Friday, 28 March 2014

Lend Lease Impressions: M18 Hellcat

Many vehicles were sent to the Soviet Union, underwent trials, and then were not selected for further orders. The M18 Hellcat (or T70 GMC, since this particular vehicle predates the standardization under the name "M18") was one of them.



"Summary

The American T70 SPG cannot be recommended for import for the following reasons:
  1. Light armour, protecting from only rifle bullets and small shell fragments.
  2. High fuel consumption:
    1. Highway: 78.5 L/hour
    2. Dirt road: 80.5 L/hour
    3. Off-road, over snow: 130.7 L/hour
      This is several times higher than the fuel consumption of other vehicles of this class in the same conditions.
  3. Using high quality gasoline as fuel makes the SPG fire prone.
  4. The off-road performance is poor.
Conclusions
A series of trials of the American T70 SPG determined that:
  1. The maximum speed is 75.6 kph.
  2. Sharp braking of the vehicle in motion faster than 45 kph results in skidding.
  3. Average speed:
    1. Highway: 43 kph
    2. Dirt road: 23.8 kph
    3. Off-road, over snow: 19.4 kph
  4. The speed of the vehicle on a paved road is limited by its insufficient stability, especially on a highway coated with iced over snow.
  5. The speed of the vehicle on dirt roads and snow is limited by the impossibility of using higher gears, due to insufficient flywheel moment produced by the hydraulic transformer.
  6. The fuel consumption is:
    1. Highway: 78.5 L/hour
    2. Dirt road: 80.5 L/hour
    3. Off-road, over snow: 130.7 L/hour
      Which is several times higher than the fuel consumption norms of vehicles of this class.
  7. The vehicle cannot cross roadside ditches or large craters due to insufficient flywheel moment of the hydraulic transformer.
  8. The maximum grade the vehicle can climb on iced over ground is 16 degrees. Higher grades cannot be climbed due to tracks losing contact with the ground. In identical conditions, the SU-76M can climb up a 26 degree grade.
  9. The maximum acceptable grade for going downhill is 24 degrees on snow.
  10. The vehicle cannot tow other vehicles of the same weight class on difficult terrain due to insufficient flywheel moment of the hydraulic transformer.
  11. The maximum tilt angle before the vehicle slips is 18 degrees.
  12. The maximum fording depth over solid ground without preliminary preparation is 1.55 meters. Larger depths cannot be forded due to water entering the engine compartment through the engine grille.
  13. The gun has good precision. At a range of 1200 meters, average horizontal deviation is 0.16 meters and vertical deviation is 0.1 meters.
  14. The muzzle velocity of the AP-tracer shell is 803 m/s.
  15. The angle of flight of the AP shell is negative: -3.6 degrees.
  16. The SPG has adequate stability when firing. After firing, the vehicle recoils negligibly.
  17. After a shot, the aiming offset is insignificant, 0-005 elevation, 0-02 traverse.
  18. Firing from short stops is possible and effective.
  19. Firing on the move is ineffective.
  20. The maximum rate of fire of the SPG is 11.4 RPM.
  21. Aimed rate of fire:
    1. Without shifting targets: 9.7 RPM
    2. With shifting targets: 7.7 RPM
  22. The maximum force on the aiming mechanisms while the vehicle is in a horizontal position is 1.0-4.5 kg for elevation, 1.5 for turret traverse.
  23. All gun mechanisms worked flawlessly and had no defects.
  24. The gunner's position is comfortable.
  25. The loader's position is cramped, and does not allow for efficient operation.
  26. The commander's position, due to a lack of commander's periscope, and insufficient protection from shell fragments and bullets, does not provide for comfortable and safe work.
  27. The driver's position and the position of his assistant are comfortable. Both crewmen can shift gears.
  28. The ammunition rack is inconveniently placed. Out of the 45 shells, only 9 are readily available for the loader. The rest cannot be swiftly used for shooting.
  29. The vehicle is reliable. No components or mechanisms of the vehicle broke during trials.
  30. In difficult terrain conditions, the hydraulic transformer does not fully pass on the flywheel moment from the engine to the transmission, reducing the speed and fuel economy of the vehicle.
  31. The double differential reduces maneuverability and stability of the vehicle. 
  32. The attachment of idlers and drive wheels ensures that tracks are taut regardless of the road conditions.
  33. The silent block connectors of track links prevents wear of the track pins.
  34. Wear on the track pins is insignificant and is equal to 0.2-0.6 mm.
  35. Unlike the SU-76M, the hydraulic double shock absorbers dampen the vehicle's oscillations.
  36. The adjustment mechanisms for the brakes and gearbox are convenient, and allow for easy adjustments.
  37. Replacing components (engine and transmission) is possible in field conditions, due to available hatches.
  38. Use M3 aircraft oil for the engine, double differential, and final drives. Use lubricating oil for the gearbox and hydraulic transformer.
  39. For fuel, use KB-70 gasoline with an addition of R-9 ethyl fluid (3 cubic centimeters per kilogram).
  40. The instruments supplied with the SPG are sufficient for full technical service."

2 comments:

  1. "At a range of 1200 meters, average horizontal deviation is 0.16 meters and vertical deviation is 0.1 meters." The dispersion of the US 76mm gun.

    ReplyDelete
  2. That is one accurate gun!

    ReplyDelete