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Float arm/ Fuel sending unit

P

Pman

Active Member
For Quick Build Wing builders that have installed the Stewart Warner Fuel Sending units, can you offer any helpful tips or suggestions on the dimensions of bending the float arm?
The plans show an approximate 3" X 3" float arm, however, wondering if anyone has more realistic/accurate dimensions?

Thank you!

Mike
 
Mike,

My '8A wings weren't quickbuild but I believe the procedure and dimensions are the same.

I used the exact dimensions on the 1/05/95 Van's drawing "Float Wire Bending Diag." that came with the senders IIRC. (3-1/4 and 3-1/4 left wing, 3-3/16 and 3-3/16 right wing.)

Then a friend (shoutout to Richard Suffoletto) pointed out that I had missed the 3/4-inch 90-degree portion that locks the wire in the slot. Ouch! Rather than obtain two new "shepard's crook" wires, I used a small amount (less than 1/4-inch) of the "X" end for the 90-degree bend.

Dry testing showed the geometry was good so I went with it. Later when I calibrated my tanks, they indicated 0 gallons when all usable fuel was gone and 15+ when full or anything above 15. (I believe this is normal and correct.) The float readings also correlate closely with the "totalizer" from the "red cube".

TL;DR Go with the dimensions on the drawing. All of them <g>.

--
Joe
 
Joe has it.

Joe has it on this one and he is correct in that you will find that you will not read the very bottom or top of the range with the "SW" sending units. We have an inverted tank on the right wing and a standard tank on the left wing. The standard tank sender will read or pickup the fuel level down to close to two gallons from the bottom were as the inverted tank unit will read only above three from the bottom. On the top end of the scale the inverted tank sender reads all the way up to 19 gallons showing were the standard tank sender tops out at around 17 gallons showing. You will quickly get used to this once you start flying your good RV. Yours, R.E.A. III #80888
 
Pman said:
For Quick Build Wing builders that have installed the Stewart Warner Fuel Sending units, can you offer any helpful tips or suggestions on the dimensions of bending the float arm?
The plans show an approximate 3" X 3" float arm, however, wondering if anyone has more realistic/accurate dimensions?

Thank you!

Mike
Click to expand...

Carefully follow the directions. The angles of the bends are critical, as is fine tuning of the bends if you want your gauges to read accurately. If you take the time to adjust the bends in the arms you can get very good accuracy at the low end of the scale. At the high end of the scale, the floats will hit the top of the tank at some level prior to the tank actually being full. This is because dihedral places the outboard end of the tank higher than the inboard end, where the fuel senders are located.

In my case, the low end readings are very accurate, but the needles don't come off of the "F" marking until I've burned 5-6 gallons a side.
 
Thanks Joe and Robert for your input----
The challenge is on the Quick Build wing, with the fuel sending unit temporarily mounted/screwed into position, visual access to the interior of the fuel tank is not possible. Without seeing the interior of the tank, determining the required float arm movement (FULL to EMPTY) is difficult.
My DWG 16A, "Wing Fuel Tank" is dated 4/21/00....., the float arm dimensions indicate "approximate 3" bend....., for more reasonable readings, I was wondering if it might be better to error on the shorter side.., that is make the arms slight less than 3" ??
Thank you Guys!

Mike
 
Pman said:
Thanks Joe and Robert for your input----
The challenge is on the Quick Build wing, with the fuel sending unit temporarily mounted/screwed into position, visual access to the interior of the fuel tank is not possible. Without seeing the interior of the tank, determining the required float arm movement (FULL to EMPTY) is difficult.
My DWG 16A, "Wing Fuel Tank" is dated 4/21/00....., the float arm dimensions indicate "approximate 3" bend....., for more reasonable readings, I was wondering if it might be better to error on the shorter side.., that is make the arms slight less than 3" ??
Thank you Guys!

Mike
Click to expand...

Follow the directions. They work. Use a multimeter to validate that the resistance through the sender hits the appropriate value for "empty" when the float hits the bottom tank skin. It may take a few tweaks to get it right, so just tack the sender in place with a few fasteners until the arm is properly adjusted.
 
Thanks Kyle...
I'm thinking of temporally mounting/attaching the fuel sending unit, then inserting a flexible viewing camera through the fuel pick up opening. Doing so, I should be able to view the range of movement of the float arm. I'm more concerned about the lower end reading, hoping to adjust the float so that at the "empty" position the float is just slight above the bottom of the fuel tank.

Thanks for the input!

Mike
 
Pman said:
Thanks Kyle...
I'm thinking of temporally mounting/attaching the fuel sending unit, then inserting a flexible viewing camera through the fuel pick up opening. Doing so, I should be able to view the range of movement of the float arm. I'm more concerned about the lower end reading, hoping to adjust the float so that at the "empty" position the float is just slight above the bottom of the fuel tank.

Thanks for the input!

Mike
Click to expand...

I have the same situation. I have the long flexible USB camera. I'm gonna try and figure out a way to insert the camera and tape it down in position to observe the float arm in the "empty" full down position.

If you get yours done successfully before me, I'd love to see how you did it.
 
Don't make too much work for yourself. Use Kyle's method of attaching an ohmmeter to the gauge. Line up the mounting holes, then rotate the flange, cw and ccw. Watch the resistance change (or not). You can quickly determine if the float is properly positioned (very close to, but not quite, at the end of motion when holes line up) and, if not, by what angle you need to bend the arm. This is easier done than said.
As others have said, the float will hit the top of the tank before it is full, due to wing dihedral.
Most modern EFIS or other electronic read outs will let you calibrate the floats.
 
BobTurner said:
Don't make too much work for yourself. Use Kyle's method of attaching an ohmmeter to the gauge. Line up the mounting holes, then rotate the flange, cw and ccw. Watch the resistance change (or not). You can quickly determine if the float is properly positioned (very close to, but not quite, at the end of motion when holes line up) and, if not, by what angle you need to bend the arm. This is easier done than said.
As others have said, the float will hit the top of the tank before it is full, due to wing dihedral.
Most modern EFIS or other electronic read outs will let you calibrate the floats.
Click to expand...

Thanks! That actually makes sense. Great idea!
 
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