Truck differences on CSX AC4400s

[Kevin B.]

Can someone explain the differences in the trucks on these two CSX AC4400s? http://www.railpictures.net/viewphoto.php?id=82398 The trucks on the trailing unit seem to be the same ones as found on most Dash 9s, but what gives with the ones on the lead unit? Thanks, Kevin

[Allen Hazen]

The trucks on the trailing unit are, as you say, like those on Dash-9 and on many AC44. This truck design has higher adhesion (less weight transfer) characteristics than the truck used on U-, Dash-7 and Dash-8 series models. It was introduced on the C44-9W in 1993, and can be used with either DC or AC motors.
It is NOT a "radial" truck: the axles are in fixed parallel positions. EMD introduced a radial truck, in which the axles can rotate independently enough so that, when going around a curve, each axle stays perpendicular to the track (and so parallel to the radius of the curve): obviously better for track and flange wear. GE didn't have a radial truck design ready when the Dash-9 and AC44 were introduced, but developed one shortly thereafter (it was retrofitted to an early CSX AC44 for testing in-- I think-- 1995). CSX liked it, and specified it for their later orders (AC44 numbered 200 and up). Canadian Pacific likes it: after getting the earlier truck on their first AC44, they have gotten later orders with radial trucks. KCS and the Mexican railroads have radial trucks on their AC44. UP tested GE's radial truck on a small number of AC44, and seems to have decided that it isn't worth the extra (?) cost and maintenance hassle: almost all their AC44 have the "Dash-9" style truck. BNSF, after getting a huge fleet of Dash-9, has started buying GE AC locomotives with -- like UP's units-- the Dash-9 truck.
I don't know why the different railroads have reacted this way. Maybe CP has worse grade/curve combinations than the western U.S. railroads, and CSX evidently wants to maximize tractive effort, often at low speeds. This **SUGGESTS** that the radial truck offers advantages in some applications and less of an advantage in others, but I don't know anything concrete.
In principle, I think GE's radial truck could be used with DC traction motors, but as far as I know no Dash-9 have been built with radial trucks.

[Joe]

The Dash 9 trucks are actually called Hi-Ads(TM) for High adhesion. No dash 9s have received radial trucks and not too many GEs have the radials, I think Allen named all the ones I know of--although all the radials are on AC locomotives.

[Allen Hazen]

Joe Lemay--
Not sure if it's a complete list. Quebec Cartier's AC44 and the AC60 of CSX and some West Australian iron ore railroad have radial trucks.
I'm curious about WHY some railroads have and others haven't specified radials on their AC44 (and none have on DC-motored GE units). As I suggested in my first post, the distribution SUGGESTS that it is railroad managements concerned with extremely high tractive effort applications (note that an AC44 is capable of sustained tractive effort much greater than a C44-9W can manage-- UP's AC44CCTE are AC44 with control software that allows them to "emulate" C44-9W by reducing tractive effort!) whospecify the radial trucks, but if some knowledgeable person wanted to tell me more....

[Jay Potter]

In the interest of clarification, EMD refers to its product as a "radial" truck; and GE refers to its product as a "steerable" truck. The steerable truck is currently compatible only with AC-traction units, not with DC-traction units.

CSXT began acquiring AC4400CWs configured with steerable trucks (units 201 and above) in 1996 in order to improve adhesion and increase wheel and rail life by reducing lateral rail forces; however those factors apply only when operating on curves. In other words, the steerable truck provides no increase in performance on tangent track; and it is more expensive than the HiAd truck.

[Allen Hazen]

Jay Potter--
Thanks for the clarification. ...Come to think of it, I have seen the word "steerable" in connection with the GE truck-- I was using "radial" as a generic term.
You say
"The steerable truck is currently compatible only with AC-traction units, not with DC-traction units."
What sort of incompatibility is involved? I think GE's AC traction motor is physically larger than their DC 752 motor (is this true? GE AC locomotives apparently all have 42-inch wheels rather than 40 inch, which is an option for DC). Is the difference enough that serious new engineering would have to be done to fit DC motors to the steerable truck?

[Jay Potter]

In answer to Allen's question, I don't know the nature of the incompatibility; but I believe it's significant enough that, at least for the time being, a railroad that might desire to order GE DC-traction "Evolution Series" units will not have the option of steerable trucks on those units.

[Jay Potter]

To supplement my prior reply to Allen's question, the incompatibility isn't in the DC traction motor itself but, rather, in the connection between the motor and the frame of the steerable truck. The current connection, which has been used only for AC traction motors, would have to be designed somewhat differently for use with DC traction motors. Apparently this would not be particularly difficult to do; but there hasn't yet been a need for it to be done.

[Allen Hazen]

Jay Potter--
I'd been thinking of writing to thank you for your earlier reply, but didn't have any intelligent comment to make. I STILL don't have anything interesting to add, but ... THANK YOU for the additional information!
(Since the features of the application that justify the added cost of the steerable truck are also the ones which make people specify AC motors, I suppose we may never see a steerable-truck ES40DC.)

[Jay Potter]

I'm hesitant to completely foreclose the possibility of GE DC-traction units being configured with steerable trucks. Although a steerable truck is more expensive than a HiAd truck, the per-unit cost differential would, of course, be much less than the cost differential between an AC-traction unit and a DC-traction unit; and, depending on track curvature, the steerable truck could result in an increase in adhesion of around 1.5%. So I could foresee a railroad viewing DC-traction units configured with steerable trucks as a "happy medium" that would enable locomotive tonnage ratings to be increased in a cost-effective manner.