Fuel tank balance

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.

--
Transpose mxsmanic and gmail to reach me by e-mail.

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.

Doug wrote:


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


Sure there is. JPI has one in their engine monitors. There are others.

I'd never heard of these, but, right you are! Check out
http://www.jpinstruments.com/edm_700.html
Quite the guage!

Newps wrote:
Doug wrote:


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


Sure there is. JPI has one in their engine monitors. There are others.

In article ,
Newps wrote:

Doug wrote:


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


Sure there is. JPI has one in their engine monitors. There are others.

I suppose it depends on what you mean by "direct measure".

Power delivered by a rotating shaft is RPM * Torque. RPM is easy to
measure directly, torque is somewhat more difficult. In any case, the JPI
gizmo doesn't measure torque. It measures manifold pressure, and fuel
flow, and intake air temperature, and maybe a few other things, and
computes how much power the engine must be delivering based on those
inputs. That's not quite the same thing as measuring the output directly.

I'm not saying that what the JPI does isn't useful. Just that it doesn't
fit my definition of "direct measure".

Roy Smith wrote:
In article ,
Newps wrote:


Doug wrote:


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


Sure there is. JPI has one in their engine monitors. There are others.


I suppose it depends on what you mean by "direct measure".

Power delivered by a rotating shaft is RPM * Torque. RPM is easy to
measure directly, torque is somewhat more difficult. In any case, the JPI
gizmo doesn't measure torque. It measures manifold pressure, and fuel
flow, and intake air temperature, and maybe a few other things, and
computes how much power the engine must be delivering based on those
inputs. That's not quite the same thing as measuring the output directly.

I'm not saying that what the JPI does isn't useful. Just that it doesn't
fit my definition of "direct measure".




As long as it's accurate, who cares?

"Newps" wrote:

I'm not saying that what the JPI does isn't useful. Just that it doesn't
fit my definition of "direct measure".




As long as it's accurate, who cares?

I would not accept as accurate a calculation that leaves out essential
parameters. It's an educated guess.

--
Dan
C172RG at BFM

Dan Luke wrote:
"Newps" wrote:

I'm not saying that what the JPI does isn't useful. Just that it doesn't
fit my definition of "direct measure".




As long as it's accurate, who cares?


I would not accept as accurate a calculation that leaves out essential
parameters. It's an educated guess.

No, it's either accurate or it's not. Compare what the JPI says to what
the chart in the POH says. If it's accurate then it is irrelavant how
it got the information.

"Newps" wrote in message
...
[...]
I'm not saying that what the JPI does isn't useful. Just that it doesn't
fit my definition of "direct measure".

As long as it's accurate, who cares?

It's only accurate when the engine is performing according to its design.

So I'd say any pilot using that sort of "power monitor" should care. It's
not a means for verifying actual power output of the engine. It's little
more than an electronic handbook translating the POH power charts to a
graphic real-time display.

Which is not to say it's not useful. I'd say it certainly is. But it's
VERY important to understand what it is and what it's not. Any pilot who
doesn't care is likely to wind up in the trees one day, trusting the display
too much.

Pete

The PT6 engine measures torque, which is shown in ft.lbs,
although the higher rated engines often use percent.

Measuring torque cost money, it isn't "cost effective" on
low powered engines.



"Roy Smith" wrote in message
...
| In article ,
| Newps wrote:
|
| Doug wrote:
|
|
| There is no percent power guage that gives a direct
measure of the
| engines output.
|
|
| Sure there is. JPI has one in their engine monitors.
There are others.
|
| I suppose it depends on what you mean by "direct measure".
|
| Power delivered by a rotating shaft is RPM * Torque. RPM
is easy to
| measure directly, torque is somewhat more difficult. In
any case, the JPI
| gizmo doesn't measure torque. It measures manifold
pressure, and fuel
| flow, and intake air temperature, and maybe a few other
things, and
| computes how much power the engine must be delivering
based on those
| inputs. That's not quite the same thing as measuring the
output directly.
|
| I'm not saying that what the JPI does isn't useful. Just
that it doesn't
| fit my definition of "direct measure".