Climb settings on a 252

[Ulysse]

When I got my training on the 252, I was told by the instructor to reduce MP to 33" and RPM to 2500 during climb. This works fine, but the POH says to stay full throttle/2600 RPM.

I suppose the manufacturer knows better. Which settings do you use? is there anything wrong with 33/2500? 

Edited June 30, 2021 by Ulysse

[WilliamR]

You actually get less cooling using 33'2500rpm. Full throttle and max rpm has better cooling.  Try it sometime and see the difference.

POH climb settings are right.  Cruise is another story.

 

William

[smwash02]

I climb at 39" / 2600 RPM and have my FF adjusted to 25.5-26GPH.

At gross it will usually give me 700-800FPM at 100KIAS and things will tend to stay under 380-390 even on a hot day. I tend to have to tinker as I climb to keep the airspeed up enough to keep things below 400.

Would love to hear others with Encore's climb rates at or near gross. I've never been able to hold 1,000FPM the whole way without bleeding under 85KIAS and things getting hot.

[carusoam]

Seeing if @gsxrpilot is around…. A topic he likes….

As far as data to use…

Engine manufacturer data is good… but isn’t adjusted for the airframe it is mounted in…

Airframe manufacturer data is good… but can get stale over the decades…

Transition Training is a nice way to borrow/purchase the latest expertise… for current operations… select a good TTer…

PPP Training is a nice way to get up to date data over a weekend in a few places around the US…  bringing a plane from Europe will add to the challenges…   

Best regards,

-a-

[Z W]

I had the same experience as you.  I was taught 32" / 2500 RPM, pitch for 500 FPM climb, as a "cruise climb" setting, to be set after climbing through 1,000 feet AGL.  I still use that for larger altitude changes in cruise, but no longer for the initial climb.

After reading it here many times, for initial climb, I have switched to full power climbs to final altitude.  For me that is 36" and 2700 RPM.  Your TSIO-360-SB engine has different max numbers (39" and 2600 RPM I think?) and 10 more HP, but I believe the consensus is the same.  At full power, set pitch for 120 KIAS, which is optimal attitude for engine cooling.  When light, and/or on a cool day, you will climb at 1000 FPM or more, and compared to the "cruise climb" settings, 1) your CHTs will be lower, 2) your ground speed will be higher during climb, reducing total flight time, and 3) you will use less total fuel to reach your maximum altitude.  It's also simpler, because you don't touch your throttle, prop, or mixture after takeoff until leveling off, which decreases pilot workload, and possibly decreases the chance of an engine or cable failure while near the ground.

Better in every way, in my opinion.  Whoever wrote the manual knew what they were doing in this case.

Edited July 1, 2021 by Zane Williams

[jlunseth]

I will add that I make these full power climbs routinely, all the way to cruise altitude, which may be in the 20s. The engine is much happier than in a “cruise climb.” I generally climb at 500 fpm, but the aircraft can climb faster, it is just a matter of keeping the airspeed up for cooling, and keeping the fuel flow at maximum.

[philiplane]

16 hours ago, smwash02 said:

I climb at 39" / 2600 RPM and have my FF adjusted to 25.5-26GPH.

At gross it will usually give me 700-800FPM at 100KIAS and things will tend to stay under 380-390 even on a hot day. I tend to have to tinker as I climb to keep the airspeed up enough to keep things below 400.

Would love to hear others with Encore's climb rates at or near gross. I've never been able to hold 1,000FPM the whole way without bleeding under 85KIAS and things getting hot.

That's a lot of fuel for that engine. You may be over-rich, costing HP, which will slow your climb rate.

What version of the engine do you have? TSIO-360-MB1? Or -LB1B? What are your full power EGT's?  

[smwash02]

2 minutes ago, philiplane said:

That's a lot of fuel for that engine. You may be over-rich, costing HP, which will slow your climb rate.

What version of the engine do you have? TSIO-360-MB1? Or -LB1B? What are your full power EGT's?  

I have a TSIO-360-SB2SB, which is what the Encore uses.

The service manual calls for 21.5-23.2 for the MB and 25.5-26.5GPH for the SB. (Just above 71-00-60)

Your point is valid-- I've done some experimenting with leaning the engine to see if the excessive fuel flow is robbing the horsepower and it helps some at the expense of cooling.

[philiplane]

In general, remember that "cooling" with excess fuel flow means reduced efficiency, which is why the CHT's will be lower. It's not really cooling at all, it's just operating with less power and less heat as a result. There are a lot of engine baffle tweaks that can maximize the cooling airflow through the cylinder heads. Those will help more than excess fuel. I also wouldn't worry about a climb with CHT's in the 390-420 range for ten to fifteen minutes. So long as you can operate below 380 in cruise, your cylinders will be fine. The heat cycle fatigue you might worry about is a product of intensity and duration together. Short excursions don't do any harm, provided they don't exceed 450 dF.

Full power EGT should be 1125 to 1250 dF. As you approach 1100 dF, power drops off significantly. I target 1200 dF in most turbocharged engines. you'll find that will occur near the top of the factory spec fuel flow setting of 25.7 GPH for the -SB engine. The 22.3 GPH lower spec will produce 1350 dF EGT.

Edited July 1, 2021 by philiplane

[smwash02]

@philiplaneThanks for the info. I aim for keeping them under 400 in the climb. I am usually under 390 unless I have something to get over or a SID. My baffles are in pretty good shape, which may be helping me there.

I don't have my JPI data on me, but I want to say I'm in the upper 1200s, low 1300s for EGTs in the climb.

[Will.iam]

My 252 with engine nearing TBO i look for 36” 2700rpm and 24FF. I have seen with the rising texas summer heat example 95d F takeoff that my FF was only 22FF. Just another data point for reference. 

I too tried the cruise climb in the winter was ok but now that it’s summer time i find I struggle to keep the engine cool. It seem counter intuitive but full t/o power does seem to keep the CHT’s cooler and I’m climbing quicker to cooler altitudes and smoother ride in this texas summer heat. What is there not to like about that?

[jlunseth]

On 7/2/2021 at 12:16 PM, Will.iam said:

My 252 with engine nearing TBO i look for 36” 2700rpm and 24FF. I have seen with the rising texas summer heat example 95d F takeoff that my FF was only 22FF. Just another data point for reference. 

I too tried the cruise climb in the winter was ok but now that it’s summer time i find I struggle to keep the engine cool. It seem counter intuitive but full t/o power does seem to keep the CHT’s cooler and I’m climbing quicker to cooler altitudes and smoother ride in this texas summer heat. What is there not to like about that?

Is 36” the max throttle in your engine? I think it is. Max power is more like 37 in a 231 with intercooler, but the lore has been to use 252 tables so everyone uses 36”. So if the A&P sets the fuel flow per the STC for the intercooler, the engine is set to make max fuel flow (usually 24 GPH) at 37, not 36. If you fly a 231 and need full fuel flow you need max throttle, which is 37.

My point is, if 36 is not max in your 252 and you need more fuel flow because the engine is not cool enough, then the solution may be to increase throttle, which is a little counterintuitive but it works. If 36 is the max you can set, well, then that’s it and the fuel flow needs to be set better.

[CoffeeCan]

48 minutes ago, jlunseth said:

Is 36” the max throttle in your engine? I think it is. Max power is more like 37 in a 231 with intercooler, but the lore has been to use 252 tables so everyone uses 36”. So if the A&P sets the fuel flow per the STC for the intercooler, the engine is set to make max fuel flow (usually 24 GPH) at 37, not 36. If you fly a 231 and need full fuel flow you need max throttle, which is 37.

My point is, if 36 is not max in your 252 and you need more fuel flow because the engine is not cool enough, then the solution may be to increase throttle, which is a little counterintuitive but it works. If 36 is the max you can set, well, then that’s it and the fuel flow needs to be set better.

Well, jlunseth, since you and I both fly 231's, I'm curious to pick your brain further on this. I'm finding this discussion VERY interesting.

This is my 3rd summer in my 1985 M20K/231, but my first summer after reading Mike Busch's "Engines" book, and in the past 2 summers I havent had occasion to fly when the OATs here in TX have been as high as they have been the past 2 weeks (high 90's to low 100's)). I'm managing my engine a bit differently now, really trying to keep my CHT's under 380 F, and I've been doing OK with that except for my #6 cylinder (the new one installed last December at my Annual from Hell). This has only been a problem for the past 2-3 flights as the summer temps have soared, BTW. 

Since I acquired my plane I have been following my POH's recommended climb settings:  36" MP and 2600 RPM. Takeoff power per POH is 39-40" and max RPM, which runs 2650-2670 in my aircraft, and I pitch for close to Vy to 1000' AGL, then reduce to 36/2600. On my last 3 flights in the heat I've immediately noticed my #6 CHT's climb into the danger zone (380+) when I make those setting changes for climb. So I've reduced power even further and flattened my climb considerably to get the temps down. Once I get up into cooler air I'm then able to increase power and climb rate as I've been used to doing, as above.  But this has led to some pretty slow climbs to cruise altitude.

So I'm wondering if I should I be following Mike Busch's recommendation and stay at WOT (39-40") and 2670 RPM, then pitch for 120+ knots vs going to the 252 settings (37" at 2600 RPM) for better cooling?  I'll be talking to my rep at SavvyMX about this as well next week, but it can't hurt to discuss with y'all on this site. 

I'm also thinking I need to have my A&P look at #6's baffles etc on my next oil change, which is coming up shortly. Thoughts?

 

Edited July 5, 2021 by CoffeeCan

[Warren]

@CoffeeCanDo you have an intercooler and upper deck pressure controller?

If so, the factory 231 recommendations do not apply.  Look at your STC for settings or follow the 252 guidelines.  I have the intercooler and upper deck pressure controller.  I climb at 2700rpm and 36" MP all the way to altitude.  Normal climb is 120 IAS and if it is really hot, I will increase to 125 or 130 for a little extra cooling -- I can always keep CHT under 400.  I find that any reduction in MP causes the temperatures to get worse, not better.

If you have a stock 231, 40" and 2700rpm will give you roughly equivalent power -- don't forget to watch your IAT if you don't have an intercooler.

I agree with Mike Busch that climbs using reduced RPM is hard on the engine.  100 rpm reduction is roughly equivalent to 1 degree of timing advance.  This is the last thing you want if cylinder temperatures are too high.

 

[LANCECASPER]

Here's the guy that helped develop the 252 and what he has to say:

 

[jlunseth]

I gather you have no intercooler. If you have an intercooler then takeoff should be a max 37” and if your A&P did his job right (followed the STC in setting the fuel) then it is set for 24 GPH at about 37”. If you have no intercooler it is set for 24 GPH at 40”. If you are running too hot in the climb, then try the counterintuitive thing and use max throttle, 39-40”. That will get your fuel flow up and the engine may run cooler.

Climbing in the heat is always a problem. I use 500 fpm, that is two minutes per thousand and if you are going high that can seem slow, but it gives you better airspeed, which in turn gives you better cooling.

I fly out west a fair amount in the summer and wind up doing long climbs when it is hot. It is practically impossible to keep all the CHT’s down below 380, especially if the aircraft is fully loaded. In my engine it is usually #2 that is hotter than the rest, probably a baffle issue. #2 is at the back, behind the others. If your #6 is hot, chances are your fuel flow to that cylinder is somewhat off from the rest, probably leaner. #6 sits behind the open intake hole and cooling is probably good, hence my guess that there is a fuel flow issue. My #2 will slip over 400 in hot long climbs and I have not found a great cure, although there are a couple of things to try.

Paul Kortopates at Savvy has some good thoughts on this issue. One thing you can do is ask your A&P to set the max fuel flow at max throttle higher than normal, say 25 GPH rather than 24. You may have to manage fuel flow at takeoff and in the climb to keep the numbers normal (22.5-24 GPH), but at least you will be able to keep them normal. Paul suggested I do that a couple of years ago and it worked pretty well for summer, out-west type flying, but you do have to work with your A&P to get it done.

The fuel flow, if set per the SID, should be 24 GPH at 40” and 2700 RPMs for the standard, nonintercooled engine. The STC for the intercooled engine has a table where the manifold pressure used to make the max fuel flow setting varies depending on OAT, but is generally around 37”. When you fly the aircraft you won’t get that max fuel flow unless you set the power where it was when the A&P set the fuel flow, i.e. 40” and 2700 for the nonintercooled engine, and 37 (or so) and 2700 for the intercooled. In your case, it sounds like the governor is set to max out at 2670 so I surmise that is what your A&P uses when he sets the fuel, but it is worth asking because he might be shading the fuel flow down to adjust for the slight lower RPMs. Not all A&Ps appreciate the problem of climbing temps in the 231, and unless yours does, you will probably see no better than 21 point something, which is not good enough. I think what they do, is set the max fuel flow, then set the idle fuel flow, and that affects that max flow, and they don’t go back and readjust the max flow upward, so in effect they have set it low. I can manage idle fuel flow with the red knob, it is the max fuel flow they really need to get right.

My perception is that there is a “bump up” in fuel flow wired into the engine’s design, so the fuel flow change is not linear as you approach full power, rather, it increases faster towards the full power setting. So a change downward from full power of even an inch will reduce full flow by a couple of GPH pretty quickly, and that in turn will cause the engine to run hotter. Paul K. at Savvy can talk this through with you, he is pretty smart about the issue.

[CoffeeCan]

jlunseth and warren... thanks fellas, that confirms my suspicioning. 

My engine does have an intercooler and Merlyn wastegate, which I should have mentioned. I've noted fuel flow to be about 24.2 gph at 40" MP, but apparently someone has set the RPM limit slightly low. 

I will run this past Paul at Savvy, as I indicated previously... I'm wondering if we need to have GAMI look at the injector for #6, as the likelihood of this being a fuel flow issue seems higher to me than other options. 

[jlunseth]

1 hour ago, CoffeeCan said:

jlunseth and warren... thanks fellas, that confirms my suspicioning. 

My engine does have an intercooler and Merlyn wastegate, which I should have mentioned. I've noted fuel flow to be about 24.2 gph at 40" MP, but apparently someone has set the RPM limit slightly low. 

I will run this past Paul at Savvy, as I indicated previously... I'm wondering if we need to have GAMI look at the injector for #6, as the likelihood of this being a fuel flow issue seems higher to me than other options. 

If you have the intercooler you should not ever use 40” for a power setting. You should make your max throttle setting to be 37”. If you use 40” you will overboost the engine. The fuel flow should be set per SID 97-3G, modified in accordance with the instructions in the STC for the intercooler. It is those instructions that use a table that tells the mechanic what RPMs to use, given a particular outside air temperature. As I said earlier, it is generally around 37”. If your fuel flow is set at 24.2 GPH at 40” it was set without regard to the STC and it is set too low. You definitely would not want to increase manifold pressure above 37”. Unfortunately, with your current fuel flow setting, at 37” you will be making max power and the fuel flow will be too low. That would be your problem. Talk to Paul, he will get you straightened out.

[Will.iam]

Sorry it took so long was busy with family. Yes my 252 auto regulates to 36” MP i can push the throttle all the way forward and the automatic waste gate takes care of the rest. I. E. I’ll maintain 36” MP all the way to crital altitude which if IIRC is 22,000 for the 252. 24FF is the top of my range for fuel flow which it is in cool weather but now that it’s heating up i see the fuel flow down some but the prop govenor up by 10 or 20 rpm. Ironically the encore engine takes the same engine and just turns up the boost up to 39” but bring back the max RPM to 2600. 

[Will.iam]

Interesting in that article he stated the factory 252 was 22gph ff. i guess with mine at 24gph I’m on the rich side of the fuel delivery so any issues with high CHT’s must be baffle issues. 

[jlunseth]

5 hours ago, Will.iam said:

Interesting in that article he stated the factory 252 was 22gph ff. i guess with mine at 24gph I’m on the rich side of the fuel delivery so any issues with high CHT’s must be baffle issues. 

The desired value should be in your Pilot Operating Handbook. It is in mine. My POH requires 22.5 - 24 GPH at full power. 24 is better in a hot weather climb. I do not have your SB engine though, I have the LB.

[Warren]

Here is the information for the TSIO-360 engines fuel flow setup.

SB range is 22.3-25.7.  I think most here will agree that you want it set at the high limit or even slightly higher.

[kortopates]

the high number should be considered the absolute minimum, preferably 0.5 to 1.0 GPH above the high number is preferred.


Sent from my iPhone using Tapatalk

[CoffeeCan]

Very interesting discussion, guys. Thanks for the info. 

I'm frankly surprised that when I got my transition training in my 231 (from a guy who should know!) I was told to use 40" as my target MP. Hmm. Maybe chagrined at having not figured this out sooner...

So after all this input and some more reading, contact with my SavvyMX guy, and taking notes, I flew back home last evening in my 231 using the NEW recommended settings for my aftermarket intercooled and Merlyn'd engine.

Ambient air temperature at KVCT at takeoff was 89 F. I set my MP at 37", and max'd the RPM at 2650. I set my climb trim to maintain IAS at 199-122 knots, adjusting airspeed up slightly a couple of times to keep peak CHT (Cylinder #6) under 380 F.  My climb rate averaged about 600 fpm and my fuel flow was 20.8 gph. TIT was 1413 at max. I climbed to 10,500 MSL just like that with no untoward elevations of my CHT's or my sphincter tone.

The engine seemed much happier. But that fuel flow seems low to me, based on the info you fellas have shared. 

Next week I am going to fly the Savvy Flight Test profile and download the data so Tom and Paul can look at it and make recommendations to my A&P as needed. But as of last night's flight, I am MUCH happier with my engine's temperatures.

Thank you all very much for your input. 

Edited July 7, 2021 by CoffeeCan

[jlunseth]

Hope we helped. I agree with your analysis of the takeoff from KVCT. Sounds like all was good but the fuel flow was a little low.

The explanation on the MP, is that the whole purpose of the intercooler is to cool the induction air. At cruise the cooling can be as much as 100 dF or more. In other words, the Compressor Discharge Temp (the temp of the air exiting the turbo) might by, say, 250 dF and the Induction Air Temp (the temp of the air entering the induction system) might be 150 or even less. The 40" setting for the nonintercooled engine assumes that the CDT and the IAT are the same. Hot air is less dense than cool air. It has less molecules per unit of volume than cool air, in particular, fewer molecules of O2. So without an intercooler, at 40" you would be feeding the engine "x" molecules of O2 to be used in combustion, and with the intercooler, you only need around 37" to feed the engine "x" molecules of O2. If you feed the engine 40" of cooled air you are feeding the engine significantly more molecules of O2 than the Pilot Operating Handbook anticipates, and thus making significantly more HP than the engine was rated for.