A stock weak field question.

The weak field should be used between Finchley Road and The City. Drivers do sometimes forget it however! Yes the trains pull off much quicker with the flag down but I don't know the top speed of the stock with it down. 40mph would be a good guess though.

I believe the driver can start with the flag down and raise it while motoring.

The East London line was also a flag down route too.

IIRC the max speed on the northern half of the Circle is 35mph so max speed of 40mph with the flag down is a good guess.

Last time I travelled Uxbridge branch, the A stock unit was not in Weak field. Acceleration better than S stock I experienced previously on the branch.
Noticed A stock at Amersham with the flag up, but I wonder whether the relatively short distances between stations from Amersham to Ricky would be better off not in weak field? From Ricky to HOH, and HOH to Finchley Rd FAST, I can see the value of switching to weak field, but since the max speed is limited to 50mph, not sure weak field is as effective?
Do the A's have speed limiters / black box recorders to prevent overspeed I.E serious overspeed 55mph+?

It's a long time since I worked on A stock, but the weak field flag should NOT be used between Finchley Rd and the City.

R stock was also fitted with weak field flags and "sometimes" used with good effect on the Wimbledon branch and out to Upminsiter. Naughty naughty.

SR stock was fitted with a weak field position on the driver's power handle and would automatically go into w/f as part of the acceleration process.

To run up through shunt/series then parallel, LT stock would generally get to about 40. SR stock much the same until the balancing speed of the motors would reach. ISTR there was a discussion on this elsewhere.

Weak field does what it says on the tin, weakens the magnetic field of the motors, so they will turn faster but take longer to do so, hence poor acceleration. It is possible to raise the w/f flag on A stock whilst moving, but the driver would need long arms to do so.

SR stock was also fitted with a series/parallel switch. this was for use on the Folkestone Harbour branch, which, at 1 in 36 was quite steep. The trains would accelerate quickly to max power to go up the hill, but not reach the parallel position.

Ive always been wondering about this but, does raising the flag whilst motoring damage the motors or any other equipment?

That doesnt answer my question

Onion's question is relevant in the event that the setting is changed in error while on the move; I am not a driver but I assume there is not a mechanical interlock to prevent this happening. Firstly I am sure that the switch contacts are not designed to withstand the sparking that will occur if the setting is changed while under power. Regarding the effect on the equipment, basic DC motor theory would state that reduction in the field coil current (by selecting weak field) will merely reduce the acceleration and enable a higher top speed. However in the reverse case, if the weak field is deselected at a speed higher than the strong field will support then a reverse emf will try to slow the train down to the lower maximum speed with consequent braking stresses on the transmission; these old trains may not like that.
Hopefully one the the drivers on the board can comment further.

But based on the above posts - lifting the flag on the move is almost impossible unless you have someone else in the cab to do it for you, due to its location?

So what happens if you forget to set it prior to starting a long fast section like HoH to Moor Park? Would you stop the train to set it or are you then committed to arriving late?

ohmslaw, the cleverer train operators will notice there is a little hook on the flag itself. In theory a piece of string could be set up to pull it upright! I'm not sure if it has been tried, but I'm laying the gauntlet down if it hasn't! ;D

Well, I think we can now draw two conclusions:

1. Mr Metman's wonderfully maverick challenge has met with no takers - what a surprise!
2. Mr Bengley has very long arms ;D

I would tend to disagree with comment 2 as ISTR the Rapid Pneumatic Accelerator (RPA) equipment accelerates at the same rate irrespective of the flag setting. It's just the weak field gives a lower rate of acceleration.

No damage would be done to anything by moving the switch while the train is moving, except perhaps to the driver's fingers when they get shut in the cupboard door!

The switch can be reached, provided you shut off and stretch across. It also isn't enclosed in a cupboard or cabinet ;D ;D

Would have thought that, being about 5-6' away from the controls. It might be possible to touch both at once, but surely very difficult to apply continual pressure to the deadmans with an outstretched arm and maintain the correct position