Part 3 of my running gear series, today looking at track return rollers. The series is looking at all the bits of a tracked vehicle mobility stuff and started here (bit.ly/30596QZ) if you want to follow the threads. 
Usual disclaimer - this is Twitter, I don’t have much space and so some things are simplified or omitted for simplicity. This is a hugely complex science; I’m just giving a flavour of the considerations inherent in AFV design. With that out the way…
Track can be supported or unsupported as it transits the top run. If supported, several track return rollers (or top rollers) are used. They prevent track bouncing/slapping and help to avoid lateral movements that could see a de-track incident via engagement with the track horns
If unsupported, the roadwheels will have limited travel before they strike the top run on an upward deflection, resulting in poor ride, excess noise, increased track wear and possible thrown tracks
A significant issue is that a travelling wave motion can develop within a length of unsupported track, creating lateral vibrational resonance. Unchecked, this may develop into significant tensional fluctuations and increase rolling resistance by 30% or more
Unsupported track by no means assures poorer ride or higher incidence of thrown track though, the Strv-103 for example had a reputation for being pretty hard to throw tracks on despite being unsupported. Nonetheless, essentially all contemporary AFV use supported track now
Using return rollers does have drawbacks in the form of additional weight, more mechanical complexity and maintenance requirements and increased rolling resistance (though less so than when the aforementioned forces are unchecked)
A light overview of return rollers Next in the running gear series will be sprockets and drive location. /end #miltwitter #tanktwitter #AFVaDay
