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Install Float Fuel Sending Units in QB Wings?

ERushing

Well Known Member
I'm getting ready to install the float fuel senders in my QB Wings. Has anyone else done this? Any suggestions?

Instructions state that the float needs a maximum clearance of 1/8" from top and bottom of tank. Also states that floats should be centered between the vent line and the aft upper tank stiffener. Unless I can figure out how to get a camera in there, I don't see how I can accomplish any of this except via blind luck.

Your suggestions would be very welcome. Thanks!
 
Also...

Make SURE that you check the B nut on the vent fitting inside the tank. Some have found it to be loose on the QB tanks...Mine wasn't but I checked it before installing the Capacitive sending units that I got from GRT...
 
Just bend the float wire per the template in the plans and you'll be fine - at least that has been my experience. It is very common for people to miss the little bend at the very end of the wire - the end that goes into the sending unit. If you forget this, the float wire will spin on the sending unit, and never give you a good reading.


Paul
 
Thanks Paul! You're absolutely right! Looking at the plans now, I would have missed that.

Any thanks for the tip, Bob. i will definitely check that nut.
 
As Paul recommends, bend it per the plans, in addition, remove the tank and put an ohmmeter on it and carefully turn the tank upside down and right side up to verify its not hitting the vent line and hanging up. Also, don't be so concerned that it hits the top. In fact, make sure it barely touches the top and hits both the top and bottom of the tank. Due to the dihedral and length of the tank, in actual use, you will not be able to get an indication until 5-10 gallons have been exhausted from the tank, so it's important that it barely touches the top of the tank and starts to drop immediately as the fuel is consumed. The actual resistance of the pot will be calibrated out during your efis setup.
 
Fuel tank sender unite

If installing the sender unites to wings that are on the bench and not on the aircraft you can check the full and empty readings by hooking up a gauge and roll the tank upside down for full reading and upside up for empty reading. At least you will know that they are working. You won't know how accurate they are unless you add fuel one gallon at a time. But at least you can see if they work..
 
Bending According to the Template

My instructions show a chart for the RV-3, then the RV 4 thru 9. No mention of the RV-10. I assume that I just use the dimensions for the RV-9, but just checking here to make sure..

Jack in Michigan
 
Hi Jack,

Check Page 18-7 of the plans. Figure 1 gives the general dimensions for bending the wire. Like the included instructions say, don't forget the little right angle bend that goes into the sender!!
 
More Questions

I did find the specific instructions for the RV-10 after I posted. However, I now have another question.

By following the instructions supplied with the 8.5 x 11 paperwork (not the plans) it tells me how to bend the tang that goes into the sending unit.

The float is offset with most of it to one side. If I follow those bend instructions, I put the larger side towards the vent line, encouraging a contact. I want to reverse the tang putting the float further away from the vent line. I see no issue, but looking for concurrence.
 
The float is reversible. I ended up cutting an access plate in the rear baffle so it ended up being a lot easier to adjust the wire for clearance. But, before that, I was able to put a flashlight (with a string attached) through the float plate hole and look through one of the holes (vent, drain, etc) and get the wire adjusted so it didn't hit the vent line or any internal structure. Several cycles of attach, check, take apart, bend, repeat.

Good luck!
 
Thanks for the help..

I just discovered that the sending units are RH and LH. Didn't know that. Now that I have that figured out, things are making a lot more sense.... I have a computer here in my workshop, and sometimes start firing out questions before my brain gets into gear...
 
Plexi

Use the access cover as a template to make one out of plexi. You can then set everything up, being able to see in the tank with the sender installed. You can also drill a big hole in the plexi to allow you to move the sender through it's range of motion and watch to make sure all is good. When you have it like you like it, swap out the plexi with the real cover and you're good to go!
 
Great Idea!

Thank you.

view
 
borescope

I used a borescope through the outlet after removing the screen. The float hit the rib, with the borescope I could tell how much to bend it. But first get a wrench into the hole and check the B nut on the vent. Find a short 9/16 to do that. A leak there will spoil your day on the first fill. Ask me how I know.
 
If installing the sender unites to wings that are on the bench and not on the aircraft you can check the full and empty readings by hooking up a gauge and roll the tank upside down for full reading and upside up for empty reading. At least you will know that they are working. You won't know how accurate they are unless you add fuel one gallon at a time. But at least you can see if they work..

I tied a string to the end of the float and used that to insure that the float hit the top and bottom of the tank when held in position.

Larry
 
Use the access cover as a template to make one out of plexi. You can then set everything up, being able to see in the tank with the sender installed. You can also drill a big hole in the plexi to allow you to move the sender through it's range of motion and watch to make sure all is good. When you have it like you like it, swap out the plexi with the real cover and you're good to go!
Did this and worked great
 

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