It sounds like you are getting what I was getting before the flow transducer was relocated IAW the Shadin STC… something which cannot be legally done on an EASA-reg aircraft.
Can anyone post a photo of the pipe which feeds the transducer?
That’s not actual power – it’s “load” (whatever it is) – I believe it’s something derived from actual power and fuel flow to make it easier for pilots to track it and keep engines in sync.
BTW max difference that I noticed on my TB20 between totalizer and actual quantity was 1 USG.
I may be dumb but surely the totaliser must be accurate, unless the pipework was bodged and turbulence is entering the sensor and making it nonlinear – like Socata did.
And I can’t see how the power v. fuel flow line can be so clean. Engines are monotonic (if always run at peak EGT or LOP) but they won’t be anywhere near linear. Throw in some funny ignition timing etc mapping in the ECU and…
I have practically the same situation as @aart with Thielert 2.0. The actual readings of FF-metar are lower than what manual specifies which results with lower quantity of fuel in tanks than totalizer shows. This has been confirmed across 400 flight hours and numerous refuelings. On my last trip to Sweden I manually tracked consumption according to values in manual which resulted in almost exact quantity shown by fuel gauges and what I refueled. I started with full tanks (76 USG) and landed after 6 hours with 8 USG in tanks, refuelling 68 USG which was consistent with what I calculated manually during the flight. The fuel gauges were showing 10 USG (5 in each tank) which I consider precise enough having in mind type of devices used for measuring. However, totalizer was showing 14 USG which is pretty much of difference.
Everything I recorded during this flight was consistent with what I usually notice when refueling i.e. when I refuel 40 to 50 USG the difference between actual quantity and what totalizer shows is 4 USG (totalizer shows more fuel left).
So a fellow DA42 owner and myself did some further testing and we came to the same conclusion:
The FF meters seriously over-read at cruise power settings and under-read at low power settings.
See the following table, comparing the actual FF (as per the manual, very accurate) to the FF reported by the FF meter (X’d line)
Would be nice if others here flying a Conti CD135 (Thielert 1.7 or 2.0) would check whether what they see on their display matches this (gal/hr, per engine):
100% 7.4
90% 6.7
85% 6.4
80% 5.9
75% 5.4
70% 4.9
65% 4.6
60% 4.3
Ideas welcome.
Dave,
The reason for the 65 gals is simple: For these tests I filled her completely ( to 76 gal as you say) but like to land with minimum 10 gal ;) So I measure the discrepancy of 5 gal on a used qty of some 65 gal.
I only use Jetfuel. Just once added 20 litres of Diesel.
I understand yr point on wiggling and making sure the tanks are full, but when I refill to completely full then things always seem to add up correctly: adding the remaining fuel left (as per the qty tranducers in the tanks) to fuel pumped in gives me a total of 76 gal. I also checked that for the individual tanks. So it’s not the refueller that screws me either 
. I also cross-checked the qty transducers when 10 gal left with the infamous manual measurement kit (you know which device I mean, the one that gets you soaked in fuel if you want measure properly 
)
She’s in annual inspection, so they’ll look at it too.
Thanks all..
Just as an aside here folks (if you don’t mind), how does one eliminate ignition “noise”? Yes I know the answers will be not simple but one has to start somewhere.
The transducer does not give out more pulses. The extra pulses seen by the indicator are crap from the ignition. Worth reading my writeup. Sorry, writing in a rush.
I’m intrigued. Firstly they guts of the system are a couple of Shadin sensors working as Peter has previously described. I’m interested in you 65USG figure as total useable is 76.4USG but I’m guessing you’ve got that one covered. Secondly, and not wishing to be condescending, are you sure you’re filling the tanks each time? The shape of the DA42 tanks is such that you can get a significant difference even if you think you’ve filled to the rim. Also, you can get small air locks between the sub-tanks and we often find a wing-waggle whilst refuelling allows you to get more in. The aux tanks also tend not to empty completely despite the L/R Aux Fuel caption on the PFD. That said, you would notice this next time you filled the aux tanks.
Finally, are you using diesel or Jet and do you swap between the two?
Peter
How does using unscreened cable cause the Floscan transducer to give out more pulses per second which is the only way it could overread?
http://www.floscan.com/html/blue/itemimages/page/201%20gas%20200a.jpg
The transducer as supplied is wired un-screened. I do see that the installation manual does show a screened harness:
On the actual installation wiring diagram there is no screening shown:
