[jhb_airlines] Re: Flight Report - 037G

  • From: "Bones" <bones@xxxxxxx>
  • To: <jhb_airlines@xxxxxxxxxxxxx>
  • Date: Sat, 1 Jan 2005 03:25:33 -0000

Two things here.

First is that the fuel burn in FSNav is based upon the aircraft data you
enter in the Aircraft drop down menu in this program. This requires you =
to
have fairly accurate data here as there are values for climb, cruise and
descent burn figures.

Assuming you have done this and FSNav's burn figures are accurate the =
next
step is one I can't answer right now but something you might be able to
check quite quickly. FSNav records the wind - it shows up at the bottom =
left
of the map display - so the test would be to zero all weather values and
check the fuel burn, then stick in some wind values and see if the burn
figure changes.

If it doesn't and FSNav only gives still air burn values then you have a
problem. You can't follow real world procedures here as we don't have =
the
planning software to interpolate upper wing values and give accurate en
route timings. I'm not even sure we have access to the 300hPa wind =
charts
(approx FL390) which pilots use. If you can find these you could take
average wind values for each 10 degree Longitude shift and get a =
reasonable
en route flight time (and therefore fuel burn). I am assuming here that =
FS
can accurately mimic real world high level wind values. Another problem =
is
the Jetstream and if FS does recognise this then things can get very
awkward.

The whole question of fuel burn is a tricky one and it is the part of =
the
CPL/ATPL exams that most pilots hate. It used to be called Perf A but I =
have
no idea if this is still in the current exam syllabus (maybe FMS =
procedures
have replaced this). A quick look at CAP402 Flight Planning Data - =
basically
a lookup table for obtaining fuel burn for different flight levels =
corrected
for varying temperatures and aircraft weights reminds me just how =
complex
the calculations were.

To give you a brief look into this sort of flying any long haul flight =
is
going to need a lot of fuel. On departure the aircraft will be very =
heavy
and it may take some time before it can reach optimum cruising level.
Typically this will be a stepped climb but at the initial lower =
altitudes
the fuel burn will be significant. This has to be calculated. Even when =
up
at optimum height the calculations are not over because, as fuel is =
burnt,
the aircraft gets substantially lighter. Less weight means more lift and =
you
could let the aircraft climb to higher levels as fuel is used up but =
this
isn't a good thing. What you actually do is stay at the same level and =
this
means that as fuel is used the aircraft goes faster. Again you don't =
want
this and so a long haul flight sees a gradual reduction of engine power =
as
the flight progresses so that the lighter weights are counterbalanced to
maintain a steady TAS and height. It was these calculations that were =
the
bane of aspiring pilots in the CPL exams.

I still have a few of my test papers here and I would have to look at =
them
for a while to recall how the figures were worked out! Interestingly the
aircraft figures used in the test were for a VC10.

bones

-----Original Message-----
From: jhb_airlines-bounce@xxxxxxxxxxxxx
[mailto:jhb_airlines-bounce@xxxxxxxxxxxxx] On Behalf Of gwinsk@xxxxxxx
Sent: 31 December 2004 16:57
To: jhb_airlines@xxxxxxxxxxxxx
Subject: [jhb_airlines] Re: Flight Report - 037G




Next, follow on, question.
I use FSNav as the indicator of fuel needed, then add ny alternate and =
get
the fuel to=20
divert, from one minus t'other. What I'm not sure of is whether FSNav's =
fuel
calculation=20
takes the winds aloft into the calculation. I suspect not.
 On a transatlantic flight this could leave me with insufficient fuel =
for a
diversion. How=20
should I factor in the forecast winds?

Gerry Winskill
gwinsk@xxxxxxx




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