LNER N7/3

[John Bateson]

I have an Connoisseur LNER N7-3 on the workbench which is to have a slight rework for the pickups (as Will L. described elsewhere recently).
It has a 1224 motor with a High Level 108:1 which gives a top speed of 47 mph, DCC fitted. It is a nice runner at the moment.
I am beginning to wonder if this is a little too slow - would these have travelled at speeds up to 70 mph for instance?
John

[Noel]

I should start by saying that I don't actually know, John; it's outside my area of knowledge. However, pending a more definitive answer I would suggest that the answer is probably not. My reason for suggesting this is that GER suburban locos were built for high acceleration and deceleration, including up Bethnal Green bank, between closely spaced station stops. Although the N7/3 had longer travel valves it also had 4ft 10in wheels, which seem rather small for 70 mph. The 5ft wheel 9Fs could do it and more, but were a later generation of engines, and it caused some surprise even then. There seems no particular reason why an N7 should have been asked to do such speeds in normal service, especially with 10 coaches on.

An anonymous article [possibly by a fairly senior divisional staff member] in Trains Annual 1964 refers to N7s as fast, but without quantification. It also states that long travel engines were mostly on outer suburban services. However, 'fast' in terms of a suburban engine would not seem necessarily to imply express train speeds, especially given that N7s, especially the long travel ones, were apparently prone to motion failures. This article also refers to their use on excursions to Colchester, and one by a former fireman in Trains Illustrated 55 [July-Sep 1985] refers to their use on non-stop Southend excursions. However, steam era holiday excursions were notoriously slow, so these longer distance trains need not imply high speeds.

Noel

[John Bateson]

Noel,
Thanks for your note. It makes a lot of sense and it keeps that particular job off my to-do list.
John

[BryanJohnson]

Hi John,
I'm puzzled how your model can achieve your stated scale 47mph.
The 12/24 motor has a fairly low no-load speed of 12,000 rpm; with a 108:1 gearbox and a maximum of 20mm drivers, I'd expect a top scale speed of around 20mph. The speed calculator on the High level website gives a result of 19mph.
By my calculations, a ratio of 46:1 would be needed to give the scale 47mph @ 12,000 rpm.
Can you confirm the configuration for the loco?
Regards,
Bryan

[Jan]

A post on the LNER Encyclopedia http://www.lner.info/forums/viewtopic.php?f=11&t=7995 has timings for electric stock from Enfield Town to Liverpool St. The N7's had to do it quicker, it seems. If someone knows the distance between ET and LS, speed could be calculated..

[John Bateson]

I suspect I may have goofed!
Just ran the High Level spreadsheet again and it comes to 19 mph, playing around with the figures I think I put the motor type (1224) rather than the max. revs. in the box!

Methinks I need to put this back on my to-do list first thing tomorrow.

Apologies to all who have had their time wasted.

John

[Noel]

The distance from Enfield to Liverpool Street in the timetable is probably less relevant than the maximum time between stations, which is four minutes, start to start, i.e. including standing time at the station. Some are as little as two minutes. This is presumably from the public timetable; the working TT probably showed minor variations, but top speeds in those conditions would not be high. With the station stops rather further apart, in general, outer suburban services, such as to Gidea Park, would have been able to achieve higher speeds, as would inner suburban non-stop services.

Sorry, John, I missed a relevant comment when I originally looked through the article in Trains Annual 1964; it contains a reference to a motion failure near Ingatestone when 69721 was doing 60 mph. Presumably this is only an approximate speed [I don't suppose N7s had speedometers, did they?] and may be an overestimate, but it gives an indication of the possibilities.

Noel