Its Cold at 25,000 ft

[DaveMC]

Just now, Davidv said:

Woah 21 gallons per minute - hope you have the Monroy's!! I know what you meant, just poking fun  

This fuel flow and power setting explains the better temps you were seeing but the TAS does seem a little on the low side... Maybe some of that junk on the wings was slowing you down.

I'm still struggling with power settings.  I've read the other threads and at higher altitudes I cant keep the CHT on #6 under 400 without cowl flaps open.  ROP  if I go LOP then all is good on the temp side.  At 21000 I was at 27 /24 (78%) IAS 138  TAS188 CHT on #6 377 and GPM of 20.4.  I am leaning to 100-125 ROP tho.

[Davidv]

1 minute ago, DaveMC said:

I'm still struggling with power settings.  I've read the other threads and at higher altitudes I cant keep the CHT on #6 under 400 without cowl flaps open.  ROP  if I go LOP then all is good on the temp side.  At 21000 I was at 27 /24 (78%) IAS 138  TAS188 CHT on #6 377 and GPM of 20.4.  I am leaning to 100-125 ROP tho.

You'll find a lot of people like 29/24 which should give you around 18 GPH and acceptable CHT's.  Of course this will vary with altitude and up that high you may always have to crack the cowl flaps and use a richer mixture.  In the mid teens you should be able to do those numbers without popping cowl flaps.  My CHT's used to run very hot and then I changed my baffle seals and it's made a huge difference.  Now my TIT is my limiting factor on fuel flow rather than CHT.  If my TIT were cooler I bet I could even run 17 GPH ROP and my temps would still be cool but I can't.

It's amazing that the book has 32/2400 Peak TIT at 16.4 GPH.  I'm not sure many Bravo engines can get that performance but I could be wrong...

[LANCECASPER]

10 minutes ago, DaveMC said:

I'm still struggling with power settings.  I've read the other threads and at higher altitudes I cant keep the CHT on #6 under 400 without cowl flaps open.  ROP  if I go LOP then all is good on the temp side.  At 21000 I was at 27 /24 (78%) IAS 138  TAS188 CHT on #6 377 and GPM of 20.4.  I am leaning to 100-125 ROP tho.

What was your TIT? Your fuel flow seems very high for that power setting. If it's taking that much fuel at that power setting to keep your CHT's under 400 something is off.

How are your baffle seals? Replacing mine with the Gee-Bee Kit brought cylinder temps down considerably.

Edit: Just saw @Davidv post at the same time as mine. .  great minds think alike . .  but what does that have to do with us .. lol?

[DaveMC]

2 minutes ago, Davidv said:

You'll find a lot of people like 29/24 which should give you around 18 GPH and acceptable CHT's.  Of course this will vary with altitude and up that high you may always have to crack the cowl flaps and use a richer mixture.  In the mid teens you should be able to do those numbers without popping cowl flaps.  My CHT's used to run very hot and then I changed my baffle seals and it's made a huge difference.  Now my TIT is my limiting factor on fuel flow rather than CHT.  If my TIT were cooler I bet I could even run 17 GPH ROP and my temps would still be cool but I can't.

It's amazing that the book has 32/2400 Peak TIT at 16.4 GPH.  I'm not sure many Bravo engines can get that performance but I could be wrong...

The baffels seem good to go no gaps or tears. when I do a ROP procedure with my JPI 900 Im leaning baised on the degrees ROP  the engine seems to run fine at 50 deg rop and the fuel flows are in the 18s-19s but my understanding is that I need to be 100 ROP if I'm running ROP.   I apologies in advance for my ignorance

[DaveMC]

4 minutes ago, LANCECASPER said:

What was your TIT? Your fuel flow seems very high for that power setting, 

How are your baffle seals? Replacing mine with the Gee-Bee Kit brought cylinder temps down considerably.

My tit on that one was 1565

[Davidv]

Just now, DaveMC said:

The baffels seem good to go no gaps or tears. when I do a ROP procedure with my JPI 900 Im leaning baised on the degrees ROP  the engine seems to run fine at 50 deg rop and the fuel flows are in the 18s-19s but my understanding is that I need to be 100 ROP if I'm running ROP.   I apologies in advance for my ignorance

Ok, just make sure they are all pointed in the right direction (forward).  Are they the sillicone type like the ones that @LANCECASPER and I replaced ours with or do they look like standard material that came with the engine?  @LANCECASPER is way more knowledgeable than me on exact degrees ROP you should be running so I'll let him comment on that.  I know people run at different numbers and you just want to keep things from getting too hot.  I was speaking with someone the other day who is very knowledgeable and he said it's really not until 1850 that the turbo blades start breaking down but I don't want to test that!

[LANCECASPER]

4 minutes ago, DaveMC said:

My tit on that one was 1565

That narrows it down to your baffle seals. Because of cylinder head temps, if you can't bring the fuel flow down to where the TIT is 1600 - 1650, the air is going over the top of your seals and not being forced down over the cooling fins on the cylinders. Shine a flashlight in there and see if your seals are forward facing when the top cowl is on. If they are limp the air will push them back and you'll lose the air over the top.

 

[jlunseth]

I do a fair amount of cold weather flying.  It is actually easier on the engine to be at -34 at 25 k than -34 at 3,000.  The cooling at 25k is alot weaker than near the ground.  My coldest was -52F and I don't recall exactly what the altitude was, I think 21k.  The engine ran cool but the temps were in operating range.  Not much heat coming off the engine though, to heat the interior, so all the windows frosted over completely and we were cold in the aircraft.  I logged the time as IMC (we had zero visibility).

Bruce Jaeger and others recommends adding some isopropyl alcohol to the fuel to prevent ice crystals from forming.  I have never had that problem, but have added isopropyl sometimes and sometimes not, and the isopropyl has not been a problem.  Just the stuff you buy for car engines, obviously not the drug store stuff which is mostly water. I believe Bruce's number was up to 3% alcohol. I don't put in that much, maybe two bottles (I think they are pints).

You probably caused the icing by turning on the TKS.  At that temperature you will not experience structural icing because it is too cold.  But you will fly through clouds that are made of ice crystals and the TKS probably melted that, and then it froze again into a slush and ran off.  Really no need for de-icing at that altitude.  What you can get is induction icing.  You fly through an ice cloud, the air intake inhales all those ice crystals and they plug the air filter.  K's have an Alternate Air door (not Alt. Static) that closes the air intake so induction air comes from inside the engine compartment where it is warm and the ice crystals are all melted.  It closes automatically,, and there is also a manual control knob.  If you are in the flight levels and MP starts to fall slowly, pull the knob.  There will be a slight decrease in power but not much.  Don't know what a Bravo has, but must have something similar if not the same. This was a problem discovered with the early 231's who were Mooney's first venture into the cold flight levels, there was just a manual door and pilots would not pull it, failing to understand what was happening.  Now the door is manual or automatic.

Ice crystal clouds are cool, if it is clear and sunny the crystals glisten.  They create a sound when they hit the airframe.

[DaveMC]

39 minutes ago, jlunseth said:

I do a fair amount of cold weather flying.  It is actually easier on the engine to be at -34 at 25 k than -34 at 3,000.  The cooling at 25k is alot weaker than near the ground.  My coldest was -52F and I don't recall exactly what the altitude was, I think 21k.  The engine ran cool but the temps were in operating range.  Not much heat coming off the engine though, to heat the interior, so all the windows frosted over completely and we were cold in the aircraft.  I logged the time as IMC (we had zero visibility).

Bruce Jaeger and others recommends adding some isopropyl alcohol to the fuel to prevent ice crystals from forming.  I have never had that problem, but have added i

Thats what I thought as well.  I think I would have been fine if I just left it off

 

[DaveMC]

1 hour ago, LANCECASPER said:

That narrows it down to your baffle seals. Because of cylinder head temps, if you can't bring the fuel flow down to where the TIT is 1600 - 1650, the air is going over the top of your seals and not being forced down over the cooling fins on the cylinders. Shine a flashlight in there and see if your seals are forward facing when the top cowl is on. If they are limp the air will push them back and you'll lose the air over the top.

 

They are forward.  I am wonding if I am leaning ROP correctly. seems like I have got to go a long way in terms of GPM to get to 100 deg ROP.   I am following the JPI 900 instructions .  I tend to watch the deg ROP more than anything else while leaning. I wonder if I should switch to FF

[exM20K]

FF calibration and K-Factor can be unreliable, but off by only a little.  In my experience, TIT gauges, when they fail, they fail dead or erratic.  Running LOP or ROP, assuming TIT is not dead, you would want to note FF delta from peak and compare it to the POH/engine manual, but you can be pretty confident that you are truly 100* or whatever ROP.

Peak can take a few seconds to find - i'm not in such a hurry to find it, and by observing the rate of change in TIT with turns of the red knob, I can tell when I have to re-lean a bit or enrichen a bit to get peak-peak.  It can be 20-30* cooler transiting the peak reading quickly.  I hope this makes sense; I'm not articulating it very well.

-dan

[LANCECASPER]

25 minutes ago, DaveMC said:

They are forward.  I am wonding if I am leaning ROP correctly. seems like I have got to go a long way in terms of GPM to get to 100 deg ROP.   I am following the JPI 900 instructions .  I tend to watch the deg ROP more than anything else while leaning. I wonder if I should switch to FF

At that power setting (27.5/24) your 20.4 gallons of fuel per hour is more than cooling your exhaust temps and ultimately your TIT. If your CHT is on #6 is that hot with that much fuel you have an airflow problem or a cylinder problem. Your engine is talking to you.

[carusoam]

DaveMC, 

Glad you stuck around and shared more of your experience...! 

We are getting a few questions we haven’t seen in a while...

Mostly because they are more Bravo specific than all Mooneys...

1) When flying ROP... 50°F is typically a tough area for engine health... I’m not very familiar with the red box and TC’d engines... it may be different... are you familiar with the red box? (Method of avoiding pre-ignition challenges at high power situations...)

2) When flying LOP... your experience will be interesting to share... some Bravo pilots have had good experience... others not as much... the Bravo’s air intake is not very well balanced... no curvy pipes...

3) The viscosity thickening of TKS fluid is interesting... we haven’t discussed that in a while... it occurs, but at a temp that water isn’t usually found...  keep an eye out for super cooled water...  even that has some limitations to how cold it can exist in...?

4) If looking for updated silicone seals for your engine/cowling... there is a thread around here that covers some nice materials and it’s supplier...

Thanks again and best regards,

-a-

[Jethro]

On 3/4/2020 at 9:12 PM, David Medders said:

Welcome aboard, Dave!

I hope you enjoy your Bravo as much as I enjoy mine.

Comments:

• Time of useful consciousness at 25,000 feet is 3 to 5 minutes -- assuming you are in good health and no rapid decompression (hard to get in a Bravo) which reduces TUC.
• If you experience an oxygen system failure, descend IMMEDIATELY. Do not ask permission, advise ATC as you begin the descent. We lost a TBM-930 a few years ago because the pilot stayed at FL250 waiting for permission to descend after a pressurization failure.
• The airspeed envelope for TKS is to ensure proper fluid coverage.
• A thorough review of the TKS flight manual supplement is a MUST to safely operate in icing conditions. It includes important limitations and procedures. TKS operation is far more involved than flipping the switch when you see ice. The supplement includes a pre-flight inspection procedure that fully tests the system. As part of the pre-flight, TKS must be primed on the ground when ice expected. From the STC supplement: "Check evidence of fluid along length of all panels."
• I run the TKS pre-flight procedure monthly (and for flight into ice) and clean the panels. TKS fluid is one of the approved cleaning agents that is conveniently delivered to the panels by the pre-flight test.
• Review AC 91-74B regarding flight in icing conditions: https://www.faa.gov/documentLibrary/media/Advisory_Circular/AC_91-74B.pdf
• Review AC 61-100B regarding high altitude operations. The AC is written for operations above FL250, but it contains information useful to our operations at and below FL250: https://www.faa.gov/documentLibrary/media/Advisory_Circular/AC_61-107B.pdf
• It is always freezing at altitude so any visible moisture means potential ice.
• I have noticed the reduction of oil pressure at altitude, but never really considered it as the pressure stays within limits.
• It is very easy to exceed Lycoming's cooling limitation (50 degrees Fahrenheit per minute) operating in very cold temperatures. Be careful with power reductions and step to the CLD value on the JPI when descending.

Tailwinds,

David

 

Excellent post, Dave