Why are Cowl Units Extinct?

[Overmod]

timz

But years before, SFe did have some sort of trouble with U28CGs and/or U30CGs. Wonder if that had anything to do with water -- didn't DOT run its U30C at 120 mph on SFe around 1974?

My guess would be that it was truck guiding instability, probably in yaw complicated by hunting behavior (which is yaw coupled to roll).

This reminded me of the fun I had hearing 'war stories' from a senior GE engineer while we were on vacation in Tortola BVI in the early Seventies.  (He is the one who recounted the story of the three IR detectors looking at the critical center bearing in one of GE's turbofan engines -- designed without recognition that what was passing the bearing had a different refractive index for IR, so when the bearing got hot there was no alarm from the triple redundant system... and the bearing would seize up with lamentably predictable results.)

He recounted a story about the initial testing of the E60CP in the suburban Philadelphia area.  Apparently the original truck had a long, "good-riding" wheelbase -- I think he said 19' but someone would have to fact-check that.  They got the engine up to some amazing high speed... at which point the lead truck derailed, turned perfectly crosswise, and the engine proceeded to try to bury herself with a bone in her teeth... DIVE! DIVE! DIVE! was the expression he used while I was laughing.  Supposedly the production locomotives were quickly and somewhat quietly retrucked...

I doubt water slosh was involved with the running dynamics of the ATSF cowl units, but someone more familiar with them would have to say something more definitive.  Certainly even though the E60CP had a (fairly large) heating-boiler water capacity that wasn't a named or even particularly likely cause of the incident.

[bogie_engineer]

Overmod

There was a collateral issue with ride quality, perhaps more with primary than secondary suspension action, with the SDP40Fs, culminating in one report I heard second- or third-hand about an engineer breaking his coccyx on the seat (not at all funny) which simply shouldn't happen on a passenger locomotive.  I think Mr. Goding has discussed some of the issues with the truck design (I wish I could recall the precise technical elements that were 'lacking' but dimly remember them as involved with lighter unsprung mass) and what was done to remediate that part of the concern.

I also heard stories of engineers unable to stay in their seats during rough ride events. When the HTC truck was released in production in 1972, it had a quite stiff vertical rubber compression pad secondary suspension to limit pitching of the truck frame during high tractive effort to minimize the weight shift between axles that occurs as a result of the motor nose forces. As the rubber pad was short, only about 3" tall, it was also stiff in the lateral direction which led to complaints of rough lateral ride when the lateral stops hit after the limited lateral travel of +/- 1.25" was reached. Three changes were made to fix the ride issue, in 1974 as I recall, consisting of 1) changing the rubber durometer to soften the vertical and lateral spring rate by about 40%, 2) opening up the lateral travel to +/-1.75 inches, and 3) adding lateral dampers between the truck frame and bolster. While not as good a ride as the SD Flexicoil truck which preceded it, the ride was improved to the point the complaints largely went away. Eventually, yaw dampers were added in the late 80's for customers complaining of truck hunting.

I've read comments that the hollow bolsters were the cause of the problems on the SDP40F's but they had nothing to do with it. The lighter bolsters lowered the yaw moment of inertia of the truck assembly which is good for hunting stability; laterally, the mass of the bolster is part of the carbody mass so it doesn't matter if the weight is in the bolster or carbody.

My personal opinion is that the HTC was not suited to 90 mph running and the SD Flexicoil truck as on the F/FP45's would have been a better choice for Amtrak. I did not work in the truck design group until 1982 so had no role in that decision, but I had enough problems at the time with exhaust silencer fatigue cracks on the SDP's and F40C's, the first production locos to get exhaust silencers.

Dave