NoahBryant

Help taking off in cold weather

21 posts in this topic

Hi All - 
I have been doing some flying up in Alaska and have run into trouble taking off.

  • I am using AFE after engine start
  • OAT is about -10C
  • I set AFE to Dry Takeoff
  • Cylinder Head Temp starts raising and is in the red before we even get to full power
  • Before I am even up to about 30 knots or so all four engines have damage

I thought it was carb icing so I:

  • Used carb heat until before takeoff
  • Turned on carb anti-ice

None of that helped

Just to be sure, I moved the aircraft to a warmer airport (OAT was 4C) and there was no problem at all with CHT

Any idea what I am doing wrong here?

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Hi!
... Maybe does the AFE close the cowl flaps to let the engine 'pre-warm', and then doesn't open them anymore for take-off..?
It is probably nonsense but who knows..?

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I just did another flight and yes, cowl flaps are on TO. On my next one I will try opening them fully to see if that helps but I'm not sure the FE will let me?

My 'fix' has just been to repair the engines once I reduce power in the air...kinda unrealistic, lol

 

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I think we had a thread a couple of months ago where CHT became a problem with low OATs..., I don't recall want came of that.  All my beta testing was in Alaska during cold weather so I don't think there is a bug.

Check your procedures, don't rely on the AFE (I refuse to use it).  Carb icing will prevent you from developing expected TO MP.  Common reason for high CHT other than airflow is low fuel flow/pressure causing lean conditions.

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The AFE could be setting excess power. Cold air is very dense, and BMEP limits will likely be reached before MAP limits.

Robert Toten

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1 minute ago, randomTOTEN said:

The AFE could be setting excess power. Cold air is very dense, and BMEP limits will likely be reached before MAP limits.

Robert Toten

That's a good point. I have found that if I fly it manually I can easily take off without going to "full power" 

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2 hours ago, downscc said:

I think we had a thread a couple of months ago where CHT became a problem with low OATs..., I don't recall want came of that.  All my beta testing was in Alaska during cold weather so I don't think there is a bug.

Check your procedures, don't rely on the AFE (I refuse to use it).  Carb icing will prevent you from developing expected TO MP.  Common reason for high CHT other than airflow is low fuel flow/pressure causing lean conditions.

Thanks Dan - I would love to ween myself off the AFE but I am still waiting on tutorial 3. In the beginning, I had tried to go without AFE but I was having trouble killing the engines, lol. 

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1 hour ago, NoahBryant said:

I can easily take off without going to "full power" 

That's not what I'm suggesting, and you will destroy the engines if you try this. The R-2800 engines have a feature in their carburetors commonly called "power enrichment" or the "power valve" which allows for increased fuel to control cylinder temperatures, and stabilize combustion to fight detonation. When you run a takeoff DRY you have no W/A to perform this function, and must rely on extra fuel. If you run less than certificated takeoff power, you can fail to engage power enrichment, leaving the engine running hotter and leaner than it requires.

The solution for piston engine aircraft is to always takeoff with an approved takeoff power setting.

But you may need to pull it back some. With such cold, dense air and with such great amounts of fuel it is possible to exceed operating pressures on takeoff, using approved takeoff settings. In this case, you must extract maximum power possible, while still respecting engine limits.

Look at Page 305 of the PMDG DC-6 Manual, titled: "LOW BLOWER POWER CHART - WET AND DRY TAKE-OFF"

In it, you will see that the various settings and limits for setting the correct takeoff power in your present conditions. In your example the values are (I assume  S.L.) -10C giving a target DRY MAP of 50.7"... Notice that the only thing which is constant on the whole chart is blower setting, RPM, and BMEP. It calls for LOW blower, 2800 RPM, and a 197 PSI.

The PMDG manual gives inappropriate limits for dry takeoffs with 2700 RPM (2050 HP), but because we cannot reset the governors as required by the FAA we cannot use them, we are restricted to using 2800 RPM for dry takeoffs (1950 HP).

The limits are then as follows:

DRY takeoff, LOW blower, AUTO-RICH Mixture, 2800 RPM, 197psi BMEP, and 53.0" at Sea Level.

You must target these limits to produce takeoff power. As you saw with the power chart, it is likely that you will exceed 197psi when using 53.0" (53" is the correct setting for a 2800 RPM Dry Takeoff, instead of 55" at 2700 RPM quoted in the manual) with such dense/cold air. Pull it back a little bit. Not such much that you kill power enrichment and damage the engines, but enough to not exceed limits and produce approved takeoff power.

 

Robert Toten

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So I just tried a takeoff from Barrow, AK (PABR). Using FSX:A (Boxed) with an OAT of -11C (ASN Weather) I reached 197psi at about 49" MAP, and after takeoff all engines are still showing green MX health.

I don't remember what the MAP actually was (it might have been as low as 45 or 46?), all I know was I very quickly hit the torque limit in such cold air.... also will full gas and no payload she LEAPED into the air lol.

 

Let us know if this helps,

Robert Toten

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Thanks Robert - Just tried a flight myself without AFE and had no trouble at all following your advice. Need to send the FE back to school, I think!

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10 hours ago, randomTOTEN said:

The R-2800 engines have a feature in their carburetors commonly called "power enrichment" or the "power valve" which allows for increased fuel to control cylinder temperatures, and stabilize combustion to fight detonation. When you run a takeoff DRY you have no W/A to perform this function, and must rely on extra fuel. If you run less than certificated takeoff power, you can fail to engage power enrichment, leaving the engine running hotter and leaner than it requires.

This is a lot of detailed systems simulation. I know that PMDG is known for detailed systems simulation, but does the PMDG DC-6 simulate engine operations to this level - carburetor power enrichment and the carburetor power valve and their relation to cylinder temperature and combustion stabilization?

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It didn't take me long to realise that the AFE puts the 'prat' in Pratt and Whitney a lot of the time, so I don't use that feature. Managing the engines yourself makes things a bit busier for sure, but then again, that's probably why most people would buy a decent simulation of the engines in an FS aeroplane in the first place, otherwise there's no fun to be had in having that realism.

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Agree, the AFE is a nice feature for those new to big props but I appreciate the complexity of this aircraft and have been manipulating throttle, prop, mixture, cowls and tanks for a long time.  Our power settings in the TSIO520  are much simpler thank goodness, I wouldn't dream of flying the DC6 without the POH open in my other screen.  I recall there was a discussion of using full takeoff power during testing but I don't recall if specifically power enrichment was discussed but I wouldn't be surprised if it wasn't baked into the FDX in some manner.  Regardless, less than full takeoff power will lengthen your takeoff roll and the time duration of the takeoff power application before reducing to climb power..., not much to be gained here.

16 hours ago, randomTOTEN said:

DRY takeoff, LOW blower, AUTO-RICH Mixture, 2800 RPM, 197psi BMEP, and 53.0" at Sea Level.

This is a good point, which was discussed here early after RTM and it is worth repeating.  The simplification of the FDX made it very difficult to set 2700 RPM for takeoff power and still have the blue lights on, so the limit of 53 inHg is very real.  To be honest, I usually set 52 inHg simply because this propeller simulation tends to overshoot the 2800 RPM by at least a 100.

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5 hours ago, Chock said:

Managing the engines yourself makes things a bit busier for sure, but then again, that's probably why most people would buy a decent simulation of the engines in an FS aeroplane in the first place, otherwise there's no fun to be had in having that realism.

I understand and appreciate the point you're making (and that Dan is making), but beg to differ - for my own flying at least.  While I recognize that there are gaps in what the AFE can do - and maybe stuff that's just plain wrong - I prefer the experience, and find it more realistic, to focus on left-seat responsibilities, know that thanks to the high level of realism, the engines can go south on me, but not be responsible for flipping every switch.  Probably reflects the fact that in real life, I couldn't function if I couldn't delegate.  There's no circumstance in which I'd give assignments to a team of writers, then rush around to each of their keyboards and actually write what I'd assign them.  I guide on the front end and edit on the back end.  The AFE fits that pattern for me, and if the feature wasn't there, I wouldn't be flying the aircraft - I avoided the A2A Stratocruiser until Captain of the Ship came along.  Now, in my defense, I know what's involved in managing a large radial engine - I learned that thanks to the A2A P-47, but to me, that was the realistic way to do it, since you've got no choice there but to be a one-man band.

Plus, the AFE has an artificial family to feed, so I don't want to throw him out of work... :cool:

Sorry, not trying to derail things, but since we're talking AFE limitations, my vote would be for PMDG to refine him if possible (and economically sensible).  

If not, I'll just apply my management skills and yell at the guy.

EDIT: Another thought - one option might be to add a dialog box that allows the pilot flying to call the power settings, with variations possible, and the AFE to apply them, sort of like the MP hold feature in the A2A Stratocruiser.  That would be even more realistic, since as I understand it, SOP is for the captain to ask the FE to set manifold, not for the FE to just use a book value.  With an option like that, you'd have authentic division of labor, and an authentic level of control from the left seat over how the engines are performing.

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17 minutes ago, Alan_A said:

I understand and appreciate the point you're making (and that Dan is making), but beg to differ - for my own flying at least.  While I recognize that there are gaps in what the AFE can do - and maybe stuff that's just plain wrong - I prefer the experience, and find it more realistic, to focus on left-seat responsibilities, know that thanks to the high level of realism, the engines can go south on me, but not be responsible for flipping every switch.

Yup, that is certainly true in the sense of the real thing being something operated by a team, and if people wish to do that, great, the AFE is a big help with that, although in a simulator we have the luxury of being able to pause the simulator, run it at slower speed etc, hit the A key and jump to different seating positions etc, so we can be both pilots if we like. And that's a good thing with flight sims and realistically simulated aeroplanes, because there are plenty of aeroplanes where you literally can't even reach certain controls, much less operate them from one particular seat.

That was one of the bad things on several big combat aircraft with two pilots which had controls laid out like that, where it really was not inconceivable that a pilot might be operating the thing solo if the other pilot got incapacitated, which of course might even have occurred on the DC-6 in its C-118  military incarnation if it ever found itself getting shot at.

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