Help Analyze Cruise Numbers - New Bravo Owner

[irishpilot]

I'm planning on going to FL180 today. After lots of reading, I'm going to try and lean for 1600 TIT using 29/2400. We will see what that gives me for CHTs.

Fly Safe,
Safety Forum Mod

[alextstone]

On 7/28/2019 at 12:25 PM, irishpilot said:

I'm planning on going to FL180 today. After lots of reading, I'm going to try and lean for 1600 TIT using 29/2400. We will see what that gives me for CHTs.

Fly Safe,
Safety Forum Mod
 

How did it go?

[irishpilot]

Didn't make it to FL180. Had a new O2 bottle installed as part of the purchase. Leak in the system. However, setting 75 ROP and cowls cracked open keeps the CHTs under 400.

Whem the airspeed increases in the descent, CHTs go down to 375 with no power change. Things are pointing to baffles.

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Safety Forum Mod

[Davidv]

I just put a baffle pirep in a new thread, let me know if you have any questions.

[philiplane]

Baffles require extra attention on the Bravo. Especially the seals around the front of the engine to the cowl. Leaks there upset the pressure differential between the top and bottom of the engine 

[MIm20c]

@irishpilot off topic but how did you get the tach time to display on the main screen?

[irishpilot]

@mlm20c, I have no idea. It was set up by the avionics shop during the pre-buy

CHT update w/20 hrs: flying high or low, as long as I run 100 ROP with cowls cracked, temps stay under 400. It is in annual now, so I'll see how baffles and injectors are doing.

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Safety Forum Mod

[Knuckledragger00]

Now I am wondering if I have the same issue!  Can’t seem to get FF much lower than 20 GPH.  This is a pic at 16,500 with cowl flaps closed.  I am 97 ROP and if I went much leaner CHT’s got almost to 400.  Any thoughts greatly appreciated (sorry for hijacking your thread).

[carusoam]

KD,

What happens when you leave the cowl flaps in trail?

Cylinder cooling becomes more of an issue as the air gets thinner. Other TC’d Mooney owners report using the flaps in trail position to aid with airflow volume...

PP thoughts only, my NA O doesn’t even have cowl flaps... 

Best regards,

-a-

[Shadow]

[mention=14366]irishpilot[/mention] off topic but how did you get the tach time to display on the main screen?

There is a software update for some of the EDMs that now shows the tach time persistently on the display.

[Knuckledragger00]

Car,

I never thought I would need to leave the CF’s open at 16,500.  Just assumed at that high altitude the OAT would be cool enough?.  

[carusoam]

You have a few forces fighting at that level... and get more interesting the higher you go... at higher power settings.

The OAT is wonderful... but the air density is also an important factor... decreasing like an NA engine’s MP with altitude... 

The higher the power setting, the more fuel gets converted to heat...

Cooling fin design is already set...

TAS is already maxed out...

air flow control is about the only adjustment left...

 

Of course all the design stuff is set, you may want to check to see if everything is still meeting the original design criteria... baffle seals still in good shape?

To be clear, i’m Not sure if Bravo owners are using their flaps in trail during cruise... that is a great question.

Best regards,

-a-

[FoxMike]

Standard temperature at 16.5K is around 4dF.  How much above that temp was the outdoor temp. on the day you were having problems.  One way to relieve high temperature problems is to reduce power some.  Less power produces less BTUs of heat.  Hot days raise the density altitude and test the limits of the engine cooling.    

[Davidv]

On 8/23/2019 at 1:41 AM, Knuckledragger00 said:

Car,

I never thought I would need to leave the CF’s open at 16,500.  Just assumed at that high altitude the OAT would be cool enough?.  

I'm not an expert in the science behind cylinder cooling, but in my experience there seems to be very little correlation between OAT and cylinder temps.  I'm sure the cold air plays some role, but the density of the air molecules traveling over the cylinders plays a much larger role.  If my understanding of cowling aerodynamics is correct, rather than the air directly hitting the cylinders first, much of the air in fact gets draw to the upper roof of the cowling where it also gets routed into the oil cooler intake.  Some of the air of course directly moves over your fins, but it makes sense that the density would play a bigger role since not all of the air is directly going through the cylinder fins.

Also, not to mention the fact that when you go higher you're using more turbo air.

[carusoam]

See if this increases your Bravo engine knowledge any..?

1) Cylinder heat adders... more fuel per time being burned increases the energy going in... MP and FF and rpm are the heat adders... if cooling is uncontrollable...

• Cut back the heat adders... (if needed)

 

2) Cylinder heat removers...

• any excess FF (ROP), or excess Airflow (LOP) takes some heat out the exhaust pipe...
• Oil flow takes heat out the oil cooler, especially with the Bravo’s wet heads...
• Cooling fins... (follow this)... air enters the top of the cowl... turns 90°, the down through the cooling fins, 90° again out into the airstream... more with cowl flaps wide open... less as the cowl flaps close more...
• high pressure at the top of the cowl, pushes air to the low pressure at the bottom of the cowl...

 

3) Consider air ducting in each step...

• in and out of the oil cooler...
• in and out of the intercooler...
• in and out of the cylinders...

 

4) Air density, AS, and OAT... are all important for Cylinder cooling... When CHTs increase, to improve cooling...

• Increase airspeed, lower the nose in the climb...
• Increase FF, go further ROP...
• Increase Airflow through the Cylinder fins, open the cowl flaps more...
• Compare your numbers to the book, and with other Bravo owners... Looking for things that have changed or worn...
• Going further LOP is not a usual option for Bravo owners...
• Keep in mind TIT is also being affected by some of these at the same time... TIT is primary for leaning, and Chts follow...
• really hot days at altitude lessens the cooling that is available.
• low density air has a lower number of molecules crossing over the fins... NA plane advantage... Cooling ability drops with the decrease in MP...

Keep in mind my knowledge of the Bravo air ducting is very limited ... as is my O air ducting knowledge... 

Anything stand out?

PP thoughts only, not a mechanic...

Best regards,

-a-

[Knuckledragger00]

4 hours ago, FoxMike said:

Standard temperature at 16.5K is around 4dF.  How much above that temp was the outdoor temp. on the day you were having problems.  One way to relieve high temperature problems is to reduce power some.  Less power produces less BTUs of heat.  Hot days raise the density altitude and test the limits of the engine cooling.    

Not sure exactly what the temp was now but it wasn’t a particularly hot day I don’t recall.  Sounds like I should go to 29 instead of 30” and maybe open CF’s a bit?  Would like to see my FF go below 20 for sure!

[Knuckledragger00]

3 hours ago, carusoam said:

See if this increases your Bravo engine knowledge any..?

1) Cylinder heat adders... more fuel per time being burned increases the energy going in... MP and FF and rpm are the heat adders... if cooling is uncontrollable...

• Cut back the heat adders... (if needed)

 

2) Cylinder heat removers...

• any excess FF (ROP), or excess Airflow (LOP) takes some heat out the exhaust pipe...
• Oil flow takes heat out the oil cooler, especially with the Bravo’s wet heads...
• Cooling fins... (follow this)... air enters the top of the cowl... turns 90°, the down through the cooling fins, 90° again out into the airstream... more with cowl flaps wide open... less as the cowl flaps close more...
• high pressure at the top of the cowl, pushes air to the low pressure at the bottom of the cowl...

 

3) Consider air ducting in each step...

• in and out of the oil cooler...
• in and out of the intercooler...
• in and out of the cylinders...

 

4) Air density, AS, and OAT... are all important for Cylinder cooling... When CHTs increase, to improve cooling...

• Increase airspeed, lower the nose in the climb...
• Increase FF, go further ROP...
• Increase Airflow through the Cylinder fins, open the cowl flaps more...
• Compare your numbers to the book, and with other Bravo owners... Looking for things that have changed or worn...
• Going further LOP is not a usual option for Bravo owners...
• Keep in mind TIT is also being affected by some of these at the same time... TIT is primary for leaning, and Chts follow...
• really hot days at altitude lessens the cooling that is available.
• low density air has a lower number of molecules crossing over the fins... NA plane advantage... Cooling ability drops with the decrease in MP...

Keep in mind my knowledge of the Bravo air ducting is very limited ... as is my O air ducting knowledge... 

Anything stand out?

PP thoughts only, not a mechanic...

Best regards,

-a-

Going to try to cut back on MP (item1) and see if that helps.  Also will try opening CF’s (item 4.3).

TIT staying very low due to CHT’s being close to 400 so haven’t been able to lean out much.  Which of course is causing me to burn 20+ GPH:(

All in all great info as usual Car!

[carusoam]

I think you may have found what is called...

Operating in fire breathing dragon mode... 

A place that some Mooney pilots use to fly safely at the highest speed available... one eye usually closed when looking at the efficiency numbers...

The only cost to operating here, is an expected Set of cylinders at about the halfway point....

When flying for business, this can make a lot of sense and pay for itself...

The NA Mooneys run into the same challenge around 5k’, lots of MP and Kias, But CHTs Over 380°F...

The most interesting flights are engine break-in related... max MP and max FF, and altering RPM every 15 minutes or so... done early in the day for coolest OAT.  for an NA plane, this is done about 1k’ AGL, Over the Atlantic Ocean makes for a good place, along the coast... FF for the IO550 is about 28gph for these flights... 

PP thoughts only, not a mechanic...

Best regards,

-a-

[Davidv]

9 hours ago, carusoam said:

I think you may have found what is called...

Operating in fire breathing dragon mode... 

A place that some Mooney pilots use to fly safely at the highest speed available... one eye usually closed when looking at the efficiency numbers...

The only cost to operating here, is an expected Set of cylinders at about the halfway point....

When flying for business, this can make a lot of sense and pay for itself...

The NA Mooneys run into the same challenge around 5k’, lots of MP and Kias, But CHTs Over 380°F...

The most interesting flights are engine break-in related... max MP and max FF, and altering RPM every 15 minutes or so... done early in the day for coolest OAT.  for an NA plane, this is done about 1k’ AGL, Over the Atlantic Ocean makes for a good place, along the coast... FF for the IO550 is about 28gph for these flights... 

PP thoughts only, not a mechanic...

Best regards,

-a-

There's always a penalty for extreme performance.  Correct me if I'm wrong @carusoam, but this is why our POH's in the Bravo tell us that we need to run at mixture full rich at 25K feet.  I have not taken my plane up that high, so I'd be curious if other Bravo owners have had to go very rich to keep the temps cool at that height.  It's also another reason why the air density has such a large impact even with cool temps.  At 25K feet the temp should be about -34 Celsius.

[Awful_Charlie]

4 hours ago, Davidv said:

There's always a penalty for extreme performance.  Correct me if I'm wrong @carusoam, but this is why our POH's in the Bravo tell us that we need to run at mixture full rich at 25K feet.  I have not taken my plane up that high, so I'd be curious if other Bravo owners have had to go very rich to keep the temps cool at that height.  It's also another reason why the air density has such a large impact even with cool temps.  At 25K feet the temp should be about -34 Celsius.

I've gone to FL200+ quite a few times, but then I don't cruise over 15GPH very often - more normally 12-14 (gas is the equivalent of 9bucks a gallon here) - 30" and 2200 RPM works well enough

[Danb]

I like Charlie have been over 20,000 but not often, I needed to be cognizant of temps during the climb, needing full open cowl flaps, I cruised at 30/2350 RPMS 1600 TIT and needed the flaps partially open, at FL 250 CHTS  were 400 for one cyl and under 400 for rest, opening cowl to full open dropped the temps significantly. I only go up for weather reasons.

 

[PaulM]

9 hours ago, Davidv said:

POH's in the Bravo tell us that we need to run at mixture full rich at 25K feet. 

Only if running 34" of MP... you can lean at 32" or less. 

"When operating above 22000 ft and at manifold pressures above 32 in Hg, only best power mixture (1650 TIT) or richer is permitted. "

I'f I'm making good power, I need to either trail the cowl flaps (say 1/2), or go lean of peak. otherwise the CHT's will go over 400. 

[irishpilot]

PIREP: The Bravo is out of a longer than expected annual and I've flown at 15k, 17k, FL180 and FL190. After replacing two cylinders and a bunch of other work, my #6 is the hottest and it is easier to keep under 400. At high alt I have to keep cowls open, but I'm seeing 180-190 KTAS, so the alt helps with speed.

I still think my baffles need work and I'm leaning towards heading down the Gami road as I fly it enough to warrant the up front costs. However, the Bravo earns it's XC reputation. It's great up high, climbs all the way to alt without issue or loss of performance. All I've noticed is the heater doesn't keep up much past 15k...it's cold up there!

Fly Safe,
Safety Forum Mod

[Steve Skinner]

I fly between 10k and FL19 dependent on wind and distance.
Almost always 100 deg ROP is 1600 TIT.
Head wind 31/2400 (20g/hr) tail wind 30/2200 (18 g/hr)
If I can’t maintain less than 200 deg oil temp and cyl less than 400 I’ll first trail cowl flaps then add fuel or reduce mp. It has to be very hot OAT to do more than trail flaps. 1st engine went to TBO with good compressions. 2nd life at 1/2 life with no issues (except turbo replacement @ 1/2 life)
To add always cruise climb at 34/24 or 35/25 and decent at 28/20 peak tit.
It doesn’t take much of a timing issue to increase temps dramatically in a Bravo.
I’d be getting it checked by a different technician.


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