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Tips on Bravo MAP and RPM at various altitudes?

Skywarrior

By Skywarrior
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Skywarrior Proficient

Skywarrior

Posted
Posted

Hello, all -


Any tips welcomed. Yes, I have read the POH. But Bruce Jaeger opened my eyes to my ignorance of recommended best practices for engine operation.


Chuck M.

johnggreen Rising Star

johnggreen

Posted
Posted

Skywarrior,


Since purchasing my Bravo in January, 2005, I have not come across anything that I would trust other than the POH and the Lycoming Operator's Manual (referred to as LOM hereafter).


If you have not read it carefully with respect to the TIO-540-AF1B, do so.  You may be surprised what is buried there.  Hint.  First go through and highlight the pages/charts that relate to your engine; then it won't seem so daunting.


I have found the information as to horsepower and fuel burn both helpful and accurate.  As to the LOP question asked by the other blogger, I called Lycoming and they said, NO.  Period, no discussion.  I don't find this a problem since the airplane is fast and reasonably efficient if you don't ask too much from your engine as far as horsepower.


I will pass along what I have "learned" from flying the airplane now for almost seven years.  I may get interrupted for supper, but if I do, I'll just start posting again later without further ado.


As you study the LOM vs. the POH, the first thing to strike you is that the high cruise settings offered by the POH are indeed HIGH!!  Meaning that for instance the engine is allowed to operate continuously at high percentages of its rated power.  Before I delve into that, let me point out that I think that is what the engine was indeed designed for as it is only putting out 270 HP at full power.  In most applications, the TIO-540 is set up to put out a lot more power.


In the A Series:  310


In the F Series:  325


In the J & U: 350


In the R: 340


The POH gives maximum cruise as being the same as climb power at 2400/34".  I'll have to do some calculations out of the LOM to see what power that is, but as a reference, 75%, 200 HP comes at 2400/30" burning 15 gph.


Got to check off for a spell, if you come on line, get that LOM out and peruse.  I'll come back later and talk about the power settings that I use and some more tidbits I found in the LOM.  Not much scientific, just what has worked for me, quite well, I might add.


JG

blacknchrome Enthusiast

blacknchrome

Posted
Posted

I'm pretty curious to see what everybody else uses for power settings too. 


I was taught 30" 2400 rpm is a safe, you-will-reach TBO setting by several of the well known 'guru's.  They also said just run 1550 TIT and don't worry, be happy.  However, sometimes that's a lot closer to peak TIT than I would think it should be run for long engine life, despite the POH allowing for MUCH higher temps.


I'm more than willing to burn the extra fuel to save on the high dollar engine...anybody seen the exchange prices on the engine lately? WOW. 


What's everybody else running?

johnggreen Rising Star

johnggreen

Posted
Posted

OK, supper done, glass of merlot, and I'm back.


Referring to the LOM, there are two charts to reference.  One, 3-82, fuel flow vs. brake hp says at the lean limit, you get 200 hp at 15 gph.  I get this fuel flow at 2400/30 at 1650 TIT at altitude.  Right behind that is the Performance Curve charts which would indicate that 2400/34" is about 90% of max hp and 2400/30 is 81%.  You can look at the charts yourself and get confused without my help.


Now, how I fly my Bravo and what I think I have learned.


First, 2400/30" is my max cruise for me, maybe in a stiff headwind, 32", but almost never.  I almost always lean to 1650 TIT.  I have GAMI's but my EGT are spread pretty dramatically particularly from #3, my hottest to #4 & #5, my coolest.  The spread is usually near 190 degrees.  Still, when I do a lean test, they are right together.  I have talked to the GAMI folks and they shrug their shoulders.  My CHT's are always really good, so I don't worry much.


I rarely even fly 2400/30" because at 2200 my engine purrs and I mean purrs.  It is as smooth as a turbine and from 2400/30 to 2200/30, I only lose 5 knots.  Even with TKS, my airplane flys faster than book, so again, I don't worry.


If I'm trying to get range, I use 2200/28" and it makes a real difference.  At gross weight, maybe a little more, I can climb to 15,000' and with this setting get 175 TAS at 13 gph all day.  I recently flew from Durango, CO to my home base, Grenada, MS, with absolutely no wind and landed with 14 gallons.


I regularly fly to Manassas, VA, KHEF, from Grenada,  KGNF, about 60 gallons usage block to block averaging the two legs; one with tailwind and one with headwind.


Even on a four hour trip, KHEF to KGNF, no wind if I pushed it up to 2400/32" I might save 13 minutes.  Not worth the noise, fuel and wear and tear.


Unless a headwind forces the issue, I try to fly at 12m to 17m.  That where the Bravo shines.  I don't fly unpressurized above 18,000, especially with my wife.  That's a subject for another thread.  Below 8,000' a good Ovation will eat my breakfast.  Hard to get over 175 knots down low unless I really push some fuel through.


Truth is, turbocharging, contrary to popular belief, is not about speed, it's about capability.  There's a lot of weather and turbulance I can go over whistling all the way.  I doubt, if you really put a pencil to it, that in a 1000 hours of use, that i average 5 knots more than an Ovation.


This is getting long, but, another point, if you will go to the LOM, chart 3-83, "Fuel Flow vs. Brake Horsepower", you will see that the efficient power settings of the Bravo engine are from about 210-220 hp down.  Above that, the curve steepens and you start pouring fuel through the engine with little return.


That should be enough info to start a spew of interest and responses among Bravo pilots.  I would like to know what settings, speeds, and fuel burns everyone else is seeing.  Mine seem to be right on book.


JG 

jetdriven Grand Master

jetdriven

Posted
Posted

John, it is my understanding that a Bravo engine just physically won't run LOP.  Some engines won't.

Lycoming is about 20 years behind the curve regarding LOP operations. The say "no" to every engine they built, becuase their lawyers tell them to. LOP can happen and is safe depending on which engine you run and how well you monitor it.  As OSH they said they are developing a LOP program, stay tuned.  Perhaps the ABS, APS, Gami, JPI, MAPA, and a few other groups can get them started.

For example the Lycoming IO-360-A runs great LOP as well as the TCM IO-520B and IO-550B engines.  In the Cirrus SR22 and Piper Malibu it is required.

Mooney POH's (and Lycoming info) depending on year and model says to cruise at Peak EGT up to 75% power, and goes on to say lean until roughness, then enrichen slightly. On our machine thats about 90 LOP.

Quote: johnggreen

I have found the information as to horsepower and fuel burn both helpful and accurate.  As to the LOP question asked by the other blogger, I called Lycoming and they said, NO.  Period, no discussion.  I don't find this a problem since the airplane is fast and reasonably efficient if you don't ask too much from your engine as far as horsepower.

JG

johnggreen Rising Star

johnggreen

Posted
Posted

Byron,


I have never had an engine that was approved for LOP.  You fly the Bravo engine with TIT settings and it seems that if you go past peak TIT, the engine roughens immediately.  Unless I'm at a low power setting (2400/28"), looking for mileage, I fly best power TIT 1650.


Don't know much about the LOP and don't see it as a big issue for my engine.  I'm mainly interested in taking care of the engine and smoothness.  Any way you figure it, fuel is a "minor" portion of total costs.


I've read the arguments, but don't really understand what the difference would be using 1650TT at a lower power setting vs. LOP at a higher power setting.  I'm certainly NOT going to experiment with this engine as long as it is feeding out of my pocket book.


I'm curious about something though if you konw.  Fuel is horsepower.  Would an engine being run at peak EGT at say 15 gph, be putting out the same horsepower as the same engine LOP at higher settings still burning 15 gph?


JG


 

jetdriven Grand Master

jetdriven

Posted
Posted

John, I know the Bravo is one airplane that plysically cannot run LOP. I am not trying to convince you.  But many will, and "approved" has nothing to do with it if the engine runs within limits LOP while it overheats ROP.

Something like fuel, that costs perhaps 20K or more in 1000 hours, is no small expense. 

BSFC,  is a unit of measure of efficiency, expressed in lb/hr of fuel per hour, per horsepower.  ROP on a Continental IO-550BA, ROP, might be .43 whereas LOP is .39.   You burn less fuel for that horsepower.  Part of the savings of LOP is reducing power (you can add MP back to recover some of that) , part is increased efficiency.

Yes the FF is actually a way to measure crankshaft horsepower when operating LOP, or really, at peak as well. You can set power with fuel flow, just like a turbine. If you are buring 15 GPH at peak, and increase MP, re-lean to 15 GPH its the same power. perhaps slightly more if the BSFC value comes down slightly more.   15 GPH ROP is going to be less power somewhat, as some fuel is not burned.

As I understand it a Lycoming in a Bravo simply will not run smoothly LOP. Continental is way ahead of Lycoming in this matter and it shows up in the fuel flow.  Its all the same aluminum as well, so it is possible. Hopefully they will see what others have been doing for about 10 years in flat engines, and 80 years in radials.

Quote: johnggreen

Byron,

I have never had an engine that was approved for LOP.  You fly the Bravo engine with TIT settings and it seems that if you go past peak TIT, the engine roughens immediately.  Unless I'm at a low power setting (2400/28"), looking for mileage, I fly best power TIT 1650.

Don't know much about the LOP and don't see it as a big issue for my engine.  I'm mainly interested in taking care of the engine and smoothness.  Any way you figure it, fuel is a "minor" portion of total costs.

I've read the arguments, but don't really understand what the difference would be using 1650TT at a lower power setting vs. LOP at a higher power setting.  I'm certainly NOT going to experiment with this engine as long as it is feeding out of my pocket book.

I'm curious about something though if you konw.  Fuel is horsepower.  Would an engine being run at peak EGT at say 15 gph, be putting out the same horsepower as the same engine LOP at higher settings still burning 15 gph?

JG

 

carusoam Grand Master

carusoam

Posted
Posted

Adding fuel to the fire....


JetD...Continental has been running LOP (Printed MAC POH) IO-550s in production mooneys since 1994 (slightly more than 10 yrs)...


Parker...most Bravos will not run LOP: this is probably why the Acclaim has a continental IO-550 in it...


It must be nice to be able run LOP and add back the lost power with additional boost...Go M20TN !!!!


Best regards,


-a-

Shadrach Grand Master

Shadrach

Posted
Posted

Quote: johnggreen

OK, supper done, glass of merlot, and I'm back.

Referring to the LOM, there are two charts to reference.  One, 3-82, fuel flow vs. brake hp says at the lean limit, you get 200 hp at 15 gph.  I get this fuel flow at 2400/30 at 1650 TIT at altitude.  Right behind that is the Performance Curve charts which would indicate that 2400/34" is about 90% of max hp and 2400/30 is 81%.  You can look at the charts yourself and get confused without my help.

Now, how I fly my Bravo and what I think I have learned.

First, 2400/30" is my max cruise for me, maybe in a stiff headwind, 32", but almost never.  I almost always lean to 1650 TIT.  I have GAMI's but my EGT are spread pretty dramatically particularly from #3, my hottest to #4 & #5, my coolest.  The spread is usually near 190 degrees.  Still, when I do a lean test, they are right together.  I have talked to the GAMI folks and they shrug their shoulders.  My CHT's are always really good, so I don't worry much.

I rarely even fly 2400/30" because at 2200 my engine purrs and I mean purrs.  It is as smooth as a turbine and from 2400/30 to 2200/30, I only lose 5 knots.  Even with TKS, my airplane flys faster than book, so again, I don't worry.

If I'm trying to get range, I use 2200/28" and it makes a real difference.  At gross weight, maybe a little more, I can climb to 15,000' and with this setting get 175 TAS at 13 gph all day.  I recently flew from Durango, CO to my home base, Grenada, MS, with absolutely no wind and landed with 14 gallons.

I regularly fly to Manassas, VA, KHEF, from Grenada,  KGNF, about 60 gallons usage block to block averaging the two legs; one with tailwind and one with headwind.

Even on a four hour trip, KHEF to KGNF, no wind if I pushed it up to 2400/32" I might save 13 minutes.  Not worth the noise, fuel and wear and tear.

Unless a headwind forces the issue, I try to fly at 12m to 17m.  That where the Bravo shines.  I don't fly unpressurized above 18,000, especially with my wife.  That's a subject for another thread.  Below 8,000' a good Ovation will eat my breakfast.  Hard to get over 175 knots down low unless I really push some fuel through.

Truth is, turbocharging, contrary to popular belief, is not about speed, it's about capability.  There's a lot of weather and turbulance I can go over whistling all the way.  I doubt, if you really put a pencil to it, that in a 1000 hours of use, that i average 5 knots more than an Ovation.

This is getting long, but, another point, if you will go to the LOM, chart 3-83, "Fuel Flow vs. Brake Horsepower", you will see that the efficient power settings of the Bravo engine are from about 210-220 hp down.  Above that, the curve steepens and you start pouring fuel through the engine with little return.

That should be enough info to start a spew of interest and responses among Bravo pilots.  I would like to know what settings, speeds, and fuel burns everyone else is seeing.  Mine seem to be right on book.

JG 

kgbpost Enthusiast

kgbpost

Posted
Posted

After accumulating about 75 hrs in my new to me Bravo, here's the number I've settled into. The key is CHT. I always try to keep the engine in a range of 380-400CHT:


Takeoff: 38"-2550RPM...fuel flow indicates 29gph


500' climb power: 34", then 2400rpm, lean to 23.5 gph, climb at 120KIAS, CHTs stay below 400, TIT 1400-1500.


Cruise: accelerate, reduce to 30", close cowl flaps, set mixture to 19gph...let things stabilize. Now lean to 1525 TIT and note CHTs. On a hot day I may need to run 19gph to keep the hottest CHT right at 400F, which would yeild a TIT in the 1500 to 1525 range. On the other end of the spectrum...cold day, I can lean much closer to 18GPH and still maintain my hottest CHT at 400F, which would yield a TIT in the 1550-1600 range. In a strong headwind i run 32" -2400RPM and set the mixture the same way.


Descent; 30"-2400RPM, push the nose over and lean a half turn for the increased cooling airflow and adjust to keep the CHTs in the 375-400F range.


Notes;


I burn 1 qt/10 hrs so oil changes are easy...I fill to 9 qts, when it reaches 8 on the stick I add a makeup quart, when it reaches 8 again I change it.


Once oil temp has built up it runs right at 200F, even on a hot day the highest I've seen is 204F.


My EGT splits run about 20, never more than 30, and no i don't have GAMIs.


I've tried LOP with my EDM-830 and the engine picked up a sligth stumble as I neared peak TIT and it never went away even WAY lean of peak. No mas.


I lean very aggressively on the ground. So much so that if you push the power forward it wont go unless I richen a turn. On takeoff crossing the holdshort line I will richen enough so the engine will accelaerate and spool the turbo...then mixture full rich...


The other technique I have experimented with quite inadvertently is reduced power takeoff. Since the boost controller requires the throttle full forward i may have inadvertantly found how to fool the controller into a reduced power TO. If the prop controller is left back 1/8" or so, The engine will maintain 2500 vs 2550RPM, but the suprising thing i found is the boost controller maintained a very comfortable 36" at 2500RPM, about 90% power. Plenty of performance under most conditions. I know we don't have tables and approved procedures for RTOP at this level, but under conditions where there is performace to spare (90% of the time in my case, and I live in Denver) It is In my opinion RTOP increases safety, comfort, longevity, etc.,. I dont use this procedure as I understand it may not be legal. I don't know. I suppose it all comes down to the way the airplane is certified to be flown. That said, this airplane was certified to be operated at 1750TIT continuously, and we all know what came of that. Even with the Bmod I havent heard of anyone operating that way, but my approved AFM says do it all day long...no problem. Ya right!


Note: above procedures work nicely for me. I am interested in any input regarding my procedures, I love to learn, and I welcome constructive critism. I'm simply sharing my experiences which is what has made this site valuable to me. Take it with a grain of salt. Brian


 

  • Like 1
jetdriven Grand Master

jetdriven

Posted
Posted

According to this, if I am reading right, you change yor oil every 20 hours? If so, why? The manufacturer's recommended interval is 50 hours IIRC.

I haven't seen any data that a reduced power takeoff in a piston engine does anything to increase economy, safety, or longevity.  You could argue it reduces safety, as you are not making as high of a perfomrance takeoff or climb, and you are lower during takeoff phase than if you were full power takeoff. Lycoming IO-540s are rated at much higher horsepowers in different appilcations and they all do full power takeoffs as well.

Quote: kgbpost

I burn 1 qt/10 hrs so oil changes are easy...I fill to 9 qts, when it reaches 8 on the stick I add a makeup quart, when it reaches 8 again I change it.

The other technique I have experimented with quite inadvertently is reduced power takeoff. Since the boost controller requires the throttle full forward i may have inadvertantly found how to fool the controller into a reduced power TO. If the prop controller is left back 1/8" or so, The engine will maintain 2500 vs 2550RPM, but the suprising thing i found is the boost controller maintained a very comfortable 36" at 2500RPM, about 90% power. Plenty of performance under most conditions. I know we don't have tables and approved procedures for RTOP at this level, but under conditions where there is performace to spare (90% of the time in my case, and I live in Denver) It is In my opinion RTOP increases safety, comfort, longevity, etc.,. I dont use this procedure as I understand it may not be legal. I don't know. I suppose it all comes down to the way the airplane is certified to be flown. That said, this airplane was certified to be operated at 1750TIT continuously, and we all know what came of that. Even with the Bmod I havent heard of anyone operating that way, but my approved AFM says do it all day long...no problem. Ya right!

 

jetdriven Grand Master

jetdriven

Posted
Posted

If it will run smoothly with the richest cylinder 30-50 LOP, and your CHTs are cool enough give it a try.  Detonation kills cylinders and a CHT rising through the roof is a sign its beginning to occur.  You can  also try cleaning the injectors, maybe it will bring them closer in spread.

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