Friday, 21 February 2014


"T-28 Characteristics:
  1. Mass: 28000 kg
  2. Suspension type: half-side long bogeys
  3. Base: L=5870 mm, L1=325 degrees, L2=262 degrees
  4. Stabilization angles: a0=4 degrees, a1=64 degrees 30', a2=57 degrees 30'
  5. Number of road wheels: 24
  6. Wheel travel: 113.5 mm
  7. Spring potential energy per ton: 9.6
  8. Modulus: 0.238 I/cm^2
  9. Effective hp per ton: 18
Note: this is not the reinforces suspension.

Evaluation of the tank:

On the robustness of the suspension.
The miserly potential energy reserve of the springs makes it easy to receive harsh blows, and destroys the suspension. Bumps 250-300 mm tall are already critical for the tank in third gear at 25 kph. 
The damage touches all elements of the suspension: balancers, levers, caps, everything up to the rivets. Since harsh blows on striking terrain are local, the carrier and road wheels, too. The overall load is comparatively small, but that should not be a cause for considering the existing robustness reserve sufficient. When the tank gets off a bump, all road wheels hit simultaneously, which deforms a series of parts. This phenomenon softens the overload. 

On shaking:
The short travel of the road wheels, large number of wheels, small potential energy reserve of the springs, and a long base result in short amplitudes of linear and angular shaking, with a large period. In terms of comfort of firing on the move, the vehicle presents a good platform.

On crew workspace:
The seats of the commander and driver are not designed for fast movement on off-road terrain.

The main idea behind the T-28's suspension is that a road wheel will share its force with other wheels in the bogey. This idea is present in the design, but only works in practice on relatively small bumps, as the wheel travel is miserly and harsh shaking happens on bumps that are 200 mm tall. When the vehicle falls at an angle, the bogey doesn't work, and the blow is very harsh to the first wheel. The kinetic energy of the entire tank, minus the first carrier's spring, is absorbed through elastic deformation of the suspension elements. 

Installation and removal are very difficult. When the outer candle breaks, the tank's skirt armour hits the ground, and makes movement impossible. In order to climb over a steep obstacle, the fenders must be removed. An advantage of the suspension is the calm movement, resulting in high precision fire on the move. A disadvantage is that half of the road wheels do not participate in the softening of the blow due to deformation of the springs. The aforementioned stresses decrease deformation and increase the harshness of the blow. 

It is reasonable to maintain the smoothness of the travel while switching to a simpler, more robust suspension.

T-29 Characteristics:
  1. Mass: 28500 kg
  2. Suspension type: individual candle
  3. Base: 3765 mm
  4. Stabilization angles:  65 degrees 40', 60 degrees
  5. Number of road wheels: 4
  6. Road wheel travel: 170 mm
  7. Spring potential energy per ton: 33
  8. Modulus: 0.224 I/cm^2
  9. Effective hp per ton: 24.9
  10. Inertia radius relative to the perpendicular axis: 2.22
Evaluation of the tank:

On the robustness of the suspension:
Due to the high energy reserve of the springs, as well as the tires, which are not counted here, the T-29's suspension is sufficiently robust, as the blow is felt far after all other tested vehicles. 
The T-29 can travel on bumps up to 0.6 meters tall at 3rd gear with almost no danger to the suspension (at 30-35 kph).
The spring stem is a weak point, as their cut is insufficient. The effective horsepower is sufficient for fast off-road movement.

On shaking:
The large spring travel of the wheel results in significant (compared to the T-26 and T-28) angular shaking, the amplitude of which is determined, in the event of a non-harsh blow, by the angle of the tank relative to its center of mass, until the full compression of the spring, in which case the harsh blow is determined by the stabilization angle and inertia. The large reserve of potential energy of the springs and tires results in large (like on BT tanks) amplitude of shaking for linear vibrations (on lower gears, the amplitude is lower than the height of the bumps on higher gears, it is higher), since the compression of the springs and rubber can throw up the vehicles to significant heights. The shaking of the T-29 is such that there is a reason to preserve this suspension design, but attempt to reduce it, with maybe a shock absorber.

On crew workspace:
The seats of the commander and driver are not designed for fast movement on off-road terrain.

The T-29 suspension type was chosen correctly.
The robustness of the suspension and convenience of maintenance are superior to the T-28.
The shaking of the vehicle is adequate. There is reason to reduce it by adding shock absorbers.

T-35 Characteristics:
  1. Mass: 50000 kg
  2. Suspension type: paired, with two degrees of freedom
  3. Potential energy of the spring per ton: -
  4. Modulus: 0.034 I/cm^2
The vehicle was not trialled. The conclusions are given as a result of calculations and logical reasoning.

The T-35 suspension allows for larger springs, allowing for a more favourable spring potential energy reserve than other paired suspensions, like the T-18 and T-46.

As expected from theoretical calculations, and confirmed by experiments, starting at 20 kph, tanks start losing contact with the ground when traversing bumps longer than their suspension travel: jumping. As a result of this, there is a strike when the tank hits the ground. The tank's movement will be characterized in two ways when moving on off-road terrain at high speeds:
  1. Non-stop jumping: losing contact with the ground and landing. Let's call this type of movement glissade. 
  2. Non-stop hard strikes from hitting bumps and falling, which leads to harsh overload of suspension elements. 
Therefore, vehicles meant to travel quickly off-road should have a high reserve of potential energy in their springs compared to static load. 

On evaluation of suspension designs:
Out of the two tested suspension designs, T-29 and BT, the T-29 is more correct."

1 comment:

  1. This was a very interesting read, as it explains some of the physical principles and engineering concerns suspension designs were working around. Bonus points for shedding some light on the somewhat obscure system used in the T-28.