Updated August 2016
These two D3 tank engines are identical in design, both fully compensated with Portescap motor/gearbox combination.
D3 no 365 ‘Victoria’ is in the pre-1905 Stroudley Improved Engine Green livery
D3 no 373 (ex ‘Billingshurst) is in the post-1905 Marsh umber livery
The photo (below) shows 'D3' Victoria on 'Plumpton Green’.
Victoria had an interesting background, built in 1892, and lasting a full 60 years until withdrawal in 1952. She had a distinguished wartime career, including downing a German fighter bomber over Romney Marsh in 1942. The plane dived at the engine with cannons firing and pierced the boiler. As he flew over the engine the pilot misjudged his height, and the uprush of steam from the pierced boiler tipped one wing of the aircraft. The other hit the cab of Victoria, and the plane crashed about 100 yards from the train. Both enginemen escaped unscathed, if a little shaken by the experience.
After repairs at Ashford, Victoria returned to traffic to work out her remaining 10 years of service.
Photo (right) shows 'D3' Victoria on 'Brighton Road, with the viaduct and bridge in the background.
There has been a lot of discussion about how to compensate 0-4-4's. This one is straightforward. It is equipped with sidebeam compensation on the two front driving axles, and a centre pivoted bogie, which is also internally compensated. This gives three points of suspension - the centres of the two side beams on the driving axles, and the centre of the beam in the bogie. The frame of the bogie just pivots about a vertical axis - no fancy swing links or anything. There is a bit of sideplay on the second driving axle, and as little as possible on the leading axle. This gives enough horizontal flexibility to negotiate B6 turnouts, and about 4' radius curves.
An overall view of the chassis, showing the basic layout - Portescap driving on the centre axle (via modified MJT gearbox), sidebeam compensation for the front two axles, and centre beam compensation for the rear bogie. The bogie simply pivots horizontally about its fixing. The bogie itself is fully compensated.
The frame spacers are copper-clad paxolin, gapped in two places to insulate the frames from each other. Electrical pick-up is from just the driving wheels.
The coupling rods are milled from steel.
A view from the underside of the bogie.
The front end, showing the sidebeams, and bearing/guide detail.