Corrections on the Thermometer Reading in an Air Stream Page: 3 of 20
[18] 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:
NASA Technical Memorandum No. 956
I. INTRODUCTION
To obtain reliable results from observations during
flight tests, the external air temperatures must usually
be known - often to an accuracy of a tenth of a degree
Centigrade. For this purpose, the N.L.L. (Nationaal Lucht-
vaartlaboratorium) employs a special type of thermometer,
namely, the so-called "distance thermometer." The latter
generally consists of a mercury bulb which, by a long,
flexible capillary, is connected to the dial located in
the pilot's cockpit, while the measuring body is located
in the air stream outside the airplane. A sun shield
serves to screen the instrument from the direct rays of
the sun. Figure 1 shows two thermometers constructed in
accordance with this principle. The only difference is
in the shape of the sun shield.
Instead of mercury thermometers it is, naturally, also
possible to use, for example, electrical-resistance ther-
mometers for the measurement of the temperature. Both
systems possess typical advantages and disadvantages. The
most important advantage of electrical thermometers, as
compared with mercury thernoneters, is their considerably
smaller time lag. Their disadvantages are mainly associ-
ated with the sensitive galvanometer required for accu-
rate measurements and which must be suitable for use on an
airplane. It is not our intention in this article to go
further into this matter. At the present time, the N.L.L.
is giving consideration to a partial replacement of mer-
cury by electrical thermometers for temperature measure-
ments in flight tests. In this report the discussion will
be restricted to the distance thermometers mentioned above,
which have been found very useful,
The difficulty is that the reading of such thermome-
ters may for various reasons differ - in some cases con-
siderably - from the true outside air temperature. In the
first place, there naturally occur instrumental errors,
which can be found by calibration. We wish to point out
here that this correction, which offers no difficulty, will
be entirely left out of consideration, so that in the fol-
lowing, wherever we speak of thermometer reading, it is
assumed that the instrumental correction has been made.
A second error is caused by the changed flow velocity
in the neighborhood of the measuring body. Even without the
use of a sun shield (which strongly affects the flow pat-.._. Y- r .. _ 3 1 1 11 11 111 1 101
nn1
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.
Van der Maas, H. J. & Wynia, S. Corrections on the Thermometer Reading in an Air Stream, report, October 1940; (https://digital.library.unt.edu/ark:/67531/metadc63173/m1/3/: accessed July 16, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.