Medium D British Interwar Light Tank

[Vinalssergio155]

That looks great and very interesting.

[waynemac]

Starting to lay out the parts. Here are two screen shots; one shows the TurboCAD worksheet at an oblique angle; the other shows a typical parts sheet in development. The worksheet seems a bit chaotic, but all the colored lines had a purpose.

I have not yet trimmed edges of all the parts to account for thickness of the card to be attached there. I typically assume a card thickness of 0.010" in my designs. Only a few of the tabs are in place.

Wayne

[CharlieC]

The Medium D had a unique suspension based on cables threaded through pulleys on the suspension bogies with springs at each end of the cable (see attached diagram). The suspension was very compliant and followed the ground contours much more closely than other sprung suspension designs.

The US Ordnance Dept trialled the suspension design in the Model 1922 tank but found the cable tended to stretch and replaced the cables with chains.

The other part of the suspension design was a track system where the track plates were free to rotate around a central core. This meant the tracks always had maximum contact with the ground. This was trailed in a modified Mark V tank in the UK but during one memorable demonstration the assembled Army officers were showered with mud and broken off wooden track plate inserts.

The Medium tanks (Marks A, B and C) were all machine gun armed. This seems to have been policy in that the tanks were designed to exploit breakthroughs created by the heavy tanks so it seems to have been thought that gun armament wasn't necessary. It would have been very difficult to fit a gun into the Medium D hull since hull had to be sealed so the tank could be amphibious. The Medium D/D*/D** was best described as an ergonomic slum, the driver couldn't see anything closer than about 20m from the tank.

Charlie

More info: The diagrams came from the patent US1329769A assigned to Philip Henry Johnson - who as Lt Col P. Johnson was in charge of the experimental workshop of the Central Workshops in France during WW1. Johnson held strong opinions that current tank designs were too slow and their suspensions inadequate. He was noted for adding a sprung suspension and a Rolls Royce aero engine to a Medium Mark A Whippet in 1918 and increased to maximum speed from 13 km/hr to 50 km/hr to the astonishment of observers. There are a whole raft of Johnson's patents discoverable with Google Patents.