A rumour about future use of D stock

Indeed, and so can a diesel generator. But in both cases it takes time for that to translate into forward motion. Rev an aeroengine up and the first thing that happens is a huge gale blown out behind you. If you could get the aircraft itself up to maximum speed instantaneously you wouldn't need long runways.

Same thing happens with a marine engine - essentially the propellor/water interface acts like a fluid coupling in a hydraulic transmission - only water is 1000 times denser than air. In a diesel-electric, it is the electric field which performs this slipping function. Without it, trains and boats and planes would all need a mechanical clutch, as in a car, to prevent stalling the engine when idling and stationary.



The performance of a three car D train should actually be slightly slower than a six car D stock train, as half a D6 has the same power but less weight than a D3 - a D6 will include at least one and usually two single-ended units, and an UNDM weighs less than a DM: moreover a double-ender has two compressors, a single ender only one.

A diesel engine will increase in revs until it wrecks itself if not fitted with a governor. This happens on occasions when the governor fails, that is why buses and coaches were and some still are fitted with an emergency engine stop. Most modern diesels are electronically governed and are stopped electronically. Lorry drivers used to stuff a damp rag into the air intake to stop a runaway diesel.

Where is it going to ?

Actually four months - but it does seem a bit tight. Assuming the first to go is a double ender, so they have the two DMs needed to make a full train. Of course, a demonstrator may not have everything the finished product would - they would presumably concentrate on the mechanicals rather than the passenger compartment. Assuming you have already got a generator capable of delivering the required voltage and don't mind, for the purposes of demonstration, where it is put, "all" you have to do is make sure it is securely fastened down and doesn't put excessive weight on the floor, connect it up to the positive and negative shoegear, and find somewhere for the exhaust to go.

Famous last words - "How Hard Can It Be?"

I am more intrigued by Serco's plans to use GBRf's Class 73/9s on the High;and Sleeper after they take over the franchise in April. As far as I am aware only one of the at least three (probably four) they will need has been started up to date. And this is no demonstrator - it's supposed to lug eight Mark 3s over Druimuachdar and back every night from April, whilst keeping the lights and aircon going.

Can we just keep in mind the D stock is limited to the speed it is allowed to do currently.