Class 91: Why do they have a lower top speed blunt end first?

[91104]

Even if they was allowed to run at 125 blunt end leading they probably wouldn't have the opportunity as the usual reasons they run blunt end first is because of a problem with the DVT or a TDM failure meaning the 91 has been run round so then the lack of a rear E70 brake control unit means speed is restricted to 110mph due to the slower application of the brakes and the other reason for a 91 running blunt end first is a light engine move meaning speed is restricted to a max of 75mph.

 

[alexl92]

One question i have always had in my head about this is the freight operations they were planning on doing with these. In my mind, i see the advantages of the second cab at the blunt end, but i don't see the reasoning behind using that end to haul freight, or the sleeper, or something else, regardless of the lower required speed. they're the same gearing each way (much much too high for heavy freight we can surely agree) so was it just because of the lack of turning ability at various stations?

I don't think the idea was they would *only* haul sleepers/freight blunt end first, but rather that since they wouldn't be doing 140mph there was no need to make both ends aerodynamically efficient.

91s have two cabs because unlike the HST power cars (which were originally designed with 2 anyway), they were designed to work as a standalone loco, not in a pair, either with a DVT on a 225 set or on freight/parcels duty.

You need that rear cab because without it, even if it hauled freight north (pointy end forwards) to somewhere where it could be turned to face south for the return journey, it would still have to have the time and routing available after that to get somewhere where it could be turned back north again ready for passenger services before its first train of the day.

The class 90s show that two pointy ends on one loco isn't a problem, so there must be a reason why they designed the other end as a blunt one.

My guess (and that's all it is) is that there must be an aerodynamic reason why at high speed - the sets were built for 140mph - it is beneficial to have the profile of the loco matching that of the coaches right along the set, rather than having that gap between the (slanted) back of the loco and the start of the first coach, even when the DVT is leading. This could also therefore explain why the sets are limited to 110ph when running with the blunt end leading.

I'm quite tired whilst writing this, so if you're reading it and it makes no sense whatever, I apologise! There's a clear train of thought in my head; whether I have managed to express it adequately or not is a different matter!

 

[HSTEd]

To be honest I think the difference might actually be primarily aesthetic.

It certainly makes them look better on the end of a set than the Class 90, which ends up with this odd cavity between the locomotive and the leading vehicle of the train.

The Class 89 was permitted to haul trains at 125mph, which would seem to indicate that the aerodynamic problems of having a trailing 'pointy-end' are not insoluble.

 

[D365]

To be honest I think the difference might actually be primarily aesthetic.

Yep, that's it.

 

[Western Lord]

When the Class 91 was designed there were still sleeper services on the East Coast and it was these that they were intended to haul blunt end first, not freight or parcels. By the time that they entered service the sleepers had gone and so they never have any need to run blunt end first in normal service.

 

[AnonymousUser1]

To be honest I think the difference might actually be primarily aesthetic.

It certainly makes them look better on the end of a set than the Class 90, which ends up with this odd cavity between the locomotive and the leading vehicle of the train.

The Class 89 was permitted to haul trains at 125mph, which would seem to indicate that the aerodynamic problems of having a trailing 'pointy-end' are not insoluble.

what is the angle of the 89s noses compared to a 91 or HST ? as the 90 has a more upright nose than the 91 and HST powercars

 

[TimboM]

what is the angle of the 89s noses compared to a 91 or HST ? as the 90 has a more upright nose than the 91 and HST powercars

Possibly more relevant than any angle comparisons is the completely different design of the 89 - it slopes all the way "out" to the buffers, compared to the "pointy nosed" design of the 90s and 91s (and HSTs).