I fly a CJ2+ and the poster earlier has been more comprehensive than I was going to be by posting a link to the manual.
I believe the CJ4 uses basically the same system.
We find the accuracy to be as Peter observes.
Fuel is a critical part of jet ops, it is quite normal to take off say from Annecy with around 3000lbs of fuel on board, and we will have the FMS telling us we do not have enough fuel to get back and giving us warnings to "Check fuel at destination". We usually land with around 1200lbs, despite the best efforts of London to have us burn more by descending us to FL260 20 before Biggin; far too low too soon.
We usually land with around 1200lbs, despite the best efforts of London to have us burn more by descending us to FL260 20 before Biggin; far too low too soon.
They do that to you as well - I thought it was just me being in a little plane. I tend to plead now to be kept high, not sure it makes any real difference. I tend to get FL200 20 before LAM - still a long way from Oxford.
Peter, are they standard or aftermarket? Float gauges in my tanks are totally useless, and I am thinking of replacing them with something better - any recommendations?
They were standard on the GT, and may have been fitted to pre-GT serial numbers too (I have no idea).
During inspections etc I have looked for the transducers. I cannot see far enough into the wing (through the filler hole) to see what is inside the fuel tank but I have seen the "dry" side of it, and it seems to just go into a hole which - at a vague memory - is something like 50mm diameter so could be retrofitted easily if you can get access to the most inboard wing rib i.e. the most inboard end of the fuel tank.
The first page in this PDF shows the standard (old) fuel metering system whereby some potentiometers (with floats attached to rotating arms) are used. That system is used in nearly all of light GA and is basically crap. The other 3 pages show the capacitive system which is very good but a lot more expensive. As with most of Socata's wiring diagrams, I have no easy way of telling which of the three applies to my late-GT aircraft but you can see the basic idea.
This PDF shows the actual parts. At the beginning it shows the old system with the potentiometers and later on it shows the capacitive transducers. I don't know who the manufacturer is; Socata allocate their own part numbers to most things so you can't find out, but it may be stamped on the components themselves. They are most likely off the shelf French parts.
It looks like Socata use two sensors in each wing tank, so that aircraft pitch is compensated for, but not roll if the aircraft is out of balance (yawing). The Cessna manual uses a lot more sensors - an impressive implementation.