Fuel Tank Volume

[Frank Brunot]

I just read with MUCH interest the side note comment in the recent issue of Comanche Flyer that all Comanches with AUX fuel tanks have only 28 gallon MAIN tanks, NOT 30 gallons as the POH says.

So my questions are:

1) Is this true for Twin Comanches as well as Singles?

2) If this is true, why does the POH still say 30 gallons?

3) If true, why hasn't the FAA issued an AD to change the POH?

I know that the POH says 2 gallons are unusable, but I was taught that unusable meant in ALL ATTITUDES. That the fuel was really there, and might be able to be used by moving the plane into some attitude. No attitude will help if the fuel is still in the truck!

If true, it also makes a difference in Wt & Bal, Useful load, etc.

If true, can we (ICS) correct the NEW, UPDATED POH's that we sell, and get this fixed?

[Ben Ayalon]

Frank
After replacing the fuel cells with new I produced a stick so I can deep the tanks, all I could fill were 28gl , I started to search for an answer and was told that the tanks are only 28 not 30. The reason for the 2gl unusable, so I was told, is due to the certification requirements laid by the FAA as otherwise Piper had to apply for new certifications. As for C&G and usefull load I don't think that 4gl make any differance.

Fly safe

Ben

[Charles Schefer]

I believe Ben is correct on that piece of history. Zach Grant told me the same thing regarding how Piper characterized the tank size in order to deal with certification. Zach told me that technically all fuel in the mains is usable (like the aux) but Piper did determine that in certain flight attitudes 1 gal might be unusable so... 28 minus 1 equals 27 usable but of course they say 27 out of 30 usable when really it's a 28gal main.

However.... in June 2013 I decided to "baseline" my fuel bladders to see exactly what they would hold. After a flight when the aux tanks were fairly low, instead of refilling (I always refuel to full fuel after every flight to keep the bladders "wet" with fuel and keep air / moisture out) I siphoned the remaining fuel out. I then drained any that remained from the belly fuel sump / sampling ports under the fuel selectors until nothing more would come out of the aux and they were dry. Then I called for fuel and had the line refill both aux tanks until the fuel was at the bottom of the filler neck of each aux. We reset the truck meter for each tank in this process.

The Left Aux tank took 15.6 gal
The Right Aux tank took 15.75 gal

Later in Sept 2013 I returned from another flight and I intentionally used mostly fuel from the mains with the intention of doing the same test. Using the same procedure described above I completely drained the main tanks until they were dry and called the fuel truck. Same process but the reference point used in filling the tanks was the top of the aft hole in the rear most side of the filler neck. This gets close to the top of the rear of the filler neck when the plane is sitting in it's normal nose up attitude on the ground. I should mention I have the small nose tire STC which helps. Again we reset the truck meter for each tank fill and here were the results...

The Left Main tank took 29.0 gal
The Right Main tank took 28.7 gal

So from this I deduced that Zach (and Ben) are correct tho I was able to squeeze a tad more in but I don't count on it. I count 84 gal total usable (27 in each main and 15 in each aux) but only when they are really topped off. After a few days I find the fuel settles just a little.

- Charles

[JIMICS2452]

I have done a complete drain and graduated refill on all tanks on a 1964 PA30 S/N 498 and a 1960 PA24-250 in order to make calibrated dip stick for them.

On the PA30 I found the bottom of the filler neck on the Main Tanks was 27 gallons and the top was 28.5, on the Aux tanks the bottom of the filler neck was 14.5 and the top was 16.

On the 24-250 the top of the filler neck was 28.