231 power settings and the POH

[chrisk]

Some time back, someone made a comment that the POH settings for the 231 were "not good".  I searched a bit in the forums, but didn't find what I was looking for.

 

So, what is it about the power settings in the POH that's not good for the engine? 

[RJBrown]

I dont have a POH to refer to but using the original settings most 231s got an engine by 1200 hours. The POH was written for the benefit of the sales dept not the longevity of the engine. With BOTH a wastegate and a intercooler AND a careful hand the life can be extended. The longest lasting,easiest handling engine for a 231 is a TSIO-520NB.

[chrisk]

Are the 35% to 75% power setting generally considered ok?  Is it just the 100% cruise power setting that is an issue?  I understand the issues with CHT, TIT, and CDT.

[kortopates]

I don't have a POH available at the moment, but my memory of the primary POH recommendation that will damage you engine is the statement to "Lean to Peak" while not exceeding 1650F TIT at the bottom of each page of the cruise performance charts. Not exceeding Peak TIT is good advice but leaning to Peak is really hard on your engine when operated at high power settings. Instead you want to be sure you are far enough Rich of Peak (ROP) or Lean of Peak.  For more background on this, read the Pelican Perch articles on Avweb and you'll get a lot of useful information. Peak is fine though when operating at lower power settings of 60% or less; in fact there is no benefit to operating LOP or ROP at 60% power or less.

 

BTW, there is no 100% Power cruise schedule in your POH, only a climb profile which is done at full rich (around 24GPH); which should keep temps cool. Your max recommended cruise is approx. 78% power, and again you'll want to increase the ROP fuel flow rates 1GPH to get beyond the red box you'll read about in the suggested articles. Of course, you could also operate your engine at higher power settings LOP, rather than ROP, assuming your engine passes the Gammi lean test, runs smoothly and you have the necessary engine monitor to do so safely; but just stay away from operating at peak while running in the higher power settings.  

Beyond that its personal preference how you want to operate your engine knowing the trade-offs.

 

Beyond that its personal preference how you want to operate your engine knowing the trade-offs.

[chrisk]

Thanks!  That is what I was looking for.  

 

And your right about the POH not having a cruise setting at 100%.  I was thinking of the power vs speed chart.   It shows 35% power to 75% power in incriments of 10%, then jumps 100% to get 231 mph.  Clearly marketing had a hand in this. 

[jlunseth]

What Paul said. Operating the engine at anything over 65% HP in cruise, at peak TIT, is just about the last thing you want to do with it if you want to keep it around for awhile. That would be doubly true if operating in the higher altitudes the aircraft is capable of where cooling becomes less effective because of the thin air. The factory max CHT of 460 is way too high for cruise operations, you should use 380 as your cruise max, and if the engine is set up well and operated properly you won't even see that very often. The saving grace of the original factory engines is that if you adhere to redlines, particularly CDT, you probably can't get up to the flight levels.

[CoachTom]

Paul,

 

231 fuel flow: "24GPH" for full rich? Is that with intercooler or Merlyn?  Just curious what others are getting as am I at 22.6gph at 2700/36"MP (Merlyn+Intercooler) on take off.

I had the TCM Bulletin on fuel flow done last year at annual, and that was what they gave me according to the numbers.

[kortopates]

Paul,

 

231 fuel flow: "24GPH" for full rich? Is that with intercooler or Merlyn?  Just curious what others are getting as am I at 22.6gph at 2700/36"MP (Merlyn+Intercooler) on take off.

I had the TCM Bulletin on fuel flow done last year at annual, and that was what they gave me according to the numbers.

The official number or setting for this and all fuel injection settings come from TCM SID97-3E. In it on page 13 you will see:

TSIO-360-GB and LB (2700rpm/40"): 23.0 - 24.7

TSIO-360-MB (2700rpm/36"): 21.3 - 23

TSIO-360-SB (2600rpm/39"): 22.3-25.7

 

So your 22.6gph is actually below spec. Personally I would suggest to keep it at the upper value of 24.7 and even a bit higher if necessary to keep TITs cool. For example,  my MB engine it set for 24.5 (actually fluctuates bewteen 24 and 25) and it keeps my TITs below 1450 while at full max power all the way to the upper teens and beyond. I learned from a longtime Mooney MSC that the TSIO-360's like to run a little richer than what SID97-3E calls for to keep things cool. But since I don't have data handy on your engine, I suggest seeking another data point from jluneth whom also runs a LB with similar if not identical config to compare TIT at full power. I'd also check STC and/or AFMS documentation, but I'd be surprised if the added intercooler and wategate change the target  max fuel flow, but the intercooler may very well reduce the corresponding resultant TIT.

 

 

see www.tcmlink.com/pdf2/SID97-3E.pdf

[CoachTom]

Thanks Paul...

 

The intercooler does affect the (of course) air density and temperature which affects saturation or stoichiometry of the fuel air mixture.  The A&P last year did the SID97-3E to my LB engine and even called the intercooler manufacturer for the differential.  after all the emails and such between everyone, the numbers for my LB with intercooler and Merlyn is back to the MB numbers...

 

Now if I can just efficiently calibrate that damn Shadin...  Always telling me I have less than the wing tank gauges...

 

Cheers!

 

TMcD

[kortopates]

Although the intercooler does affect air density, our TCM turbo controllers are extremely simple and can only sense manifold pressure - so it can only regulate fuel flow by MP. In contrast the Bendix RSA systems senses mass air flow and therefore is effected by temperature. Due to the limitations of our controllers is why I felt it should make no difference. I would have expected that you would need the same richer LB FF GPH but at the lower MP that Airflow Systems power chart says will be 100% power. But out of curiosity, what guidance did they provide?

The MB engine has a very different tuned induction system which warrants a slightly better bsfc, the SB, with the same parts, different setup, needs a bit more fuel for the added 10HP from increased boost.

But still, I think your best gauge of having an adequate FF in full power climb is seeing a sufficiently low TIT, well below cruise TIT.

[jlunseth]

Just a footnote on intercoolers. They are basically a radiator and like any radiator can get dirty. I had my A&P clean mine about three years ago, it had alot of dust and stuff between the fins. Made a big difference to the differential temperature (diff. between CDT and IAT). Was not expensive, but it was awhile ago so I don't remember the cost. You don't want to go at it ham handed though. The fins a thin and bend easily, so too much pressure, either water or air, will bend them together.

[dham1956]

If you have a wastegate, inter cooler,gami injectors and engine monitor just start at 33 mp full rich and quickly pull the mixture back to 11.5 gph. This is 75% power lop.

[SkyBound]

Dham1956, what RPM combination do you typically fly at with the 33" MP at 11.5 GPH?  Could you share the TAS values you typically see at various altitudes?  Thank you.

[jlunseth]

Tom, I was reading through this and saw your post from last May about slightly low fuel flow. Probably your engine is set up properly. It is set up to produce 24 gph at 40", and if you have an inter cooler, full power is more like 36". So if you use 36 the fuel flow will be lower. I sometimes use 38" on takeoff just to get the higher fuel flow to keep the engine cool on hot days.

[dham1956]

Skybound, I like to run about 2550-2600rpm. I like the higher rpm because I believe the internal combustion pressure is better utilized mechanically later in the stroke. In my opinion that results in lower cht's. The true air speeds are typical of published airspeed vs altitude at 75% power. After all you are developing 75% of 210hp. Doesn't matter which side of peak your on and LOP is cooler and a safer place to be.

[dham1956]

Also the higher the throttle setting at a given fuel flow the leaner the mixture. So once your lop a higher mp at a given fuel flow should result in cooler temps because the combustion event is slowed by excess air.

[SkyBound]

Interesting point, I have been guided in the opposite direction, to use lower RPM during LOP operations.  I experienced 2400-2500 RPM to be the optimal range in my plane.  I experimented with 2300 RPM, but find it hard to keep CHTs cool there needing to trail cowl flaps and seeing a significant drop-off in speed.