Packard DR-980

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Packard DR-980

The Packard DR-980 was an air-cooled aircraft engine made by the US manufacturer Packard . The DR-980 was a four-stroke engine with nine cylinders in a star arrangement , which worked on the diesel principle . The first powered flight with a diesel engine was achieved with it on September 18, 1928, and in May 1932 a record of 84 hours and 32 minutes that lasted 55 years.

history

On August 18, 1927, a license agreement was signed between the President of the Packard Motor Car Company , Alvan Macauley , and the German engineer Hermann Dorner for the development of an aviation diesel engine using construction details and engine components from Dorners. Together with the chief aviation engineer of the Packard company, Lionel M. Woolson, the work was started that led to the historic maiden flight of a diesel-powered aircraft, a Stinson Detroit , in September 1928 . Woolson was responsible for the weight reduction during development, Dorner for the combustion process.

From May 1929, the first overland flights were carried out with the Stinson Detroiter . During this time, the Packard company set up a factory in which 500 engines could have been built per month. In May 1931 the above-mentioned long-term flight record was set. Despite these initial successes, the project was ultimately unsuccessful and was discontinued in 1933 after series production of a few copies. In addition to the accidental death of chief developer Lionel Woolson in 1930, the hasty start of production of the not yet fully developed engine prevented commercial success.

From a technical perspective, the low fuel consumption, the less flammable fuel and the relatively simple technical structure were offset by the disadvantages of odor nuisance, the design-related deficient exhaust system, smoke and soot development, vibrations and susceptibility of the injection pump elements. The engine was competing contemporary Otto aircraft engines on the performance initially equal or even superior to, this ratio returned to the introduction of aviation fuel with 87 or even 100 octane beginning of the 1930s and the associated increase in performance of gasoline engines to.

construction

The DR-980 was a single row radial engine. It was designed in performance, dimensions and weight so that it could be used as an alternative to the popular Wright J-5 . Due to the high cylinder pressures and strong mechanical forces resulting from the diesel principle, it was necessary to deviate considerably in some points from the design of Otto aircraft engines customary at the time.

The crankcase was cast in one piece from a magnesium alloy. A cover, which also supported the rear crankshaft bearing, was only screwed on on the back. In order to avoid tensile forces on the very light-weight housing, the cylinders were not screwed to the housing with stud bolts , but instead were all clamped against the housing together with two ring-shaped steel tires running outside the housing. One hoop each was arranged in front of and behind the cylinder level at the level of the front and rear housing walls. At the base of the cylinder there was a support flange, in which a groove-shaped groove for this hoop was incorporated on the front and back.

The crank mechanism consisted of a main connecting rod and eight secondary connecting rods that were hinged to its foot. In order to relieve the crankshaft from the torque peaks caused by the high compression, the counterweights on the crank webs were pivotably mounted and provided with a strong return spring. This should dampen the effects of the non-uniform torsional forces. For the same reason was between the front and tail shaft of the propeller , a torsional vibration damper arranged with rubber blocks as a damping element to torsional vibrations from the propeller hub keep.

The steel cylinders are designed as sack cylinders , the combustion chamber wall and the cylinder liner are one part. This also contained the valve seat for the single valve as well as a bore for the injection nozzle in the upper rear area of ​​the cylinder jacket , and in later versions for a glow plug . On the outside, a ribbed light metal cylinder head was screwed onto the floor of the combustion chamber , which contained the valve guide, the common inlet / outlet channel and the rocker arm mechanism. The valve was arranged off-center to give the incoming fresh air a swirl. The common inlet / outlet channel ended in a length of pipe through which the airstream flows, in which the combustion air entered at the front and the burned exhaust gas exited at the rear. For gas exchange , the valve was opened approximately two piston strokes long and acted during the upward movement after the expansion stroke only as a discharge valve at the subsequent downward movement as an inlet valve, wherein the flow in the gas channel reversed.

In later models, throttle valves were added to these intake / exhaust ports on the fresh air inlet side at the front, in order to be able to better reduce the idling speed of the engine when throttling.

Technical specifications

  • Cylinder: 9
  • Gas exchange: 1 valve per cylinder, OHV valve control
  • Cylinder bore: 122.2 mm (4 13/16 ″)
  • Stroke: 152.40 mm (6 ″)
  • Cubic capacity: 982 cubic inches, corresponds to approx. 16 liters
  • Continuous output: 225 hp at 1900 rpm
  • Compression ratio: initially 16: 1, series copies 14: 1

use

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