Fuel selector question

es330td wrote:
In the email I got from AOPA ePilot training tips today there is a
discussion of fuel starvation that makes regular mention of the fuel
selector switch. All my flying is done in a CE172 and the first and
last time I worry about the switch is during pre-flight when I confirm
that it is on both. I fly on both and never fly any other way and to
be honest, outside of gravity flow issues when parked on an incline I
cannot think of why one would want to select one tank at a time vs
both.

Frankly, on a C-172 I can't think of any reason either. But different aircraft
have different systems. As you move up the Cessna line you will find aircraft
that don't offer the "both" option. None of the Pipers do. In fact, I can't
think of a general aviation low wing aircraft I ever flew that offered "both" as
an option. So in that situation you:

1. Take off and land on the fullest tank.

2. Switch tanks every 30 minutes to keep the aircraft from becoming heavy on
one side.

3. If you have to manage both inboard and outboard tanks, I prefer to burn the
outboards first so that the remaining fuel has less effect on balance. Of
course, some aircraft require specific handling.

On the C-402 for example, you had to burn a good 30 minutes on the outboards
(which were its mains) before you could switch to the inboards. When you
switched to the inboards, the fuel actually went from the inboards to the
outboards to the engine. If you didn't make room first by burning the outboards
first, the fuel pumped from the inboards would just be pushed through the
overflow valves on the outboard tanks and then you get to sprinkle the landscape
with expensive avgas.

4. Bottom line: read the manual and follow their directions.


--
Mortimer Schnerd, RN
mschnerdatcarolina.rr.com

"Mortimer Schnerd, RN" mschnerdatcarolina.rr.com wrote in message
...
Frankly, on a C-172 I can't think of any reason either.

http://www.caa.is/datadir/bsdata/img...s/72-07-02.pdf

Karl

"Mortimer Schnerd, RN" mschnerdatcarolina.rr.com wrote in message
...

On the C-402 for example, you had to burn a good 30 minutes on the
outboards (which were its mains) before you could switch to the inboards.
When you switched to the inboards, the fuel actually went from the
inboards to the outboards to the engine. If you didn't make room first by
burning the outboards first, the fuel pumped from the inboards would just
be pushed through the overflow valves on the outboard tanks and then you
get to sprinkle the landscape with expensive avgas.

You got that partially right. The aux tanks each have their own electric
fuel pump that pushes the fuel throught the selector valve and on to the
engine driven fuel pump. Excess fuel from the engine driven fuel pump is
routed back to the main (tip) tanks. The reason for running on the tip
tanks first for 60 (or 90 for the large aux tanks) minutes is to make room
for this bypass fuel.

--

*H. Allen Smith*
WACO - We are all here, because we are not all there.

"Allen" wrote in message
. ..


"Mortimer Schnerd, RN" mschnerdatcarolina.rr.com wrote in message
...

On the C-402 for example, you had to burn a good 30 minutes on the
outboards (which were its mains) before you could switch to the inboards.
When you switched to the inboards, the fuel actually went from the
inboards to the outboards to the engine. If you didn't make room first
by burning the outboards first, the fuel pumped from the inboards would
just be pushed through the overflow valves on the outboard tanks and then
you get to sprinkle the landscape with expensive avgas.

You got that partially right. The aux tanks each have their own electric
fuel pump that pushes the fuel throught the selector valve and on to the
engine driven fuel pump. Excess fuel from the engine driven fuel pump is
routed back to the main (tip) tanks. The reason for running on the tip
tanks first for 60 (or 90 for the large aux tanks) minutes is to make room
for this bypass fuel.

--

*H. Allen Smith*
WACO - We are all here, because we are not all there.


Correct for the AUX tanks. However, the optional locker tanks function
just like Mortimer said.

Al G

Allen wrote:
"Mortimer Schnerd, RN" mschnerdatcarolina.rr.com wrote in message
...

On the C-402 for example, you had to burn a good 30 minutes on the
outboards (which were its mains) before you could switch to the inboards.
When you switched to the inboards, the fuel actually went from the
inboards to the outboards to the engine. If you didn't make room first by
burning the outboards first, the fuel pumped from the inboards would just
be pushed through the overflow valves on the outboard tanks and then you
get to sprinkle the landscape with expensive avgas.

You got that partially right. The aux tanks each have their own electric
fuel pump that pushes the fuel throught the selector valve and on to the
engine driven fuel pump. Excess fuel from the engine driven fuel pump is
routed back to the main (tip) tanks. The reason for running on the tip
tanks first for 60 (or 90 for the large aux tanks) minutes is to make room
for this bypass fuel.


Oops... it's been a while.



--
Mortimer Schnerd, RN
mschnerdatcarolina.rr.com

On Fri, 5 Oct 2007 11:04:50 -0400, "Mortimer Schnerd, RN"
mschnerdatcarolina.rr.com wrote:


Frankly, on a C-172 I can't think of any reason either. But different aircraft
have different systems. As you move up the Cessna line you will find aircraft
that don't offer the "both" option. None of the Pipers do. In fact, I can't
think of a general aviation low wing aircraft I ever flew that offered "both" as
an option.

My Beech can't draw from both.

I've been in Turboprop Cessna Grand Caravans (I know, not a 172) who
would draw fuel from the left tank faster than the right tank, so the
left would be shut off for periods of time to even the fuel.

On many Cessna 172s you are REQUIRED to run on either left or right (not
both) above 5000'

Karl
http://www.caa.is/datadir/bsdata/img...s/72-07-02.pdf


"es330td" wrote in message
ups.com...
Sorry if this is dumb (I am only at 8.3 hours toward my PPL)...

In the email I got from AOPA ePilot training tips today there is a
discussion of fuel starvation that makes regular mention of the fuel
selector switch. All my flying is done in a CE172 and the first and
last time I worry about the switch is during pre-flight when I confirm
that it is on both. I fly on both and never fly any other way and to
be honest, outside of gravity flow issues when parked on an incline I
cannot think of why one would want to select one tank at a time vs
both.

On Oct 6, 4:25 am, "karl gruber" wrote:
On many Cessna 172s you are REQUIRED to run on either left or right (not
both) above 5000'

Karlhttp://www.caa.is/datadir/bsdata/img/adnotes/72-07-02.pdf


Many cessna 172's? How many were not modified -I've not seen the
required placard...

Cheers

On Fri, 05 Oct 2007 18:38:09 -0000, wrote:

On Oct 6, 4:25 am, "karl gruber" wrote:
On many Cessna 172s you are REQUIRED to run on either left or right (not
both) above 5000'

Karlhttp://www.caa.is/datadir/bsdata/img/adnotes/72-07-02.pdf


Many cessna 172's? How many were not modified -I've not seen the
required placard...

The modification was to add a new vent line. I don't know any on the
flight lines I have access to that weren't done. They also all
complied with AD79-10-14R1 (new vented fuel caps) at the same time.

On Oct 6, 12:47 am, es330td wrote:
Sorry if this is dumb (I am only at 8.3 hours toward my PPL)...

In the email I got from AOPA ePilot training tips today there is a
discussion of fuel starvation that makes regular mention of the fuel
selector switch. All my flying is done in a CE172 and the first and
last time I worry about the switch is during pre-flight when I confirm
that it is on both. I fly on both and never fly any other way and to
be honest, outside of gravity flow issues when parked on an incline I
cannot think of why one would want to select one tank at a time vs
both.

If you ever get to a situation where you are worried about fuel, you
switch to one tank and start your watch, when that tank runs dry
(engine splutters) you will have a very good idea of how much flying
time you have left. This knowlege will enable you to decide if your
chosen alternate airfield is in reach or if you neeed to start your
precautionary landing procedures (looking for a paddock etc.)

Cheers