4 replies to this topic

[Cerulean]

I have recently rejoined AE after a long time spent away. I had to come back

I have a small issue. I have a route that flies JAX-NAS using a B717, however I think the fuel required is way off.

DETAILS:
NAS - JAX (Roundtrip)
Distance - 457nm

Cost in detail:
Fuel required Fuel cost Discount Total fuel cost
63,188.90 lb $ 24,643.67 $ 24.64 $ 24,619.03

I don't think that the REQUIRED fuel for a 457 NM uses 69,188 lbs. The plane itself holds only 24,600lbs in 3 tanks. (I've fueled many aircraft in my years )

Not sure how this is figured out, but I think it needs a slight adjustment.

[Elchie]

Yeah,

I think the fuel calculation is not correct. So right know it works this way

flow = engines x (tsfc x thrust) x (1+ageFactor)

[ageFactor is depending on aircrafts age, right now its something around 0.008 or so, minimal value]

Required fuel is then calculated this way:

fuel = ((distance/speed) x flow + flow )* 2

(+ flow = fuel reserve for taxi, take-off, landing)
(*2 = roundtrip)

In your 457nm example this means:

- tsfc B717-200 in the database: 0.37
- thrust: 21000
- speed: 442

flow = 2 x (0.37 x 21000) = 15540 [ignoring the age factor for the example]
fuel = ((457/442) x 15540 + 15540) x 2 = 63214

The problem here is: The data within the database comes up with the TSFC at full power, but usually the flight is not operated within full throttle, so this will result in exploding fuel requirements.

Any idea how to calculate the tsfc/thrust down to cruise-power? Or any idea of a better calculation-mode?

[Elchie]

I think we have to extend the data in the database by the fuel burn/hour for every engine and change the formula used.

I set it on my list, but it will take some time.

[Cerulean]

I am no expert, but I do know from friends that flew A319's were required by policy to take off using full power only on the first flight of every day. All other takeoffs were done at normal settings, usually depending the altitude of the airport, would range from 92-96% N1 power setting. The higher the field the more power.

So for instance depart NAS you would basically only use a 92% N1 setting at takeoff, and for a place like DEN would require a 96% N1 setting.

Thats from talking to real pilots, how to incorporate that into the game will be a challenge.

I used to fuel many aircraft and just to use as an example UPS flew B757-200 from SLC-DEN it only burned roughly 8000 lbs thats including push back to parking.

Airtran, in B717's, from MCO-ATL only needed as little as 12000 lbs to fly that route and that includes the mandatory 45 minute fuel reserves.

Of course these numbers would be doubled as a round trip, but just to give you some possible ideas.

If we knew what each engine typed burned/hour that may make it a little easier.

[Chaostah]

That would make the fuel-part really complicated... but i think the choice in engine type would be more important then.