Visible evidence of instability...

Iknow nothing of locomotive bogie running stability, as discussed in the letter on page 39 of the April issue, except that instability is to be avoided (David Bancroft discussed the issues of pony truck side play, in response to tech ed Harry Billmore’s experiences at Fairbourne– Ed). However, readers may be interested in an observation that I made when I was young.

When I was still only 12 years old I had to use a pedestrian grade crossing in the Don Valley of Toronto four times a day to attend school. The crossing guard was a retired railroader of broad knowledge who also had much patience for railroad questions posed by youngsters; I got to know him well.

One day he spotted an express locomotive in the distance approaching at speed, at that location running at about 40-50 mph. He suggested that I stand close to the track (he would make sure that I was safely clear of the line) and to watch the front four-wheel truck (bogie) of the loco.

As the locomotive came closer I could see that the truck was banging from side to side quite viciously. I have to infer that this effect was common to the class since my mentor could not have identified the individual locomotive in adequate time. As far as I can remember he referred to the locomotive in question as a Hudson.

It was also the first time I had seen a real case of what I learned later was dynamic instability.

“As the locomotive came closer I could see that the truck was banging from side to side quite viciously...”

The Editor replies: No matter how much study one carries out in the classroom learning about various physical forces at work, there is no substitute for seeing the effects they have for real!