A1A vs B1-1B

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A1A vs B1-1B
Posted by SD60MAC9500 on Monday, September 14, 2020 7:46 PM
 

While Wabtec uses a A1A Dynamic Weight System for its C4 units. Using an "air dump" per say on the middle axle which adjust axle height based on tractive effort.. Progress P4's use a B1-1B axle setup. What are the pros and cons of each setup? I do recall reading about traction issues with the A1A setup. Specifically with E-units. From what I understand when E-units were the norm in passenger service for most of the western roads. They didn't like the performance from the A1A truck and went to F-units for better traction. Clarification on this subject would be appreciated.

 
 
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Posted by SD70Dude on Monday, September 14, 2020 7:55 PM

None of the A1A trucked passenger units had any sort of weight transfer system off the idler axles, and EMD also did not offer dynamic braking on theirs until the E8.  I believe the DB issue was a big factor in SP and Rio Grande purchasing PA's instead of E's. 

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Posted by timz on Tuesday, September 15, 2020 10:12 AM

SD60MAC9500
They didn't like the performance from the A1A truck [on E-units]

Far as us fans know, all the RRs thought the E-unit truck was just fine. Some RRs wanted more TE and used four Fs instead of three Es, but that's not the truck's fault.

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Posted by bogie_engineer on Tuesday, September 15, 2020 12:27 PM

timz

  

SD60MAC9500
They didn't like the performance from the A1A truck [on E-units]

 

Far as us fans know, all the RRs thought the E-unit truck was just fine. Some RRs wanted more TE and used four Fs instead of three Es, but that's not the truck's fault.

 

I agree that the E truck was fine, weight shift was similar to the F/GP truck. I believe it was the need for more TE than 4 motors of an E at 1.5 times the weight of a F unit with that extra weight wasted in idler axles on E's. The shorter wheelbase of the two axle truck would have done better on mountain curves as well.

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Posted by bogie_engineer on Tuesday, September 15, 2020 12:46 PM

SD60MAC9500
 

While Wabtec uses a A1A Dynamic Weight System for its C4 units. Using an "air dump" per say on the middle axle which adjust axle height based on tractive effort.. Progress P4's use a B1-1B axle setup. What are the pros and cons of each setup? I do recall reading about traction issues with the A1A setup. Specifically with E-units. From what I understand when E-units were the norm in passenger service for most of the western roads. They didn't like the performance from the A1A truck and went to F-units for better traction. Clarification on this subject would be appreciated.

 
 

 

The reason why EMD chose the B-1 motor arrangement was that there is less weight shift within the truck at the powered axles than an A-1-A would produce given the high traction motor arrangement with all motors on the same side of the axle within the truck.

To compensate for not having the clap-trap arrangement with the air cylinders pulling up on the middle axle to shift someweight to the end axles, EMD biased the static axle load to favor the powered axles so the unpowered axles are lighter under all conditions. 

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Posted by D.Carleton on Thursday, September 24, 2020 10:45 AM

As we are on the subject of A1A trucks please permit me a slight tangent. The FL9 was developed by EMD as “more F-unit” than an F9 or FP9. (As we all know it was later adapted in the dual-mode platform for the New Haven.) The larger/heavier locomotive necessitated an A1A rear truck. The forward truck was originally a standard Blomberg. I had always assumed that if ATSF or GN or some other road had ordered an FL9 the rear truck would have been the same as an E-unit. But then I realized that having two trucks with different wheel sizes would be less than ideal. Was the Flexcoil A1A always meant to be on the FL9?

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Posted by Overmod on Thursday, September 24, 2020 10:56 AM

D.Carleton
Was the Flexcoil A1A always meant to be on the FL9?

Note that we start with an assumption: that only four motors is all you'd need.  That is certainly sensible for even a D-block 567, but just about any post-'64 passenger purpose would involve a 16-645 at least, and three motored axles in that weight-accommodating truck might begin to be useful... it certainly would be for any electric dual mode application on a road with practical as opposed to, er, facultative electric-operation capability.

The Flexicoil on the rear was as I recall chosen solely because an E-unit style swing-hanger truck wouldn't accommodate third-rail shoes (more precisely the beam and paraphernalia associated with mounting them).  That of course is also the rationale behind substituting  a two-axle Flexicoil on the production locomotives when only one shoe per side proved dubious in NH practice.

Why would ATSF or GN have any use for an FL9?  Anything they would do with electrification would be overhead wire... and hence have superior truck design...

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Posted by D.Carleton on Thursday, September 24, 2020 1:25 PM

Overmod
Why would ATSF or GN have any use for an FL9?  Anything they would do with electrification would be overhead wire... and hence have superior truck design...

Again, the FL9, as originally intended, was to be a larger F-unit with larger steam generator capacity. Only later was the design modified to be the now legendary and long lived dual-mode locomotives of New York area commuter lore. Yet imagine an FL9 in warbonnet paint and stainless steel side panels leading the Super Chief over Raton. Instead ATSF and others went with six-axle EMDs with steam generators as they saw the end of their passenger services on the horizon.

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Posted by Overmod on Thursday, September 24, 2020 2:10 PM

I had always read that the L in 'FL' stood for electric, rather than 'longer than an FP unit' (and that the weight requiring the extra axle was in heavy electric gear).  I can't imagine, though, that you of all people would not know the actual details.

It would interestingly follow that ATSF with its then reliance on steam-ejector AC might find FLs valuable in providing double steam generators and lots and lots of (weighty) water for them in a single unit, but I can't help thinking they would benefit still more from a unit with five driven axles and proportionally more engine power to match, which the engine of an SD24 might have offered in the longer carbody.

The real 'road not taken' was not keeping the bulldog E-unit nose on those E-unit-replacement FP45s or the standard-cab SDPs -- as the Australians notably did on a similar locomotive class.  Imagine a warbonnet on a streamlined nose with the side panels of an F40C... Stick out tongue 

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Posted by 16-567D3A on Thursday, September 24, 2020 3:56 PM

Another reason the A1A Flexicoil was specified was to keep axle loadings within the Park avenue viaduct weight restrictions.The Early specifications for the FL9 had indeed included a straight Diesel long distance passenger version with either a single high-capacity steam generator or dual standard generators and four water tanks with 2.850 gal. there also may have been a straight electric version.EMD also did preliminary design on a F18 1800hp version.the second order of FL9s were 1800hp. Specifications were made for a Super F20 using the 567D2 prime mover but by 1960 the Road switcher was the railroads prefered option. What may also contributed to the end of the bull dog nose was the complexity and cost of its construction. the spring 2015 Classic Trains on the 75 anniversary of the F unit pg 40-41shows a picture collage of a F nose being fabricated and the drawings from the patent application.

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Posted by Overmod on Thursday, September 24, 2020 5:25 PM

16-567D3A
Another reason the A1A Flexicoil was specified was to keep axle loadings within the Park Avenue Viaduct weight restrictions.

Was the Flexicoil that much less in weight than a three-axle Blomberg equivalent?  

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Posted by 16-567D3A on Thursday, September 24, 2020 8:07 PM

 I am unable to locate the actual weight of both truck types. There were light frame and heavy frame versions of the  A1A Blomberg truck.the change to the strengthened main frame was about 1952.while the A1A trucks are interchangeable there is a noticable height difference of the heavy version in the frame next to the idler axle as well as a weight increase per truck.The A1A passenger truck wheelbase is 169 inches. The B-A1A FL9 Flexicoil truck wheel base is 163 inches so i would assume with the smaller general size there would also be a lighter weight.looking at photos the FL9 FC is smaller and less substantial than an E-A1A.

 

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Posted by D.Carleton on Thursday, September 24, 2020 11:47 PM

Overmod
The real 'road not taken' was not keeping the bulldog E-unit nose on those E-unit-replacement FP45s or the standard-cab SDPs -- as the Australians notably did on a similar locomotive class.  Imagine a warbonnet on a streamlined nose with the side panels of an F40C... Stick out tongue 

Completely, totally, 100% agree. Ironically the "bulldog" was in production downunder well into the Amtrak era. However, NRPC closely emulated the ATSF pattern for passenger trains: the SDP40F in stead of the FP45 and Superliners for bilevels. It worked perfectly...on the ATSF, not so much everywhere else.

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Posted by Overmod on Saturday, September 26, 2020 1:07 PM

D.Carleton
It worked perfectly...on the ATSF, not so much everywhere else.

Well, that is, until ATSF started running dual-service with the FP45s and started to modify the noses.  If I recall correctly (and this may well have been partly supposition even at the time) one of the reasons for the CF7 program was the cost involved in similar modification for the bulldog noses on the 'donor' F units ... which would have applied to any 'E' nosed 645-engined locomotive not conveyed to Amtrak.

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