How did the Chinese solve the balancing problem on the 2-10-2?

[Overmod]

Ah yes, Wikipedia.  Note how many things are wack in that description.

It's precisely when the drive is on the third axle (of the 2-10-2) that the 'nosing' is most extreme, this not only being at the worst position relative to the yaw axis, but also because a longer (and by definition more massive, and therefore possessed of greater inertia) main is required.  

On the other hand, a longer main gives better rod angularity, which is why the very latest Berks also had the drive on the third axle back of the cylinders.

In my humble opinion, it would be very unwise to draw conclusions about 2-10-2s using Prairies as the dynamic example.

Note the Wikipedia 'weasel words' 'if unrestrained either by a long wheelbase of by the leading and trailing trucks', which applies to early Prairies but not even the later ones with improved guiding (as on the LS&MS, not exactly poster children for either slow or yaw-ridden locomotives!)

The issue at the rear really had to await the second flavor of Delta truck (see Alfred Bruce's book for the construction details) which provided positive control far behind the trailing axle.  The advances with leading axles were pretty much applied to 2-10-4s... which are the evolutionary step forward from Santa Fes just as Berkshires are an advance on Mikes.  The proper dynamics remain the same, though, in keeping the point of action as far outboard in the rigid frame as you can manage.  And not, not, not using springs for side control.

There is a rather famous story about a Reading 2-10-2 that was more than usually prone to nosing even at low speeds (look at a picture of one and you'll understand why!)  Someone in the P&R design department... probably the same bright spark who tested that double-pin-guided 4-4-4 disaster of about the same vintage... decided that positive side control of the lead truck would help the situation, and used two stiff springs opposing each other in the lateral plane to give compliance and at least some measure of progressive loading.  This is OK so far, but he forgot (1) about SHM in springs, and (2) about any damping other than friction.  The thing built up track-kinking levels of resonance quickly, and often; the story goes that one of the Reading mechanics actually met the engine about 70 miles into its maiden voyage and torched the spring mechanism so it no longer 'aided' things.

For a good guide in how to build a 2-wheel lead truck, look at the design on N&W 1218.  This very neatly separates truck roll and swing from equalization, and uses progressive loading with the engine's weight for the side and restoring control.  (The 'missing' piece for high speed was apparently tested in the '50s by using 'Fabreeka' composite shear springs like those on centipede tenders -- but I have so far been unable to find hard results from that testing...)

Look at the methods used to 'tame' T&P 610 in 1938 (available in a 'free' bundle of articles online) and you will see how much of the nosing problem was addressed.  (This is particularly valuable looking at 610, because she kept the weird articulated Woodard trailing truck that gives very little effective 'steering' against yaw to the back of the abbreviated main frame, making the locomotive act like a 2-10-0 with very long overhang...)

RME

[GP-9_Man11786]

Overmod

Is that "Iowa" a Freudian slip?  ;-}

[Note:  I am not a QJ expert.  More specific information should be available from Iowa Interstate or Corman people (who were very knowledgeable about the valves, and should know suspension and guiding issues better than about any other English-language reference source), or perhaps in Wardale's Red Devil book.  Ask this question over on RyPN, too]

Do you mean the balance problems inherited from the Russian design?  Or something more recent?

I don't recall the QJs being used in service at high speed, but the 'usual suspects' approaches: lighter Boxpok wheels, less lateral distance and lighter mass in the rods, and so forth would have applied.  

When there is not a high-speed augment problem, the traditional way to deal with 'nosing' in balancing is to overbalance more of the reciprocating component of the mass of the main rod, crosshead, piston and rod, etc.  This reduces the effect of the inertial force (far greater than the steam thrust on the piston!) that tends to rotate something like a 2-10-2 about its yaw center.

Better lateral compliance on lead and trailing trucks is probably a more important part of the situation -- it certainly was developed to a high degree on N&W power in the '50s.  'Catch' for the QJs is that they have inside-bearing lead trucks, and there's a limit on how effectively the lateral can be applied there (as opposed to an outside-frame truck).  Certainly the Delta-type trailer gives very effective compliance at that 'end', as the centering rockers or cams or whatever are about as far back in the chassis as they can be, and have a proportionate lever arm to work on.

My first step, if there is indeed a remaining 'nosing' or 'hunting' (yaw coupled with roll) couple in the vehicle dynamics, would be to provide a proper outside-bearing truck, and stiff lateral control.  As on the J's, this would increase the effective rigid wheelbase for short-period motion, and probably limit some of the effective cross-level suspension travel -- so you would need better track stiffness or strength in the horizontal plane, and good control of line, level, and cross-level in the track alignment.  (But I do not recall those elements being 'wanting' on the lines where the QJs last ran in China).

The chief thing to watch is to avoid resonance effects that build up the yaw or other motions.  That might involve determining where any 'critical speeds' are, and avoiding them in use.

The "Iowa" was autocorrect mageling the word "how." Anyway here's how Wikipedia explained the balancing problem I s referring to:

"As with the 2-10-2, the major problem with the 2-6-2 is that these engines have a symmetrical wheel layout, wherein the centre of gravity is almost over the center driving wheel. The reciprocation rods, when working near the center of gravity, induce severe side-to-side nosing, which results in severe instability if unrestrained either by a long wheelbase or by the leading and trailing trucks. Though some engines had the connecting rod aligned onto the third driver, like the Chicago and Great Western of 1903, most examples were powered via the second driver, hence the nosing problems remained with the type.^["

[Overmod]

Is that "Iowa" a Freudian slip?  ;-}

[Note:  I am not a QJ expert.  More specific information should be available from Iowa Interstate or Corman people (who were very knowledgeable about the valves, and should know suspension and guiding issues better than about any other English-language reference source), or perhaps in Wardale's Red Devil book.  Ask this question over on RyPN, too]

Do you mean the balance problems inherited from the Russian design?  Or something more recent?

I don't recall the QJs being used in service at high speed, but the 'usual suspects' approaches: lighter Boxpok wheels, less lateral distance and lighter mass in the rods, and so forth would have applied.  

When there is not a high-speed augment problem, the traditional way to deal with 'nosing' in balancing is to overbalance more of the reciprocating component of the mass of the main rod, crosshead, piston and rod, etc.  This reduces the effect of the inertial force (far greater than the steam thrust on the piston!) that tends to rotate something like a 2-10-2 about its yaw center.

Better lateral compliance on lead and trailing trucks is probably a more important part of the situation -- it certainly was developed to a high degree on N&W power in the '50s.  'Catch' for the QJs is that they have inside-bearing lead trucks, and there's a limit on how effectively the lateral can be applied there (as opposed to an outside-frame truck).  Certainly the Delta-type trailer gives very effective compliance at that 'end', as the centering rockers or cams or whatever are about as far back in the chassis as they can be, and have a proportionate lever arm to work on.

My first step, if there is indeed a remaining 'nosing' or 'hunting' (yaw coupled with roll) couple in the vehicle dynamics, would be to provide a proper outside-bearing truck, and stiff lateral control.  As on the J's, this would increase the effective rigid wheelbase for short-period motion, and probably limit some of the effective cross-level suspension travel -- so you would need better track stiffness or strength in the horizontal plane, and good control of line, level, and cross-level in the track alignment.  (But I do not recall those elements being 'wanting' on the lines where the QJs last ran in China).

The chief thing to watch is to avoid resonance effects that build up the yaw or other motions.  That might involve determining where any 'critical speeds' are, and avoiding them in use.

[GP-9_Man11786]

Iowa did the Chinese overcome the balance problem and tendency to nose in their QJ 2-10-2s? I know the problem was inherent to the wheel arangent as ell as the 2-6-2. That's why most American 2-10-2s were slow-speed locomotives.