Forum: F-35 Lightning II

r2d2 wrote:

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

F-16XL had 'em.

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Atle wrote:

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 wasn't counting weapons and I wasn't using Gripen NG numbers. The JAS39C was taken as 2.25/(2.25 + 6.60), the F-35A was taken as 8.39/(8.39 / 12.7) tons.

dwightlooi wrote:

I wasn't counting weapons and I wasn't using Gripen NG numbers. The JAS39C was taken as 2.25/(2.25 + 6.60), the F-35A was taken as 8.39/(8.39 / 12.7) tons.

Now I understand what you mean. I saw it in the context of Corsair1963's posting and thought you meant Gripen NG, as he did. For the 39C the numbers are probably quite close, even if I would have used 2400 kg of fuel and 6800 kg empty weight, but the result is almost the same.

For the F-35A I would be interested to know where you found the 12700 kg empty weight though.

Atle wrote:

dwightlooi wrote:

I wasn't counting weapons and I wasn't using Gripen NG numbers. The JAS39C was taken as 2.25/(2.25 + 6.60), the F-35A was taken as 8.39/(8.39 / 12.7) tons.

Now I understand what you mean. I saw it in the context of Corsair1963's posting and thought you meant Gripen NG, as he did. For the 39C the numbers are probably quite close, even if I would have used 2400 kg of fuel and 6800 kg empty weight, but the result is almost the same.

For the F-35A I would be interested to know where you found the 12700 kg empty weight though.

The currently flying AA-1 is 13.1 tons. The weight optimized AF-1 and the production aircrafts are about 400 kg lighter, having benefited partially from the 1.2 ton weight reduction achieved during the weight attack on the "B" variant some of which is applied to all variants. 12.7 tons is an estimate since we do not have AF-1 weight data. However, were you to take the mass as 13.1 instead of 12.7 tons it'll amount to a 0.9% difference -- quite academic in the context of the discussion.

dwightlooi wrote:

However, were you to take the mass as 13.1 instead of 12.7 tons it'll amount to a 0.9% difference -- quite academic in the context of the discussion.

I agree with Dwightlooi, very minimal for the discussion at hand, speaking of the Lightening II's A "conventional" variant, but... When talking of the B variant, that 0.9% will be a sizable chunk of weight considering the engine will have to counteract each and every pound it is trying to lift. (or land)

Most sources state the F135-PW-600 for the B (AKA - STOVL) makes 39,800lbs of thrust in "hover," making this the MAXIMUM weight the F-35B will be able to operate in any type of pure vertical flight.

17,600lbs from the engine exhaust
18,500lbs from the LiftFan
3,700lbs from the roll posts
-----------
39,800lbs of vertical thrust

Notice how the -600 has lost over 10,000lbs of thrust in hover from the -100's MIL rating of 28,000. The -600 extracts horsepower to drive the LiftFan, and bleeds air from the N2 compressor to feed high-pressure air through the roll posts for stability. I'm certain the 90* bend of the 3 Bearing Swivel Nozzle (3BSN) in hover mode will also act to reduce thrust. (One can't change flow 90* without reducing velocity/flow to some degree)

It would be interesting to know the SFC of the -600 in MIL-hover compared to the basic -100's SFC. It wouldn't be very important operationally as you don't fly around in hover all day, but to someone like me it would indicate how "hard" the engine is working to maintain that all that power.

Keep 'em flyin' Thumb

TEG

mil_hobbyist wrote:

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.

lb/HR/lb st

That_Engine_Guy wrote:

17,600lbs from the engine exhaust
18,500lbs from the LiftFan
3,700lbs from the roll posts
-----------
39,800lbs of vertical thrust

Impressive publicly-available figures!

During the hover mode, when the lift-fan is engaged, the engine will act as if it were a very-high-by-pass-ratio turbofan, i.e.
(Lift-fan airflow + engine-fan airflow)/(Engine core airflow)
Higher by-pass ratio will result in more fuel-efficiency. On the other hand the bending-nozzle, roll-posts and transmission will reduce engine's net output.

So may be not that much hard??? We will see how those values balance.

Is it correct?

That_Engine_Guy wrote:

dwightlooi wrote:

However, were you to take the mass as 13.1 instead of 12.7 tons it'll amount to a 0.9% difference -- quite academic in the context of the discussion.

I agree with Dwightlooi, very minimal for the discussion at hand, speaking of the Lightening II's A "conventional" variant, but... When talking of the B variant, that 0.9% will be a sizable chunk of weight considering the engine will have to counteract each and every pound it is trying to lift. (or land)

Most sources state the F135-PW-600 for the B (AKA - STOVL) makes 39,800lbs of thrust in "hover," making this the MAXIMUM weight the F-35B will be able to operate in any type of pure vertical flight.

17,600lbs from the engine exhaust
18,500lbs from the LiftFan
3,700lbs from the roll posts
-----------
39,800lbs of vertical thrust

Notice how the -600 has lost over 10,000lbs of thrust in hover from the -100's MIL rating of 28,000. The -600 extracts horsepower to drive the LiftFan, and bleeds air from the N2 compressor to feed high-pressure air through the roll posts for stability. I'm certain the 90* bend of the 3 Bearing Swivel Nozzle (3BSN) in hover mode will also act to reduce thrust. (One can't change flow 90* without reducing velocity/flow to some degree)

It would be interesting to know the SFC of the -600 in MIL-hover compared to the basic -100's SFC. It wouldn't be very important operationally as you don't fly around in hover all day, but to someone like me it would indicate how "hard" the engine is working to maintain that all that power.

Keep 'em flyin' Thumb

TEG

What are your general thoughts on the P & W F-135.............Is it a leap forward compared to todays P & W F-100's and GE F-110's???

r2d2 wrote:

During the hover mode, when the lift-fan is engaged, the engine will act as if it were a very-high-by-pass-ratio turbofan, i.e.
(Lift-fan airflow + engine-fan airflow)/(Engine core airflow)
Higher by-pass ratio will result in more fuel-efficiency. On the other hand the bending-nozzle, roll-posts and transmission will reduce engine's net output.

So may be not that much hard??? We will see how those values balance.

Is it correct?

No, Fuel flow WILL increase at MIL-Hover, and the engine will consume more fuel (PPH) in MIL-Hover versus MIL.

Quote:

JSF119-SE611S was equipped with a vectoring nozzle and a powered clutch on the front of the LP (Fan) shaft, which, could transmit shaft power to the remote LiftFan. The power extracted was about 25,000 HP. The engine needed to operate at an increased turbine temperature, with a larger turbine for additional power. This power was needed to drive the engine fan and LiftFan together when engaged.

There is no way to extract 25,000HP from the low pressure turbine without adding additional fuel for power needed. The engine will essentially be driving TWO fans from one core. The core will need to work extra hard to drive both fans. (to include the roll posts which "bleed" pressure and the clutch/gearbox for the LiftFan)

Corsair1963 wrote:

What are your general thoughts on the P & W F-135.............Is it a leap forward compared to todays P & W F-100's and GE F-110's???

FYI - Engine designations don't get "dashes" behind the engine type specifier.

F100
F110
F135
TF30
J75
YF120
YF102R

The "dashes" go into the sub-type; F135-PW-100, or J75-P-17

Cheers

Yes IMO; if you've read any of the public info concerning the IHPTET program... Which the F135 is a direct result of...

Quote:

The Integrated High Performance Turbine Engine Technology - IHPTET (pronounced "IP-tet") - initiative is a joint DoD/NASA/Industry effort, with the objective of developing and demonstrating advanced engine technologies capable of more than doubling turbine engine power-to-weight ratio and reducing specific fuel consumption (SFC) by 40% over modern production engines. The specific top-level goals for turboshaft and turboprop engines, as well as for turbofan/turbojet and expendable engines, are shown in figure 1. These goals are to be achieved with no compromise in life and durability levels relative to the 1987 state-of-the-art. For the turboshaft/turboprop class this means 6,000 hours for creep/stress rupture, 15,000 cycles for low cycle fatigue in the compression system, and 7,500 cycles for low cycle fatigue in the hot section (combustor, turbines, and exhaust systems).

Some Goals of Phase III (in 2003) based on 1987 "state of the art" (AKA F100/F110):

Thrust/weight
+100%
Combustor Inlet Temp (SFC)
+400 ºF
Production Cost
-35%
Maintenance Cost
-35%

The F135 is a "new generation" of engine even above that of the F119. With it's advanced design, 40% fewer parts, advanced prognostics, and greater efficiency it is a great leap forward; much like the F-35 is a leap over the F-16C Block 52... Two Cents

Keep 'em flyin' Thumb

TEG

That_Engine_Guy wrote:

r2d2 wrote:

During the hover mode, when the lift-fan is engaged, the engine will act as if it were a very-high-by-pass-ratio turbofan, i.e.
(Lift-fan airflow + engine-fan airflow)/(Engine core airflow)
Higher by-pass ratio will result in more fuel-efficiency. On the other hand the bending-nozzle, roll-posts and transmission will reduce engine's net output.

So may be not that much hard??? We will see how those values balance.

Is it correct?

No, Fuel flow WILL increase at MIL-Hover, and the engine will consume more fuel (PPH) in MIL-Hover versus MIL.

Quote:

JSF119-SE611S was equipped with a vectoring nozzle and a powered clutch on the front of the LP (Fan) shaft, which, could transmit shaft power to the remote LiftFan. The power extracted was about 25,000 HP. The engine needed to operate at an increased turbine temperature, with a larger turbine for additional power. This power was needed to drive the engine fan and LiftFan together when engaged.

There is no way to extract 25,000HP from the low pressure turbine without adding additional fuel for power needed. The engine will essentially be driving TWO fans from one core. The core will need to work extra hard to drive both fans. (to include the roll posts which "bleed" pressure and the clutch/gearbox for the LiftFan)

Corsair1963 wrote:

What are your general thoughts on the P & W F-135.............Is it a leap forward compared to todays P & W F-100's and GE F-110's???

FYI - Engine designations don't get "dashes" behind the engine type specifier.

F100
F110
F135
TF30
J75
YF120
YF102R

The "dashes" go into the sub-type; F135-PW-100, or J75-P-17

Cheers

Yes IMO; if you've read any of the public info concerning the IHPTET program... Which the F135 is a direct result of...

Quote:

The Integrated High Performance Turbine Engine Technology - IHPTET (pronounced "IP-tet") - initiative is a joint DoD/NASA/Industry effort, with the objective of developing and demonstrating advanced engine technologies capable of more than doubling turbine engine power-to-weight ratio and reducing specific fuel consumption (SFC) by 40% over modern production engines. The specific top-level goals for turboshaft and turboprop engines, as well as for turbofan/turbojet and expendable engines, are shown in figure 1. These goals are to be achieved with no compromise in life and durability levels relative to the 1987 state-of-the-art. For the turboshaft/turboprop class this means 6,000 hours for creep/stress rupture, 15,000 cycles for low cycle fatigue in the compression system, and 7,500 cycles for low cycle fatigue in the hot section (combustor, turbines, and exhaust systems).

Some Goals of Phase III (in 2003) based on 1987 "state of the art" (AKA F100/F110):

Thrust/weight
+100%
Combustor Inlet Temp (SFC)
+400 ºF
Production Cost
-35%
Maintenance Cost
-35%

The F135 is a "new generation" of engine even above that of the F119. With it's advanced design, 40% fewer parts, advanced prognostics, and greater efficiency it is a great leap forward; much like the F-35 is a leap over the F-16C Block 52... Two Cents

Keep 'em flyin' Thumb

TEG

As always I appreciate you extensive knowledge on the subject and insight........Thanks Again Very Happy

That_Engine_Guy wrote:

r2d2 wrote:

During the hover mode, when the lift-fan is engaged, the engine will act as if it were a very-high-by-pass-ratio turbofan, i.e.
(Lift-fan airflow + engine-fan airflow)/(Engine core airflow)
Higher by-pass ratio will result in more fuel-efficiency. On the other hand the bending-nozzle, roll-posts and transmission will reduce engine's net output.

So may be not that much hard??? We will see how those values balance.

Is it correct?

No, Fuel flow WILL increase at MIL-Hover, and the engine will consume more fuel (PPH) in MIL-Hover versus MIL.

Fuel consumption WILL increase for sure. However in terms of fuel efficiency, i.e. SFC;

Remember that MIL is 28000 lb (approx & acc to sources)
and MIL-HOVER is 39800 lb (acc to your post & of course WITHOUT A/B)

I would be surprised to know if the
PPHMIL-HOVER is 39800/28000 times PPHMIL
(i.e. same SFC for both modes)

Am I missing something?

Forum Veteran Joined: Jul 01, 2007 - 07:22 PM Posts: 605

What I want to know is why I can't have all 39.8 in mil. I know the lift fan makes a lot of that, but why not increase the temps in the turbine to make up for it. The FTIT is supposed to be able to go up to 3600 degrees right? By the way, TEG you stated that mil is 28000 in the A model but when I added your numbers up for the roll posts and the engine exhaust I came up with 21300 pounds. What am I missing?

r2d2 wrote:

Fuel consumption WILL increase for sure. However in terms of fuel efficiency, i.e. SFC;

Remember that MIL is 28000 lb (approx & acc to sources)
and MIL-HOVER is 39800 lb (acc to your post & of course WITHOUT A/B)

I would be surprised to know if the
PPHMIL-HOVER is 39800/28000 times PPHMIL
(i.e. same SFC for both modes)

Am I missing something?

You're missing that the engines EPR (Engine Pressure Ratio) will be reduced by two factors. 1) Bleed air from the compressor, will reduce the operating pressure ratio of the engine while operating at it's maximum N2 RPM, reducing efficiency and 2) Extracting 29K horsepower from the core gas-stream will reduce the exhaust velocity of the core-flow.

So both reducing the pressure in the core, and reducing exit velocity of the air you reduce thrust. To make up for this fuel flow WILL increase to increase turbine temperature in an effort to compensate, but to what extent is unknown. So with a reduced thrust, and increased fuel flow the engine should have a somewhat higher SFC. I'm not sure how the engineers will figure in the extra airflow/thrust of the LiftFan in SFC calculations...

My Two Cents

says the engine will not operate as efficiently (SFC wise...) while in MIL-Hover. It may not be much; example: IF (and it's only a guess) the MIL SFC is 0.700 then MIL-Hover SFC may be 0.750 or 0.800. Again; this isn't an operational indicator, who hovers all day???

Ever see how much smoke is generated by the F402-RR-408 of the Harrier while in hover...? While running with water injection thrust increases another 2,500lbs, but water injection also increases fuel flow... More power but even less efficient. (Hence smoke...)

SnakeHandler wrote:

What I want to know is why I can't have all 39.8 in mil. I know the lift fan makes a lot of that, but why not increase the temps in the turbine to make up for it. The FTIT is supposed to be able to go up to 3600 degrees right? By the way, TEG you stated that mil is 28000 in the A model but when I added your numbers up for the roll posts and the engine exhaust I came up with 21300 pounds. What am I missing?

I think we're confusing each other Snake...

The total thrust available for MIL-Hover would be 39.8K. But you notice the engine is only producing 17.6 of that. If you took off in MIL during a conventional take-off you'd be getting 28K... The "main engine" is converting the "lost thrust" into horsepower, translating it forward through a shaft into the gearbox and LiftFan, and making it back into "lift-thrust"

I think you're missing the losses in thrust incurred from the additional turbine work while the LiftFan is engaged, roll-post ducting, and 90* bent nozzle.

The reason you can't have 39.8K during a conventional MIL take-off is airflow. Between the engine's MIL airflow, and the LiftFan's airflow you can generate 39.8K total. Without the LiftFan, the engine won't be able to move that much air at MIL alone, so you use 'burner. Cool

Keep 'em flyin' Thumb

TEG

Forum Veteran Joined: Jul 01, 2007 - 07:22 PM Posts: 605

Gotcha, thanks. Next question then. Turbo-SCRAMjet? Twisted Evil

SnakeHandler wrote:

Gotcha, thanks. Next question then. Turbo-SCRAMjet? Twisted Evil

Do I feel the sound of a Turbo-SCRAM jet thread....? Cool

EDIT: Link - http://www.f-16.net/f-16_forum_viewtopic-t-11591.html

Forum: F-35 Lightning II

F-135 or F-136 fuel burn rate