Sunday, October 18, 2015

Bending Fuel Level Sending Unit’s Float Arm

In addition to the mechanical Moeller fuel gauge, the RV-12 fuel tank is also equipped with a sending unit that is connected to the SkyView … this allows the Dynon unit to receive fuel level information so it can be shown on the primary flight display. When the sending unit’s float arm is removed from the box, there is already a hooked end to capture the float …. However, the rest of the arm is straight and requires the builder to make two bends per the plans. The plans would suggest the drawing is 1:1 but on the plans there are measurements for 6 1/4" that do not match the drawing … my drawing appeared to be a little shorter. Decided to bend the float arm as shown in the drawing but used the measurements shown in the drawing. Below is a photo of the drawing and the sender unit arm after the first bend was completed.
Completed first bend of the sending unit’s float arm.

A vice was used to secure the float arm and the bends were made by using a piece of wood to bend the arm … doing this leaves the metal rod as straight as possible. Once the bends are completed and the excess rod cut off, the float rod slips onto clips on the sending unit’s arm. Ohm readings were made and were almost spot on to the published 30 to 240 ohms as the float arm is moved through its full range of motion.
Completed float arm attached to the fuel level sending unit.

At this point the plans have the builder temporarily install the sender unit onto the tank to check for clearances and to adjust the float position. At the bottom of travel, the top of the float is to be 1 5/8" off the bottom of the tank … and at the top of travel, the float is to be 10 1/4" off the surface of the bottom of the tank.  I used a ruler with two pieces of tape to identify the low level and high level and used that to make the adjustments. Also, the float arm is not to rest on the T-1208 baffle.
Top of the float in the low position is approximately 1 5/8" off the bottom of the tank.
Top of the float in the high position is approximately 10 1/4" off the of the bottom of the tank.
After completing the adjustments to the float arm, there should be clearance between the T-1208 baffle and the float arm. Looks good, I can get my finger between the two.

Today the plan is to install the top skin of the fuel tank … more fuel tank sealant fun, can’t wait ... not.