Tips on Bravo MAP and RPM at various altitudes?

[kgbpost]

Quote: jetdriven

[jetdriven]

What is Scott's reasoning that the Lycoming, Continental, and Mooney don't know?  To consider the source, the more oil changes you do the more they bill you.

25 hours is an old tradition from before full flow oil filters. Engines just had a screen then.

Quote: kgbpost

 Scott at Arapahoe Aero recommended every 25 hrs for this enigine. my attitude is oil is cheap.

 

[kgbpost]

Quote: Shadrach

 Really? What should it be at 100% power?

[kgbpost]

Quote: jetdriven

 

[Shadrach]

Quote: kgbpost

[Parker_Woodruff]

400 dF is too hot, even if you're ROP.  Get that takeoff fuel flow handled.  Numbers per Shadrach are 28-29 GPH, but I've seen setups around 31 GPH.

[Shadrach]

Quote: Parker_Woodruff

400 dF is too hot, even if you're ROP.  Get that takeoff fuel flow handled.  Numbers per Shadrach are 28-29 GPH, but I've seen setups around 31 GPH.

[kgbpost]

Quote: Shadrach

More is probably better as you've stated. You can always pull the mixture knob back a bit if you don't need it, but you can't push further than the the stop when you need more... 

[kgbpost]

Quote: kgbpost

More is probably better as you've stated. You can always pull the mixture knob back a bit if you don't need it, but you can't push further than the the stop when you need more... 

[Shadrach]

Quote: kgbpost

More is probably better as you've stated. You can always pull the mixture knob back a bit if you don't need it, but you can't push further than the the stop when you need more... 

[kgbpost]

Quote: kgbpost

[Shadrach]

There are a lot of factors to account for in the combustion process. It is possible to make less power in a more abusive way with an AC engine. High internal cylinder pressures (ICPs) translate to heat and fatigue. An engine can make a given power level by achieving a high peak ICP with relatively low mean ICP through the power stroke or with a lower peak ICP and a relatively higher mean ICP (peak and mean are closer to the same value). Which do you think is better for the engine for a given HP, the hammer, or the steady push? This is the reason most who've studied combustion science on some level recommend avoiding ~50ROP,  it is the best way to hammer a combustion chamber and piston.

There''s a lot more to the story than just HP numbers.

Watch you CHTs the next time you do a RTOP and tell me what you see. It probably won't be dramatic nor easy to normalize as OATs are different every day. You may or may not see a CHT bump from the reduced RPM. The reduced MP may negate any CHT rise, but it is possible that you're not being as kind to your engine as you think you are.

[kgbpost]

Quote: Parker_Woodruff

That fuel flow is much too low for an M20M.

[kgbpost]

Quote: Shadrach

There are a lot of factors to account for in the combustion process. It is possible to make less power in a more abusive way with an AC engine. High internal cylinder pressures (ICPs) translate to heat and fatigue. An engine can make a given power level by achieving a high peak ICP with relatively low mean ICP through the power stroke or with a lower peak ICP and a relatively higher mean ICP (peak and mean are closer to the same value). Which do you think is better for the engine for a given HP, the hammer, or the steady push? This is the reason most who've studied combustion science on some level recommend avoiding ~50ROP,  it is the best way to hammer a combustion chamber and piston.

There''s a lot more to the story than just HP numbers.

Watch you CHTs the next time you do a RTOP and tell me what you see. It probably won't be dramatic nor easy to normalize as OATs are different every day. You may or may not see a CHT bump from the reduced RPM. The reduced MP may negate any CHT rise, but it is possible that you're not being as kind to your engine as you think you are.

[KSMooniac]

I'll put in another plug on this forum for the Advanced Pilot Seminar (www.advancedpilot.com) as it is the single, most-informative way to learn all about operating a piston aircraft engine.  You guys running turbos should especially be interested as there is a greater opportunity to do harm to the life of the engine, and the seminar will teach you more than you can imagine...

[johnggreen]

Ross,

What you said about TIT's, and EGT's was pretty much my understanding; like I said, the fellow at GAMI pretty much shrugged his shoulders and said the only relevant numbers were the temps where peak came for each cylinder.  As I think I said, my peaks are all pretty similar.  Interestingly, to get to peak EGT's without going over 1750 TIT, you have to do your peak test at low power.

Now understand, that I don't ever fly at peak TIT. I fly at 1650 except in climb.  At the low, long range, setting of 2200/28, peak TIT is usually just over 1650, maybe 1665 or so.  CHT's are never a problem.

As to problems.  About four years ago, during annual, the shop, Mooney shop, said I had some oil coming out of the #2 exhaust. The concensus was from the shop, Lycoming, and Coy Jacobs that it was from a metal gasket or ship that has something to do with the oil cooling.  To make a long story short, we tried several things and nothing worked.  Finally, my real mechanic, not the Mooney shop, suggested having the cylinder redone, which we did at John Jewel's.  Don't know about the shim/gasket, but did have some excess wear around the exhaust stem.  Problem solved.  For the benefit of other Bravo owners, if you start seening raw oil inside your cowling, check your exhaust manifold.  No, I would not have suspected it either.  

JG

[johnggreen]

KGBPOST,

Brian,

I read your post on how you fly your Bravo.  Concur with everything except, compared to me, you run your engine very rich.  Or maybe compared to you, I run mine lean.  The POH gives 1650 as best power and that's where I run it.  Doggone if it doesn't work too.  Go either way and I seem to lose a few knots.

My CHT's are just never an issue, never.  Hardly ever see 370 which I believe is due to a really good job of baffling when my engine was overhauled as a result of the crankshaft AD at 500 hours.

I have spent my life in the construction business. Sold out a few years ago, but still have a good bit of equipment on my farm---yes mostly diesels, but I have owned about a million gasoline generators, tamps, saws, fans, etc.  I have, after all these years, come to the conclusion that for every power setting, there is an appropriate mixture; too rich is just as bad as too lean.

Please don't take me as the guru, but I think you should work toward leaner settings and see how the corresponding numbers of your engine respond.

On a common note, I too lean aggressively on the ground and never have a fouled plug.

JG

[kgbpost]

John,

I'm going flying tomorrow (rediculously nice flying weather here right now). I'll post some solid #s at various settings and we can all compare. Tightening up the baffling would be an excellent place to start to get the temps down I agree.

On my 91 the old style mech guages are junk (sorry, they are!) I'm relying on my EDM-830 and it doesnt always agree with what the steam guages say. I do know the EDM830 says my TIT and CHT are hotter than what the old style guages indicate.

I Farm...same as Construction... we just make less.... until recently anyway. I did fly for the Airlines for awhile...they almost cured me of aviation...but I'm back on the farm now, and back in love with flying again. Cheers. Brian

 

[Shadrach]

Brian, if you think the gauges out of your 91 are junk you should see the fuel and CHT gauges that came in my 67 F compared to what the EDM says... There a joke, I'd fly without the EDM if I had to, but I'd be nervous and antsy with the lack of information.

[johnggreen]

Brian,

Even with the more modern guages of my 2000 Bravo, they don't fully agree with the EDM, but won't go into that now.  Two points I would like to make that may help you.

Regardless of what the guages say, you can pretty easily figure out if your cylinders are peaking at about the same time.  Pick what you think is your first cylinder to peak and peak it.  Then go to others one at a time and just see about how much leaning it takes from the first to peak to each of the others.  Any guage reading will help as you do this because you are really just looking for relationships.

CAUTION:  Don't start looking for peaks except at low power settings, like 26 inches or less or your TIT #'s will go out of sight.

Secondly, get out your Lycoming Owners Manual and study the charts for your engine.  I think they will give you some good references that you may be running too rich.  What they will tell you is that most operators are running their Bravo's at pretty high power settings.  It would seem from chart 3-84 that 75% at some altitudes and temps may come as low as 2400/28".

I know that in my Bravo, 2200/30" @ 1650 is a real sweet spot.  Smooth, quiet, fast, and efficient.

Familiarize yourself with the LOM and go play.  I think I'm going to shoot some approaches under the hood so we'll both have some fun.

Oh yea, now I'm ranching so I suppose we have a lot in common.  Cutting hay for Texas today.  No, I"m not goughing.

JG

[kgbpost]

Heres what My 91 Bravo did on a test run today. I didn't have as much time as i'd hoped but I did several readings at several mixture settings. I must start by saying that i think my TIT probe may be suspect...I believe it may be reading 50dF+- low. Everything else seems to jive. It sure runs smooth and seems happy.

Also, to correct my previous post it did make 29.2GPH FF at 100% Power today.  OAT at 9,500 was 65F today and these numbers are all with cowl flaps fully closed. I wish I had time to go higher but i just went east at 9500 and took readings at 30"MP and then turned around and climbed to 10500 and took reading at 32". Heres what i saw:

*Note: the #5 CHT shares probes with original guage so EDM indicates low on #5 CHT by 80Df or so.....

PA 9,200', OAT 64dF, GW 3100

RPM 2400 - MP 30",  Peak TIT; 1697dF at 16.6 GPH,  Peak EGT cyl 6; 1510 dF,  OilP; 71psi,  Oil Temp 202dF

Cruise Setting: FF 18.5 GPH       results: TAS 184KTAS     TIT 1545dF

cyl#) EGTdF/CHTdF       1) 1415/399    2)1405/379    3)1408/399   4)1421/394   5)1409/311*   6)1398/392

As the old saying goes "your mileage may vary". I do know from my experience so far I could slice a good .5 GPH on a cooler day. It was 64F at 9,500' on the Last day of September at 11 in the morning...La Nina I guess?

As you can see I'm running 100dF ROP +/- and all CHT are under 400dF. Also note the 23dF EGT spread which I believe to be good for no-GAMIs. Regardless of the suspiciously low TIT the engine seems to be happy here.

I did various runs today but one that may be of interest was another LOP try. The EDM-830 is sweet for this...too bad i wont get to use it!... By the time I got the Richest clylinder to 40dF LOP it started an extra rythm, like a slight miss, and that was it for me. The FF was down to 12.6GPH. I don't know how far they say you want to run LOP on the Richest cylinder but I wanted to see at least 50 to be comfortable but couldnt get there. CHT's were low.

Honestly I'm pretty happy with the numbers it ran ROP at 9'500.

FYI - I gained 5 KTAS running at 32"MP vs 30" and burned another 1.0 GPH.

I will look into getting a new TIT probe on order. I'm sure theyre not cheap but thats the only thing I'm suspicious of at this point. I don't want to get burned by parts scarcity so I'm planning ahead. Thats probably a supplier part anyway?

And thanks again for the insights from all the knowledgable folks in this forum.  Fly safe. Brian

 

 

[Shadrach]

Quote: kgbpost

Heres what My 91 Bravo did on a test run today. I didn't have as much time as i'd hoped but I did several readings at several mixture settings. I must start by saying that i think my TIT probe may be suspect...I believe it may be reading 50dF+- low. Everything else seems to jive. It sure runs smooth and seems happy.

Also, to correct my previous post it did make 29.2GPH FF at 100% Power today.  OAT at 9,500 was 65F today and these numbers are all with cowl flaps fully closed. I wish I had time to go higher but i just went east at 9500 and took readings at 30"MP and then turned around and climbed to 10500 and took reading at 32". Heres what i saw:

*Note: the #5 CHT shares probes with original guage so EDM indicates low on #5 CHT by 80Df or so.....

PA 9,200', OAT 64dF, GW 3100

RPM 2400 - MP 30",  Peak TIT; 1697dF at 16.6 GPH,  Peak EGT cyl 6; 1510 dF,  OilP; 71psi,  Oil Temp 202dF

Cruise Setting: FF 18.5 GPH       results: TAS 184KTAS     TIT 1545dF

cyl#) EGTdF/CHTdF       1) 1415/399    2)1405/379    3)1408/399   4)1421/394   5)1409/311*   6)1398/392

As the old saying goes "your mileage may vary". I do know from my experience so far I could slice a good .5 GPH on a cooler day. It was 64F at 9,500' on the Last day of September at 11 in the morning...La Nina I guess?

As you can see I'm running 100dF ROP +/- and all CHT are under 400dF. Also note the 23dF EGT spread which I believe to be good for no-GAMIs. Regardless of the suspiciously low TIT the engine seems to be happy here.

I did various runs today but one that may be of interest was another LOP try. The EDM-830 is sweet for this...too bad i wont get to use it!... By the time I got the Richest clylinder to 40dF LOP it started an extra rythm, like a slight miss, and that was it for me. The FF was down to 12.6GPH. I don't know how far they say you want to run LOP on the Richest cylinder but I wanted to see at least 50 to be comfortable but couldnt get there. CHT's were low.

Honestly I'm pretty happy with the numbers it ran ROP at 9'500.

FYI - I gained 5 KTAS running at 32"MP vs 30" and burned another 1.0 GPH.

I will look into getting a new TIT probe on order. I'm sure theyre not cheap but thats the only thing I'm suspicious of at this point. I don't want to get burned by parts scarcity so I'm planning ahead. Thats probably a supplier part anyway?

And thanks again for the insights from all the knowledgable folks in this forum.  Fly safe. Brian

[johnggreen]

KGBPOST

Your numbers look pretty good to me.  Speed/fuel almost exactly same as mine.  I do think you need to address baffling though.  I doubt that I would have seen 360 CHT under those conditions.

JG

[Robg]

Quote: jetdriven