JPI EDM 450 Fuel Flow - Tune or Leave Alone?

[greghughes]

I recently purchased and had installed a JPI EDM 450 fuel flow computer. I flew with it running the past few days and then topped off the tanks to see how it performs.

This thing's pretty cool. Here's the verdict on fuel measurement for the first tank:

Computer says fuel used since tanks topped off: 34.2
Actual fuel required to re-top the tanks to the same level was: 32.5

A difference of +1.7 gallons, which means it measured just about 5% over actual - so not too shabby in my mind. I suppose I could tweak the k-factor to make it even more accurate if I want to, but I'm wondering how picky people tend to be? If nothing else, having a 5% margin in terms of extra fuel on-board due to a small measurement error can be a good thing, right?

What would you do? Adjust or leave it as-is?

 

[cirrusmx]

I recently purchased and had installed a JPI EDM 450 fuel flow computer. I flew with it running the past few days and then topped off the tanks to see how it performs.

This thing's pretty cool. Here's the verdict on fuel measurement for the first tank:

Computer says fuel used since tanks topped off: 34.2
Actual fuel required to re-top the tanks to the same level was: 32.5

A difference of +1.7 gallons, which means it measured just about 5% over actual - so not too shabby in my mind. I suppose I could tweak the k-factor to make it even more accurate if I want to, but I'm wondering how picky people tend to be? If nothing else, having a 5% margin in terms of extra fuel on-board due to a small measurement error can be a good thing, right?

What would you do? Adjust or leave it as-is?

sorry, to bash your new purchase, but it is really easy to be even more accurate using an e6b and still have the couple grand in the wallet.

 

[SCCutler]

My 450 is accurate to within a tenth of a gallon, in most instances. I say, tweak it up. You'll spot trends and trouble much more easily that way.

 

[N801BH]

I LOVE my 450........

I also run a multitude of fuels, from straight 100LL to straight auto gas,, The fuel scan module is sensitive enough to pick up the different specific gravity of the different gas.... 95% of the time I keep the mixture at 75% auto fuel that has Ethanol in it and 25% 100LL so I have found a average k factor the unit works best at.. The number is written down in my plane and I can get it for ya for reference...

Ps... About every five gas filll ups, I drain my fuel system completely and compare what is left with what the 450 says I should have. Properly calibarated the 450 is deadly accurate...

 

[greghughes]

sorry, to bash your new purchase, but it is really easy to be even more accurate using an e6b and still have the couple grand in the wallet.

Well, anyone who'd spend a couple grand on a EDM 450 should probably stick to E6B. Mine was less than a quarter of that and frankly. And there's no way I could determine how much fuel has actually been burned with an E6B.

And (sidebar here) it always strikes me as amusing how predictable the remaining portion of the sentence is when the author starts it with the words "Sorry ... but."

 

[greghughes]

My 450 is accurate to within a tenth of a gallon, in most instances. I say, tweak it up. You'll spot trends and trouble much more easily that way.

Will do. Can't hurt to get it closer to exact. And good point about trend tracking, had not thought about that.

I LOVE my 450........

I also run a multitude of fuels, from straight 100LL to straight auto gas,, The fuel scan module is sensitive enough to pick up the different specific gravity of the different gas.... 95% of the time I keep the mixture at 75% auto fuel that has Ethanol in it and 25% 100LL so I have found a average k factor the unit works best at.. The number is written down in my plane and I can get it for ya for reference...

Ps... About every five gas filll ups, I drain my fuel system completely and compare what is left with what the 450 says I should have. Properly calibarated the 450 is deadly accurate...

I'm not as into fuel blending or changing as you are, mine runs of 100LL and that's it. And while I probably won't drain my tanks, I am sure I will be measuring very carefully when I fill up and keeping track of the numbers each time. So, I will tweak the K-factor and keep watching the numbers!

 

[tmyers]

Greg, I think the 450 is a great addition to your airplane, I for one an enjoying the fact that the 700 I installed lets me know how much (calculated) fuel is left in the tanks when I fire it up. I have an E6B but it is not nearly as accurate as a simple calculator. The down side to both the calculator and the E6B is the fuel flow portion. the 450 and the 700 are recording an accurate fuel flow based upon time to give you the total fuel burned and fuel left. An E6B can't do that and the FF you put in the E6B is a guestimate at best.

I agree with SC tweak it.

YMMV

 

[Lance F]

Tweak it. That's what the K factor is for. Frankly every month I compare actual purchased with what my EDM says I used. This comparison is most accurate when one does complete top offs. Like Spike there's no reason not to have your accuracy within a couple of tenths.

And (sorry) I've had a very happy 2,500 hours or so never using an E6B other than for FAA writtens.

 

[poadeleted20]

My 450 is accurate to within a tenth of a gallon, in most instances. I say, tweak it up. You'll spot trends and trouble much more easily that way.

Concur, although mine's part of an EDM unit, not a standalone fuel device. Takes about 60 seconds to do.

 

[Skylane81E]

Agree with those who say tweak, get it right or take it out IMO.

The choice between the two is rather easy is it not?

 

[airdale]

Tune! Absolutely.

Been there, done that. The most important thing I learned is that "full" can vary quite a bit depending on the person doing the fueling. For a PA-28 with 48 gallon tanks. "full" can vary by a gallon or more (2-3%) per tank.

So, sorry to say, the +5% results from your one fill might be +1% or even -2% on the next.

So ... what you need to do is to log JPI readings and actual fill amounts for a longer period, like maybe 200 gallons. From those results calculate a new K factor. Then adjust that K factor to be slightly conservative, to taste. Maybe set it so the JPI gives you 10.2 gallons burned when it's really 10. That fudge reduces your risk that a tank might be under-filled a bit.

So what if it's underfilled? Well, if you have an airplane with multiple tanks like a Cherokee Six and you're on a long trip, you might want to burn tanks almost to fumes but not to the point where the engine quits and the pax get upset. Been there, done that too. IMHO having four tanks with three gallons each is not the same as having three tanks on fumes and one with twelve.

... fuel flow portion. the 450 and the 700 are recording an accurate fuel flow based upon time ...

Actually not. JPI uses a fuel flow transducer, almost certainly a turbine meter, that actually measures the flow. Each pulse from the transducer means a certain (minuscule) amount of fuel has passed through it. So they just have to count the pulses. Time has nothing to do with it.

... it is really easy to be even more accurate using an e6b ...

If you're using it as a calculator IMHO this is a ridiculous statement. If you have marked and calibrated it carefully to use as a dipstick, maybe. But how would you get it into the tank?

 

[Jaybird180]

I thought these devices were standard equipped with a FF measuring sensor.

 

[JOhnH]

If I am careful to fill each tank the same way each time, the FS450 is super accurate. But sometimes I am in a hurry and don't pack it as tight. Or sometimes I am planning a longer flight and pack in as much as I can. It can vary by a gallon or so.
If I pack it real tight then fly for 4 hours, I might use about 30 gallons. The 450 will usually say I burned ~29.8 to 30.2
But then if I fill it up in a hurry, I might only put in about 28. That can account for about a 2 gallon difference.
The moral of the story is to top off the same way every time, and at first don't use one fill up to judge. Calculate your difference over several fill ups.

 

[N801BH]

If I am careful to fill each tank the same way each time, the FS450 is super accurate. But sometimes I am in a hurry and don't pack it as tight. Or sometimes I am planning a longer flight and pack in as much as I can. It can vary by a gallon or so.
If I pack it real tight then fly for 4 hours, I might use about 30 gallons. The 450 will usually say I burned ~29.8 to 30.2
But then if I fill it up in a hurry, I might only put in about 28. That can account for about a 2 gallon difference.
The moral of the story is to top off the same way every time, and at first don't use one fill up to judge. Calculate your difference over several fill ups.

I must be different then most... I NEVER use the "top off" button.. I always insert the amount of gallons I added... On my last test of the 450 I was only off by 2 gallons in 400 gallons burned.. To me that is amazing the 450 can calculate that close....

 

[JOhnH]

I must be different then most... I NEVER use the "top off" button.. I always insert the amount of gallons I added... On my last test of the 450 I was only off by 2 gallons in 400 gallons burned.. To me that is amazing the 450 can calculate that close....

Your way is better. Mine is lazier. But either way, I am always amazed at it's accuracy. It has really helped us avoid quite a few unnecessary fuel stops because of our confidence in it over the old gauge that was only right at FULL or EMPTY and was a SWAG anywhere else.

 

[airdale]

I thought these devices were standard equipped with a FF measuring sensor.

The JPIs, at least, can be bought with or without fuel flow. To add it to an existing installation, you just add the fuel flow sensor.

 

[slacktide]

sorry, to bash your new purchase, but it is really easy to be even more accurate using an e6b and still have the couple grand in the wallet.

I had a carb problem and was using 2GPH more than book values when leaned per the POH for that RPM. It was blazingly obvious on my fuel flow, because I couldn't go leaner than 12 GPH without it stumbling. Coincidentally, this happened on one of the few long endurance flights that I make, and if undetected, I would definitely not have had enough fuel to make my destination.

How would your E6B method have detected this latent failure?

 

[JOhnH]

sorry, to bash your new purchase, but it is really easy to be even more accurate using an e6b and still have the couple grand in the wallet.

You may keep the money in your wallet, but you are not going to be more accurate.
There are a lot of things that those on this board do that would save us a lot of money if we didn't do them. Some people are even silly enough to buy an airplane with a parachute built in, or have all-glass cockpits.

 

[cirrusmx]

You may keep the money in your wallet, but you are not going to be more accurate.
There are a lot of things that those on this board do that would save us a lot of money if we didn't do them. Some people are even silly enough to buy an airplane with a parachute built in, or have all-glass cockpits.

i fly one of those with the parachute. LOL

i would never sretch a flight to were i need to rely on the fuel totalizer to within tenths of a gallon, thats illegal . To play it safe, one hour reserve on the cirrus at 75% power would mean three hour legs. Also, i fill up 92 or 64 gals and take it from there. with my burn rate calcs i am pretty darn accurate; way more than i care for.

 

[greghughes]

... i would never sretch a flight to were i need to rely on the fuel totalizer to within tenths of a gallon, thats illegal ...

Yeah, neither would I, ever. That's not why I installed it. The fuel flow meter lets me know how much fuel - in gallons per hour - I am burning at that moment. It amazing how much a little leaning and a tiny throttle adjustment makes when you can see it in real time. The main reason I installed it is to allow me to have more information about the actual behavior of the airplane systems, in addition to the calculated planning information. If used well, more information - especially about fuel usage and availability - can be a very good thing.

• Metered fuel used since last fill/add
• Metered/calculated fuel remaining in tanks
• Metered current fuel burn in GPH
• Caluclated fuel until empty at current burn rate (in hours/minutes)
• Alerts for low gallons and low fuel time remaining
• Using GPS connections, gallons to destination or to next waypoint (at current burn rate)

I also check fuel levels manually and know how much is there (and that there's no water in the tanks), and I won't put blind trust in the computer. I do manual fuel calculations in planning before I fly. It's the combination of information that makes the EDM 450 (and similar instruments) worthwhile, IMHO.

 

[greghughes]

I had a carb problem and was using 2GPH more than book values when leaned per the POH for that RPM. It was blazingly obvious on my fuel flow, because I couldn't go leaner than 12 GPH without it stumbling. Coincidentally, this happened on one of the few long endurance flights that I make, and if undetected, I would definitely not have had enough fuel to make my destination.

This is a *great* example of exactly why fuel meters can be so useful. Long cross countries where the fuel is burning faster than you realize due to an undetected malfunction = Bad News.