Elvas Tower: Q: Adhesion and braking - Elvas Tower

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Q: Adhesion and braking

#1 User is offline   Genma Saotome 

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Posted 29 April 2018 - 07:38 PM

4 questions:

  • On real railroads is adhesion a factor in the braking of freight and/or passenger cars?
  • If yes, is there a defined set or parameters and values to put into .wags?
  • Is KUJU's Adheason() parameter used in any way by OR?
  • Does Adhesion vary by weight or is it a fixed factor used to adjust some other numbers?


#2 User is offline   Genma Saotome 

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Posted 09 May 2018 - 03:06 PM

bump.

#3 User is offline   Lindsayts 

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Posted 10 May 2018 - 12:34 AM

Adhesion availible for traction on a steel wheel on a steel rail is aprox a third of the weight on the wheel, for braking though the amount of adhesion availble drops to around 10%, ie if an axle has a 20 ton load maximum braking force availible will be around 2 tons. tractive effort availible will be around 6 tons. I have a number books that go in some depth in to railway physics and all say the same thing. Adhesion for braking (from memory) does decrease slightly with increasing speed.

Doing a mathematical look at the results of emergency braking tests of Victoria's (Australia) VLocity DMU's shows that this 10% figure for braking adhesion is correct (Note 1). The is no where in MSTS to use this. The advice though when setting up maximum braking force in MSTS is use the figure for the weight on an axle in kilograms as Kilonewtons. ie axle load 20,000kgs, maximum braking force will be 20Kn. This relies on the conversion factor from Kilgram force to kilonewtons being aprox 9,8, ie aprox 10%.

Note 1: I have yet to find an decent explantion of why brakiing adhesion is so far below the coeffiecient of static friction.of steel on steel.

Lindsay

#4 User is offline   Genma Saotome 

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Posted 10 May 2018 - 07:38 AM

So it is relevant then... and no doubt dry steel on steel will be different than when it is wet.

Does Open Rails account for this in any way?

#5 User is online   espee 

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Posted 10 May 2018 - 07:46 AM

Under the experimental tab, I am guessing this is only for traction and not braking ?

Should probably check the manual...

Attached Image: adhesion.jpg

#6 User is offline   ErickC 

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Posted 10 May 2018 - 09:15 AM

AAR brake ratio requirements are:

Minimum (loaded): 8.5% for TOFC/COFC, 11% for all else
Maximum (loaded): 13% (all)
Maximum (unloaded): 38%
Minimum handbrake ratio: 10%

This explains pretty much everything, including the relationship to adhesion:

http://www.standards.../freightcar.pdf

To calculate the correct braking force, multiply the car's weight by the correct brake ratio for your piece of stock. Remember to take the load or lack thereof into account. I believe that modern cars use a load/empty switch for this purpose in real life. It would be great if OR could implement this feature at some point.

#7 User is offline   R H Steele 

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Posted 10 May 2018 - 10:55 AM

View Postespee, on 10 May 2018 - 07:46 AM, said:

Under the experimental tab, I am guessing this is only for traction and not braking ?

Should probably check the manual...

Attachment adhesion.jpg

Regarding the experimental tab (Adhesion proportional to rain/snow/fog)...I remember reading a thread here, (cannot find it now) that OR does not distinguish between rain, snow, or fog...treating all the same.
Also it was stated in thread that snow (especially light snow) has less effect on adhesion than rain. Did I get any of that correct?

Here's some links to other adhesion threads

http://www.elvastowe...hesion-in-snow/
http://www.elvastowe...els-and-autumn/

#8 User is offline   copperpen 

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Posted 10 May 2018 - 11:13 AM

I think that braking adhesion exists in OR because excessive brake force on a lightly loaded wheelset will cause it to stop rotating and the sim reports a wheelslip.

#9 User is offline   steamer_ctn 

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Posted 10 May 2018 - 01:43 PM

OR supports wheel skid or slip. So as Copperpen suggests the application of excessive brake force will reduce (or stop) the wheel from rotating, and hence depending upon the adhesion between the wheel and the rail the wheel may go into a skid condition. In this case the brakes become ineffective.

The value of brake shoe adhesion for each car can be seen in the Brake Force HUD. Also in this HUD is the Loco and Wag Adhesion, which shows the current value of the friction coefficient between the wheel and the rail. This value varies with environmental conditions, such as rain, snow, etc.

The ADVANCED adhesion option needs to be selected for wheel skid on braking to operate.

EDIT: Edited after reviewing OR code.

#10 User is offline   Genma Saotome 

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Posted 11 May 2018 - 07:43 AM

Peter, where does adhesion for different conditions exist?
  • Kuju's Adheasion()?
  • A new OR Parameter for .engs only?
  • A new OR Parameter for .engs and .wags?
  • Only in the code?


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