Engine Monitors

[INA201]

I'm in the process of upgrading from a JPI700 without fuel flow to a JPI900 with all the goodies.  While reading the manual I became curious about k-factor, fuel flow accuracy, fuel used, MPG, and percent power.  Are you guys who have a modern engine monitor pleased with the accuracy of the parameters above?  Any tips? 

Thanks

[Bob_Belville]

13 hours ago, INA201 said:

I'm in the process of upgrading from a JPI700 without fuel flow to a JPI900 with all the goodies.  While reading the manual I became curious about k-factor, fuel flow accuracy, fuel used, MPG, and percent power.  Are you guys who have a modern engine monitor pleased with the accuracy of the parameters above?  Any tips? 

Thanks

I've had a 930 in a '66E for 5 years. The FF is extremely accurate. I set up a spread sheet to track actual fuel purchased vs. JPI USED for 10 fill ups and adjusted the K factor. I've continued to maintain the spread sheet and find the JPI is within 1% of actual. That's less the 1/2 gallon which is well within the variation of filling the tanks.  The MPG is a simple division and is accurate. The % power works great as well, I have not changed the power factor since my original calibration flight and it shows a value that matches the OM charts over a wide range of power settings. I run LOP most of the time and the % power LOP matches the formula for LOP which is 10 gph = 75% (200 hp engine). 

I know only the 930 so I can't compare but imo the 930 does everything you'd need. And I suppose the 900 is identical except for the inferior display screen.

Edited January 17, 2018 by Bob_Belville

[gsxrpilot]

9 minutes ago, Bob_Belville said:

And I suppose the 900 is identical except for the inferior display screen.

Correct 

[N6758N]

16 minutes ago, Bob_Belville said:

I know only the 930 so I can compare but imo the 930 does everything you'd need. And I suppose the 900 is identical except for the inferior display screen.

Hey now Bob! Some of us have to go through life with inferior sized things, I found your comment about my puny little 900 screen highly offensive. 

[Bob_Belville]

Size envy. What can I say? If you've got it, flaunt it. 

[gsxrpilot]

I actually think the screen sizes of the 930 and 900 are a wash. If you install a 930, it will be on the right side of the panel, and far away from the pilot therefore the large screen is important. If you install the 900, it can go on the left side of the panel directly in front of the pilot and therefore the large print edition isn't required and the small screen is just perfect.

[N6758N]

Yeah, what Paul said...

[Bob_Belville]

This debate has been cycled through MS several times.

Suffice to say we're all 3 fans of robust EDMs who do not agree about what information should be in the primary scan, field of vision.

Without debate, EDMs are not present for AVIATE, NAVIGATE, or even COMMUNICATE. (And Paul, as an avid formation flyer, knows that his plane will not instantly disintegrate even if he does not constantly scan the OAT.)

But hey, it's your privy.

[jlunseth]

I have the 930.  The fuel flow is extremely accurate, 0.1 gal. out of 50 gallons used.  I am less enamored with the %HP.  It is an algorithm, and JPI does not disclose the formula.  It also depends on which type of lean function you choose, LOP or ROP.  This makes sense, because LOP, the %HP is dependent on fuel flow and not MP, and ROP it is dependent mainly on MP.  However, I don’t bother with the LOP lean function most of the time, it is not very accurate in my aircraft, too many things are changing so the peak point, by the time you get to a degrees-LOP reading, is not valid any longer.  If you don’t bother changing to LOP leaning when you operate LOP, then the %HP will be reading %HP ROP and not LOP.  On the ROP side, my %HP is off by a fair amount, probably 6 or 7 percentage points. The fuel gauges are not particularly accurate, but that is because they depend on the senders in the tanks, and I have the original factory senders.  

[Bob_Belville]

@INA201, seriously, note that in the pic of my 930 above, that the FF and % power agree for the LOP condition I'm running. (The EGT graphs with the bars coming from the top down indicate the deg F LOP for each cylinder. 

[Bob_Belville]

3 minutes ago, jlunseth said:

I have the 930.  The fuel flow is extremely accurate, 0.1 gal. out of 50 gallons used.  I am less enamored with the %HP.  It is an algorithm, and JPI does not disclose the formula.  It also depends on which type of lean function you choose, LOP or ROP.  This makes sense, because LOP, the %HP is dependent on fuel flow and not MP, and ROP it is dependent mainly on MP.  However, I don’t bother with the LOP lean function most of the time, it is not very accurate in my aircraft, too many things are changing so the peak point, by the time you get to a degrees-LOP reading, is not valid any longer.  If you don’t bother changing to LOP leaning when you operate LOP, then the %HP will be reading %HP ROP and not LOP.  On the ROP side, my %HP is off by a fair amount, probably 6 or 7 percentage points. The fuel gauges are not particularly accurate, but that is because they depend on the senders in the tanks, and I have the original factory senders.  

I agree with this analysis of % power. So I do use the LOP Lean Find function to get the info displayed above. FWIW, I just replaced the old resistive float senders with the digital CiES at the same time I increased the bladders to 64 gallons usable. I made one flight so time will tell but I suppose they will be more accurate. It will be a while, I am now down for a few weeks to convert to @Sabremech's beautiful cowl.  

[FloridaMan]

Fuel flow is extremely accurate (within 1 gallon over 50+ gallons consistently; that puts it within pump and top-off tolerances). You'll probably need a snubber in the line for the manifold pressure line. There are a couple annoying things. First, when I cut power to land I get a yellow warning light when oil pressure drops below 60psi, even though it's technically "in the green." The second, and even more annoying thing, is that the fuel pump on my new engine is in spec, but the original panel instrument had a FP limit of 30psi, even though the engine limitation is 45psi. When at idle or reducing power, FP goes as high as 31PSI and I get a red blinking warning during critical stages of flight. This is stupid, asinine, and puts me at increased risk in that I have a blinking red warning light during critical stages of flight and creates a situation where I have the option of being unnecessarily distracted to verify and clear the error, or that I become complacent with a red warning light. 

Edited January 16, 2018 by Antares

[jaylw314]

The accuracy of fuel flow meters is based on the fuel pressure in the fuel metering system, which is supposed to accurately reflect the fuel flow.  I suppose there are ways this can fail, but practically it is very accurate.  My refueling technique is probably off by +/- 1.5 gallons, which is greater than the error from the fuel flow.  Of course, getting the K-factor dialed in takes a few tries, but if you do it like Bob's post, it should just take a few flights to be very accurate.  I didn't, I just adjusted it halfway each time over a few refuels (If my current K-factor is 72.0k and I calculate 73k from a refuel, I adjust it to 72.5k), and I'd estimate I'm within +/- 1 gallons now.

[larryb]

Old analog flow meters are pressure based. Modern electronic ones use a transducer which gives a pulse for a fixed amount of fuel. The monitor just counts the pulses.

[jlunseth]

I am pretty sure i have the old style paddlewheel sensor for fuel flow.  It is highly accurate.  There is a calibration process that your mechanic must do correctly to result in a good reading.  When I first got my JPI, the pilot could access and tweak that process, but I noticed that after a firmware upgrade it was grayed out, so only my mechanic (a JPI dealer) can access it.  It matters little for me, mine is set properly.

The “sender” issue applies generally to the 930 series.  Many of the sensors are supplied and installed with the JPI.  In combination, they will result in more sensitive readings.  My old factory RPM gauge, for example, would not have “seen” a difference between 2700 RPMs (redline) and 2710.  My JPI can see that.  Where the factory senders are still in place, such as for fuel, the JPI readout will be exquisitely accurate, but it can only tell you what the senders tell it. 

The problem with the Lean Find function is the design of my aircraft.  The MP and fuel flow are interlinked, so if you change one, the other changes with it to attempt to maintain the original fuel/air ratio.  To use the lean find function in my aircraft, you would start over on the rich side with a setting and then lean over to the lean side, after choosing LOP leaning on the JPI.  It is so far to go, and the MP is changing as you lean the fuel flow, that by the time you get to what appears to be your desired lean of peak point (say 20 degrees lean of peak) the peak point is no longer valid.  It is just easier for me to do the “big pull” over to the lean side and use the settings that I know work, or to do the leaning by setting up what I think is a good LOP setting and then enrichen back to peak, and then back lean again if I want to know how many degrees lean I am.  One actually uses the ROP lean function to do this, because it determines peak as the first cylinder to peak (LOP leaning uses the last cylinder), and of course then I am on the lean side with the JPI set to ROP leaning so the %HP reading is meaningless, it is using a ROP alogrithm to determine %HP.  Mine is a turbo.  Turbos that maintain MP as the fuel flow is leaned out, will not have this issue.

It is worth saying that the ROP and LOP lean functions in the JPIs have nothing to do with whether you are actually lean of peak or rich of peak.  They are only labeled that way.  ROP leaning means “first cylinder to peak,” LOP leaning means “last cylinder to peak.”  The monitor does not know if you whether the engine is actually on the rich side or on the lean side.

Edited January 16, 2018 by jlunseth

[xcrmckenna]

Upgrading from an 830 to a 900 should the K factor be the same?


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[Marauder]

26 minutes ago, xcrmckenna said:

Upgrading from an 830 to a 900 should the K factor be the same?


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Only if you re-used the same transducer.

[INA201]

Thanks for all the feedback!  Looks like %HP is the trick to make accurate. I didn't have fuel flow before so I'm guessing using fuel flow whether LOP or ROP combined with MP and RPM will yield a better %HP than the JPI900?? 

[carusoam]

Summary...

1) Accuracy from a 700 to 900 series should be very similar...

2) The 900 May be more quick with its computing power.

3) things that can cause variations... K factor for the FF / totalizer. Kfactor needs to be calibrated and set the first time... it can be sensitive to installation.  Length of straight pipe in and out, far from 90° bends.  Read the installation instructions...

4) %BHP For LOP is a direct calculation of FF. If FF is calibrated then %LOP will be as well.

5) %BHP for ROP is at best a real guess...  a certain portion of fuel is used for cooling, not for hp.  The device has to calculate the FF for the number of °ROP, the change in FF, since peak.  This would require actually going through peak each time, which isn't typically done on the climb out, until leveleling off... it could make estimates based on usual °F ROP...  their calculation has evolved over time...

Heck even the Continental pilots don't know the %BHP... If it is based on 280, 310, or 100% of 500+ hp...

6) Using MAPA Numbers Of MP + Rpm/100 work close enough for defining the transition to LOP...  The 65% guideline often used...

7) expect some installation glitches from wiring.  Most signals are tiny voltages, the oilT is a tiny current running through a temp sensitive resistor.  Noises from ignition wires can be a problem...

8) The 900 is a more modern, more powerful computing device and has tested and proven robustness for use as primary instrumentation.

9) Like The 700 before it, you want to watch how it works before relying on it.

10) learn how to download the data and print its graphs.  You can see immediately everything working as expected, or not.

Post some graphs and photos...

 

best regards,

-a-