Forum: F-35 Lightning II

yeah, but if you have 1.5 hours of gas and are moving 600 miles per hour... THAT is what makes aviation invaluble. the ability to move X weight of Y(ordenance, cargo, etc) Z miles in the least time.

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I understand that, but you cant discount the inefficiency. If flying didn't have distance and time over traveling by car then it wouldn't have made it for over 100 years so far. So I have a question then, because of fuel consumption is it really easy to lose track of how much you're using? Ive always wondered how pilots every once in a while end up bailing out because of no fuel left.

Every now and then I guess they run out of altitude and options at the same time.

Salute

As with the actual thrust, the fuel flow curve is not a straight line from zero pph to max pph.

The jet motors have a very sharp "hooK" at the top end of the power requested input. TEG-breath can explain this, as can Roscoe.

So I can use half power and burn "x" pounds per minute. At full power I am burning four or five times that. You have to run a series of test profiles and see what speed you get at a certain power setting, and note the fuel consumption. Then you plot the data and see the best speed for miles-per-gallon.

The fans are awesome when you are not using burner and have the throttle lever pulled back. You don't fight like that, but you must get to the fight with as much gas as you can.

I would be interested to plot the thrust versus the power lever/rpm, or whatever they use these days. As basic aero laws dictate, thrust must equal drag to maintain a constant speed.

later,

And Merry Christmas to all

Gums

That_Engine_Guy wrote:

Quote:

Specific fuel consumption (SFC) is the conventional fuel efficiency metric for jet engines. This metric assumes different forms.

For turbojets and turbofans, SFC is often referred to as the thrust specific fuel consumption (TSFC) and is the ratio of the fuel flow rate to the thrust. Clearly, low values of TSFC are good. Measured in pounds of fuel per hour/pounds of thrust, which is usually shortened to 1/hour. In Systeme Internationale (SI) units, SFC is measured in units of kilograms of fuel per second/kiloNewtons of thrust). When only one value of TSFC is reported for an engine, it is often the TSFC corresponding to the military thrust level, rather than the maximum (augmented) thrust level.

F100-PW-229
(MIL) 17,800lbs @ 0.726 lb/Hr/lb st
(MAX) 29,100lbs @ 2.060 lb/Hr/lb st

F110-GE-129
(MIL) 17,000lbs @ 0.745 lb/Hr/lb st
(MAX) 29,000lbs @ 1.900 lb/Hr/lb st

F414-GE-400
(MIL) 14,700lbs @ 0.840 lb/HR/lb st
(MAX) 22,000lbs @ 1.850 lb/HR/lb st

F119-PW-100
(MIL) 25,000lbs @ (~0.800?) lb/HR/lb st (Speculation varies between 0.600 - 0.860...)
(MAX) 37,000lbs @ (~1.950?) lb/HR/lb st

F135-PW-100
(MIL) 28,000lbs @ 0.886 lb/HR/lb st
(According to J@ne'$, but seems too high? 0.700 is more likely)
(MAX) 43,000lbs @ (~1.950?) lb/HR/lb st

F136-GE-100 (According to J@ne'$)
(MIL) 26,000lbs @ ?
(MAX) 40,500lbs @ ?

(~x.xxx?) figures based on "guesstimates" from differing public sources, figures are still guarded for this type of performance data

SFC does change with speed and altitude; comparative figures are typically given for static-sea level data.

SnakeHandler wrote:

Yeah, but the key is that we'll have to use much less power to maintain loiter in the Lightning than in the Viper. I'd be surprised if we have to use more than 3-5k pounds per hour most of the time, much like the Viper.

I agree with SnakeHandler; with ALL that power, you won't need much to just fly around in a loiter or cruise. The full MIL thrust will be used for penetration and egress. MAX will be used for escape or engagements. It is the same benefits gained by the newer engines in the Viper, you use less throttle overall and save fuel over the mission compared to the original PW-200s.

Keep 'em flyin' Thumb

TEG

So, the fuel burn is very similar between the F414-GE-400 (.840 lb/HR/lb st) vs F135-PW-100 (.886 lb/HR/lb st) WOW..........or am I miss interpreting the information??? Confused

F414-GE-400
(MIL) 14,700lbs @ 0.840 lb/HR/lb st
(MAX) 22,000lbs @ 1.850 lb/HR/lb st

F135-PW-100
(MIL) 28,000lbs @ 0.886 lb/HR/lb st
(According to J@ne'$, but seems too high? 0.700 is more likely)
(MAX) 43,000lbs @ (~1.950?) lb/HR/lb st

Gums wrote:

Salute

As with the actual thrust, the fuel flow curve is not a straight line from zero pph to max pph.

The jet motors have a very sharp "hooK" at the top end of the power requested input. TEG-breath can explain this, as can Roscoe.

So I can use half power and burn "x" pounds per minute. At full power I am burning four or five times that. You have to run a series of test profiles and see what speed you get at a certain power setting, and note the fuel consumption. Then you plot the data and see the best speed for miles-per-gallon.

The fans are awesome when you are not using burner and have the throttle lever pulled back. You don't fight like that, but you must get to the fight with as much gas as you can.

I would be interested to plot the thrust versus the power lever/rpm, or whatever they use these days. As basic aero laws dictate, thrust must equal drag to maintain a constant speed.

later,

And Merry Christmas to all

Gums

So, its not likely the F-22 would fly "Super Cruise" for much of its flight profile. As it would still burn less fuel at subsonic speeds. Of, course it has the option when the need arises............correct???

Corsair1963 wrote:

So, the fuel burn is very similar between the F414-GE-400 (.840 lb/HR/lb st) vs F135-PW-100 (.886 lb/HR/lb st) WOW..........or am I miss interpreting the information??? Confused

F414-GE-400
(MIL) 14,700lbs @ 0.840 lb/HR/lb st
(MAX) 22,000lbs @ 1.850 lb/HR/lb st

F135-PW-100
(MIL) 28,000lbs @ 0.886 lb/HR/lb st
(According to J@ne'$, but seems too high? 0.700 is more likely)
(MAX) 43,000lbs @ (~1.950?) lb/HR/lb st

Don't get hung up on those figures, they may not be accurate as SFC is a performance indicator that is often misrepresented or unreleased for military engines.

The F135 should have a much better SFC than the F414, it is almost a generation newer. Also do some research on the F414 and read about how it didn't exactly live up to GE's claims of a 35% increase in performance over the F404. (So much that the DoD/GAO did a study of it...)

As for what GUMS stated above, turbine engines get worse SFC the higher the thrust gets. A quick example is the ATG1500 of the M1A1 Abrams Tank. Between 45MPH and 60MPH fuel consumption doubles! Shocked

This is why the engine is "governed" to only 45MPH.

Below is a generic chart showing how SFC is computed over an engine's ENTIRE envelope.

Just like a GE90-115B in a B777, the F135 of the F-35 won't be used at MIL power all the time. If you run the numbers of a GE90 running at it's MIL, sea level static SFC, range versus fuel data for the B777 is drastically below what Boeing puts in the sales brochure.... Rolling Eyes

Aircraft (Civil or Military) don't fly around all the time at sea-level, standing still, or at maximum power... Doh

There are lots of people running the numbers on the F135 and F-35, don't get wrapped around our simple thoughts and math calculations on a public forum... Most of the data your asking about is most likely C|@s$iFiEd and true numbers won't be released for years... Cheers

Keep 'em flyin' Thumb

TEG

Salute

To corsair...

You guys are all talking about an engine performance number for an engine that is flying all by itself.

The motor is pushing along an airframe that has drag. So a basic fuel flow stat is not worthwhile unless you add the plane it is powering.

The Viper actually has less drag than most automobiles, even with the gear down. Neat, huh?

So you have to use that thrust per gallon number and then crank in the drag of the plane. Oh yeah, turn real hard and increase your induced drag and you see how much extra power you need.

The Viper could hold nine gees at about three hundred and sixty knots until it ran outta gas. At that time, it had the highest sustained turn rate of anything flying.

So let's define the parameters here. Max range? Best turn? Top speed?

Gums sends ...

Last edited by Corsair1963 on Dec 25, 2008 - 12:45 AM; edited 1 time in total

Gums wrote:

Salute

To corsair...

You guys are all talking about an engine performance number for an engine that is flying all by itself.

The motor is pushing along an airframe that has drag. So a basic fuel flow stat is not worthwhile unless you add the plane it is powering.

The Viper actually has less drag than most automobiles, even with the gear down. Neat, huh?

So you have to use that thrust per gallon number and then crank in the drag of the plane. Oh yeah, turn real hard and increase your induced drag and you see how much extra power you need.

The Viper could hold nine gees at about three hundred and sixty knots until it ran outta gas. At that time, it had the highest sustained turn rate of anything flying.

So let's define the parameters here. Max range? Best turn? Top speed?

Gums sends ...

I understand what you are saying about thrust vs drag. Yet, won't the F-35 likely have an advantage from the start. Because it carries its fuel and weapons internally..........

That_Engine_Guy wrote:

Corsair1963 wrote:

So, the fuel burn is very similar between the F414-GE-400 (.840 lb/HR/lb st) vs F135-PW-100 (.886 lb/HR/lb st) WOW..........or am I miss interpreting the information??? Confused

F414-GE-400
(MIL) 14,700lbs @ 0.840 lb/HR/lb st
(MAX) 22,000lbs @ 1.850 lb/HR/lb st

F135-PW-100
(MIL) 28,000lbs @ 0.886 lb/HR/lb st
(According to J@ne'$, but seems too high? 0.700 is more likely)
(MAX) 43,000lbs @ (~1.950?) lb/HR/lb st

Don't get hung up on those figures, they may not be accurate as SFC is a performance indicator that is often misrepresented or unreleased for military engines.

The F135 should have a much better SFC than the F414, it is almost a generation newer. Also do some research on the F414 and read about how it didn't exactly live up to GE's claims of a 35% increase in performance over the F404. (So much that the DoD/GAO did a study of it...)

As for what GUMS stated above, turbine engines get worse SFC the higher the thrust gets. A quick example is the ATG1500 of the M1A1 Abrams Tank. Between 45MPH and 60MPH fuel consumption doubles! Shocked

This is why the engine is "governed" to only 45MPH.

Below is a generic chart showing how SFC is computed over an engine's ENTIRE envelope.

Just like a GE90-115B in a B777, the F135 of the F-35 won't be used at MIL power all the time. If you run the numbers of a GE90 running at it's MIL, sea level static SFC, range versus fuel data for the B777 is drastically below what Boeing puts in the sales brochure.... Rolling Eyes

Aircraft (Civil or Military) don't fly around all the time at sea-level, standing still, or at maximum power... Doh

There are lots of people running the numbers on the F135 and F-35, don't get wrapped around our simple thoughts and math calculations on a public forum... Most of the data your asking about is most likely C|@s$iFiEd and true numbers won't be released for years... Cheers

Keep 'em flyin' Thumb

TEG

Well, it clear that its hard to even speculate without any real hard evidence. What I was really trying to get at.........Some claim the Gripen NG with 7,000 lbs of internal fuel. Has a similar range to the USAF forthcoming F-35A with 18,500 lbs of fuel. Seems very hard to believe the range is similar if the fuel burn is anywhere close with the Lightning carrying about 2 1/2 times the fuel. Even with drag taken into account. Especially, if the F-35 carried internal weapons and the Gripen was forced to carry several draggy stores????? Confused

Salute

I could give a damn about the SFC numbers for an engine on the test stand.

What I saw in the Viper was the "seven pound" rule.

Come off target and climb at best range speed and get home.

Rule-of-thumb was seven pounds per mile. Add in what your reserve was desired at home and voila.

So we could come off tgt two hundred miles away and used fourteen hundred pounds of JP to get home.

Not too shabby.

The SLUF was about the same.

Merry Christmas to all

Gums...

Corsair1963 wrote:

What I was really trying to get at.........Some claim the Gripen NG with 7,000 lbs of internal fuel. Has a similar range to the USAF forthcoming F-35A with 18,500 lbs of fuel. Seems very hard to believe the range is similar if the fuel burn is anywhere close with the Lightning carrying about 2 1/2 times the fuel. Even with drag taken into account. Especially, if the F-35 carried internal weapons and the Gripen was forced to carry several draggy stores????? Confused

Well you have to do some math to get a general idea.

Gripen NG's F414 static (standing still) ,no intake, sea-level has an SFC of 0.84 lb/HR/lb and at MIL power of 14,700lbs that means in one hour it would burn 12,348lbs of jet fuel.

That is UNINSTALLED raw engine data. As you can tell from the chart I shared above; speed, and altitude have an immense effect on the SFC. In that example the engine could have an SFC anywhere between 0.35 and .85 depending on where it is in the flight envelope. Also figure in what Gums is saying; this doesn't account for the aircraft the engine is in. If you need to use more power to fly, the SFC at that specific time will be higher; lower throttle settings will drop the SFC.

Example: The F100-PW-229 has a static SFC of 2.060 at MAX. In the F-16 flying at 20K feet and MACH 1 the ACTUAL SFC at MAX will be MUCH different. The same PW-229 installed in an F-15 may have a different SFC than the F-16's SFC given the same conditions.

Now back to our initial figures; we'll assume the F135's SFC is 0.700lbs/Hr/lb st for this example. (That is my "guesstimate" until I see a "real" number from PW... Rolling Eyes

)

Lightening II's F135-PW-100 static (standing still) ,no intake, sea-level has an SFC of 0.700 lb/HR/lb and at MIL power of 28,000lbs that means in one hour it would burn 19,600lbs of jet fuel.

So on internal fuel the Gripen NG could fly 34 minutes at MIL loosely based on standardized static test conditions of the uninstalled engine.

The Lightening II could fly 56 minutes given the same unbelievable situation... Rolling Eyes

Again, all loosely based on raw uninstalled engine performance without any regard or account of installation, configuration, or flight performance of the aircraft. (Like taking off with 2.5X more fuel!?!...)

This a little clearer now?

Think of it in auto terms? Say a Chevy V-8 used in the 1972 Corvette is the "same" as a 1972 Chevy Pickup. Both have a maximum HP of say 300, and use X gallons per minute, (On a dyno) we'll call it SFC. The Corvette will get better highway mileage and acceleration than the Pickup and may even have a greater range with a smaller tank; even though BOTH engines have the same SFC Cheers

Keep 'em flyin' Thumb

TEG

singularity wrote:

TimmayMan wrote:

I think they are saying .7 pounds per fuel, PER POUND OF THRUST, per hour.

Hmmm, that would make alittle more sense. But at that rate I dont think the f-35 would have a very long endurance with internal fuel, and that would be on MIL power. But again, I have been up for quite a while and am very tired, so I may just be not getting it right now.

I dont have and couldnt give any specifics on internal fuel load for the F-35 but last I heard was that it was more than a F-16 w 2X 370 gal wing tanks and a 300 gal centerline tank.

That_Engine_Guy wrote:

Think of it in auto terms? Say a Chevy V-8 used in the 1972 Corvette is the "same" as a 1972 Chevy Pickup. Both have a maximum HP of say 300, and use X gallons per minute, (On a dyno) we'll call it SFC. The Corvette will get better highway mileage and acceleration than the Pickup and may even have a greater range with a smaller tank; even though BOTH engines have the same SFC Cheers

Correct but it is the four-cylinder Mazda (i.e. the Grippen) out there that confuses Corsair1963's mind.

Corsair1963 wrote:

That_Engine_Guy wrote:

Corsair1963 wrote:

So, the fuel burn is very similar between the F414-GE-400 (.840 lb/HR/lb st) vs F135-PW-100 (.886 lb/HR/lb st) WOW..........or am I miss interpreting the information??? Confused

F414-GE-400
(MIL) 14,700lbs @ 0.840 lb/HR/lb st
(MAX) 22,000lbs @ 1.850 lb/HR/lb st

F135-PW-100
(MIL) 28,000lbs @ 0.886 lb/HR/lb st
(According to J@ne'$, but seems too high? 0.700 is more likely)
(MAX) 43,000lbs @ (~1.950?) lb/HR/lb st

Don't get hung up on those figures, they may not be accurate as SFC is a performance indicator that is often misrepresented or unreleased for military engines.

The F135 should have a much better SFC than the F414, it is almost a generation newer. Also do some research on the F414 and read about how it didn't exactly live up to GE's claims of a 35% increase in performance over the F404. (So much that the DoD/GAO did a study of it...)

As for what GUMS stated above, turbine engines get worse SFC the higher the thrust gets. A quick example is the ATG1500 of the M1A1 Abrams Tank. Between 45MPH and 60MPH fuel consumption doubles! Shocked

This is why the engine is "governed" to only 45MPH.

Below is a generic chart showing how SFC is computed over an engine's ENTIRE envelope.

Just like a GE90-115B in a B777, the F135 of the F-35 won't be used at MIL power all the time. If you run the numbers of a GE90 running at it's MIL, sea level static SFC, range versus fuel data for the B777 is drastically below what Boeing puts in the sales brochure.... Rolling Eyes

Aircraft (Civil or Military) don't fly around all the time at sea-level, standing still, or at maximum power... Doh

There are lots of people running the numbers on the F135 and F-35, don't get wrapped around our simple thoughts and math calculations on a public forum... Most of the data your asking about is most likely C|@s$iFiEd and true numbers won't be released for years... Cheers

Keep 'em flyin' Thumb

TEG

Well, it clear that its hard to even speculate without any real hard evidence. What I was really trying to get at.........Some claim the Gripen NG with 7,000 lbs of internal fuel. Has a similar range to the USAF forthcoming F-35A with 18,500 lbs of fuel. Seems very hard to believe the range is similar if the fuel burn is anywhere close with the Lightning carrying about 2 1/2 times the fuel. Even with drag taken into account. Especially, if the F-35 carried internal weapons and the Gripen was forced to carry several draggy stores????? Confused

The F135 produces about 2.5x more thrust than the Gripen's engine, so the total fuel burn (not per pound of thrust) should be about that much higher.

Forum: F-35 Lightning II

F-135 or F-136 fuel burn rate