Calibrating a Fuel Flow Transponder

[CoachTom]

 

I have a Shadin that needs an adjustment...

 

Is there a way to accurately measure fuel flow?  I have found with the M20K, that I have too much burping in the fuel cell and can never replicate the amount if I was to refill to the rim.  The anti siphon flap and the level I fill to changes within 15 minutes sometimes, sometimes not.  So, very unpredictable as to calibrating by cumulative usage.  Long or short flight, too many variables as I cannot get the Shadin to match the refill.  Sometimes over, sometimes under...

 

Is there a way to just run the electric pump with the prime button and fill a graduated volume?  Is there a limit as to how long the prime switch should be or the pump run?  As I prime, the Shadin reads 1.7 gph, so, is that flow too low to use as a valid volume?  If I let it run for 10 minutes (1/6 of hour), I should get (1.7gph=13.6 pints) 2.3 pints? 

 

Any and all smart ideas would be greatly appreciated! 

 

[N601RX]

Make the measurement and adjustment over several tank of fuel keeping track of how much you add each time and any filling errors will be negligible.  Flowmeter accuracy varies over flow, so the low flow calibration may not be that accurate.

[thinwing]

the adjustment is made by software by changing "K"factor ...its alittle hit and miss but first need to start with known quanity..like empty tank/full tank ..than measure fuel actually used and measured by the shadin fuel totalizer....the manual than will talk about what k factor adjustment is needed...its trial and error..and can take a few tries to get it dialed in

[Txbyker]

JPi uses a formula to narrow the margin.

New k factor = (indicated fuel used) x (current K factor) / (actual fuel used)

Then do it again substituting the new K factor as the current K factor on following trips.

[jetdriven]

 

 

I have a Shadin that needs an adjustment...

 

Is there a way to accurately measure fuel flow?  I have found with the M20K, that I have too much burping in the fuel cell and can never replicate the amount if I was to refill to the rim.  The anti siphon flap and the level I fill to changes within 15 minutes sometimes, sometimes not.  So, very unpredictable as to calibrating by cumulative usage.  Long or short flight, too many variables as I cannot get the Shadin to match the refill.  Sometimes over, sometimes under...

 

Is there a way to just run the electric pump with the prime button and fill a graduated volume?  Is there a limit as to how long the prime switch should be or the pump run?  As I prime, the Shadin reads 1.7 gph, so, is that flow too low to use as a valid volume?  If I let it run for 10 minutes (1/6 of hour), I should get (1.7gph=13.6 pints) 2.3 pints? 

 

Any and all smart ideas would be greatly appreciated! 

 

 

If you run the electric pump for ten minutes, its likely to fail, and rebuilds start at about 1200$ on up.   The only way I have found it to top it, then let it sit 30 minutes, top it again, then run it down to near empty, then refill as before. Then count the gallons used, the gallons the Shadin said it used, and adjust the K factor. 

 

If you have any bends in the fuel line within 4-6" of the transducer, or it is not mounted with the wires on the top, it will never be accurate. At different fuel flows it under or over counts.

[Cruiser]

I'm not sure why you are having problems with the fueling?

Do not use FULL/ADD on the Shadin. Use the ramping method.

 

The Shadin FF should be updated with the actual gallons you added to the tanks. The totalizer will continue to record gallons used until you reset it. DO NOT reset the Shadin but check it and keep track of the gallons added over several flights. You should get a feel for how much difference you are seeing between the amount of fuel added and the amount on the totalizer. Adjust the Shadin K-factor per instructions. 

You should be able to get the FF to be accurate to a couple of tenths of a gallon.

[CoachTom]

Thanks guys!

 

I know the procedure to do the math is easy and the actual K-Factor change is published. 

 

Believe I am just going to have to keep a log and track the fuel better as I cannot replicate the refuel to the "same" level to validate the fuel used.  Maybe over a couple of tankful's, I will be able to close in on the target.

[kortopates]

...  I have found with the M20K, that I have too much burping in the fuel cell and can never replicate the amount if I was to refill to the rim.  The anti siphon flap and the level I fill to changes within 15 minutes sometimes, sometimes not.  So, very unpredictable as to calibrating by cumulative usage.  Long or short flight, too many variables as I cannot get the Shadin to match the refill.  Sometimes over, sometimes under...

 

Tom, are you trying to fill to the very rim, or the base of the anti-siphon flap? it sounds from your description that you are trying to fill to the very rim. You do realize that our Mooney tank capacity is based on full being at the anti-siphon valve - not above to the rim. The only exception being the newer models that have cut-outs in the filler neck to make it easier to fill the tank to the top.

That's not to say you can't put in more fuel above the anti-siphon plate, but you'll experience the difficulty you're describing and should have more fuel and weight than your placarded/POH capacity.

 

+1 for what Byron says about how easy it is to burn our your electric pump. A Mooney pilot on my field told me his unfortunate story on how he did this twice trying to use his elec fuel pump to empty his tanks for maintenance. When the pump failed after a couple minutes, he first thought it was due to being a very old pump, but after an expensive rebuild it happened again pretty quickly. Never again!