Fuel Senders

[J12345T]

Hi All,

I am currently conducting due diligence on an RV6 (fully completed and flying ~200hrs). An issue regarding the fuel quantity indications has come up which I need your help to answer.

As far as I am aware the tanks are currently fitted with non-Vans capacitive type sender units. I believe these units came from a KC-130 tanker aircraft!!

The attached pictures have been obtained from the original builders web site. The kit was completed by its current owner hence there is a lack of knowledge as to this phase of the construction. The pictures show a long black tube which I presume is the capacitive sender mounted at an angle inside the tank with sender wires coming out of one end (the root end I think).

The problem I have is that these units are not currently connected and as far as I’m aware have never been connected or tested. The reason for this is that the aircraft is fitted with Vans type float gauges which are not compatible with the sender units. I think the intention was to develop some sort of electronic translator for the senders to the gauges. Regardless, I now need to decide if the aircraft is worth persuing knowing I have to fix this problem.

Two proposals have been tabled. The first was to demount the tanks, remove the old sender units and fit the Vans float type sender units. Connect up and problem solved. From the pictures however, it appears that each tank is different and one of the sender units will be impossible to access from the access hole. The other tank’s unit appears to be accessible from the inner bay? Also, the units appear large, too large to accommodate Vans float units without first removing them; ergo the access problem.

The second option was to replace the float gauges with compatible capacitive gauges however, it is not known or been proven that the current sender units will in fact function and if they do what gauges they will be compatible with.

My problem is that the current owner didn’t build this section, I am not an expert, my friends who have built their own RV’s can’t give me an answer, Vans support my conclusions that removal is required but access will be a problem. I’m now turning to you folks at for some advice; butcher the tanks, try to get the correct gauges, or abandon the purchase entirely??

I hope you can help.

Regards,

James.

[Mel]

You have way too many unknowns here. I would seriously consider removing the current senders and installing the standard float senders. Otherwise, you could be chasing unknowns for a long time.
On the tank with the flop tube, you will have to cut an access hole in the rear baffle for removal and installation.

[chaskuss]

James,
Mel's advice may be your best bet. That said, there is no way to know what the design perimeters are for those capacitance senders, without testing them. That is the first thing I would do before making a decision. If it turns out that they work, you still have two options. If they do not work, you want to know that before wasting time and money on them.
As a first step, my advice is to obtain a copy of Jim Weir's series of articles on a DIY [do it yourself] capacitance gauge system. The articles explain how to make a transducer circuit to convert the capacitance signal to a voltage signal, like that used in the float type senders. This unit will allow your capacitance senders to work with conventional fuel gauges, like those sold by Vans or Mitchell.
Jim's article ran in the June, July and August 2000 issues of KitPlane Magazine. Using a DIY transducer will allow you to tailor the sending units already in place to the fuel gauges you have. [To ensure accuracy] I have a copy of the articles on how to do this. I will need your email address to send it to you. FYI, do NOT post your email address onto your reply. Send it to me via PM [private message] or click on my user name. The page you will be taken to will allow you to send me an email [privately, so that your email address is not broadcast to the entire Internet].
Charlie

[J12345T]

Hi,

Thanks for your replies.

What would be the best way to go about testing the probes. Is it simply a matter of conecting up a capacitance meter to the leads and see what happens or is there more to it than that?


Cheers.

JT

[chaskuss]

Originally Posted by J12345T

Hi,

Thanks for your replies.

What would be the best way to go about testing the probes. Is it simply a matter of connecting up a capacitance meter to the leads and see what happens or is there more to it than that?


Cheers.

JT

JT,
You would need to connect the tester with the tanks empty, and then again with the tanks fuel of gasoline. It would be better yet if you tested them empty, 1/4 full, half full, 3/4 full and finally full. This would show you not only that the senders function properly, but what their functional range is. That info is needed to properly configure the transducer circuit.
Another fact you should be aware of is that the capacitance of ethanol is vastly different from gasoline. That means that capacitance senders are NOT practical for use with ethanol laced gasoline blends, unless you used the same blend exclusively. That is not a practical idea, at least in this country.
Charlie