time calculation

[adrian8891]

Good day pilots

I have a question about planned arrival time calculation.
How to accurately calculate it?
If I would use time from Flightplan of FSX then I would be way much later. Speed from fsx is 470kts for Airbus what is way above
0.82mach at fl380, so its overspeed

What is your method to calculate it? I try 500nm for 1h + around 20-30 minutes for ground operations.

[Leftcoaster]

Aerial navigation uses True Airspeed (TAS), which is Indicated Airspeed (IAS) corrected for atmospheric conditions where the greatest variable is altitude. However,
when an aircraft flies a flightplan, the actual time is determined by Ground Speed, which is TAS corrected for wind vectors and other complex factors. These can only
be predicted so planning using TAS provides a constant value to work with.

So you are mixing values as neither mach or IAS have any place in navigation time and distance calculations. Real pilots have computers; hand-held circular
slide rules such as the E6-B used since the early 1930's or modern electronic flight management systems to convert IAS to TAS.

For modern aircraft I would suggest looking at a site like Flight Aware (flightaware.com), finding the route that you want and see how much time is planned for in the
real world. Assuming you're using FS9 or FSX, these values should be achievable in the simulators within a couple of percent under most conditions and assuming a
reasonably accurate FDE in the model that you're using.

Once you know the projected TAS at your planned cruise altitude and weight, the time is a simple speed and distance calculation where T=D/TAS.

Almost all of my FsP flights are in the propliner era and the better freeware models come with extensive charts and tables giving TAS, fuel flow, cruise altitude and
power settings for different weights and conditions but these are only applicable in still air. Generally in that period they would incorporate a 15% headwind reserve
into the flight time for fuel planning but the projected arrival time was based on the basic distance/time solution.

I would suggest seeing what happens in real life with airlines that are using your preferred FS model and working backwards. The FsP flight reports generated after a
flight provide valuable information concerning times and fuel usage for the climb, cruise and descent phases of all of your flights. This hiistorical information can be
very useful because it provides accurate data on how your FS models actually performed. The only caveat here is that FsP seems to use ground speed but it is still
useful for planning purposes.

I should add that the GPS in FS, as in the real world, provides ground speed (TAS + wind vectors, density etc) and so is useful for arrival time calculations but less so for planning purposes in many situations. Without an E6-B or equivalent the rule of thumb calculation for IAS to TAS is:

TAS=(IAS * .02) * (Alt/1000) + IAS

For example give:

367 KIAS
FL 34

(367*.02) * (34000/1000) + 367 = TAS :: 7.34 * 34 + 367 = TAS :: 249.56 + 367 = 616.56 = 617 KTAS. This figure should be sufficient for most FS purposes although it omits a number of important vairable and so has no place for real-world aviation usage.

Aerial flight planning and navigation is too much fun to be left to flight management computers and faceless technocrats but the latter have resulted in pilots flying into cumulo-granite with much less frequency than the "good old days".

Good luck.

-C



Post Edited ( 06-19-15 18:47 )

[adrian8891]

That is what I call "explain"! Thank You!