Why do we switch tanks?

Oliver- I think you misread which rules I meant. I was mention my work FOM rules. ;)

On the tank issue- Our airport was warned, by the tank company, not to get below a specific level because of exactly the issue Tim is talking about. I believe our tank starts picking up the bottom sludge around 4". The only time we are ever that low is for inspections and cleaning.
 
The fuel gauges in our wagon are so bad, when they get below half I start wanting a fill.

I go by hours(burn) more than the needles on X/C.

I swear Cessna ripped off an old Chevy truck I once had. When the needles finally come off full, they nose dive to empty. :eek:
 
My 1967 Mooney POH recommends first hour on one tank, then switch to the other tank and run it dry, then back to the original tank. I've done this ONCE just to check and it was a non-event. As soon as I switched tanks the engine started immediately. I just don't see the need to so although some do it regularly. In long flights I will use my fuel totalizer to run one tank almost empty (within a couple of gallons) in order to maximize my usable fuel on the remaining tank. I never go below one hour reserve in VFR or 1.5 in low IFR.
 
txflyer said:
The fuel gauges in our wagon are so bad, when they get below half I start wanting a fill.

I go by hours(burn) more than the needles on X/C.

I swear Cessna ripped off an old Chevy truck I once had. When the needles finally come off full, they nose dive to empty. :eek:
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My Subaru fuel needle sticks to F for about 70-100 miles and then acts like it fell off a cliff. Plus it's off by 3-4 gal usable at E.
 
bartmc said:
A guy a few years back landed a 182 on the highway south of Hamilton Montana with a dead engine and an entire wing full of fuel.
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Less than a year ago, some guy crashed his PA28 on a hillside near Petaluma with one wing full of fuel, at night in low IMC.

He flew in from Oregon when his engine quit over Pt Reyes. While maneuvering to try to glide into Petaluma, the engine restarted briefly, then stopped again. The impact showed evidence that one wing burst (the whole rivet line was torn on the wing) and the other didn't, and there was a nasty fire.

So, we don't know for sure he didn't switch tanks, but the distance, symptoms (including the restart on turns), and wreckage are all consistent with that. As you might guess, he isn't around to tell us precisely.
 
With full tanks I switch at 10 gallons used and at 30 gallons used. After three hours it is time for a break anyway. I also know how much fuel is left in each tank. With the bladders they appear very empty after only an hr of flying.
 
BGF_Yankee said:
Just because you have a BOTH setting doesn't mean that fuel comes out of both tanks at an even rate...(
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It doesn't matter, the fuel tanks are in the wings overhead, the fuel selector valve is in the floor. As long as there is an unobstructed cross vent between the two tanks it is impossible for pressure in a lower or even empty tank to displace fuel from the opposite tank at the selector.

It is possible however if the cross vent is absent or obstructed.
 
MAKG1 said:
Less than a year ago, some guy crashed his PA28 on a hillside near Petaluma with one wing full of fuel, at night in low IMC.

He flew in from Oregon when his engine quit over Pt Reyes. While maneuvering to try to glide into Petaluma, the engine restarted briefly, then stopped again. The impact showed evidence that one wing burst (the whole rivet line was torn on the wing) and the other didn't, and there was a nasty fire.
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I give pilots benefit of the doubt first ... maybe he had a clogged vent and couldn't get fuel from that tank.:dunno:
 
danhagan said:
I give pilots benefit of the doubt first ... maybe he had a clogged vent and couldn't get fuel from that tank.:dunno:
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One of the reasons I won't run a tank dry. If there is a problem of any sort with the other one I want to be able to switch back to the last known good configuration.

Of course you know that is the same philosophy a squirrel uses when he's almost all the way across the road, get's spooked and runs all the way back across to the last place he knows he was safe.
 
Silvaire said:
One of the reasons I won't run a tank dry. If there is a problem of any sort with the other one I want to be able to switch back to the last known good configuration.

Of course you know that is the same philosophy a squirrel uses when he's almost all the way across the road, get's spooked and runs all the way back across to the last place he knows he was safe.
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Exactly your last known good configuration was, "almost empty". That doesn't do you much good.:lol:
 
Henning said:
Exactly your last known good configuration was, "almost empty". That doesn't do you much good.:lol:
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For the story at hand, switching every 30 minutes would have meant the last known configuration was half full. He was less than 50 miles from his destination. If he had a clogged vent that the NTSB couldn't find, he would have found it out while still over Oregon, with hours of reserve fuel to find an IFR alternate and land.
 
I used to have a K35 Bonanza. Its fuel system made running the aux tanks dry a desirable thing to do.

It had two main tanks that held 25 gallons each; and two aux tanks that held 10 gallons each. Mains could only be selected one at a time, but on the 'aux' position fuel was drawn from both aux tanks together.

The fuel injection system drew fuel from the tanks at the rate of about 20 gph. But at cruise the engine was only using around 12 gph. If running on a main tank, the excess fuel was returned to the tanks from whence it came; but if running on aux, excess fuel was sent to the left main. If the left tank was already full, then fuel got pumped overboard.

Only main tanks could be used for takeoff and landing.

So the drill was to first use an hour out of the left main. Then the aux tanks were used, good to the last drop. It only took about 45 minutes for the 20 gallons to be emptied from the aux tanks, while the gauge for the left main tank would be rising as fuel was pumped into that tank. I'd watch for the first flicker of the fuel pressure gauge indicating fuel exhaustion in the aux tanks, then switch to the right tank, and usually there was no change in engine sound.

Since fuel left in the aux tanks was unavailable for landing anyway, switching away from the aux tanks five minutes before empty meant ten minutes less endurance. So it was best to run 'em dry.
 
What kind of idiot designed that fuel system?

Recirculating fuel is a good thing (it suppresses vapor lock), but it's silly to pump it elsewhere from whence it came.
 
German guy said:
Frankly, I don’t see how the concept of running one tank empty in order to get an precise idea of the actual remaining fuel, and to have all of the remaining in one tank would interfere with the rules, as long as the difference doesn’t exceed the aircraft’s limitations.

I think that it actually increases the safety, as this strategy improves the awareness regarding the remaining fuel and as it also avoids the situation that tanks will have to be changed at a possibly very late phase of the flight.

I might be overly cautions, but I always end up with at least two hours of fuel left in the tanks, what makes long cross countries somewhat inefficient.

The reason is, that I plan for 1 – 1.5 hours of reserve, depending on the availability of fuel along the route, to deal with possibly necessary deviations or unexpectedly unfavorable wind conditions.

Roughly another hour however comes from my conservative assumption regarding fuel consumption and that I neither want to run a tank dry nor change from one almost empty tank to the other, which does also not have much fuel left in it. 1 hours worth of fuel in the Archer is just about 4.5 – 5 gal. per side. I would not feel comfortable to find myself on the final approach, wondering if I REALLY still have 4.5 gallons left in this tank or whether I should rather switch to the other tank, of which I am just as uncertain regarding the remaining fuel. As a result, I toss around almost 10 gal. of ‘unusable’ fuel. To have a reality check at a comfortable altitude, when one tank runs dry, and to have all the remaining fuel in the other tank, would make me a lot less nervous…

Even though there is no max. allowed difference between the Piper Archer’s fuel tanks, it is definitely noticeable, if one wing gets significantly lighter than the other. As my wife is quite a bit lighter than me, I would plan for having the remaining fuel towards the end of the flight on her side.

I thought about how to apply this to my next longer cross country flight and came up with this idea:

Taxi, takeoff + first 40 min. of flight, left --> 80 min. right --> Run left tank dry (approx. 100 min), take time --> All the remaining fuel is in the right tank, approx. 60 min. (still very conservative, as the other tank supplied the taxi, takeoff and climb to cruise altitude)

This strategy should provide me with a max. difference between the tanks of no more than 60 min. or about 10 gal. + maybe 4 – 5 gal reserve due to this conservative approach.
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Good plan. On more than one occasion I have landed at a more or less rural airport only to learn that the electricity was out and the gas pumps did not work (duh). Good to have enough on board to get to the next potential fueling station.

Bob Gardner
 
Perezhr said:
My 1967 Mooney POH recommends first hour on one tank, then switch to the other tank and run it dry, then back to the original tank. I've done this ONCE just to check and it was a non-event. As soon as I switched tanks the engine started immediately. I just don't see the need to so although some do it regularly. In long flights I will use my fuel totalizer to run one tank almost empty (within a couple of gallons) in order to maximize my usable fuel on the remaining tank. I never go below one hour reserve in VFR or 1.5 in low IFR.
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I'll have to see if the c model I fly mentions the same thing in the POH. Do you have bladders or wet wing? With the bladders our gauge shows empty and full...but in between it is pretty much worthless. The fuel totalizer is accurate within .1 gallons after many top offs.
 
MAKG1 said:
What kind of idiot designed that fuel system?

Recirculating fuel is a good thing (it suppresses vapor lock), but it's silly to pump it elsewhere from whence it came.
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Continental Fuel injection runs a loop of fuel in excess of consumption to have it return to the same of multiple tanks, greatly complicates the fuel valving system either mechanically or operationally. The Twin Cessnas with multiple tanks all work the same way, as long as you understand what is happening, it is very simple to manage.
 
Mike5250 said:
I'll have to see if the c model I fly mentions the same thing in the POH. Do you have bladders or wet wing? With the bladders our gauge shows empty and full...but in between it is pretty much worthless. The fuel totalizer is accurate within .1 gallons after many top offs.
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I have a wet wing and my fuel gauges are not great either. My fuel totalizer is also pretty accurate. It's really what I use to manage the fuel.
 
I was never a fan of flying by timers to switch tanks. I'd always forget, be late, and the timing error snowballs leaving me feeling sad.

A better strategy, IMO, is to get in tune with the plane and switch when one side feels heavy. That makes me feel happy.
 
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