Question for the group about correct amount of fuel.

[buzz]

Thought I would toss out a question for the group about how much fuel is really usable in my tank.

1. So my P2008 manual says Capacity of individual tank is 13.7 gals and total usable fuel is 27.4 gals

2. On another page is says total fuel capacity is 27.5 gals

3. On another page it says fuel tanks 13.7 less the unusable fuel =1.1 gals

So my question has to do with the unusable/usable fuel. What is your interpretation of how much usable fuel is in my tank. If my tank is holding 13.7 gals is my usable fuel 12.6 gals?  If so that does not match with point 1 that says total usable is 27.4  Additionally if my fuel indicator says 13.7 gals is there actually 14.8 gals in the tank or is the unusable all ready calibrated out of that indication?

Sorry if these are stupid questions. The manual information doesn't seem consistent.  Points 1 and 3 appear to be in conflict.

[Glenn]

Hey Buzz,

Do a search of TecnamTalk for some information about usable fuel.
For what it's worth, I can burn 16 gallons out of my P2008 tanks.
Just my experience. Your plane may be different but the POH is wrong.

Glenn

[Flocker]

Mark G should chime in on the unusable number - I recall that he's run a tank dry before in one wing.
I can attest that the total fuel capacity is 16 gal per side.

[Glenn]

Jan 12, 2018 0:43:04 GMT Flocker said:

Mark G should chime in on the unusable number - I recall that he's run a tank dry before in one wing.
I can attest that the total fuel capacity is 16 gal per side.

Both Mark G and I have done that.  Running one tank dry is nothing new. 
The airlines did it on all long distance routes back in the days of round engines.

Glenn

[geobuff]

My testing on my Astore has shown the tank labels (13.5 per side) to be accurate. For example. I did a long x-country run where I ran my tanks down to 2 gallons per side (on the gauges). Then I drained the tanks in the hanger and found exactly 2 gallons remaining in each tank. I they filled the tanks, which were now totally empty, , and they took exactly 13.5 gallons per side. The bottom line here is I now believe the numbers. As they say on the TV commercials, 'your results may vary'.

[montanapilot]

Tecnam's specs show the Astore's fuel capacity as 29 gallons. From your testing (good for you for doing that), it looks like the capacity is 27 gallons.

[Glenn]

Jan 12, 2018 15:12:45 GMT montanapilot said:

Tecnam's specs show the Astore's fuel capacity as 29 gallons. From your testing (good for you for doing that), it looks like the capacity is 27 gallons.

And that is EXACTLY the reason running a tank dry should be done. 
It either confirms the number in the POH or provides the a better number.

Otherwise, available fuel is unknown which may one day...ruin your whole day! 

Glenn

[buzz]

Hi guys thanks for the responses. My question isn't about how much we can put in a tank. My question has to do with accuracy. Yes I do believe (at least according to my Skyview reading and fuel slips) that you can put in at least 16 gals.

Glenn you said you can burn 16 gals from a tank. Do you believe there is an additional 1.1 gals in the tank unusable as the manual says?

Flocker you said your tank total capacity is 16 gals. Do you believe 14.9 gals is usable and that there is 1.1 unusable?

Geo you said you believe your tank labels for Astore at 13.5 are accurate. For accuracy do you also have an unusable amount on top of the 13.5 or is the unusable subtracted from 13.5?

Sorry to sound so picky. Not trying to prove anybody wrong. I just want to ensure I have a full understanding of my fuel because I find the POH wording confusing. Yes I know I should fill then drain my tanks.

[Ed Midgley]

If you run a tank dry in level flight then for all practical purposes the tank is dry. All manufacturers list some unusable since they don’t want the liability of you running out and crashing. Also in a slipping turn it’s possible to unport the pickup and stop the engine with less than the unusable fuel on board.
Ed

[Glenn]

BUZZ,

Accuracy of the your fuel gauges?  Well that depends on who calibrated your system.  When my tanks are full the gauges say 15 gallons.  I asked Shannon Yeager about this when I flew my new plane home in May 2016.  He responded that he could walk me thru re-calibration if I wanted to do that.  

I have not run the left tank dry inflight.   When I fly on the right tank, my left tank quantity increases (as expected).  When I'm flying max range I land with all available fuel in the left tank.  After landing, fuel added to the right tank has never been less than 16 gallons and has never been more than 16.2 gallons.  The difference could be explained by maneuvering or pump accuracy.  In my hangar, I've drained the left tank by using the gascolator (on the firewall) and fuel required to fill the tank was 16.1 gallons.  We should all be aware that fueling on a ramp that is not exactly level can change these numbers. 

My tanks each have 16 gallons usable as long as I'm not doing any crazy maneuvering.  Come to think of it, I never do any crazy maneuvering.  

Glenn

[Flocker]

Jan 12, 2018 20:58:47 GMT buzz said:

Flocker you said your tank total capacity is 16 gals. Do you believe 14.9 gals is usable and that there is 1.1 unusable?

I've never run them dry, but I did fill them gallon by gallon from empty to calibrate my dipstick. 16G per side. Mark has run them dry. Let's wait for him to chime in.

[ChiMike]

I have a 2015 P2008t. I have the same 13.1 placards references earlier. So rough math says 1/4 tank is a bit over 3 gallons—therefore to fill requires 10. It took almost 13. Each side. Hmmmmmm. A couple of more tests revealed the same. No matter what my gauge said, the amount needed to fill the tank added up to total tank capacity of a little over 16 gallons a side. Spread sheet, gauge pictures before and after, the empirical method utilized.

So—one last test: left tank, half; right tank, as close to empty as I dared—somewhere between E and 1.5 gallons. 75-80 degree day. To fill, it took 8 on the left and 15 on the right—mogas, 5 gallon cans I’d filled myself exactly.

Subsequent purchases from the 94 Nolead Avgas truck here at Gary have been spot on to the same calculations.

My conclusions on MY plane: my dial gauges are accurate to 1/2 gallon, level, from my visual interpretation that is always conservative, my fuel used calculation from my GTN 650 is spot on, and my tanks hold a bit more than 16 per side—call it 16.2 or so.

Yet the calculated weight, based on the POH and placards for a full load is only 157.2 lbs, not 194. Sweet!

[MarkGregor]

Sorry for the slow response. It is my experience the P2008 fuel tanks likely hold 16 plus gallons per side. In level flight without turbulence I would expect all will be usable. With that said I think we need to follow the numbers provided by Tecnam. Yes that likely leaves fuel in the tanks but it is what is published and leaves a safety margin.

If I am trying to maximize distance between fuel stops I do burn one tank empty because I prefer to have all remaining fuel in one tank to minimize the chance of unporting a fuel tank in a bank or turbulence.

Also keep in mind that some of our 2008s return fuel to one tank and others return to both tanks. If you intend to maximize legs it might be wise to have a tech determine which tank or tanks are being returned to and when.

Fuel gauge accuracy is a whole nother issue. I would call it unwise to assume every 2008 fuel gauge will give the same reading when measuring the same amount of fuel. Comparing between owners may not be that useful. About all we can do is compare the gauge reading to the actual amount needed to refill the tank.
Most all of us would like to have an accurate fuel totalizer. Maybe in the future!

I know this doesn't really answer your question Buzz. I wish I could give the complete answer you want.

Mark

[buzz]

Thanks everybody for your ideas. This helps me better understand how others are approaching their fuel management. Good stuff.