LASoctoberB6
Posts: 1936
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1 Different Engine Than Other Three

Wed Mar 07, 2007 2:58 pm

what was the point in putting one new engine and leaving the other three with old ones? why didnt they just make 4 and slap them all onto the plane?
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KELPkid
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RE: 1 Different Engine Than Other Three

Wed Mar 07, 2007 3:29 pm

What are you talking about, GE's engine test bed aircraft?

Well, what if you're testing a flight regime where the engine might not keep running? At least you've got 3 of a known quantity that will keep you airborne and take you home  Wink
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LASoctoberB6
Posts: 1936
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RE: 1 Different Engine Than Other Three

Wed Mar 07, 2007 4:22 pm

http://www.geaviation.com/engines/commercial/genx/firstflight.html
yea i forgot to post the link to it....its been a ruff day... wouldnt it be easier to test two engines?

[Edited 2007-03-07 08:23:00]
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atlamt
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RE: 1 Different Engine Than Other Three

Wed Mar 07, 2007 7:23 pm

Well they are testing a new engine design. Much safer to have three older proven engines there if the new one fails.
Fwd to MCO and Placard
 
N231YE
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RE: 1 Different Engine Than Other Three

Wed Mar 07, 2007 11:39 pm

One different engine? Why not three!:

http://i127.photobucket.com/albums/p152/N231YE/367-803engines.jpg
 
darkblue
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RE: 1 Different Engine Than Other Three

Wed Mar 07, 2007 11:47 pm

Quoting LASOctoberB6 (Reply 2):
wouldnt it be easier to test two engines?


Just curious, why would it be easier to test two engines? The crew of flight engineers already have their hands full testing one engine, why complicate things by adding more engines?

During flight test the job of the other 3 engines is to keep the aircraft flying. This allows the crew of flight test engineers to focus on the one test engine. On the first couple flights, the test engine may not even be used at critical phases (i.e. during takeoff) until it demonstrates that it can operate safely in the air.

Also, throughout an engine development test program, unexpected things can and will happen. That's the point of engine testing, you want to find problems and fix them before your customers start flying your engine. So no matter how much time and effort is put into engineering design before testing, engines will break. The goal is to find all the big issues during ground test and fix them before flight test. However, Murphy's Law still governs in the air, so if something can go wrong, it will. The flight crew needs the capability of shutting down the test engine if needed.
 
CF188A
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RE: 1 Different Engine Than Other Three

Thu Mar 08, 2007 1:57 am

back in the day I dont think they cared as much about efficiency. It was pretty cool just to get your feet off the ground and use the fuel gauges as a clock to determine how much longer one could remain airborne... hence... efficiency!
Dream as if you'll live forever. Live as if you'll die tomorrow~ RIP ... LJFM
 
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Starlionblue
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RE: 1 Different Engine Than Other Three

Thu Mar 08, 2007 2:19 am

They once hung a JT9D (I think) from one of the pylons on a B-52, replacing the two existing engines. This was during testing for the Boeing C-5 proposal. There's a picture in "Boeing - Planemaker to the World". IIRC, the engine had as much thrust as three of the original B-52 engines.



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Fly2HMO
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RE: 1 Different Engine Than Other Three

Thu Mar 08, 2007 4:46 am

Quoting N231YE (Reply 4):
One different engine? Why not three!:

OK seriously, who's bright idea was that?
 
KELPkid
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RE: 1 Different Engine Than Other Three

Thu Mar 08, 2007 6:39 am

Quoting Starlionblue (Reply 7):
They once hung a JT9D (I think) from one of the pylons on a B-52, replacing the two existing engines. This was during testing for the Boeing C-5 proposal. There's a picture in "Boeing - Planemaker to the World". IIRC, the engine had as much thrust as three of the original B-52 engines.

IIRC, this is how the JT9D was tested for the 747 program. There was simply a lack of other aircraft at the time with the required wing clearance  Wink
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FredT
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RE: 1 Different Engine Than Other Three

Thu Mar 08, 2007 6:48 am

How abut three and a half engines? Big grin

Trident 3E, with a booster engine. Man, I want to find a performance manual for that beauty...

Rgds,
/Fred

P.S. You've heard the old joke about the B52 crew who demanded priority due to an engine out, right? Another pilot in the pattern: "Oh no, the dreaded seven engine approach..."  Wink
I thought I was doing good trying to avoid those airport hotels... and look at me now.
 
LASoctoberB6
Posts: 1936
Joined: Thu Nov 09, 2006 4:23 pm

RE: 1 Different Engine Than Other Three

Thu Mar 08, 2007 7:21 am

Quoting DarkBlue (Reply 5):
engines will break.

i dont know why, but ive never thought that could happen..
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Starlionblue
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RE: 1 Different Engine Than Other Three

Thu Mar 08, 2007 10:39 am

Quoting KELPkid (Reply 9):

IIRC, this is how the JT9D was tested for the 747 program.

I looked it up and we are both right. B-52s were used for both the C-5 and the 747 engines.

BOEING JB-52E
Two B-52Es were modified for use as engine test beds. One aircraft (B-52E-55-BW, S/N 57-0119) was used to test the General Electric TF-39 for the Lockheed C-5A Galaxy program. The TF-39 was mounted on the right inboard engine pylon in place of the two J57s normally installed. The single TF-39 turbofan, rated at about 40,000 pounds, had as much thrust as four J57 turbojets on a standard production B-52E.

Another aircraft (B-52E-85-BO, S/N 56-0636) was similarly modified to test the JT9D turbofan engine for the Boeing 747 program.


There's a pic of one of the Es here: http://www.nationalmuseum.af.mil/factsheets/factsheet.asp?id=2628
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