Steam & Excursion > Did Tractive Effort Include the Booster Power?

Did tractive effort ratings on steam locomotives include the power from a booster ( 12,000 LBS Tractive Effort ) if a locomotive was so equipped ? 

Not usually. Tractive effort with booster was usually a secondary rating and stated as such. I believe PRR may have been a notable exception.

Posted from iPhone

On Reading T-1 4-8-4s, it was a separate item, as shown on this RDG diagram.
There is also at least 1 YT video out there that shows activation in the 2102 on a recent Rambles trip.

---

Interesting, if not sort of useless trivia - 
The booster engine alone on SP 4449 generates slightly more tractive effort than the D&RGW 169 (4-6-0) does in its entirety!

Maybe not so useless, might win a beer bet...

S_W

bmoore765 Wrote:
-------------------------------------------------------
> Not usually. Tractive effort with booster was
> usually a secondary rating and stated as such. I
> believe PRR may have been a notable exception.

The only Pennsy engines I can think of that had boosters were the J1 2-10-4's. Were there others?

Thanks to those of you who responded to my question on boosters on modern steam power. 

CPR_4000 Wrote:
-------------------------------------------------------
> bmoore765 Wrote:
> --------------------------------------------------
> -----
> > Not usually. Tractive effort with booster was
> > usually a secondary rating and stated as such.
> I
> > believe PRR may have been a notable exception.
>
> The only Pennsy engines I can think of that had
> boosters were the J1 2-10-4's. Were there others?

A few K4's had boosters as did the Q2.

Frisco always added the TE from the booster separate. xx,xxx loco xxxx booster.

Tractive Effort is a theoretical computation representing the amount of force an engine can deliver to start a train or keep it moving.  Therefor, boosters are mounted on the trailing truck (smaller wheels than the drivers) and are shut off and the gear drive disengaged  once continued movement is achieved.  

Horsepower is a calculation representing the engines ability to move the train at sustained speed.

-LD

T&P included the booster on the 2-10-4's.  But on drawings also listed them seperately.  Pay your money, take your choice.

Stevo_Weimario Wrote:
-------------------------------------------------------
> Interesting, if not sort of useless trivia - 
> The booster engine alone on SP 4449 generates
> slightly more tractive effort than the D&RGW 169
> (4-6-0) does in its entirety!
>
> Maybe not so useless, might win a beer bet...
>
> S_W


Good luck with that. At the Red Frog (overlooking Cape Horn) we’re pretty much on to you…
SR

One more factor. Drawbar pull is the actual force measured by a dynamometer car at the tenders coupler. It is, effectively, tractive effort minus the force taken to move the locomotive.

And, by design, Tractive Effort is as close as possible to 25% of the locomotives weight on drivers, since 25% is the coefficient of friction of a steel wheel on a steel rail. Any additional tractive effort and you get wheel slip.

-LD



Edited 1 time(s). Last edit at 11/17/25 10:38 by LarryDoyle.

> Did tractive effort ratings on steam locomotives include ...

If "ratings" means the numbers that appear on
a locomotive diagram from the maker or the RR,
then the booster is roughly never included.
But articles in railfan magazines often do
include it, trying to make their subjects as
impressive as possible.

If you're ever wondering about a particular engine,
it's usually easy to calculate the main-engine-only
TE yourself, given the pressure and dimensions.
About the only complication is limited cutoff.
 

In case you were wondering ...
Tractive Effort is the theoretical figure obtained by the formula:
   T.E. = .85 x (P x C^2 x S) / D

where P is the normal boiler pressure 
           C^2 is the diameter of the cylinders, squared
           S is the cylinder stroke
           D is the diameter of the drivers

The factor 0.85 is a factor to allow for cutoff and inefficiencies and the loss of steam pressure in the throttle, dry pipe, superheater, and valves between the boiler and the cylinders.

-LD
 



Edited 2 time(s). Last edit at 11/18/25 10:37 by LarryDoyle.

BoilingMan Wrote:

> Good luck with that. At the Red Frog
> (overlooking Cape Horn) we’re pretty much on to
> you…
> SR

Wow!  Is the Red Frog still there?  Has the food gotten any better?  We've gone to lots of places mainly for the view, as long as the food was OK.  Frog's food was not.

For our group, we all met working for the AFT 50 (!!!) years ago, it’s more or less a central location and the view of Cape Horn is an attraction for sure. The food varies somewhat with whoever’s at the grill that day. Frog Burgers are fairly reliable, hot dogs are hot dogs, and I’ve pretty well given up on the pizza. (Costco frozen I imagine)
I don’t think much of the fries, but everyone else seems to like them okay.
There was a meatball sandwich a while back that I really liked- but it’s been missing in action for some time now.

The beer’s cold!
SR

bigsavage Wrote:
-------------------------------------------------------
> On Reading T-1 4-8-4s, it was a separate item, as
> shown on this RDG diagram.
> There is also at least 1 YT video out there that
> shows activation in the 2102 on a recent Rambles
> trip.

Please educate me.  What does "RDG" stand for?

Thanks.

It simply means Reading, the RR’s reporting mark (on freight cars etc)
SR

sf1010 Wrote:
-------------------------------------------------------
> bigsavage Wrote:
> --------------------------------------------------
> -----
> > On Reading T-1 4-8-4s, it was a separate item,
> as
> > shown on this RDG diagram.
> > There is also at least 1 YT video out there
> that
> > shows activation in the 2102 on a recent
> Rambles
> > trip.
>
> Please educate me.  What does "RDG" stand for?
>
> Thanks.
One acronym too much for you to handle?