Actual Fuel quantity vs. indicated

[Scott Aviation]

So came time to do my weight and balance on the plane and didnt have time to drain all the fuel so I filled it to the bottom of the triangle indicator in my 64 Gall. fuel tanks in my 201 which clearly states its 25 Gallon mark. Does anyone know off the top of their head if this is a true representation of 25 gallons or 25 plus the 2 gallon non-usable level? etc. Any insight would be great, other than draining my tanks again I have no way of telling.

Thanks.

chris

[jeckford]

Im not an expert but from what I understand and have been told the fuel Tab is fairly accurate for 25 gal plus unusable fuel.  You have to make sure the plane is level though for it to be accurate. 

 

My wife is originally from Vancouver....love the Nanaimo bars..

[Bennett]

Why don't you just fill both tanks to the very top (level airplane), and subtract the weight of 64 gallons of fuel (6.02 pounds per gallon)? That would leave the 2 gallons unusable fuel as part of the aircraft empty weight. (Or subtract 66 gallons times 6.02 pounds per gallon for empty tanks). 

[jetdriven]

Quote: scottaviation

So came time to do my weight and balance on the plane and didnt have time to drain all the fuel so I filled it to the bottom of the triangle indicator in my 64 Gall. fuel tanks in my 201 which clearly states its 25 Gallon mark. Does anyone know off the top of their head if this is a true representation of 25 gallons or 25 plus the 2 gallon non-usable level? etc. Any insight would be great, other than draining my tanks again I have no way of telling. Thanks. chris

[kortopates]

I noticed Bennett was using 6.02 and Byrons POH is showing 6.0 lb/gal for fuel - yet neither is correct and I was puzzled till I saw the date of Byrons POH. The POH is generally always the official source, but in this case Byrons '77 POH's, is quoting the weight of 100 octane (from 100/130 - dyed green) that we no longer use, the correct weight for 100LL (blue) is 5.82 lb/gal. Which is what Bennett should find in his POH.

Those of you using 6.0 lbs/gal are robbing yourself of some useful load. For example in my 252 with 75.6 usable, the difference is 13.6 lbs.

Also, the newer POH weighing instructions have you do as Bennett suggest to weight the plane with full fuel and full oil and then subtract the usable fuel weight at 5.82 lb/gal. An optional method they provide for my K model is to drain the tanks entirely as described in Byrons older POH using the electric boost pump and add back on the unusable fuel (1.5 gal) and fill oil to capacity (8 qts). (BTW, I know of two people that have burned out their boost pump running it continuously to pump a tank empty, so be careful if you use that method.)

Personally, I think I prefer the using the original method of weighing with the tanks empty as described in Byrons POH. Primarily because it takes all the guess work of finding exactly full - which the factory defines as at the base of the filler neck - not the top. Except for the newer R and TN models that have the modified 102 gal filler necks that are really are measured to the top.

[jetdriven]

FWIW I drained out the tank by wedging a tool under the pull drain ring and letting it run out. It takes an hour to drain 10 gallons. That fuel  boost pump overhaul is $1,150 now and it has huge letters on it to never run dry.

Ours has bladderswhich complicates things further, and full, it will hold another 2 gallons if added slowly. I drained it all out as noted above and it only took 26.5 on the left although it is placarded for 27.2. 

5.82 LB/gallon is a great idea to increase useful load without an STC. Not adding newly installed equipment to the W+B that weighs under one pound is another.

[Bennett]

Paul, thanks for the clarification of the weight of one gallon of aviation fuel.  I used 6.02 pounds per gallon as that is the number I found on a few web sites - most just used 6 pounds per gallon. A couple of weight and balance apps also used 6 pounds per gallon, and I was suckered into using that number.  Nice to pick up a few more pounds of useful load.  When I had my K (converted to the 261 Trophy conversion) we made made many mods to her, and each time (several Mooney shops) we did the tanks full and subtract the weight of the fuel (and full oil) method. Also I never read the section about "to the base of the filler neck". For long flights I always have the tanks filled brim full, even letting the fuel settle, rock the wings, and then add the bit more than can be done at that point.  

I had a LSA built in the Czech Republic, and I never trusted their numbers for tankage.  I drained the fuel completely, and then re-filled to the top to find out what the real number was: less than advertised.  Also, when I had my Monroy conversion done for the 261, we ended up with a bit over 115 gallons in the wings - more than what we expected, or what some other Mooneys had. Didn't really beieve it, so we went through the whole process of draining, and refilling - still ended up putting 115 gallons in her.  I hate draining fuel. I used many plastic gas tanks, and worried about the potential of sparks setting off an explosion. I kept peiople away, and used evey caution I could think of, including grounding the airplane, but the plastic tanks were not grounded, and I was careful not to bang or scrape anything.  Thats why I prefer the fill and subtract weight method, and now that Paul has given us a better number than "6", I'm happy. 

[Bennett]

Paul, and all.

Finally went to the airplane and looked at my POH (issued 9-4-81) It shows under ( Weighing (page 6-3) to "top off the tanks" (no mention of "base of the filler neck") and subtract the weight of the fuel: 64 gallons at "6 lb/gal". I guess there are several variants of the POH for M20Js. I do like the number 5.82 lbs/gal, but I haven't found it outside of Paul's posting. Any suggestions where I can find where Mooney says it is OK to use this number? Thanks.

[carusoam]

Bennett,

My 94 Ovation POH uses 5.82 #/gal for 100LL...

This is from the factory in the "airplane weighing procedure".

The phrase "top-off" is used to explain how much fuel to put in.  

Hope this helps...

-a-

[Bennett]

Quote: carusoam

Bennett,

My 94 Ovation POH uses 5.82 #/gal for 100LL...

This is from the factory in the "airplane weighing procedure".

The phrase "top-off" is used to explain how much fuel to put in.  

Hope this helps...

-a-