Klc317 From United States of America, joined Nov 2004, 14 posts, RR: 0 Posted (10 years 2 months 1 week 21 hours ago) and read 7514 times:
Everytime I fly or look at an airliner, I can't help but notice how puny the engine pylons look in comparison to how much force is exerted on them. Does anyone have a webpage or more info about what these look like inside and what materials are used to construct them and how they are attached to the airplane and engines? I would assume that all the fuel, heater, and other lines run through there too. They obviously are more beefy than they appear, but I'm just curious...thanks!!
Dl757md From United States of America, joined May 2004, 1562 posts, RR: 16
Reply 1, posted (10 years 2 months 1 week 20 hours ago) and read 7447 times:
Structurally, pylons are very complicated. I'm not an expert on them but here is a general description of how a pylon works. There are forged attach fittings that attach to the front spar and underside of the wing. A complicated box built up from sheet metal and more forgings is fastened to the fittings. There are also strut braces which are tubes that attach to the wing and the front portion of the pylon and serve to carry loads from the front of the pylon to the wing in a cantilever fashion. This entire structure is then covered with an external skin. You don't externally see any of the load carrying structure of the pylon. Pylons are inspected rather frequently and if cracking is found you will usually find it on all pylons of the same configuration eventually. When we have encountered this at DL pylon mods were designed incorporating titanium doublers, triplers, and quadruplers to reinforce the cracked areas. The mods were then incorporated on the entire affected fleet.
I didn't find any good photos of a pylon in the database but I did find this picture of Dl ship 252 having it's pylon repaired in DEN.
The #1 engine was run into by ground equipment damaging the engine and pylon. The pylon was removed and sent to the DL TOC in ATL for repair and then sent back to DEN along with a new engine to be refitted to the aircraft. Cant remember how long it took but I will try to find out and get back.
If you look at the pylon where it transitions from the forward horizontal firewall to the aft vertical firewall (about where the 2nd upper access door is) you'll see a complex shaped doubler. You'll notice it is on both visible pylons. Just about every classic you see will have this double, sometiems you'll see a tripler. This was an area that is highly prone to cracking. The interior structure has been strengthened with stronger materials (usually some titanium alloys). The doubler you see is the only visible sign of this modification.
B747FE From Hong Kong, joined Jun 2004, 230 posts, RR: 4
Reply 4, posted (10 years 2 months 5 days 20 hours ago) and read 7074 times:
Just to add a little bit more:
The nacelle struts or pylons are basically frame and skin structures.
This structures are riveted and bonded together to form a torque box.
Outside, the skin form the fairings to provide smooth air flow. Inside the structure hold frame; bulkheads; stringers and spars. Mostly, aluminum alloys are used here.
Now in the case of the P&W JT9D, the engine is attached to the nacelle struts in three places, one at the forward end and two at the aft end.
These mounts are designed to absorb engine thrust, vertical and side loads, and to allow axial and radial growth due to thermal expansion.
Regarding materials, steel, stainless steel and titanium are used due to high strength and heat resistance required.
As stated above, that area is frequently inspected by different methods and several AD's and SB's has been issued for modification. (NW and El Al engine separation accidents)
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