Usable fuel on '67 F?

[Lood]

I am under the impression that my '67 F has all its 64 gal of fuel to use. Someone else differed with me and referred to the FAA type certificate data sheet for the M20 series and specifically the F and J models. According to that document, 15.0 lbs of fuel in these airplanes are not useable.

I just can't lay my finger on it quickly, but I am very sure that I read somewhere that my Mooney didn't have any unusable fuel and is able to burn all 64 gals. I scanned through my POH, but nowhere does it mention anything with regards to unusable fuel, only that it carries 64 gal.

Can anyone give me the correct version, please?

[FloridaMan]

My wings have been resealed, but I have run the right tank dry in my '67F and it took 34 gallons to refill it. Please verify this, but I believe the POH specifies to run one tank for an hour, switch tanks, run the other tank dry, and then switch back to the tank you started with. There were no cautions about doing it any other way. I prefer to manage my fuel by starting on one tank, running it for a specified time to ensure reserves on the other tank and then switching as I don't want my reserve fuel split between tanks and I figure I'll have at least the time remaining on the second tank as I burned on the one I climbed out on. You'll see the fuel pressure drop off before the engine quits and that's when I switched over, but it stumbled for a couple seconds after the transition.

[1964-M20E]

In my 67F I have 54.x gallons usable but I have the O&N bladders so I have less usable fuel than original. The paperwork with the bladders listed 2.X gallon unusable. The POH for the older planes does not dwell on usable or unusable fuel this is before the lawyers started getting involved.

[Seth]

John-

My former F model had bladdders as well and I had the same exact capacity as yours. I knew I had 50 useable gallons - at 11 gallsons an hour, that was 4.5 hours. I tried to never fly for more than 4 hours, usually not more than 3.5 (though I admit I did a few times). I also never ran a tank dry.

-Seth

[DrBill]

I too have new O&N bladders and I have an INCREASE in capacity to 54.8 gal (27.4 / side). All of it us "useable" to me in cruise but only 25 gal /side is "usable" by FAA standards which includes slipping to either side on final to stay on line during a crosswind landing and electing to use a slip vs crab.

BTW the difference in old and new bladders is the cap. The old caps make it so that the tanks cannot be filled as high as the new caps.

I have run a tank dry on purpose but I don't do it regularly. It took 27 gal to fill.

BILL

[Wildhorsesracing]

I have run a tank dry on purpose but I don't do it regularly. It took 27 gal to fill.

I had that same discussion today at the FBO for my BFR. My instructor suggested the same thing, fly high and run one tank out purposely then refill it to find out how much is usable.

[Lood]

I once drained my tank in order to make a calibrated dip stick and the tank actually took 34 gals when I refilled it. Below is the reply from my AME:

"Good question. The 64 gallons is all useable fuel. The unusable is 15 lbs on your F model which would be in addition to the 64 gallons.

In other words the tank capacity is 34,5 gallons."

This makes sense in my case, but if I only fill with 64 gals, is the 15.0 lbs unusable still in effect, IAW, do I now only have 62 gals usable?

[1964-M20E]

I once drained my tank in order to make a calibrated dip stick and the tank actually took 34 gals when I refilled it. Below is the reply from my AME:

"Good question. The 64 gallons is all useable fuel. The unusable is 15 lbs on your F model which would be in addition to the 64 gallons.

In other words the tank capacity is 34,5 gallons."

This makes sense in my case, but if I only fill with 64 gals, is the 15.0 lbs unusable still in effect, IAW, do I now only have 62 gals usable?

The fuel pickup is slightly higher than the bottom of the tank where the drain valve is located this is why you will get the difference and lets you drain off any water. I say you have 64 gallons usable with 68 gallons total 4 gallons unusable.