AFE not maintaining carb air temp

[et31 39]

Hi,

I read in the Introduction manual that the AFE is supposed to maintain a carb air temp of 15C but in all phases of flight with the AFE on this is remaining at around -5C.

While the AFE is enabled I am unable to manually control this and the only way to manage this is to abort the AFE and do it manually.

Is anyone else experiencing the AFE not managing this?

Kind regards

Greg

 

 

[scandinavian13 5,192]

14 hours ago, et31 said:

Is anyone else experiencing the AFE not managing this?

The manual doesn't go into more detail, as it's only the intro, and diving into a deeper discussion of carb icing would've been a bit much.

The AFE isn't maintaining carb heat because it's determined that it's not needed. Ice requires cold and water. If the carb inlet temp is below the icing risk zone (yellow on the gauge), then there's no need to apply heat (it'll put you into the risk zone, and the extra heat to bring you above the risk zone degrades performance). Any carb heat brings your performance down (hotter, less dense air), so if you're not in the risk zone, it's best to leave it off. From the water perspective, while you can pick up carb ice from high-humidity conditions, you do need moisture of some sort to collect in a cold environment to cause it. Low humidity, or no visible moisture conditions mean that it's not likely that this will occur.

[et31 39]

1 hour ago, scandinavian13 said:

The manual doesn't go into more detail, as it's only the intro, and diving into a deeper discussion of carb icing would've been a bit much.

The AFE isn't maintaining carb heat because it's determined that it's not needed. Ice requires cold and water. If the carb inlet temp is below the icing risk zone (yellow on the gauge), then there's no need to apply heat (it'll put you into the risk zone, and the extra heat to bring you above the risk zone degrades performance). Any carb heat brings your performance down (hotter, less dense air), so if you're not in the risk zone, it's best to leave it off. From the water perspective, while you can pick up carb ice from high-humidity conditions, you do need moisture of some sort to collect in a cold environment to cause it. Low humidity, or no visible moisture conditions mean that it's not likely that this will occur.

Thanks for that Kyle - clears that up 

[Wothan 173]

Agree with Kyle

Also if carburator temperature is below ÷10°C then eventual moister will be in the form of ice crystals and thus not form ice in the carburator. So essentially You would only need carburator heat if temperatire is between ÷10 and +20°C if in moisterous air (Inside clouds, rain, snow, drizzle, etc.)

As also outlined by Kyle, You want to keep Carburator heat use to it´s minimum in order to preserve performance.

Carburator icing is also more likely to occur with low throttle settings, while not as common with wide open throttles, cause it´s the venturi effect that causes temps to drop to freezing point above 0°C (Thats why carburator icing can occure also between 0 and 20°C).

The venturi effect can actually make the temperature drop by 20°C, which makes carburator icing likely even in summer time.

[downscc 1,327]

4 hours ago, Wothan said:

So essentially You would only need carburator heat if temperatire is between ÷10 and +20°C if in moisterous air (Inside clouds, rain, snow, drizzle, etc.)

Don't confuse carb heat with airframe icing.  Here in very humid gulf coast Texas carb icing is extremely likely at 80F / 27C at low manifold pressures.  There is significant pressure drop in the throat of the carburetor (that is how it suck gas into the air) and decrease in pressure is a decrease in temperature (Boyles law).

[Wothan 173]

True - thats basicly what I have written, not saying that it cannot occur at higher temperatures, but then it´s more likely during descend, due to the lower throttle setting.

[PMDG777 231]

14 hours ago, Wothan said:

True - thats basicly what I have written, not saying that it cannot occur at higher temperatures, but then it´s more likely during descend, due to the lower throttle setting.

I think Dan is talking about the first half, you're talking about airframe icing which is a different issue.

I live in Perth, Australia and in summer we get >40C and very very dry yet carburettor icing is still an issue. You're right with low power settings though.

[stephenjdecatur 0]

Above, Kyle asked if anyone else is having this issue. Although the FE seems to do his job in all of the individual phases, he seems to be very happy to leave the carb air heat levers untouched no matter what the weather, even with the guage in the yellow. I've flown this wonderful airplane (thank you PMDG) about half way around the world now in all kinds of icing conditions. I've yet to see him touch those levers.(Even in descent). Some airplanes are much more prone to icing than others (Continental vs Lycoming), is this the case here?

P.S. I am loving this airplane! The FDE is perhaps the best of all the simulator aircraft I've had experience with.

Stephen Decatur

[scandinavian13 5,192]

35 minutes ago, stephenjdecatur said:

in all kinds of icing conditions

What's your definition of icing conditions?

I apologize for the doubt, but most simmers' idea of 'icing' conditions is defined as simply 'cold', when in fact icing requires the additional provision of water.

[stephenjdecatur 0]

You're absolutely right Kyle. This is a mistake most flight simmers seem to make. I guess if you've never been through any RW flight training it might be unusual to assume that on what seems to be a "beautiful" summer day that you should have to worry about icing. (It was a surprise to me). It was many years ago, but I still remember my lessons. So, I was just wondering if this particular engine configuration was more resistant to icing than the GA aircraft I used to fly, or is the use of carb air heat so different from what I was taught as a GA pilot. By the way, thank you for your reply.

Stephen Decatur

[downscc 1,327]

2 hours ago, stephenjdecatur said:

So, I was just wondering if this particular engine configuration was more resistant to icing than the GA aircraft I used to fly, or is the use of carb air heat so different from what I was taught as a GA pilot.

Even GA aircraft vary... always pull carb heat in a Cessna and rarely in a Piper.  The DC6 POH is your authoritative guide for operating the aircraft. The section on pg 278 is a simplified overview, and basically says use only as much carb heat as required in icing conditions (humid and/or  -5C/15C carb air temp) and don't takeoff or land with carb heat on.  I am very cautious with carb heat and only apply it if I strongly suspect carb icing might be a problem. Most the time I will simply monitor the engine instruments and if I start to see a falling MP or BMEP then I consider the application of carb heat.  If you are paying attention you get plenty of warning before it becomes a serious problem.  In other words, I don't like using it in the DC6 unless I feel it is warranted.

[stephenjdecatur 0]

Thank you for your reply Dan. Yes, I know that GA aircraft can be different from one another as well as from other aircraft, hence my reference to the difference between Lycomings and Continentals. What is interesting to me, is that common doctrine, at least among the instructors and other experienced flyers I have known is that carb heat is used ideally before any actual icing (in the carburetor) has occurred and is normally an all or nothing affair, some I've heard say that partial use of carb heat can be counterproductive.

I've done some searches, but have not been able to find anything that relates specifically to DC6 accepted procedures in suspected carburetor icing conditions. Do you happen to know if your method is the one actually used by DC6 pilots? Of course for us, within the sim it all comes down to how it was coded, but I really am curious to know, in the real world, how carburetor icing was dealt with while flying this aircraft. (Only PMDG or A2A aircraft could have sparked this discussion). Once again, thanks.

Stephen Decatur

[downscc 1,327]

20 hours ago, stephenjdecatur said:

Do you happen to know if your method is the one actually used by DC6 pilots?

We have several DC6 pilots on the team that fly in several different environments, none of them pointed out any error in the POH with regard to application of carb heat yet the topic came up several times.  The reference I cited said use only as much as necessary... you pretty much have to go by the POH written by Douglas.