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By: - 12th July 2010 at 13:22 Permalink - Edited 1st January 1970 at 01:00
Unless you are a Su-27/30/MKI or anyother behemoth, you wouldn't want to go on a mission relying completely on your internal fuel capacity.
By: - 12th July 2010 at 13:40 Permalink - Edited 1st January 1970 at 01:00
How long is a piece of string?
By: - 12th July 2010 at 16:05 Permalink - Edited 1st January 1970 at 01:00
One of the major redevelopments of the jet fighter engine into the modern type we see today is efficiency, the main benefit an F404 class turbofan has over a J79 class turbojet is fuel efficiency for sustained thrust output, particularly in the cruise condition. It's actually a similar story with piston engines and supercharger developments back in WW2 when they were cutting edge, multiple speeds, multiple stages, intercooling, etc. In actual fact top speed listings aren't as much a reflection of how speedy an aircraft is, as it is what its flight envelope is like, a Ki-84 looks nowhere near as quick as a Mustang on paper but actually it's damn near uncatchable at the 3-5km combat altitude (where the Mustang's strength is an effortless high speed cruise up around 7km alt, the fantastic thing about it was being so clean it was tremendously fuel efficient in the long range escort scenario at bomber cruise height, whilst retaining contemporary but not necessarily superior fighter performance at the typical combat heights).
Fuel load and specific fuel consumption is certainly one of the main considerations for pilots irrespective of their job. A jet fighter pilot or a civilian recreational pilot are both aircraft pilots first, then the other takes second place (if you can't fly the plane capably you're not going to make a very good jet fighter pilot).
When learning licensing, including military licensing (perhaps moreso) one of the main lessons revolve around calculating fuel loads and fuel usage, with efficient reserve for the flight plan. Carrying too much reduces overall performance efficiency, reduced efficiency means increased requirements, it's a vicious circle.
The idea is that the pilot aims for maximum efficiency and governs his aircraft through the flight plan with a conscious idea of everything that's going to happen at least one step ahead. As they say in flight training, probably the biggest adjustment from something like driving a car is the fact you can't just stop off at a gas station in the clouds and ask for directions, check the oil or top up your fuel. If you don't plan it on the ground, you don't have it on the flight. Yet at the same time it is counterproductive to carry anything you don't need in an aircraft, which performs better the more efficiently it is trimmed, that includes in terms of fuel consumption.
It is counterproductive to carry more fuel than you need for a mission. Airframe stresses are increased, loading is increased, carrying any useless payload reduces overall performance efficency, it is conceivable to have less range carrying more fuel. A low altitude penetration will use much more fuel over a short distance than a high altitude intercept over a longer range. Altitude raises your combat radius, payload increases fuel requirements in climb regimes, these factors must be balanced for the mission requirements.
In the Flanker for a basic counter-air mission a fuel load roughly the same as the internal fuel load of an Eagle, about 5tons is common. For a straight intercept with a high loiter or a low altitude penetration attack role it might carry the maximum 9tons but has reduced G-loading limitations until some fuel is burned off.
If you are just responding to a basic counter-air mission that isn't going to lead you too far from friendly airbases, carrying the full fuel load just means you're going to take up and bring back literally tons and tons of weight you just don't need, and some of your extra fuel is burnt in order just to carry the extra fuel, it's that vicious circle of counterproductive surplus.
For most modern, twin engine supersonic fighters you want something like 4-5tons for air superiority, 8-9tons for penetration strike or force interdiction and it really depends on the circumstances for interception, Russians sort of combine the CAP and intercept missions in PVO (high loiter periods followed by GCI interception at high speed), so again you want as much fuel as you can get, but for the actual interception phase you either want as little as possible (high climb rates and acceleration) or a very high performance aircraft that can overcome large fuel loads with sheer thrust and aerodynamics (like a Foxhound). The F-16 in interceptor layout for example carries 3tons fuel for a rather short mission to respond to GCI directors, climb high and fast, kill intruders and RTB, never straying more than 200 miles from a friendly airfield and never loitering to take in the scenery.
Part of the reason for subsonic, dedicated attack aircraft like the S-3 Viking, A-10 or others is fuel efficiency. They can make about 4tons fuel work for them like it takes twice as much fuel to do the same thing, carrying the same loads with a supersonic aircraft. Even where complexity in the increased technological environment means they aren't necessarily less expensive, they are much more efficient for their specific mission type.
Similar story with penetration strikers, designed to cruise very fast at low altitude that would take much more fuel to do in an air superiority fighter that is designed for best performance at high altitude. The SEPECAT Jaguar was very popular for a long time because its performance is as good as a much more expensive fighter when at low altitude, it's a great strike fighter even though it's no good for air superiority for reasons more than just avionics. It also uses less fuel to go supersonic at 100ft than an Eagle and at that height an Eagle isn't really any faster with their throttles firewalled. A Jaguar is as fast as a MiG-21bis or an F-104 at 100ft, the old school treetop hotrods.
Problem is it doesn't go much faster when you climb, where the others double their speed capabilities with altitude.
So these are an example of the possible factors when considering the question of "how much fuel is enough?"
By: - 12th July 2010 at 20:50 Permalink - Edited 1st January 1970 at 01:00
A Jaguar is as fast as a MiG-21bis or an F-104 at 100ft, the old school treetop hotrods.
How fast is that?
By: - 12th July 2010 at 20:53 Permalink - Edited 1st January 1970 at 01:00
Just how much fuel do you need for a combat mission?
As much as it is physically possible, and that includes not just the onboard fuel, but also a top-off from a tanker right before entering the danger zone. The more, the better.
By: - 12th July 2010 at 21:07 Permalink - Edited 1st January 1970 at 01:00
As much as it is physically possible, and that includes not just the onboard fuel, but also a top-off from a tanker right before entering the danger zone. The more, the better.
Might I say as someone who has actually had to do this that you are absolutely correct. I cannot remember any mission flown in my experience where anything less than a full internal fuel load plus whatever was needed in external fuel was put on the jet.
Not saying this fueling to less than capacity hasn't happened of course...but in my time such a thought would be highly unusual. The only exceptions I can think of were record breaking attempts and airshows where fuel wasn't critical. Normally, we thought that the only time we would have too much fuel was if we were on fire.
By: - 13th July 2010 at 11:49 Permalink - Edited 1st January 1970 at 01:00
How fast is that?
Much faster than a Mirage 2000, similar to a MiG-29 or a Strike Eagle, not as fast as an F-111.
About 1350km/h.
By: - 13th July 2010 at 14:13 Permalink - Edited 1st January 1970 at 01:00
Much faster than a Mirage 2000, similar to a MiG-29 or a Strike Eagle, not as fast as an F-111.
About 1350km/h.
Do you have a speed reference? All I can find is a source that gives a M1.1 speed at low altitude.
I know how fast a F-104G will go on the deck. 800KIAS. I've done it many times. I doubt a Jaguar will match that.
By: - 13th July 2010 at 14:28 Permalink - Edited 1st January 1970 at 01:00
Might I say as someone who has actually had to do this that you are absolutely correct. I cannot remember any mission flown in my experience where anything less than a full internal fuel load plus whatever was needed in external fuel was put on the jet.Not saying this fueling to less than capacity hasn't happened of course...but in my time such a thought would be highly unusual. The only exceptions I can think of were record breaking attempts and airshows where fuel wasn't critical. Normally, we thought that the only time we would have too much fuel was if we were on fire.
How about the A-10A, when in general your claim is correct.
By: - 13th July 2010 at 14:45 Permalink - Edited 1st January 1970 at 01:00
How about the A-10A, when in general your claim is correct.
Same for A-10s.
The point is that planners don't tailor internal fuel loads for specific missions. Planners do add external tanks depending on mission requirements. It's not unusual for pilots to go to the tanker after takeoff to "top off" prior to beginning the mission.
Whatever initial performance penalty that may be incurred with a full fuel load is more than offset by the range and endurance benefits that amount of fuel.
By: - 13th July 2010 at 18:26 Permalink - Edited 1st January 1970 at 01:00
I agree with you Alfa Kilo.
But, Vanir is right about the Flanker though..
Its internal fuel tanks are huge, and a normal take-off is between 5.500-6.500kg(5.600kgf to be excact) of fuel + what ever weapons load out.
Well thats what the Jane's and all other sources have claimed all this time.
Also he is quite right about which type of mission require more or less amount of fuel.
However Vanir.
There is one thing to re-consider now with the RuAF Flanker case.
That is the fact the Russian air force is these days closing down a whole number of airbases.
And Consentrating its remaining Su-27 fleet with many other type of aircraft.
Now, fewer airbases especial in peace time operation mission, would logical involve longer legs/range missions.
Also taking into account the poor status of the RuAF these days..
One can't help wonder if the 'normal' takeoff weight of the Flanker just have increased lately..:confused:
Also the upgraded AL-31FM1 engines of the Su-27SM have rated thrust of 13.500kgf.
And the latest Flanker in the RuAF have engine rated 14.500kgf.
This means eighter shorter takeoff lenght or it could take-off with more internal fuel.
Also the fact that the new Flanker is perhaps capable of supercruising.
I know it is not beeing optimized, but nevertheless the fuel consumption goes up when going at full mil-power.
Hense the fact it is perhaps more prudent to carry more fuel at take-off.
Last as i mention above, fewer Airbases means the remaining units, Especially the Flanker have to 'cover' larger territory than before.
And it beeing more crucial the reach it faster in a intercepting mission means more fuel consumption.
Which all boil down to my point, more internal fuel take-off for the RuAF Flanker.
Thanks
By: - 13th July 2010 at 21:56 Permalink - Edited 1st January 1970 at 01:00
But, Vanir is right about the Flanker though..
Its internal fuel tanks are huge, and a normal take-off is between 5.500-6.500kg(5.600kgf to be excact) of fuel + what ever weapons load out.
That is about the same as the F-4 internal fuel load...and a little less than the F-15's.
I have read that the overload fuel capability almost doubles that amount but this quantity is seldom carried. Odd that an airframe would be designed to be large enough to carry a fuel quantity that would seldom be used. That might be a first for a fighter.
It was said that...
It is counterproductive to carry more fuel than you need for a mission. Airframe stresses are increased, loading is increased, carrying any useless payload reduces overall performance efficency, it is conceivable to have less range carrying more fuel.
...This may sound good at first glance, but I'd like to see some examples of fighters that were fueled to less than fuel internal fuel for a given mission. Also, I'm not too sure about the bit about more fuel reducing range...someone will have to explain that.
Perhaps that claim is suggesting that a high altitude cruise profile flown at optimum speed for distance with internal fuel only will give a better range than a low altitude, high speed profile flown with external tanks? Maybe, but that's like comparing apples to oranges. The better comparison is to use the same altitude and airspeed for both fuel loads and then compare distance.
By: - 14th July 2010 at 09:17 Permalink - Edited 1st January 1970 at 01:00
alfakilo;1609608]That is about the same as the F-4 internal fuel load...and a little less than the F-15's.I have read that the overload fuel capability almost doubles that amount but this quantity is seldom carried. Odd that an airframe would be designed to be large enough to carry a fuel quantity that would seldom be used. That might be a first for a fighter.
Yes, the legasy Flanker can with ease top up to 9600kg of internal fuel depending on if its an UB or not..
I'm not sure this is entirely accurat, but here is some Wiki stuff on the topic:
In addition to its considerable agility, the Su-27 uses its substantial internal volume for a large internal fuel capacity. In an overload configuration for maximum range, it can carry 9,400 kg (20,700 lb) of internal fuel, although its maneuverability with that load is limited, and normal load is 5,270 kg (11,620 lb).
For the new Su-35S which are target for IOC in 2011-12, they have an increased internal fuel tanks.
More fuel in the wings and in the stabz too.. about 11.500kgf total.
On top of that, it comes with plumed wing station for DT.
Now what kind of mission would require that amount of fuel..:confused:
First thing that comes to mind is re-deployment of Flanker squadrons without the need of airial tankers.
Don't know if this is a new RuAF requirements or not..:confused:
Cause think about it, Russia is a huge country, and on top of that fewer airbases in the future RuAF structure.
It was said that......This may sound good at first glance, but I'd like to see some examples of fighters that were fueled to less than fuel internal fuel for a given mission. Also, I'm not too sure about the bit about more fuel reducing range...someone will have to explain that.
Yes i agree, i think it is only the Flanker which can do mission with reduced fuel load out.
Its understandeble if one look at this:
Empty weight: 16,380 kg (36,100 lb)
Loaded weight: 23,430 kg (51,650 lb)
Max takeoff weight: 30,450 kg (67,100 lb)
Quite heavy with max fuel/loadout, surly it affect the kenetic performance.
But than again we don't really know to what extend..
On peace time mission, i'm sure RuAF Flankers use between to 70-99% fuel load out.
Other fighters pretty much allways tops up internaly on every mission.
Perhaps that claim is suggesting that a high altitude cruise profile flown at optimum speed for distance with internal fuel only will give a better range than a low altitude, high speed profile flown with external tanks? Maybe, but that's like comparing apples to oranges. The better comparison is to use the same altitude and airspeed for both fuel loads and then compare distance.
Yes agreed.
I don't know how to measure the extra drag penalty with external fuel tanks vs without them.
But there should be a difference on the issue..
Anyway, as a rule TD should gain some extra range regardless.
Thanks
By: - 14th July 2010 at 15:58 Permalink - Edited 1st January 1970 at 01:00
How much fuel is enough depends on the mission. When F-105 or F-4s bombed Vietcongs attackign the perimeter of the airbase internal fuel was more than enough.
By: - 14th July 2010 at 20:53 Permalink - Edited 1st January 1970 at 01:00
I don't know how to measure the extra drag penalty with external fuel tanks vs without them.
USAF flight manuals publish drag coefficient numbers for anything carried on the jet...pylons, external tanks, weapons and weapons racks. All of these would be added up and would then be one of the parameters used to compute range and endurance from the performance charts. The range of drag index values went from zero to as much as 120 or so.
For the F-4, for example, a wing external fuel tank had a coefficient of 6.4 as compared to the centerline fuel tank's 9.6 or the pylon bomb rack without weapons of 6.8. Add 3 Mk-82LD to that rack would bring the total up to 10.1. Let's look at the jet with two inboard bomb racks (20.2) and two external wing fuel tanks (12.8)...this was a typical load for my missions in Vietnam. The total drag coefficient would be 33. For a low altitude cruise at 10,000' and 480KTAS, the external tanks added about 600lbs/hr to the total fuel flow...not a huge amount, but depending on mission length, something that could become a factor, particularly if the bingo fuel was a high number.
By: - 14th July 2010 at 21:36 Permalink - Edited 1st January 1970 at 01:00
The excellent books by Rowland White "Vulcan 607" and "Phoenix Squadron" have some very interesting sections in them about mission planning in respect of fuel. They might be a good start if you want something in enjoyable laymans terms.
By: - 15th July 2010 at 15:36 Permalink - Edited 1st January 1970 at 01:00
USAF flight manuals publish drag coefficient numbers for anything carried on the jet...pylons, external tanks, weapons and weapons racks. All of these would be added up and would then be one of the parameters used to compute range and endurance from the performance charts. The range of drag index values went from zero to as much as 120 or so.For the F-4, for example, a wing external fuel tank had a coefficient of 6.4 as compared to the centerline fuel tank's 9.6 or the pylon bomb rack without weapons of 6.8. Add 3 Mk-82LD to that rack would bring the total up to 10.1. Let's look at the jet with two inboard bomb racks (20.2) and two external wing fuel tanks (12.8)...this was a typical load for my missions in Vietnam. The total drag coefficient would be 33. For a low altitude cruise at 10,000' and 480KTAS, the external tanks added about 600lbs/hr to the total fuel flow...not a huge amount, but depending on mission length, something that could become a factor, particularly if the bingo fuel was a high number.
The excellent books by Rowland White "Vulcan 607" and "Phoenix Squadron" have some very interesting sections in them about mission planning in respect of fuel. They might be a good start if you want something in enjoyable laymans terms.
Interesting.
Thx for the input.
I've read that the excellent high lift for the Flanker has an adittional reward for the total range of the Aircraft.
That beeing said, the AL-31F engines might nullify this reward(poor fuel consumption)..:confused:
Also that using a DT on the center hardpoint on a Flanker, give it a very high penalty in Drag-coefficient.(Su-34 in this exsample)
Perhaps this has something to do with its high lift ability beeing disrupted somewhat..
Can somebody pls give some light these subjects?
Thanks
Posts: 493
By: talltower - 12th July 2010 at 13:18
Fuel management is one important factor, as for fighter pilots, because preservation of their flying machine is paramount as attrition replacements simply for running out of fuel in combat are hard to come by.
Why lose a multi-million dollar machine simply because you could not return to base or reach a tanker?
At least one fuel bag can help keep your plane aloft longer.
Many fighter aircraft fly with external fuel tanks to either get to the combat zone and spend more time on station before bingo fuel.
Is internal fuel merely enough?