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747-400 engine differences

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747-400 engine differences

Old 9th Dec 2022, 23:38
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Originally Posted by tdracer
It would never sell - at least not enough to make it worth the effort. But thanks for the thought.
It is not the money that matters. It is the fact that you were able to get information out that will be forever gone. it is like the test pilot books I am reading. Fantastic information about companies and aircraft that we would otherwise never get to know.
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Old 9th Dec 2022, 23:41
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Originally Posted by fire wall
Fortunate to have flown all 3
Eng Ice Crystal Icing events a concern but suspect much the same for all power plants.
GE90-115. It is nice to not have to worry about such minor things as an all engine flameout.
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Old 9th Dec 2022, 23:42
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Originally Posted by main_dog
Except, very little residual thrust on the RR needed to add quite a handful of thrust to get going on taxy if heavy,
Beats riding the brakes on a light aircraft.
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Old 9th Dec 2022, 23:47
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I would be interested to know why two PW4000's cannot be started at the same time while CF-6 has dual starts.
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Old 13th Dec 2022, 18:02
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Originally Posted by HOVIS
Just my tuppence worth.
From a line maintenance point of view the RR has always been easier to service. The gearbox is on the fan case with all the accessories. Starter motor, IDG, Fuel and oil pump packs etc. Access is simple, just open the fan cowl and away you go. The GE and PW philosophy was to cram as much as possible around the hot core section which means you need a pump to open the C Ducts/ Thrust Reverser halves. More time consuming and in my opinion more difficult access.
The GE CF6 is a brilliant bit of kit though. Incredibly reliable.
I agree, and would like to add another view:
Although being rather a desk driver and havnt touched hardware for a long (too long?) time, I always found the wiring on the T700 (and other RR engines) superior to CF6 / PW for my part of the job - proper routings, markings, colour codes. It always seemed to me as if in GE/PW, the wiring guy came last in the design phase and had to find his ways along all the obstacles along his routes. And I somehow got along with the RR manuals much better.
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Old 16th Apr 2023, 20:18
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Originally Posted by MarkerInbound
Never flew Rolls powered 74s and dont know much of that geeky stuff but operating GE engines was easier. We could start 2 at a time versus one Pratt at a time. And GE just uses N1 and not EPR so less to look at.
Ahh the annoyance towards EPR spans across manufacturers... it seems

In the IAE A320 or the 340-600, I find the EPR to be rather unintuitive to use... especially since I started studying the 737NG first.
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Old 18th Apr 2023, 01:06
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Originally Posted by tdracer
It would never sell
It would if you could get it translated into Chinese.
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Old 18th Apr 2023, 01:56
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Originally Posted by Zar_1
Ahh the annoyance towards EPR spans across manufacturers... it seems

In the IAE A320 or the 340-600, I find the EPR to be rather unintuitive to use... especially since I started studying the 737NG first.
In the IAE 320, Im only vaguely aware that its there. I use N1 for just about everything.
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Old 18th Apr 2023, 02:49
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Wow, an old thread comes back to life
OK, starting (must have missed this first time around). In general, the PW4000 was harder to start than the CF6-80C2. It was standard practice to spin the PW4000 up to close to max motoring before putting the fuel on - the CF6 you could turn on fuel at 15% N2 and get a reliably good start. So the Pratt took more air to start. When Boeing built the LCF (aka Dreamlifter) for hauling around 787 parts, they removed the APU (putting a fuel line through where they spit the fuselage to load/unload was too big a challenge), so ground carts were needed for starting - turns out it needed to be pretty good ground cart to get enough air to reliably start.
EPR vs. N1 is a long standing controversy. N1 has a huge advantage of being an easy measurement relative to EPR which requires reliable measurement of two pressures - one in an area that can be prone to icing (inlet EPR probes require ~ 500 watts of power to heat - which also makes reliable temperature measurements tricky). OTOH, EPR is better related to actual thrust - and the thrust/EPR relationship is pretty much constant (TO EPR is pretty much constant below cornerpoint temperature). N1 has that whole messy square root of theta temperature meaning thrust set N1 changes with temperature.
Wiring (and to a lesser extent plumbing) - Rolls certainly looked like it was designed. Pratt and Rolls both just sort of added it when everything else was done - it looks like a mess.
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Old 18th Apr 2023, 10:01
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Yeah N1 is definitely easier to calculate, since it's kinda a Tachometer by design... and yes, EPR is the more accurate of the 2.

An innovation that I've seen (ig in the A350) is the presence of 'calculated thrust' gauges which are meant to be more intuitive to use.

So, the PW4000, if given inadequate bleed... would give you a nasty Hot Start or the FADECs would auto-cut the fuel and turn the start into a Dry Crank Motoring phase?
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Old 22nd Apr 2023, 15:04
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TD , a belated thanks to you [ and all engineers ] for safely designing , making , servicing all our flying machines for the last 52 yrs .
I'd buy your book ..
It's a delight to read your explantions and stories . You have the knack of making them understandable and enjoyable to an old tractor driver with wings .
Seem to remember we could auto start 2 Rolls on 744s until you got Hot 'n High .. Then 1 . Then Manual start .
Agree on the Rolls sound , whether inside or out the -22bs on our by then old Tristars forever embedded . More like a big diesel winding up before fuel goes in . And 'wot a privilege to have handled 4 Rb 211-524Hs on t/o .

rgds condor .
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Old 23rd Apr 2023, 09:25
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Is the manual start done so that the N1 is higher than normal, when fuel is injected?

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Old 23rd Apr 2023, 15:44
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https://blog.kotobee.com/self-publis...pros-and-cons/

Originally Posted by tdracer
It would never sell - at least not enough to make it worth the effort. But thanks for the thought.
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Old 23rd Apr 2023, 21:35
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Originally Posted by Zar_1
Yeah N1 is definitely easier to calculate, since it's kinda a Tachometer by design... and yes, EPR is the more accurate of the 2.

An innovation that I've seen (ig in the A350) is the presence of 'calculated thrust' gauges which are meant to be more intuitive to use.

So, the PW4000, if given inadequate bleed... would give you a nasty Hot Start or the FADECs would auto-cut the fuel and turn the start into a Dry Crank Motoring phase?
"Calculated Thrust" is simply measured EPR compared to the max rated EPR for those conditions. Perhaps slightly more intuitive, but still has all the potential issues as EPR. I had some friends that spent a lot of time working on a "0-100" thrust measurement. They finally decided that - while there were various ways to make it dimensionless, in the end it really wasn't any better than simply using N1 and/or EPR.

Autostart wasn't basic on the PW4000/747-400 - autostart was an add-on box called an SCU (Supplemental Control Unit). It didn't work very well though...

Junkman - I'd still have to make all the effort to write the darned thing...
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