"Tanks on both" checklist item

Tony Cox wrote:

"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.


No 'supposedly' about it. Ours locked at 7500' on a humid day because one of
my partners didn't believe it could happen and didn't follow the procedure.
Fortunately an airport was within glide range. Strangely enough, by the
time he landed the engine was running fine again....
--
Frank....H

"COUGARNFW" wrote:

Amazing...all those answers by 172 owners and no one of them went to the net
to find the "truth".

The question is why is the selector placed in the "BOTH" position for
landing, not why is the selector placed in some other position above a
certain altitude for certain models.

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?

Not really related to 172's, but our RV-6 has no "both" position... either
left, right, or off. You just have to remember to switch them occasionally.

Also, IIRC the 150 has just "on" and "off".

"Bob Martin" wrote in message
...
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?

Not really related to 172's, but our RV-6 has no "both" position... either
left, right, or off. You just have to remember to switch them
occasionally.

Also, IIRC the 150 has just "on" and "off".
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

Koopas Ly wrote:

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?

It's basically to ensure that you will have fuel through the entire takeoff. The
reason it's done for landing is in case you need to go around. The idea is that,
even if one tank goes empty or has some other problem, you will have a steady
supply of fuel.

The only time that fuel is set to one particular tank is on the
ground.

Then you don't have to worry too much about it, do you?

I've never used fuel from only one tank in flight. Why would
someone do that?

I do it in my Maule to equalize fuel burn. It will draw down the left tank more
rapidly than the right if I don't. I believe most Cessnas are worse in this
regard than my aircraft; my 150 certainly was.

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

Yep. In my Maule, the lower tank will overflow through the vents if this is not
done. My 150 (which didn't have the option of selecting tanks) would do the
same if the vented tank was the lower one. Note that my Maule will do this even
if the selector is set to "off". Dunno if that's the case with a Cessna.

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".

On 04 Dec 2003 14:50:32 GMT, (COUGARNFW) wrote:

Amazing...all those answers by 172 owners and no one of them went to the net to
find the "truth".

If you go to Google and fill in "Airworthiness Directive for 172 fuel system",
you will get a string of answers and some really foolish conclusions (like this
string) that are worth reading.

Just tried that -- the only one that came up was your post.


One states...my plane has the placard to not fly on both above 5,000 feet, but
I did and the engine quit at 8500. Sigh (mine).

If you know how to get to rec.aviation.owning of the Usenet, the string is
there.

Note that the problem is model/version specific.

Neal

On Thu, 04 Dec 2003 18:58:52 -0500, "Jay Somerset"
wrote:

On 04 Dec 2003 14:50:32 GMT, (COUGARNFW) wrote:

Amazing...all those answers by 172 owners and no one of them went to the net to
find the "truth".

If you go to Google and fill in "Airworthiness Directive for 172 fuel system",
you will get a string of answers and some really foolish conclusions (like this
string) that are worth reading.

Just tried that -- the only one that came up was your post.

Are you guys talking about AD 72-07-02?

The text is he

http://www.airweb.faa.gov/Regulatory...D?OpenDocument

Don

"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

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.)

Not really related to 172's, but our RV-6 has no "both" position...
either
left, right, or off. You just have to remember to switch them
occasionally.

Also, IIRC the 150 has just "on" and "off".
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'.


Ok, that makes sense now... thanks