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Can fuel flow be calibrated?


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My UBG-16 seems to be reading my fuel flow quite incorrectly.  I’ll set the stage.  Wednesday evening I flew from KTYL to KDVT with full fuel.  For the entire flight, my FF was showing around 11.5 to 12gph at 20” and 2450rpm. Leaned 25 ROP.  Very close to an hour in the air.  I would expect to have burned at least 12 gallons.  Last night, I flew KDVT to KVGT, I did not top off since KTYL.  Flight time was right at 2 hours (pretty strong headwinds).  FF was showing similar, around 11.5 gph, roughly the same power settings.  I expected to burn about 24 gallons (including taxi fuel, etc)  So, given the ‘displayed’ burn rates, I expected to top off and take on about 36 gallons at KVGT.  Instead, filling the tanks to the brim took only 25.1 gallons.  Couldn’t get in another ounce.  

So, it would appear my average fuel flow is more along the lines of 8.5 gph than 11.5.  Is this something that can be calibrated?

Pic leaving Las Vegas, about 8pm last night.   I love flying at night, so beautiful. 

20180406_203711.jpg

Edited by ragedracer1977
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Your ‘display’ can be calibrated using a K-factor. The k-factor reads pulses from an in-line fuel paddle wheel turbine that might be off. Look up how to change the k-factor in your display then you can use this formula to get closer:

 

(indicated fuel used / actual fuel used) * existing K factor. = new K factor to set

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Most fuel flow sensors have a k-factor stenciled onto them, as not two are really the same. Before doing calculations, see if the k-factor given at the transducer corresponds to the one set in the electronics.

If that is the case, you need to conduct a series of test flights where you can really check out what is happening. Full fuel, then do the flight, note down all parameters and compare calculated vs real uplift at destination. If you can find out that it is consistently wrong by the same percentage then you have a base to work from.

In your current case, the FF errs on the safe side so changing the k-factor might change that to something unsafe if it's not done with due diligence.

I would in any case consult the manufacturer of your ff computer as well. Quite possibly, the transducer itself may be faulty which means however that you will not get better results with a new k-factor but could instead be setting yourself up for a situation where it shows less than it should. The implications of that do not need much explanation I guess.

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My advice is to consistently fill your tanks to the top for 3-4 fill ups and write down exactly how much your fuel burn is on your EM each time. Add the amounts together and use your manual to readjust the k factor. 

Ive got mine down to less than 1/2 gallon error over a 40 gallon fill up. 

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30 minutes ago, Urs_Wildermuth said:

Most fuel flow sensors have a k-factor stenciled onto them, as not two are really the same. Before doing calculations, see if the k-factor given at the transducer corresponds to the one set in the electronics.

If that is the case, you need to conduct a series of test flights where you can really check out what is happening. Full fuel, then do the flight, note down all parameters and compare calculated vs real uplift at destination. If you can find out that it is consistently wrong by the same percentage then you have a base to work from.

In your current case, the FF errs on the safe side so changing the k-factor might change that to something unsafe if it's not done with due diligence.

I would in any case consult the manufacturer of your ff computer as well. Quite possibly, the transducer itself may be faulty which means however that you will not get better results with a new k-factor but could instead be setting yourself up for a situation where it shows less than it should. The implications of that do not need much explanation I guess.

I'm thinking something is faulty.   Maybe wearing out?  I used to be able to get the FF down to under 8gph with 17/2400 and aggressively learned, but now I pretty much can't get it under 10gph no matter what.  And my actual fuel burn tells me that something isn't jiving.  

I'll drop a line to EI and see what they have to say

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Brice @ragedracer1977, before you go, consider these ideas....

 

Getting or determining the k factor is key...

filling and refilling the tanks the same way each time is equally important...

Comparing to book numbers is often quite helpful...  use one tank for all the start, T/O, and landing parts of the flight, and do the study using the other, nicely filled, tank of fuel...

Missing a gallon of fuel can easily be attributed to the slope of the ramp, or the time required for air to escape from the top of the tank.

If you get some really wacky FF numbers that are too high... expect a continuous stream of air bubbles are entering the fuel line upstream of the sensor...  the bubbles get counted as fuel going by, the engine then drinks more of the fuel/bubble mixture to make up for the loss of energy caused by the bubbles...

A known source of a continuous stream of air bubbles... a worn selector switch for the fuel tanks.  Some blue stains occur while the engine is not running, while the fuel sneaks out and evaporates.... when the engine is running, it draws air in through the small gap that has worn in...

PP thoughts only, not a mechanic or fluid dynamicist....

Best rgeards,

-a-

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I'm thinking something is faulty.   Maybe wearing out?  I used to be able to get the FF down to under 8gph with 17/2400 and aggressively learned, but now I pretty much can't get it under 10gph no matter what.  And my actual fuel burn tells me that something isn't jiving.  
I'll drop a line to EI and see what they have to say


It really sounds like your k factor is off. Also make sure you have the correct fuel flow transducer. My EI uses a FT60 and the JPI has both a gravity and fuel pump version.

You should be able to look at the k factor that is set. The default is 29.00. If you see that number, you can be sure it hasn’t been calibrated.

The advice above is how you set it. I spent a lot of time tweaking mine and it is within 0.2 gallons at fill up.


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If it was accurate at one time and not now I would check that the FF sensor is still good and that the K factor has somehow gotten changed by accident.

Averaging over multiple flights helps to get a good reading.  We have bladders and when filling I fill one side, fill the other and then go back and fill each side a second time. This allows time for the fuel to flow to all the tanks.  

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On 4/7/2018 at 9:53 AM, ragedracer1977 said:

I'm thinking something is faulty.   Maybe wearing out?  I used to be able to get the FF down to under 8gph with 17/2400 and aggressively learned, but now I pretty much can't get it under 10gph no matter what.  And my actual fuel burn tells me that something isn't jiving.  

I'll drop a line to EI and see what they have to say

I have been fighting the same thing with my FP5.  It was reading very well but is dong the same thing you described.  I spoke with EI and they said the sensor rarely has problems,  EI seems to think it is air bubbles or fuel vapor bubbles interfering with the sensor.  EI suggested a fuel line loop above the sensor which in my case is a little difficult considering where it is located.  I have been trying to figure out how I want to do this to try it.  Mine at altitude and longer flights usually will settle down and read pretty close short flight it's hit or miss.  Here are two recent flights FP5 uses vs pumped.  Even with averaging makes chasing K factors interesting.

FP5                                           Pumped 

35.6                                            34.5

14.5                                             12.9

 

The FP5 on my previous Mooney was rock solid never a problem.

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Flew KDVT-KVGT-KDVT today.  Total time including taxi was 4.2. My UBG does not totalize, but it was showing 11.3GPH flow (never less than 10.9) for essentially the entire cruise portion of the flight.  I planned on burning 39.5 gallons (I’m conservative on fuel).  I burned 33.4.  Going off the UBG, I should have burned at least 46 gallons.  True average GPH was ~8gph.

I think it might be time to send the unit back.  I also noticed today that cyl 1 was bouncing all over the place temp wise.  200 degrees egt to 1300 in a split second and everywhere in between.  It might not be the fuel meter at all. 

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2 minutes ago, ragedracer1977 said:

Flew KDVT-KVGT-KDVT today.  Total time including taxi was 4.2. My UBG does not totalize, but it was showing 11.3GPH flow (never less than 10.9) for essentially the entire cruise portion of the flight.  I planned on burning 39.5 gallons (I’m conservative on fuel).  I burned 33.4.  Going off the UBG, I should have burned at least 46 gallons.  True average GPH was ~8gph.

I think it might be time to send the unit back.  I also noticed today that cyl 1 was bouncing all over the place temp wise.  200 degrees egt to 1300 in a split second and everywhere in between.  It might not be the fuel meter at all. 

All the reading bouncing a little?  Checking the ground to the unit (to vac pump) might help. 

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2 minutes ago, ragedracer1977 said:

Is there a good (read easy) way to test that?

Just make sure all the fittings are tight and in good shape. The fuel selector is a bit harder. You have the glass gascolator  between the fuel pump and the carb. That should stop any bubbles or at least let you see them. When mine did that, I just took the whole sensor setup apart, cleaned all the threads on all the fittings and put it back together with fuel seal. It started behaving after that.

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On 4/7/2018 at 9:35 AM, MIm20c said:

My advice is to consistently fill your tanks to the top for 3-4 fill ups and write down exactly how much your fuel burn is on your EM each time. Add the amounts together and use your manual to readjust the k factor. 

Ive got mine down to less than 1/2 gallon error over a 40 gallon fill up. 

That’s what I did.  Fill the tanks yourself so you know there is no flight line error and the tanks are filled to the same level every time.  Do it over three or four fill ups so that any error gets averaged out.  Then adjust your K factor if it needs it.  I did this with mine, and it turned out the fuel flow was very accurate, within .1 gal. out of 50 gallons.  I use fuel flow (fuel used) to determine how full the tanks are and where the fuel is, rather than the gauges, which are not very accurate.

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Brice just has a UBG-16. It is not a totalizer so your method doesn't work.

For a stand alone fuel flow, fill both tanks, take off and climb on one tank, get the plane stabilized with a constant fuel flow. Switch tanks and fly for a time, the longer the better. record the time and fuel flow. Switch back to the tank you took off on and land. Fill up the tank you did the test run on and record the fuel used and calculate the actual fuel flow.

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When I installed my UBG-16 I recall the fuel flow module had an adjustment to calibrate the reading while measuring flow. I adjusted the module to read the same as my previous flow meter with the electric fuel pump on open throttle and full rich mixture.

Another method is to time how long it takes to fill a one gallon container.

Disconnect the fuel line from the carburetor

Insert the line to a 1 gallon container.

Set your stop watch and turn on the electric pump.

Stop your watch when the container reach 1 gallon.

GPH = 3600/seconds

For 5 gph it would take 12 minutes or 720 seconds.

José

 

 

UBG-16 EGT.jpg

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+1 for tweaking the K factor.  Rather than making many adjustments over time, I've found that averaging over the course of 4-5 fill ups works very well.

I'll fill up at the same location (important because of levelness of ramp and ability to fill tank), record fuel taken then compare to what totalizer says I should have used.  After repeating several times I'll recalculate K factor and reprogram.  Has worked like a charm with both JPI units I've owned.

That said, I'm sure to set the K factor to a rate that is very slightly ahead of actual burn.  I prefer the JPI to indicate a slight overconsumption than the opposite. 

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