I apologize if this covers material or opinions expressed in previous threads or posts.

As part of the discussion of Matt Austin's post on the double Belpaire boiler, this was asked:

> It would be great if the T1 group would consider the Double Belpaire
> boiler and Franklin's long compression poppet valve gear that was also
> a feature of Lima's proposed 4-8-6. And if they would incorporate
> the ACE3000's balanced opposed cylinder drive, they would have a design
> more than capable of 130 mph. But of course it wouldn't be a T1.

In order to avoid hijacking or distracting from that thread, here is a discussion just of T1 issues.


The double Belpaire will not fit on a T1, due to the interference between the lower Belpaire 'hips' and the 80" drivers. Much of the advantage of the wider throat can be achieved, if needed, by use of the Cunningham circulators (which move the 'upcoming' circulation source in the legs to the effective downcoming circulation regions in the convection section).

The long-compression valve gear is not particularly different externally from the type B that was used on engine 5500. I do expect that with modern materials, some of the 'line contact' issues in providing variable cam profiles for a spherical follower can be overcome, especially in a locomotive expected to see only limited and special service. Much of the work PRR did around 1948 to fix the valve-breakage problems on the type A T1s (for example, centrifugal casting of the valves) can be adapted to the rotary-cam version as well.

On the other hand, I have to wonder if some of the approach in the type D system (which uses duration of lift in a modulated way to simulate "cutoff" characteristics in a speed-dependent way) might be more workable than a continuous-contour shifting cam setup. As mentioned, most of the pieces on the surviving type D instantiation are 'right-sized' for one engine of a T1...

In my opinion, the Withuhn conjugated duplex, as described in the ACE patent literature, is not ideally suited to a high-speed express locomotive, and I personally favor the adoption of a Riley-Deem-style geared conjugation arrangement (detent-phased 45 degrees or 135 degrees rather than synchronized, to give eight rather than four torque peaks per revolution) for which there is room when type B outside gear drive to the camshafts is used.

I don't consider the application of geared conjugation to a T1 sufficient to justify a "T2" designation... or even a T1b. Note that PRR did not see fit to give 5500 a different designation, although it gave the piston-valve conversion the 'T1a' class.

If there is a "T2" the drive will almost certainly be retained as conventional duplex; the likely difference being that (as on the S1) the drivers would be taken up to 84" and all four mains and piston rods will be equal length, with the cylinder blocks immediately ahead of the leading driver pair. Conjugation would likely remain between the main driver axle of the forward engine and the leading driver axle of the rear engine. The lateral-acting independent brake as a means of slip and traction control would be fitted in addition to tread braking. It remains to be seen whether vertical clearance issues would permit the use of a higher-pitched boiler.

There is very little question that a T1 built with dynamic zero reciprocating overbalance will be capable of 130-mph-plus speeds. Whether it is appropriate to run a reciprocating steam locomotive at those speeds (other than on a dynamometer) is a very different question.

I'd improve the T1 by making it an SP AC-9 as it worked in service out of El Paso.

Robby

Wondering just how many folks here could follow all of that without having to do at least some research....

It was a little salty, wasn't it?

The Withuhn conjugated duplex system was described in Trains Magazine and also in patent 4 426763. Hugh Odom has a good page at

http://www.trainweb.org/tusp/ult.html

at the end of which are links to a technical paper and the patent (scroll down a bit in the patent page and it gives you a .pdf download link).

The problem for high speed is that the inside conjugating rods must be cranked on the main drivers. This in my opinion would either substantially weaken them in torsion or require a type of 'tunnel crank' with comparativelly large roller bearings and boxes. The alternative proposed by Riley Deem, a Lima engineer (to address the slip issue on Q2s without using the butterfly servo valves) was to gear the two engines together rather than use rods; this system is not dynamically balanced in all planes like the Withuhn system, but more easily accommodates for differential driver wear and suspension motion (there is a reason the ACE patent makes so much out of regular driver machining to keep all the diameters equal!)

I had to reproduce the Deem system from first principles, with the partial assumption that only conjugating forces have to run through the gear, and that to maintain some of the value of the duplex principle the engines should only 'lock' together when one of them is actually slipping. This can be done with a Ferguson viscous clutch, or magnetorheological clutch, which engages progressively when differential rotation occurs.

Since I also recommend a fast-acting version of independent brake on each engine, the lock-up time of the conjugating system can be comparatively long; its primary use is for slippery conditions at low speed, where an effective '4-8-4' is easier to handle, and for unattended management of high-speed slip propagation, where countertorque needs to be passed to an engine that has momentarily broken adhesion to keep it from merrily spinning up to high cyclic rpm, but it would be 'counterproductive' to brake the wheelrim to prevent this acceleration.

The non-fancy description of phasing is that the cranks of the two engines are set via soft detenting in the conjugation mechanism to run 45 degrees apart, either with respect to angle, or to keep the direction of vertical acceleration of the rodwork masses roughly balanced on each side of the locomotive. I expect to do some computer modeling of these configurations to see how much actual difference there would be at very high speeds.

There are several methods to manage vertical 'augment' forces remaining in the drive assembly, but they all involve fairly high forces in the main driver axles (at least comparable to forces in the main pins, which you may note were progressing to an alarming extent in large American power developed late in the game, the Milwaukee F7 and the Niagara being two examples.

The type A Franklin valve gear on the T1s used derived crosshead drive to what was essentially a little set of radial valve gear enclosed in a box, which then drove an oscillating camshaft. Cleverly, all this was incorporated in the frame casting; not so cleverly, you could only get into this box from the top... which involved getting in between the boiler and frame to work on the things. On the rear engine this box sits exactly where the donjugating shaft of a Deem system has to run.

The type B system's drive is like Reidinger valve gear in that the camshaft runs through the center of the cambox, over the cylinders, and is driven from its ends via Cardan shaft drive from a gearbox centered on an external return crank. This is entirely external, relatively easy to adjust and maintain, and makes the frame design MUCH simpler. It would appear that the very heavy support brackets used on historical examples of type B were not strictly necessary; the system on the surviving type D locomotive is much lighter although no less competent.

The valid question:

At what point in this process of "improvements" do you effectively cease to be "replicating" a PRR T1, and how much support from "slobbering Pennsy foamers" do you thereby lose as a result?

As much as I may support the idea of creating an "improved design modern steamer" to keep the "torch" of main line steam burning bright, it seems that if you pitch the idea of replicating a PRR T1 to the masses and then turn around and build something totally new that only superficially looks like a T1, you're going to turn off a lot of potential supporters.

I saw some of this in play with the PRR 1361 restoration in the 1980s, when a lot of folks who put money into the project expressed disappointment (to understate it quite) that they weren't seeing 1361 in full cry on the PRR main line or around Horse Shoe Curve, and were aghast at suggestions that it go over to the likes of the New York & Long Branch for some operations.

Skip the T1 and build a Pennsy Q2. An equally gorgeous and under-developed locomotive.

Valid question indeed.

The T1 replication is not about building the locomotive 'warts and all' just to see if all the problems were really as bad as folks said they were. Where there are known problems, there are fixes. Remember that at this point in the design, it's important to make sure that every problem, reputed or recognizable, has at least one good, buildable solution.

As noted, the Trust has already decided not to use the lateral-acting independent brake, because it would provide a manifestly non-original appearance in service. However, it's likely that some expansion of firebox and chamber size will be made, to suit the engine better for general operation and permit use of some of the alternative fuels.

Part of the approach -- and I understand where this clashes with a strict preservationist approach -- is that the improvements will be internal or invisible for the most part, and generally acceptable to anyone but PRR rivet-counters otherwise. Use of modern Timken bearing technology and M-942 grease lubrication is 'unprototypical' technically; are you going to complain to the Fire Up 611 people because they're modernizing the engine-truck bearings? The boiler convection section is likely to be all-welded, with different steel from the (disastrous) alloy originally used -- even PRR would likely have gone to welded construction had the T1s been kept in first-line service into the early '50s, and even if not, a number of roads had to build or commission replacement boilers PDQ (including, interestingly enough, ATSF 3463).

The choice of 5500 as the 'prototype' was intentionally made to facilitate the use of outside valve drive. Deem's original proposal for the Q2 was, I believe, around 1949, answering the evolving maintenance problem with the butterfly system; if the high-speed slipping problem with the T1 is as serious as I suspect it to be, sustained high-speed operation of the engine may involve some sort of 'automatic' slip management acting within a partial driver revolution, but not involving rapid change of either the throttle position or the effective cutoff (high-speed slipping as I expect it to show itself is not usually a continuous-adhesion issue requiring cutoff or throttle 'trim')

Wagner throttles to 'bias' the forward engine slightly when starting or running in slippery conditions are a 'better' solution then downsizing any portion of the steam circuit to the forward engine, or sleeving the cylinders there. They also represent contemporarily available technology

The principal area I can think of where there's going to be 'unprototypical' change is in the cylinder jacketing, which I expect to be 'fatter' with better lagging and overcritical water circulation. Again, the Truat hasn't decided if those features would be included on the actual locomotive 5550 as built, although I consider them significant.

The Snyder preheaters have what I consider a minimal visible effect; the Cunningham manifolds do represent some additional piping, but these are contemporary devices that PRR might well have chosen to apply to the T1s to improve them in service. (They are also fairly easily removed with little visible 'footprint' if unwanted for a given purpose...)

One key discussion is whether or not to retain use of a one-piece cast engine bed, at high cost and relatively lower assured quality compared to a fabricated frame, to maintain prototypical integrity. I don't see major harm in doing the frame differently; others may of course differ and not be wrong. Whatever the chosen frame design is, it will be extensively modeled and virtually tested before anything is actually fabricated, and at that time I expect more pointed discussions about available choices and what they entail.