Haulage capabilities

[Hatfield Shed]

In the long-distant past did someone not recommend 3 oz adhesive weight for each 10 tons in the prototype? ...

Never seen that suggestion before. The 3 oz:10T relationship for the pacific and V2 adhesive weight of 66T results in 20 oz, pretty close to the 600g adhesive weight I aim at for a class 8 pacific.

My method started out based on the BR power class, with pragmatic adjustments, now from a baseline of 250g target minimum on the driven wheels for tender locos of class 3 or lower, with increments of 50g added for MT or F and wide firebox, and for each power class above 3. Having the centre of mass as near the middle of the coupled wheelbase as possible is happily easy on wide firebox traction.

[earlswood nob]

Good morning all

Three oz for every ten tons seems a lot for me.

This would mean the my U1 should weigh over 50 oz. It does weigh almost a kilogram with the boiler full of lead. I've had to disassemble the centre chassis as it was bowing with the weight. It currently is waiting for some square brass rod to beef it up.

Earlswood Nob

[Hatfield Shed]

I would suggest 'pragmatic adjustment' of the guideline result. Once the model has sufficient traction for the layout operation requirement, it is enough.

I had an old Triang-Hornby 9F converted to loco drive with the mechanism from the Mainline N2, and got the weight up to 800g. This enabled it to manage a 60 wagon goods on a wet rail and into a headwind. Until the day came that two wheels shifted on the axles and the rods were seriously bent. (Good motor, the Airfix GMR copy of the MW005; the one that did this still running as well as ever thirty years on.)

[4812]

I think my 'scale weight' source may have been an article about a 9F model, in the MRN about 60 years ago. The author's name has gone totally I'm afraid. I do remember that it inspired haulage trials at the club involving thin string, a pulley, and weights. My weighted Binns Road N2 did quite well.

[Hatfield Shed]

...I do remember that it inspired haulage trials at the club involving thin string, a pulley, and weights...

The necessary equipment came as standard on the A level physics syllabus (which at the time encompassed Newtonian mechanics up to special relativity!) and with a physics master who quite enjoyed model railway to boot. Still use this very method.

[earlswood nob]

Hello from sleepy Surrey

I dug my Dean Sidings Robison L1 last night. I have put some lead in the side tanks, but it still weighs slightly less than 8oz. It is powered bu a Mashima 1620 driving through a High Level 60:1 gearbox.

It will haul the equivalent of 50 wagons.

The speed reduction through a low speed gearbox is possibly why I get such good haulage power with a light weight.

Malcolm (Earlswood Nob)

[Hatfield Shed]

There are two further factors, not yet mentioned, which are significant: the coefficient of friction between tyre and rail which depends on the metal compositions of both; and the precision of the mechanism parts such that all driven wheels present the tyres in plane contact with the rail head to avoid energy being lost moving the locomotive vertically in particular.

The latter effect is why the best rigid chassis mechanism will lose some traction on bumpy track; while a mechanism with independent springing copes better. My own observations suggest that having kit wheelsets skimmed on a lathe once on their axles for identical diameter and profile, is worthwhile.
(A proof of the principle can be found in a RTR OO model with two different wheel diameters both driven at the same rotational rate, Hornby's Brush 2. As it approached the limit of its tractive capacity, it would slow and speed up unpredictably. Reaming out the plastic gear axles of the small wheels so they were able to slip, and leaving the traction duty to the four larger diameter wheelsets eliminated this effect.

[Atlantic 3279]

I had an interesting experience of the Airfix copy of the MW005 motor, mentioned favourably in an earlier post in this thread. My first Mainline N2 moved smoothly enough, but it sounded like gravel being poured down a washboard. Much close observation of running at very low speed with the body off revealed that the frame plates of the motor were not a perfectly tight fit. One of them was vibrating as the turning motor's magnetic field varied, and with the motor on a less than perfectly rigid plastic rear overhang of the chassis, normally within the plastic "resonating box" of the straight-sided bunker and tanks (with plenty of gaps to let the sound out), the consequences were unsurprising. I managed to jam a piece of card into the loose joint in motor frame, greatly reducing the vibration and noise, but the lack of rock-steady support for the motor and the presence of the resonating body ensured that it was never really quiet...