Bravo LOP

[johnggreen]

Bravo Owners,

I have made a few passing comments about trying LOP in my Bravo over the past few months.  Back last winter, I took the Advanced Pilot Seminar on LOP operation and have made a few stabs at using it on my airplane.

I keep working on it and yes, I can run LOP, but the benefits as far as incresed miles per gallon have been minimal.  Reducing the fuel flow at the cost of a significant loss of airspeed seems to pretty much defeat the purpose.

I thought I would post a few comments as to what I have experienced and "believe" to be accurate for your consideration.  I know there are a lot of Mooney Space members who successfully use LOP on other engine models.  With all due respect, I don't think their comments carry much value as to our engines and though I read, consider and respect those comments, take them with a huge dose of salt.

First, my engine is equipped with GAMI's and I have a spread of about 0.6 gph from the leanest to the richest cylinder.  Also, my engine is very well baffled and CHT's are simply not an issue when running ROP.

Comments/findings:

1.  The peak EGT's of this engine vary considerably depending on altitude and temperature.  Meaning that I have not, at this point, been able to identify a "starting point" for finding peak EGT on my richest cylinder which is the critical number for finding the appropriate LOP setting.

2.  The EGT's are slow to change and stabilize as you lean the engine near peak EGT.  This is not true of the TIT temps.

3.  Finding peak EGT of the richest cylinder, because of the comments in 1. and 2. is a slow, tedious process that distracts me from flying the airplane and watching for traffic.

4.  Going from peak TIT to 50 degrees LOP with CHT's results in a substantial, unacceptable reduction in airspeed.

5.  Yes, I said from peak TIT which is easy to find to 50 LOP/CHT which is difficult to find.

6.  Fuel flows and airspeed reduce with similar correlation.

7.  Adding back MP to gain some of the airspeed back, requires a significant increase in MP to do any good and fuel flows increase as well.  I didn't think that fuel flows in this configuration would/should respond accordingly.

So far, the end result is that, yes, I get lower CHT's and EGT's, but when those are already well within acceptable limits, what has been gained?

The reduced fuel flow is almost entirely matched with reduced airspeed for a negligible increase in miles per gallon.

I'm going to keep working on it and see if I can work some of the bugs out that would make LOP beneficial.  At this point, I am skeptical.

Jgreen

 

 

[Cruiser]

John,

I am not quite following your description for the leaning process.

What are you doing when you say "to 50 LOP/CHT which is difficult to find" do you mean 50 LOP/EGT?

What engine monitor are you using? The JPI probes are very fast. Response should be almost instentanious.

[N9660M]

John, I tend to agree based on around 200 hours experience with running my M20F LOP that the added mpg may not be as significant as some believe.

I have noticed that my oil stays cleaner between changes, and have also read several places that when torn down for overhaul the cleanliness of engines run LOP is better than those run ROP.  Overall, believe that LOP ops is probably healthier for the engine.

Jim

[jetdriven]

The MPG improvement is around 15-20% going from 11 GPH ROP 155 KTAS to 9 GPH 148 KTAS LOP.  This is 8K or below cruise, above that altitude the difference is less.   Part of this is improved efficiency from the LOP BSFC of .39, and part of it is from flying 3-5% less percentage of power than the ROP setting.

[johnggreen]

Cruiser,

Sorry, I misspoke, but your interpretation is correct.  Getting the leanest cyliner to 50 LOP/EGT is tedious and the numbers are slow to stabilize.  The TIT temps react faster but even those are far from "instantaneous" .  My engine monitor is an EI.  It is my impression, which could be erroneous, that the slowness is not a guage issue as much as turbo related , but I truly do not know.  One reason for that impression is that my fuel flows are somewhat slow to stabilize as well.  I think it would be substantially quicker on all accounts if the engine were NA.

Byron,

At this point, my Shadin is indicating a MPG improvement of maybe 5/10ths MPG, but that is with some speed loss.  I think that I am going to have to give the engine a lot more MP to keep the same speeds.  Now, understand, I am approaching this very carefully, because my engine runs like a sewing machine, performs great at ROP, and I don't want to do anything wrong.  Yea, I know what can go wrong if you're going cooler?  I don't know, I'm just not taking any chances.

Also, I am starting this procedure from about 65% power to avoid any encounter with the red zone.  My Bravo is fast enough that I just don't ever see the need to operate above 65% power anyway.  I am starting at 2200/28".  After leaning, to LOP, I am increasing MP to 32".  Fuel flows at peak TIT at that power were just under 13 gph. After making the mixture and power adjustments, my fuel flow was 11.8.  Those fuel flows are not exact as, like the EGT and TIT numbers, it takes time for my fuel flows to stabilize as well.  Even with that increase in power, I will be truing about 5 knots slower or so it appears.  CHT's dropped about 25 degrees, but they were less than 350 degrees ROP.

All of this was done Friday at 7,500' and it was hot as hell, ambient I mean!

This "testing" is going to have to be repeated several times and at various altitudes.  The last time I tried it at 15,000, I couldn't get my MP up enough to keep anywhere near the speed I had at peak TIT; like down 15 knots.  Since I fly most missions above 12,000', if that will be SOP, LOP is DOA for me.

Now, understand that I am not doing this for any savings in fuel.  Fuel is such a small part of my operating expense that I'm just not motivated.  If I could keep the performance and lower temps with some fuel savings, then I am more prone to go to the trouble.

Jgreen

[johnggreen]

This site does some strange things sometimes.  My original post on this subject is gone and my name is on someone elses pic and post.  

Jim,

I may be repeating myself, but, with the turbo on my engine nothing comes quickly as I lean.  Both egt's and fuel flows drift some and take time to stabilize.  I don't have a clue as to why.  I have acutally thought, seriously, about using the old, "lean until it stumbles then richen until it smooths out".  Then richen to be sure my leanest cylinder (which is predictable) is still LOP.  Why wouldn't it work?

Jgreen

[Awful_Charlie]

I think you are trying too hard John!  50 LOP is a long way back on the power curve, and I wouldn't bother trying to get that far back for the marginal increase in efficiency - for me anywhere between peak and 25 LOP is good enough for efficiency, and still brings the CHTs down enough.  I'm GAMI equipped too, although I think they need a tweak, as the order varies depending on MP, RPM and altitude.  I'm still trying to correlate this.

1) Use the sun visor fuel flows as a starting point, they all work out to be generous (ie ROP) for me

2) just lean slowly and consistently, when you hit peak, pause a moment an let the numbers settle, this will probably get you to 10-20 LOP for a start due to the lag.

3) I'm a JPI user, so don't know what EI offers for finding peak, but guess there is some function to make it easier.  I would be most surprised if the EI accessibiity was less user friendly than JPI!

4) It will be slower, but my feeling is that you're overdoing it at 50 LOP - try for 25 or so

5) Goes back to 3 - surely EI can give you an easy way to find this point?

6) When LOP, power is directly proportional to fuel flow (actually to fuel flow by mass and not by volume! It is volume that the fuel flow transducer measures), so airspeed being proportional to fuel flow makes sense

7) When you add back MP, the fuel flow should increase to maintain the air/fuel ratio you got to when leaning.  It is by adding back the fuel flow that you are making more power again.  Another way to achieve the same result would be to start from a higher than desired power setting, and then lean to LOP and accepting the lower power there.

I normally cruise at 30"/2200 and just LOP, which runs in about 13 US/Hr.  IAS and TAS vary by temperature and altitude, but say 170-180 KTAS in the mid to high teens would be fairly normal.  I was out playing yesterday for max range/endurance, and got level flight at 6.2US/Hr, but that's not getting anywhere quickly!  It is more that half the speed that double the fuel flow would offer though! 

The TIO540AF1 that we have does not have the best fuel specifics in its class, and if you go to the engine manual, you'll find it peaks out at about 0.44 BHP/lb at 70% or so, which corresponds to about 14GPH.  Of course by going a bit slower you can get some airplane efficiency, albeit at the cost of engine efficiency.

I've noticed that the standard Shading FF instrument I have is 'damped' for the display, and the JPI is far faster reacting in Lean Find mode despite using the same transducer, I don't know what EI offers you in this respect.

My take on it is that as long as you are at peak or lean of it you are out of the CHT red box (and I don't have a CHT problem either in the cruise, a sustained climb at 120KIAS might need to open the cowl flaps a 1/3 to keep them under 380-400) and you are close enough to the efficiency point on the engine that further gains would be made with selecting the best altitude for the wind and unloading the junk from the baggage bay!

Ben

[johnggreen]

Ben,

I think you make several good points.  The most important is that 50 LOP is probably too far.  My EI does have a leaning function.  The challenge is to not run through it or it seems to mess the instrument up and I have to start over.

From 30"/2200, after you lean, how far do you have to push your MP up to get the speed back and how much speed do you give up in that configuration?

My Gami spread varies from day to day, altitude, and power settings, but 6/10ths is about the closest they ever get.  What about yours?  I would feel better at a 0.3 or 0.4 spread.

I'm flying to New Orleans Thursday and will try your suggestions.

Jgreen

[Awful_Charlie]

After leaning, I don't tend to add MP back, just accept the reduced power (but then I started higher than your 28"), but have been known to add 1 or 2". I've not really looked at how much speed I lose, as I do the leaning quite soon after levelling from the climb, and closing the cowl flaps, so the speed has been varying quite a lot in the few minutes before.

As for GAMI spreads, bit of a sore point. I've been extacting the Lean find figures into a spreadsheet for a while, here are the results for 30/22: as you can see there is a lack of consistency, although the general trend is that #5 or #2 is the last to peak

Cylinder order, Flow difference, Altitude

4 6 3 1 2 5 1.1 ?

4 1 6 3 2 5 0.6 A025

1 4 6 3 5 2 0.8 A025

4 6 1 3 2 5 0.8 A040

4 6 1 2 3 5 1.2 A040

4 6 3 1 2 5 2.0 A040

4 6 1 3 2 5 1.1 FL055

4 1 6 2 3 5 1.2 FL055

4 6 3 5 1 2 1.2 FL055

4 6 1 3 2 5 0.7 FL060

1 3 4 6 5 2 1.4 FL060

4 3 1 6 2 5 0.4 FL100

1 3 4 6 2 5 0.7 FL100

4 6 1 3 2 5 0.8 FL100

4 6 3 1 5 2 0.9 FL100

6 1 4 3 5 2 0.9 FL110

4 6 3 2 1 5 1.0 FL110

4 6 1 3 2 5 1.0 FL110

1 4 6 3 2 5 0.3 FL120

1 4 6 2 3 5 0.8 FL120

4 6 1 3 2 5 1.2 FL120

4 6 3 1 2 5 0.6 FL130

4 1 3 6 2 5 1.4 FL130

4 1 3 6 2 5 0.7 FL140

6 4 1 3 2 5 1.0 FL140

4 1 6 2 3 5 0.6 FL150

4 3 6 1 2 5 1.0 FL150

4 6 1 3 2 5 0.8 FL160

1 6 3 4 2 5 1.0 FL160

4 6 1 3 5 2 1.6 FL160

1 3 6 4 2 5 0.5 FL170

4 6 1 3 2 5 0.6 FL170

4 6 1 3 5 2 0.9 FL170

6 1 4 2 3 5 1.1 FL170

4 1 3 6 5 2 1.1 FL170

4 6 1 3 5 2 1.1 FL170

1 4 6 3 5 2 1.4 FL170

3 4 6 1 2 5 0.6 FL180

6 1 3 4 2 5 0.6 FL180

4 6 1 2 3 5 0.7 FL180

1 2 3 4 6 5 0.7 FL180

1 3 4 6 2 5 0.9 FL180

1 4 6 3 2 5 0.9 FL180

1 4 6 3 2 5 1.0 FL180

4 1 6 3 5 2 1.1 FL180

1 4 6 3 5 2 1.2 FL180

4 6 1 3 2 5 1.2 FL180

6 1 3 4 2 5 1.3 FL180

6 4 3 1 2 5 1.5 FL180

4 6 1 2 3 5 1.6 FL180

4 6 1 3 5 2 0.4 FL190

6 4 1 3 2 5 0.6 FL190

4 6 1 3 2 5 0.9 FL190

6 4 1 3 5 2 1.4 FL190

4 6 1 3 2 5 1.5 FL190

1 3 4 6 2 5 0.8 FL200

1 4 6 2 3 5 1.3 FL210

[johnggreen]

Ben,

I would be curious as to how much speed you are losiing without increasing MP.  I'm losing over 15 knots; totally unacceptable.  As for your spreads, I would be very bothered by them.  I usually see closer numbers before installing GAMI's.  I think you might want to contact GAMI and discuss the matter.

Jgreen

[Awful_Charlie]

I don't wait for ages to let the speed stabilise all the way up before doing the red pull, so couldn't really say how much speed it loses, but doubt it is as much as 15KIAS.  As for the spread, yes, it is a sore point - GAMI have suggested getting more sample points, and checking for induction or upper deck to injector leaks, which we will do at the annual at the end of the month.

[TLSDriver]

Spoke to Gami about running LOP with my Bravo.

Here is what they said:

1) Most Bravo engines don't like running LOP.

2) Even if yours does most Bravo owners can't stand the speed loss.  They purchaesd a Bravo to go fast.  

3) Exhaust systems on the Bravo are getting hammered running LOP.  Any money saved on fuel could be offset by costly repairs.

 

.... just the messanger.

 

 

David

 

[TLSDriver]

Spoke to Gami about running LOP with my Bravo.

Here is what they said:

1) Most Bravo engines don't like running LOP.

2) Even if yours does most Bravo owners can't stand the speed loss.  They purchaesd a Bravo to go fast.  

3) Exhaust systems on the Bravo are getting hammered running LOP.  Any money saved on fuel could be offset by costly repairs.

 

.... just the messanger.

 

 

David

 

[jetdriven]

1600 TIT is the same LOP or ROP.   But, I have heard from many sources, that the big Lycoming in the Bravos not efficent, and will simply not run well LOP.  IIRC I think Don Kay threw a few grand on injectors, plugs, etc and in the end, still did not work.  Now, the 252 or ovation......

[AndyFromCB]

Quote: TLSDriver

Spoke to Gami about running LOP with my Bravo.

Here is what they said:

1) Most Bravo engines don't like running LOP.

2) Even if yours does most Bravo owners can't stand the speed loss.  They purchaesd a Bravo to go fast.  

3) Exhaust systems on the Bravo are getting hammered running LOP.  Any money saved on fuel could be offset by costly repairs.

 

.... just the messanger.

 

 

David

 

[TLSDriver]

I'm not quite sure how the exhaust is getting hammered any more or less in the theoretical Bravo LOP situation? What kills the exhausts on Bravos is running the recommended TIT of 1750, 100 degrees higher than any other lycoming. I stay at 1650 or below at 30/2400, burn about 15-16 per hour, in return I get 190knots in the upper teens. What's not to like about that. Or run 24/2200, burn 11.5gph, get 160knots at 12,000. Or 205 on 21.5 but just for a few minutes when I level off to make myself feel good.

 

I would love to figure out how to get 160kts on 11.5gph at 12,000.  

Can you share how you set up for that?

David

[AndyFromCB]

David,

I reviewed my notes from my previos flights, 24/2200, pulled to peak at 12,000 gives me a fuel flow of 11.5 per hour at less than 1650 TIT. The speed I get is about 155knots, not 160knots, sorry. I find my Bravo with TKS is still about 5knots faster than the book at all power settings. My TKS panels are extremly well blended in and my gear doors are adjusted correctly. My fuel flows seem to match the book up until 32/2400 when are about 1 gph higher. On 16gph, I get 185, not 190, 190 requires pumping about 17 thru the engine. I was a bit optimistic in my memory ;-)

Now, I haven't flown the airplane with a new engine yet. If I get back into town before the weekend, I might, or I might wait for Bruce Yeager to show up next week to give me a new check out, being I haven't flown anything for 4 months now, unless you count operating an autopilot on a Pilatus for a couple of flights.

Andy

[TLSDriver]

Not to change the topic but have you worked with Bruce before?  I could use a 'tune-up.'

[Skywarrior]

Quote: TLSDriver

Not to change the topic but have you worked with Bruce before?  I could use a 'tune-up.'

[AndyFromCB]

So I went up yesterday again to play with the engine. With the surface temperatures at 80 degrees, no problems whatsoever keeping the temperatures below 400 even in climb, about 360 in cruise between 24 to 30mp, now at 2300rpm, with cowl flaps closed. When it was 95 to 100 on the surface, I needed to leave them 1/2 open in cruise.

Seems to me that dropping RPM to 2300 has a pretty good effect at reducing my fuel flows with minute effect on speed, engine still runs ultra smooth as opposed 2200 where I feel some vibration kicking in.

In any case, I tried running between 25 to 50 degrees LOP at 24/2300 and 27/2300. Engine seems to run just fine at these settings, yes my CHTs do drop about 20 degrees to about 340. However, the speed loss is big, about 5 to 7 knots depending on the setting. You can feel it when you push the mixture back in to go over to ROP side, the plane just jumps and starts accelerating. I'm going to stick to running right at peak at these settings. TIT peaks below or right at 1650, fuel flow is between 12.5 to 15.5 gph, speed between 160 to 175 at 12,000 feet. AT 25 or so LOP, I can save about 2gph but I'm not sure the speed loss is worth it.

Still can't get over the deck angle climbing at 85knots. Wow.

As to training with Bruce, well worth it, I think I mentioned it before, but we spent 12 hours together and I feel much more comfortable with the airplane than before.