PMSoares

High CHT's during Takeoff

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Hello DC-6 flyers! 

 

After purchasing the DC-6 I started flying across the Caribbean, in nice weather , in order to gain more experience with the aircraft type, and was able to fly several uneventful flights. Then I decided to fly over the ORBX Alaska sceneries. Installed the fantastic Everts livery and off we go. 

Most of the Caribbean flights were being flown without the aid of the AFE. I was being able to set up the DRY takeoff power setting 52.5" and although the OAT was quite high (ranging between 25 up to 32C) , takeoff CHT's were well within the green range (usually between 190 and 210 C). Cowl flaps were at 3 degrees. During climb, CHT's stayed below 200C all the time and after 10 legs, engine wear was still in the green band, as expected. 

During my first takeoff from, PANC, OAT was -10C, and surprisingly during the takeoff roll CHT's rose to an unacceptable 280C. Mixtures were at Auto Rich, Cowl Flaps were set at 3 degrees , carb heat was cold and takeoff power setting was 52.5" MP. Every time I attempted to takeoff, I suffered from very high CHT's and excessive engine wear (orange band) even with cowl-flaps set at 4 degrees, 6 degrees and even full open. Eventually I was able to takeoff with the help of the AFE, and this time CHT's were high, but within limits. The cowl flaps, surprisingly were set at  8 degrees by the AFE, possibly in order to keep CHTs within the limits. 

Is anybody experiencing such a situation like this? I would expect high CHTs in a high OAT takeoff... What am I doing wrong? 

 

Any help would be appreciated. Meanwhile I've decided to bid some Caribbean flights... 

 

Thanks for the attention! 

 

Paulo M. Soares

 

 

 

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POH takeoff cowls are 4 deg, and I've done 80% of my DC6 flying in either Alaska or So Texas without problem. Regardless of takeoff power, that power setting must come down to METO and I use 2600/45 for that value and must come down again to climb power after you have cleaned up and accelerated to 170 KIAS.  You just mentioned takeoff power and nothing about technique so I don't know how long you leaving takeoff power set.  Also, while on the ground before takeoff doing taxi maneuvers and engine run ups the cowls should be wide open.  Agree, a CHT rise to 280C is unacceptable and should result in immediate reduction of pitch an power.  Your POH maximum is 260C for takeoff and climb.

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11 hours ago, downscc said:

POH takeoff cowls are 4 deg, and I've done 80% of my DC6 flying in either Alaska or So Texas without problem. Regardless of takeoff power, that power setting must come down to METO and I use 2600/45 for that value and must come down again to climb power after you have cleaned up and accelerated to 170 KIAS.  You just mentioned takeoff power and nothing about technique so I don't know how long you leaving takeoff power set.  Also, while on the ground before takeoff doing taxi maneuvers and engine run ups the cowls should be wide open.  Agree, a CHT rise to 280C is unacceptable and should result in immediate reduction of pitch an power.  Your POH maximum is 260C for takeoff and climb.

Hello Dan, 

 

Once again, thanks for the quick reply. The problem is occurring anytime the temperature is below 32F/0C. I'm applying takeoff power exactly by the book (30 inches until stabilizing then slowly advancing the throttles to the dry manifold pressure limit according to carburetor temperature (49.6 for a -20C carb temp). The cowl flaps were set at 4 degrees and before applying power the CHTs were in the 190-200 C range. Also it's worth noting that even with the AFE turned on (and I assume he would set the power in a proper way in order to protect the engines from damage) this is happening. I'm aware that those radials shouldn't be run at high power settings for a long time. I'm aware that the maximum time at TO power is limited to 2 minutes, and I usually reduce the power to METO just after the gear is retracted. This not seems to be the problem, since the CHTs are exceeding the maximum, just a few seconds after power is set. And if the temperature is at or above +1C there is no problem with the CHTs. But if I reduce the OAT just a little bit further (to -1C for example) the CHTs during the takeoff roll jump to very high values in a few seconds. Could you please try to reproduce this takeoff editing the weather manually to a temperature of 1C and then attempt a takeoff in a negative temp ( -5C for example). For the time being, I'm turning the engine damage OFF for below zero C takeoffs. 

 

Thanks for the attention!

 

Paulo M. Soares

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Having said I flew beta this past winter in Alaska I was very reluctant to take the time to verify your observation, but I did.  I set up a DC-6A at KABQ on a winter day and set AS16 to manual weather with a METAR of 140542Z 36008KT 9999 FEW068 FEW088 BKN158 M05/M12 A3007.  Temperature is -5C to use your example.  Set cowls to 4 deg and did remainder of pre-takeoff checks and noted CHTs had risen slightly since I changed them from wide open but they were still about 180-190C.  Dry takeoff with 52/2800 power until gear up and flap retraction and acceleration to about 120 and noted CHT about 200C and kept her in METO until 170 KIAS and CHT hadn't nudged from 200C.

In the real world a high CHT immediately after applying power points to a lean mixture or equipment problem.  I've seen loose fuel line couplings cause this.  In the simulator for it to be occurring only when below 0C but not at 0C is just plain weird and must have something to do with the way the wx engine is set up or configured.  Is the free air temperature doing anything weird (it should decrease at 1.5 deg / 1000 ft climb on std day)? Look for a cause that is not a bug in the DC6 because I don't think we can establish that as the problem.

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I'm having the same issue that Paulo is having, except that it still hapens with +1C.

I made a test with 3 situations, on the same airport:

  • PAFA 012210Z 00000KT 9999 FEW012 SCT017 BKN070 BKN200 M20/M21 A3082
  • PAFA 012153Z 00000KT 10SM FEW070 00/00 A3082
  • PAFA 012153Z 00000KT 10SM FEW070 01/00 A3082

I was using the AFE in all these 3 situations. All of them gave me a high CHT during the takeoff.

In the video below you can see the takeoff with +1C.

What I realized during my flight was that, as high as the external temperature, as low as the CHT will be.

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I think you need to manage the cowling flaps and your power settings differently.

Keep cowling flaps open and at minimum 6-8° until you really take off.

You do your power check on MAP 30 in and expected +2100 RPM with cowling flaps fully open prior entering the runway.

Once you your are aligned on the runway and want to take off, then you close them to 4° and release brakes once you have 30 MAP and continue to slowly move throttles to MAP for take off. The plane needs to roll when you move from 30 to 55 in MAP!

On the vids from Everets, the FE typically closes the CF only once the plane started rolling and that is in cold weather there too.

 

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3 hours ago, metzgergva said:

I think you need to manage the cowling flaps and your power settings differently.

Keep cowling flaps open and at minimum 6-8° until you really take off.

You do your power check on MAP 30 in and expected +2100 RPM with cowling flaps fully open prior entering the runway.

Once you your are aligned on the runway and want to take off, then you close them to 4° and release brakes once you have 30 MAP and continue to slowly move throttles to MAP for take off. The plane needs to roll when you move from 30 to 55 in MAP!

On the vids from Everets, the FE typically closes the CF only once the plane started rolling and that is in cold weather there too.

 

Well, that's different from the POH. In the POH we have:

2.5. PRE take-off

(1) Flight instruments—check.

(2) Wing flaps-“20°” down.

(3) Cowl flaps—“4°” open.

(4) Fuel booster pumps as required.

(5) Air conditioning controls—SET.

(6) Captain’s instrument and radio inverter opposite to first officer’s.

(7) Controls—gust lock disengaged and controls FREE.

(8) Mixture controls—“AUTO RICH.”

 

This also means that the AFE takeoff does not work in low temperatures. Is that right? It should be at least documented.

I'll try your procedure and check if it works as soon as I can.

Thanks Alexander

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From the video posted, it looks like a mixture issue.

Are you guys able to verify that the AFE is actually setting the mixtures to full rich before bringing the engines up to takeoff power? A lean mixture would result in detonation, which would cause your CHT's to soar, and for the MX window to show damaged engines after your reject.

Do you guys have hardware mixture levers? Do you leave them in the full rich position when flying the DC-6? I noticed that my hardware mixture lever affects the engines, even though there is no motion of the VC mixture levers. Any other possible interference with the PMDG mixture control logic?

If you try the takeoff with notifications displayed, do any error messages pop up during the takeoff?

I really am at a loss as to what you're experiencing, but this could be an avenue of investigation.

 

Robert Toten

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1 hour ago, randomTOTEN said:

Do you guys have hardware mixture levers? Do you leave them in the full rich position when flying the DC-6? I noticed that my hardware mixture lever affects the engines, even though there is no motion of the VC mixture levers. Any other possible interference with the PMDG mixture control logic?

That would make lots of sense.  That rapid of rise of CHT on application of power looks like to me a mixture problem.  I cannot tell what's causing it but the fuel flows at max dry should be greater than 1400 lb/hr/eng.  Also note the takeoff power real world is 55/2700 RPM and since we do not have the prop high pitch locks modified we should be using 53/2800 (pg 287).  Using 55/2800 is wrong and the AFE should be fired if he/she is doing that.  I prefer 52/2800 because this prop simulation is sloppy at the high end and normally overshoots to 2900.

Personally, I never used the AFE during beta and I'm not going to now. 

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8 hours ago, metzgergva said:

I think you need to manage the cowling flaps and your power settings differently.

Keep cowling flaps open and at minimum 6-8° until you really take off.

You do your power check on MAP 30 in and expected +2100 RPM with cowling flaps fully open prior entering the runway.

Once you your are aligned on the runway and want to take off, then you close them to 4° and release brakes once you have 30 MAP and continue to slowly move throttles to MAP for take off. The plane needs to roll when you move from 30 to 55 in MAP!

On the vids from Everets, the FE typically closes the CF only once the plane started rolling and that is in cold weather there too.

 

Hello Alexander! 

The power settings are being managed by the AFE, so I suppose they should be correctly set. Both me an Felipe Bachian are setting the mixtures at rich before takeoff. I can send you a video showing three takeoffs performed with exactly the same technique, the only difference is the  OAT, and the results are completely different if the temp is above or below zero. 

 

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20 minutes ago, downscc said:

That would make lots of sense.  That rapid of rise of CHT on application of power looks like to me a mixture problem.  I cannot tell what's causing it but the fuel flows at max dry should be greater than 1400 lb/hr/eng.  Also note the takeoff power real world is 55/2700 RPM and since we do not have the prop high pitch locks modified we should be using 53/2800 (pg 287).  Using 55/2800 is wrong and the AFE should be fired if he/she is doing that.

Personally, I never used the AFE during beta and I'm not going to now. 

Yes. It seems to be a mixture problem, but as I have stated before, the mixtures are correctly set at  Auto-Rich before takeoff, cowl flaps are correctly set. I don't have any axis assigned to the mixture controls. Surely the CHTs should rise during takeoff, and rise to a much higher value if either  the mixtures or cowl flaps are not correctly set, but the question is that the CHTs are rising to more than 300 degrees almost immediately... 

 

Also regarding Takeoff Manifold Pressures. It must be noted that at very low temperatures, the takeoff MP should be even lower (49.8 at a carburetor temp of -20C) and even doing that, the temperatures are exceeding the max values. It should also be noted that at  high tropical temperatures (above 35C OAT) doesn't seem to affect the CHTs during takeoff.

 

Notwithstanding this minor issue, the plane is absolutely joyful to fly, and once again thanks for the attention! 

 

 

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5 minutes ago, PMSoares said:

but the question is that the CHTs are rising to more than 300 degrees almost immediately... 

I agree, that is the question, and it's not normal and in fact I cannot reproduce it.  However, the problem is not so rare as to not have a couple of folks observing it.  Like I said earlier, the only time I've ever seen CHT rise that fast in the real world was when there was a mechanical problem directly affecting fuel mixtures.  In one case there was fuel flowing all over the engine and it scared the bejeebers out of me.  I don't know what could cause it in the simulator.

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2 minutes ago, downscc said:

I agree, that is the question, and it's not normal and in fact I cannot reproduce it.  However, the problem is not so rare as to not have a couple of folks observing it.  Like I said earlier, the only time I've ever seen CHT rise that fast in the real world was when there was a mechanical problem directly affecting fuel mixtures.  In one case there was fuel flowing all over the engine and it scared the bejeebers out of me.  I don't know what could cause it in the simulator.

I'm sure that the PMDG team will be able to trace the root cause. By the way, this is happening both with and without AS16 running, so I don't believe it's related to the weather engine being used. 

 

Regarding your real-life high CHT event.. Yes... It would scare me a lot also! Hopefully in the simulator we have an unlimited supply of spare engines :gaul:

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1 minute ago, PMSoares said:

I'm sure that the PMDG team will be able to trace the root cause.

If it can be reproduced.

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Update, I just tried this takeoff in FSX:A with an OAT of 0C

CHT's were in the normal operating range.

8 hours ago, downscc said:

Using 55/2800 is wrong and the AFE should be fired if he/she is doing that.

In the posted video, the AFE was using the correct dry takeoff setting of 53/2800

 

Robert Toten

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