Fuel Tank Capacity

[planepilot1]

(Have discovered a strange thing-----I have been accessing this site from my office and the items I open there seem to have disappeared form the site when I open back up here at home. Strange?)

I read the various bits about fuel tank capacities, unusable fuel, etc. My contribution is that I have a 56 C-172 with a tailwheel conversion, 600-6 tires and my spinner sits just a little higher than the average stock 170, but lower than a 180. Same tanks, etc, etc as a B model 170. Twice I have drained the fuel from my left fuel tank by removing the sump drain. I don't know whether there was any fuel left in the tank or not, but all drained out in the 3 point setting that could. I had the fuel selector turned to the right tank or off (don't remember for sure). I then filled the tank completely at an FBO. Both times I put 19.6 gallons in what is supposed to be a 21 gallon tank. I too suspect that the tank might hold "some" more fuel if the plane had been in a cruise attitude. I suspect that if the tank were sitting on the bench in a perfect attitude it could hold 21 gallons, but in the plane with the 3 point attitude and in normal/everday operation where one wing is possibly higher than the other one I doubt that I or others will average getting more than 38-39 gallons onboard and furthur doubt all of that would be easily useable. I don't want to find out!

By the way George I appreciate your opinions whether I agree with them or not. All of us should be willing to use this source to learn what we can. If we don't agree with George or others, that's OK, but lets not rag on George or others just because we might have a difference of opinion.

My 2 cents worth!

N6888A

[N1478D]

Me Too Frank! There must be something wrong with cable or something up here in North Texas. The posts I read at the office have disappeared now that I am home also.

Wish I could contribute something about unusable fuel. Just know that the three different safe places that I have put the CLEAR skyhawk fuel stick are really good ones. Have not been able to find it again now for the third time.

Am sure that over the past months there would have been an opportunity to react as if I was being lectured, if I would have chose to put out the effort to react that way. Understanding that smiles and other body language cannot be seen in this media, have tried to treat all responses as good natured ribbing. Really, if you have a different opinion than others, it's a chance for all of us to see something from a different perspective, and possibly learn something. If you have a different opinion than George, just fly past him in YOUR 170, he can't stand being passed. It is disturbing to see personal attacks on George, after all that he does for us.

[zero.one.victor]

I have pretty much the same to report as Frank. After totally draining the fuel out of my ragwing,I decided to calibrate my dippin' stick,5 gallons at a time. I have the extra (4th) tank in my ragwing for a total of 50 gallons,25 per side. I marked 10,15,and 20 gallon levels (5 gallons didn't register on the stick). Judging from the markings on the stick,and where it comes up to the bottom of the filler neck,there is room for MAYBE 3 gallons more in 3-point attitude. That makes it 23,which amazingly enough is the placarded usable amount. How about that!
What's weird about it is that the weight of unusable fuel is added to the weight of the empty airplane in doing the W&B calc's,which is why I drained the gas in the first place. I drained out the gas at the gascolator with the airplane in the level attitude,then lowered it back down to 3-point attitude & pulled the sump drains--got maybe another half gallon that way.
So I have to agree that the unusable fuel would appear to be the last bit that won't go in when the airplane's 3-point. But that's not how it's figured in the W&B.
If figuring real-life usable fuel,I would drain the tanks in level attitude,then add gas & mark my tank-dipper as I went,for real-life usable fuel indication--which is what I did.

Eric

[wa4jr]

All I have to say is that I consider it a lot more fun to spend my time flying around in this great WX than spending time draining and refilling my fuel tanks over and over. I don't ever plan my flights to use more than 30 gallons and am quite happy not second guessing the designers about whether they are correct about how much fuel my tanks hold. If you can indeed use the full 41 gallons...great! If you can only use 37.5 gallons as the manual says, that is fine too...either way if you get into the area in which this argument really matters, you need to work on the fuel planning a bit better Come on fellas...let's go fly!