and he notes - The SD 7/9 offered no advantage as far as weight distribution, but did deliver much higher tractive effort for heavy freight use (or passenger service). Here are some statistics taken from this site:
http://www.geocities.com/guilford_350/emd.html GP9 - Wt. 249,000 lbs or 28 tons per axle with 46,000 lbs TE SD9 - Wt. 368,000 lbs or 30 tons per axle with 73,000 lbs TE The SD24 offered only a modest increase in Tractive Effort (75,000 lbs) but weighed more (376,000 lbs). It was essentially an SD9 with a turbocharger and its only advantage was that it operated more efficiently. Only four class A roads bought them: AT&SF, CB&Q, Southern and UP. (UP had more cabless than cab units - 30 A's and 45 Bs). Clearly the SD series was meant for mainline service while ALCO's RSC series (6 axle) were meant for (but not limited to) lighter rail operations. Comparing an RS to an RSC: RS3 - Wt. 245,000 lbs or 30 tons per axle with 52,000 lbs TE RSC3 - Wt. 257,000 lbs or 21 tons per axle with the same TE The difference is the A-1-A trucks. There weren't many built - only 70 RSC2s and 19 RSC3s. ALCOs RSD15 series did compete with GM's SD24 series but not as big a big seller. Comparing an SD24 to an RSD15: SD24 - Wt. 376,000 lbs or 31 tons per axle with 75,000 lbs TE RSC15 - Wt. 363,000 lbs or 30 tons per axle with 79,000 lbs TE While the ALCO models offered higher tractive effort, GM had taken the lead in market share. In the 40s and early 50s, diesels replaced steam and horsepower (or builder) wasn't so much a consideration as economy. With increased labor costs, as well as per unit costs in post-Korean War years, railroads looked to efficiency and higher output, especially where bigger steam was being replaced. While ALCO offered higher tractive effort GM locos were easier to maintain and required fewer spare parts. By the late 50s some bean counter figured out that three unit lashups cost less to operate than four and the real high output race began when diesels began replacing diesels. Raleigh in Maine where its raining! At 09:00 AM 10/20/2006, David Engle wrote: >As I understood it, the SD-7 was introduced to spread out the weight of the >engine so it could run on lighter branchline rail. Except maybe on the >DM&IR, I don't think the concept of a bigger and heavier engine with more >pulling axles and greater tractive effort came along until the SD-24, which >was several years behind the competing models, including the (IF-ME) >TrainMaster, and the (Alco DL-600) Alligator. Conjecture only. > >----- Original Message ----- >From: "G. Elems" <<mailto:gelems%40sbcglobal.net>[EMAIL PROTECTED]> >To: <<mailto:S-Scale%40yahoogroups.com>[email protected]> >Sent: Friday, October 20, 2006 12:46 AM >Subject: {S-Scale List} More SD7 thoughts > >I like this discussion about modeling the SD7. I was curious as to the size >difference the SD7 presented to the GP7. It turns out the SD7 isn't really >that much longer and the overall engine is smaller than the PA-1 and FM >Trainmaster. The "too big" argument doesn't hold up IMO. [Non-text portions of this message have been removed] Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/S-Scale/ <*> Your email settings: Individual Email | Traditional <*> To change settings online go to: http://groups.yahoo.com/group/S-Scale/join (Yahoo! ID required) <*> To change settings via email: mailto:[EMAIL PROTECTED] mailto:[EMAIL PROTECTED] <*> To unsubscribe from this group, send an email to: [EMAIL PROTECTED] <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
