Fuel tank balance

Typically low wing aircraft "can't" have a "both" setting. Now there
are exceptions (if it has a header tank). So on low wing aircraft
(which HAVE to have fuel pump(s)), you typically have just left and
right. Now I am talking about small GA aircraft, not military or
transport aircraft.

If you have to have a fuel pump, then usually you have two, so you have
a backup if one quits.

As for the mixture, that is very important and often used. Most systems
now have an EGT (exhaust gas temp) guage and you use that temperature
to set the mixture. There is also a procedure for setting the mixture
based on rpm. At altitudes above 3000' (some use 5000), the mixture is
set leaner than full rich on the ground before takeoff at runup.

Marty Shapiro writes:

Have you ever driven a non-turbocharged car from a low lying city up into
the mountains, like above 5,000' MSL?

I don't know. I think so, since some of the cities north of me were
around 7000'.

Also, the design of the aircraft engine is such that once it is started,
the engine driven magnetos provide the spark to keep it running. You can
have total electrical failure and the engine will keep on running. How do
you stop the engine after you land?

By cutting off fuel, but that's a simple switch or valve. It seems
that there are a lot of other complicated adjustments to worry about.

By now I would have expected that powerplant manufacturers would have
built automated systems to handle much of this; indeed, it was
possible even before the age of computers.

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Doug writes:

If you have to have a fuel pump, then usually you have two, so you have
a backup if one quits.

As for the mixture, that is very important and often used. Most systems
now have an EGT (exhaust gas temp) guage and you use that temperature
to set the mixture. There is also a procedure for setting the mixture
based on rpm. At altitudes above 3000' (some use 5000), the mixture is
set leaner than full rich on the ground before takeoff at runup.

How do I determine how much actual propulsive thrust I'm generating?
I see a throttle setting, manifold pressure, RPM, and pitch, but I'm
not sure how to set all this in order to increase or decrease total
thrust. I've been reading the FAA's handbook, but I'm still not very
clear on how it works. My _impression_ is that I advance throttles to
provide more power, and then set propeller pitch to the green range in
order to translate engine power into optimum thrust. Is that right?
But apparently manifold pressure is supposed to be telling me
something, too.

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"Marty Shapiro" wrote in message
...
Have you ever driven a non-turbocharged car from a low lying city up into
the mountains, like above 5,000' MSL? If you did, you would understand
why
the pilot has to manipulate the mixture.

Unfortunately (for the purpose of your example anyway, which is otherwise an
excellent one) most if not all modern cars use an air mass meter to ensure
correct fuel metering. High altitude driving doesn't require a carb
readjustment any more...the car's engine just compensates. Less power is
the only noticeable symptom, and I doubt most drivers are with-it enough to
notice that.

Also, the design of the aircraft engine is such that once it is started,
the engine driven magnetos provide the spark to keep it running. You can
have total electrical failure and the engine will keep on running. How do
you stop the engine after you land?

Well, you could use the fuel cut-off valve, or you could short out the
p-leads to the magnetos, as alternatives to setting the mixture to the fuel
cut-off setting.

IMHO, the main reasons that aircraft engines require so much fiddling is
two-fold: one is that aircraft engines operate at constant settings for most
of the time they are on; another is that improvements cost big bucks in the
form of certification costs, bucks that most pilots won't pay when the
current (albeit ancient) technology suffices.

Pete

"Roy Smith" wrote in message
...
In article xwhRg.1082$Rp3.261@dukeread12, "new_CFI"
wrote:

as far as left/right/both/off, normaly you set it on both and forget it.
some planes have left/right/off, I alternate every 15 min.

Every 15 minutes? That seems a bit excessive. Once an hour should keep
things pretty much in balance. If you want to get fancy, do your first
switch after a half hour, then every hour after that.



I switch every 1/2 hour, on the 1/2 hour. I burn from the left tank when the
minute hand is on the left side of the clock (30 - 59 minutes past the
hour), and the right tank when the minute hand is on the right side of the
clock (0 - 29 minutes past the hour). That way I can tell by looking if I
remembered to switch tanks.

The least I've ever landed with was 14 gallons (out of 50). That was 2 legs.

Piston engines use percent power. So if you want to cruise at 65% power
(and burn fuel at the rate stated for that power setting), you look in
the aircraft manual for the rpm setting and manifold setting that gives
65% power (there may be more than one). For any given percent power,
you will get better fuel economy if you use the lower rpm and higher
manifold pressure setting. (This is akin to going up a hill in a car in
a high gear and full throttle. Such procedure uses less fuel than
downshifting and using say, 3/4 throttle).

There is no percent power guage that gives a direct measure of the
engines output.

You can also derive percent power from fuel burn if you have an
accurate fuel flow meter. The rule of thumb is 12 horsepower per gallon
per hour. So if you are burning 12 gallons an hour that is 120
horsepower. If the engine's max horsepower is 180 then you are at
120/180 percent power.

Things like this give pilots on long flights something to do....

Thrust is something a little different. Airplanes with jet engines use
thrust (whose unit is pounds) for their power settings, I believe. I'm
no expert though. I do know you don't use thrust for small gasoline
driven prop engines like in Cessnas and Pipers.

well, for me, more often is easter to remember. And on those long flights,
its the only thing to do.... unless you have a ADF and can find a good AM
station.

"Peter Duniho" wrote:
IMHO, the main reasons that aircraft engines require so much fiddling
is two-fold: one is that aircraft engines operate at constant settings
for most of the time they are on; another is that improvements cost
big bucks in the form of certification costs, bucks that most pilots
won't pay when the current (albeit ancient) technology suffices.

I believe FADEC (Full Authority Digital Engine Control)[1] systems are the
aviation equivalent of the automobile systems that automatically handle
mixture control. Aerosance[2] offers FADEC systems for ~$7k for FI piston
engines. I thought I read somewhere that someone building an experimental
was planning on installing a FADEC system and was going to whimsically use
the tortoise and hare (or is it turtle and rabbit?) symbols at the
throttle.

[1] http://en.wikipedia.org/wiki/FADEC
[2] http://www.fadec.com/index.asp

"Peter Duniho" wrote in
:

"Marty Shapiro" wrote in message
...
Have you ever driven a non-turbocharged car from a low lying city up
into the mountains, like above 5,000' MSL? If you did, you would
understand why
the pilot has to manipulate the mixture.

Unfortunately (for the purpose of your example anyway, which is
otherwise an excellent one) most if not all modern cars use an air
mass meter to ensure correct fuel metering. High altitude driving
doesn't require a carb readjustment any more...the car's engine just
compensates. Less power is the only noticeable symptom, and I doubt
most drivers are with-it enough to notice that.


Not too noticeable until about 8,000'. Then it gets noticeable. Above
11,000' it gets very, very noticeable. Go to Pike's Peak and see what
happens!

Also, the design of the aircraft engine is such that once it is
started, the engine driven magnetos provide the spark to keep it
running. You can have total electrical failure and the engine will
keep on running. How do you stop the engine after you land?

Well, you could use the fuel cut-off valve, or you could short out the
p-leads to the magnetos, as alternatives to setting the mixture to the
fuel cut-off setting.


I had to do that once in a C172. I pulled the mixture and the cable came
out in my hand. I turned the fuel to off with the engine at idle and it
took almost 6 1/2 minutes for the engine to stop.

IMHO, the main reasons that aircraft engines require so much fiddling
is two-fold: one is that aircraft engines operate at constant settings
for most of the time they are on; another is that improvements cost
big bucks in the form of certification costs, bucks that most pilots
won't pay when the current (albeit ancient) technology suffices.

Totally agree.


Pete




--
Marty Shapiro
Silicon Rallye Inc.

(remove SPAMNOT to email me)

Mxsmanic wrote in
:

Marty Shapiro writes:

Have you ever driven a non-turbocharged car from a low lying city up
into the mountains, like above 5,000' MSL?

I don't know. I think so, since some of the cities north of me were
around 7000'.

Also, the design of the aircraft engine is such that once it is
started, the engine driven magnetos provide the spark to keep it
running. You can have total electrical failure and the engine will
keep on running. How do you stop the engine after you land?

By cutting off fuel, but that's a simple switch or valve. It seems
that there are a lot of other complicated adjustments to worry about.

By now I would have expected that powerplant manufacturers would have
built automated systems to handle much of this; indeed, it was
possible even before the age of computers.


mixture works like this:

its a fule to air ratio. x:y... so as you climb and air density
decreases the amount of fule require to keep the ratio constant,
changes. So, the amout of fuel you send to the engine needs to be less.
Thats where the mixture controll comes in. If you don't have the Pilots
Handbook of Aeronautical Knowledge, there is a good explanation of
it....if you don't have it; you can download it from the faa website.
If you need the link Ill post it, but I have to run….