I don't believe the differential pressure measurement carburetors vs.
airbox will give much of an early warning.
By the time the pressure regulator is unable to maintain the small
differential pressure the total (forward) flow, in the best case, is
already down by more than half (total flow is normally at least twice
the 33 l/h maximum carburetor flow, and many more times the actual
carburetor flow in most conditions, f.i. in cruise at lower altitudes
when fuel consumption is low and turbo pressure is low).
I see the differential pressure measurement as a check on the correct
operation of the combination: pressure regulator + return line.
To get a really early warning of deterioration one would have to
constantly measure the performance of all between tank and pressure
regulator input; the 2 ingredients are: total flow and total pressure
difference between regulator input and tank. A microcontroller would
need to learn the reference curve (total flow vs. total pressure
difference) when an installation is in "reference condition". A display
would show actual total flow as a % of reference total flow at actual
total pressure demanded (determined by actual turbo operation).
Jos once mentioned that he checked total forward flow (by defeating
return flow pulses - or only their inclusion in the flow calculation -
don't remember) as part of his before-takeoff checklist. This seems to
me a good way to notice at least slow deterioration early (but higher
altitudes would sometimes provide an excuse for a somewhat lower total
forward flow than expected).
But I need to get on with building instead of daydreaming.
Jan de Jong
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