Sim doesn't replicate similar conditions for the Trainee Sim Pilot!...... ...!

[quote]Another 2-cents

On my rare, occasional flights aloft in the Club's Cessna 150/150, the accompanying CFI always has a grin on his face when he sees my hands constantly playing tunes on the Trim Wheel.....and fiddling with the Carb Heat Knob!.. ... ...!

I automatically do the same thing in the Sim Cessna as well... ...!

Paul...G-BPLF... ...!

Last bit of advice, make sure you grab the carb heat handle and not the red knob next to it.  Lets just say I had a oh **** moment once when I received a 1000 rpm drop in a descent when checking for carb ice.  

[quote]Last bit of advice, make sure you grab the carb heat handle and not the red knob next to it.

I was just entering a straight-in downwind when I went through my before landing checklist and checked the carb heat.  When I received a major rpm drop I pushed it back in and pulled it again to see if it happened again.  Then I realized which handle I had.  Fortunately the engine restarted on its own, but even if it hadn't, I was in perfect position to turn base to final for the crosswind runway.

I did that once, too, abeam the numbers.  

On my rare, occasional flights aloft in the Club's Cessna 150/150, the accompanying CFI always has a grin on his face when he sees my hands constantly playing tunes on the Trim Wheel.....and fiddling with the Carb Heat Knob!.. ... ...!

I automatically do the same thing in the Sim Cessna as well... ...!

Paul...G-BPLF... ...!

I used to get yelled at a lot for "flying with the trim"... I almost weaned myself of that, but nothing cures it once and for all like flying something with a trim wheel you can't get your hands on easily (Cub- it's in the front, along with the carb heat), or one that is awkward (Champ- it's overhead, just behind the front seat, so you have to reach up and back).  ;D