Bladders, CiES, and calibration

[Marauder]

Just now, Kris_Adams said:

Does this process sound correct?:

1) drain fuel at the fuel drains

2) level the plane

2) add the 1.25 gallons unusable fuel per tank--this is the amount listed in the O&N STC doc's

3) calibrate this as the zero fuel level

4) begin adding fuel and calibrating the EI?  I should be able to get an additional 32 gallons per side on this step?

Thanks again for hanging in on this thread!

-Kris

If the 1.25 gallons is unusable for your 64 gallons system, then yes. Be interested in what you can squeeze in. 

[Bob_Belville]

30 minutes ago, Marauder said:

If the 1.25 gallons is unusable for your 64 gallons system, then yes. Be interested in what you can squeeze in. 

Draining tanks via the sampling drain under the wing is awfully slow. We disconnect the fuel line downstream of the electric boost pomp and use that pump to transfer fuel to 5 gallon containers. My question would be: at the point that the boost pump is sucking air why isn't any fuel that's below that line to the engine, through the boost pump, that the very definition of unusable? Other than for initial W&B, what do I care how many ounces, pints, gallons, that might be? 

For youse guys adding back the nominal "unusable" based upon the manual, how do you know the tank was absolutely dry empty? ISTM a more precise method would be to put at least 4 or 5 gallons in the tank, pump it "dry" using the boost pump, and then start calibrating from zero usable. 

(Level the plane including raise the tail if that's called for.)

[N6758N]

1 hour ago, Bob_Belville said:

Draining tanks via the sampling drain under the wing is awfully slow. We disconnect the fuel line downstream of the electric boost pomp and use that pump to transfer fuel to 5 gallon containers. My question would be: at the point that the boost pump is sucking air why isn't any fuel that's below that line to the engine, through the boost pump, that the very definition of unusable? Other than for initial W&B, what do I care how many ounces, pints, gallons, that might be? 

For youse guys adding back the nominal "unusable" based upon the manual, how do you know the tank was absolutely dry empty? ISTM a more precise method would be to put at least 4 or 5 gallons in the tank, pump it "dry" using the boost pump, and then start calibrating from zero usable. 

(Level the plane including raise the tail if that's called for.)

You're thinking too logically for the FAA Bob! I actually think what you're saying makes a lot of sense. In the case of the bladders, the fuel pick up tube inside the inboard is actually adjustable, so depending on the installation, it could suck more (or less) fuel than the next plane. So to get the most accurate unusable fuel , using the Belville method would be most preferred in my book. 

[Bob - S50]

To answer multiple questions:

We drained our tank through the gascolator.  When it stopped, we were only able to get less than another quart out through the sump valve.

I suspect the 1.25 gallons that is considered unusable is because the pump might start sucking air at that point even though some fuel will still flow.  However, if the situation ever arises to give me the opportunity, I plan to see how long the engine will run after our gauge says zero.

When we calibrated our tanks, we did add the 1.25 gallons unusable and set that as zero on our Aerospace Logic gauge.  We were then able to get about 31.5 gallons usable in the tank after that.  That's 63 usable vs the published 64.  Pretty darn close.

[Marauder]

20 hours ago, Bob_Belville said:

Draining tanks via the sampling drain under the wing is awfully slow. We disconnect the fuel line downstream of the electric boost pomp and use that pump to transfer fuel to 5 gallon containers. My question would be: at the point that the boost pump is sucking air why isn't any fuel that's below that line to the engine, through the boost pump, that the very definition of unusable? Other than for initial W&B, what do I care how many ounces, pints, gallons, that might be? 

For youse guys adding back the nominal "unusable" based upon the manual, how do you know the tank was absolutely dry empty? ISTM a more precise method would be to put at least 4 or 5 gallons in the tank, pump it "dry" using the boost pump, and then start calibrating from zero usable. 

(Level the plane including raise the tail if that's called for.)

I removed the sump and had my hands full trying to keep up with the flow of the remaining fuel I had onboard. 

As for the “how did I know it was empty”. I did the Forrest Gump “stupid is as stupid does” thing. I stuck my borescope into the tank through the inboard sender hole. 

[carusoam]

If you use the gascolater to drain the tank...

It takes fuel from the tank, using the fuel pick-up lines...

When it starts sucking air, that would be the end of the useable fuel...

There will be unused fuel left in the tank below the pick-up. That would be the unusable fuel...

removing the drain valve is emptying fuel that can't be accessed by the fuel pick-up.

the drain/sampling valve is lower than the pick-up.

The pick-up is a round shaped tube that is laying near the bottom of the tank...

Of course this all is depending on attitude and roll angle for getting the last useable drops into the pick-up.

 

PP thoughts only. Trying to describe what you guys might be seeing while you solve this challenge...

Best regards,

-a-

[PHPilot]

Sub question: I have a 1967 M20F Executive 21, JPI EDM 900, CiES senders, 64 gallon wet tank. Between the installation manual and this thread I got the procedure down on how to drain, fill and calibrate. Thanks to all. The current fuel level calibration is many gallons off. Indicates 5 and mechanical float gauge on wing shows 11-13 which is very close. Fuel flow is perfect. So for now.... does anyone have the set calibration numbers for a like model to share? The 1/4, 1/2, 3/4, and full values that seem successful. Each plane installation is difference and should be a custom set-up, which I will in about 64 gallon of time. It's so far off now it can't get any worse really. 

[carusoam]

PHP,

We have a guy that is pretty good if he is listening...

@fuellevel... question about Mooney fuel tank calibration accuracy issue....

One thing to be aware of.... the mechanical gauges in the wing are accurate for ground, level, filling... and will be a little off compared to the instrument panel gauges that know they are in a few degrees nose high attitude while on the ground...

Unfortunately, this doesn’t equate to many gallons off...

Have you seen the thread when @Marauder installed his Cies gauges... Terry had put in some extra effort during the install to get everything coordinated properly...  See if there is anything in there that helps...

Best regards,

-a-

 

[PHPilot]

Thank you for your reply. Yes, his work, and others' comments, about this is the best thread I've found here. I never thought about 2 axis leveling or alternating the fills on the right and left tanks. 

[fuellevel]

I will look to see if I have calibration data for that specific model and configuration.

Yes you can be quite a bit off if you don’t level and brace the aircraft properly. Our advantage is that we can measure very small vertical changes in fuel level, it can also be a curse. Privately let me know who did the install and when I am in the area I can demonstrate why being careful and accurate is important.

We have suffered through the idea that fuel level is crap in GA and it will remain so. Unfortunately if you don’t take care with any system, original resistive, ours or any others it will perpetuate the myth.

I will check the database when I get to the office




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[fuellevel]

Reading through this - did Kris get his aircraft to read correctly. I’d hate to think he is still off 6 gallons.

So if you set K factor from the fuel replaced at the same ramp attitude as the example - you are likely to get the same result.


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[carusoam]

Seeing if @Kris_Adams is around... I think the above message may be for you...^^^^

-a-

[kris_adams]

Thanks Anthony! 

@fuellevel  We've re-calibrated the ei/tanks several times but it still seems that the EI/Cies combinations shows about 12 gallons used when my EI totalizer shows 10 gallons burned.  As the tanks burn more the EI/Cies appear to get closer to what the EI totalizer (and fuel pumps say).  I think I may need spend a little more time adjusting the K factor a bit.  Not perfect but much closer than I ever was before the new senders.  I actually trust what the senders say as I'm pretty sure I normally have a gallon or two more.  Will write back after I do some more testing.  Thanks for checking.  Super cool that a vendor/supplier is following up here!  -Kris

[fuellevel]

No problem. Because K factors are set for the aircraft as a single number. When in actuality there should be at least three and potentially 4. Let me explain when we correct the flow to the spinning wheel in the flow transducer the response is not exactly linear. So K factors should be different from taxi to take off to cruise to descent. While that may be needlessly or overtly accurate it is what we would do if we built fuel transducers. K factors set to average flight will converge to an accurate solution on getting to the end of the average flight. Keep me informed


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[carusoam]

Interesting insight on the paddle wheel accuracy, Scott.

Best regards,

-a-

[PHPilot]

Mr Fuel Level.....Thank you for your time and attention. Standing by.

SDJ

Edited May 15, 2019 by PHPilot

[Bob - S50]

One other thing to consider.  I'm not sure which, but I was under the impression that some digital fuel gauges only have you set 4 or 5 fuel points during calibration.  Is that the case for the EDM900?  For my AeroSpace Logic FL202, calibration occurs in 2 gallon increments which is 17 data points for each wing of my M20J.

Fuel level (float level) may not be linearly related to fuel on board.  That is, a one inch drop in float level might correspond to 7 gallons when the tank is full but 5 gallons when nearly empty.  If the gauge assumes a linear relationship between calibration points, that could result in some inaccuracy.  How much I don't know.  The more data points used during calibration, the less significant the error will be.

Just thinking out loud (or more accurately with my fingers).