HST question on power control

[silverfoxcc]

I found this quote by a well known transport journalist on the Ufton Nervet accident.Can someone explain what he actually means as to me it doesn't read right?

'As the front slowed down, the rear was still at speed,and the train jackknifed
in the middle with catastrophic results'


How can a fixed buckeye unit have the rear part going faster that the front. Surely the rear power car would be shut down at the same time as the front one?

I think physics and kinetic energy may have something to do with the jackknife more that the 'rear still being at speed' but as i am neither a HST driver nor a scientist i will defer to better qualified people. ( or perhaps i am being too pedantic?)

 

[najaB]

...or perhaps i am being too pedantic?

Probably. They are just badly wording that the momentum of the carriages and rear power car caused the jackknife.

 

[pdeaves]

How can a fixed buckeye unit have the rear part going faster that the front. Surely the rear power car would be shut down at the same time as the front one?

Don't forget that at the point of impact, even if the brakes were on, the front would slow down at a much greater rate than the rear, having (effectively) an extra strong brake suddenly applied. After a very small time period, the forces sort themselves out, by which time the damage is done.

 

[daikilo]

I found this quote by a well known transport journalist on the Ufton Nervet accident.Can someone explain what he actually means as to me it doesn't read right?

'As the front slowed down, the rear was still at speed,and the train jackknifed
in the middle with catastrophic results'


How can a fixed buckeye unit have the rear part going faster that the front. Surely the rear power car would be shut down at the same time as the front one?

I think physics and kinetic energy may have something to do with the jackknife more that the 'rear still being at speed' but as i am neither a HST driver nor a scientist i will defer to better qualified people. ( or perhaps i am being too pedantic?)

In this accident, where an HST hit a car on a level crossing, the leading power car imediately derailed initially parallel to the track then was deviated by facing points, causing in to dig into the ballast. The following vehichles then also derailing then piled up against it. The rear power car did not initially derail. The braking efficiency was thus different between the front and rear of the train. Most couplers were damaged or broke.

From that I conclude that the comment of the journalist is either irrelevant or misleading.
RSSB report from Railwaysarchive: http://www.railwaysarchive.co.uk/documents/RSSB_Ufton001.pdf

 

[rebmcr]

"As the front slowed down" does not refer to braking, it refers to the collision.

The front power car slowed down quickly because it hit the road vehicle, whereas the rear power car carried on moving forward and squashed the passenger cars.

 

[gimmea50anyday]

Bear in mind the front of the train had a car wedged underneath it and both were jammed into the pointwork and digging up the dirt in the process. A lot of kinetic energy would have been absorbed at the front of the train by this while the rear of the train would stilk have been at speed, possibly still providing traction power as the data feed to cut traction and apply the brakes may not yet hace reacted on the PCs systems. (Tenerife air disaster the Pan Am planes engines were still running at full power despite the plane being wrecked because the control system for the engines were destroyed) Plus its own weight and kinetic energy would have to go somewhere. This no doubt cascaded through the derailing train via the buckeyes thereby causing the train to jacknife around itself as the motion kinetic energy had to go somewhere, most likely in the form of friction energy of the already derailed coaches PC and car as well of those coaches being bent or crushed during the crash. This same phenomenea caused the bending of the coaches at Ladbroke Grove and Hatfield as both sides of the coach were bent around the OHLE stanchions.