Bulleid rebuilds - Was it for the better?

I don't know about that. Smoothing over all the lumps and bumps down the side is bound to make some difference. Cd is much more than just a sharp front. It would be interesting to chuck all the different streamlining designs in a wind tunnel and get some numbers - especially with regard to crosswinds as well.

 

True, though if that is a concern, you also have to think about streamlining the whole train, especially tidying up the underframes (à la LNER Coronation) and I've never seen any evidence that Bulleid planned a whole "air smoothed" train, rather than just a locomotive.

I think studies of railway locomotives were done in wind tunnels in the 1930s and 1940s, and I am pretty certain that Bulleid had access to one during the development of the MNs, but in most cases, I believe the studies were primarily concerned with clearing smoke and steam from around the front of the loco, rather than reducing drag, although in some cases that may have been an incidental benefit.

The issue of poor visibility caused by drifting steam had come to prominence in the 1920s on account of the combination of multi-cylinder designs (with softer exhaust meaning the steam wasn't ejected at such velocity) coupled with larger boilers meaning shorter chimneys. The combination of those factors meant it became a serious problem around that time as locomotives started to be built up to close to the loading gauge limit in size: it is noticeable that the widespread adoption of smoke deflectors started in the 1920s.

Tom

 

True enough, and probably do-able at a basic comparison level using OO gauge models I would have thought, if you had the kit to do it?

 

Using OO gauge models wouldn't be that helpful, you need to maintain the reynolds number. You can do this by increasing the speed for the smaller model, or using a different fluid. Thankfully computer simulation is available making it a bit easier.

Ultimately though i imagine a streamlined train pulled by a non-streamlined locomotive would be more effective than a streamlined locomotive with a set of standard carriages.

 

Attached document on the subject. Sorry that the focus is not too good on a couple of pages.

 

I was thinking of just a subjective comparison of one design to another eg A4 > Coro > MN > P2 > the GWR abortion. Oh, and then there's the B17 too.

 

Thanks, very interesting!

 

You forgot the schools


http://www.scienceandsociety.co.uk/results.asp?image=10452981

 

Interesting. So the MNs were almost certainly worth doing (break even 1962), but possibly not the West Countries (break even 1966). Its always instructive looking at these sorts of papers and seeing where the money is really spent.

 

If you were going to all the trouble of setting up the tunnel etc it would make sense to use the largest models you could obtain.

 

well i did tell you on 7th oct, but apart from those who kindly messaged me to obtain a copy of the BR testing report, no one seems to have taken much notice till now! always go back to the primary source documentation, rather than rely on secondary source stuff!
sorry i couldnt work out how to add same to the forum - how did The Crimson Pirate manage to do same whereas i failed miserably despite trying?
cheers,
julian

 

Thread resurrection again - I know Daimler ultimately switched from sleeve valves to pushrod-actuated overhead poppet valves on the last few V12s, and on the ensuing straight-eights, sixes and finally the Edward Turner V8, but also, the Bristol Aeroplane Company used sleeve valves in their various radial engines (Pegasus, Mercury, Hercules, Centaurus etc) which were perfectly reliable as far as I am aware. In the Beaufighter, they led to a very fast yet quiet aircraft, nicknamed by one of our enemies as "Whispering Death". There are even a few Hawker Sea Furies running their original Centaurii on the racing circuit at Reno, pushing north of 5000hp with no problems. However, parts availability is near non-existent, which has led to many being converted to run big American radials instead. So, is the problem one inherent to the sleeve valve itself, or specific to the Daimler and Bulleid applications thereof?

 

It's the sleeve valve itself, I believe - nice in theory but very prone to problems in practice due to differential expansion etc. The engines do need to be warmed up & cooled/shut down gently to minimise problems.

 

So how did Bristol manage to make it work so well? If they'd been that bad we'd have lost the war!

 

They are very different beasts.

An aero engine works in a generally clean environment, quite unlike the somewhat ash-filled conditions inherent on a railway. The Leader engine had to operate in a speed range of between about 0 r.p.m. to about 350 r.p.m. or so (with 5'1" drivers, 60mph is 330rpm), typically with maximum torque at minimum revs, whereas an aero engine tends to work at fairly constant rpm once warmed up.

Finally, I suspect that Bristol spent considerably more man hours on developing their aero engines than Bulleid had available for the Leader. The problems were worth solving because the sleeve valve configuration bought certain theoretical advantages to radial aero engines over conventional valves, whereas with the Leader, the theoretical advantages over conventional locomotives were simply not worth the development effort, especially with the promise of a step-change in cleanliness and efficiency of locomotives by using diesels on the horizon.

Tom