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Jet Engine Heat Usage  
User currently offlinejetmech From Australia, joined Mar 2006, 2699 posts, RR: 53
Posted (4 years 3 months 1 week 1 day 11 hours ago) and read 8943 times:

G'day Techies,

I found an interesting diagram about the P&W F135 engine, which powers the F-35 aircraft. I find it interesting that the waste heat is supposedly the same wether the lift fan is operating or not. I thought the amount of waste heat may be less with the lift fan operating. What do you think?

http://upload.wikimedia.org/wikipedia/commons/6/68/JetEngineGraph-LiftFan.PNG

http://en.wikipedia.org/wiki/Pratt_&_Whitney_F135

Regards, JetMech


JetMech split the back of his pants. He can feel the wind in his hair.
5 replies: All unread, jump to last
 
User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 1, posted (4 years 3 months 1 week 1 day 9 hours ago) and read 8923 times:

Quoting jetmech (Thread starter):
I thought the amount of waste heat may be less with the lift fan operating. What do you think?

If the fan is running, it's extracting power from the turbines, which means less energy entering the nozzle, but it also means a bigger pressure drop in the turbines so the nozzle can do less work. At least as far as PW concerns, the energy extracted to the lift fan is exactly balanced by the energy not extracted by the nozzle, so the amount of waste heat holds constant. That makes some sense in my head, although I doubt it works out exactly that well in real life.

Tom.


User currently offlinefaro From Egypt, joined Aug 2007, 1558 posts, RR: 0
Reply 2, posted (4 years 3 months 1 week 1 day 5 hours ago) and read 8879 times:

Quoting tdscanuck (Reply 1):
If the fan is running

Is the F135 a pure turbojet or am I seeing things? I can't seem to find a fan stage ahead of the compressors...

Faro



The chalice not my son
User currently offlinerwessel From United States of America, joined Jan 2007, 2368 posts, RR: 2
Reply 3, posted (4 years 3 months 1 week 18 hours ago) and read 8752 times:
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Quoting faro (Reply 2):
Is the F135 a pure turbojet or am I seeing things? I can't seem to find a fan stage ahead of the compressors...

That looks like a fairly generic jet engine diagram. There are good cutaways on P&W's site:

http://www.pw.utc.com/StaticFiles/Pr.../Images/f135-ctol-cutaway-high.jpg

http://www.pw.utc.com/StaticFiles/Pr...Images/f135-stovl-cutaway-high.jpg

You can clearly see the bypass area (small though it may be, at about .57).


User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 4, posted (4 years 3 months 6 days 17 hours ago) and read 8570 times:

Quoting faro (Reply 2):
Is the F135 a pure turbojet or am I seeing things? I can't seem to find a fan stage ahead of the compressors...

I meant the lift fan...the shaft going out the front in the OP's image feeds a RR lift fan ahead of the engine.

Tom.


User currently offlinejetlife2 From United States of America, joined Jul 2006, 221 posts, RR: 25
Reply 5, posted (4 years 3 months 6 days 6 hours ago) and read 8497 times:

Horribly irrelevant diagram on wikipedia. Single shaft turbojet used to illustrate a turbofan - lift fan combination! LOL. Someone with the time and energy should replace it. JetMech you are just the man for the job.

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