Climb Setting question

[Shadrach]

5 hours ago, MIm20c said:

One thing I’m certain of is the io-550 and the o-360 create a lot more heat in the cylinders at 2700 vs 2500. This heat can normally be held to safe levels with airflow and fuel. But if it can’t the power should be reduced. 

Don’t be so certain. RPM is but one factor in CHT. Cylinder pressures are higher at 2500 compared to 2700 all other things being equal.

[PT20J]

5 hours ago, MIm20c said:

One thing I’m certain of is the io-550 and the o-360 create a lot more heat in the cylinders at 2700 vs 2500.

"A lot more heat" would likely be from increased power output at the higher rpm as the increased frictional heating from 200 rpm should not be great. The way to test this is to stabilize in level flight at 2500 rpm and note the airspeed and CHTs and then increase the rpm to 2700 and reduce manifold pressure until you get the same airspeed and note the CHTs.

[carusoam]

Take an example of what happens when going from 2500 to 2700 rpm at WOT...

The IO500 goes from producing 280 to 310hp... drinking 25 to over 27 gallons of gas per hour...

Quickly, you can skip the math to see... more fuel gets burned in the same cylinders in the same time...

No additional surface area has been added to improve the cooling...

cooling won’t increase until the DeltaT rises....

 

For another example... the IO550(g) gets swapped out for the IO550(n) the cylinder cooling fin design is the big difference between the two... Unfortunately I don’t have any data to go with the change....  

 

Best regards,

-a-

[MATTS875]

Thanks for all the help. It’s a lot to digest but I get the picture.  All the information is appreciated 

[Hank]

10 minutes ago, carusoam said:

Take an example of what happens when going from 2500 to 2700 rpm at WOT...

The IO500 goes from producing 280 to 310hp... drinking 25 to over 27 gallons of gas per hour...

Quickly, you can skip the math to see... more fuel gets burned in the same cylinders in the same time...

No additional surface area has been added to improve the cooling...

cooling won’t increase until the DeltaT rises....

 

For another example... the IO550(g) gets swapped out for the IO550(n) the cylinder cooling fin design is the big difference between the two... Unfortunately I don’t have any data to go with the change....  

 

Best regards,

-a-

More fuel is burned at 2700, increasing the heat produced. But the resulting higher airspeed creates more airflow through the baffles, increasing engine cooling. I don't have any realistic numbers for any of this . . . Need empirical data or input from someone like @testwest who probably already has the data.

[PT20J]

1 hour ago, Shadrach said:

Furthermore, for a given velocity, drag is less in climb then in it is in level flight at the same velocity.

Good observation. In a climb, the weight and lift vectors are out of alignment by an angle equal to the velocity vector angle relative to level. This means that the lift is slightly less than the weight (the difference is made up by a component of the thrust vector). Less lift means less induced drag, and the induced drag is a significant component of the total drag at climb speeds. Think of a jet fighter with a thrust-to-weight ratio >1 in a vertical climb: Lift - and therefore induced drag - are zero. The effect is small for our airplanes, but it is there. 

[Shadrach]

1 minute ago, PT20J said:

Good observation. In a climb, the weight and lift vectors are out of alignment by an angle equal to the velocity vector angle relative to level. This means that the lift is slightly less than the weight (the difference is made up by a component of the thrust vector). Less lift means less induced drag, and the induced drag is a significant component of the total drag at climb speeds. Think of a jet fighter with a thrust-to-weight ratio >1 in a vertical climb: Lift - and therefore induced drag - are zero. The effect is small for our airplanes, but it is there. 

Thank you picking up where I lazily left off! There are numerous white papers available online that detail what you’ve nicely summed above. Pretty dry stuff, but the finer points are out there for those that are interested.

[carusoam]

Related to Hanks post...

Full throttle in the climb... often we maintain a climb air speed of 120ias... roughly... for good cooling.

We could change the ias to adjust cooling.

I used 120mias for my M20C...  and 120kias for my M20R...

 

related to Skip’s post... a zero lift climb... that would be a nice HP/Wt ratio...   

 

PP thoughts only, not a mechanic or a CFI ...

Best regards,

-a-

[Shadrach]

13 minutes ago, Hank said:

More fuel is burned at 2700, increasing the heat produced. But the resulting higher airspeed creates more airflow through the baffles, increasing engine cooling. I don't have any realistic numbers for any of this . . . Need empirical data or input from someone like @testwest who probably already has the data.

That’s only part of the CHT equation. Lower RPM=lower piston speed=higher cylinder pressure=higher heat transfer per combustion event. 

Edited March 6, 2019 by Shadrach

[PT20J]

1 hour ago, carusoam said:

Another interesting topic...

at high rpm... the prop is resting on the stops...

I thought that for a long time...

thinking if my govenor breaks... my O360 is going to hit max rpm and I can fly around at max power and 2700 rpm...

 

Then one day... my gov leaked it’s fluids internally... and max power was well beyond 2700rpm.... in overspeed territory....

Fair enough, i’ll Pull the power back some to keep 2700 rpm with my newly fixed pitch O360...

Pulling the prop back so 2700rpm is maintained, is no where near max power... 

getting the gov’s leak figured out became an immediate top priority...

So don’t expect that your prop’s blades are actually sitting on the mechanical stops...

The low pitch stop is set so that the static rpm is nearly redline with the engine at full power. At this point the governor is out of the picture. During takeoff acceleration, the increased airspeed unloads the blades slightly and the prop wants to turn faster. The governor kicks in to keep the rpm at redline. If the governor fails in flight and the prop goes to the low pitch stop, then the airspeed will drive the prop above redline and the only means you have to control this is to reduce airspeed and/or throttle. 

[carusoam]

2 minutes ago, PT20J said:

The low pitch stop is set so that the static rpm is nearly redline with the engine at full power. At this point the governor is out of the picture. During takeoff acceleration, the increased airspeed unloads the blades slightly and the prop wants to turn faster. The governor kicks in to keep the rpm at redline. If the governor fails in flight and the prop goes to the low pitch stop, then the airspeed will drive the prop above redline and the only means you have to control this is to reduce airspeed and/or throttle. 

Sounds like my M20C needed to be set up better.... 

It lost its crank seal, aluminum disc inside the shaft.... and was trying to overspeed while flying around the traffic pattern...

The prop control was bottomed against the panel and held 2700rpm pretty well, normally... that was set up correctly... 

But, when the gov went off line, the prop must have found the physical stops in a place that resulted in more than 2700 rpm...

It failed the prop control test during the run-up.... after that...

Best regards,

-a-

[David_H]

By pulling back to 26-square, one has the potential to catch a misbehaving prop before getting too far away from the airport without sacrificing very much performance. 

Edited March 6, 2019 by David_H

[Shadrach]

26 minutes ago, David_H said:

By pulling back to 26-square, one has the potential to catch a misbehaving prop before getting too far away from the airport without sacrificing very much performance. 

Misbehaving props almost always reveal themselves by hunting on takeoff.

[Cyril Gibb]

10 hours ago, Hank said:

Why pull power to descend??? I only make two changes from cruise to descent:  push yoke forward to establish 500 fpm descent and trim away forces; periodically reduce throttle and advance mixture to keep cruise MP & EGT settings. Climbs start at 100% power, but that declines as altitude increases, often to ~65%, so Climb is 100-65%; Cruise is 65%; Descent is also at 65%.

Hank, why advance the mixture ?  I just drop the nose and leave everything alone.  The mixture will effectively become more lean during the descent as the air density increases.  With the mixture leaning, the power decreases without the need to reduce throttle.  My GAMI spread is excellent, so I can usually go very very lean without issues. Occasionally, I might add a touch of mixture only if I get some engine roughness, and then to slow for the pattern.

[MIm20c]

22 minutes ago, Cyril Gibb said:

Hank, why advance the mixture ?  I just drop the nose and leave everything alone.  The mixture will effectively become more lean during the descent as the air density increases.  With the mixture leaning, the power decreases without the need to reduce throttle.  My GAMI spread is excellent, so I can usually go very very lean without issues. Occasionally, I might add a touch of mixture only if I get some engine roughness, and then to slow for the pattern.

Hank and I have a C, the GAMI spread is a little larger

[Hank]

1 hour ago, Cyril Gibb said:

Hank, why advance the mixture ?  I just drop the nose and leave everything alone.  The mixture will effectively become more lean during the descent as the air density increases.  With the mixture leaning, the power decreases without the need to reduce throttle.  My GAMI spread is excellent, so I can usually go very very lean without issues. Occasionally, I might add a touch of mixture only if I get some engine roughness, and then to slow for the pattern.

My carb doesn't have the tight intercylinder fuel flow spread of your injection system, so I must manage things more actively. 

BUT since rebuilding my doghouse and carb heat box, I can now sometimes run up to 25°LOP!

Edited March 6, 2019 by Hank

[steingar]

I once read in these very pages that Mooneys like mine burn less oil if climb is set to 25 square.  Oil is expensive, and where I live is quite flat, so I've been doing just that.  Oh yeah, and my POH says to, so I get to be compliant as well.

My best guess is the issue is of insufficient importance to warrant 3 pages of discussion.  But why let a thing like that stop us?

[Andy95W]

3 pages? Nah, it's way more than that.  We go round and round about this subject every year or two.

[rxo188]

18 hours ago, Shadrach said:

An IO360 will handle that kind of abuse, but that doesn’t mean it’s a good idea. I know some old Bob Kromer articles suggest 100ROP in climb above 3000’, but it’s hard on the cylinders and gains you little in climb performance.

CHTs heat up to the 360s. I have thermocouples on each can. All temperatures are within manufacturer limits.

[Jerry 5TJ]

In the Ovation climb was limited by CHT.  Normally I would cruise climb at 120 KIAS using whatever ROP power setting that would keep cynlider head temperatures reasonable.  Slow descents are made  at cruise power.  

Contrast to PT6A where we climb using max permitted torque until the altitude where temperature limit is reached, climb at max TIT temperature thereafter.  Once level,  power as required to sustain redline indicated airspeed.  Since speed is at the limit in cruise power reduction is needed for descent.  

This topic does surface frequently.  I suspect it does so because none of us feels our plane climbs fast enough.  Perhaps excepting Hyett when he’s flying his English Electric Lightning using full reheat. 

Edited March 7, 2019 by Jerry 5TJ

[Shadrach]

2 hours ago, rxo188 said:

CHTs heat up to the 360s. I have thermocouples on each can. All temperatures are within manufacturer limits.

 Certainly. I am absolutely familiar with the manufacture’s limits. You're running an air cooled engine. If the OAT is -5°C and your power setting yields CHTs of 360° What do you think they would be when the OAT is 27°C?  Do you think it matters?

Edited March 6, 2019 by Shadrach

[Shadrach]

1 hour ago, steingar said:

I once read in these very pages that Mooneys like mine burn less oil if climb is set to 25 square.  Oil is expensive, and where I live is quite flat, so I've been doing just that.  Oh yeah, and my POH says to, so I get to be compliant as well.

My best guess is the issue is of insufficient importance to warrant 3 pages of discussion.  But why let a thing like that stop us?

‘Tis true that this is a horse that gets bludgeoned  every year or so.  I still think the discussion is useful. Not because I think we all need to adhere to some collective climb procedure, but because it’s a good idea to understand why you’re doing what you’re doing.  Doesn’t matter how many years we do this, there will always be folks who don’t know why they’re doing what they’re doing. I’ve certainly fallen into that category before and it’s these kinds of discussions that were enlightening. 

[Oldguy]

59 minutes ago, Shadrach said:

‘Tis true that this is a horse that gets bludgeoned  every year or so.  I still think the discussion is useful. Not because I think we all need to adhere to some collective climb procedure, but because it’s a good idea to understand why you’re doing what you’re doing.  Doesn’t matter how many years we do this, there will always be folks who don’t know why they’re doing what they’re doing. I’ve certainly fallen into that category before and it’s these kinds of discussions that were enlightening. 

And there are those of us who missed the prior year's discussion and still have a lot to learn. Maybe not every rehashed thread has golden nuggets in it, but for those of us who are noobs (and everyone is at some point) when it comes up, it certainly helps.

[MIm20c]

2 hours ago, Jerry 5TJ said:

In the Ovation climb was limited by CHT.  Normally I would cruise climb at 120 KIAS using whatever ROP power setting that would keep cynlider head temperatures reasonable.  Slow descents are made  at cruise power.  

I have to agree with this. You really need to watch the CHT’s on warm/hot days. You can’t just fix the problem with FF, the power noticeably drops off when you go above 28 gph. I also noticed that engines with higher hours are not as “strong” and will have less problems with high CHT’s in the same conditions. Dial the prop back to 2550 at 2-3k and all cht problems go away. 

[testwest]

Hi Hank and everyone

I wish I had cowling pressure and cooling data! But thanks for thinking of me.

My opinion is that the difference between true airspeed and calibrated airspeed can be thought of as a virtual tailwind, going from zero to a pretty decent number the higher you go (all other things being equal). So a cruise climb speed (or quantified cruise climb profile Vz, as many in this thread are using *thanks, it's really cool to see that* ) decently balances the climb rate versus velocity-made-good to the top of climb. The higher speed should help cooling, the Target EGT fuel flows were established to allow the airplane to pass the part 23.1043 requirements.

But why is everyone having to work so hard to keep their engines cool in climb, when they are supposed to be able to stay in limits when flown as designed? Here is a stunning master's thesis that might have answers, the premise is that the FAA formulas for correcting flight test ambient conditions to standard may not be correct.

https://repository.lib.fit.edu/bitstream/handle/11141/1138/STUTH-THESIS.pdf?sequence=1&isAllowed=y

One of the advisors to this paper is my friend (and SETP Fellow) Ralph Kimberlin, with his guidance this thesis is one you can take to the bank. Happy reading!