True Air Speed?

[johncuyle]

I would bump up your RPM to 2500.  Everything that I am reading says 2500 is optimum for our engines with a 2-blade: Mapalog M20K, 231

I've read that article many times and it has a lot of great information and suggestions but I really have to question the cruise power recommendations. He recommends cruising at 50 ROP. Always. 50 ROP is exactly where you shouldn't cruise (well, 40, but still) according to the APS guys. I trust Kromer to know everything there is to know about the model, how to handle it, idiosyncracies of the type, details specific to the installation, and so on, (and I do follow his advice to climb at high power) but I trust Deakin & Co. On how to lean a turbocharged engine. Optimal prop RPM ought to be a function of the prop, and I have a totally different prop than the one in that article (McCauley two blade hot prop versus the three blade non hot prop in that piece) so I wouldn't necessarily expect it to have the same optimal RPM, and possibly not the same as the bootless two blade. Is there data backing the 2500 RPM number across the board for all props certified for the 231?


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[Bryan]

I hear you, the more information the better.

Everyone I know, around here, that runs a 2-blade on a 252 or 231 runs it at 2500.  Always at cruise.  Most power settings articles I have read in Mapa and other publications say 2500 is optimal.  If 2400 works better for you or you found better recommendations - go with it.  Is 2500 perfect for YOUR prop/engine - I am no aerospace engineer.  I use and am happy with 2500.

APS teaches LOP, LOP, LOP so get on with that if you believe them.  Speed is money so to get that extra speed, you are going to have to spend that extra money either in fuel (ROP) and or engine (75%+ and possibly sooner engine O/H).

[Northern Mooniac]

It sucks that 75% is that hard on the engine. 10.5gph works great and the speed was reasonable. I did about 145-150 so I can easily plan for 140. If I am really in a hurry I can do rop and get 160 true. But the fuel savings is so huge it blows my mind.

i ran my tit at 1590 for about 60 lop I think that's ok?

ignore the HP percentage I need to get that setup properly. That will be another post!

 

first pic is running rop

second is running lop. I ran 2400 rpm and i found it was smoother than 2500?

[carusoam]

Nothing very magical about 75% being hard on the engine...

above 65%, there is a sliding scale of the risk of detonation.

Detonation is both harmful and near impossible to detect.

as for smoothness, the slower you go the smoother it gets.

One thing that can improve the smoothness is having the prop dynamically balanced.

The APS guys do a great job of training engine ops.  Really helpful for Turbo owners.

How does that sound?

Best regard,

-a-

[johncuyle]

In the first picture you can see your CHT up at 380+.  The APS guys recommend 380 as maximum continuous for longevity reasons.  See Carusoam's post.  In the second picture you can see your CHTs are down in the low 360's.  When cruising in the second configuration, you ought to be able to slightly increase your power output (more throttle or more revs, fuel flow will increase with either, maintain the same mixture relative to peak TIT, which is tricky on the 231) a bit while staying south of 380 CHT to get some of the speed back while still saving a bunch of gas, keeping the engine out of the red box, and keeping everything cool enough, cooler than the top ROP picture.  TIT will likely be the limiting factor there, but you have a little headroom.  My engine also seems smoother at 2400, but keep in mind running higher MP and lower RPM to achieve a power level does tend to increase CHT.  The best option, if you want more speed, is probably not to run ROP, it's not to fly so darn low.  If you want to go fast, make 15,500', 16,500', and 17,500' your go-to VFR cruise altitudes.  Try heading up to 16,500 and running the power configuration in the second picture (keep an eye on TIT and CHT) and see what you think.

[Northern Mooniac]

What do you run for a TIT?

i tried running higher MP but 30in and 2400 rpm had the engine running so smooth it was awesome. 

[Northern Mooniac]

What do you run for a TIT?

i tried running higher MP but 30in and 2400 rpm had the engine running so smooth it was awesome. 

[johncuyle]

I don't have a good engine monitor so I run very, very conservative power settings. I rarely see higher than 1450 TIT in cruise. Here's an economy cruise up a little higher. TIT was about 1425. I'm having an intercooler installed at annual and I'll probably run about the same power settings figuring that the lower intake charge temperature will keep the CHT about the same while the engine produces a little more power (with slightly more fuel flow) and I'll see a little bit more speed.


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[Northern Mooniac]

I guess I'll have to do more reading to see if those tits I ran are bad. 1590 would be 60 LOP so I should be ok?

[johncuyle]

1650 is maximum continuous redline on TIT.  Max transient is higher than redline but time limited.  1590 is 60 degrees lower than maximum continuous redline.  That's not the same as 60 degrees lean of peak unless TIT just happened to peak at exactly maximum continuous.  For the power settings in the picture above, I peaked at about 1500, so at 1425 I was about 75 degrees lean of peak.  With better monitoring I would happily run 25 LOP provided it kept me at least, say, 50 degrees below maximum continuous (so 1600 degrees or so.)  Check some of the LOP running threads via search for opinions on good TIT limits to extend turbo life.   In my case operations are more about leaving a wide enough margin I'm pretty sure I won't have to do too much mid-run top end work without actually knowing what's going on with five of my cylinders.  A turbo overhaul mid run is relatively affordable compared to a top or replacing a few jugs, and I've budgeted for one.

Not pictured in the image above is my CHT gauge.  The needle on mine tends to be more or less vertical, covering part of the degree symbol and the vertical line on the F.

[Northern Mooniac]

Honestly, for the amount of money I can save on fuel, I could easily afford that turbo overhaul lol. For now I think I found my new cruise settings. Once I get my o2 fixed I'll try going higher but I'm a 2 hour leg the difference in time was minimal vs run rop (maybe 15 mins) and it's about $100-$125 per leg cheaper...that adds up fast!

[johncuyle]

Honestly, for the amount of money I can save on fuel, I could easily afford that turbo overhaul lol. For now I think I found my new cruise settings. Once I get my o2 fixed I'll try going higher but I'm a 2 hour leg the difference in time was minimal vs run rop (maybe 15 mins) and it's about $100-$125 per leg cheaper...that adds up fast!

Definitely get the O2 fixed. You'll love gaining a couple knots per thousand feet or so on the same gas. One thing, just to be clear, you mentioned 1590 as 60 degrees lean of peak. There is no specific TIT for peak. Peak TIT varies based on ambient air temperature, altitude, and power setting. Apologies if you know this, nobody bothered to explain it to me in 100 hours of flying before I bought my 231.

Since you have a multi probe engine monitor, the leaning technique I would use when transitioning from climb to cruise would be to level off, let the plane accelerate a bit, reduce the MP to your desired setting minus a couple inches, reduce RPM (MP will come up a couple inches) then pull the mixture slowly but steadily back until you feel a power reduction (around half a GPH less than what you expect, pull the mixture over a four count or so). While you pull the mixture watch the EGT. They should increase then decrease slightly before you feel the plane decelerate. Close cowl flaps. Then twist the mixture to enrich, again watching EGT. When the first cylinder stops increasing and starts decreasing (peaks and then starts going ROP by a degree or two) note the highest temperature that one cylinders EGT hits. That temp, whatever it is, is peak EGT. Lean the mixture back out until that EGT drops 50 degrees. That is pretty close to 50 degrees LOP. (I say pretty close because leaning the mixture will cause MP to drop, which will drop whatever peak EGT is to some number you can't actually know.)

The other five cylinders will all be leaner (they never peaked but will all cool off along with your richest cylinder). That temperature could be anything. Note that I haven't mentioned TIT yet, that is intentional. Now check TIT to be sure it is a comfortable temperature for you (below 1650.) Keep an eye on the CHT to make sure the hottest stays under 380. If you do this technique but the TIT or CHT are too high, try a reduced power setting (lower MP or lean a bit more or both) to keep temperatures under control. Up high some temperature will be the limiting factor on power output.


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[jlunseth]

On 8/6/2017 at 4:14 PM, Northern Mooniac said:

I have an 81 M20K. New to me with about 20-30 hours on it so far, so still trying to figure it out.

The plane has TKS, merlyn waste gate, intercooler and gami injectors.

My aspen will usually show a true airspeed speed of 155-160kts between 9000 and 12,500. Is this pretty normal or am I missing a bit of speed?

I also find that I'm burning 14-16gph.

still playing around with settings but doing about 33.4 and 2400rpm at 10500 on the way home from Oshkosh gave me about 160kts true.

Temps at 10500 were about 13 degrees so my middle cylinders were running at about 390, could have probably opened up the cowl flaps a bit.

Does this sound like normal operation?

I did also recently put in new baffles from bee gee and they seem to be working much better, however on climb i go back to 36" and 2600 rpm and I can usually do about 500-700fpm and keep my #1 cylinder under 400 degrees.

 

any tips are appreciated!

I haven't been here for awhile so I missed this, sorry.  I don't see a power setting in here, I agree with another fella who said 14-16 gph is too much fuel. 

My 75% HP ROP setting is generally 29", 2450 RPMs, 13.3 gph.  According to my JPI930 that is around 100-125 ROP, which is good.  You would not want to get closer to peak than that, while ROP, I don't think.  With that setting I would see about the same speeds you were seeing, maybe 5 kts. more.

However I have been flying LOP mostly, for some time.  Now, my caveat is that I am in the last hundred hours to TBO, so I am not worrying too much about whether I will need a mid-TBO top overhaul.  But my LOP setting seems to agree with the engine, and actually gives me a little more speed than a comparable ROP setting (so they are probably really not comparable).

I use 2450 RPMs, 34" MP, and do the big pull to get back to 11-11.1 GPH.  When LOP, according to the APS folks, HP is dictated entirely by fuel flow, and is unrelated to MP.  The formula for the TSIO360 is 13.7 x fuel flow=HP, then divide the HP by 210 (total rated HP) to get percent HP.  At 11, you are right at 70%HP.  

So why the 34"?  There are two ways to make a mixture leaner.  With MP at a set number, you can reduce the fuel flow.  Of course, using the formula, that reduces HP.  Or you can increase the amount of air in the mixture, in other words increase MP.  So I want 70% HP, that's 11.0 GPH, if I want the mixture leaner at that fuel flow I increase the MP.  It works well.  I keep my eye on TIT.  The TIT limit for constant operation is 1650 dF.  I keep my TIT at or under 1600.  If it starts to drift up too high, I reduce the fuel flow (and the power).  This actually gives me a few more knots than what I had thought was 75% HP ROP, I think though that my JPI is not reporting a good ROP %HP number, so my ROP setting may be less HP than I think.

The one problem I seem to have is high altitude operation.  Because of poor cooling my temps - particularly TIT - tend to creep up uncontrollably in my 70% LOP setting when I get up above 12k, when that happens I just go ROP, I am getting more TAS up there anyway.  

Its pretty slick, cruising along at 160-165 TAS and 11.0 GPH at 12k.  I have 3-400 hundred hours doing mainly this, and the engine is holding up very well.

One other hint is that the MP and fuel flow are interlinked so you change one you are going to change the other.  I take off at 36-37"", 2700 RPM, full rich.  At cruise I bring the MP back just a little bit, say to 34", because the next step is going to make it increase.  The next step is to reduce RPMs to my 2450, I am sure 2500 would work fine.  Then I do the big pull, pull the fuel flow back in one smooth pull until I can feel the plane decelerating.  Then adjust the fuel flow to 11.0 and tinker with the MP and fuel flow until I get 34" and 11.  Seems to work well.

Hope that helps.

[Northern Mooniac]

Thats basically what i've been doing. So thanks very much for that!

I've been running 32" 10.5gph and 2500rpm and getting about 145-155kts at 11500.

I did a flight from CYQR to KFAR on tuesday. keep in mind I had a 30kt tail wind and 30kt headwind going home.

I did 150true at 10.5 gph going down and only used 20 gallons.

I did 1701 true at 18hpg rop coming home and cost almost $300 cdn to fill up lol. vs $97usd....LOP is awesome. I'm hooked.

I do also notice I burn less oil and there is jsut that much less black soot on the bottom of my plane.

[FlyWalt]

On 8/8/2017 at 1:11 PM, Hank said:

Your turbo will really shine when you take it up into the flight levels and catch those great tailwinds! Things I can only dream about . . . .

On that note, does anyone have a portable O2 system to sell?

[anthonydesmet]

On 8/8/2017 at 0:13 AM, KLRDMD said:

Never fly a TSIO-360 series engine at 75% power in cruise unless you want to do at least one, and maybe two top overhauls before TBO. 65% power, LOP with no CHT above 380º and they live a long and happy life and will probably exceed TBO without a top overhaul.

Concur.  Just a Private Pilot option but I bought a 262 because of speed, economy and to go higher to get into smoother air and away from the <10K traffic.  If your not up in mid-teens your not taking full advantage of why you bought a TSIO-360.  Granted mine is a 262 with an MB and I fly at 65%, between 12-18K.  2400 RPM and with a MB that puts MP around 24.5.  I like 100 deg ROP for best power.  This puts my CHT'S around 350, cowl flaps closed, TIT at 1400.  All set with my fuel flow at 12.5GPH.  my result KTAS is 180KTS +/- 2 to 3 knots.never had a problem with plugs and I do borescopes x 2 a year and my valves look great.

 

i do think your numbers are off a bit but is would,try cruising higher and different ROP and LOP settings after you do your GAMI spread checks before you really start to think something is up.  

[KLRDMD]

1 minute ago, anthonydesmet said:

I fly at 65%, between 12-18K.  2400 RPM and with a MB that puts MP around 24.5.  I like 100 deg ROP for best power.  This puts my CHT'S around 350, cowl flaps closed, TIT at 1400.  All set with my fuel flow at 12.5GPH.  my result KTAS is 180KTS +/- 2 to 3 knots.

65% power will give you a specific true airspeed at a specific density altitude. Your engine doesn't care if it gets to 65% power ROP or LOP. If you're flying 65% power ROP,  flying 65% power LOP will get you the absolute identical true airspeed on a LOT less fuel with lower intra-cylinder pressures and essentially the same temperatures you see ROP.

You can fly 30" MP,  2500 RPM and 10.0 GPH for 65% power LOP and get the same airspeeds you get now.

It is the magic of LOP 

[anthonydesmet]

12 hours ago, KLRDMD said:

65% power will give you a specific true airspeed at a specific density altitude. Your engine doesn't care if it gets to 65% power ROP or LOP. If you're flying 65% power ROP,  flying 65% power LOP will get you the absolute identical true airspeed on a LOT less fuel with lower intra-cylinder pressures and essentially the same temperatures you see ROP.

You can fly 30" MP,  2500 RPM and 10.0 GPH for 65% power LOP and get the same airspeeds you get now.

It is the magic of LOP 

KLR is spot on.  The point I just wanted to bring out is because density altitude changes and air temperature effect your true airspeed and you have a turbo, you are taking better advantage of why we all bought a turbo because your resultant true airspeed will be higher.  Over to the individual if you want to run ROP or LOP.

 

 

[KLRDMD]

3 hours ago, anthonydesmet said:

Over to the individual if you want to run ROP or LOP.

I have yet to hear a cogent argument for running ROP over LOP, assuming the engine runs LOP properly and you're flying a turbo.