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Float/Capacitance fuel sending units

cwharris

Active Member
I?m about to start on my tanks and so I was wondering if I can install BOTH the Float Style Sending Units that come with the Wing Kit and also install a Princeton Capacitance fuel probe sending unit. I would use the Probe units as my primary sending units that would get wired into my EFIS System and then I would wire the Float Style Units that come with the kit to a stand-alone back up fuel Gauge. Has anybody tried to install both types of sending units? Is this something that I should do or not do?
 
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In theory? Less susceptible to variance due to disturbance of the fuel in flight. No moving mechanism.

In practice? Having flown a mix of aircraft with both, I still seem to ignore gages and stick the tanks. If you're building now, why not. I would much rather prefer a good fuel totalizer. [Which reminds me...the D-10EMS is on the way ! ]

Now...if you could build in a cork sight gauge a la stearman/cub...:)
 
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I know the capacitive senders sound good in theory, and I know lots of builders go this route, I am just not sure if it is a better way of doing things in our application. Capacitive systems are the onLy way to go due to the design characteristics of some aircraft fuel cells, but not so much our small tanks. Capacitive fuel quantity systems require maintenance eventually. Even though there are no moving parts all it takes is some oxidation on the electrical connections to cause some wildly erratic or inaccurate indications. Capacative systems are not tolerant of imperfect connections, crimps, soldering of coax center conductor pins, shielding, FOD and many other variables. Eventually you will have to clean and re-tourque, or reterminate connections, and to be able to accomplish this you will need access to the inside of the tank. Access inside of the -14 and -10 tanks requires cutting and installing access panels in the rear tank wall.
 
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Go with the capacitance senders and use your fuel flow and watch as your backups.

I have the Dynon SkyView with their capacitance senders and am always amazed at how accurate they are!
 
With the current technology we have in EFIS with the calibrated/mapped fuel levels, all the systems are very accurate when they are working.
Any of the different system types can fail.
Once we got rid of the wire wound resistor fuel level sensors the reliability seemed to go up.
I have maintained a large # of RV's for many years (currently 8 airplanes) and in that time I have replaced one mechanical fuel level sensor.
Of the problems I have heard of that others have had probably half of them are self induced (damaged during installation, etc.).
 
Thanks for all the input. Looks like I'm sticking with the Float Sending Unit that comes with the kit. Thanks again.
 
Having now flown with a red cube measuring fuel flow, and having seen how accurate flow measurement can be, I don't think i'd put level senders in tanks at all if I could avoid it. One red cube in each wing root, dip the tanks before each flight, and you'll know fuel level more than accurately enough for VFR operations. The only downside is that it requires remembering to set the totals when you fill or top up the tanks.
 
The only downside is that it requires remembering to set the totals when you fill or top up the tanks.

A king air recently augered in for this very reason (told the totalizer he topped off when he didnt). We should use what he have, carefully and in concert with the other systems. Wait...does the stick count as a system? It should...
 
On the topic of fuel..

Has anyone installed a low fuel warning sender / critical fuel device in any of the 14 tanks? Would love to see/hear those recommendations as well.
 
I installed an optical low fuel sender from aircraft extras see pics

I had to get some custom fuel flanges made. Same person that makes the Vans Flanges. Sorry I lost my email thread with him so I don't have the contact info. Vans does.

I also Installed CiEs fuel senders See this thread.

https://vansairforce.net/community/showthread.php?t=190035
 

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Having now flown with a red cube measuring fuel flow, and having seen how accurate flow measurement can be, I don't think i'd put level senders in tanks at all if I could avoid it. One red cube in each wing root, dip the tanks before each flight, and you'll know fuel level more than accurately enough for VFR operations. The only downside is that it requires remembering to set the totals when you fill or top up the tanks.

Careful here. Fuel flow senders are only as good as the assumptions they operate under, specifically:
- You start off knowing how much fuel is in the plane.
- The fuel that leaves the tanks only goes to running the engine (this is the one that bites you).

For my planes the flow sender is what I use to know fuel remaining to the 1/2 gallon. The floats are calibrated to provide an accuracy of a gallon (when in the reading range) so are perfect to backup the fuel totalizer to make sure I’m not loosing fuel (or the tanks really were topped off at the last fill).

I got burned on this once - the float senders provided truth.

Carl
 
Have you tried these yet? That looks like an awesome idea!

Tom

Tried them as in flown with them? Not Yet. I'm in Covid corrosion purgatory (waiting on Fuse QB #2). Ops tested with voltmeter, Yes. The fuel senders work great, the Optical senders work great too. CiES fuel senders are supper sensitive, so way more data points than standard sensor (60 vs. Infinite.)

https://ciescorp.net/documentation/comparative-fuel-sensor-technology/float-system-accuracy/

One could easily program a low fuel amount into a glass panel and skip the extra work of an optical sender. But for extra redundancy warning the optical sensors are an easy way to go if you are building a tank.
 
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