Hey Guys (& Girls)

I'm putting together a spreadsheet of TSFC's for different engine types. I'm also trying to put together a crude range calculator for engines on different aircraft.

I've just started to see if it can even be done and i'm not getting the ranges i would expect. My workings are as follows, does anyone see where i'm going wrong?

CFM56-7B20 is rated at 91.6kN of Thrust. At 100% N1, it burns 0.91KG of Fuel per second. This gives it a TSFC of 0.035752

TSFC = FF per Hour (KG/HR) / Force Of Engine Produced (N)

Fuel Flow Per Hour @ Cruise = TSFC * Force Of Engine @ Cruise

FFPH @ Cruise = 0.035752 * 77.8kN (Force @ Cruise = 80% of Max Force Avail)

This now means that the FFPH at cruise is around 2784.6kg per hour which when you multiply by two (for 2 engines) is equal to 5569.2.

Eurocontrol produce figures of average fuel burns of aircraft flying through their airspace. For the B737-700 series, i can expect to burn 43 kg per engine per minute at cruise, 450kts, FL330.

Which when calculated is 43 * 60 (FF Per Hour) multiplied by 2 (for 2 engines) and that comes to 5160. This means my numbers are not that far from the Eurocontrol data (and could be closer just by reducing the cruise N1)

Now to calculate range at cruise divide total fuel available (Max Fuel Capacity) by the FF Per Hour to get the Time that you can fly... Which when multipled by your speed will give you range.

My problem lies here, I've got data which says the B737-700 series engine has a fuel capacity of 21000kgs which at 5569kgs per hour gives the aircraft a mission time of 3hrs 46mins and at 450kts a total range of 1711nm (Which is WAAAAY off the actual range of 3100nm).

Technically, i should be calculating ranges further than what the manufacturer say because i'm assuming the aircraft to be in flight with full tanks.

Anyone help me out?