Usable Fuel?

[JimCNY]

What is the usable fuel in a PA-22/20 with stock 18-gallon wing tanks? I can't find that in the manual. I'm planning for my first long cross-country (New York to Sun-N-Fun). Will it hurt the engine to run the right tank out on one of my legs and then get an accurate fill amount at the gas pump?

Is there any chance that it would be different in the right tank than the left (of course, I would not want to run the left tank dry and then have to maneuver on a low right tank)?

Thanks for the help,
Jim

[joewcasey]

You always run the risk of sucking in contamination when you run a tank dry. With that said, I've run the right dry (without intentending to) and it took right at 18 gals to fill it. On a normal trip, I'll usually figure 1 gallon unuseable per side. Works well enough.

[6811]

HI I will also fly from the north(ma) to sun in fun. Running a tank dry is not a good idea but I do it all the time on long flights so I know what fuel I have where. Usable fuel by definition is the fuel that can be used in all flight attitudes (climbs, descents, and turns) In straight and level flight quite often you can run a tank all the way to dry including "unusable fuel" Which is why I run a tank dry in airplanes with multiple tanks. In my pacer when I have run a tank dry I switch tanks and it always roars right back to life. It looks like I will have three airplanes in my group going to Sun N Fun a PA 28, a C172, and my PA22/20 Hope to see you at Sun N Fun I always a good time when I go.

[Gilbert Pierce]

Every time I have run a tank dry it has taken at least 18 gallons to fill it.

You know that little sump below the rear tank outlet holds about a quart of fuel and the quick drain is right in the bottom of it so if you religiously sump your tank before the first flight of the day you are not likely to draw anything into the carb because there won't be anything there. That is of course if you didn't pump in a gallon of water at last refuel point and didn't check it.

[Gilbert Pierce]

6811
When you get to Sun'N Fun look me up. I will be in a RED Clipper.
Gilbert

[Steve Pierce]

I run my right tank out on a regular basis. Never a problem except to the passengers not expecting it. :o Hope to see you at Sun & Fun. I'll be in tan Pacer with droop tips but hanging around that Red Clipper. :lol:

[JimCNY]

Thanks guys!! That helps a lot. I'll plan on using up to 32 gallons and I should be good with my reserve. I do sump the low point under the cockpit before every flight so I'll consider running the right tank dry. I'm a little nervous about it so not sure I want to. It might be good to experience though and I'm planning to cruise at 8500 ft.

I'll try to look you all up down to Sun-N-Fun.
Jim

[Hillbilly]

Jim thats a nice looking pacer in your avatar, yours?

[JimCNY]

Yes, but I can't claim credit for how nice it is. I and a partner bought it from David Grimm. My partner has since decided he wanted a Beech Baron but I'm loving the dickens out of the Pacer.
Jim

[Hillbilly]

No matter, nice ship.

[JimCNY]

Thanks!!!

[Gilbert Pierce]

You also need to sump each wing tank before each flight and after refueling. You will get the water out before it ever gets to the underfloor sump.

[Bultaco Jim]

I also have emptied both tanks in the air - yes, at different times! I put back 18 gals. in each. I also flew in steep right-hand circles with less than 1/4 full in the right tank, without a hiccup. This was done over the airport. I just like to know my airplane. I would never take off like that though! Jim

[Stephen]

BJ, good to know that you would not take off with empty tanks. But, I'm not so you about you guys flying around until you tank runs dry. I like the sound of my engine running.

[Bultaco Jim]

I just wait until the first hiccup, I don't wait for the engine to quit. I like that drone too! Jim
P.S. This is done just the one time, just to know the actual usable fuel.....probably won't need this info ever. These things hold so much fuel, I always plan a 1hr reserve. That's still a 4 3/4 leg on the Colt, and, 4 1/2 hrs on the Pacer. The Pacer has the aux. tank.

[JimCNY]

So, you definitely get some warning before things go silent?

[Gilbert Pierce]

I have no qualms about running a tank dry in the Clipper. Do it regularly with no problems. HOWEVER-I alway warn my wife that it is going to run out.
I have never gotton a miss or stumple. Cruise power one second and dead silence the 2nd. Switch tanks and I am back to cruise power as fast at it went dead.

[joewcasey]

Running a tank dry is definately not a habit, I think I've done it all of three times in goin on 2.5 years of owning the airplane. I also ONLY do it on the right tank, with a reasonable amount in the left.

[Bultaco Jim]

That's interesting, Gilbert. Mine will stumble very slightly, wait 10 seconds, then stumbles about twice as much. I don't wait around for whatever comes next! Jim

[Stephen]

I still don't get this running the tank dry thing. Since my bladder is far too small and butt is too weak to come close to flying it to its max range, I've never cared about using the last drop of gas. As fuel comsumption rates vary depending of conditions, I use a conservative figures and dip check fuel tanks prior to T.O. Knowing what you have in the tanks at T.O. seems to me just as useful as running a tank dry to "knowing" that you still have "X" amount of fuel in the other tank. Hey, we each have our own methods. I'll stick to scaring the s---- out of my wife other ways. She dose not seem to like flying under low overcast across open water, "even when I tell her I promise not to run a tank dry".

[Gilbert Pierce]

My left fuel tank has the original Clipper fuel gage which is extremely accurate. The right fuel gage is only accurate when the tank is full. It shows empty with anywhere between 4 to 6 gallons in it. I like to land with one hour of fuel minimum. So, on a long trip if I am concerned about alternatives (wx) I run the right tank dry. Then I know exactly how much fuel I have. I also have fuel flow gage and computer but don't necessarily trust it either and so I use a dual timer mounted on the windshield post to time the fuel burn in each tank.. Am slightly annal about how much fuel I have.
One thing the fuel flow gage has taught me is the fuel flow increases exponentially with power setting and varies with altitude which means the timer ain't all that accruate either.

[Stephen]

I have been flying a C-177RG, which has a fuel flow gauge and is used for leaning. That is one of the few features I really like in this plane. What a difference leaning makes in the 0-360. I agree on the trust factor for these gauges, but I would love one in my plane.

[JohnW]

Gilbert; if it were MINE, I'd be wanting to know that when that gauge reads "E" it is about to be empty! Who cares what is says when you fill it? Not one among us sweats the load when we have MORE FUEL than the gauge reads, but by golly, what pressure you be "enjoying" should you ever NEED to know when it's EMPTY!

[Gilbert Pierce]

John, I agree with you. However the float is halfway up the side of the tank. When the float hits the bottom of the tank there is still fuel behind it.
The float reads 28 ohms when the tank is full and zero before it gets empty so the arm needs adjustment. I need to pull the tank out and "recalibrate" the float arm. We did not get your 160 or so inches of snow this winter so I have not wanted to quit flying long enough to pull the tank out. I started once to take the gage out with the tank installed and decided I wasn't ready for that either. I have a Univair butt rib which makes it more complicated.
So I have back up systems. Plan on landing with an hours worth of fuel, Time the tank burn, carry my reserve in the left tank with an accruate gage and last but not least a fuel computer that as always with +- 0.3 gallons used when I fill up, normally I have 0.2 to 0.3 gallons more then the fuel flow shows. I also have a calibrated dip stick I made to stick the tanks with prior to flying if they are not full. I have never landed the airplane with less then 5 gallons of fuel left except for the time my gascolator dumped out about 15 gallons in flight. It got replaced by one of Steve's Aircraft units.

The only really accruate fuel tank gage I ever saw in an airplane was the Model A Ford gage in my Clipper nose tank wich has been removed and the same gage in my Vagbond.
When I had the Nose tank in the Clipper I always knew exactly how much fuel I had and I always know how much fuel is in my Vagabond.

[Bultaco Jim]

I disagree with those who don't think that they need to know exactly what's in their tanks.These Pipers with 18 gal tanks seem to be consistant, but that isn't the case with all planes. My best friend had a bad experience with his Aeronca L3 shortly after purchase. The former owner had modified the header tank, in effect, lowering it. My friend did his calculations for a X-C based on the published tankage. Now , this plane only holds 12 gals, so you are always going to arrive with not much! The plane ran out of fuel 20 miles out, because 3 gals were now unusable. The former owner had just never tested it.
By the way, My buddy made the airport! He found that if he dived- the engine caught again for a while, putting the gas above the carb briefly. So, he did his best Porpoise immitation and dead sticked in in, right in front of the FAA guy. (who slapped him on the back and said "well done") You just never know.

[rexandkim]

Running a tank dry is not for sissy's and I am a big one. Rex did this one day and while it was sputtering he reached down to flip to the other tank and pushed on the yoke. Of course we nose down a little. I was terrified! I thought I was going to have a heart attack. I made Rex SWEAR he would NEVER do that again. Our teenage son tells the story of the time we almost dove out of the sky and crashed.

:o

[Stephen]

I fully agree that it is important to know how much fuel is in the tanks. Besides being full when you take off or empty while in the air, timing the flight and/or using gauges are all we got to go on (which is only an approximation). I think that the SC sight gauge is one of the best ways to go. My old J-3 wire on a float was slick too, until it would stick all the way in the up position.

[joewcasey]

Two of the three times that I ran a tank dry was when I was at the end of a long trip where headwinds had increased significantly beyond the forecast, near the end of the trip. I wanted to make sure I had used every drop in the right tank so I wouldn't be tempted to use it in the pattern. I don't make running low on fuel a habit, but I do fly a lot in ND, MTand WY, and over the years, the distances between fuel pumps has increased significantly. Also, as we all know, high density altitudes in a PA20 or 22 require that you watch your fuel loads (especially with only 135 hp out front). I've never had to put more than 31 gallons onboard, and I do believe in knowing your airplane. I don't recommend that you go out and fly on the bottom half, but I've gotten to know mine very well during our time together and am just as comfortable flying with 8 gallons as I am with 36. Depending on conditions, 8 gallons can be very desireable.

[rmalone]

There she goes again. Always has a story about one of my adventures. ;)

[59pacer]

I do it frequently on long trips, as I can't see the point of having a small amount in 2 tanks, rather than the total in the left. Any small amount of fuel in the right tank is unusable when you might need it on an unexpected missed approach, and there is more chance of 'un-porting' if you need to sideslip. From changing to the left tank, it takes a slow 5 count to resume full power, about half the current certification requirement.

[PACERGUY]

I usually cough the right tank on long trips than finish on the left. It is best to let passengers know ahead of time. I have site gauges but they are not as good as my EI fuel flow. It is within .1 gal for a 18 gal tank. I have right and left only on my fuel selector so fuel keeping track of fuel is a lot easier. I have friends have a both only fuel and they have a lot harder time keeping track of remaining fuel. Real hard when you do a few pee breaks.
DENNY

[Bender]

I routinely run the right completely out on long trips as well. I climb out on the left and figure my fuel burn at 12 gph (15 minute climb = 3 gallons). Once at altitude I get the engine leaned out, power set for cruise, hack the clock and switch to the right tank. When the right burns out I can divide 18 by time (hours) to get my exact fuel burn for that particular day, throttle setting, altitude, etc. Then I have a very good estimate as to how long the remaing 15 gallons in the left is going to last.