Mike Staley asks the following question:
Why do Turbojets have a cruise rating of 1.0, FMP of 3.5 and Afterburner of 12 and Turbofans have a cruise of 1.0, FMP of 4.0 and an afterburner of 24? Turbofans are supposed to be more modern then turbojets, being more reliable and more efficient.
Shouldn't this be reversed? We keep getting a combat radius of less then 300 nm at medium alt with a 15% reserve, 10 minutes on FMP, 5 on afterburner. For an F-16C Block 40, with 2 600 USG wing tanks and a 300 USG centerline with 4 AMRAAMs and 2 AIM-9s....that sounds a bit skewed.
Chris Carlson answered:
Mike, the fuel consumption values in the rules are correct. Turbofans are more efficient at subsonic speeds than turbojets and this is reflected in the cruise range in Annex B. For example,
| Mig-27 | F-16C |
|---|---|
| Engine Type: Turbojet | Engine Type: Turbofan |
| Internal Fuel: 4600 kg | Internal Fuel: 3162 kg |
| Cruise Range: 950 nm | Cruise Range: 1100 nm |
| Consumption: 4.84 kg/nm | Consumption: 3.16 kg/nm |
This clearly shows that at cruise speed, a turbofan is much more efficient than a turbojet. The reasons why the cruise modifier are both 1.0 is that we normalized ALL fuel consumption to a cruise throttle setting for the particular engine. Because a turbofan has about 40% to 50% of the air flowing into the combustor, vice 100% for a turbo jet, there is a lot more oxygen in the exhaust. More oxygen means I can dump more fuel in the afterburner to get more thrust. Basically, an afterburner on a turbofan gets a 65% increase in thrust compared to a 50% increase in a turbojet. Thus, a turbofan consumes about 25% more fuel than a turbojet in afterburner mode. This and the far greater overall thrust capacity (twice that of a turbojet) account for the higher fuel consumption for turbofan aircraft.
BT
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