Fuel Decision in Military Aviation
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Fuel Decision in Military Aviation
Hi,
one of our most imported decision in commercial aviation is about fuel to be loaded.
How is it handled in military aviation? E.g: Do fighters always top off? How is it handled on carriers? Etc,
Thank you for your answers.
LW20
one of our most imported decision in commercial aviation is about fuel to be loaded.
How is it handled in military aviation? E.g: Do fighters always top off? How is it handled on carriers? Etc,
Thank you for your answers.
LW20
Just fill 'er up. For a very short sortie (quick transit, air test, display etc) you may take a lighter load.
I've never had to do a C of G calculation either.
BV
I've never had to do a C of G calculation either.
BV
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LW20,
Perhaps I can help a bit.
In my experience, most land based jet fixed wing sorties are fully fuelled, at least the internals. With external tanks, again usually fully fuelled.
On carriers, this is definitely not the case, especially if weapons are being carried. For catapult launch fuel load is often juggled against other factors (e.g. Wind over deck, sea state, individual aircraft weight, stores carried, catapult condition, sortie profile) to allow a safe launch from the ship.
For STOVL ops, it was usually full fuel, given the fairly limited fuel loads available on the first generation (Harrier) airframes. Howeve, this could be traded against weapon loads for short sorties.
For all carrier launches, there will also be detailed CG calculations to support application of correct trim and propulsion system settings.
Complicated stuff, this naval aviation.
Best regards as ever to all those doing the sums out there on the ocean deep,
Engines
Perhaps I can help a bit.
In my experience, most land based jet fixed wing sorties are fully fuelled, at least the internals. With external tanks, again usually fully fuelled.
On carriers, this is definitely not the case, especially if weapons are being carried. For catapult launch fuel load is often juggled against other factors (e.g. Wind over deck, sea state, individual aircraft weight, stores carried, catapult condition, sortie profile) to allow a safe launch from the ship.
For STOVL ops, it was usually full fuel, given the fairly limited fuel loads available on the first generation (Harrier) airframes. Howeve, this could be traded against weapon loads for short sorties.
For all carrier launches, there will also be detailed CG calculations to support application of correct trim and propulsion system settings.
Complicated stuff, this naval aviation.
Best regards as ever to all those doing the sums out there on the ocean deep,
Engines
HB,
My good friend Engines will doubtless correct me here, but the energy provided by the cat stroke would not be improved by making the run longer; in fact, in might start to slow? Your assumption about lifting light on fuel and AAR is a valid one, and used by several aircraft to achieve max ordnance at take off, whilst still retaining a margin against, say, the loss of an engine. Unfortunately, Naval AAR is somewhat lacking at the moment (and, save possible "buddy-buddy") not an option of the RN/RAF F-35 Sqns when embarked, unless, of course, they operate within range of land based AAR.
Helicopters are forever making fuel/payload/range trades - exacerbated if you are operating at high Density Altitude. For example, in the CH47 you'd normally fly full internals in the UK, whereas in Afghan you'd typically refuel to approx 2/3rds to give you some planning margin (as, with the exception of the Mk3, the CH47 doesn't have a fuel dump). If you are lifting an ultra-heavy load you would plan to burn down to the min required fuel. This was always a challenge in the FI as you could often be tasked to lift heavy items some way away from the nearest fuel.....
My good friend Engines will doubtless correct me here, but the energy provided by the cat stroke would not be improved by making the run longer; in fact, in might start to slow? Your assumption about lifting light on fuel and AAR is a valid one, and used by several aircraft to achieve max ordnance at take off, whilst still retaining a margin against, say, the loss of an engine. Unfortunately, Naval AAR is somewhat lacking at the moment (and, save possible "buddy-buddy") not an option of the RN/RAF F-35 Sqns when embarked, unless, of course, they operate within range of land based AAR.
Helicopters are forever making fuel/payload/range trades - exacerbated if you are operating at high Density Altitude. For example, in the CH47 you'd normally fly full internals in the UK, whereas in Afghan you'd typically refuel to approx 2/3rds to give you some planning margin (as, with the exception of the Mk3, the CH47 doesn't have a fuel dump). If you are lifting an ultra-heavy load you would plan to burn down to the min required fuel. This was always a challenge in the FI as you could often be tasked to lift heavy items some way away from the nearest fuel.....
In the SAR world, there's a bit of compromising between performance and endurance to be done. For instance, if you are going to rescue someone from a mountain, you don't want much fuel on board, but if the position is uncertain, you need enough fuel to find them first. If the task is a search, you need to establish (based on weather and availability of other assets) whether you want to arrive with plenty of fuel to give you a worthwhile amount of time to search, or arrive with not much fuel to allow you to deliver MRT quickly onto the hillside (takes a long time if you can only move 3 or 4 at a time!). Throughout all of this, one has to remain aware of distance to the nearest fuel site, what time that fuel site is open, how easy it will be to get there based on day/night/weather etc etc.
In the RAF SAR Force, we used to hedge our bets somewhat and have the aircraft approximately half full - 3000lbs of fuel would give nearly 3 hours endurance (enough to get to the job and arrive with enough performance to winch, get the casualty to hospital and find a refuel site in most cases). There was always a bowser on hand to top up the aircraft if a longer-range job (or search) came in. If one wanted to take full fuel, the aircraft needed to be stripped due to the weight of the role equipment. Inevitably, this took a bit of time but a lot of the stuff could be removed fairly quickly - it was only taking the seats out etc which took a bit longer, and on a proper long-range job the crew would take time to check the fuel plan before launching so the engineers had time to strip stuff out anyway.
At least one unit used to reduce the standard fuel load in the summer because the mountains were on the doorstep, whereas other bases were further from the hills so would burn more fuel getting there. If one arrived on scene without sufficient performance, there was always the option to chuck fuel over the side, but it's not a popular move given how many SAROps take place in National Parks...I only saw this done once when a visiting Captain gassed up the aircraft to MAUM ready for a good long training sortie all over the Highlands in glorious summer sunshine, and we promptly got scrambled to two cragfast climbers who had made it almost to the top of Ben Nevis...cue dumping of fuel most of the way down the Great Glen, and more on scene when we got there and tried to hover and still ran out of power
.
In the RAF SAR Force, we used to hedge our bets somewhat and have the aircraft approximately half full - 3000lbs of fuel would give nearly 3 hours endurance (enough to get to the job and arrive with enough performance to winch, get the casualty to hospital and find a refuel site in most cases). There was always a bowser on hand to top up the aircraft if a longer-range job (or search) came in. If one wanted to take full fuel, the aircraft needed to be stripped due to the weight of the role equipment. Inevitably, this took a bit of time but a lot of the stuff could be removed fairly quickly - it was only taking the seats out etc which took a bit longer, and on a proper long-range job the crew would take time to check the fuel plan before launching so the engineers had time to strip stuff out anyway.
At least one unit used to reduce the standard fuel load in the summer because the mountains were on the doorstep, whereas other bases were further from the hills so would burn more fuel getting there. If one arrived on scene without sufficient performance, there was always the option to chuck fuel over the side, but it's not a popular move given how many SAROps take place in National Parks...I only saw this done once when a visiting Captain gassed up the aircraft to MAUM ready for a good long training sortie all over the Highlands in glorious summer sunshine, and we promptly got scrambled to two cragfast climbers who had made it almost to the top of Ben Nevis...cue dumping of fuel most of the way down the Great Glen, and more on scene when we got there and tried to hover and still ran out of power
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In the C130 world at Lyneham it was routine to offload freight in favour of more fuel, just so you didn't need to stage at Gander when travelling west. I'm sure it was in the best interests of defence to fly fuel rather than cargo....
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Going back a bit now, like 65 years, on a Shackleton it was 1,200 gallons for pounding the circuit, 2,200 gallons for a 6 hour training flight which might include radar homings, ship photography and bombing and gunnery, and full tanks (3,292 gallons) for more serious stuff. The Flight Engineer did a weight and balance sheet for all the longer flights.
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HB,
Evalu8ter is, as usual, bang on the money. There is a close link between USN catapult designs and USN aircraft, and longer cats would not deliver much improvement, as aircraft end speed is as good as it already can be.
Another factor is ship design - the CVN flight deck is essentially sized by the requirement to get 4 catapults installed. Longer cats would mean a new flight deck, and a longer ship, which would need more power, so an extra reactor.....
Launching off the cat at low fuel straight to a tanker usually happens when the aircraft design has gone wrong - the Buccaneer S1 was so badly underpowered it could only launch at low weights, with low fuel. Or it can happen if an exceptionally heavy weapon load is carried - a very rare event.
Hope this helps
Best regards as ever to those going off the cat
Engines
Evalu8ter is, as usual, bang on the money. There is a close link between USN catapult designs and USN aircraft, and longer cats would not deliver much improvement, as aircraft end speed is as good as it already can be.
Another factor is ship design - the CVN flight deck is essentially sized by the requirement to get 4 catapults installed. Longer cats would mean a new flight deck, and a longer ship, which would need more power, so an extra reactor.....
Launching off the cat at low fuel straight to a tanker usually happens when the aircraft design has gone wrong - the Buccaneer S1 was so badly underpowered it could only launch at low weights, with low fuel. Or it can happen if an exceptionally heavy weapon load is carried - a very rare event.
Hope this helps
Best regards as ever to those going off the cat
Engines
The reason in the civvie world for taking off with a precomputed fuel load, doing takeoffs from other positions than the beginning of the runway, and not using full available power is an economic one.
That said I can only talk for fast landbased jets, where the most useless things are the fuel left on ground and the runway behind the aircraft.
Concerning the fuel there were sorties, which called for less fuel due to tactical and structural reasons. It is no good to go into a WVR engagement with three full outboard tanks. Either those stayed at home, were not refueled, or were flown dry with sometimes sensless maneuvers. In the F4 we could refuel the jet without the fuselage tanks 5 and 6, which was used for a quick combat dart sortie over the north sea close to our airbase.
That said I can only talk for fast landbased jets, where the most useless things are the fuel left on ground and the runway behind the aircraft.
Concerning the fuel there were sorties, which called for less fuel due to tactical and structural reasons. It is no good to go into a WVR engagement with three full outboard tanks. Either those stayed at home, were not refueled, or were flown dry with sometimes sensless maneuvers. In the F4 we could refuel the jet without the fuselage tanks 5 and 6, which was used for a quick combat dart sortie over the north sea close to our airbase.
I believe that the Buccaneer S1s used to do that. Launch with weapons loaded and a light fuel load then go straight to a buddy fitted Scimitar tanker.
Calculating takeoff fuel was pretty crucial when operating in the tropics in the Victor K1 tanker. Max fuel load was 86k pounds, but this could be down to 55k when taking off from, say, Masirah, with temps in the high 40s.
We were once down to transit from Marham to Leuchars to position for an exercise, when our aircraft, which had 40k of fuel on board for the 40 minute flight, went u/s before takeoff. The only alternative aircraft available had 86k on board, and my impatient flight commander captain wouldn't wait for it to be defuelled. I spent most of the transit jettisonning around 40k through the pods to get the aircraft down to max landing weight. I can imagine how well that would go down in the civvy world!
We were once down to transit from Marham to Leuchars to position for an exercise, when our aircraft, which had 40k of fuel on board for the 40 minute flight, went u/s before takeoff. The only alternative aircraft available had 86k on board, and my impatient flight commander captain wouldn't wait for it to be defuelled. I spent most of the transit jettisonning around 40k through the pods to get the aircraft down to max landing weight. I can imagine how well that would go down in the civvy world!
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one of our most imported decision in commercial aviation is about fuel to be loaded.
How is it handled in military aviation? E.g: Do fighters always top off? How is it handled on carriers? Etc,
How is it handled in military aviation? E.g: Do fighters always top off? How is it handled on carriers? Etc,
However, military transport and patrol aviation is more similar to commercial aviation. You compute the amount you need for the mission, plus reserves, and load that. In the US P-3 community we computed the amount needed for the mission, plus reserves, and then added 6 klbs "for the wife and kids".
The SR-71 never took off with max fuel. They ALWAYS took off with a light fuel load and then hit a tanker to top off. They essentially never went anywhere without tanker support.
The B-52 has a higher max inflight gross weight than max takeoff gross weight. So when taking off with a big payload requiring long range, they would load enough fuel to reach or nearly reach max takeoff weight and then hit a tanker to add sufficient fuel to reach their max inflight gross weight.
Last edited by KenV; 23rd Mar 2016 at 14:04.
I am not sure where you have got that from, but you are wrong - it was never routine! If some of the freight was a top priority and had a specific time frame, then it could be a possibility, but such occurrences were and are rare.
Also, flights are rarely scheduled further than Gander or Goose because of Crew Duty Time restrictions and most had the option of a flag stop at Keflavik to ensure that the maximum payload would be offered.
I don't own this space under my name. I should have leased it while I still could
On the Vulcan the normal fuel uplift was full except when the calculated fuel burn on a short sortie would have given a landing weight above normal maximum. Typically air tests or displays would be fuelled to minimums for the sortie.
I suspect you are really looking for short leg comparison. For the short hop UK-Malta, once flown in under 2 hours, we still fuelled to max.
However I know an ex-RAF nav on Britannias with Britannia quit as all he did was fuel economics - minimum sector fuel uplift with expensive fuel - maximum cheap fuel uplift compensure with cost of carriage etc.
I suspect you are really looking for short leg comparison. For the short hop UK-Malta, once flown in under 2 hours, we still fuelled to max.
However I know an ex-RAF nav on Britannias with Britannia quit as all he did was fuel economics - minimum sector fuel uplift with expensive fuel - maximum cheap fuel uplift compensure with cost of carriage etc.
I don't own this space under my name. I should have leased it while I still could
I recall one Nimrod case, it was in Norway when it was decided to recall it to UK. Normally it would be refuelled to full with expensive fuel but to save money it would pick up minimum route fuel. However base was closed so it would have to night stop in Prestwick, pick up enough not so expensive fuel and make the flight next day to Kinloss. So cost was X Krona of fuel, plus Y £ of food and accommodation plus Z £ of not so expensive fuel. As this was cheaper than X Krona of fuel and Y Krona of food and accommodation the crew was ordered too fly to Prestwick.
The maths took some time to calculate before they were ordered back to UK. They then played the crew duty card.
The maths took some time to calculate before they were ordered back to UK. They then played the crew duty card.
Masirah in the hot....
.....in 1970 during the build up to Ex Bersatu Padu ISTR. The Lightnings were being ferried out and needed a fair amount of refuelling. (Our Shacks were doing the SAR cover in mid Indian Ocean and had been gone hours before.)
There were "no go" marker posts on the runway edge to trigger an abort.
We watched as the first Victor roared off down strip at max chat, past the no go markers and appeared to fly into a huge whirling cloud of sand and appeared several minutes later and several miles out to sea desparately looking for height. There might have been a sweaty palm or two in the second one as he too used every bit of concrete and (maybe some sand) for a repeat performance.
I didn't envy them one bit.
The Ancient Mariner
There were "no go" marker posts on the runway edge to trigger an abort.
We watched as the first Victor roared off down strip at max chat, past the no go markers and appeared to fly into a huge whirling cloud of sand and appeared several minutes later and several miles out to sea desparately looking for height. There might have been a sweaty palm or two in the second one as he too used every bit of concrete and (maybe some sand) for a repeat performance.
I didn't envy them one bit.
The Ancient Mariner
RedhillPhil
Not really true, RedhillPhil. We used to launch with full internal fuel - with a catapult launch TOW was never an issue. But the SFC of the beast was appalling and we used a Scimitar to top up about 25 mins after launch to give us a decent range.
Not really true, RedhillPhil. We used to launch with full internal fuel - with a catapult launch TOW was never an issue. But the SFC of the beast was appalling and we used a Scimitar to top up about 25 mins after launch to give us a decent range.