Forum: F-35 Lightning II

mil_hobbyist wrote:

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.

Yet, this get back to a one for one comparison...............Take a Gripen with full internal fuel and 2-2,000 lb PGM and 2- BVR Missiles. Then compare it to a F-35A with the same weapons load all internally........now throw in the ~ fuel burn for each at there best flight profile? Question

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mil_hobbyist wrote:

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.

Yet, this get back to a one for one comparison...............Take a Gripen with full internal fuel and 2-2,000 lb PGM and 2- BVR Missiles. Then compare it to a F-35A with the same weapons load all internally........now throw in the ~ fuel burn for each at there best flight profile? Question

Remember that the f35 carries its weapon load and fuel internally not because of aerodynamic reasons but because of the low-observability thing.

It is true that external weapons (or tanks) increase drag for each particular a/c. However that shouldn't be interpreted as any a/c with external payload are more draggy than the ones without. The f35 is perhaps more draggy than the Grippen even if the Grippen carries that weapons load (i.e. 2x A2G + 2x A2A) externally.

r2d2 wrote:

Remember that the f35 carries its weapon load and fuel internally not because of aerodynamic reasons but because of the low-observability thing.

It is true that external weapons (or tanks) increase drag for each particular a/c. However that shouldn't be interpreted as any a/c with external payload are more draggy than the ones without. The f35 is perhaps more draggy than the Grippen even if the Grippen carries that weapons load (i.e. 2x A2G + 2x A2A) externally.

Actually, its both. Internal weapons and fuel are ALWAYS significantly less draggy than the same weapons and fuel carried on on external pylons. This is why the F-102/106 carries internal missiles, the B-2 and B-52 carries internal bomb loads instead of slimming down their airframes and lugging stuff around on external pylons.

Regardless, the F-35 is most likely the least draggy aircraft amongst any fighter that carrying 8400 kg of fuel and 5700 lbs of ordnance no matter how they carry it. The Gripen is a smaller aircraft with half the empty weight, so its drag when clean ought to be lower than an F-35A; although it is unlikely to to be half. The F-35 also has more than twice the thrust. So, basically it should out accelerate, out climb and in practical combat scenarios out run the Gripen. And, that for all intents and purposes, is good enough.

For a rough comparison on endurance, one should consider not so much total fuel, but fuel fraction. The F-35A has a fuel fraction of about 40% -- that is, when it is fully fueled, its fuel load is roughly 40% of its total weight. The Gripen on the other hand, has a fuel fraction of 25%. The F-35A hence has 1.6x the amount of fuel per unit take off mass and should have at least 1.6x the range all else being equal. However, all else is not equal. Additional drag in combat configurations tend to favor internal weapon loads. Larger engines tend to be more efficient than smaller ones. Also, even when the exterior shape is identical except for scale, the larger the aircraft the more efficient it becomes. Take an A380 and create a 1/2 scale replica and it'll be less efficient -- this is why it is necessary to consider the Reynolds number when conducting wind tunnel testing using scale models.

dwightlooi wrote:

Internal weapons and fuel are ALWAYS significantly less draggy than the same weapons and fuel carried on on external pylons.

I will rephrase that as;
''Internal weapons and fuel are significantly less draggy than the same weapons and fuel carried on on external pylons for that particular a/c.

dwightlooi wrote:

Regardless, the F-35 is most likely the least draggy aircraft amongst any fighter that carrying 8400 kg of fuel and 5700 lbs of ordnance no matter how they carry it.

Amount of fuel is not important but mission range as well as weapon load are important, IMO. So is the f35 the least draggy a/c amongst any other fighter with the same range and 5700 lb of ordnance? I'm not that much sure.

dwightlooi wrote:

For a rough comparison on endurance, one should consider not so much total fuel, but fuel fraction. The F-35A has a fuel fraction of about 40% -- that is, when it is fully fueled, its fuel load is roughly 40% of its total weight. The Gripen on the other hand, has a fuel fraction of 25%. The F-35A hence has 1.6x the amount of fuel per unit take off mass and should have at least 1.6x the range all else being equal.

And less fuel fraction is better for similar ranges or we should expect an increased range for the a/c with more fuel fraction as you say.

Pls note that I'm not saying that the Grippen is superior; Because it is NOT. But the figures about range for example makes me think that the f35 engineers sacrificed a more aerodynamic design in favor of low-observability.

Of course these are my opinions.

Corsair1963 wrote:

Yet, this get back to a one for one comparison............... Take a Gripen with full internal fuel and 2-2,000 lb PGM and 2- BVR Missiles. Then compare it to a F-35A with the same weapons load all internally........now throw in the ~ fuel burn for each at there best flight profile? Question

You're also talking about an aircraft with 360* sensor coverage, stealth, etc...

Everything comes with a price... $$$ and performance. If it wasn't worth the penalties it wouldn't be a feature of the F-35. (Or the F-22)

r2d2 wrote:

It is true that external weapons (or tanks) increase drag for each particular a/c. However that shouldn't be interpreted as any a/c with external payload are more draggy than the ones without. The f35 is perhaps more draggy than the Gripen even if the Grippen carries that weapons load (i.e. 2x A2G + 2x A2A) externally.

I highly doubt the F-35 is MORE draggy than a Grippen with weapons. Even if it is though, I bet the F-35 with weapons would penetrate into hostile airspace much further (both geographically and chronologically) than a Gripen with weapons; at which drag becomes a mute point... Rolling Eyes

Again IMO the F-35 will take any military into the future further than a "non-stealth" platform.

r2d2 wrote:

But the figures about range for example makes me think that the f35 engineers sacrificed a more aerodynamic design in favor of low-observability. Of course these are my opinions.

Who's to say the range figures that have been released to the public are completely accurate.. Shrug

We know what they want us to know, nothing more, but much less!

Many of the questions you are getting "speculative" guesses and opinions about here would meet with a stern "sorry sir but I can't comment on that type of performance data" if you asked an official source.

Sure there are fliers, displays, web-sites, sales-pitches, public-announcements, press-releases but who is to say they are 100% accurate? Wink

Take if from some of the people "on the inside" of the industry. We see things that most of the public, and many government officials don't see. Unless you have "need to know" or are part of an official government procurement team evaluating the latest equipment, you won't get "actual" data for leading edge military equipment.

Even older equipment on the Viper is often deemed "competition sensitive" or "proprietary" so much so that we're not even allowed to talk about it with others unless they have that "need to know"

Again; don't get hung up on what has been released, or leaked, or calculated, or speculated, or guessed.... the F-35 is an aircraft that will fly for years before all of it's TRUE performance and capabilities are known.

Keep 'em flyin' Thumb

(Merry Christmas Cheers

)
TEG

r2d2 wrote:

Remember that the f35 carries its weapon load and fuel internally not because of aerodynamic reasons but because of the low-observability thing.

It is true that external weapons (or tanks) increase drag for each particular a/c. However that shouldn't be interpreted as any a/c with external payload are more draggy than the ones without. The f35 is perhaps more draggy than the Grippen even if the Grippen carries that weapons load (i.e. 2x A2G + 2x A2A) externally.

The F-22 and F-35 both carry weapons and a great deal of fuel internally for a number of reasons. Which, does include Stealth but also Lower Drag..............Its funny on how some look at the F-35 and see a big bulky aircraft and assume its has lack luster performance.

Yet, the F-22 has a very similar Aerodynamic Profile and is even larger! Question: If, such a design is so inefficient.........How does the F-22 Super Cruise at high mach for extended periods???

Seem like a double standard to me...............

Let's not forget both are produced by Lockheed Martin.

Note: While, I am not expert I find it hard to believe a Gripen NG with external PGM's and AAM's. Is more aerodynamic than a clean Lightning II. Especially, consider just to over come the drag of external fuel tanks. You need to burn ~ half the fuel in the tanks just to carry them! Of course than doesn't even touch the RCS issue................

Corsair1963 wrote:

The F-22 and F-35 both carry weapons and a great deal of fuel internally for a number of reasons. Which, does include Stealth but also Lower Drag..............Its funny on how some look at the F-35 and see a big bulky aircraft and assume its has lack luster performance.

Yet, the F-22 has a very similar Aerodynamic Profile and is even larger! Question: If, such a design is so inefficient.........How does the F-22 Super Cruise at high mach for extended periods???

Advanced gas-turbine aircraft engine technology! Cool

YF120
F119-PW-100
F135-PW-100/-400/-600
F136-GE-XXX

SCRAM
PDE

I'm sure there are others that aren't even being discussed...

Read about some of the "public" information here:
http://www.wpafb.af.mil/shared/media/do ... 29-021.pdf

Gives you a little idea how serious the USA is about it's engine technology!

Keep 'em flyin' Thumb

TEG

Don't forget that Mach 3 without afterburner turbine that RATTLRS is suppose to demo. . .sometime. Question

That_Engine_Guy wrote:

Corsair1963 wrote:

The F-22 and F-35 both carry weapons and a great deal of fuel internally for a number of reasons. Which, does include Stealth but also Lower Drag..............Its funny on how some look at the F-35 and see a big bulky aircraft and assume its has lack luster performance.

Yet, the F-22 has a very similar Aerodynamic Profile and is even larger! Question: If, such a design is so inefficient.........How does the F-22 Super Cruise at high mach for extended periods???

Advanced gas-turbine aircraft engine technology! Cool

YF120
F119-PW-100
F135-PW-100/-400/-600
F136-GE-XXX

SCRAM
PDE

I'm sure there are others that aren't even being discussed...

Read about some of the "public" information here:
http://www.wpafb.af.mil/shared/media/do ... 29-021.pdf

Gives you a little idea how serious the USA is about it's engine technology!

Keep 'em flyin' Thumb

TEG

WPAFB does a great deal of research...................I've been to the base a couple of times over the years and always stopped at the Air Force Museum.

Oh..............I love the International Air and Trade Show in nearby Dayton! Salute

r2d2 wrote:

dwightlooi wrote:

Internal weapons and fuel are ALWAYS significantly less draggy than the same weapons and fuel carried on on external pylons.

I will rephrase that as;
''Internal weapons and fuel are significantly less draggy than the same weapons and fuel carried on on external pylons for that particular a/c.

Any amount of extra internal fuel and weapons are significantly less draggy than the same weapons and fuel carried on on external pylons for ANY aircraft design with technology being relatively constant. Unless you really, really, really screw up.

sferrin wrote:

Don't forget that Mach 3 without afterburner turbine that RATTLRS is suppose to demo. . .sometime. Question

Ahhh yes.... The YJ102R for the RATTLRS... Cool

An old quote from the "Is the Turbojet Dead" thread...

That_Engine_Guy wrote:

I've also found some information concerning the YJ102R.

Jane's Aero-Engines wrote:

In August 2004, Allison Advanced Development Co. (AADC) shared with Lockheed Martin a USD175 million five-year contract for the Rattlers (revolutionary approach to time-critical long-range strike) hypersonic unmanned vehicle. Part of the National Aerospace Initiative, and administered by the Office of Naval Research, the Rattlers mission is long-range strike. Its YJ102R turbojet-based combined-cycle engine is being designed as "an inexpensive propulsion system for Mach-4+, with advanced turbine cooling and no afterburner, yet with cruise specific thrust six times that of the Pratt & Whitney J58". If the eventual J102R should find a manned application, it will feature in Jane's Aero-Engines. In any event, its technology can hardly fail to read across to the propulsion of future Mach-4+ manned aircraft. In July 2005 AADC was renamed Rolls-Royce North American Technologies Inc.

MACH 4+ air breathing cruise missile with long range.... Bad news for bad guys... Twisted Evil

"Sharing" $175 million is hardly dead!

I'd love to see some performance data on THAT engine...

Or perhaps PW's SJX61-2!?! Shocked

A SCRAM jet capable of MACH 4.5 - 6+ using JP7! Not Worthy

Keep 'em flyin' Thumb

TEG

dwightlooi wrote:

For a rough comparison on endurance, one should consider not so much total fuel, but fuel fraction. The F-35A has a fuel fraction of about 40% -- that is, when it is fully fueled, its fuel load is roughly 40% of its total weight. The Gripen on the other hand, has a fuel fraction of 25%. The F-35A hence has 1.6x the amount of fuel per unit take off mass and should have at least 1.6x the range all else being equal.

How have you come to those fuel fractions? When using the official data for Gripen NG at http://www.jsfnieuws.nl/wp-content/JSF1 ... UT2008.pdf I get a fuel fraction of 29% on internal fuel only and 6 A2A missiles.
Whith external fuel the fuel fraction becomes 46%

I also made the same calculation for F-35 and used the official data at http://www.lockheedmartin.com/products/ ... tions.html , however the internal fuel was not precise enough so I used http://www.jsf.mil/downloads/documents/ ... t%2006.pdf for that even if its a bit old.

Whith that data I got a fuel fraction whith 6 A2A missiles at 37% on internal fuel only, and 43% on both internal and external fuel, using two 428 US gallon drop tanks.

These numbers are quite consisten whith the official numbers on combat radius and range provided by Lockheed Martin and Saab.

I'm sorry. My posts contain comments made on publicly available figures. If those figures are erroneous what can I say?

I'm ready to see Vipers with conformal-AMRAAM-bays, soon Wink

Corsair1963 wrote:

Yet, this get back to a one for one comparison...............Take a Gripen with full internal fuel and 2-2,000 lb PGM and 2- BVR Missiles. Then compare it to a F-35A with the same weapons load all internally........now throw in the ~ fuel burn for each at there best flight profile? Question

When you speak of fuel burn being similar, are you referring to fuel consumption per pound of thrust (lb/lbt/hr) or total fuel consumption? Sorry, I'm not familiar with the conventions.

Forum: F-35 Lightning II

F-135 or F-136 fuel burn rate