231 Usable Fuel

[xftrplt]

According to the POH and the placards at the fuel fillers, the usable fuel of my '81 K is 75 gal.  (No bladders.)

Twice I've checked the usable fuel by running tanks to engine sputter.

Each tank takes 32.5 gal., filling above the flapper to the neck.  The aircraft is missing 10 gal. of capacity!

Any ideas/suggestions?

TIA

[FAST FLIGHT OPTIONS LLC]

You have to put the last 5 gallons in real slow.  Just because fuel is stuck above the flapper doesn't mean the tank below is exactly full. Not sure this makes sense but I know it to be the case in my K

[xftrplt]

Quote: 201-FLYER

You have to put the last 5 gallons in real slow.  Just because fuel is stuck above the flapper doesn't mean the tank below is exactly full. Not sure this makes sense but I know it to be the case in my K

[231flyer]

I concur.  i usually ask for a top off after I land and then again before I am ready to go.  Typically the difference is around 9-12 gals. The wing compartments have anti-slosh vents and tend to trap air.  One of my flying mentors(20 yrs ago) advised me store the plane with tanks full to prevent condensation. I have lived by the maxim and the added benefit is the gas has plenty of time to settle and free up space for the last few gallons.

[aviatoreb]

Quote: xftrplt

According to the POH and the placards at the fuel fillers, the usable fuel of my '81 K is 75 gal.  (No bladders.)

Twice I've checked the usable fuel by running tanks to engine sputter.

Each tank takes 32.5 gal., filling above the flapper to the neck.  The aircraft is missing 10 gal. of capacity!

Any ideas/suggestions?

TIA

[xftrplt]

Thanks, all.  WILCO. 

[Piloto]

Sometimes when the tanks are resealed the mechanic applying the sealant may plug the upper vent holes on the tank ribs. This will cause air to be trapped on the upper part thus limiting the amount of fuel that can be put in. If the drain bottom holes on the ribs are plugged not all the fuel will be drained out. This can be inspected by inserting a borescope through the filler hole.

José

[xftrplt]

Quote: Piloto

Sometimes when the tanks are resealed the mechanic applying the sealant may plug the upper vent holes on the tank ribs. This will cause air to be trapped on the upper part thus limiting the amount of fuel that can be put in. If the drain bottom holes on the ribs are plugged not all the fuel will be drained out. This can be inspected by inserting a borescope through the filler hole.

José

[xftrplt]

FWIW, I just returned from a round trip to Vero Beach, FL, flown nonstop both ways from western MD.   There were headwinds southbound (5+45 enroute), and knowing my actual usuable fuel was critical.  I suggest being ABSOLUTELY sure of your usable fuel, by whatever EMPIRICAL method you choose, not relying on specs.   I personally think running each tank until the engine stutters in flight is the only sure method, but I know this has been addressed and debated before in detail.