Fuel Rod Length

[TCUDustoff]

My friend's 39' cub had the "neck" on his fuel cap break and my rod was rusting real bad. We ordered a new cap / float assembly from Wag Aero with the intent of me using the rod and he using the cap. Brilliant! Got it Friday and noticed the fuel rod is WAY longer on the J-3 than the Taylorcraft. Since they are both 12 gallons tanks, I would have thought the dimensions would have been similar enough that they would be very close. Wrong!

Could somebody measure the length of their fuel rod for me? Mine looks like it has been cut and re-bent before, so I am not 100% sure it is correct. The header tank is full of fuel right now and I really don't want to have to drain it and go to the pump and re-calibrate.

[Hank Jarrett]

I would put just enough fuel in the tank for minimum reserve and put the float, rod and cap in, then bend the 90 in the wire and clip it off so the rod just touches the cap tube when you are at minimum legal fuel. The loss of wire weight will cause the rod to touch just BELOW minimum fuel (which none of us fly at, right?)

Hank

[Robert Lees]

The Cub tank is inherently different. Apples & oranges.

By coincidence, just today I've started making new fuselage tank float gauges for my two BC-12D Taylorcraft, because I've noticed they have both began to sink in the fuel. Wear & tear. Because these cannot be purchased, I exercise "Owner Produced Parts" regulations.

I have started with the cork, and for this I've purchased two demi-john corks, drilled a pilot hole through them and glued them together, wide-end together. I'll varnish them in due course.



I also purchased some lengths of stainless rod, 2mm diameter 500mm long (plenty of length in hand, as the girls say).



I know it needs to be heat-treated to get the bends right; a short sharp flame should allow me to get the bends in the wire without cracks or stresses. I plan to have the length such that after the top bend of the wire stops bobbing on the top of the fuel cap, I have 20 minutes of fuel remaining. It's easy to test this in anger if you have a full wing tank, a working wing transfer valve and about 10 seconds of altitude; I've always done so on each B model Taylorcraft I've flown.

I'll update these photos as I progress.

Rob

[Mark Bowden]

I might suggest another bend dimension. Chock the wheels and level the aircraft

With an empty tank place the bend in the wire with the cork sitting on the bottom so the bend is at the top of the cap neck opening for the wire.

Put 3 gallons in the tank with the aircraft still leveled (flight attitude)

Make a mark on the rod at the top of the cap neck and paint from this point UP, Red. This is 45 minutes of reserve.

Put another 3 gallons, 6 total. Make another mark at the top of the cap neck and paint a white ring on the rod, 1/2 tank indication.
Now you have an approximate point to transfer the wing tank.

You have to do this leveled because the indication will be in error in ground attitude. The rod will always "descend" at different rates becuase the cross-section AND profile of the tank are not consistant.


I suggest 3 gallons because at some point, likely around 1-2 gallons, there won't be enough fuel to support the rod and it will bottom out before empty.


But it's still best to use a watch or flight timer.

Part number trivia: Taylorcraft 65 HP cap and guage, B-A38-2
Mark

[TCUDustoff]

After some additional thinking, I realized this was a stupid question -- the size / density of the float used will change what rod length is needed to indicate VFR reserve. *sigh*

So I flew the plane for about two hours to get the fuel close to reserve (on the old fuel cap) and then drained the rest of the tank after putting the airplane into level-flight attitude. I had a 2.5 gallon gas can, so I filled that up and emptied into the header tank. I marked the new rod and then repeated the exercise with another 2.5 gallons. I did some interpolation and swagged 3 gallons and used that second mark to bend and cut the fuel rod.

While doing this, I put the tail down between fills and marked a new universal fuel rod at the 2.5 and 5 gallon amounts. I then added more fuel (in tail down attitude) and got 7.5 and 10 gallon marks. Now I have a fuel rod calibrated for ~ 3 gallons in flight attitude (guaranteed more than 2.5 gallons) and a fuel rod to check on the ground.

All in all, the longest part of this was taking the cowling off and transferring fuel between containers. I will do a few test flights to verify my calibration and, once successful, I will post some pictures in case anybody else buys the Wag-Aero J-3 cap in the future.

[Robert Lees]

Don't over-think it; just make sure you have more fuel on board than you think! Err on the right side.
Rob

[astjp2]

Save some headache and install the univair J3 one, works perfectly.