"Tanks on both" checklist item

The flight school where I rent from has all late-model Cessnas, and there
is no doubt that they do not drain evenly.

I've heard several "urban-legend" style explanations for the uneven
drainage issue, and I don't claim to know which one is accurate. However,
they don't generally seem to drain unevenly enough to have any significant
impact on weight and balance...

Now I actually did all my PPL training in a low-wing Tampico that did not
have a "both" option. And a year or so later, when I started flying
Cessnas, I saw the "both" selector as a major convenience, and I took
advantage of it. But a while ago, I flew in a friend's Bonanza, a low-
winger, and we were talking about fuel management. And he reminded me of an
EXCELLENT reason to switch tanks during flight even if there is a Both
selector. I think someone on this thread mentioned briefly...

Basically, let's say your flying West, into a headwind. It's a little
stronger than expected, and so you're all ****ed off, and gunning the
engine up a bit to try to make up some of the ground speed. Maybe you're at
a different altitude than planned, and for whatever reason you're not
leaned out as well as you could be. Based on your "optimum" calculations,
you think you have 5 hours of fuel. But between the headwind, and not
flying optimally as planned, you use 10% more fuel than expected, and you
are going to use 10% more time than expected...

Bottom line, you now need a fuel stop, but you don't know it...

If your fuel selector is on Both, you get one shot. Your right tank may run
dry first, but you won't have any idea until your completely dry in both
tanks. You get to glide to the nearest golf course and call for help.

If you are switching tanks every 1/2 hour, and your right tank runs dry,
it's like an alarm. Your engine fails, and you do your ABC checklist,
switch tanks, and get your power back. You can take a moment to calm down,
figure out what happened, and find the nearest airport with services and
fuel up. You get a "second chance". Of course, it's not guaranteed - you
might only have a drop of fuel in the other tank. But flying on both
guarantees you to be a glider on empty...

Ever since that conversation, I fly "low-wing" style once airborne, and
switch tanks to both on taxi, takeoff, and landing only...



Peter R. wrote in
:

Koopas Ly ) wrote:

Is the procedure of only using one tank only applicable to certain
C172 year/models? I've flown a variety of 172's from late 60's models
to brand new 2002's, and have always used "both" tanks during
flight...just wondering...

Switching tanks is not in the '02 172 CRUISE checklist, but it is
something that I do to maintain an even balance across both tanks.
This is because the difference (at least in the '02 172SP I fly)
between the two after a long flight can be substantial.

Rules To Fly By And Not Run Out Of Fuel:

I routinely run the outboards dry on long cross countries (know your
airplane on this issue).. This cross checks my fuel burn against the clock
since I know exactly how much was in the tank when I selected it... Running
it dry removes fuel gauge error from the equation... I'm usually within five
minutes...

I fly by the clock, not the fuel gauge... If the gauge gets too far from
what the clock says it should be (either full or empty), we put down and
refuel to see what the heck is going on... this only happened once - a
sticky gauge

Lastly, I never get into the last hour of fuel for any reason... 60 minutes
of fuel left on the clock is "bingo time" and it is put it on the ground.. I
have landed and refueled just twenty minutes from my destination because I
hit bingo before I got there... One of the locals back at the home field
thought I was nuts... But then, he has had an engine run out of fuel while
taxing in from the runway one time, so what do you think I feel about his
opinion...

Denny - an old pilot...

"Dave Butler" wrote in message
...
Dan Thomas wrote:

Lots of old pilots didn't trust fuel gauges, which is still a
wise attitude.

"Judah" wrote in message ...

I've heard several "urban-legend" style explanations for the uneven
drainage issue, and I don't claim to know which one is accurate. However,
they don't generally seem to drain unevenly enough to have any significant
impact on weight and balance...

The crossfeed issue on the 172 (why the left tank drains faster) is not
an urban legend. If you are a Cessna Pilot's Association member they
will send you a brief on what it is and how to fix it by tweaking the tank
vent.

I have an oblique answer to this question. I'm building an airplane
that seats four and is a high wing monoplane. The fuel tanks are in
the wing root, just like most high wing Cessnas. The plans show that
the fuel outlets should be placed near the wingroot but in different
locations fore and aft from each other. One tank has an outlet near
the wingroot by the trailing edge, the other tank has the outlet near
the wingroot but towards the leading edge.


Since it's a homebuilt, you have some flexibility in how you do things. Why
not put in two ports for each tank - one fore one aft. That way you can slip
and nose down and get fuel no matter which tank is selected? Try talking with
the designer of the plane about this - it might be worth considering.

Jose

--
(for Email, make the obvious changes in my address)

In article ,
(Corky Scott) wrote:



The designer implied that this is a standard aviation design (the
different locations for the fuel outlets).

The way your fuel system is designed is a good idea. On the 182 I owned
the fuel tank outlets were in the same position fore/aft for each tank
so it isn't an industry wide standard.

--
Dale L. Falk

There is nothing - absolutely nothing - half so much worth doing
as simply messing around with airplanes.

http://home.gci.net/~sncdfalk/flying.html

Judah wrote:

If you are switching tanks every 1/2 hour, and your right tank runs dry,
it's like an alarm.

Right. You switched tanks 3 minutes ago. Hope you're right over an airport.

George Patterson
Some people think they hear a call to the priesthood when what they really
hear is a tiny voice whispering "It's indoor work with no heavy lifting".

Dan

From an 'old' pilot.

We used to fly 30 minutes on a tank and then switch to other tank
(back and forth). This manual switching kept the fuel inbalance to a
max of 30 minutes fuel which was very manageable. Trying to feed from
both tanks for any period of time always caused a inbalance.

Also knew fuel burn and could compare fuel used and remaining, to fuel
gauge.

For landing, fuel was switched to fullest tank (check list item).

In 'heavy iron' and max range, would run tank dry. In GA, never
planned that long a duration so never had a engine stoppage caused by
empty tank.

Safety is as safety does.

Big John

On 4 Dec 2003 17:19:07 -0800, (Dan Thomas)
wrote:

"Tony Cox" wrote in message thlink.net...
"Koopas Ly" wrote in message
om...

The only time that fuel is set to one particular tank is on the
ground. I've never used fuel from only one tank in flight. Why would
someone do that?



Some models of 172 *require* you to select a single tank
above 5000', due (supposedly) to vapor lock problems.

Check your POH.


Lots of old pilots didn't trust fuel gauges, which is still a
wise attitude. They'd sometimes fly on one tank until it ran dry and
the engine quit, then switch to the other and know exactly how much
they had left and how much they'd burned. This doesn't work well if
the tanks are very far off the airplane's centreline, as the imbalance
can require increases aileron input, causing more drag and tiring the
pilot. It can also panic passengers and create unpleasant cabin odors
and extra janitorial work after the flight.

Dan

I don't have a "both" on my Mooney and I DO NOT miss it. "Both" just
means that if you ever run out of gas, you're really out of gas. The
Cessna 140 I used to fly would drain all the gas from the left before
touching the gas in the right (its not the same as the C-150, there is
no interconnecting hose in the 140).


-Robert



(Koopas Ly) wrote in message . com...
Good day all,

With regards to fuel tanks in a C172, why does the takeoff and landing
checklists both call for the fuel selector handle to be in the "both
tanks" position?

The only time that fuel is set to one particular tank is on the
ground. I've never used fuel from only one tank in flight. Why would
someone do that?

Also, why is the fuel selector set to one tank during refueling? Is
it to minimize crossfeeding?

Thanks,
Alex

(CVBreard) wrote in message ...
Lots of old pilots didn't trust fuel gauges, which is still a
wise attitude. They'd sometimes fly on one tank until it ran dry and
the engine quit, then switch to the other and know exactly how much
they had left and how much they'd burned.

I'm an old pilot, don't trust fuel gauges and purposely ran a tank dry...only
once...scared the hell out of me and my wife. Never did that again. :-)

(Longer story, but that's the short version.)

Danm good thing you didn't have a "both" selector or you may not have
been here to tell about it!

-Robert

An an example, the Swift (low wing) is just "both". There are a lot of
examples of low wing planes with "both".

In my Mooney, if I ever run out of gas, I'll just switch tanks. Thank
God there isn't a "both"!



There is a significant difference here between low wing, and high wing
designs. If you have a low wing aircraft, and have a 'both' selector, if one
goes empty, air is sucked into the system by the fuel pump, and fuel
delivery stops. Hence low wing aircraft with a 'both' position, have to have
a central 'sump' from which the fuel is drawn. On high wing aircraft, where
the fuel is delivered by gravity, if one tank goes dry in the both position,
fuel will still feed from the other. Hence 'both', is relatively unusual on
low wing designs, but more common on high wing planes. This is why your RV6,
doesn't have a 'both'.

Best Wishes