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Replacing Existing Engines With "ng" Engines

Thu Jan 20, 2005 8:04 am

Greetings all,

Just curious. Is there a specific reason why, for example, a 747-100 could not have a derated, say PW4000, replace the old engines? Thrust is an issue of course, but I included the possibility of a derated engine.
I'm not a real aeronautical engineer, I just play one on
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RE: Replacing Existing Engines With "ng" Engines

Thu Jan 20, 2005 9:06 am

I suspect it has more to do with the compatibility of engine accessories then the engine itself. The electrical, pneumatic, hydraulic, etc systems on the original engine all mesh perfectly with their wing or airframe-mounted components.

I'd imagine it would be easy to simply replace the engine itself. Maintaining systems compatibility would be another story. Hopefully someone more knowledgeable can confirm or deny this.


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RE: Replacing Existing Engines With "ng" Engines

Thu Jan 20, 2005 9:31 am

In the example you used there are several issues. First the engine pylon would have to be redesigned. The wing structure on the 400 wing is different than the pylon attachment on the 100. But, the biggest issue would be the certification process required by the FAA/JAA.

In most re-engine modifications, there is a incredible amount of engineering work to be done for the mods. All of this normally makes the process cost prohibitive.

In the example of the 747-100, there are several very expensive ADs out. Plus the aircraft falls under the aging aircraft program. Both are extremely costly. The -100 also suffers from a very light gross weight making it even less suitable for any engine mods.
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RE: Replacing Existing Engines With "ng" Engines

Thu Jan 20, 2005 5:12 pm

On the purely practical side : The NG engines are digital, the 741 cockpit/controls are string and cams. So you need a new cockpit. And then the wiring throughout the aircraft needs to change to suit, and that ain't cheap.

Obviously, you don't want to suffocate the passengers, so cabin air supply is required. The NG engine don't supply that, so you need another new system...

The thrust levels for the NG engine are higher that the example 741 engines, so what do you do? Operate the same engine at lower speed/thrust ? Then you carrying around a heavier engine than you need. Redesign the engine to get the weight out ? You'll then need a new FBO test. Use that extra thrust ? The aircraft just wasn't designed for it.

Really, you'll just spending loads of money to end up with an aircraft that's probably no better than more recent (743?) aircraft, available cheap from the deserts.

To use a technical phraseology "It's no good trying to polish a turd".

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