ROP vs LOP

[NewMoon]

I am certain this question has been asked but this is geared specifically to Acclaim owners. I am thinking of stepping back into the model (have owned 2 prior) and wanted to throw out the hook again.

If 100 ROP creates CHT's that are <~370° in cruise, besides additional costs for fuel burn, why run LOP?

Seems like at least at 12kts loss in TAS? 

Appreciate any helpful discussion. 

[M20TN_Driver]

LOP is about more than cooler CHTs.  If you talk to the folks most knowledgeable on the topic (the folks at Savvy), they will tell you the engine runs MUCH cleaner LOP.  So less lead buildup on plugs, carbon, etc.   When I'm flying LOP, my CHTs are usually around 300-320.  TIT is ~1580.   Not sure where 100 ROP would put your TIT but the cooler TIT also saves your turbos.

To each his own.  If you want to go fast--fly ROP.  LOP you are def going slower.  I have an M20TN type S.  I fly high and LOP for most operations.  Flying higher will get you back a good deal of the lost speed...if you are so inclined.

[NewMoon]

8 minutes ago, M20TN_Driver said:

LOP is about more than cooler CHTs.  If you talk to the folks most knowledgeable on the topic (the folks at Savvy), they will tell you the engine runs MUCH cleaner LOP.  So less lead buildup on plugs, carbon, etc.   When I'm flying LOP, my CHTs are usually around 300-320.  TIT is ~1580.   Not sure where 100 ROP would put your TIT but the cooler TIT also saves your turbos.

To each his own.  If you want to go fast--fly ROP.  LOP you are def going slower.  I have an M20TN type S.  I fly high and LOP for most operations.  Flying higher will get you back a good deal of the lost speed...if you are so inclined.

Appreciate your thoughts, just sent you a DM. How far LOP do you run? 

[M20TN_Driver]

I’m typically greater than 50 LOP.  I usually settle in between 14.7 gph and 15gph.  

[dkkim73]

I've got a fairly narrow GAMI spread, usually around 0.4gph (actually measured a bit lower recently). I did a Savvy Profile yesterday at 19" MAP and ran 120F LOP before significant roughness. At higher power 29-30.5"/2500, I can usually run at least 100F LOP, targeting TIT below 1600. I have had some knowledgeable people say not to worry about 1600 TIT, many others though also use it as a practical working limit for longevity. If I need to go faster or more economically, I'll target the leanest cylinder and go 50F lean of that, which often ends up in the low 1600's at those settings. Runs very smooth and cool CHTs that way. 

I can pick up about 5-9 kts typically going ROP, but I usually only do that running to pass ahead of a bunch of cells or if I'm feeling time pressure on the ground. The fuel savings and lower CHTs (this ICPs) are otherwise well-worth it to me. The plane is slicker than snot, so it's fast even LOP. 

You know you want back in...

[NewMoon]

16 minutes ago, dkkim73 said:

I've got a fairly narrow GAMI spread, usually around 0.4gph (actually measured a bit lower recently). I did a Savvy Profile yesterday at 19" MAP and ran 120F LOP before significant roughness. At higher power 29-30.5"/2500, I can usually run at least 100F LOP, targeting TIT below 1600. I have had some knowledgeable people say not to worry about 1600 TIT, many others though also use it as a practical working limit for longevity. If I need to go faster or more economically, I'll target the leanest cylinder and go 50F lean of that, which often ends up in the low 1600's at those settings. Runs very smooth and cool CHTs that way. 

I can pick up about 5-9 kts typically going ROP, but I usually only do that running to pass ahead of a bunch of cells or if I'm feeling time pressure on the ground. The fuel savings and lower CHTs (this ICPs) are otherwise well-worth it to me. The plane is slicker than snot, so it's fast even LOP. 

You know you want back in...

Oh I am itching to get back in...if I could save 5-7 gph and give up 5kts, thats a good deal. I just don't think that is how it comes out. My perception is that you lose 10kts and save 5 gph. Looking for guys to give some real world stats. Otherwise I like to run at 29.5/2450rpm/100ROP

[LANCECASPER]

51 minutes ago, dkkim73 said:

The plane is slicker than snot, so it's fast even LOP. 

The standard Acclaim is slicker than snot.

The Acclaim Type S is slicker than snot on a door knob.

[dkkim73]

50 minutes ago, NewMoon said:

Oh I am itching to get back in...if I could save 5-7 gph and give up 5kts, thats a good deal. I just don't think that is how it comes out. My perception is that you lose 10kts and save 5 gph. Looking for guys to give some real world stats. Otherwise I like to run at 29.5/2450rpm/100ROP

I haven't been running ROP a lot recently. Next time on I'm a faster XC I'll run some comparison. 

Here's  data point running a little hotter on a recent trip where I ran it a bit more aggressively: 

29"/2500/16.4gph, 1620TIT, 50F LOP of the leanest cylinder, 198KTAS about 16K MSL, OAT -10C (CHT's 281 to 323 [cyl 5])

I didn't get an ROP data point to match.  

 

[NewMoon]

27 minutes ago, dkkim73 said:

I haven't been running ROP a lot recently. Next time on I'm a faster XC I'll run some comparison. 

Here's  data point running a little hotter on a recent trip where I ran it a bit more aggressively: 

29"/2500/16.4gph, 1620TIT, 50F LOP of the leanest cylinder, 198KTAS about 16K MSL, OAT -10C (CHT's 281 to 323 [cyl 5])

I didn't get an ROP data point to match.  

 

Ok, great real life data. So 8kts tas loss for 5.5gph less fuel. No winds or tail wind that works. Appreciate you sharing

[Schllc]

Funny how annoying it can be to see any loss of speed. Even saving 5gph. 
I also see 5-8 knot loss from ROP to LOP, if you are at 12kts you are too lean. 
With the emag and a good spread I can get almost to 200deg lop before the roughness gets concerning. 
with a good gami spread my typ profile is 27.5” 2450rpm and about 16.5-.8gph ROP and about 14 LOP.

I did have a general question for others. 
When I’m getting used to a new engine/plane I the the lean process a few times, after that I pull to fuel flow for tit without regard for what peaks where.

I dont really see the purpose of leaning slowly based on why every time.  
I have never noticed my engine varying which cylinder peaks first and even if it did, and tit is the goal, what does it matter unless there is a real anomaly in EGT’s

[exM20K]

ROP vs LOP: 

5% faster on 25% (at least)  more fuel. 21.5 vs 16.5 for me at 30.5x2400

Significant range reduction (my 80% trip is 750NM.) or…

Significant payload reduction b/c extra fuel and larger reserves ROP

Sloppy and wasteful vs. Elegant and Precise.

Fueling, induction and ignition problems easier to diagnose LOP.

There are some good profiles available in ForeFlight.  See for yourself as applied to your 80 or 90% trip.

I’m not opposed to burning extra fuel when there is a meaningful performance or safety bump (the 310 HP climbs at 130 KIAS / 1500 FPM / 36-37 GPH.)  Astonishing performance that is out-climbing the engine-out descent rate by a factor of almost 2. Climbs out of icing or in an obstacle departure benefit bigly.

Just do it.  There’s a bunch (compared to past years, anyway) for sale right now.

-dan

[exM20K]

45 minutes ago, Schllc said:

When I’m getting used to a new engine/plane I the the lean process a few times, after that I pull to fuel flow for tit without regard for what peaks where.

Similar, ish.  I don’t care much about absolute TIT, and remember, in the Acclaim, you’re seeing only the odd cylinders. I know why my richest cylinder is and occasionally confirm its cruise EGT is 50 lean of its peak if I’m bored.  I pull for target FF.

YMMV

-dan

[LANCECASPER]

With the flexibility of the Acclaim and how well it runs LOP, and how many different power settings you can use, it's like having an Acclaim, and Ovation and an Encore wrapped up into one airplane.

[dkkim73]

2 hours ago, Schllc said:

When I’m getting used to a new engine/plane I the the lean process a few times, after that I pull to fuel flow for tit without regard for what peaks where.

I dont really see the purpose of leaning slowly based on why every time.  
I have never noticed my engine varying which cylinder peaks first and even if it did, and tit is the goal, what does it matter unless there is a real anomaly in EGT’s

Discussed this with Brian. 

The issue is that TIT and EGT probes wear and indicate lower temps. So you can drift further and further from peak over time. 

Shorter term I think it's fine and it's definitely safe, you might just fly further and further LOP over time. Or ROP I suppose. 

I suspect if I go 50-75F rich of richest cylinder I'll get more speed and less fuel burn, but higher TIT and thus potentially less longevity. I just don't spend much time in that world. Will try to get a data point in the future. 

[NewMoon]

11 hours ago, exM20K said:

ROP vs LOP: 

5% faster on 25% (at least)  more fuel. 21.5 vs 16.5 for me at 30.5x2400

Significant range reduction (my 80% trip is 750NM.) or…

Significant payload reduction b/c extra fuel and larger reserves ROP

Sloppy and wasteful vs. Elegant and Precise.

Fueling, induction and ignition problems easier to diagnose LOP.

There are some good profiles available in ForeFlight.  See for yourself as applied to your 80 or 90% trip.

I’m not opposed to burning extra fuel when there is a meaningful performance or safety bump (the 310 HP climbs at 130 KIAS / 1500 FPM / 36-37 GPH.)  Astonishing performance that is out-climbing the engine-out descent rate by a factor of almost 2. Climbs out of icing or in an obstacle departure benefit bigly.

Just do it.  There’s a bunch (compared to past years, anyway) for sale right now.

-dan

Appreciate your perspective Dan. And yes ~10% of the fleet is currently for sale based on my calcs

[kortopates]

Discussed this with Brian. 
The issue is that TIT and EGT probes wear and indicate lower temps. So you can drift further and further from peak over time. 
Shorter term I think it's fine and it's definitely safe, you might just fly further and further LOP over time. Or ROP I suppose. 
I suspect if I go 50-75F rich of richest cylinder I'll get more speed and less fuel burn, but higher TIT and thus potentially less longevity. I just don't spend much time in that world. Will try to get a data point in the future. 

in reality it’s just TIT probes because they see a continuous stream of hot gas slowing burning off their tip. Whereas EGT probes only see a short burst when the exhaust valve briefly opens on the exhaust stroke. EGT probes usually go at least the life of the engine while the TIT probes will only last 500-600 hrs.


Sent from my iPhone using Tapatalk

[kortopates]

By far the Acclaim and Ovations 550’s are the best performing LOP in the fleet. It would be shame to not leverage this capability its many operational advantages including benefits to the engine. See Dan’s list above.


Sent from my iPhone using Tapatalk