Did this improve performance? Streamlined King + Castle

This thread has drifted so far from streamlining of two particular classes that I think either it ought to be renamed or a lot of the recent posts should be split off to a new thread; but for either case I'm blowed if I can think of a good title to cover the diversity of subjects.

 

Centrifugal force does exist as an application of Newton's First Law of Motion: an object either remains at rest or continues to move at a constant velocity and direction unless acted upon by a force. The force which applies to prevent it moving in the straight line and forces it to follow a circular motion is Centripetal Force.

Trying to rotate two or more wheels of a different diameter in contact with a fixed object (track) at the same rpm most definitely wastes energy, and therefore power. The two wheels are attempting to rotate at different rpm and the force required to prevent that does detract from what could otherwise be applied to the rails to move the train. As I have already stated, a train's rolling resistance on a curve is higher than on straight track for this reason, irrespective of any theoretical advantage to coning the tyres.

 

No, it really doesn't...
What does exist is momentum/inertia.

 

AIUI Creep is about grip. Maximum friction between rail and wheel (or road and rubber tyre). So more likely to increase rolling resistance than reduce I should have thought, but could be wrong.

 

I may be utterly misunderstanding this, but isn't the dimension of momentum that of a force?
Kind regards
Jos Koopmans

 

Thanks for the replies, all really interesting.

I get the bit about Newton's first law. The classic example is the conker swinging round on a string. There is no force forcing it outwards, centrifugal or otherwise. Instead, the conker is trying to continue in a straight line, but is prevented from doing so by an inward force known as centripetal force, in this case provided by the tension in the string.

As to "creep", I have always understood that the coefficient of static friction is always greater than that of sliding friction, and that as soon as soon as the force rises to the point where static friction is overcome and sliding (slip) commences, the frictional force force falls away instantly. Happy to be corrected, however, as O-level physics was a long while ago, and steel on steel may well be a special case.

Could it be the that the electronics in modern locos are pushing the traction at each wheel to the point where slipping starts, and then reducing it to allow grip to be reinstated, so as to determine the limits of adhesion? Doing this several times a second would result in a slight over-rotation of the wheel. This would make sense to me.

As to what to call a spin-off thread, I'm stumped as well. Maybe something to do with the physics of loco adhesion?

Dave

 

Back to the question, yes the streamlining did make a difference and on a first run one of the two engines overshot the station because of less air resistance for braking. Modern streamlined cars had the same problem initially with brakes overheating, until the brakes were suitably uprated. As for why the GWR didn't continue the experiment, I think it can be surmised that the added work maintenance-wise, not to say also the not over-great appearance together weren't considered worth any slight performance gain. It also has to be remembered that Kings and Castles had all the power needed for trains at the time, so streamlining would just have been a luxury at typical GWR express speeds.

 

I can't believe that. It has been shown that a proper streamlined engine like a Duchess or an A4 showed no advantage over a conventional loco at anything under 90mph. The flavour of the month in the 1930s was streamlining and was pushed hard by the marketing departments. Of course the GW board wanted some of it. I think the half hearted effort with the King and the Castle was Collett just taking the p***

 

He did a great job with the diesel railcars though. Lined up with the A4 & Duchess at the nrm, just needs a malachite green spam can to complete the set. He wanted to dieselize the Great Western and perhaps didn't want to make express steam look modern maybe?

 

I think AEC had already designed the streamlining before finding a customer for the railcar design.

 

Based on these figures and a simplified frontal area of 13'1" x 9' I work out that the standard pacific has a drag coefficient of 0.56 and an A4 has a drag coefficient of 0.33. It's quite a significant difference, but i would have expected them to of been much higher! I may of made a mistake but the given values fit in well with the figures calculated.
Extending it up gives these figures
100mph
Std- 450Hp
A4- 264Hp
120mph
Std- 778Hp
A4- 456Hp
140mph
Std- 1236Hp
A4- 724Hp
160mph
Std- 1845Hp
A4- 1081Hp

 

The tables show savings with reference to relative air speed, frequently starting from 60mph and ranging up to 150mph. Given that UK designs are not high power to weight ratio machines then quite modest savings should be viewed as advantageous. The power saving at 60mph might be modest into still air but running into a headwind of any significance was seen as significant- hence the 150 figure.
Streamlining was something that the general public at large was becoming aware of and this awareness was capitalised upon in the commercial activity of the more forward companies but "flavour of the month"? We continue to work on the science of air flow to this day.

 

I don't know the full explanation for it, but from the world of offroad driving (and some knowledge of how traction control systems work) I understand there is an optimal point of slippage where it is possible to transmit maximum power to whatever surface you are trying to make progress on.

The optimal point is not static between the rate of the vehicle travel moving forwards and the effective distance covered by the wheel/tyre and the surface, ie. there must be some slipping occurring to achieve maximum mechanical grip.

Chris

 

If there are any figures for other locos as to regards to power to overcome air resistance at any speed I can work out Cd for them too, and especially if anyone has the values for bathtubbed coronations, air smoothed Bulleids and GWR streamlined I'd be pretty interested to see how they compare. I'm guessing values I used to calculate the Cd of A3(?) vs A4 relate purely to locomotive alone, or at least difference between them at the head of an otherwise identical train.

 

I'm glad I'm not the only one. The train may have overshot the station but the idea that it was down to the' streamlining' on these locos is the stuff of nonsense.

 

It might well have been a good prompt excuse for somebody with a quick mind. But. I wonder. Given that drivers here - and motormen on the Southern - remarkably
didn't have any sort of speed indicator, could the fairings behind the safety valve or funnel have upset the view over the boiler that someone used as a braking mark?

Was there anything to indicate that speedometers were appreciated in the war time blackout?

Is it known what streamlined locomotives had speedometers? Did Collet's King and Castle have them? (In their early days the A4s had French speed recorders)
I would guess that for any trials where an accurate speed had to be known - and certainly any speed records - there would have been something, however, I am not so sure
in normal service - drivers may simply have carried on as usual and never habitually used them so it was no critical priority to ensure they worked. Indeed drivers may
have arrived fine quite oblivious to wether they worked or not.

 

Mostly speedometers were removed during the war, as spare parts became virtually unobtainable.

 

My understanding is that those devices were speed recorders, not speed indicators - in other words, they could provide a record of the speed attained for study afterwards, but weren't easily seen while driving. From memory, the surviving recorder on Mallard is tucked away under the fireman's seat, not really visible to a driver who is looking forwards.

Tom

 

There were both types, recorders and indicators. The LMS used 'speed indicating equipment', possibly as well as recorders. But as said, these were removed during the war except from the Turbo 6202, where drivers otherwise had great difficulty estimating speed.

 

Thinking about it what about drag from carriage sides? Didnt the LNER Streamline sets have screens under the body & between the carriages