bsfc for lycoming io-360?

[haymak3r]

I've noticed with my gi-275 eis, that I don't have the %hp reading. I believe during the setup, that there was a field that was missed so that not all the parameters were met to provide that percentage.

I believe it is the bsfc. in the install manual there is a given number:

Minimum Brake Specific Fuel Consumption
◦ Defaulted to 0.39 lb/hr/BHP

I can't for the life of me find this number. 

 

This is what I found for what is required to get the % power:

Percent Power requires the following gauge inputs: RPM, Manifold Pressure, Fuel Flow, and OAT, as well
as inputting the Max Rated Horsepower, Max MAP, RPM at Max HP, and the Minimum Brake Specific
Fuel Consumption (BSFC). Refer to Section 5.7.1 for engine configuration settings.

 

Either the bsfc or maybe the OAT??? is missing. I get OAT from my G5. Im not sure if I've seen OAT on the 275... 

 

Any help would be awesome!

 

Thanks,
Chris

[N201MKTurbo]

You should be able to calculate it from the operators manual. Take the 100% power fuel flow, convert it to Lbs. and divide it by 200.

You might get a better number by using a lean cruise power setting.

[haymak3r]

Thanks. I see now that this was easier than I was making it out to be, lol.

From my POH, at sea level, best power gives me 110.5 lbs/hr for fuel flow. This gives me a bsfc of .5525.

 

But, you're saying I would be better off using a lean cruise power setting? Would I want to use the economy cruise @ sea level numbers? Or use and actual cruise alt that I normally cruise at.

Sea level would yield = .325

Cruise at 10k = .3075

 

Thanks,
Chris

 

[N201MKTurbo]

Those are all good questions. I don't know the answer. It all depends on the algorithm in the scanner. I would contact Garmin for clarification.

Your lean numbers are closer to their default number. FWIW 

[AH-1 Cobra Pilot]

31 minutes ago, haymak3r said:

Sea level would yield = .325

Cruise at 10k = .3075

Although I have not looked at the IO-360 specifically, I can tell you those numbers are way too low.  A large CAT diesel, which is very efficient, will get a BSFC of about .34, while a turbine/turbo-shaft will be about .43.  You could expect something between those, probably about .39.

[jaylw314]

The number I hear tossed around is that best hp/gal in an IO-360 (8.7:1 compression ratio IIRC) is 15.  That's a BSFC of 0.40 pph/hp.

FWIW, I wouldn't trust the % HP reading on any monitor for precision measurement unless I knew HOW it was calculated.  It seems monitors have two ways of calculating %HP:

• Some kind of proprietary and secret algorithm
• Some correction factor times fuel flow 

If it's the latter, it makes sense to use a correction factor based on how you typically cruise, so if you cruise at best power, figure your hp/gal at best power.  If you cruise LOP, figure your correction factor for that.

I don't know the GI-275, so I'm not clear which way it goes.

[haymak3r]

Completely agree, and have read that before too, which is why I am not fully understanding how this plays in to that % power representation.

 

For the numbers above. It is not 100% power, rather in the poh, sea level at econ cruise yields 75% power, and at 10k, it is 70% power. I may go with the sea level best power number of .5525, and then if the % power number shows up on the display, I will pull power, and note the % power versus what the book says I should be at for that given power setting. Thoughts on further adjusting the number to match what the book says? I sort of feel that the numbers in the poh may not be as accurate as real world power. Maybe closer if the engine were 'fresh'.. but at least it's a starting point I suppose.

[haymak3r]

Ok. I waited the hour and spoke to garmin...

The calculation wants a bsfc of best power at normal cruise altitude to be provided. As with anything from a support org, I will take that with skepticism, and test test test. 

And with that knowledge I will have .3775 put in. And see if the % power field shows up.

 

Cheers!

[0TreeLemur]

Found this bit of marketing on the interwebs:

 

[haymak3r]

I checked the config, and I had a BSFC listed already. It was set at .38, so basically what I was going to use.. I am missing OAT. That's the problem. I need to have my avionics guy connect the g5 to the gi-275 I think, to get the 275 OAT.  Wish this was done during install. 

[jlunseth]

I don’t have the engine EIS but I have the ADI and there is an auxiliary number. You get to choose one thing to put in that little block and there are lots of choices. I use TAS. That might be the number you are looking for but numbers for the EIS. Should be in the manual.

[Shadrach]

I think .38 is optimistic but close to best BFSC.  The reality is that using a BSFC input to calculate power is not very precise as BSFC varies significantly across the mixture spectrum. I picked two random 100 ROP settings from my POH and the calculations yielded .436 and the other .446.

[haymak3r]

Thanks. Once I get the oat sensor installed, I'll start seeing about how close it is based off my poh.. If it is 1-5% off to me that is good enough. I really want to just make sure that I am not leaning above the 75% range. More of a safety factor than anything else. I fly fairly low sometimes while training, and so I can easily be above 75% even with some power pulled. As time goes on, I am sure I'll be able to remember more power settings with altitudes to know when it is safe to really lean out or not.  But that time has not come yet haha.

[Ragsf15e]

On 2/1/2023 at 3:18 PM, haymak3r said:

Thanks. Once I get the oat sensor installed, I'll start seeing about how close it is based off my poh.. If it is 1-5% off to me that is good enough. I really want to just make sure that I am not leaning above the 75% range. More of a safety factor than anything else. I fly fairly low sometimes while training, and so I can easily be above 75% even with some power pulled. As time goes on, I am sure I'll be able to remember more power settings with altitudes to know when it is safe to really lean out or not.  But that time has not come yet haha.

I agree it’s useful as a check.  My jpi % power seems pretty close to the poh when ROP and it’s really close LOP.  I don’t know what the use as an algorithm ROP, but if you use lean find-LOP, they must just be multiplying ff by ~14.5?

I hop it works for you!

[carusoam]

We kinda have enough data we can calculate a number to work really well…

Most people want enough accuracy so when the instrument is showing 65%BHP we know we are safe to go lean…

Otherwise, what else are we using the bhp number for?

1) T/O power?  MP, RPM, FF…  bhp is implied…

2) Landing power? MP, RPM… 

The ROP %bhp numbers are always going to be suspect… because we don’t have an air flow sensor… we have an MP sensor that kinda works, just not the same…

The LOP %bhp numbers are dead on… because we use an accurate FF gauge… the limiting part of the AF ratio in the LOP regime…

Are we just looking for a more accurate number to display, because we have the display?

Best regards,

-a-

[haymak3r]

Originally, I was thinking this number was not put in to my config, and that's why I didn't have the %power at all. But it's the OAT senser. Once that is installed, then I should be good to go.

 

Cheers!