Do fighter aircraft always carry full internal fuel ?

[stealthflanker]

Yeah, as i kinda never really find a good answer. maybe it's better to ask here.

So do fighter aircraft always carry full internal fuel load during sortie ? Or does that depend on mission range ? (say long range mission...carry full, but for short range, half tank is fine)

Thanks for everyone's attention.

 

[Foo Fighter]

I expect them to use the same method as that used on the A-4. Pack in the stores for the sortie and top up once airborne. Gets by the maximum weight limit.

 

[stealthflanker]

I see. Thanks.

 

[Jeb]

When you're flying a mission profile with stores, I imagine you always want to have full tanks either on takeoff or after the first tanking. Rule of thumb is, if you're not low on fuel yet, you're going to be soon.

 

[paralay]

Su-27 is not always, as its "external fuel tank" is inside the aircraft

normal fueling - 5270 kg
maximum fuel charge - 9400 kg

 

[stealthflanker]

Su-27 is not always, as its "external fuel tank" is inside the aircraft

normal fueling - 5270 kg
maximum fuel charge - 9400 kg

Thanks. Is this the same for the Su-35 ?

 

[paralay]

Of course, only the numbers are different

 

[riggerrob]

When I worked (ground crew) on Canadian Air Force helicopters and fighters, we always filled internal fuel tanks. This reduced the risk of fuel exhaustion in flight, but we ground crew worried more about hangar fires.
Full tanks meant less “ullage.” Ullage is fuel fumes in partially filled tanks. Ullage is far more flammable than liquid fuel.

 

[kaiserd]

Su-27 is not always, as its "external fuel tank" is inside the aircraft

normal fueling - 5270 kg
maximum fuel charge - 9400 kg

I remember a similar set-up re: Voughts proposals (and their competitors proposals) in the competition won by the design that became the F-8 Crusader (I’d recommend referring to the American Secret projects fighters book for details); i.e. not having external drop tanks but having their equivalents (“over-load tanks” if I’m remembering the terminology correctly) internally (that when used don’t generate extra drag but do impose reduced G-limits and other performance reductions due to the extra weight and structural aspects).
Haven’t heard of this type of set up very often explicitly referenced in other non-flanker-related contexts (additional internal tank in the P-51D Mustang that was only filled for the longest missions due to causing a bit of stability issue until emptied?).
However for all I know may well be loads of other examples

 

[Tony Williams]

Haven’t heard of this type of set up very often explicitly referenced in other non-flanker-related contexts (additional internal tank in the P-51D Mustang that was only filled for the longest missions due to causing a bit of stability issue until emptied?).

Same for Spitfires on escort duties in late-WW2. They were given an extra fuel tank behind the cockpit.

 

[overscan (PaulMM)]

Su-27 airframe had the physical room for the fuel due to other design considerations, however a full fuel load impacts thrust/weight ratio and maximum G load. Hence the normal load / maximum load.

 

[Tony Williams]

Su-27 airframe had the physical room for the fuel due to other design considerations, however a full fuel load impacts thrust/weight ratio and maximum G load. Hence the normal load / maximum load.

Fuel in internal tanks is worth far more than in external tanks, because the external tanks increase drag, and a significant proportion of the fuel they carry is used up in overcoming the extra drag. So it's a great idea to have the internal capacity available for when needed.

 

[dan_inbox]

Fuel in internal tanks is worth far more than in external tanks, because the external tanks increase drag, and a significant proportion of the fuel they carry is used up in overcoming the extra drag. So it's a great idea to have the internal capacity available for when needed.

That is true until contact.
After contact, externals can be jettisonned in a sec to restore T/W and manoeuverability, whereas internal fuel, you are stuck with it for much longer.
Then it's not such a great idea to be a lame overloaded duck if it can turn into a furball.

But yes indeed, any fuel that will be spent before the contact zone, it's better if you can carry it internally.

 

[Tony Williams]

Fuel in internal tanks is worth far more than in external tanks, because the external tanks increase drag, and a significant proportion of the fuel they carry is used up in overcoming the extra drag. So it's a great idea to have the internal capacity available for when needed.

That is true until contact.
After contact, externals can be jettisonned in a sec to restore T/W and manoeuverability, whereas internal fuel, you are stuck with it for much longer.
Then it's not such a great idea to be a lame overloaded duck if it can turn into a furball.

But yes indeed, any fuel that will be spent before the contact zone, it's better if you can carry it internally.

Fair point!

 

[riggerrob]

Yes!
Both P-51D and later Spitfires had extra fuel tanks aft of the pilot's seat.
The P-51 tank was sort of L-shaped to wrap under the pilot's seat. Both types of long-range internal tanks moved the centre of gravity farther aft. Most P-51 warbirds had those fuel tanks removed decades ago to be replaced by a second seat. The extra fuel is no longer needed because few warbird owners are 19-year olds with asses tough enough to survive 7 hour missions.
Farther aft is more aerodynamically efficient - because of less trim drag from the horizontal tail. The disadvantage of an aft C. of G. is less pitch stability. Less stability makes the pilot work harder. C. of G. too far aft means that you may not be able to recover form a spin. Many of the prototypes lost are lost because pilots were testing the maximum aft C. of G. but could not recover from the stall-spin. A few prototypes are fitted with moveable ballast to reduce that risk.