Reducing to 25/2500

[Raptor05121]

So I'm prepping for my complex ride here shortly, and coming from 100+ hours of fixed pitch props, why does the POH recommend pulling MP back to 25" and RPM to 2500RPM right after takeoff? Is this more for noise abatement? I'm partial to full-throttle ops with the enrichment circuit offering additional cooling, I'm just curious if everyone follows this procedure and why.

[gsengle]

What airplane/engine? Likely because your engine isn't rated for more than 25/25 continuously.

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[Raptor05121]

M20C, O-360 180hp. Rated 2700RPM 180hp continuous as far as I know. My only restriction is below 15", 1900-2300 for harmonics.

[rbridges]

I've seen lots of people say they go full throttle/full prop until they reach their altitude.

[orionflt]

I have a 62 C model and my flight manual does nor specify pulling back to 25/25 for climb, infact it just says full rich. later revisions of the flight manuals and POH's have given more guidance in best operational procedures but I do not recall any from our era (60/70's) ever specifically recommending 25/25, I think that was more institutionalized by instructor. after you clear any obstacles 25/25 gives you sufficient climb power combined with noise reduction and fuel economy. I personally will also start leaning for best power as I am climbing, I found if I leave it at full rich I lose a lot of power as i get higher in my climb due to the mixture becoming too rich.

Brian

[Raptor05121]

Page 18 of the 1966 M20D owners manual, states:

"Recommended power setting for climbing is 2500 rpm and 25 inches manifold pressure."

As such, I've got it in my checklist, but I think I want to fly it a few times using the 25/2500 method and full throttle/2700 climb and see what I like better.

[Shadrach]

Alex, it's just a sign off, not really "a ride". For your check out, ask the instructor what he likes/wants...then do that. After the ride is over, you can fine tune your SOP. I tend to agree with you that WOT is the best option. Anything less prolongs climb and may generate higher CHTs.

[egarcia77035]

I agree with Raptor, my 66 E I use the option of 25/25 or full throttle.  I am not limited by harmonics or rpm.  My mechanic who has years of Mooney experience prefers full throttle until altitude for continued climb or cruise is met.  I pull back to 25/25 once established in climb out of traffic pattern if going away.

[DXB]

My '68C POH recommends reducing rpm to 26 after takeoff.  It describes "normal climb" setting as 26/26.  Based on the info I've gleaned, pulling throttle back after takeoff makes little sense  as it cuts out the auto-enrich circuit on the carb, leading to hotter temps.  And supposedly the engine does just fine at 2700.  Presently I just climb at 2700, WOT, full rich to lower altitudes (<4000).  If doing a long climb, once above  3000, I run 2600 rpm, WOT, and lean slightly to maintain EGTs closer to where they were after takeoff.  For enroute climbs at altitude, I use 2500-2600 rpm at whatever MP I can get at WOT.  My practice may not be entirely sensible either - I'm sure others will correct.

[Shadrach]

Just now, Raptor05121 said:

Page 18 of the 1966 M20D owners manual, states:

"Recommended power setting for climbing is 2500 rpm and 25 inches manifold pressure."

As such, I've got it in my checklist, but I think I want to fly it a few times using the 25/2500 method and full throttle/2700 climb and see what I like better.

Norman (Testwest) our resident test pilot authored a paper on this subject using a modified M20J. I don't believe that his analysis showed any benefit to climbing partial throttle; but instead showed that it was less efficient and slower.

[markejackson02]

Bob Kromer wrote a series of articles a few years back that said for all the normally aspirated Mooneys, WOT and full RPM were the best way to climb, unless noise was a consideration in which case dialing back the prop was okay.

 

[Raptor05121]

5 minutes ago, Shadrach said:

Alex, it's just a sign off, not really "a ride". For your check out, ask the instructor what he likes/wants...then do that. After the ride is over, you can fine tune your SOP. I tend to agree with you that WOT is the best option. Anything less prolongs climb and may generate higher CHTs.

Yeah I know, he's already told me its a simple 1.0 in the logbook for the signature, but I've got 5.0 dual required by insurance as well, so we will be going up several times in a week.

So from what I'm reading- I'll do a few climbs at 25/2500 and some others at WOT/2700 and pick my favorite. I'm all about lowering CHTs so im sure the WOT is where I'll be. I assume you guys also cruise WOT for best induction flow as well?

[orionflt]

My personal technique when I am climbing out of the pattern is to reduce the RPM's to 2500 and keep the throttle wide open, lean for best power during the climb.

Brian

 

[flyboy0681]

1 hour ago, Raptor05121 said:

 Is this more for noise abatement?

Mooney's are known for a lot of things, but disturbing the peace is not one of them.

[steingar]

Yeah, not a check ride of the complex.  I usually back off a bit if I'm not really going anywhere and not trying to get lots of altitude.  Keep the engine happy.  If I'm on a trip I stay WOT until I hit my cruising altitude.  Might even stay WOT depending on the altitude I fly.

[carusoam]

A few things to mull over in your head while making this decision...

 

Back in the 60’S...

- there were no JPIs

- there was no FF

- there was no shared data on MooneySpace

- there were no POHs

- owners manuals were written by non-technical people (marketing, sales, managers, typists, lawyers?)

- some data came from engine suppliers that wasn't developed using the actual airframe.

- few carb temp gauges were installed.

 

Today...

- the most recent POH for a C is from the mid 70's.  It has a lot of data that the owner's manual doesn't (get both)

- logic and experience tells pilots to make no throttle changes until reaching an altitude that allows for a gliding return to safety...

- understand the second fuel jet in the carb. Decide when to have it on or turn it off.

 

Tomorrow...

It is a challenge early on to follow this much detail while still learning how to fly the plane.

- you will someday leave the flaps in the T/O position while accelerating past Vfe.

- you will someday leave the aux fuel pump on.

- you will someday leave the gear down.

- once you have done one of these, you realize how easy it is to leave the gear up while landing...

 

In the meantime...

- You will do really well by following the procedures laid out in the most recent POH.

- When you have them comfortably down, with all the modern instruments available, you can expand into modify your climb procedure.

 

This is just stuff I learned here.  Except the stuff about the POH.  That, I got in Y2K direct from W. E. Wheat by telephone...

I am only a PP, not a CFI or mechanic...

Best regards,

-a-

[201er]

1 hour ago, flyboy0681 said:

Mooney's are known for a lot of things, but disturbing the peace is not one of them.

Except for Sue! She's been a bad girl!

[ArtVandelay]

One difference between the examples of tomorrow and gear up...gear up has a audio warning, you probably should test it once in a while, and if pulled for flight training, don't forget to push the circuit breaker back in.

There seems to be a huge difference between 2700 and 2600 rpm, in noise alone, not sure about performance, one of these days i plan on doing a 2600 take off to see.

[1964-M20E]

For take off and climb it's WOT the only thing I touch after gear and flaps is I will back RPM off to 2600 for noise and begin leaning mixture above 3000 feet.

 

 

[flyboy0681]

Just now, teejayevans said:

There seems to be a huge difference between 2700 and 2600 rpm, in noise alone, not sure about performance, one of these days i plan on doing a 2600 take off to see.

A few years ago when I bought into my partnership I noticed that during takeoff the most the tach would show was 2600 and I knew from reading the manual that it should have been 2700. I flew it for almost a year that way until I asked the A&P to check it out. It turned out that the governor needed an adjustment and the moment he changed it the difference in power and noise level was appreciably different.

[rbridges]

IMO it's just a matter of deciding on prop rpm.  Within a few minutes, you're more than likely going to be under 25" of manifold pressure unless you're a turbo.

[carusoam]

RPM vs sound... (Observed from the ground)

2500 rpm is loud...

2700 rpm is impressively loud...

 

RPM vs Power... (Ovation example)

2500 rpm is 280hp

2700 rpm is 310hp (200rpm is a 10% difference in power output)

T/O run for 280hp is 1200'

T/O run for 310hp is 800' (400' is a 30% difference)

 

expanding this to a 100 rpm drop on an IO360...

- less sound.

- less power.

- longer T/O run.

- less climb rate.

- less fuel burn rate.

on the T/O run cross check the rpm coming up to red line with the FF.  This is proof that the engine is most like producing full power and delivering it to the prop....

You will need to know what the FF should be for your set-up.

Best regards,

-a-

[Hank]

In my C, I takeoff and climb to cruise altitude WOT/2700. When I think about it, I lean to Target EGT in the climb; when I forget, I'll eventually notice a really low EGT and start leaning then. I've made few enough departures at high DA requiring leaning for takeoff that it's an unusual event and thought out in advance.

After talking to Bob Kromer, I tried a round trip flight ~2.5-2.6 hours each way, WOT/2500 and leaned 50º ROP. Used lots of extra gas [>1 gph additional burn], saw little speed or temperature difference. A couple of weeks later, made another round trip just over 2 hours each way using my SOP, and was back down to 9 gph block time. After leveling off and accelerating, I pull the throttle back just enough to make the MP needle move, to disengage the auto-enrichment circuit at full throttle. Then I set RPM [at 2500 if around 7000-7500 or higher, I always double-check my Performance Tables on my kneeboard].

In the long run, it's your engine and will be your overhaul, so run it the way you want to. This is how I choose to run mine.

[carusoam]

For anyone that hasn't read the Bob Kromer articles specific to their model...

Bob is an engineer who worked at Mooney in a modern post Bill Wheat kind of way.  He covered real world flying techniques for the C around Y2K.  It is worth pulling them out to read them if you haven't seen them yet...

Best regards,

-a-

[DXB]

14 minutes ago, Hank said:

In my C, I takeoff and climb to cruise altitude WOT/2700. When I think about it, I lean to Target EGT in the climb; when I forget, I'll eventually notice a really low EGT and start leaning then. I've made few enough departures at high DA requiring leaning for takeoff that it's an unusual event and thought out in advance.

After talking to Bob Kromer, I tried a round trip flight ~2.5-2.6 hours each way, WOT/2500 and leaned 50º ROP. Used lots of extra gas [>1 gph additional burn], saw little speed or temperature difference. A couple of weeks later, made another round trip just over 2 hours each way using my SOP, and was back down to 9 gph block time. After leveling off and accelerating, I pull the throttle back just enough to make the MP needle move, to disengage the auto-enrichment circuit at full throttle. Then I set RPM [at 2500 if around 7000-7500 or higher, I always double-check my Performance Tables on my kneeboard].

 

POH leaning procedure definitely seems antiquated for these old carb'd planes.  With increasing experience, I'm pretty much settling down into something close to Hank's SOP above for my C.  I agree that the speed gain I perceive from running at 100 ROP (best power per POH) versus as lean as it will tolerate without roughness or high CHTs is barely perceptible, whereas the fuel consumption difference is massive.  The POH's recommended compromise between "best power" (100 ROP) and "best economy" (25 ROP) by running at 50 ROP is also where engines are supposed to experience greatest stress per Mike Busch's writings on leaning.   Their so-called best economy number of 25 ROP is also based on a single EGT reading from the cylinder that is supposed to be leanest.  In my growing experience after installing a good engine monitor, the leanest cylinder actually changes between flights, and sometimes during a flight.  The 25 ROP figure may have been intended to provide a safety buffer for such factors when only monitoring EGT on a single cylinder.  I find that that my engine starts running rough at 10-20 degrees LOP on the leanest cylinder, and  I do just fine running a stoichiometric mixture after finding this rough point.  I typically enrich by another 10 degrees to the ROP side just for some more buffer for changing conditions.  Fuel economy and performance both seem excellent this way.