Power setting while on the clime on Mooney M20J

[jetdriven]

http://www.openclip.net/Benchmark/IntroducingVz.pdf

[N9201A]

I remember hearing "25 squared" when first getting checked out in a 172RG by a wizened 22 year old, 300-hour CFI.  "Don't we lose manifold pressure as we climb?" I asked, having studied the new information about "Manifold Pressure."  "Yes," the CFI said.  "So we will be at 25 inches in a couple of minutes by 4,000 feet, and below it after that," I said.  "Yeah, that's true" he replied.  "We don't have an operating limitation, do we? (remembering my friend's Cessna185."  "Um, no."  "So, why do we do that?"  "Well, we cannot operate oversquare, he said authoritatively, ending any discussion." 

I never did get a real answer from that CFI, but I discovered John Deakin's Pelican's Perch...where Old Wives Tales die!  I remember him citing Bob Hoover, whose Aerostar routinely made TBO despite going from full-power, to feathered, to high-rpm descents within a very short period.  He also explained big differences between our simple flat engines and the turbo/supercharged corncob radials that were the most complex piston engines ever produced.

Many years later and now a CFI, I have flown with many a pilot who were fed the same "garbage in" input and recite it without justification..."can't be oversquare"..."reduce stress on the engine"...or my favorite, "my CFI told me"....Not THAT guy, again?!    

It's great to see that old "25 squared" nonsense, which may in once have had some factual basis in a B29 or DC6, beaten to smithereens!  Seeing that reassures us of the quality of expertise on this board...I hope the OP benefits from the wisdom imparted.

And, if you're reading this and have a good reason to reduce power in your 201 on climbout, prolonging the time you are below the altitude needed to make the impossible turn, increasing your workload in the pattern, and forcing your bird to climb on 180HP instead of 200HP, please 'mansplain' it to me...

[midlifeflyer]

5 hours ago, N9201A said:

I remember hearing "25 squared" when first getting checked out in a 172RG by a wizened 22 year old, 300-hour CFI.  "Don't we lose manifold pressure as we climb?" I asked, having studied the new information about "Manifold Pressure."  "Yes," the CFI said.  "So we will be at 25 inches in a couple of minutes by 4,000 feet, and below it after that," I said.  "Yeah, that's true" he replied.  "We don't have an operating limitation, do we? (remembering my friend's Cessna185."  "Um, no."  "So, why do we do that?"  "Well, we cannot operate oversquare, he said authoritatively, ending any discussion." 

I never did get a real answer from that CFI, but I discovered John Deakin's Pelican's Perch...where Old Wives Tales die!  I remember him citing Bob Hoover, whose Aerostar routinely made TBO despite going from full-power, to feathered, to high-rpm descents within a very short period.  He also explained big differences between our simple flat engines and the turbo/supercharged corncob radials that were the most complex piston engines ever produced.

Many years later and now a CFI, I have flown with many a pilot who were fed the same "garbage in" input and recite it without justification..."can't be oversquare"..."reduce stress on the engine"...or my favorite, "my CFI told me"....Not THAT guy, again?!    

It's great to see that old "25 squared" nonsense, which may in once have had some factual basis in a B29 or DC6, beaten to smithereens!  Seeing that reassures us of the quality of expertise on this board...I hope the OP benefits from the wisdom imparted.

And, if you're reading this and have a good reason to reduce power in your 201 on climbout, prolonging the time you are below the altitude needed to make the impossible turn, increasing your workload in the pattern, and forcing your bird to climb on 180HP instead of 200HP, please 'mansplain' it to me...

Brilliant! 

But you could have left out "wizened 22 year old." It could have as easily been a "wizened 77 year old" spouting the same nonsense, which was once thought of as gospel? Heck even most our POHs tell us to fly in the Red Box!

[jetdriven]

8 hours ago, N9201A said:

I remember hearing "25 squared" when first getting checked out in a 172RG by a wizened 22 year old, 300-hour CFI.  "Don't we lose manifold pressure as we climb?" I asked, having studied the new information about "Manifold Pressure."  "Yes," the CFI said.  "So we will be at 25 inches in a couple of minutes by 4,000 feet, and below it after that," I said.  "Yeah, that's true" he replied.  "We don't have an operating limitation, do we? (remembering my friend's Cessna185."  "Um, no."  "So, why do we do that?"  "Well, we cannot operate oversquare, he said authoritatively, ending any discussion." 

I never did get a real answer from that CFI, but I discovered John Deakin's Pelican's Perch...where Old Wives Tales die!  I remember him citing Bob Hoover, whose Aerostar routinely made TBO despite going from full-power, to feathered, to high-rpm descents within a very short period.  He also explained big differences between our simple flat engines and the turbo/supercharged corncob radials that were the most complex piston engines ever produced.

Many years later and now a CFI, I have flown with many a pilot who were fed the same "garbage in" input and recite it without justification..."can't be oversquare"..."reduce stress on the engine"...or my favorite, "my CFI told me"....Not THAT guy, again?!    

It's great to see that old "25 squared" nonsense, which may in once have had some factual basis in a B29 or DC6, beaten to smithereens!  Seeing that reassures us of the quality of expertise on this board...I hope the OP benefits from the wisdom imparted.

And, if you're reading this and have a good reason to reduce power in your 201 on climbout, prolonging the time you are below the altitude needed to make the impossible turn, increasing your workload in the pattern, and forcing your bird to climb on 180HP instead of 200HP, please 'mansplain' it to me...

I leanred that back in the 172RG in flight school too. 25 squared, thats the gospel in that 180HP carbureted engine. So, off we go, Tulsa to Dallas. Pull that power back religiously, dont want to blow up the engine.   Nevermind that 2700 RPM is listed in the cruise charts for the same airplane.  Add MP back one inch at a time, a few minutes later its full throttle and 2500 RPM, barely climbing. We leveled off at 9500' about 90 miles from Tulsa. Looking back, that was really ignorant and wasteful.

[Hank]

4 minutes ago, jetdriven said:

I leanred that back in the 172RG in flight school too. 25 squared, thats the gospel in that 180HP carbureted engine. So, off we go, Tulsa to Dallas. Pull that power back religiously, dont want to blow up the engine.   Nevermind that 2700 RPM is listed in the cruise charts for the same airplane.  Add MP back one inch at a time, a few minutes later its full throttle and 2500 RPM, barely climbing. We leveled off at 9500' about 90 miles from Tulsa. Looking back, that was really ignorant and wasteful.

Wow . . . . Let's do some math. (Erik will like this, even though I'm but a simple engineer.) 

9000 feet divided by 90 miles means you averaged 100 feet/nm in the climb.

Now the engineer comes out, as I must assume a flight speed for the 172RG, which I've neither flown nor even stood near. My carbureted, 180 hp Mooney climbs at 100 mph, and 105 mph = 90 knots, so let's use 90 knots and see where we end up.

Looking at that nice table conveniently printed in every set of approach plates, we see that the table starts at 210 feet/mile = 320 fpm at 90 knots and a 1.0° climb angle. Thus your 100 feet/mile at 90 knots groundspeed is half of that, or 160 fpm and 1/2° climb angle. Assuming a 180hp 172RG can climb at 90 knots, my Cessna experience is all at 160hp and less, and I never took one that high. So I will further assume that your actual performance was not quite this good . . . .

Long climb? You betcha. Hot engine? Certainly. "Nice to the engine"? Not a chance! (the polite answer!)

[Andy95W]

I'm just gonna go ahead and be contrary for a bit.  (Not about oversquare- I think that's ridiculous- try telling a 252 owner not to operate oversquare.)

My answer (and the way I always taught students) was that it depends on factors like smoothness and temperatures.  I'll use my M20C as an example, and I just flew it today and checked some numbers.

After climbing past the altitude of the impossible turn, I do pull rpm back a bit for vibration and noise reasons.  My airplane seems to like 2500-2600 rpm, depending on how it's feeling that day, so that's what I do.

For manifold pressure, it depends mostly on OAT.  Today was 85°F OAT, and at 115-120 mph, my hottest cylinder was #4.  All knobs full forward, 27"/2700, #4 was about 402°.  At about 25"/2550, it was 388°.  Guess what- I climbed out at about 25 square- for the reasons noted above.

Fuel injected engines are a bit different, in that the way fuel is metered is much more linear than for a carburetor.  So again, it depends.

Other airplanes don't have a full engine monitor, so you only know one CHT (and depending on conditions, it may not be the hottest).  So again, it depends.

And somebody is probably going to point out that at less than full throttle, I'm losing the benefits of the economizer circuit that provides additional fuel.  I'll just say that the carburetor adds fuel to keep CHTs below the redline of 500°, and in the green arc on the M20C of below 460°.  No thanks.  The laws of thermodynamics are pretty straightforward- more power = more heat.

[Hank]

39 minutes ago, David Herman said:

I use 25 squared. I tried the other way ... the cylinders got HOT. Tried each way several times ... our C seems to like 25 squared. I think our carbureted Cs are a different animal than our fuel injected brethren. We have an engine monitor. 

I've been climbing my C at WOT/2700 for the last 600+ hours. I'll try a slow 25² climb soon and see what the difference is.

Need to have a C model get together to compare techniques and results. I'd also like to trade rides with someone to see the difference that my 3-blade Hartzell makes, both in Rate of Climb and in vibration (I've heard so much about the bad vibrations that my prop is supposed cause, I'd like to see the standard; I checked my dynamic balance at annual last year, it was .01 ips.).

[mikefox]

I always climb at full throttle and at a safe altitude back the prop just off the stop into governing range.  No issues ever and no limitations in the M20J.  

[jetdriven]

Is there any evidence of any sort that climbing at 2700 RPM is detrimental to engine life in an M20J?? Flip your sunvisor down it’s a listed cruise RPM.. 

[N231BN]

Stop picking on "old radials," normal cruise power is 30" and 2000 RPM.

[Bartman]

Last year I tried climbing at 2,600 and 2,500 to see if it made any difference in oil consumption/leaking and initially I thought it did, but after more data it was negligible if any difference.  Now I'm back to 2,700 climb. I lean every 1,000 ft to target 1,250 target EGT up to 5,000 then start leaning 25 more degrees every 1,000 ft so if I go to 11,000 ft I'm at 1,400 on EGT.  Mine peaks about 1,500 so I figure I'm 200-250 ROP or more down low, then closer to 100 ROP by the time I level in cruise. If I'm climbing over 10K then I will climb even closer to peak EGT.  

If I'm around 7-8k then I lean about 10-15 LOP. If I'm above 10K then I usually lean to peak EGT. Yesterday we enjoyed 340 CHTs at 11K running at peak EGT. Before we installed new baffle seals we had CHT issues especially if we landed for fuel and departed with a hot engine.  Now it will go up to 370 sometimes like that, but never over my alarm set at 380 anymore. 

[jetdriven]

1 hour ago, N231BN said:

Stop picking on "old radials," normal cruise power is 30" and 2000 RPM.

maybe this old? Never run oversquare. There's got to be a reason somewhere!

 

[Hank]

4 hours ago, jetdriven said:

maybe this old? Never run oversquare. There's got to be a reason somewhere!

 

In that plane, the original engine rotated around the stationary cam, maybe that's where the rule started?.

[N9201A]

9 hours ago, jetdriven said:

maybe this old? Never run oversquare. There's got to be a reason somewhere!

 

Ha!  That is a very cool-looking radial, but every Flying Circus pilot knows that the Dreidecker was a ROTARY! 

And face-fulls of castor oil resulted in a, ahem, condition that precluded wasting time on such macht-nicht debates!  

[N9201A]

19 hours ago, jetdriven said:

Is there any evidence of any sort that climbing at 2700 RPM is detrimental to engine life in an M20J?? Flip your sunvisor down it’s a listed cruise RPM.. 

Good question - hope someone has an answer, if such data is out there.

My observation is many pilots "perceive" that their engine "likes it better."  Like with cars/motorcycles, many people who get to pay for repairs are reluctant to take their machinery to its limits, whether redline, max braking, or max lateral acceleration.  I remember seeing many a superbike rear tire replaced with the center worn flat, but the new-tire "rubber hair" (technical term vent spews) on the sidewalls, reflecting little cornering effort.  And that's their privilege...those who write the checks, write the rules.  But that is a preference, not data-driven nor binding on anyone else. 

Certainly 2400 is quieter than 2700, and 2400 is fewer RPMs than 2700.  But I have never seen anything objective claiming some detriment operating within POH RPMs.  After 20 years, my valves and combustion chambers look pretty good according to every A&P who's examined them.  (Now I've jinxed myself!!)

[Marauder]

Good question - hope someone has an answer, if such data is out there.

My observation is many pilots "perceive" that their engine "likes it better."  Like with cars/motorcycles, many people who get to pay for repairs are reluctant to take their machinery to its limits, whether redline, max braking, or max lateral acceleration.  I remember seeing many a superbike rear tire replaced with the center worn flat, but the new-tire "rubber hair" (technical term vent spews) on the sidewalls, reflecting little cornering effort.  And that's their privilege...those who write the checks, write the rules.  But that is a preference, not data-driven nor binding on anyone else. 

Certainly 2400 is quieter than 2700, and 2400 is fewer RPMs than 2700.  But I have never seen anything objective claiming some detriment operating within POH RPMs.  After 20 years, my valves and combustion chambers look pretty good according to every A&P who's examined them.  (Now I've jinxed myself!!)

 

If it will make anyone feel better, the Lycoming O-360 found in the original Robinson R-22 helicopters were designed to run between 3,000 and 3,400. It’s loafing at 2,700.

 

 

Sent from my iPhone using Tapatalk Pro

[bradp]

I tested 2500 vs 2700 RPM on climb out last week and the only thing I got using the lower RPM was 200 fpm less climb performance. 

DNR OWT. 

[Gary0747]

I remember seeing a red box APP somewhere but can’t seem to find it now?

[MyNameIsNobody]

Full forward MP/RPM during climb.  Also full rich.  Climb at 120MPH indicated with cowl flaps open.  Open Ram Air at sub 2500MP.  Cylinders are happy.  I have noise canceling headset for noise.  Get to cruise altitude and reduced RPM more quickly.  Not “unsafe”=safe...

[bradp]

Red box graph 

[Ned Gravel]

On 5/23/2018 at 3:39 AM, jetdriven said:

http://www.openclip.net/Benchmark/IntroducingVz.pdf

This is a great read.

I also talked to Norman in the Mooney Caravan tent last year and he very easily convinced me to change my cruise climb speed from 120 mph to 130 mph for this reason.  The science is sound and the numbers are sound.  This is not a game changer for my engine.  It is a game changer for my time enroute.  I already pull the mixture back to the takeoff roll EGTs and at 1000' AGL, I switch the configuration from Vy (or Vx depending on conditions) to 120 mph cruise climb.  I used to also drop from 2700 RPM to 2500 RPM at that transition point.  Not anymore.  

Cowl flaps closed and CHTs are at 320 to 350 max anyway (I have a really, really good doghouse).  So absolutely no strain on my engine to drop the nose ever so slightly and climb at 130 mph.  No change in CHTs and mixture adjusted every two minutes or so for Takeoff EGT numbers.  Keep the governor all the way in at 2700 RPM until TOC.  From Rockcliffe that puts me well beyond my initial VOR fix and enroute, but it will shave at least 3 minutes off my time for almost any flight.

[jetdriven]

Literally for free 

[Bob - S50]

15 hours ago, David Herman said:

I just posted this on another thread. I’ve read it many times.

I’d be happy to climb WOT/2700 if the CHTs would stay below 400° ... Our C just doesn’t like it ... I’ve tried Cruising LOP and using the techniques he recommends:  1) cracking the throttle and 2) using a little carb heat ... it just doesn’t like it.

I’m currently using 25”/ 2500-2550 RPM in the climb and setting 100° ROP in cruise ... both are the techniques recommended in the OM ... 

 

David,

If your CHT's are too hot in the climb, and assuming your baffling is good, instead of 25/25 for the climb, try 2700/25 and keep the climb speed well above V_y.  You'll make more power, climb better, and I'll bet your CHT's will be lower.  Once you're established in the climb, if you want to change power either up or down, do it with the throttle not the prop.  Running at 2500 RPM pushes the peak pressure closer toward TDC which increases the pressure and temps inside the cylinder which in turn gives you higher CHT's.

If you try it, let me know if it helps.