71000 Matters

I didn't know 6245 had been fitted with a kylchap - you learn something new...………

Townend says in Top Shed they also experienced problems with tube cleaning with the cowls in situ -- so they just missed those out !

 

errr… without , thankyou . I see 2968 s point about overpower , no point in having what you can't use , but the potential for speed (which also couldn't be used ) has interest .
120mph on level track at 20% ??? maybe ….

 

You may also be interested in some of the articles about Dr. Porta's South African engine "Red Devil" - he modified an engine to produce much higher horsepower by improving the combustion, boiler and valve gear - unfortunately it became extremely difficult to handle being very prone to slipping across the speed range. It's an interesting story without a great ending. If 71000 were able to produce, say 50,000lb of TE what would you do with it - she is perfectly capable of handling anything the present steam on the mainline programme is likely to throw at her. Faster acceleration to get up to line speed - not if she cannot keep her feet. Blue riband climb of Shap or Ais Gill - ditto. A great steam engine design is about balance - frame strength, boiler capacity, combustion rates, adhesion ratios and a thousand other things - perhaps that's why CME's took a while to get to the top of their profession (although 'puters would help!)

 

Wrong chap!

The various possible modifications along Porta/Wardale lines can increase the available power from a steam locomotive but they make no difference to the TE.

I agree with that part.

 

Not like this hasn't been looked at before.... the Loading gauge effectively limits the boiler diameter. Ideal boiler tube ratios limit the length of the Boiler ( indeed the duchess goes a little far in this regard) and a big enough firebox suggests wide rather than long
- a Pacific wheel arrangement is a neat fit to that boiler shape and is good for fast running - but to get more adhesion
-4-8-2, this is starting to look very long unless you use much smaller driving wheels...
- 2-8-2 is a bit better but is not an ideal high speed vehicle but since even a brand new high stepping pacific is only allowed 90mph not so much of a problem So put your Duke of Gloucester boiler on a 2-8-2 on 5 ft 8" wheels, get a derog to run 75mph....and it will show the P2 a thing or two

Take a step back and think deep firebox rather than wide (ie GWR) and you end up with up 2-8-0 or 4-6-0 and bank on the better combustion of a GCPS to allow more sensible sizing and you have - 5AT.

 

Apologies - I should have named David Wardale with assistance from Ing L D Porta - the rest of my comments stand - the example of improved TE was to keep the discussion from getting completely off track - I understand the relationship between evaporation rate, cylinder ihp etc. but most enthusiasts readily recognise TE as a yardstick. Thanks for your reply.

 

Wardale gives in "The Red Devil" a tiny increase of the TE. Interesting is his table 31 regarding the axle loads. The original SAR 25 class engine had between 18.7 and 19 metric ton loads. For his 26 class they succeeded
in loading most of the extra weight on the bogie and truck, while giving the front axle 17.9 ton and the others from front to back 19.8, 19 and 19.2. No wonder it liked slipping!
Kind regards
Jos

 

I'm just wondering if it would be sensible to include exhaust back pressure in the calculation of T.E. I've always thought of T.E. as being relevant when stationary or running very slowly, where back pressure shouldn't have much effect.

 

Tractive Effort is the force applied by the locomotive to the rails to move itself and the train along them. It isn't constant, though, and varies with a number of factors, including speed. With a steam loco, it is at its highest when the loco is stationary and just starting; once moving, it will begin to fall exponentially. The rate of decrease will also vary from one loco class to another; it will be pretty rapid with a slow goods engine but far more slowly with an express passenger type.

It is the Tractive Effort which is recorded on the rollers of a testing station or by a dynamometer car. In the latter case, it is the TE delivered to the train via the drawbar, so less than that delivered to the rails. The results are then converted to either Rim Horsepower or Drawbar Horsepower via a mathematical formula, and if from a dyno car, Indicated Horsepower from yet another formula. Each calculation, of course, introduces assumptions and errors, which is why indicating is more reliable.

 

Were there any locomotives, other than the rack type, which could actually apply their theoretical TE to the track without slipping?

 

Depends on how close the Nominal and Actual TEs conformed, but it is said that the Stanier three-cylinder 2-6-4Ts would start without slipping in full gear and the second valve fully opened.

 

I imagine Holden's GER Decapod would have been up there in a league table of surefootedness

 

and the GCR 4-6-0s

 

Now THAT would be something I'd love to see and hear! I remember seeing 8F No. 8431 with 6 on, at Oakworth a good few years ago... Baking hot day. I couldn't see just how far the gear had been pulled up, but the radius rod was just about at the limit of its travel in the bottom of the expansion link, so couldn't be far off full-gear. The driver just pushed the regulator straight up into the roof, and off it romped, not a hint of a slip.

Richard.

 

Back on the subject 71000 - don't recall any serious slipping incidents from herself.. Good adhesion ? or does the valve gear help?

 

The calculated figure for tractive effort:-

te =. 85 x piston diameter squared x boiler pressure
100 x driving wheel diameter in inches.

Surely can only be used to produce a figure to compare one locomotive type with another as the formula itself assumes square cylinders rather than round ones that have a much smaller area.. Thus it is quite meaningless in giving any realistic figure.

 

Have seen more erudite formulae than this ( no of pistons, stroke etc) but this Doesn't assume square pistons . Its simply that the Pi 's cancel out
(factor of circumference Pi D and The area of the piston face Pi r squared)

 

Don't forget to multiply by the piston stroke and allow for the number of cylinders, a well
In doing a proper calculation for this it's actually the mean effective pressure that is required. In the absence of an indicator diagram to establish the true value for simplicity this is generally taken to be 85% of boiler pressure.
From first principles, in one complete revolution of the wheels (pi x D) the piston moves twice the stroke (s x 2) and the effective force over one revolution is piston area (pi x d x d /4 ) x mean effective pressure (mep). Thus, each cylinder produces a force of
(pi x d x d x mep x s x 2)/ (pi x D x 4) at the wheel which cancels out to give (d x d x mep x s)/(D x 2) for each cylinder

 

Apologies - the stroke got left out. For some reason am unable to activate 'Edit' to correct it.

 

I've seen enough slipping from the total adhesion Double Fairlies to know they can't! Bearing in mind a loco needs sufficient grunt to overcome inertia from rest, I suspect there's always going to be scope for slipping.

The Pennsy T1 new build has taught me that, with a heavy hand on the regulator, these modern duplex locos could cheerfully start slipping when accelerating loads towards 3-figure speeds .... quite a terrifying proposition!

Another thought .... the step down gearing employed in the drive of many rack locos rather stuffs up standard TE calculations anyway.