Friday, 4 August 2017

GWR Large Prairies: Work In Progress, Cab

This week we take a look at the cab of the Large Prairies. Although very similar to the 5200 class they still have enough differences that it required a full build rather than a copy and paste and we also took the opportunity to improve the details of a majority of the controls.

We've been very fortunate to have the input of one of the footplate crew of 5199 so we have been able to make sure that every tap and lever turns the exact right amount and in the correct direction, a detail that's not always easy to find out.

We've also been really lucky to have help from another footplate crew member (this time of 9466, amongst others) and between the two of them we now have an all new brake simulation for Advanced Mode that adds even more to the realistic experience we offer to you in Victory Works products.

To explain how it works, the following is taken from the upcoming Large Prairies manual:

The vacuum brake is used to pull the brake shoes away from the wheels by creating a vacuum in the pipes connected to them. The brake has 3 settings, brake off which forces a vacuum into the pipes and takes the brakes off, brake on which lets air into the pipes and applies the brakes, and brake running which holds the vacuum steady at its current pressure.
The brake pressure gauge shows the current pressure in the system, from 0” (on) to 25” (off).
In basic mode all of this can be controlled by the brake lever.

Keys: ‘ (apostrophe), ; (semicolon)

Advanced Mode

In Advanced mode the GWR large prairies require the use of the Large Ejector to release the brake, the brake lever being used to apply it. You will also need to be aware of the brake reservoir which is now accurately simulated.

Important: Note that in Advanced mode the F4/F5 HUD brake pressure may NOT be representative of the engines brake gauges and you should use the gauges in the cab to operate the engine correctly. Please also note that the setting of the lamp head codes is now CRITICAL to the operation of the brakes so that the engine knows how much of the train is made up of fitted (vacuum braked) rolling stock.

Vacuum brakes operate by having a pressure difference between a “train pipe” and a “reservoir”. When the train pipe is less than the reservoir then the difference between these pressures is how hard the brakes are applied. The brakes are fully released with a difference of approximately 22” or more, and fully applied with a difference of approximately 5” or less.

However these systems are not airtight and therefore when leaks occur the train pipe and the reservoir (although leaking much slower than the train pipe) will trend towards 0”. The way create to create a vacuum in both systems on the prairies is to use the large ejector which will create a vacuum in the train pipe, and once the train pipe pressure reaches the same as the reservoir then an automatic valve will open and the reservoir pressure will increase as well.

The large ejector is steam powered and requires a pressure of at least 90 psi in the boiler so be careful to manage this properly or you may not be able to release the brakes.

Keys: Large Ejector - P, Shift P

In addition to the large ejector (which is steam driven) the large prairies also have a mechanical vacuum pump (powered by a piston) which will start to work when the locomotive is travelling at approximately 10 mph and will apply pressure to the train pipe to counter any leaks. The pump can hold the vacuum up to 25” and on a short train can even create vacuum in the train pipe up to 22” or 23”. This creates the effect of slowly releasing the brakes when you are braking at speed and you may need to use multiple applications of the brake lever to stop the train.

To this point we have referred to the train pipe as it applies to the engine, however on a fitted train (where some or all of the rolling stock is fitted with vacuum brakes) this pipe is shared along the whole train via flexible connecting pipes. This means that the ejector and pump are creating vacuum along the whole length of the train and so this will increase the time that it takes to create or release pressure from the train pipe. In addition fitted stock have their own reservoirs so even if the train pipe is at 0” and engine reservoir falls to 0” (no pressure difference and therefore no brake application on the engine) the train will still be held by the brakes on the rest of the fitted stock. When running light or on a totally unfitted train you do not have this “backup” and it is advisable to apply the handbrake when stopping for any length of time as the train and pipe reservoir will slowly drain to 0”, releasing the engine brakes.

In Train Simulator there is no way for the engine to know what stock it is pulling so the prairies use the player selected head code to indicate how much of the train is vacuum fitted.

The head codes and percentages are as follows and on changing lamps (see section on head code setting below) you will see a message describing the code and how much of the train is fitted with vacuum brakes.
A: Express passenger 100%
B: Stopping passenger 100%
C: Parcels, perishables, etc. 100%
D: Express freight 100%
E: Express freight 50%
F: Express freight 0%
G: Light Engine 100% (can have 1 or 2 brake vans which would be fitted)
H: Through freight or Ballast 0%
J: Through mineral or Empty 0%
K: Pick up/Branch freight 0%

So if you are pulling a passenger train (using head code A for example) then the brake simulation will use 100% of the length of the train to calculate how long it takes to gain and lose pressure in the train pipe.

Finally, although not required for standard operation you can manually release pressure from the brake reservoir using the Reservoir Drain Valve next to the driver’s front window.

Although this may seem daunting to begin with it soon becomes second nature and we found it really added to the immersion of driving these large tank engines and it will enable you to pull away and stop in a much more realistic fashion than with the default in-game braking system.

Next week we'll be back with some in-game pictures of all the engine classes. So that's the 5100, 5101, 6100 and 8100, all of which will be included in the upcoming Large Prairies pack.

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