Forum: F-35 Engine

Hey all, after reading/hearing about the F135 I am a little confused. The output of the F135-PW-100/400/600 is around 43000 lbf (wet) ((wiki soz)) Yet the F35b can generate in excess of 40000 lbf dry in STOVL(PW-600)???. With the introduction of shaft driven lift system, to me, this engine must now produce more torque while still producing acceptable thrust. So, what is the difference between F135-PW-100/400 to F135-PW-600? if any?? How will the change from free flow exhaust to a restriction (swivel outlet) affect the power output/back pressure? In full dry thrust the nozzle is 'narrow', does the swivel/bend act in a similar way so the nozzle remains 'open' to produce similar power outputs???
I realise the 40000 lbf figure is combined thrust with the lift fan, I'm more confused as to the change/difference between turbo fan and turbo shaft..
Thanks for your time...

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beepa, this thread is a start: http://www.f-16.net/f-16_forum_viewtopi ... rt-60.html
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http://www.flightglobal.com/blogs/the-d ... -by-s.html

The second thread is for an hour worth of videos in 3 parts that has the 'designer' of the engine explain some stuff about it as I recall. However he has also written another lecture: F-35 - Inventing the Joint Strike Fighter Dr. Paul Bevilaqua - Lockheed Martin Skunk Works - 12 Oct 2009 (mentioned on this thread: http://www.f-16.net/f-16_forum_viewtopi ... -240.html)
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http://www.f-16.net/index.php?name=PNph ... p;p=176792

Genesis of the F-35 Joint Strike Fighter Paul M. Bevilaqua (7.7Mb PDF)

JOURNAL OF AIRCRAFT - 2009 WRIGHT BROTHERS LECTURE - Vol. 46, No. 6, November–December 2009

http://pdf.aiaa.org/getfile.cfm?urlX=-% ... 0%20%20%0A

http://www.nps.edu/Academics/Institutes ... ighter.pdf (4.5Mb) This is not the best but will help if you watch the video also.

There are a heap of explanations of various kinds/brevity on the web and in PDFs - I'll post some more links in this reply soon.... Again the designer explains on this link:

http://www.designnews.com/article/1558- ... he_fan.php
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http://en.wikipedia.org/wiki/Paul_Bevilaqua
_________________

A bit off topic but interesting:

http://www.designnews.com/article/10219 ... Skills.php

Thanks spaz....time to do my homework.... Slap

In short, I believe the explanation is that the lift fan uses some of the shaft power to accelerate a comparatively large air mass to a lower velocity. This is a more efficient use of power, and makes it possible to generate large amounts of lift (thrust) without using the afterburner.

In a simple example, if you double the air mass flow rate and halve the exit velocity, you can get the same amount of thrust for half the power (energy per unit time) input.

I'm sure TEG can expound further.

So we'll split this up real quick; first the F135-PW-600 (STOVL sub-type) Figures (in bold) from PW's F135 site used for discussion:

Maximum Thrust (in pounds): 43,000 / (191.3 kN)
This is with nozzle straight in conventional flight mode, FULL augmentation available to the pilot, engine operates like the -100/-400

Intermediate Thrust (in pounds): 28,000 / (128.1 kN)
You'll notice this is the same for all variants in conventional flight, but will change when the LiftFan is engaged as some of the 'thrust' is converted to HP to drive the LiftFan. Some thrust is also lost by bending the exhaust; the flow is slowed in the bend, reducing it's velocity. This is why the 'Main Engine' thrust is lower in a hover or in STO mode. More details to come.

Short Takeoff Thrust: 38,100 (169.5 kN)
This is with nozzle swiveled down approximately 45% (or so) and LiftFan engaged. NO augmentation available as nozzle is 'bent'. Thrust from LiftFan directed down/rearward as commanded through vanes.

Hover Thrust: 39,400 / (175.3 kN)
(total vertical thrust of all components breaks down as follows)

Main Engine: 15,700 (thrust from rear nozzle, 90* bend, HP extracted for LiftFan, provides 'aft post' of thrust.)
Lift Fan: 20,000 (LiftFan pulls HP from gas-stream via the Low Pressure turbine, provides 'front post' of thrust)
Roll Post: 3,700 (Ducts on sides of engine, keep aircraft 'balanced' on front/rear posts)

Bypass Ratio
Conventional: 0.56
Powered Lift: 0.51

Overall Pressure Ratio
Conventional: 28
Powered Lift: 29
(You may notice BPR/OPR are different for the -600, but this is mostly done by the operating mode of the engine, all 3 variants are identical until the extra parts are installed on the -600. Drive shaft, 3 Bearing Swivel Nozzle, and Roll Posts.)

The F135-PW-600's FADECs will shift the motor's operating parameters, (vane positions, pressure ratio, fuel flow, nozzle ratio, etc) to provide extra 'power' to spin up the LiftFan during STO or VL situations. When you extract additional power from the engine's exhaust gasses for the LiftFan when engaged to the Low Pressure Turbine, the engine must compensate. You can't get rotational energy for the extra fan without giving up some thrust from the main engine. 'Bleeding' high pressure air from the core compressor will also lower the engine's power; not as much air is being moved through the combustion chamber, or out the rear nozzle.

Say you extracted 100% of the 'power' from the exhaust gasses of a turbine engine, you'd have a turboshaft engine that makes HP not Thrust. All the power from the hot gas is taken up by the turbine, the result is a hot breeze from the exhaust but no 'push'. The 'push' was internal against the turbine blades (sometimes called buckets) and converted into rotational HP to drive something else (like a prop, rotor-head, or transmission). You may notice in a high by-pass ratio engine, there are many low pressure turbines needed to extract LOTS of HP to turn that huge fan up front. As a result the fan of such engines give most the thrust, and the core's thrust is limited due to the turbine extracting so much power from the exhaust stream.

Now on to the F135-PW-100/-400

Maximum Thrust (in pounds): 43,000 / (191.3 kN)
You'll notice this is the same for all variants in conventional flight

Intermediate Thrust (in pounds): 28,000 / (128.1 kN)
You'll notice this is the same for all variants in conventional flight, but will change when the LiftFan is engaged as some of the 'thrust' is converted to HP to drive the LiftFan. Some thrust is also lost by bending the exhaust; the flow is slowed in the bend, reducing it's velocity. This is why the 'Main Engine' thrust is lower in a hover or in STO mode.

Bypass Ratio: 0.57

Overall Pressure Ratio: 28

Now the F135-PW-100/-400 are basic jet engines, augmented low by-pass ratio turbofans. Their thrust is 'conventional'. The only major difference would be the -400 having been 'Navalized' for salt water corrosion resistance. It may use different materials or have special coatings to prevent ocean going corrosion.

beepa wrote:

How will the change from free flow exhaust to a restriction (swivel outlet) affect the power output/back pressure?

To answer this directly, it's not the nozzle that's pulling power as much as a turbine that is extracting HP and reducing exhaust gas velocity from the core of the engine. The Roll Posts are also 'bleeding' air from the core. The nozzle bend will reduce velocity somewhat, and yes that will reduce thrust some too. All add up to change the 'dry thrust' of the 'main engine' as the -600 uses STO or VL mode.

beepa wrote:

In full dry thrust the nozzle is 'narrow', does the swivel/bend act in a similar way so the nozzle remains 'open' to produce similar power outputs???

Yes the engine can compensate some, but changing the back-pressure too much (more or less) will affect the stall margin of the engine's fan. The Roll Post operation also adds stress to the engine and would also affect stall margin. The engine will use the methods mentioned above to compensate for the additional loads during STOVL operation.

Clear as mud? Shocked

Follow on questions? Shrug

Keep 'em flyin' Thumb

TEG

Thanks TEG, interesting info about the STO mode thrust.

Great info as always T.E.G. always learn something from your posts. Thumb

One question (and I apologize if the answer is right in front of my face and I blinked and missed it Doh

) doesn't the F-35B STOVL version also need to have it's engine "navalized" - IE: using slightly different metals and/or coatings to resist the salt water environment it will spend most of it's time in?

FlightDreamz wrote:

...doesn't the F-35B STOVL version also need to have it's engine "navalized" - IE: using slightly different metals and/or coatings to resist the salt water environment it will spend most of it's time in?

Most likely yes, but such changes are typically very minor. The F135-PW-100/400 will differ less than say the F110-GE-100/400 did.

In the F110 case the Tomcat had very different aircraft (B2) accessories than the Viper. In the case of the Viper, all B2 accessories are airframe mounted on the ADG, where the Tomcat had generators and hydraulic pumps mounted to the engine.

With the F135/F-35 combination those differences in accessories and mounting will be very minimal. I haven't read specifically where the F135-PW-600 is based directly on the -100 or -400, but that would be a safe assumption that the -600 will have at least some of the -400's features too.

The only issues I would see there is the weight penalty that the USN might be willing to suffer that the USMC may not. Say making a gearbox from some sort of titanium alloy versus magnesium? Something that would add more weight to the -600 than acceptable for STOVL use. In such cases the -600 may have a lighter coating applied. It would serve the same purpose by keeping the salt away from the metal in components to prevent corrosion, but would be more prone to damage than simply using a less salt vulnerable base metal that wouldn't require a coating or special handling at all.

Most sources I've read on this topic say something to the effect as; "-600 similar to the -100/400 with the addition of... LiftFan, Roll Posts, and 3BSN." I'd guess it will be somewhere in between the two, but not 'identical' to either.

Keep 'em flyin' Thumb

TEG

Once again TEG an excellent post Not Worthy

, thanks for your input, now, as i'm not the sharpest 'tool in the shed' it's time to read (and re-read) your post/posts...After 5yrs of following your posts (as well as other senior members) I have a great respect (and a fair share of jealously) of your (and other senior members) professionalism...Thanks all!!

Forum: F-35 Engine

F135 Question