The A2A Simulations Community

Perhaps I've missed this but, i'm guessing this is some kind of ram air because turning it on increases carb intake temp at the expensive of power, but i've been cruising at 21000 with a -16c carb temp to apparently no ill effect on the plane except a little extra power to cruise a tad higher, am I risking carb icing here?

Dudley? I'd love your input on this one

Sorry so long in answering. Been quite busy lately.

The story with carb heat is complex. There is the real world condition and the FSX condition.
In discussing the FSX issue with Hal Bryan recently (Lead Aces Team for FSX) Hal couldn't recall if humidity was factored into the base FSX code but thought that it hadn't. This being true, the equation for carb ice is incomplete for replicating an actual icing condition as humidity as well as temperature is a factor.

This being said, both Allison and Merlin engines run fairly ice free due to the fact that they use pressure carbs instead of float carbs. For A2A at this point anyway, what we have is a modeled "effect" for carb heat being applied but it's arbitrary and done without icing conditions being present due to the FSX limitation.
Stay tuned on this, as down the line it may be possible to replicate a humidity factor through accusim.
So what it amounts to right now is that you can compensate for temperature but not humidity in FSX.
Just keep your carb air temp between -10 and +15 degrees c and you should be fine as far as the Allison goes.
Hope this helps. This is my understanding on the issue at this point.
DH

I notice a lot of airplanes, even ones with fuel injected engines(no carburator) suffer from FSX's idea of Carb Ice. hitting the 'h' button clears it up.

_________________
"The knack of flying is learning how to throw yourself at the ground and miss." - Douglas Adams

Doesn't the appearance of wing vortice in FSX take the humidity into account ? (this, and the AoA of course)

Not absolutely certain about how the 1's and 0's are stacked in FSX to allow a vortice effect but I'm pretty sure that this effect is possible without consideration to a global humidity factor being present.
DH

it is actually the water in the air that freezes when the pressure drops as the air passes through the venturi. The symptoms would be poor drive-ability and stalling, particularly during warm-up or after extended cruise in cold and humid conditions.
All that BS and i've never seen heated carbs on a bike, not doubting you though, the idea may be to shorten the warm up time in an effort to reduce.

_________________
Vinyl Stickers, Pocket Folders, Custom Folders, Custom Banners

The Dew Point is present in the Metar string, so relative humidity calc should follow from that.

_________________
1)i7 980x 4.35 ghz, gtx 470s SLI, Matrox th2go, Creative x-fi
2)i7 2600k, Gigabyte z68x, gtx 285s sli

Just completed an email communication with a friend who was an FSX lead for MS.

Quote from him on the issue;

"I am pretty sure the carb icing was generalized and not specifically modeled using humidity. I know being in-cloud was a factor as well as temp (of course). I wanted to move to developing weather and reactions based on the smaller components, but we never got that far."

End of quote.

Dudley Henriques

You seem to be responding to something that was never said.

Here is my quote:

"The Dew Point is present in the Metar string, so relative humidity calc should follow from that"

I never said that default FSX did or didn't do anything with humidity and carb icing, only that the Dew Point can be pulled out of the Metar. I said that the relative humidity can be computed, via very simple equations, from the Dew Point, which is available to the coders. I can read the SDK, and I would be highly surprised if the Accusim coders couldn't make a reasonable estimate of water content in the air at the point of the intake. Precisely what happens to the calculated moisture content once its inside the Carb to form the ice is the reason that God invented Matlab/Simulink.

_________________
1)i7 980x 4.35 ghz, gtx 470s SLI, Matrox th2go, Creative x-fi
2)i7 2600k, Gigabyte z68x, gtx 285s sli

Spider

I understand your quote. The issue being discussed isn't whether or not moisture content CAN be programmed into FSX. I think we all agree that it's possible.
The fact that there is a dew point in the METARS isn't an issue either, as that is simply a message. Whether or not that dew point is actually linked to a global humidity index in FSX is quite another matter.
There are icing EFFECTS modeled into the FSX atmosphere, but HOW these effects have actually been coded into the sim and what links trigger them is the main issue we've been discussing...............at least what I am discussing anyway.
I inserted that quote simply because you seemed to think that because the dew point was mentioned in the METARS there "should" be a connection to a humidity index. The quote from two of the ACES leads simply advanced what you had said to the understanding that they had not proceeded that far into the programming to reflect a humidity index.
So whatever the links are in FSX that create icing, according to the FSX lead team, a global programmed moisture content doesn't seem to be the trigger.

Dudley Henriques

Yes, I understand



I think this is where we are failng to communicate: The local dewpoint, contained as it is within an FSX data struct, and accesible via Simconnect IS what you are referring to as a "humidity index", convertible by a few simple equations into whatever you want it to be, percentage RH, moles-per-liter, whatever is needed. It isn't a matter of what I think "should" be, it is a matter of fact from page 96 of Simconnect interface document. Obviously I realize that any A2A carb Ice model will be complicated, and the general per-station moisture content of the air as it contributes to carb ice in the P-40 is but one factor, but it is there. As far as default carb ice modelling goes: Whatever Aces did for its default carb ice model for default aircraft, was never going to be used by A2A in any case, humidity or not, so I'm not sure how Aces did it even matters to the P-40, or why it came up in the conversation in the first place.

Anyway, I look forward to carb icing being modelled in the future for this airplane. It would be another nice feature that I think would really round some things out.

_________________
1)i7 980x 4.35 ghz, gtx 470s SLI, Matrox th2go, Creative x-fi
2)i7 2600k, Gigabyte z68x, gtx 285s sli

Thanks everyone for the information you've provided here, It's really interesting, Even if it's not truly in FSX I will try to maintain the carb temps listed

Sorry to be blunt, but why did MS do a half-job of the modelling? There was no reason for it to be inaccurate since FS98. They should have concentrated less on the round earth model and more on the bits that mattered.

Did anyone at ACES have a degree in physics or mathematics? This should be easy for them.

Best regards,
Robin.

_________________
A2A/AccuSim. 'nuff said!

I have found a use for the P-40 carb heat. If you set it to 'cold & dark' and let it sit for a little while on a cold moist day and then try to start. Even with the throttle cracked to the usual spot for ~1000RPM, it sputters and has trouble firing, turning on carb heat will clear that up.

Cheers
TJ

_________________
"The knack of flying is learning how to throw yourself at the ground and miss." - Douglas Adams