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Curvature of PW JT8D engine assembly?

Posted: Sat Jan 08, 2022 5:51 pm
by convair880mfan
Does anyone know why there is curvature in the Pratt and Whitney JT8D powerplant? Looks as though the gas flow does now follow a straight through path. Also seems like the curvature originates in the afterbody behind the core engine.

Re: Curvature of PW JT8D engine assembly?

Posted: Sun Jan 09, 2022 1:55 am
by Starlionblue
Just a guess but it could have something to do with aligning to the local airflow. If you look at an 727 from above, or indeed at a DC-9/MD-80, you can see how the engines are not parallel to the midline, and even curve a bit to follow the fuselage.


Re: Curvature of PW JT8D engine assembly?

Posted: Sun Jan 09, 2022 3:16 am
by Dalmd88
It has to do with what you are calling the engine. Looking at the first pic of the engine on the trailer, the true engine is sitting directly above the trailer. Every part that is hanging fore or aft of the ends of the trailer are just inlet or exhaust ducts and the thrust reverser.

With a bare JT8D if you put a level on the front flange (were the inlet mounts) of the engine and the rear flange (the ring above the trailer wheels) , you would find them to be parallel.

Re: Curvature of PW JT8D engine assembly?

Posted: Sun Jan 09, 2022 4:25 am
by convair880mfan
Those explanations make sense to me. Thanks so much. Here is a photo of a fuselage mounted JT8D. It seems that the engine is canted slightly downward from front to back including the intake duct but that the rear duct [after the turbine section] cants upwards. Perhaps this is an optical illusion. I am not referring to the part of the center JT8D engine in the same photo. Can't tell for sure.

Re: Curvature of PW JT8D engine assembly?

Posted: Wed Jan 12, 2022 4:35 pm
by Clydenairways
The first post is a pic of a 737-200 engine which was subject to a design change after the 737-100 went into service. The exhaust pipe and reverser type was originally under the wing, but this needed to get modified due to problems in service with the reverse thrust causing the weight on the main wheels to lift up and reduce braking effectiveness.
The modification by adding a long pipe aft of the wing and the DC9 style buckets was the remedy for this, but i guess they needed to angle the new additional pipe in order to achieve this.

As far as im concerned the DC-9 and 727 JT8's look fairly straight and much shorter in comparison.

If you look at pics of very early 737's you can see the original engine layout.