The Anonymous Widower

Thoughts On The Aerodynamics Of A Class 91 Locomotive

The Class 91 locomotive is unique in that it the only UK locomotive that has a pointed and a blunt end.

The Wikipedia entry has external and internal pictures of both cabs, which are both fully functional.

The speeds of the locomotive are given as follows.

  • Design – 140 mph
  • Service – 125 mph
  • Record – 161.7 mph
  • Running blunt end first – 110 mph

The aerodynamic drag of the train is determined by several factors.

  • The quality of the aerodynamic design.
  • The cross-sectional area of the train.
  • The square of the speed.
  • The power available.

The maximum speed on a level track, will probably be determined when the power available balances the aerodynamic force on the front of the train.

But with a train or an aircraft, you wouldn’t run it on the limit, but at a safe lower service speed, where all the forces were calm and smooth.

If you compare normal and blunt end first running, the following can be said.

  • The cross sectional area is the same.
  • The available power is the same.
  • Power = DragCoefficient * Speed*Speed, where the DragCoefficient is a rough scientifically-incorrect coefficient.

So I can formulate this equation.

DragCoefficientNormal * 125*125 = DragCoefficientBlunt * 110*110

Solving this equation shows that the drag coefficient running blunt end first is twenty-nine percent higher, than when running normally.

Looking at the front of a Class 91 locomotive and comparing it with its predecessor the Class 43 locomotive, it has all the subtlety of a brick.

The design is a disgrace.

Conclusion

This crude analysis shows the importance of good aerodynamic design, in all vehicles from bicycles to fifty tonne trucks.

 

If

 

 

October 11, 2019 - Posted by | Transport/Travel | ,

1 Comment »

  1. The issue going blunt end first was that the bow wave lifted the pantograph or similar, not the overall aerodynamics – with several MW it can do 140mph with a several hundred tonne train even when pushing from the back.

    Comment by R. Mark Clayton | October 11, 2019 | Reply


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