Have a question for you all. Once in a while I travel alongside a train at maybe 40 mph and I notice a railcar wiggling, actually the trucks are going back and forth sideways. What causes this and what keeps the car from coming of the tracks? Does the engineer feel it? To me it is wild but scary to see.
In fact, sometimes you see it coming when your standing alongside the tracks. Makes you want to run the other direction. [:O]
You’re probably standing alongside a line with jointed rail that is in need of some heavy maintenance. The distance between the joints in the rail and the truck centers on the cars coincides at 39 feet, which starts and amplifies the rocking as each car hits the low joints.
…I wouldn’t stand too close to that operation in the area you describe.
If this is the train buff i know he is standing or driving by ribbon rail main line the one i run on. ( shattuc) What he is describing is a car that is hunting the track, engines do it to, if its a car doing it no we dont feel it ive looked back and have seen this happening and see them comming on other trains it does get your attention… as to why a carknocker will haft to exsplain but it has to do with worn barrings but it is a guess. Now when a engine does this it makes for a very uncomfortable ride. ive had some engines so bad that ive bought milk to drink with a sandwhich and it shook so bad i had butter in 20 miles.
There is always some some side to side movement as a car goes down the track but it is usually minimal . When it gets real bad the detectors will usually pick it up as a " Truck hunter defect " which requires an ispection by a car knocker . It is usually caused by broken or worn ride control springs , or worn truck side frame parts , or a broken transom on a truck . All of which cause the car to be Bad Ordered and the parts repaired or replaced .
Truck hunting - somehow the track department is responsible for this too???
There he goes, looking in the mirror again![swg][swg][swg]
You know those engineers, always have to have the hair just right, in case they have to wave or something…[:D]
Truck hunting is a form of mechanical resonance- which is essentially a weakness in lateral stability of the freight car as it is pulled along the rails- can be caused by both by worn car components or worn railheads. Truck hunting is most common at speeds greater than 40 MPH- the reason for this can be best demonstrated in physics terms. The faster a train travels the greater the forces around the train increase- the stress on the freight car itself increases as the slack is pulled out through the car’s couplers making the train akin to a string pulled tight between two posts (think- guitar strings or “acoustic resonance”). As the train’s speed increases the strain on the “string” becomes greater, which creates more energy- if there are any flaws in the superstructure (worn components, railheads etc.) this creates an effect similar to strumming the string- i.e. vibration, the lateral instability. Due to the fact that the car is coupled to a larger moving object, the excess energy created by this instability is expended through the wiggling. If the problem is not corrected in time it is possible that this can cause a serious derailment.
The other issue that was mentioned by Paul earlier is a little different from truck hunting- this is harmonic rocking. While it also has to do with lateral instability and is another form of mechanical resonance-harmonic rocking is more common at speeds between 12-24 MPH- this is caused when a heavy car encounters low joints on jointed track- this creates a reptitive pendelum type rocking that can literally rock the car off the tracks.
…Sounds like serious truck hunting if it happens often on almost each train that passes a certain point on the RR would have a damaging effect on the track.
Also, I wonder if the wheel surface profile might have an effect to minimize or maximize the truck hunting.
Wheel and rail profile can both influence hunting. But the big causes are what carknocker1 cites.
RWM
I am not a railroader, so take this for what it is worth, but I have read that covered hoppers are most susceptible to harmonic rocking because of their high center of gravity. When I worked in Sayre, PA, I witnessed that rocking often as the local salt train departed. As the train accelerates the hoppers seem briefly wildly out of control. Crew members have told me that sometimes the wheels rise off the rail when the rocking is at its worst. The curve in front of the old LV station seems to exacerbate the phenomenon. I would guess that an empty car would be more likely to rock than a loaded one. And yes, this is on jointed rail with about 40 foot hoppers.
I was a carman for 35 years, most of the time when a car came in the shop you do what has to be done and thats it!! You replaced truck springs only when they are broke.
I was on board the Gettysburg Railroad behind steam with a very long open car, probably a converted flat. That thing did quite a bit of wiggling. The Heavyweights provided a much better ride on the same track.
Viewing the train from the outside in certain locations, the wild rocking is something to behold.
Now here is another issue that I call pump. When a railcar comes off the roadcrossing at speed, there is a descent as the rail drops under the weight of this car. Sometimes I think the wheels clear the rail completely briefly on the way down.
These days there are detectors that bad order cars for truck hunting , its not as simple as looking at the trucks anymore. Usually the roller bearing adapters need changing along with the bolster wedges .
Some of you are getting the 2 things mixed up. the harmonic rocking ( running jointed rail 16-21mph) is the cars rocking side to side uniform rocking of the car swaying might be a better term to use. this wiggling is a truck ( and ive seen both ends doing it) shacking or wiggling at the bottom only its so violent of a movement that you hear the rails and wheels going sching similar to a grinder on a hollow pipe but with quick motions. it happens at speeds above 35mph
All part of the job description…
Ed, what would the “or something” be?
Pretty hair trumps closed eyelids every time! [;)]
I actually felt the truck hunting experience on one occasion.
I was on the Silver Meteor years back approaching Tampa on the welded “A Line”. As expected we were rocking as normal. I left the Lounge Car and sat in an Amfleet II coach. I had ridden trains many times before and was familiar with harmonic rocking, but I could feel this car literally wiggling hard, side-to-side over the rear truck! As if a giant hand were grabbing those axles shaking them between the rails. We were cruising at about 60 mph, slower than the usual 79mph.
Needles to say, I certainly DID NOT enjoy that sensation, which I’m convinced was truck hunting. It stopped once we slowed down to about 40mph as we entered Tampa’s city limits.
Wow, perhaps that’s the same thing I felt a few months ago on Amtrak just outside Philly on the Harrisburg line. I could not hold a cup of coffee for any amount of effort! Frankly, it was enough to scare me