Fuel tank balance

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

with 4 main body tanks fore to aft
2 wing tanks (1 each wing)
2 Main tanks 1 each side over each nacelle of 2 engines each (4 engines)
and 1 weapons bay tank added, #20,000# apprx
other two weapons bays carry 54, 500# gravity weapons
Total full up fuel load, apx 210,000#, aircraft weight, apx 200,000#,
weapons, 27,000# plus racks (4,000#) Take off weight, apx 441,000#, Max GW
for take off 477,000#

-Starting with full fuel all tanks, all tanks feed to the Mains.. keep the
mains above 10,000 #
-Burn from tanks 1 and 4 first (apx 18,000pph at this weight)
-Trap 35,000# fuel between the body tanks number 1 and 4 tanks for CG
control later in the flight
-Move 35,000# trapped fuel between tanks 1 and 4 to maintain CG when wings
sweep
-Burn off body tanks 2 and 3
-Burn off the weapons bay tank
-Burn off the wing (if fuel imbalance in wings we can cross feed, more than
10,000# fuel imbalance will cause roll control problems) may have to cross
feed if one or more engines on the same side are shut down
-Now down to 10,000# in each main and 35,000# in tanks 1 and 4 (total
55,000#)
-You best be at the IAF for the primary airport, 55,000 is enough to weather
divert to the approved alternate (apx 13,000pph fuel flow) and land with apx
20,000-25,000# in the tanks..

-Fuel slosh.. 20,000# is just 10,000# in each main tank, direct feed to the
engines
-Not enough weight forward to keep nose wheel steering squat switch engaged
for ground taxi,
you need to be above 7,000# each tank to start the approach

BT

"Mxsmanic" wrote in message
...
Is there any reason to drain fuel tanks in any way other than
symmetrically in normal flight? I notice that most aircraft have
complex controls for fuel flow from the tanks, and I wonder if there
are things one is suppposed to do during normal flight, or if this is
just to provide for possible equipment failures or a need to shift the
center of gravity of the aircraft in an emergency.

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

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".

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.

Mxsmanic wrote:
Robert M. Gary writes:
working by itself.

Okay, but that's an exceptional situation. For a normal flight, do
you have to change the fuel settings? I know Lindbergh did, but that
was an unusual aircraft.

If you ran all your gas out of one tank you would only have 1/2 the
capacity. I switch tanks every hour.
-Robert

Mxsmanic wrote:
Doug writes:

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.

Set power using throttle to the appropriate setting on your manifold
pressure. If you fly around full throttle down low you'll over stress
your engine. At cruise you usually leave the throttle full forward
(unless you have turbo charged).
You can't set the propeller pitch but you can adjust the propeller RPM.
Higher RPMs are good for higher power but for cruise you want something
less. Your POH will show you a manifold pressure(throttle)/RPM (prop
control) combo for the power setting you are looking for. We usually
refer to it as say 23/25 (meaning 23" manifold pressure, 2500 RPM).

Dumping extra fuel into the cylinders is good when climbing but not so
good during cruise. In cruise we lean the plane out for a more optimal
mixture. You car does the same. For the same RPM your car will set a
higher mixture during acceleration vs. in freeway driving. Most planes
have a EGT (exhaust temp ) to measure mixture, but you can do it just
by sound in a more basic plane.
Planes don't do this all at once for the same reason I have to shift my
car, because they don't use an automatic system. There are such systems
out there for planes but they are very expensive since it would be very
bad if it didn't work correctly.
-robert