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Aviation History
1940
1940 - 0934.PDF
295a Supplement to THEAIRCRAFT ENGINEER NO. 15th Year March 28 1940 GERMAN SUPERCHARGER TESTS By Dr. ING. P. F. MARTINUZZI (Continued from page 8, February 29, 1940) MANY tests have also been made on the effect of thearrangement of the diffuser vanes. Fig. 8 shows theimprovement brought about by fitting diffuser vanes to a vaneless, low-efficiency blower for a radial en- gine. This type of blower is still used in great numbers. Though blowers seem to fit radial much better than V-type engines, in reality the small available outer diameter and the separate inlet pipes to the single cylinders, which pre- vent the use of a spiral volute, cause radial engine blowers to be less efficient than other types. In the case of Fig. 8, the absolute gain of 7 per cent, represents a relative gain of 20 per cent over the vaneless type. The reduction in engine inlet temperature can make an enormous difference, particularly with air cooling. While the use of difluser vanes is very advantageous in blowers with insufficient diffuser diameter and no spiral volute, the effect is not the same when, as in the case of Fig. 9, the supercharger tested has a spiral volute. Curves 1 to 4 show test results with different diffuser vane arrange- ments, while curve 5 refers to the same diffuser without vanes. It will be seen that the vaneless arrangement gives not only, as usual, a much flatter curve, but also better absolute values for the efficiency, which is not usual. This WITHOUTDIFFUSER VANES Influence of diffuser vanes on low-efficiency radial engine supercharger. 5,000 4.000 3.000 2.000 O6- Oad 05- O-4- O-3- O-2- 0-1- 0 mC n-2 2 0 )C 0,00 3 O • 1 OR. 4 O P.M. 5 0 l 6 O \ \ \ 7 0 [FIG. 9 \1\ —-•- \\\\ 3 8 O- \j\ 2 1 V 9 1 5 • Vj 0 1- — — 5 ••••• 1 1-2. Influence of diffuser vane arrangement on medium-efficiency supercharger with spiral volute. Curve 5 refers to a vaneless diffuser. is explained, however, by the fact that the blower tested had a very narrow spiral volute. Apart from the test with- out vanes, it will be noted what a difference a properly adjusted set of vanes can effect on both efficiency and shape of the pressure curve. The effect of diffuser vane angles on a very efficient super- charger with web type impeller are shown in Fig- 10. The curves i to 5 correspond to different vane angles shown ifl -
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