In last 10 pages members have discussed SUPERCRUISE, Fuel consumption & F-35 performance. The engine performance Vs airframe performance is a very very tricky thing, especially with 5th gen IWB concept.
F-35 is an intentional blunder bcoz of export, otherwise why export ban on F-22 even for allies?
Supercruising is not about just squeezing out thrust from engines but also aerodynamic shaping of jets, lifting body, variable cycle engine, inlet geometry control, pressure recovery & air flow management, etc.
NOTE - Afterburner thrust & MTOW are not required to consider. 50-70% fuel & std. A-A load is used.
An immediate benefit is range of AAMs & ARMs.
Higher the launch altitude & velocity, higher the missile rage. At certain altitude where a particular engine gives max supercruise w/o revealing IR signature by afterburner, will give certain range to missiles, higher will be NEZ (No Escape Zone).
View attachment 259598
While launching missile, Supercruising jet has better chances to conceal IR signature compared to afterburner using jet.
While evading missile also there are strategies & tactics to dodge leading/lagging hit-point missile, where Supercruise at M 1.8 will be very effective consecutively comapred to other jets using afterburner & losing fuel rapidly.
Someone wrote that Supercruise is not efficient due to exponential increase in transonic wave drag & fuel will rapidly get depleted, which is correct but the drag rapidly decreases also after Mach 1.
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So ideally an aircraft should supercruise beyond Mach 1.8 at least. The danger zone is 0.9 to 1.5
Also, there is the "Whitcomb Area Rule" to shape a fuselage of jet to reduce the drag. Supersonic Area rue also there as per which the aircraft body need to be within the Sonic-Cone. These rules are being used in almost all jets i think. there could be more rules which we civilians enthusiasts may nor know yet.
Another reason cited is it needs an excessively powerful engine which means its fuel efficiency will be lowered compared to using a smaller engine. There is no rule like this, especially with upcoming variable cycle engines. Higher bypass ratio engines are bigger with better fuel efficiency.
In my limited knowledge IDK if we have any formula to calculate thrust & fuel required at 100% level, given the dimensions & weight of engine. Engine thrust/weight ratio & fuel consumption varies. Given any engine with an inlet diameter, it is upto designer how much thrust can be squeezed out. Engineers either do not know that limit or it is above top secret.
The parameters which influence thrust & fuel economy of engine are all of its design parameters & operating conditions -
- Compression or Pressure ratio - how much air can be compressed
- with how many fan, low pressure, high pressure compressor stages.
- Air mass flow per second
- combustor design
- Turbine inlet temperature
- # of high & low pressure stages
- Afterburner design
- Bypass ratio
- fixed/variable cycle engine
In theory there is a formula F=Ma = M(Vout-Vin) where V is air velocity at intake & exhaust.
But
practically, how fast will a jet go at 100% power depends on
- airframe weight at the time
- engine design
- altitude (air density), friction force.
- airframe design producing certain amount of lift & drag due to friction & shockwaves.
- special feautures like shock compression lift.
2 same jets with different wing & fuselage design but with same # & type of engine(s) will have different performance.
Different sources give different data on Supercruise
For example F-22,
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Fuel consumption is measured in units like g/KN/s or lb/lbf/hr, called SFC or Specific Fuel Consumption.
F-22's F119 engine's SFC with
inlet dia. 100cm at 100% power (116-120.3 KN) is around 17 g/KN/s.
2 engines, so
F-22 SFC is 34 g/KN/s at 100% power &
Sup.Cr. Mach 1.5-1.8 (514.5-617.4 m/s).
So 3.94-4Kg/s fuel for covering 514.5-617.4 m/s or
128.6-156.7 m/Kg or 6.38-7.77 gm/m.
Empty weight 19.7 T + 50% fuel 4.1 T + full IWB 8 AAMs 1.1 T = 24.9 tons
Airframe T/W ratio at 100% power = 2x(116 to 120.3)/9.8 /24.9 =
0.94 to 0.98
Fuel per ton = (3,940-4,000)/24.9 =
158.23-160.64 gm/s/T.
F-35's F-135 engines SFC with
inlet dia. 109cm at 100% power (128.1 KN.) is around 20.3 g/KN/s.
Sup.Cr. M1.2 (411.6 m/s).
So 2.6 Kg/s fuel for covering 411.6m.s or
158.3 m/Kg or 6.31 gm/m.
But to go this extra 30m/Kg-fuel Vs F-22, the SFC is increased from 17 to 20.3 g/KN/s.
F-35A Empty weight 13.3 T + 50% fuel 4.15 T + 4 AAMs 0.6 T = 18.05 tons
Airframe T/W ratio at 100% power = 128.1/9.8 /18.05 =
0.72
Fuel per ton = 2,600/18.05 =
144.04 gm/s/T.
So we see that F135 engine has more thrust but higher SFC than F119 engine,
& F-35 goes further /Kg fuel, consumes less fuel per unit distance, per ton of body BUT has lower T/W ratio and cannot supercruise.
GE F-414 engine's SFC with
inlet dia. 79cm at 100% power (57.8-61.83 KN) is 20.5-23.25 g/KN/s depending upon model. 75 KN JV engine is planned.
2 engines, so
AMCA SFC will be 41-46.5 g/KN/s at 100% power.
So
2.37-2.87Kg/s fuel will be used.
AMCA empty weight 12 T + 50% fuel 3.25 T + 4 Astr MK3 SFDR 0.88 T =
16.13 tons
T/W ratio at 100% power = 2x58/9.8 /16.13 =
0.73
Fuel per ton = (2,370-2,870)/16.13 =
146.93-177.92 gm/s/T.
When new engine with 75 KN dry thrust will be available then hopefully 6 AAMs will be carried.
T/W ratio at 100% power = 2x75/9.8 / (16.13 + 0.44) =
0.92
Then hopefully AMCA will supercruise around M 1.5
NOTE - Among these 3 engines F414 is smallest engine with highest SFC at 100% power.
NOTE - IDK what is the SFC of these engines at say Mach 0.7 & what is the throttle position. I think these kind of parameters are secret. Sometimes these fiigures are calculated at full IWB load, sometimes AA load + 50%-80% fuel dpending upon fuel left after reaching 35-40K feet altitude & supercruise speed.
Rafale's M-88-2 engine's SFC with
inlet dia. 70cm at 100% power (50KN) is 22.14 g/KN/s.
2 engines, so
Rafale SFC is 44.28 g/KN/s at 100% power &
Sup.Cr. Mach 1.4 (480.2 m/s).
So 2.21 Kg/s fuel for covering 480.2 m/s or
217.28 m/Kg or 4.6 gm/m.
To go this extra 59 m/Kg-fuel Vs F-35, the SFC is increased from 20.3 to 22.14 g/KN/s.
EF-2000's EJ-200 engine's SFC with
inlet dia. 74cm at 100% power (60 KN) is 21-23 g/KN/s.
2 engines so
EF-2000 SFC is 42-46 g/N/s at 100% power &
Sup.Cr. Mach 1.5 (514.5 m/s).
so 2.52-2.76 Kg/s fuel for covering 514.5 m/s or
186.41-204.16 m/Kg or 4.9-5.36 gm/m.
So we see that
Rafale with empty design weight 8.5 T, 492 sqft clipped delta wing & 50KN engine can supercruise at M 1.4
but F-18E/F with empty design weight 14.5 T, 500 sqft. trapezoidal wing & 58 KN engine cannot due to 6T weight increase due to carrier-ops MLG & other things & higher drag wing.
Now after knowling fuel used, distance traversed per second at Supercruising speed with 100% thrust level, if people can obtain the same data at say Mach 0.7-0.8, then merit/demerit of Supercruise can be debated.
But the R&D to increase speed, distance travelled in minimum fuel used will never stop.
rbt-defense.blogspot.com
comapred to 12-13' long BVR-AAMs weighing 160-220 Kg. Where exactly did u hear that? I don't communicate with DoD people. I'm not journalist. IDK.
something like AGM-88G AARGM-ER. On January 12, 2024, Lockheed Martin was awarded a contract to integrate its modified version with all three F-35 variants.
