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Unusual center sill

Dave Nelson
 

I’m working on a 3d model of the early 1940’s AAR standard 70 ton flatcar and the centersill is rather odd.  The “web”/vertical sides are separate flat plates, not rolled with flanges, each is not (as best as I can tell) welded to anything.  There is a top plate and small L’s that rivet everything together.  What I cannot understand is the later elements, specifically they are not flat over the entire run of the web plates.  There are two drops, the second of which is ~4 inches and while this second drop does span the majority of the length of the web plate there are several feet at each end where both the top plate and side L are well above the vertical web. 

 

To which I say WTF?

 

 

I’ve attached a screen shot of one sill plate and side L to show what I’m seeing.  Anyone have any idea what is going on here?

 

Dave Nelson

Robert G P
 

I have limited knowledge here, but can only guess it helps structural integrity on the ends? 

Could it have something to do with the draft gear pocket? 

-Rob

Mike Clements
 

The 70 ton car is the one with the bolster and couple covers flush with the deck, right (ie NYC, ERIE and NH among others)? If so I think I know what is going on. 

Mike Clements
Wakefield, MA
nyc65.wordpress.com

Jack Mullen
 

It's a consequence of minimizing the deck height. Between bolster and striker, the height of the top of the centersill is controlled by the coupler height and center plate height, and is a minimum of around 3'5". If you design so thsurface of the word decking is no higher, you've made the deck as low as practicable, but that requires piecing the decking around the bolster and centersill cover plates.
By dropping the top of the centersill by a few inches between the bolsters, the deck planks in that area can run full width of the car, over the centersill.
Take a look at the general arrangement plan and section views.
Other cars such as PRR F30 and various iterations of GSC's cas underframe do the same thing for the same reason.

Jack Mullen

Mike Clements
 

I was heading there Jack but after seeing this photo I’m not sure. This is a Lot 721-F car. The end flanges seem to sit completely below the deck already, so why go lower in the middle? Note the use of wooden stringers (to conserve steel during the war?).

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Mike Clements
Wakefield, MA
nyc65.wordpress.com

Mike Clements
 

Looks like IO didn't like my image. Here is another try. 

I was heading there too Jack but after seeing this photo I’m not sure. This is a Lot 721-F car - a war emergency AAR 70 ton flat. NYCSHS has 722-F (cars for IHB) photos as well, but this is the best view of the underframe. The end flanges seem to sit completely below the deck already, so why go lower in the middle? I'm not sure the NYC followed the same design as what you are looking at, what exactly lies under that steel plate down the middle is not clear. The drawing I was able to find (11/88 Mainline Modeler) of the Erie car which is the plan the AAR adopted as the standard, had a sill that was right to the bottom of the deck boards. Note the use of wooden stringers (to conserve steel during the war?). The thickness of the stringers appears to be about the same as the dip in the middle of your prototype, perhaps they put them atop the sill to conserve weight and steel? A wild guess really. Let us know what you find out. 



--
Mike Clements
Wakefield, MA
nyc65.wordpress.com

Dennis Storzek
 

Who was the car builder? If P-S, just order copies of the drawings from the Pullman Library at the Illinois Railway Museum. Contact info on this page: https://www.irm.org/pullmanlibrary/

Dennis Storzek

Tim O'Connor
 


Early AAR 50 ton flats (Union Pacific?) were built with wood stringers. Perhaps some 70 ton cars were also built that way.
I vaguely recall (perhaps incorrectly) that Byron Rose's AAR 50 ton resin flats had the wood stringers. But I could just be
confused. :-

On 1/9/2023 9:00 PM, Mike Clements via groups.io wrote:

I was heading there Jack but after seeing this photo I’m not sure. This is a Lot 721-F car. The end flanges seem to sit completely below the deck already, so why go lower in the middle? Note the use of wooden stringers (to conserve steel during the war?).



--
Tim O'Connor
Sterling, Massachusetts

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