I keep a little wall display of loco technical information on all my locos, thanks to that great site http://www.thedieselshop.us/
In entering my latest data, I noticed that these EMD SDs had very large radii (57 degrees) like an EMD E6 or something, despite having a modest length compared to an E unit.
I imagine there is some clearance constraint or something. Even a Dash 9 requires only 21 degrees.
Any of you out there familiar with the real thing?
AFAIK, when curvature is expressed in degrees, it’s the number of degrees change in direction relative to 100 feet of travel. By that definition, a 57 degree curve is a lot tighter than a 21 degree curve. IIRC, an 18" radius curve is the equivalent of a 44 degree curve. Also, IIRC, a Big Boy could take a 20 degree curve.
Are you sure you’re looking at the data correctly?
Here’s a table of degrees to radius: http://www.trainweb.org/freemoslo/Modules/Tips-and-Techniques/degrees_of_curve_to_radius.htm
Andre
There is something seriously wrong with those numbers. Remember that the higher the degree of a curve the sharper the radius. A 60 degree curve would be equal to about 13.8" radius in HO scale. A 22 degree curve is approximately equivalent to a 36" radius curve in HO scale.
So if these numbers were correct the SD7 would be able to go around a much tighter curve than the dash-9. The D&RGW tried to use an SD7-9 on the Monarch branch after they converted it to standard gauge. The units could not handle the 18 degree curves. Two GP30s got the job.
I also seem to recall that the minimum curve for an SD45 was 10 degrees.
The numbers you have must mean something else rather than degree of curvature.
I think you are confusing degree of curve with radius. The ‘small’ the degree of curve, the BIGGER the radius is. for example:
20 degree - 288’ radius
25 degree - 231’ radius
50 degree - 118’ radius
Most older units like a GP or F unit will require about a 45 degree(150’ radius). Larger units like the SD70ACe require about a 29 degree curve(about 185’). Why diesel shop lists a super sharp 57 degree(about 105’ radius) curve may be a typo? And these numbers many times are not coupled to a train.
A 20 degree curve is super sharp on the prototype and usually will only be seen in a terminal area. Most mainline curves are under 10 degrees and sweeping 2 degree or 1/2 degree curves are usually seen in open areas where there are few speed restrictions.
Jim
I also seem to recall that the minimum curve for an SD45 was 10 degrees.
Interesting then that the site the OP originally mentioned lists the minimum of 30 degrees (roughly the equivalent of a 26" curve in HO scale).
OTOH, I don’t know as I trust the data at the site. Especially as it lists 39 degrees for a GP9 vs. 57 for an SD9. That would mean a longer engine with longer trucks would be more nimble than a smaller one.
It’s like claiming a 767 can out turn a 737.
Andre
In George Cockle’s “Union Pacific 1977-1980”, he lists the maximum curvature (minimum radius) “as a single unit” of an SD7 as 23 degrees (34.5 " in HO). That seems to fit a bit better than 57 degrees (14.4" in HO). Now curiously, he shows the minimum radius “as a single unit” for SW10’s, SW7’s, SW9’s, and TR5’s as 57 degrees. I think what we have here is a misprint or perhaps, more likely, a data transposition.
And for SD45’s, he shows 17 degrees (46.6" in HO) for “with train”, and 22 degrees (36.1" in HO) for “as single unit”.
Ed
Here’s a conversion table.
Thanks, gentlemen. I have it now.
Despite any misprints or errors on the data pages, it makes sense that the higher the minumum radius listed in degrees, the tighter the track that can be handled.
The SD7s etc. then can manage tighter track than the Dash 9 and it all makes sense.
What I don’t know about real railroading shrank a little bit for me now.
edit: now when the data site shows things like the E6s being able to handle track like the smaller SD7s I have to determine if the E series was really built like that for some reason…or it is a misprint.
Keep in mind the length of the body isn’t as important as the length of the wheelbase. An E unit (particularly an E-6 with it’s extended nose) has a longer body than the SD-7/9 but much of it sticks out before and after the trucks compared to an SD-7/9 where the trucks are closer to the ends of the body.
The SD7 and SD9 were 60’ 8-1/2" long at the coupler faces, with a wheelbase of 35’. The E-6A was 69’ 1" long and had a wheelbase of 42’ 8". (In comparison, an SD-80MAC is 80’ 2" long.)
Ah, that I knew.
A check of the specs tells us that the truck center to center distance for an E6 is 57 feet, and for an SD9 is 48 feet. And both, of course, are six wheel trucks. I looked that up first.
I suspect the data from the link you have in the original post is faulty. According to that site, the SD-7 and E-8 both can take a 57 degree curve, where the GP-7 and SW-7 require a 39 degree curve. As noted in earlier posts, the higher the degree, the sharper the curve, so it seems to be saying an E unit can take a sharper curve than an SW switcher can.
[%-)]