Bombers: Fuel Over Tarrget

[Zipper730]

I'm not sure if there's a generalized formula for fighters and bombers for the following

• Fighter: The percentage of fuel at the point in flight where the aircraft must turn-around in order to be able to land with reserve?
  
• Bomber: The percentage of fuel at the point in flight where with/without weapons, the aircraft must turn around in order to be able to land with acceptable reserves or at all?

As I understand it, in the era of jet-aircraft: There is an assumed amount of fuel that would be expended starting the engines up, taxiing to the runway, taking off, climbing to altitude, cruising into the target area, a certain amount of time allotted for the engines to be at high power settings or afterburner, followed by fuel allotted to cruise back to base, and loiter a certain period of time (I know that in the era of propeller driven aircraft, there was a specified time that covered engine start-up, taxi, and warm-up the engines).

In the old days (1942-1945), loiter time seemed to be around an hour, though I'm not sure what the expected loiter times changed to from WWII to Korea, and the Korea-Vietnam, and Vietnam-Present era.

I'm not sure as for jet-fighters how much time is allocated for combat either from Korea to Vietnam, and Vietnam to modern day. If I recall in WWII about 30 minutes was expected for combat with 20 minutes for either normal rated maximum power, and 10 minutes at either military power, with 5 of those 10 minutes at WEP (piston driven aircraft).

I'm not really sure what rules apply for bombers.

 

[stona]

For British bombers the fuel reserve was set by the Groups for each mission. The 'Command Value' was given by Bomber Command for each aircraft type, essentially a graph showing how much fuel was required for a given range and load, but an investigation showed that the Groups added an extra 200 gallons, on average to this figure. It also conceded that this was reasonable as,

"The principle allowances which are not covered in the existing Command graphs are those for possible diversion, landing congestion, extra consumption over heavily defended targets and strong winds."

It was also accepted that this extra 200 gallons would cover such eventualities as fuel loss due to enemy action, getting lost and bad engine management.

It was thanks to this Group reserve that accidents and losses due to fuel shortage for Bomber Command aircraft made up a minute percentage of all losses.

As an example, taking the reserve into account, the actual miles flown per gallon for a Halifax III fell from 1.0 (as calculated in the Command Value) to 0.78.

Cheers

Steve

 

[Shortround6]

I'm not sure if there's a generalized formula for fighters and bombers for the following

• Fighter: The percentage of fuel at the point in flight where the aircraft must turn-around in order to be able to land with reserve?
  
• Bomber: The percentage of fuel at the point in flight where with/without weapons, the aircraft must turn around in order to be able to land with acceptable reserves or at all?

(I know that in the era of propeller driven aircraft, there was a specified time that covered engine start-up, taxi, and warm-up the engines).

In the old days (1942-1945), loiter time seemed to be around an hour, though I'm not sure what the expected loiter times changed to from WWII to Korea, and the Korea-Vietnam, and Vietnam-Present era.
If I recall in WWII about 30 minutes was expected for combat with 20 minutes for either normal rated maximum power, and 10 minutes at either military power, with 5 of those 10 minutes at WEP (piston driven aircraft).

I'm not really sure what rules apply for bombers.

There wasn't a hard and fast rule and even the general rules varied form air force to air force and perhaps even theater to the theater.
The British at one point had a radius of action of the range minus one hour at cruising speed. That is a 1000 mile range at 200mph was reduced to a 400 mile radius of action. Obviously the radius change not only with bomber type but the payload and amount of fuel carried,

As Stona has pointed out, some units padded the "general" rule, especially in Europe as prevailing winds are from the west. They knew what the wind was on take-off, what the wind would be on return a number of hours later was a prediction and if wrong???????

Most of this was worked out before take-off and routes into the target an routes back were figured out. Both routes in and out could have several large dog-legs which make a hash out of relying on fuel gauges to indicate when to turn back. Route in could be a different length than the route out.

Planners would use Flight operation instruction charts from the pilots manuals to determine fuel needed for different cruise speeds and altitudes in addition to warm up and take-off. a 30 minute to hour reserve was planned for head winds, finding the home airfield in bad weather and/or orbiting the field/diverting to another due to high numbers of aircraft or an accident on the runway.

If done right and without combat damage NO bomber should have to break formation to return home due to being short of fuel.

having to abort a mission before reaching the target due to lack of fuel shows a real lack of planning.

I would note that a BIG difference between piston powered planes and early jets that caused a lot of problems for the jets was that the early jets didn't throttle down well. That is to say that while you could throttle back a piston engine and drop the fuel consumption considerably per hour of flight that didn't work so well on the early jets, yes you could throttle them back but there was no rich or lean settings

For instance a P-80A at 12,000lbs take-off at 35,000ft was good for 1000 miles at max continuous (96%Max rpm) with 470 gals of fuel (drop tanks empty) but going to max range condition (whatever rpm gave the desired speed) only boosted the range to 1175 miles. Less than a 20% difference. Fuel per hour was 220 gallons at 96% rpm and 180 gallons and hour at max range settings.
And jets gave much better range at high altitude than low down. Ar 10,000ft the same 470 gallons was good for 500 miles at max continuous (96%) or 550 miles at max range settings.

Later jets got better but the Korean war jets were still pretty poor.

 

[pbehn]

Some points.


In UK several air fields were constructed on the coast for damaged or short of fuel aircraft to land.

Europes prevailing winds are not 100% prevalent. I have flown with strong tail winds between UK and Netherlands in both directions, on the exact route taken by RAF bomber crews. The winds at 20/30,000 ft bear no relation to those on the ground.

 

[Shortround6]

There were often a number of meteorological flights per day (often performed by obsolete aircraft) to measure the winds aloft in various parts of the British Isles. Both for navigation and for AA fire control. However the further from the UK the less detailed the information became. A few high performance aircraft may have penetrated German airspace for better data but this obviously had risks attached.
It also required either radar tracking or observation of the ground to chart the difference between indicated speed and ground speed.
It might also require several legs to be flown to get the real wind direction (even wind 30 degrees off the tail could give a good boost to ground speed.)

 

[Zipper730]

For British bombers the fuel reserve was set by the Groups for each mission. The 'Command Value' was given by Bomber Command for each aircraft type, essentially a graph showing how much fuel was required for a given range and load, but an investigation showed that the Groups added an extra 200 gallons, on average to this figure. It also conceded that this was reasonable as,

"The principle allowances which are not covered in the existing Command graphs are those for possible diversion, landing congestion, extra consumption over heavily defended targets and strong winds."

It was also accepted that this extra 200 gallons would cover such eventualities as fuel loss due to enemy action, getting lost and bad engine management.

Makes sense

Both routes in and out could have several large dog-legs which make a hash out of relying on fuel gauges to indicate when to turn back. Route in could be a different length than the route out.

That's a good point...

I would note that a BIG difference between piston powered planes and early jets that caused a lot of problems for the jets was that the early jets didn't throttle down well. That is to say that while you could throttle back a piston engine and drop the fuel consumption considerably per hour of flight that didn't work so well on the early jets, yes you could throttle them back but there was no rich or lean settings.

Ok

 

[XBe02Drvr]

In the jet age US Navy every pilot maintains a realtime "howgozit" so that at all times he/she knows what the current bingo fuel is. When you hit bingo you break off your mission and establish a max range profile back to the boat or a shore base. There are many constantly evolving variables in this equation, such as atmospherics, current location, aircraft condition, and even available tankers. If the only airborne tanker goes sour and there's a major dirty weather nighttime recovery in progress, with low visibility, high wind, and a pitching deck, plus the nearest land base is 400 miles away, your bingo fuel number just jumped way up. With 13 birds aloft, vertigo becoming endemic, pilots boltering repeatedly, no gas aloft and no usable bingo ashore, somebody's going swimming before the night is over. Another "night in the barrel".
Cheers,
Wes

 

[Shortround6]

The newer jets (mid 50s and on?) are a lot better than the old jets for fuel economy when throttled back.
The P-80A clean at 35,000ft burned 5 gallons a minute at combat power, 3.66 gpm at max cruise and 3 gpm for max range.
at 10,000ft it burned 10gpm combat, 7.83gpm at max cruise and 6.16gpm for max range.

For comparison an F4U with R-2800-8 could burn 4.8gpm at combat/military power, about 4gpm at max continuous but could drop to about 1.5gpm for max lean cruise and under 1gpm for max endurance.
The Piston engines also gave the best economy (fuel per minute or hour ) down low although range was often better high up. The Jets offered way more range high up but then had to get down to land.

The Early jets gave best range using about 60% of the fuel per minute that combat settings did. The Piston planes could cruise at 33% to 20% of the fuel burn per minute of combat settings.
The jets were much more critical of fuel management than the piston planes.

The P-80 manual gives a recommended descent of mach 0.50 and a range of 105 miles to descend from 35,000ft. while using 30 gallons of fuel. It also has a chart for range while descending with power off (GLIDING) at 177mph indicated airspeed, and the distance without drop tanks is 115 miles from 35,000ft. A loooong time to contemplate your sins

Not sure how many pilots manuals gave glide distances

 

[XBe02Drvr]

Not sure how many pilots manuals gave glide distances

Every pilot manual I've ever seen, ancient or modern, civil or military has given some sort of info on glide performance, be it a glide distance table or a glide ratio graph. Even a brick like the F-4, which, like the F-16, has been successfully dead-sticked to a landing, or at least a "survivable arrival". There's actually a YouTube of an F-16 deadstick event. An F-102 is reputed to have accomplished it IN IMC!! at NAS Memphis during the hurrivac for Camille in 1969. This from controllers who were on the scopes that day. Has anybody ever heard of an F-104 or a Vigilante pulling it off? Or a Thud?
Cheers,
Wes