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Su-27 range and fuel questions

PG_69

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I'm a little confused as to the single seat Su-27 vs the two seat Su-27UB fuel and ranges.

Janes has the Su-27 as:
11775 L fuel
3680 km range

The Su-27UB has "1,500 kg increase in empty weight, no reduction in internal fuel capacity."
3000 km range


Brasseys has the Su-27:
Up to 12000 L fuel in 5 tanks (2 in wing centre section, 2 outer wings, 1 tail boom).
3720 km clean
2800 km with 10 AAM (1090 km radius at high altitude)

Su-27UB
3000 km clean


Sukhopi site: http://www.sukhoi.org/eng/planes/military/su27sk/lth/
Su-27SK range
3530 km with 2 R-27R, 2 R-73
9400 kg fuel of which 5270 kg might be standard.

Su-27UBK: http://www.sukhoi.org/eng/planes/military/su27ubk/lth/
3000 km with 2 R-27R, 2 R-73 (530 km difference)
Fuel looks the same


Does anyone have official figures for the Su-27UB fuel and an explanation of the range decrease, possibly:
1) Higher drag of the two seat cockpit and the 1500 kg weight?
2) There is a decrease in Su-27UB internal fuel? Looking at images it does look like the second seat eats into fuselage space, so I could believe this.
3) Anything else - CoG with the Su-27UB?

Any ideas on the individual fuel tank capacities and the order in which fuel is used from the tanks?


Janes has 6600 of the 11775 litres being normal operational fuel load. "Higher figure represents internal auxiliary tank for missions in which maneuverability not important"

Brasseys has 9400 kg of which 6000 kg is normal and the remaining 3400kg is an 'internal auxiliary tank'.

So for short range missions the aircraft would only be fuelled with 6600 L. What are the agility restrictions with full internal fuel? Which tank is the internal auxiliary - fuselage, tailboom or wings?

For long range missions are there any restrictions with the internal auxiliary fuel tank. Is this tank used first?
 
A

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I think you have answered the questions yourself.

The extra weight and diminished fuel capacity , and also the aerodynamics accounts for the diminished range. Just look up the specs of the new Su-35BM vs the Su-30 MKI for good measure.
 

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