"British Embassy, Moscow
British Military Mission in the USSR
Moscow, May 15th, 1944
To: Mr. Lieutenant General Lebedev
Copy: Mr. Chief of the NKO Department of External Affairs
The War Ministry asked me to provide it with brief information on the suspension of the Ferdinand self propelled gun. It is especially interested in the diameter and length of the torsion bars, their position, and the distance between the axles. A diagram with specified sizes would be very valuable, especially if accompanied by a description of the performance of the suspension.
I would be most grateful if you supplied me with the aforementioned data.
Lieutenant General, Head of the British Military Mission in the USSR."
"Suspension of the Self Propelled Gun "Ferdinand"
The suspension of the Ferdinand self propelled gun consists of six bogeys, three per side. All bogeys are identical and interchangeable. The rear bogeys are turned by 180 degrees compared to the front two bogeys on each side.
The bogey design is as follows:
- Torsion bar tube
- Suspension arm
- Rubber pad
- Torsion bar
- Front wheel axle
- Rear wheel axle
- Front wheel
- Rear wheel
- Upper lug
- Dry liner
- Lower lug
Performance of the suspension
a) Installation of the bogey
Fig. #2. The suspension under static load.
When the bogey is installed on the vehicle, the weight of the vehicle on one bogey causes the suspension arm to turn relative to the center of the front wheel. The axle of the front wheel turns with the suspension arm. The lugs on the axle and the dry lines will twist the torsion bar.
As the suspension arm turns, the rubber pad will eventually hit the torsion bar tube, and further turning of the suspension arm will deform the rubber pad, as well as twist the torsion bar.
b) Elevation of the front road wheel
Fig. #3: The suspension with the front wheel elevated.
When the front wheel drives on top of an obstacle, the torsion bar turns clockwise around the axle attached to the hull of the vehicle. The elevation of the front wheel axle causes the torsion bar tube to rotate around the axle of the rear wheel, which moves to the left.
The turning of the suspension arm causes further deformation of the rubber pad. The lugs and dry liner cause the torsion bar to twist further.
After the rubber ceases to deform, the suspension arm can no longer move relative to its axle as the front wheel elevates, as the right end of the suspension arm is up against the torsion bar tube, and the torsion bar can no longer twist. The suspension begins to act as a rigid system, transferring all shocks to the hull of the vehicle. The torsion bar can twist only as long as the rubber pad can deform.
c) Elevation of the rear wheel
Fig. #4: The suspension with the rear wheel elevated.
When the rear wheel elevates, it turns the torsion bar tube around the axle of the front wheel due to deformation of the rubber pad. The suspension arm, and therefore the front axle and upper lug remain still, impeding the elevation of the lower lug, which it attached to the torsion bar. As a result, the torsion bar twists. After the rubber pad ceases to deform, further elevation of the wheel does not twist the torsion bar. All shocks will be rigidly passed on to the hull of the vehicle."