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Deflate and level.


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2 minutes ago, mooniac15u said:

The M20J maintenance manual contains this note:

"AIRCRAFT MUST BE LEVEL TO CALIBRATE FUEL GAUGES"

I'm guessing the M20F manual contains similar guidance.

Yes, the JPI manual says the same thing.  

Regardless, I want them to be 'accurate' in flight.  Jose, you are right, the fuel level changes with attitude, but a vast majority of the time is spent in level cruise.  In addition, it gets rid of the "Fuel Mismatch" message on the EDM.  That message comes from the difference between fuel onboard calculation and indicated fuel in the tanks.

 

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Aerospace logic is the same.  They are to be accurate in flight so the plane is supposed to be in the level flight attitude during calibration.

However, I also want it accurate on the ground so I'll make a conversion chart.  After calibration is done, put the plane back on the ground with one tank full and the other empty.  Move fuel one gallon at a time from the full tank to the empty tank and note the readings on the gauge.  Once both tanks have half a tank, you should have a conversion chart that allows you to know how much fuel you really have based on a reading on the ground.

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All done on the left tank.  Used jacks and leveled.  It takes about 6" of lift on the jacks to level the plane.  

I set the JPI for 0, 8, 16, 24, 32 gallons.  Interestingly, at 32 gallons the fuel is a solid 2.5 to 3" from the filler neck.  When the plane was back on the ground, that number was closer to an inch.  I could have maybe squeezed two more gallons in.

Here are some pics of the calibration.

https://goo.gl/photos/ndQnoAtr8sZ839H3A

The 'white out' pics of the tank are with it leveled.  

It was fun flying it empty.  Now I know how much time it takes to start running again.  It's longer than you think. It was a solid 8-10 seconds before it was running again.   Would not be fun down low.   

@Bob - S50:  Funny you mentioned a conversion chart.  That is exactly what I am planning!

Edited by Guitarmaster
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 Interestingly, at 32 gallons the fuel is a solid 2.5 to 3" from the filler neck.  When the plane was back on the ground, that number was closer to an inch.


Very interesting info. Thanks for noting it.


Sent from my iPad using Tapatalk
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Oops, sorry about that. I was only considering the thought that you were making calibrated dip sticks.

Just to nit pick. At what speed does Mooney say the plane is "level" in level flight. I know at slow speeds, a plane flies really tail low. I presume that the difference between level is pretty small at reasonable flying speeds, but there must be some differences.

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Daver demonstrates some accuracy here!

The levelness of the plane is measured by the horizontal seam or the top edge of the radio rack access panel...

since I'm not there, relied on the rivets for the horizontal seam...

lined the photographed seam up along the bottom of my iPad screen...  to find that his plane is level and his photographic skills are equally level!  :)

The long body is known to be about 4° pointed skywards with all three feet on the ground...

Best regards,

-a-

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