Unstable boxcar

[WSOR 3801]

Empty bulkhead flats are known for hunting as well. It's fun seeing one coming at you at 50 per when you're out giving a roll by inspection....

Mike WSOR cndr

[mvlandsw]

Some railroads restrict trains with empty cars to 50 mph for this reason. On CSX the restriction does not apply to empty intermodal cars. I am guessing that this is because longer cars are not affected as much.

[monkeyman2]

I saw that once the train wasn't evn breaking 10 mph too..It was a shortline

[Grinandbearit]

I saw an 89 ft Flat with three new Chev cab and chassis being whipped to pieces on an eastbound CN freight one evening. I'm sure whoever bought these rigs wondered why they had a very short life!

[wabash1]

yes what you saw was a condition called hunting ... and all cars are subject to this . i have had engines do the same thing hit 45 mph and start hunting. then hit a low spot and start jumping its got so bad at track speed that i was glad to stop for train meets 2 hrs before it was nessesary.

[M636C]

Thanks for the wishes, mudchicken. It was a nice fine day (Wednesday 26 January) for the celebrations this year.

Adrian, hunting is really a resonance problem. If a normal truck hits uneven track, it will oscillate from side to side, but the energy will dissipate and the truck will return to normal running. The problem with "hunting" is that the combination of conditons that cause the problem don't allow the oscillation to die out, because each side to side movement builds up energy, rather than allowing it to die out. Sometimes it is because the wavelength of the sinusoid is close enough to the rail length that the truck hits a rail joint each time it has flange contact. This doesn't happen on welded rail, of course, but hunting does occur on all types of track. The pattern of wear on the wheels is important. One one of our braver mechanical engineers thought he had a perfect wheel profile, so it was machined at great expense onto a pair of wheelsets and we took it out with video cameras aimed at the truck. (This was years ago, and we only had black and white cameras). The truck hunted for the full trip, loaded or unloaded, so the wheels came out and were returned to AAR profile that day! We never let him forget that, either!

Peter

[adrianspeeder]

Doesn't resonance have somethin to do with it?

Adrianspeeder

[mudchicken]

Excessive Truck Hunting, probably accentuated by improper loading/ poor weight distribution.....Our Aussie bud (Happy Belated Australia Day!) is dead on.

[M636C]

This phenomenon is called "hunting". It usually occurs above a "critical speed", which can vary according to the condition of the wheels, the load in the car and the resistance to rotation of the truck. 50MPH would be a likely speed for a car to start "hunting" if the conditions were right, particularly if the car was empty.

The truck just moves from side to side following a sinusoidal path, being deflected off each rail by flange contact.

I've only seen it once, the leading end of a container wagon at about 70MPH. The container was moving about 3" to 6" side to side compared to that in front.

I did experience it in a Lounge car once. I was with a track engineer from the Norwegian State Railways. We just looked at eachother and we both knew what was happening. I tried to explain the problem to the car attendants, but they didn't have a clue about the problem. It is very unusual for passenger cars to suffer this problem. In that case, the car had been modified from clasp braking (brake shoes each side of the wheel) to one sided braking. I think the axle guide clearances had increased as a result of all the brake force in a single direction. We noticed the problem on the "Indian Pacific" just out of Sydney, but the car hadn't derailed as we rolled into Perth three days later, so I guess it was OK.

Peter

[robscaboose]

This was a constant shaking or quivering of the car . It seemed the wheels were not tracking properly. I observe ithis for several miles & then had to turn off from the tracks.

[Anonymous]

Ever have a hopper full of coal do that near you?

[xx(] i learned that it can fling em' 30 feet... *boom* right on the head...[:I]

hey its pittsburgh, it rains uphill....

[Mookie]

Could be a dip in the tracks. We watched ours do the hula for quite a while before they finally fixed the track.

[Anonymous]

I've seen similar several times...I think the way the car is loaded has something to do with it....Seems like I wass either told, or read somewhere, that a car loaded with weight very high in the car can start the car rocking in pendalum motion, which the air currents outside the box tend to magnify

[robscaboose]

[?][?] This morning I was driving south of Tuscola Ill along the IC/CN tracks when I overtook a SB train. Near the end of the train was a CSX boxcar that looked like it was "shaking" & the front & rear trucks seemed to be alternating (almost like it was fishtailing) from one side of the tracks to the other. The boxcar was behind a hopper & the train was moving along at about 50mph.

It really stood out & I have never seen this before.