The Design of Airplane-Engine Superchargers Page: 4 of 23
[21] p. : ill.View a full description of this report.
Extracted Text
The following text was automatically extracted from the image on this page using optical character recognition software:
N.A.C.A. Technical Memorandum No. 839
offset by the disadvantages of small pressure heads per
stage, difficulties in manufacturig and in safe operation
of the-very thin blades, the low critical speeds of the
multi-stage arrangements, and the difficulty in mounting
when engine driven. In what follows therefore, only cen-
trifugal superchargers with radial wheels will be consid-"
ered. At adiabatic compression without losses the deliv-
ery or pressure heads, pressure ratio, and temperatures
for these wheels are shown on figure 3.
II. CHARACOTERISTOICS AND PZRFORMANOI OF VARIOUS
CENTRIFUGAL SUPERCHARGERS
The wheel with buckets or blades open at both eides
(fig. 4a) is probably the oldest form of impellur. The
radial blade type with 90o exit angle has not been zde-
parted from in supercharger design because of the necessi-
ty of high peripheral velocities and pressure rise per
stage, although this form of blade compared to the back-
ward curved blades has disadvantages in operating condi-
tions and efficiency.1) An advantage of the blade open at
both sides is the elimination of axial stresses on the
bearing. An improved wheel form has also been applied in
Germany, whereby the blades receive short radial ribs on
their rear sides. In DYL tests on a steel impellor of this
type, the peripheral velocity could be raid for short-
time intervalsed; to 605 meters per second (20,000 feet per
minute) without the setting up of a permandht expansion.
The half-open impeller (fig. 4b) is the type applied
in by far the greatest number of new engine superchargers.
The construction materials are high quality aluminum alloys.
l>0n the question of the effect of an exit angle of 900 on
the efficiency, the reader is referred to the paper "Un-'
tersuchungen uber den Einflus des endlichen Schaufelab-
standee in radialen Kreiselradern," by 0. Hansen, Braun-
schweig 1936, who shows that in spite of the increase of
the delivery pressure with increasing exit angle, the effi-
cienocy need fall -off only an insignificant amount.
.2 )Longer operation was impossible on account of the too
high sliding velocities in the bearings._ __ ___
3
Upcoming Pages
Here’s what’s next.
Search Inside
This report can be searched. Note: Results may vary based on the legibility of text within the document.
Tools / Downloads
Get a copy of this page or view the extracted text.
Citing and Sharing
Basic information for referencing this web page. We also provide extended guidance on usage rights, references, copying or embedding.
Reference the current page of this Report.
von der Nüll, Werner. The Design of Airplane-Engine Superchargers, report, October 1937; Washington, D.C.. (https://digital.library.unt.edu/ark:/67531/metadc63351/m1/4/: accessed July 16, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.