Performance model

[NovemberCharlie]

Hi all,

I was just wondering something about the fuel burn performance model.
Does this model take into account the fuel burn off in flight? (I.e. higher fuel consumption at the start of the cruise phase and lower just before descent)

If so, planning tech stops (if they are needed) would be more optimal halfway through the flight in stead of close to the arrival/departure airport..

Wondering if anyone nows more about this...

Kind regards,

NC

[Continental Sky]

https://www.airwaysim.com/game/Manual/Aircraft/Performance/

While the basic flight trajectory is calculated on a fleet group level the fuel burn is counted for each individual aircraft, since all of them are different. The factors affecting the basic fuel burn for flight are aircraft model, engine variant, weight variant and possible installed upgrades (such as hushkits). The actual fuel usage for each flight is calculated in a similar detailed manner like the whole performance of the flight: the system uses the taxi, takeoff, climb, cruise, descent and landing performance and fuel usage databases to calculate the fuel usage for the various stages of the flight to form the total trip fuel for the flight.

[Sami]

It's very detailed, you can read more here: https://www.airwaysim.com/game/Manual/Aircraft/Performance/

For the models of which we have high accuracy data (the v.2 performance model) the fuel usage is within 1-3% accuracy compared to real flights (data based on actual flight manuals and compared to actual real-life flight sectors with fuel burn data from actual flight operations). Naturally this is not available for all models yet, and for some (such as planes from 1950s or planes that only flew as prototypes) it can't be that accurate.

[knobbygb]

IF you experiment a little with choosing tech-stops you'll see that it does make a difference and you are correct - having the tech-stop at half distance is most efficient, not just for the overall fuel burn but for the actual flight duration.  Having the optimal tech-stop actually makes the flight shorter (in time) as you have the best combination of climb-rates and so the aircraft gets to cruise speed more quickly too. Win-win.

You do also have to take winds into account and having an off-track (not on the great circle route) tech-stop can actually be better sometimes. (Longer track = more fuel but better winds = shorter duration = less fuel).  For this reason I found certain (rare) cases where a very early or late tech-stop can be better.