Porche’s X-shaped engine

German tank development followed a very predictable course. This included engine development. After experiments in the 1920s and early 1930s, German tanks settled on the Maybach V-shaped series. These gasoline engines that worked at high RPM (about 3000) were characteristic for German tanks. They were used until the end of the war, although some began to think about an alternative as early as 1941-42. Ferdinand Porsche was among those who had his own idea about what a tank engine needs to look like.

Simmering-Graz-Pauker is best known as a producer of train cars and locomotives.

The first attempt to build a diesel engine was undertaken by Daimler-Benz in 1940. The MB 809 and later MB 507 were unlucky. Work on diesel engines was not abandoned. Porsche K.G. picked up the relay, working closely with Austrian companies. The new team created a brand new engine known as the Simmering-Graz-Pauker Sla 16. This was an X-shaped air cooled diesel engine which opened a whole new direction in development of tank engines. However, Germany did not have time to make use of the fruit of this labour.

The predecessor of the SLa.16 was initially developed for the Typ 205, shown here in its configuration as of October 1942.

Limping Jagdtiger

The German Jagdtiger tank destroyer was built in two variants: one with a Porsche suspension and one with a Henschel one. The former was deemed poor and removed from production. This fact is stated in every publication dedicated to the Jagdtiger, but is not discussed in detail. In this article we won't stop at brief descriptions, questionable overviews, and conclusions, but instead will discuss how German late war tank suspensions were developed, cover the Porsche suspension, then present the history of the Jagdtiger's suspension in the appropriate context. Our tale will be based on an analysis of the design rather than compilations of opinions of other authors.

Lever Forces

Driving a tank is not like driving a car. In order to turn, you do not simply turn a wheel, but must wrestle with levers controlling an engine with many hundreds of horsepowers, dragging a beast that weighs tens of tons. That is not an easy task. CAMD RF 38-11355-2884 (from litl-bro's repository) covers the forces involved in driving a T-34-85 and an IS-3.

The span the levers travel was divided into 6 equal parts. Forces for the first 5 include only the force to move the lever, but forces for the last part include the force to bring the friction clutch into action and stop the tank completely.

The first vehicle that is tested is a T-34-85 #381105 from factory #112 (Krasonye Sormovo). This tank travelled 1010 km before this test. 

Lever position	Force in kg		Difference in kg
	Right lever	Left lever
1	21.5	24.0	2.5
2	26.0	30.0	4.0
3	28.5	33.0	4.5
4	34.0	37.0	3.0
5	33.0	37.0	4.0
6	29.0	34.0	5.0

Now, for turning the tank in place.

Gear	Force in kg		Difference in kg	Turn radius
	Right lever	Left lever
1	37	34	3	In place (180 degrees)
2	40	38	2	Same
3	40	39	1	8 meters (extrapolated from 90 degree turn)

Next is another T-34-85, #872024, from factory #174 (Voroshilov factory). This tank travelled 1002 km before these trials.

Lever position	Force in kg		Difference in kg
	Right lever	Left lever
1	26.0	24.5	1.5
2	29.0	30.0	1.0
3	33.0	32.0	1.0
4	37.0	37.0	0
5	37.0	37.0	0
6	35.0	35.0	0

Gear	Force in kg		Difference in kg	Turn radius
	Right lever	Left lever
1	42	39	3	In place (180 degrees)
2	46	44	2	Same
3	46	45	1	8 meters (extrapolated from 90 degree turn)

Next is a T-34-85 #664479 from factory #183 (HPZ). The tank was basically new, just out of factory trials, and travelled 100 km. 

Lever position	Force in kg		Difference in kg
	Right lever	Left lever
1	23.0	23.5	0.5
2	28.5	27.0	1.5
3	30.0	29.0	1.0
4	35.0	35.5	0.5
5	37.5	37.0	0.5
6	36.0	34.5	1.5

Gear	Force in kg		Difference in kg	Turn radius
	Right lever	Left lever
1	38	36	2	In place (180 degrees)
2	44	41	3	Same
3	44.5	44	1.5	8 meters (extrapolated from 90 degree turn)

As you can see, the new tank does a little bit better. 

Now, for the IS-3. The tank travelled 500 km before trials. The lever range was split into only three sections:

1. From the initial position to first position (the planetary mechanism friction clutch is off, the small brake belt is taut).
2. First position to second (brake belt of the stopper drum is taut).
3. Brake belt of the stopper is at maximum tautness. 

Lever position	Force in kg		Difference in kg
	Right lever	Left lever
1	32	30	2
2	16	16	0
3	30.0	30	0

The IS-3 is heavier, but more modern. As a result, driving it does not take more force than driving a T-34, and sometimes, much less force.

Lever position	Force in kg		Difference in kg
	Right lever	Left lever
1	23.0	23.5	0.5
2	28.5	27.0	1.5
3	30.0	29.0	1.0
4	35.0	35.5	0.5
5	37.5	37.0	0.5
6	36.0	34.5	1.5

Now, for turning around:

Gear	Forces to move the lever from the initial position to the first (smooth turn)		Turn radius in meters	Forces to move the lever from the first position to the full position (turn in place)
	Right lever	Left lever		Right lever	Left lever
1	30	29	14	25	25
2	29	27	14	22-35	22-35
3	28	28	15	20-40	20-40
4	26	26	15	18-40	18-40
5	24	24	Maneuver not performed
6	20	23
7	16	20

CAMD RF 38-11355-2890 contains similar measurements for a much larger set of tanks. The conditions for turning around are different: instead of a half-turn or a quarter-turn, tanks made multiple turns. The first turn did not count, and only the subsequent turns (where the mud that was removed by the first turn did not affect the trial) were recorded.

The following tanks underwent trials:

• T26E3 (Pershing), having travelled 1030 km
• M4A2(76) (Sherman), 4000 km
• M24 (Chaffee), 1200 km
• Jagdtiger, 260 km (this specific one)
• Panther, 648 km
• Tiger H, 900 km
• Comet, 1100 km
• T-34-85, 1010 km
• T-44, 570 km

First, the tanks that can neutral steer:

Name	Right lever forces	Left lever forces	Difference	Note
Panther	5	5	0	Tank turned easily
Jagdtiger	5	5	0	SPG turned easily
Comet	20	21	1	Tank turned after three attempts

Then all of them in first gear.

Name	Radius (meters)	Right lever force	Left lever force	Difference
T26E3	9.5	35	34	1
M4A2(76)	10	30	30	0
M24	7	12	11	1
Panther	6	6	6	0
Jagdtiger	7	4.5	4.5	0
Comet	3	16	18	2
T-34-85	In place	32	34	2
T-44	In place	13	12	1
IS-3	In place	41	39	2
Tiger H	6	13	14	1

The next table's turns were also done in first gear, but for a radius of 10 meters (the worst radius in the previous table).

Name	Right lever force	Left lever force	Difference
T26E3	34	32	2
M4A2(76)	30	30	0
M24	13	14	1
Panther	5	5	0
Jagdtiger	5	5	0
Comet	14	15	1
T-34-85	30	30	0
T-44	11	10	1
IS-3	32	32	0
Tiger H	10	12	2

Let's try a slightly easier task, turning in first gear with a 15 meter radius.

Name	Right lever force	Left lever force	Difference
T26E3	22	25	2
M4A2(76)	22	23	1
M24	9	9	0
Panther	5	5	0
Jagdtiger	5	5	0
Comet	12	12	0
T-34-85	27	29	2
T-44	10	10	0
IS-3	30	31	1
Tiger H	10	12	2

Minimum radius again, this time in second gear:

Name	Right lever force	Left lever force	Difference
T26E3	37	39	2
M4A2(76)	34	35	1
M24	16	17	1
Panther	12	15	3
Jagdtiger	5	5	0
Comet	19	21	2
T-34-85	35	36	1
T-44	11	12	1
IS-3	32	33	1

"Conclusions

1. The most effort is required to turn the IS-3 (30-41 kg), T26E3 (23-39 kg), T-34-85 (27-36 kg) and M4A2-76 (22-35 kg).
2. The least effort is required to turn German tanks T-V (5-15 kg), T-VI (10-14 kg), English "Comet I" tank (12-20 kg), German Jagdtiger SPG (5-14 kg) and domestic T-44 tank (10-13 kg).
   The T-V, T-VI, Jagdtiger, and Comet require little effort due to a hydraulic servo and a special turning mechanism design (planetary mechanisms with additional power input from the engine).
   The T-44 requires little effort due to altered input levers and a servo spring.
3. The M4A2-76 requires less effort than the T26E3, despite similar design. This is due to the tank's smaller size and longer lever lengths.
4. The T-V, T-VI, Jagdtiger and Comet tanks can turn in place when the gearbox is set to the neutral gear due to a special planetary turning mechanism with additional power input from the engine. 
5. Turning domestic T-34-85 and IS-3 tanks, as well as American T-26 and M4A2-76 tanks requires great effort, and tires out drivers during long marches."

For those of you that think 35-40 kg is high, the effort required to turn a Pz38(t) reached 60 kilograms, according to Aleksei Kalinin's Panzerkampfwagen 38(t), Tactical Press, Moscow, 2013, page 125.