To the best of our knowledge here, nothing at any time was ever done to any American built locomotive incorporating two sets of drivers under one boiler (and that includes Mallet or compound, simple articulated or duplex-drive locomotives) to allow any sort of control over synchronization of the driver sets, or prevention thereof. No control over this exists, and nothing was designed in or out to allow or prevent synchronous or asynchronous operation vis a vis driver position on differing engines.
The forces that are developed in a locomotive with two sets of drivers are no different from those developed in a single-engine locomotive, although very serious problems regarding dynamic augment are usually mitigated since the driving forces are split. For example, even with serious dynamic augment problems I've never read of any articulated locomotives pounding rail to the point where it kinked, but the NYNH&H I-5 class 4-6-4 locomotives did do this when delivered. That episode led to a thorough re-examination of Baldwin's balancing principles, and led to a general industry-wide discussion on cross-counterbalancing. The locomotives were rebalanced to a new formula including better understanding (or better consideration percentage-wise for force and mass) of cross-counterbalancing and the problem was solved.
Shortly after this, the NYC tested the J-3 4-6-4 locomotives on greased track with extensive film documentation and while the locomotive did lift all six drivers off the rail at very high speed, the speed wasn't in the normal operating range. A maximum of 164 MPH or somewhere thereabouts was achieved, machinery wise.
I recall having read that the PRR's Altoona test of the T-1 Duplex was notable not only for the power developed but for longitudinal surging of the locomotive, and that the Q-2 Duplex locomotives suffered from this to some point as well. However, although the T-1 was regarded as somewhat slippery I've also never read of any pounding to the point that the locomotives were inoperable at high speed -- in fact they did run nearly 120 MPH a few times, at least once fairly well documented. My point here is that we're looking at a different kind of effect, longitudinal instead of vertical, again related to percent balance and percent cross-counterbalance and while notable it didn't prevent operation of the locomotives as intended. (Other things did.)
Generally all of my points here are just to indicate how well balancing was understood - and you can still find this information today if you look for it. Nowhere am I aware of serious balancing problems with articulated locomotives - for the most part, as mentioned and implied, forces and operating speeds were such that any problem with balance wouldn't have been worse than with contemporary 2-8-2 or such locomotives.
While it's an oversimplification, it's important to understand that slip or spin simply due to dynamic augment won't occur unless the force being applied by rotating mass and piston thrust can overcome the force of the weight on one side of a locomotive frame and lift the drivers -- or lift the main drive axle wholly without lifting coupled axles. However, in any event nothing happens to alleviate the force of the weight so that if weight transfers to the other axles a slip usually does not occur. In fact, increase of contact patch and increase of force per unit area between driver and rail tends to reduce slip probability (absent a track perturbation) not increase it, so that with axles coupled tendency to slip is less. (As an aside, the Franklin Tender Booster, with two axles coupled, operated on the principle that when the clutch was engaged, variation in springing and leverage actually caused the truck to unload one axle of weight and transfer it to the other to increase contact and force / area, making the truck not slip even if the tender were lightly loaded.)
While the discussion of the forces that cause steam locomotive engines to pound, or slip, or surge is very interesting and deserves still to have many pages written about it, there's nothing particular per se about a locomotive having two engines, and any relation of synchronization of those engines, that merits closer examination vis a vis that synchronization at least as far as I'm aware. While the interaction of dynamic forces with two engines on one locomotive produces different overall accelerations to the locomotive as a whole as compared with a single-engined locomotive, the effect didn't require modification or control specifically.
-Will Davis
The forces that are developed in a locomotive with two sets of drivers are no different from those developed in a single-engine locomotive, although very serious problems regarding dynamic augment are usually mitigated since the driving forces are split. For example, even with serious dynamic augment problems I've never read of any articulated locomotives pounding rail to the point where it kinked, but the NYNH&H I-5 class 4-6-4 locomotives did do this when delivered. That episode led to a thorough re-examination of Baldwin's balancing principles, and led to a general industry-wide discussion on cross-counterbalancing. The locomotives were rebalanced to a new formula including better understanding (or better consideration percentage-wise for force and mass) of cross-counterbalancing and the problem was solved.
Shortly after this, the NYC tested the J-3 4-6-4 locomotives on greased track with extensive film documentation and while the locomotive did lift all six drivers off the rail at very high speed, the speed wasn't in the normal operating range. A maximum of 164 MPH or somewhere thereabouts was achieved, machinery wise.
I recall having read that the PRR's Altoona test of the T-1 Duplex was notable not only for the power developed but for longitudinal surging of the locomotive, and that the Q-2 Duplex locomotives suffered from this to some point as well. However, although the T-1 was regarded as somewhat slippery I've also never read of any pounding to the point that the locomotives were inoperable at high speed -- in fact they did run nearly 120 MPH a few times, at least once fairly well documented. My point here is that we're looking at a different kind of effect, longitudinal instead of vertical, again related to percent balance and percent cross-counterbalance and while notable it didn't prevent operation of the locomotives as intended. (Other things did.)
Generally all of my points here are just to indicate how well balancing was understood - and you can still find this information today if you look for it. Nowhere am I aware of serious balancing problems with articulated locomotives - for the most part, as mentioned and implied, forces and operating speeds were such that any problem with balance wouldn't have been worse than with contemporary 2-8-2 or such locomotives.
While it's an oversimplification, it's important to understand that slip or spin simply due to dynamic augment won't occur unless the force being applied by rotating mass and piston thrust can overcome the force of the weight on one side of a locomotive frame and lift the drivers -- or lift the main drive axle wholly without lifting coupled axles. However, in any event nothing happens to alleviate the force of the weight so that if weight transfers to the other axles a slip usually does not occur. In fact, increase of contact patch and increase of force per unit area between driver and rail tends to reduce slip probability (absent a track perturbation) not increase it, so that with axles coupled tendency to slip is less. (As an aside, the Franklin Tender Booster, with two axles coupled, operated on the principle that when the clutch was engaged, variation in springing and leverage actually caused the truck to unload one axle of weight and transfer it to the other to increase contact and force / area, making the truck not slip even if the tender were lightly loaded.)
While the discussion of the forces that cause steam locomotive engines to pound, or slip, or surge is very interesting and deserves still to have many pages written about it, there's nothing particular per se about a locomotive having two engines, and any relation of synchronization of those engines, that merits closer examination vis a vis that synchronization at least as far as I'm aware. While the interaction of dynamic forces with two engines on one locomotive produces different overall accelerations to the locomotive as a whole as compared with a single-engined locomotive, the effect didn't require modification or control specifically.
-Will Davis
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