Apr 19 2010, 10:39 PM
I am not sure what engine this is. If it's an RB211 missing it's rear engine covers or something. But I have never come across a photo or have ever seen a 757 with these engines. Like I said. Maybe it's just the engine covers of the RB211 that got replaced.DHL 757-200
Apr 20 2010, 12:05 AM
Perhaps the angle? Here's another picture of the same frame showing the RR logo.http://www.airliners.net/photo/British-Air...-236/0743014/L/
Apr 20 2010, 03:30 AM
I have seen this engine style on quite a few old ones. I presume they made a minor change on the RR engines at some point, eliminating the tail cone (if you look down the back of a more recent RR one there's no cone inside) and lengthening the fairing.
Apr 20 2010, 12:41 PM
Interesting. Wonder what the tangible benefits are (clearly there must be some for it to be cost-effective).
Apr 22 2010, 11:22 AM
I am not familiar with that specific engine. But if you guys are sure that the engine type stayed or is the same I could have an answer.
Older engines used to have the engine Nozzle fitted right around the hot air section of a turbofan engine (Circlular-ring-nozzle). The cold air stream (only passing the fan) and the hot air stream (passing the turbine) can expand quite ideal which makes for a good thrust. The only negative side effect for now days is its noise emmision due to the cold and hot air streams not being internally mixed. The higher the difference of air temperature to the ambient air around the thrust stream the louder it gets. On a side note the loudest part of a jet engine is the airflow at the air intake and its nozzle.
Newer engines are refittet with different nozzles to achieve quieter engines. The Nozzle (or tail cone as Kilrah put it) around the hot air stream is not missing completely but it got a lot shorter. Therefore the nozzle is now fitted around the cold air stream coming from the fan (Circular-nozzle). This still allowes sufficient propulsion of the air exiting the engine and allows the gas streams to blend while exiting the engine. This cools the gas stream down a bit. The ripping air pressure (causing the noise) is lower due to a smaller difference in temperature between the ambient air and the hot air exiting the nozzle. The sonic deflection is now also directed towards the rear compared to the Circlular-ring-nozzle where it could point directly towards the ground.
In the end it is all about noise abatement. Propably that DHL jet doesn't fly into airports with high noise abatement policies and therefore is not refitted with the newer nozzle version.
Apr 22 2010, 01:11 PM
Very interesting and cool info Chill. Thanks for that.
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