Mercedes-Benz T80

Posted by: bannarit in Member Blogs

 

The story of the LSR set on a public highway reminded me of another attempt to again break the record on a similar venue. I did some research and this is the result.

One of the most successful German auto racers of the pre WWII period, Hans Stuck, was determined to set the world's Land Speed Record (LSR), and convinced M-B to build a special racing car for the attempt. The fact that Stuck was a favorite of Hitler, who himself was a racing fan and officially sanctioned the project, may have had something to do with M-B's agreement to take on the project. As the record attempt was to be made on German soil, Hitler viewed the project as another potential propaganda triumph of German technological superiority. This was to be another LSR attempt carried out on a public highway rather than a race course. Stuck was to drive the car over a special section of the Dessau Autobahn (now part of the A9 Autobahn) which was 25 m (82') wide and 10 km (6.2 miles) long with the median paved over.

Planning began in 1937 with the selection by M-B of Dr. Ferdinand Porsche as the mechanical designer, and the aircraft designer and aerodynamics specialist Josef Mikci responsible for the body design. The car was to be called the T80. Porsche first envisioned a maximum speed of 550 km/h (340 mph), but after George Euston's and John Cobb's successful LSR run of 1938-39, the target speed was raised to 600 km/h (373 mph). By the completion of the project in late 1939, the target speed was made still higher at 750 km/h (465 mph).

The powerplant chosen was the Daimler-Benz DB 603 inverted V12, derived from the DB 601 aircraft engine which powered, among other models, the Messerschmitt Bf 109, one of the most lethal fighters in the Luftwaffe. In fact, the DB 601 powered a Messerschmitt Me 109 to a world's speed record of 754.6 km/h (468.9 mph) in 1939. While the 601 had a displacement of 33.9 L (2,069 CID), weighed 700 kg (1,540 lb) dry, and developed 1,360 HP at 2,600 rpm, the 603 displaced 44.5 L (2,715 CID), weighed 910 kg (2,002 lb) dry, and had an output of 2,830 HP at 2,800 rpm. Among other aircraft, it powered the Heinkel He 219 and the Messerschmitt 410.

With a 60 deg bank angle, blade and fork con rod construction, and roller bearing rather than plain bearing big ends, it employed direct cylinder injection and utilized a gear driven centrifugal supercharger. Interestingly, the left block had a CR of 7.5:1 while the right block had 7.3:1. This has never been satisfactorily explained perhaps because of the massive technical document destruction that took place in Germany during WWII. One theory, not universally accepted is that the unusual side placement of the supercharger with possible resultant inequality of flow between banks may have been responsible. Having raised the target speed to 750 km/h, Dr. Porsche calculated that 3,000 HP would be required to achieve this goal. Consequently, the engine was tweaked to reach this level.

The engine was designed to run on a mixture of methanol (63%), benzene (16%), ethanol 12%), acetone (4.4%), avgas (2%), and ether (0.4%). Methanol/water injection was used for charge cooling as an anti-detonant.

The Daimler-Benz company was formed in 1926 when Daimler Motoren Gesellschaft (the parent company of Mercedes) merged with Benz. The company quickly entered the liquid-cooled V12 aircraft market. The prototype DB 600 engine was built in 1934. The engines were built in Stuttgart-Unterturkheim where the M-B car factory was (and still is) located, and also in other locations to fulfill the needs of the Luftwaffe during WWII. Since the DB series engines were direct injected, they had an advantage over carbureted Allied aircraft such as the Spitfire whose carbs were affected by negative Gs during flight maneuvers (thank God for Miss Tilly's orifice). It's been said that the experience M-B gained in the high performance aircraft field helped shape the engineering excellence of the company after WWII in the postwar automobile industry.

In order to transmit the torque to the road surface, the vehicle was designed to ride on three axles, the two rear being powered. In final form, the T80 was over 8 m (27') long, and weighed 2.7 metric tons. Aerodynamically, the car incorporated two small wings at its midsection to prevent the vehicle from veering off course at speed through a downforce mechanism patented in 1939 by Mikci. The enclosed cockpit, low sloping hood, rounded
fenders, and elongated twin-tail booms were Porsche designed. The Cd was a low 1.8.

The record attempt was set for January 1940 during "RekordWoche" (Record/Speed Week) but the events of September 1939 obviously resulted in its cancellation as well as those of any other motorsport activities scheduled to take place in Europe. During the war, the engine was removed from the car and the vehicle was moved to Karnten, Austria for safekeeping. Surviving the war, the T80 was eventually moved to the M-B Auto Museum in Stuttgart where it can be seen, minus the engine, today.

In 1947, John Cobb in the Railton Mobil Special at Bonneville raised the LSR to 634 km/h (394.196 mph), 116 km/h (72 mph) slower than the 750 km/h (465 mph) projected for the T80 in 1940. Over the years, many people have urged M-B to restore the T80 to its original specifications to see if it could meet its projected goal. Undoubtedly, such a run if it did occur would not take place on the modern Autobahn system.

FYI, Cobb's car was powered by engines built by the British company Napier and Sons, Ltd. The Napier Lion aircraft engine was designed and first built in 1917 (this is not a misprint). It was a W12 with 60 degs between each of the three banks, 4-valve per cylinder, DOHC (total 6-camshafts) engine. The two Napier Lion engines used by Cobb had earlier been used in aircraft flown in the 1929 Schneider Air Trophy Race. Each engine developed 1,250 HP at 3,600 rpm. The rear engine drove the front wheels, and the front engine the rear wheels with no driveline connection between the two so Cobb (a WWII pilot) had to keep the throttles balanced in addition to his other duties. The car weighed 3-tons and had no tail fin to keep it straight at speed.

References:

http://www.absoluteastronomy.com/top...cedes-Benz_T80

Allied Aircraft Piston Engines of World War II, by Graham White; Section1, Chapter 6: Napier, pages 155 to 180.

 

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