[From nobody Mon Jan 14 08:17:49 2013 Received: from mta3.snfc21.pbi.net (mta3.snfc21.pbi.net [206.13.28.141]) by mail-sf1.pacbell.net (8.9.3/8.9.3) with ESMTP id NAA25958 for <pghpcc@mail-sf1.pacbell.net>; Wed, 24 Nov 1999 13:09:46 -0800 (PST) From: JacksoRE@STVINC.COM Received: from sjc3-1.relay.mail.uu.net ([199.171.54.122]) by mta3.snfc21.pbi.net (Sun Internet Mail Server sims.3.5.1999.09.16.21.57.p8) with ESMTP id <0FLQ002WW041O8@mta3.snfc21.pbi.net> for pghpcc@mail-sf1.pacbell.net; Wed, 24 Nov 1999 13:09:39 -0800 (PST) Received: from portal.stvinc.com by sjc3sosrv11.alter.net with SMTP (peer crosschecked as: [63.75.14.242]) id QQhqto19593; Wed, 24 Nov 1999 21:09:31 +0000 (GMT) Received: from notes.stvinc.com by portal.stvinc.com via smtpd (for [199.171.54.122]) with SMTP; Wed, 24 Nov 1999 21:00:38 +0000 (UT) Date: Wed, 24 Nov 1999 15:28:00 -0500 Subject: Re:FW: PCC Acceleration & Speed To: billvigrass@hillintl.com Cc: pgcraig@bechtel.com, pghpcc@pacbell.net Message-id: <OFEFBDFF01.5E1FC7E1-ON85256833.007429A8@stvinc.com> MIME-version: 1.0 Content-type: text/plain; charset=us-ascii X-MIMETrack: Serialize by Router on Notes/STV(Release 5.0.1|July 16, 1999) at 11/24/99 04:08:50 PM X-Priority: 3 (Normal) As I recall, the original goal was 4.75, which is easy enough to achieve. (only requires 21% adhesion) Some properties cut that back to 4.0. Without access to their records, we can only speculate as to why. It might be related to substation loadings. It is a fact that the less time spent on resistance, the less power is used to heat the resistors. A low-rate dc car (LIRR and MNRR are classic examples) wastes more power, although substation peak loadings may be lower. Such things are not always understood in this industry anymore. The street railway properties would probably have had power problems with large scale switch to PCC cars, but for most of them, the losses in traffic and peak car requirements during the 30's resulted in the power systems not being loaded to max anymore. So, a change from 4 40hp motors to 4 55hp motors, such as in Pittsburgh (although they did have a good fleet of souped-up cars with motors good for nearly 60 hp), would not be any problem. Along this line, probably the only place where a switch to PCCs lowered system horsepower was in San Francisco Muni, where 4 60hp motors was the rule on the old stuff. By the late '70s, SEPTA's fleet had got so mis-maintained that many cars would spin wheels on dry rail. You had to have a light foot to hold it down to 4.75! Given that modern cars have automatic, highly sophisticated spin and slide control, the 3mphps rate is unnecessarily low. Most cars have brake rates up as high as 4, so one wonders why the accel. rate has to be held back. Not very consistent. In terms of passenger injury, people standing up to get off are just as much at risk as those aboout to sit down, yet we worry about one and not the other. It's a strange world these days. regards, Russ J. ____________________Reply Separator____________________ Subject: FW: PCC Acceleration & Speed Author: "Vigrass, Bill" <billvigrass@hillintl.com> Date: 11/9/99 2:12 PM Of possible interest. Bill -----Original Message----- From: Fred Schneider [mailto:fschneider@dli.state.pa.us] Sent: Tuesday, November 09, 1999 1:38 PM To: pittsburgh-railways@dementia.org Subject: RE: PCC Acceleration & Speed The PCC used shunted fields to reduce torque when starting ... a way of cushioning the start ... explains the fact that the speed curve gradually curves upward for the first second or a little longer. -----Original Message----- From: Jim Holland [mailto:pghpcc@pacbell.net] Sent: Sunday, November 07, 1999 5:50 PM To: PRCo -- WP -- JTC -- The Big *3* Subject: PCC Acceleration & Speed Greetings! Have already archived the other posts, but Dr. Fred corrected himself on PCC acceleration downgrading from 4.75 mphps to 4.25 mphps. I mentioned that I had always seen the former figure. The chart on pages 56-57 of *PCC The Car That Fought Back* show statistics for a wide variety of cars for comparison. It shows the original PCCs to be 4.75 mphps and Pgh 1600 to be 4.0 mphps; balancing speed is 42mph and 40 mph respectively. Before these books, my main source of information was an article entitled *The American P.C.C. Car* published in the British *Passenger Transport Journal* of 1945.12.14. On page 348 it lists the acceleration as 4.75 mphps and it shows a graph of the acceleration which you had mentioned. In 60 seconds the car was at 37-38 mph but had gone only 2,700 feet, not a whole lot more than half a mile! It is in this same article where I got the speed figure for climbing grades. On page 349 in the second column under the heading *Start*(?), I shall quote the whole paragraph: "Fig. 2 shows the typical speed-time, distance-time curves for a car weighing 38,000 lbs. on the level. The rate of acceleration grows gradually at the start but is required on test to achieve 4.75 m.p.h.p.s. in from 1 to 1 1/4 seconds. The rate of change of acceleration must not exceed 5.5 m.p.h.p.s. in any quarter second interval. The maximum speed is 42 m.p.h.; balancing speed is 28.5 m.p.h. up a 6 per cent gradient." Didn't know they could measure so closely then! I wasn't and am not challenging your figures; it seems that both figures are correct. It certainly makes sense that as the car got heavier, performance would drop. Sound has much to do with our perception of speed as we have already mentioned! Rail joints were 30-40 feet apart on average and are not conveniently located like model snap track - they are often staggered and there are also shorter pieces of rail. Heading outbound thru the Mt. Wash tunnel in the good ol' PRCo days with rail joints at 28.5 mph sounded more like the car was doing well over 50 - but obviously it wasn't. Doing 30 mph on the surface would seem like an extremely fast ride! I stood at the north end of the McKinley Park trestle (1959-1960) and filmed two different outbound cars. The second car sounded so much faster that it took my breath away and made my heart stop! Yet one cannot perceive the difference in speed by watching the movie - without sound! It was then that I realized the futility of silent movies and hoped for a way of simultaneously recording sound. About five years later I got a portable Akai tape recorder while on duty with Uncle Sam's Canoe Club in the South Pacific (and that was a real clunky thing in those days) hoping to use it in conjunction with making movies of the Pgh. streetcars, but never did! James B. Holland ------- -- --------- Pittsburgh Railways Company (PRCo), June of 1949 -- June of 1953 To e-mail *off-list,* please click here: mailto:pghpcc@pacbell.net N.M.R.A. Life member #2190; http://www.mcs.net:80/~weyand/nmra/ ]