Wheel Squeal on Tight Curves

Background/Facts: Yesterday, May 14, 2012, New Jersey Transit's Princeton Shuttle (Dinky, if you will) running between Princeton Junction on the Northeast Corridor and downtown Princeton was running with only a single Arrow III MU instead of the usual pair of two singles. (They use two singles for redundancy rather than a married pair.) As this line leaves Princeton Junction it follows a rather tight curve that produces quite the high pitched squeal as the train traverses the first half mile or so of track. On this day I happened to notice that the wheels were absolutely silent. Today, May 15 the second car was back in service and with it the squeal.

Now, I apologize for: (a) starting this discussion in this forum but as I view it as more of a generic engineering issue than a New Jersey Transit issue I didn't think it belonged in the NJT forum; and (b) the excess background but I don't know how familiar those of you in this forum are with the local landscape.

Questions: Could running a single car really reduce the wheel rub and resultant squeal to nothing? I would have thought it was related to each truck's position relative to the rail and that shouldn't change just by being coupled to another car should it? Does being coupled to another car reduce the degree to which a truck can successfully navigate a curve of a given radius? Is it possible that the entire curve was greased yesterday but the effect is gone within 24 hours?

Thanks, and mods please feel free to relocate this someplace more appropriate if necessary or to redirect me to a prior discussion if my feeble search effort could have been better.

I could be wrong but I imagine truck design plays a factor in wheel squeal on curves, as well as its pivot point on the car?

That's the reason for 'greasers', or curve greasers to be more exact, to cut down on wear in curves.

To be more precise, perhaps the one vehicle had lube sticks installed for the wheel flanges, and the other didn't?

These are long/thin rectangular waxy-looking things that are spring-loaded to press against the wheel flanges.

They are dramatically effective at reducing flange wear on curves (which you hear as squeal).

There are no grease stick holders on the Arrow 3 MUs. There is a rail greaser going east before the "big curve". So a train might not squeak going east to Princeton Junction, but going west, it might as there isn't a greaser before the curve when going west.

I see what your asking and its quite interesting.....I have noticed you can get wheel squeal with a light engine but not always, but it seems you always have it when there is more than one car/loco.

I think part of it might have to do with how tight the guage is on the actual wheelsets and how flexible the truck is. Brand new wheels with brand new flanges are going to be tighter than a worn wheelset with thinner flanges. A wheelset with a little play/thinner flanges isn't going to be nearly as tight and therefore probably not squeak as much

Now when you have a car coupled behind, i would assume that the forces on the coupler to the inside of the turn when pulling the car behind would put strain/pressure on the rail on the inside of the curve. Even tho the cars you are talking about are both powered (MUs) there would still be pressure on the couplers.

A perfect example of the stresses at play when a train going around a turn is when a train "stringlines" which is when it gets pulled right off the track when going around a curve.

This is the best pic I could find...

http://www.railpictures.net/viewphoto.p ... 033&nseq=2

Maybe they installed a flange lubricator at that location?

GF

Thanks everyone. I think JT has got the right combination of things. The single car had probably been on the branch a week or two and might have had some extra play in the trucks and thinner flanges from all the wear. Additionally, even though the couplers are not directly connected to the trucks I'm guessing there's got to be some added pressure there when cars are coupled.