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Question about Carb Heat in manual

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Page 04<18 says that during the landing approach you have to turn on the Carb heat (step 6). Immediately after that the manual says to check for a RPM drop and the rise: if that happens, leave the CH on, if not, turn it off. So... this step is only a check? You only turn it on to see if there is a differrence in RPM and if not you should turn it off again? I was used to turn it on during landings and keep it on...

Never really had to actually think about this stuff... ;)

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Hi,

I have no experience on the Katana (neither simulator, neither reality) but I can tell from use of the carb heat on Pipers and Cessnas. On the PA-28 it is used during approach and landing to avoid carb icing. If there is a slow drop in RPM during cruise it is turned on to see if there is carb icing.

As this is normal procedure on most GAs, I think this is also true for the Katana.

Hope that helps.

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The carb on the Rotax 912 is not really known for carb icing, but it can happen. I've already had it happen in the sim and applying carb heat too late did exactly what it does in the real world - not much. So it's definitely procedurally advisable.

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Ok, I'll use it then during appr and landing!

BTW Everyone already knows the Carb Heat knob is on the left? It is labeled wrong in the English VC's! The Carb heat and Cabin heat stickers are accidently switched.

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Ok, I'll use it then during appr and landing!

BTW Everyone already knows the Carb Heat knob is on the left? It is labeled wrong in the English VC's! The Carb heat and Cabin heat stickers are accidently switched.

Yes, I wrote it already to Marcel and it´ll be fixed with the next patch...in the german ones, its correct.

cheers, stephan

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Ok, I'll use it then during appr and landing!

BTW Everyone already knows the Carb Heat knob is on the left? It is labeled wrong in the English VC's! The Carb heat and Cabin heat stickers are accidently switched.

Lol thanks,

André

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The carb on the Rotax 912 is not really known for carb icing, but it can happen. I've already had it happen in the sim and applying carb heat too late did exactly what it does in the real world - not much. So it's definitely procedurally advisable.

I had one flight in the Katana and we had carb icing in cruise... ;)

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From the preview thread back then, I know that Marcel has set up some icing things around the plane too, so I'm excited to get into some rw weather where these come into play.

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Yep - you definitely need that carb heat. Caught me out a number of times when trying circuits in this thing...

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Yep - you definitely need that carb heat. Caught me out a number of times when trying circuits in this thing...

It might be slightly more prevalent than in the real deal, but the consequences are significant! Best you can do while waiting for the carb heat to do its thing is raise the flaps and use the gliding capacity of the basic airframe - it will fly quote happily on a partially-blocked airway but it struggles when you throw flaps into the equation.

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Last flight in the katana i had to use the carb heat the entire flight my manifold pressure kept dropping if i didnt turn it on. It was a rainy day and about 6 degrees celcius.

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Last flight in the katana i had to use the carb heat the entire flight my manifold pressure kept dropping if i didnt turn it on. It was a rainy day and about 6 degrees celcius.

Very good conditions for icing. The problem is, if already ice has been accumulated and not been melted away completely, it will freeze more and faster if you turn carb heat off.

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Very good conditions for icing. The problem is, if already ice has been accumulated and not been melted away completely, it will freeze more and faster if you turn carb heat off.

Good point. Once icing is prevalent, unless you dramatically change environments (possible in a pressurised 350hp leather-bound gentlemans carriage, less so in a 100-horse Katana) it tends to stay prevalent. Once in use it should stay in use.

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Ok nice too know this normal behavior for the Katana.

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Thanks for that information... :-) Yesterday I did a flight and turned on the carbheat as I was beginning to descend from 6000f to 2500f @ 6C OAT. After descending I had some miles to fly at that 2500, so I thought I could/must take the heat out again until the next descend for approach and final... The result was a maximum CHT with enginefault after landing... Was that the result of taking the carbheat out in between? After you latest post, I guess so.

Cheers, Stephan

Ps.: I'm glad, that my first real flightlesson yesterday was on a normal C172R.... ;-)

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<br />Page 04<18 says that during the landing approach you have to turn on the Carb heat (step 6). Immediately after that the manual says to check for a RPM drop and the rise: if that happens, leave the CH on, if not, turn it off. So... this step is only a check? You only turn it on to see if there is a differrence in RPM and if not you should turn it off again? I was used to turn it on during landings and keep it on...<br /><br />Never really had to actually think about this stuff... /><br />

I was trained to always apply carb heat when I'm in the air and the manifold pressure is below 20". That forms a habit and I don't have to worry about figuring out if the weather is likely to cause carb icing.

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I was trained to always apply carb heat when I'm in the air and the manifold pressure is below 20". That forms a habit and I don't have to worry about figuring out if the weather is likely to cause carb icing.

Nice rule.

Makes me wonder though if you can ruin something by having the carb heat on too long? Can something bad happen when you have it on when it's not needed?

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In a warm regime, the active carb heat may reduce quite some power output on the go-around attempt when left at on (which shouldn't happen but maybe does). Just guessing though.

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Nice rule.

Makes me wonder though if you can ruin something by having the carb heat on too long? Can something bad happen when you have it on when it's not needed?

In reality carb heat effect is quite small in the Rotax. Unlike most GA aero-engines, carb heat in the Rotax is accomplished by warming the throttle body via hoses directing coolant from the cylinder heads.

The intention is to keep the body above freezing, preventing ice from forming as a condensate.

As such there is very little effect on the air flowing through the carb - and so little effect on the power at lower power settings. The heat applied is therefore modest - and consistent - so there is very little risk to leaving it on for extended periods, except for the reduction in power that a warmer stratified charge represents.

As I said, I don't have much experience with needing carb heat in the real Katana, (Rotax engines generally are far less susceptible to carb icing than the much larger bore/stroke slow-turning aero-engines with their larger volume of transient air) but in a typical British Summer we applied carb heat on finals and left it on until after touchdown for pragmatic reasons - IF carb icing starts, this system is NOT a DE-ice system but an ANTI-ice system, so it is quite slow to have an effect.

NOT the sort of thing you want to discover on short finals with full flaps... :o

I'm guessing the addendum advice in the Normal Operations manual for Katana 4X is entirely based on the somewhat unsubtle icing effect in FSX, not correct OP for the real deal. In the real world you get plenty of audio, visual and visceral clues about the incipient onset of carb icing, cues which are entirely absent in the sim.

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About carb icing... as Simon said it depends a lot on the engine. but I meet a lot of people who think you need low temperatures for that to happen. But as a standard rule, any temperature under 12 degrees C (so 12 degrees above the freezing point of water!) can lead to icing.

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Carb icing is caused by the induction air being squuuuueeeeeeeezed as it is compressed by the carb venturi - accelerating gas reduces in temperature, and if it's carrying moisture from the atmosphere then ice can form on the body of the venturi or the throat of the carb body or even on the butterfly itself.

As such, and as Mathijs says it is NOT temperature dependent, it is a function of temperature, air density and moisture content:

carbicingfromcaassl14.gif

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Actually there is a greater risc experiencing Carb icing on summerdays than in the winter, because in summer the air is often more humid.

Often the venturi effect in the carburetor will lower the inlet air temperature by 10°C this means that carb icing can occur when inlet air temperature get´s below 10°C.

With an outside temperature of 25°C at sea level this means that temperature have to drop 25÷10 = 15°C for carb icing to set in. In a standard atmosphere temperature will drop by 2°C for each 1000 ft.

10°C OAT is then reached at 15/2 x 1000 = 7500 ft. If there is any moisture at that altitude, either clouds or haze, carb ice than becomes a hazard.

The venturi effect is dependent on throttle position. The more the throttle is closed the higher the temperature drop, caused by the venturi.

So carb icing might not show up when flying with full or high throttle setting, but will then set in when reducing throttle.

Dewpoint is an expression for how much moisture a certain airmass can contain before it starts to condesate as water droplets. The hotter the air, the more moisture the airmass can contain.

In winter times the air has often been so cold for a longer time period that most moisture allready has condesated and thus not contained in the air anymore. This at least holds true for latitudes equalling northern europe.

BTW: On the Catalina X we simulated carbicing as a function of expected humidity vs temperature, since FSX own carb icing doesn´t funktion very well.

Finn

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