fuel flow accuracy

[jamesm]

I have an EI CGR30C&P with EI Fuel Flow sensor I had changed over the years  from a Insight G3 then to CGR30C but had the Insight Flow sensor a few years ago swapped it to EI Fuel Flow sensor in a '67 M20C carburated engine. I usually only fly about 1hr to 1.5 hrs occasionally do the longer flights were I require fill up to get to my finial destination.  I am seeing about 1 gal to maybe at the worse 2 gallon difference between Fuel totalizator and the actual tank quantity reading .  I have played with fuel flow K-factor before but found it real time consuming for the results that I was seeing. So I am curious to know other people's with their various Engine Monitor  installations and setup's  what kind of fuel flow accuracy Fuel totalizator versus  Fuel Quantity after a flight?

 

Thanks in Advance,

James

[vik]

The worst I have seen was 0.5 gallons to the tank. Usually within 0.3 gallons. It took about 4 changes of the k-factor to get to it. I did not find it too time consuming. Just calculate the coefficient, than new k-factor and put it in. Very simple.

Vik

 

[Tim-37419]

JPI has a spreadsheet on their website to help adjust the kfactor.

 

 

[oregon87]

Easiest method to adjust the k-factor is as follows:

 

1. Fill the tanks.

2. Program the CGR-30P for full fuel.

3. Fly for an hour or two, leaned out in cruise.  As fuel flow is not linear, it's not beneficial to go knock out a bunch of touch and goes for an hour in an effort to dial in the k-factor.  You want to do so where the aircraft will be spending the majority of its time.

4. Upon landing, note the fuel the 30P calculated was used.

5. Refill the tanks.  This is the actual amount used.

6. Using your existing k-factor, the formula below can be used to calculate a new k-factor to be entered manually.

 

Calculated Used x Current K-Factor

---------------------------------------

                  Actual Used

 

After a few flights and adjustments, you should have it pretty well dialed in.  Many owners are happy with the accuracy of the total fuel to .5 gallon, others have worked the process to .1 gallon.

 

As always, if you have any follow up questions, feel free to message me.

 

Dave

[MikeOH]

One more data point: I have a EI FP-5L.  My tanks hold 64 gallons, I usually fill when I get down to 20 gallons, so 44 gallons to fill.  I'm typically off between .5 and 1 gallon.

[FlyingDude]

Pump counters are calibrated to standard temperature (60F in US I think). That's because the energy is in the mass, not volume. The density changes by 3% with 20C change in temperature.

https://ised-isde.canada.ca/site/measurement-canada/en/laws-and-requirements/volume-correction-factors-aviation-gasoline

This is assuming that pumps are functioning perfectly as intended.

So when you pay for 50gl in Michigan winter at -10C you pump 48.5gl whereas in the summer with 35C temp, you pump 51.5gl. My jpi 700 is usually spot on between December-February. In other periods, it shows higher consumption (actual pumped fuel less than fuel consumption on jpi). I'm not sure if the computer compensates fuel flow counters (k is 30000 etc pulses per gallon) for temperature. Though fuel temp will not match ambient temp after the plane sat under the sun for a bit. Not to mention, my jpi oat sensor is located in the air scoop and reads 5C higher than the Garmin probe out in the outboard...

[Pinecone]

Pumps pump gallons.  So when you put 50 gallons in the airplane, you put 50 gallons in.

But if you put 50 gallons of fuel at -10, if you were to warm it up to +20, you would have 51.5 gallons.

But we burn fuel by the pound, and since we do lean, you should be getting the same performance (range) for the same pumped volume.

[jlunseth]

I have used the procedure Oregon87 outlines. It works well. I haven’t done it for awhile because everything is working well. I have CiES senders and a JPI930. I still find that fuel flow is the most accurate method of determining how much fuel is in the tank, but you also need to measure the tank, that is, run it nearly dry and fill it yourself. You can’t just assume the factory number is accurate.

[Marc_B]

I have aux tanks so this makes it difficult to really accurately have a reproducible known fuel amount. I go to full fuel in both the main and aux, let it sit for 15 min and it’s an inch lower in the aux. put another gallon in, wait another 15 min…put more fuel in. So I tried to do this the other day just out of curiosity and FF showed I burned 17.5 gal, but I put in 17.1…but if I waited longer I’m sure I could possibly have added more. Current K-factor was 61150. Not sure if this was just number from install?
For those with Monroy aux tanks…what is the most accurate way to adjust K factor?

My thought was maybe deal with sub aux tank fuel quantity and a stick measurement. Not quite sure what’s the most fuel I can add before any fuel goes into the aux from mains? Guessing 18 or so gal?

[Pinecone]

On my 252, it is about 25 gallons total to see fuel in the aux.  27.5 gallons for a measureable amount.

About all you can do is to either really fuel the airplane, fly and do it again.  For this, you pretty much need to have some jugs to get the tanks really full.

Or you can fuel the exact same way.  Fill main, cap, fill aux, wait 10 minutes, fill again and call this full.

 

[larryb]

I kept records of every fill for a number of trips and fillups, a few hundred gallons worth. The default K reading was within a couple %. It’s too hard to get an accurate number in one fillup.

[Rick Junkin]

The Garmin G3X Touch EIS automatically adjusts the K factor if you enter the actual fuel used, but it only adjusts for half the difference between actual used (the amount of fuel you add to top off) and measured used. This helps account for small inconsistencies in the top off level and helps avoid going hard over in one direction or the other with your adjustments. It's sort of a poor man's Kalman filter.

To accomplish this manually you would use oregon87's formula to determine the "new" K factor, and then add the old and new K factors together and divide by 2. That yields the K factor value to enter into your instrument. Wash, rinse and repeat. It will take a few iterations but will keep you close and headed in the right direction throughout the process.

Cheers,
Rick

[FlyingDude]

On 11/23/2023 at 7:11 PM, Marc_B said:

let it sit for 15 min and it’s an inch lower in the aux. put another gallon in, wait another 15 min…

I did that once.  I got in the FBO to take a leak and when I came out, the fuel was also leaking from the air vent.  The 2nd leak was not relieving...

The upper ribs in the tanks have air holes in them, because as you fill the tank up fast with fuel, some air gets trapped.  Those holes do not let air out as fast as the pump sends fuel, so you hear a post-fill gurgle.  That's why you get that 1" level drop.  However, I've never overfilled the tanks again.

[Aerodon]

On 11/6/2023 at 4:53 PM, vik said:

The worst I have seen was 0.5 gallons to the tank. Usually within 0.3 gallons. It took about 4 changes of the k-factor to get to it. I did not find it too time consuming. Just calculate the coefficient, than new k-factor and put it in. Very simple.

Vik

 

The JPI calibration is only as accurate as the fuel pump you are using (temperature related) and the consistency in filling to the brim.  If you refill after each flight and make an adjustment, you will be chasing your tail.  Best to do 5 flights, add up all the numbers and do one adjustment.  Also eliminate any flights that you may have doubts about.

Should be able to get under 1G and more like 0.5G error.

 

Aerodon

 

 

[Kejidog]

Hi.  I haven’t been on here in a long time but finding this thread has me thinking that I should adjust my KFactor. I have a G4 with FF in my 182.  It always reads that I have less fuel in the unit than i actually have in the tanks.  I mostly use it for back up planning. I’d rather it be that way than the other.   Looks like i have some number crunching to do. 

[Will.iam]

On 11/23/2023 at 6:11 PM, Marc_B said:

I have aux tanks so this makes it difficult to really accurately have a reproducible known fuel amount. I go to full fuel in both the main and aux, let it sit for 15 min and it’s an inch lower in the aux. put another gallon in, wait another 15 min…put more fuel in. So I tried to do this the other day just out of curiosity and FF showed I burned 17.5 gal, but I put in 17.1…but if I waited longer I’m sure I could possibly have added more. Current K-factor was 61150. Not sure if this was just number from install?
For those with Monroy aux tanks…what is the most accurate way to adjust K factor?

My thought was maybe deal with sub aux tank fuel quantity and a stick measurement. Not quite sure what’s the most fuel I can add before any fuel goes into the aux from mains? Guessing 18 or so gal?

My fuel totalizer is down to the seconds in accuracy but you are not going to like how to do this. I have aux tanks too so finding full is a guess at best so i flew one tank dry at cruise. Land put in 5 gallons calibrated from the pumps and verified in my 5 gallon gas can. Put the 5 gallons into the empty tank. Take off in cruise reset totalizer as you switch tanks. Note what the total fuel used is when the engine sputters and switch back to other tank and land. When i first did this i was showing 5.3 gallons used. Now the totalizer turns over to 5.0 right as the engine starts to sputter. I’m +-0.1 on the totalizer now. It’s very repeatable too. 

[wombat]

On 12/20/2023 at 11:35 AM, Will.iam said:

My fuel totalizer is down to the seconds in accuracy but you are not going to like how to do this. I have aux tanks too so finding full is a guess at best so i flew one tank dry at cruise. Land put in 5 gallons calibrated from the pumps and verified in my 5 gallon gas can. Put the 5 gallons into the empty tank. Take off in cruise reset totalizer as you switch tanks. Note what the total fuel used is when the engine sputters and switch back to other tank and land. When i first did this i was showing 5.3 gallons used. Now the totalizer turns over to 5.0 right as the engine starts to sputter. I’m +-0.1 on the totalizer now. It’s very repeatable too. 

I actually do like how you did that, a LOT.   Do it within easy gliding distance of a long runway, at significant altitude.   If you someone is uncomfortable with this, they should probably practice their engine failure procedures until such time as they are comfortable.

[Marc_B]

@Will.iam Agreed!  I think this is probably the most accurate way to do this calculation if you have aux tanks.  Plus it would make it easy to then fill the tanks on that side and develop a tank stick or at least fill to full and corroborate how many gallons it holds based on pump/fuel total.  I like it!

[Schllc]

All of my totalizers with the g1000 have been within .3 gallons at worst and .1 gallon at best. 
This was verified to my satisfaction by fueling myself at the same airport, same pump and same position on the ramp. 
my tanks say 51 gallons, but you can easily put another 2 (maybe more) gallons per side past that with patience. 
if you have monroy tanks, the only way you will ever know how much you really have is when you fill up. That’s the downside to monroy’s, the upside is you almost always have more than you need!

[Pinecone]

You can, and I did, calibrate a dipstick for Monroy tanks.  You just have to measure at each filler at each increment of fuel.  And wait between adding fuel and measuring the fuel level.

[Marc_B]

I have this from my AFMS/POH.  There's a page on the STC docs for 14.5 gal with speed brakes or one for 17 gal total for aux without speed brakes.  I've never specifically calibrated it to see how accurate for my install, but it is pretty close based on informal fueling.

[Pinecone]

That is great, but doesn't tell you how much total.

I calibrated  Fuel Hawk and FuelStik for my plane (252 with Monroy with spedbrakes).

I wrote and article for Mooney Flyer on the process. Present Position (themooneyflyer.com)

Attached is the results.

Fuel Measurements.pdf

[Marc_B]

1 minute ago, Pinecone said:

That is great, but doesn't tell you how much total.

It does if your wing gauges are accurate...i.e. have 25 gal in mains on the wing gauge (should be accurate on the ground) + 2 inches in aux tank = 33 gal for that wing.  Of course not near as accurate as a calibrated stick...more of a "did the line crew put fuel in the right tank" kinda thing.

5 minutes ago, Pinecone said:

I calibrated  Fuel Hawk and FuelStik

The interesting thing from my Fuel Hawk is that I'm not sure what the numbers actually imply...  i.e. it's not an inch scale, and not a cm scale; so I imagine that it's calibrated to a specific tank, but not sure what make or model...

[Pinecone]

The Universal one seems to have some random scale.  It is not inches (which would have made sense).

In the table I attached, I also measured the fuel level in the Fuel Hawk if it was needed at some point.

Unless you have calibrated the wing gauges, they may not be accurate.

If you look at the PDF, at 1/2 inch in the aux, I had added 27.5 gallons, but the sight gauge read about 22, so 4.5 in the aux.