Classic Trains Article, Winter 2010, Pages 80-81 - Weight, Adhesion, Tractive Effort And Speed

Thanks for the heads up, Ken.

I have been trying to get all my yard work ready before my hip replacement surgery later this month, and I have not been able to stay awake long enough to read through that issue. That is a great shot of the engine.

It looks very clean considering the extremely heavy war time usage.

Terry

 

Best of luck on your surgery, Terry.

I had my left hip replaced 2 years ago. If it was not for that, my current issue with the broken right leg would not be as manageable as it has been.

It is great to be in NO pain!

Dan

 

Thanks, Dan.

I am looking forward to having no pain.

I may have to relearn how to walk, though, as I have developed a distinct limp. I am looking forward to starting my layout this winter. I need to be able to carry the supplies into the house and up the stairs.

I think my grandson does not believe me anymore when I tell him we are going to have a real layout. He and a friend of his from church love to play with the trains.

I can run on the simple track running around the room, so having some variety of routes will be more fun, plus being able to run trains in different directions.

Terry

 

It is like riding a bicycle, a quick return I am sure.

At least, mine was.

Dan

 

Too bad the Classic Trains 4300 article was so short and the picture so small!

Cannot believe Kalmbach could not find a bigger and better photograph.

Nice little remembrance though.

Tom

 

Need to keep an eye out for the January issue of the NMRA publication Scalerails.

There is a little bit of Frisco coverage coming up.

Brad

 

Wow, I wonder who the author is?

 

Well, despite whoever the author might be, the editor did a pretty good job, and the pictures tell the story anyway!

Brad

 

Joe Collias' book, Frisco Power, lists the horsepower of the 4300s as 4800 hp, and the 4400s as 4400hp.

The 4300s had boiler pressure of 250 pounds and the 4400s at 210 pounds, which would probably account for a difference in horsepower.

Glad you liked my article in Classic Trains.

Frederick Clem

 

Tractive effort does not consider the weight on drivers. Weight, and hence adhesion affects the drawbar pull but not the tractive effort.

TE on a two cylinder engine is calculated by a simple formula, D² x S x P x F/d, where D is cylinder diameter in inches, S is the stroke, P is the boiler pressure in psi, F is a factor which varies according to who is doing the calculation and d is the driver diameter.

The variability of F is due it being something of a fudge factor to allow for losses in the steam path between the boiler and pistons. Typically in U.S. practice it would be around 85%, which is a useful estimate for low speed work.

Now you will see that weight on drivers has not entered yet. TE is simply a measure of the force delivered at the outside face of the wheel.

Where weight matters is in adhesion. Too high a TE for a given weight on drivers and you get powerful machine that cannot start a train because it slips badly on starting.

Typically designers worked around an adhesion ratio of about 4. That is the total weight on drivers should be about 4 times the tractive effort.

A significantly lower figure makes for a slippery engine. The TE is still calculated the same way, but the maximum pull at the drawbar has gone down because of lack of adhesion.

Note the number of drivers does not affect the calculation, only the total weight on drivers.

 

Aidrian rightly notes that frictional forces or adhesion is independent of the number of drivers.

As counter-intuitive as it may seem, friction has nothing to do with surface area.

Only the coefficient of friction of the materials in contact with each other and the pressure between the two materials enter into the equation.

 

The booster engine is just a second, two cylinder, steam engine, and Cole's formula would be used calculate its TE.

The power was transmitted to the axle via a set of gears, and the gear ratio would have to factored into the calculation.