Airliner floor strut material and manufacture.

[RPstress]

Does anybody know what these tend to be made of these days?

Also, what's the favoured method of manufacture? (Especially if composite, but if metal then do they tend to have integrally forged ends?)

Finally, what sort of loadcase tends to design them? Is there a significant tension case?

I'm a bit (ok, totally) shy of experience in this sort of thing.

 

[737eng]

If you are requesting info on the floor beams. Typically machined from an aluminum extrusion, 7050-T73511 or 7050-T76511 is typical.

Some aircraft have carbon floor beams with titanium fittings on the ends to tie to the aluminum frames.

Load cases:
Pressure (tension)
flight loads (depending on condition will induce tension in upper or lower cap)
emergency crash conditions (depending on condition will induce tension in upper or lower cap)

Don't forget about lateral loads.

 

[RPstress]

Maybe my terminology is off.

I mean the struts that typically go from a short way up from the bottom of the frames to one side of the cargo floor up to near the ends of the floor beams. They're sometimes vertical, sometimes a bit on the slant.

However, thanks 737eng for the quick reply. (And floor beams are of interest too!)

 

[SWComposites]

The struts are typically aluminum rather than composite due to potential impact damage in the cargo bay. I don't know if the ends are typically integral, but I ssuspect for assembly reasons they may not be. If I recall correctly, the sizing load cases are emergency landing cases., which tend to put large loads on the floor structure and supports. Yes, they have significant tensile loads for some conditions.

 

[RPstress]

Thanks SW. Interesting.

-RP.

 

[rb1957]

and, if you're attaching the floor to the pressure shell in a way that the OEM didn't, you can be inducing load into the shell (under pressure).

 

[40818]

RPStress. The vertical supports your talking about are only generally found on larger aircraft types. The 737 doesn't have or need them.
Contrary to popular belief, the passenger (cabin) floor loading isn't driven by emergency landing/crash loads, but by explosive/rapid decompression which develops massive pressure differentials in the cargo bays and cabin.
The purpose of the vertical struts is to support the floor beam and to prevent overloading of the floor beam to frame joint. This allows a more slender frame at that position, which gives more floorspace on the cabin floor to fit wider seats into. Floor beam to frame joint interfaces are complicated things. The 737 has no supports, and boeing find it very hard to get anymore out of them, especially since they gave all the data to Spirit!!
Anyway, the floor beam to frame interface has major effects (reversal) of the frame bending moments, imagine an equal pressure, due to more area above floor than below, the frame tries to expand radially more above the floor beam due to internal pressure than below floor. gthis difference gives rise to the frame below floor trying to bend inwards just past the joint.
What are you trying to engineer/reverse engineer?

 

[berkshire]

RPstress (Aerospace)
Following the Sioux City crash with a DC 10, Douglas modified the floor struts and retrofitted Titanium struts in place of the Aluminum ones.
I spent 3 months making the new ones.
I believe this was done for fire resistance in a crash situation rather than a structural one.
B.E.

 

[RPstress]

Thanks guys.

Ti struts sound expensive! I don't know how many are in a fuse (if you have them - I didn't know that narrow bodies tend not to), but in a big airliner I guess there might be 150 odd.

I have an interest in composite ones, and I vaguely rememered hearing (about fifteen years ago?) that a couple of companies were making fancy carbon ones for this application. However, I had no idea which way the industry had gone.

We've been using steel (usually 15-5PH) ones in turboprop nacelles for a while. Ti is always tempting because of a bit of a weight save, mainly due to the ends being lighter.

Fit with integrally forged ends is an issue; you can either ignore it and try to jumble the space frame together or get fancy with an eccentric bush or similar. With a structure like a fuse I can see it being even more of an issue.

-RP.