Acceleration/Decceleration rates

[Deleted]

I'm interested to know what the service acceleration, service decceleration, and emergency decceleration rates are on different tube stocks, particularly the older stocks. The only stocks I can find information on is the 95TS, which according to Alstom is designed to have service acceleration and decceleration of a very high 1.3m/s2 and 1.34m/s2 respectively (which I assume is only when it's performance is unleashed in a few years), and the 92TS which under ATO accelerates and deccelerates at 1.15m/s.

[Deleted]

You posted
districtdave.proboards39.com/index.cgi?board=Trains&action=display&thread=1134516586

in December, but did not elicit any replies. I know I've seen figiures quoted around for summat like 1.32m/s for 78's but am NOT sure if thats the exact distance/speed. I will try and locate where I saw it. Probably in with all my gumph in the locker!

[Deleted]

tubeoperator92 said:

You posted
districtdave.proboards39.com/index.cgi?board=Trains&action=display&thread=1134516586

in December, but did not elicit any replies.

Oh so I did, fading memory!

[DrJimi]

FWIW, anecdotal data re the D78 says it stops in its own length (approx 107m?) from 30mph in Brake 3. Checking my MSTS model (for which I gleaned these data) shows I used a brake force of 23Kn for a DM unit weighing 29.18t. Using force = mass * decel rate yields about 1.27m/s^2 for Brake 3. This yields a stopping time of 10.5 secs if Brake 3 were left 'on', and a more realistic 15 secs or so if the brake were 'feathered' back to Brake 1 approaching a stand.
I would also be very interested in any other data, especially for the older stocks.

[Deleted]

drjimi said:

FWIW, anecdotal data re the D78 says it stops in its own length (approx 107m?) from 30mph in Brake 3. Checking my MSTS model (for which I gleaned these data) shows I used a brake force of 23Kn for a DM unit weighing 29.18t. Using force = mass * decel rate yields about 1.27m/s^2 for Brake 3. This yields a stopping time of 10.5 secs if Brake 3 were left 'on', and a more realistic 15 secs or so if the brake were 'feathered' back to Brake 1 approaching a stand.
I would also be very interested in any other data, especially for the older stocks.

Sorry, excuse my ignorance, but is "brake 3" the maximum service brake, one before emergency braking?

[DrJimi]

4 levels of braking (Brake 1...4) + Emergency. These use the 3...7 steps of the 7-step Westcode brake system (i.e. Brake 3 would be step 5 of 7). If these steps apply linear levels of braking (as previous comment from T/Ops in an older thread suggests), then Brake 4 should be Brake 3 * 6 / 5, Emerg = Brake 3 * 7 / 5. So Brake 4 (full service brake) should be (per my numbers) 1.27 * 6 / 5 = 1.55!?!? That feels high to me, but I stress that despite understanding the basic operation of the Westcode I'm NOT an expert. Knowing the pressure readings (at the brake cylinder) for each step would reveal all I feel. I'm also curious as to the relationship between brake pressure and actual braking force and actual decel rate (the latter two should be related simply by mass, ignoring brake fade).
Hopefully someone with far more inside knowledge than I (SB?) can comment further.

Sorry if I'm muddying the water.

/Jimi

[Deleted]

1.55m/s2 would be very high. 1.3m/s2 is the highest acceleration and decceleration rate that people can comfortably stand (according to research), and is usually the emergency decceleration rate. Rubber tyred and LIM trains can have much higher design acceleration and decceleration rates (I've seen figures over 2m/s2) , but I doubt that they are used to their full potential in service as they would be dangerous.

[Phil]

Not sure about LU stock, but an HST doing an emergency stop from 125mph has an AVERAGE deceleration of 1.3 ms^-2.

This would imply that LU stock with their superior brakes and lower running speeds could well exceed that figure in EMG.

[solidbond]

While I have absolutely know idea what the actual deceleration rates are, I can tell you that the brake pressure on a D stock is broken into 7ths by the Seven Step Relay, and that each 7th is equal to approx 8psi. Thus, Service 1 = 3/7 = 24psi, Service 2 = 4/7 = 32psi, Service 3 = 5/7 = 40psi, Service 4 = 6/7 = 48psi and Emergency is all 7/7 and is equal to approx 56psi. Although I should point out that the actual brake cylinder gauges on the D stock are calibrated in Bars not psi

[Hutch]

As a matter of comparison, the Metrolink trams in Manchester were designed to accelerate at 1.3 m/s² with normal service braking giving a deceleration rate of 1.3 m/s². If the emergency magnetic track brakes are deployed the deceleration increases to 2.6 m/s².

[Deleted]

hutch said:

As a matter of comparison, the Metrolink trams in Manchester were designed to accelerate at 1.3 m/s² with normal service braking giving a deceleration rate of 1.3 m/s². If the emergency magnetic track brakes are deployed the deceleration increases to 2.6 m/s².

For fairly obviously safety reasons road running trams have to have very high emergency decceleration rates. I'd be interested to see how many people would be floored by a full emergency brake application!

[Phil]

stephenk said:

For fairly obviously safety reasons road running trams have to have very high emergency decceleration rates. I'd be interested to see how many people would be floored by a full emergency brake application!

You should have seen how easy it was to floor the punters in a Bristol RE doing an emergency stop!!! Never had to do one for real, but often did if there were stroppy kids standing up on the schools. Advantage was, if they didn't fall over at least they ended up beside you (or against the windscreen) so you could have a few words with them.
Seriously, those buses could stop as fast as any car.

(not far off thread....)