A point not yet mentioned. 5 gallons left in each tank of my Tundra, when the two tanks hold 58 gallons, is a lot less depth of fuel in the tank than if the two tanks held 42 like in a Maule or 36 like a Citabria. Running down to the last 10 gallons leaves the same amount of fuel in each but could call for a different way to manage the remaining fuel even though they could all have the same engine and fuel burn/hr. There might not be a one size fits all on whether it is best to have all remaining fuel in one side or the same amount in each.

According to the Type Certificates, my old 172B had held 42 gallons and 39 usable. The 175 holds 52 but only 42 usable. when I have the cowl off I am going to run it dry with the wings level using the fuel pump (Avcon conversions have fuel pumps) and then fill it from there. I am going to consider this my "out of fuel and going down" fuel level. Then I am going to fill it again making a new wooden dipstick. That way I will know exactly where the fuel quits flowing. When I'm flying, the sloshing of any extra fuel will hopefully add a few miles if I am ever dumb enough to get that low.

My current mount (C150/150TD) has a simple on-off fuel valve. I like it. My old 170 had off-left-both-right, and I ran it on both all the time. I know people who say that you're an idiot to do that, most of them have some procedure for running on one tank for an hour, the other tank for 45 minutes, then back to the first tank for 30 minutes, etc. Pretty complicated and confusing, and a lot of oportunities for error.
What's wrong with running on both? If you have gas in one or both tanks, you'll get gas. Note that at least one mod (Eddie Trimmer's) for tube-n-fabric Piper fuel systems is to replace the left-right-off selector with one that has a both position.

Eric

For the last year and a half I have used a foolproof way to always land with plenty of fuel in the tanks. Part of my pre flight is to drink a 20 oz pepsi. I have 64 year old prostate so I will have to empty my bladder long before my 182 bladders fill with air. My personal bladder does not have the usable it used to have.

Might not work for you young guys. You will have to be more scientific than me.

Tim

Jaerl wrote:when I have the cowl off I am going to run it dry with the wings level using the fuel pump (Avcon conversions have fuel pumps) and then fill it from there. I am going to consider this my "out of fuel and going down" fuel level

Might want to keep a close eye on the temps when you do that.

qmdv wrote:For the last year and a half I have used a foolproof way to always land with plenty of fuel in the tanks. Part of my pre flight is to drink a 20 oz pepsi. I have 64 year old prostate so I will have to empty my bladder long before my 182 bladders fill with air. My personal bladder does not have the usable it used to have.

Might not work for you young guys. You will have to be more scientific than me.

Tim

I'm with you on this one, Tim. My bladder and back limit is about 3 hours. After 3 hours I'm ready to land and stretch my legs and pee!! I don't do too many long cross country's anyway. And I get fuel about every chance I get. 99% of the time, I'm by myself, so the extra fuel is usually not a problem on most warm days. I don't like to fly when it's hot anyways, so DA is not much of an issue neither. The longest I ever went was from Caldwell, ID to Bishop, CA (over Fallon, NV and a little head wind) and I still had over an hour worth of fuel in the tanks. It was just over 4 hours and that was long enough!!

Heck, you guys haven't discovered that once those beverage bottles are empty, you can refill them... Range extenders--just make sure you keep the refills separate from the factory filled types. My back tells me when to land, generally, but having sixty gallons available makes your choice of fuel stops more flexible. You don't have to fuel up every time you land, necessarily, and prices vary wildly from place to place. I find cheap fuel, I tank up.

MTV

Those empty bottle are not much of an option. As the prostate got bigger--You gan guess the rest of the sentence.

Tim

So, what are you saying, Tim--Depends?

MTV

Always thought this required placard for the Luscombe T-8F was interesting:
1. Use left tank for take-off and until at least three-fourths fuel is expended.
2. Use right tank until expended.
3. Use left tank thereafter.

Whee,

I'm not that familiar with the Luscombe's fuel system, but I'm betting that the left tank has both a forward and aft fuel outlet in the tank, while the right tank has only an aft outlet. This is the setup in the Super Cub, which has recommendations similar, but in the operating handbook.

The idea is that a fuel tank must be able to supply fuel to the engine in all NORMAL flight attitudes. If you are at minimum fuel, and descending to land, not having a forward fuel pickup point can mean the engine runs out of fuel.

As an example, the Top Cub has a 50 gallon fuel capacity, but a whopping 6 gallons of that is unusable fuel, since the airplane has no header tanks. That's a lot of excess weight to haul around, but....it meets the certification requirements.

MTV

mtv wrote:Heck, you guys haven't discovered that once those beverage bottles are empty, you can refill them... Range extenders--just make sure you keep the refills separate from the factory filled types. ..........MTV

"Hey this apple juice tastes funny".......

Jaerl wrote:..... when I have the cowl off I am going to run it dry with the wings level using the fuel pump (Avcon conversions have fuel pumps) .....

It'll drain just about as quick if you just disconnect the line from the gascolator at the inlet side of the boost pump & turn on the fuel valve.

Sounds good, I'll drain it with gravity first then hit the pump to see if I can get any more.

And, while draining the gas, bond the airframe to the bucket you're draining the gas into. THAT is a great way to get a fire going. And, to date it doesn't sound like your luck is the best with that airplane anyway--no point in making it worse. A piece of safety wire run from the gascolator to the bucket works fine.

MTV

Maybe I should switch to Full coverage Insurance too!

And while you're at it, you might as well check the screen in the boost pump too. This is often overlooked at annual inspections, as is the inlet screen at the carb.
If you have a round Facet pump, like most Avcon (and similar) conversions, you get at the screen by unscrewing the bottom of the pump.

Eric

Thanks Eric

It is the round Facet pump and I seriously doubt it has been checked yet.

Jerry

Wasn't there an AD or bulletin on the 172 fuel system? Due to vapor locking or something like that, it was either mandatory or recommended to run on one tank except at high power settings or landing.

Hey Eric
Good Call! Looked like a cat must have been living in the tanks. I pulled a couple hairballs out of the fuel pump. Still, it looked a lot better than the tanks. When I drained them a few months ago, I got what looked like the tin foil off a gum wrapper, half a a big spider and a whole bunch of dirt. That was all I had to see before I pulled and cleaned both tanks.

Another question. If I just drain and fill one tank to make a new dipstick, when I switch the fuel selector to "Both" will it transfer fuel from one tank to the other? Or to say it another way, If the selector is on "Both" do the tanks equalize?