I just found out that PRR I-1's had blind 2nd, 3rd, & 4th drivers.

(may '74 Trains Article)

Does this reduce adhesion? Can the effect be readily quantified?

I wouldn't think that they would have any significant effect on tractive effort. Any "boost" in traction that flanges provide would seem to be canceled by the friction they would add.

On the same subject, note that the Chinese QJ's (like the one recently posted on its way to Kentucky) had blind center drivers.

If your curves are really sharp enough to need the feature, you may have to install "blind driver rails" to prevent them from dropping to the inside of the curve. Examples can be seen in photos of the wreck of the PRR New York to Atlantic City train at Delair, N.J. in 1943.

Do you mean blind driver tires instead of "rails?" Typically, locomotives with blind drivers had wider tires. I believe this feature can be seen on the PRR M1 at RRMofPA in Strasburg.

Yes, indeed, he meant rails. Although blind driver tires are wider, some curves are so sharp that the center driver could fall off the rail inside or outside the gauge. I supervised the rebuilding of a siding into a feed mill in Mifflinburg, Pa. some years ago which featured such rails on the inside and outside of the gauge on the S-curve off the main into the mill. The usual freight power on the branch was H-9 and H-10 2-8-0's and G-5 ten-wheelers.

I would also note that at the former PRR roundhouse in Northumberland, Pa., several sharp curves featured wooden crossing "logs" placed to support the blind drivers of the I-1's that inhabited the building.

Hello Gentlemen,
In reviewing R.P. Johnsons chapter on Tractive Effort, there is no reference to the impact of flanged vs. blind drivers on tractive effort.
There is comment on the factor of adhesion, but even there it is only concerned with rail condition and wheel materials.
The basic formula is:

T= K x P x C(squared) x S
___________________
D
K= A factor relating to Pressure drop from the boiler to the cylinder
P=Boiler Pressure
C=Diameter of the cylinders
S=Stroke
D=Driving wheel diameter
T=Tractive effort
Throughout the entire commentary(some 35 pages) there is no reference made to the absence of flanges or any influence otherwise.
From experience, the flanges DO impact the rolling resaistance of a locomotive, however the term Tractive Effort as defined by Johnson is "...the calculated,theoretical starting force". Further, more eloborate equations from other sources (i.e. AAR, Goss, Cole, Kiesel) also do not take into account the aspect of flanges or the lack thereof.
Hope this is of some help.
Respectfully,
Dave Griner
wasatch-rr-contractors.com

I do mean rails for the blind drivers. On a sharp enough curve, with a long enough rigid wheelbase, they won't be on the running rails! The junction at Delair, N.J. was a PRR example. The particular curve was used by the Nellie Bly and other express passenger trains between New York and Atlantic City.