THE HIGH SPEED
- Chapter 3: Transonic Wind
Tunnel Development (1940 -1950)
- TRANSONIC AIRFOIL
-  The Germans
employed an interesting variant of the "small-model" technique to
obtain two-dimensional airfoil data in their large (2.7 meter)
high-speed tunnel. Test models of about 1-foot chord were mounted
in the center of the tunnel between large, thin, wire-supported
end plates (ref. 66). An impressive amount of systematic data was
produced by this setup in 1943 and 1944 (see Chapter II).
- Langley was slow to accept either the
German or Italian semi-open techniques for airfoil testing.
Recalling his early difficulties with the open-throat 11-inch
tunnel, Stack was suspicious of the semi-open configuration and at
the same time chagrined that it had not come from Langley. The
best that he would say for it was, "a marked reduction in choked
range" had been achieved (ref. 54).
- On his arrival in 1945, Ferri had been
surprised to learn that NACA  had not tried to
develop a semi-open tunnel. However, he had had so much difficulty
with flow pulsations above Mach 0.95 that he was reluctant to
recommend that we become involved with one. C. duP. Donaldson was
stimulated by Ferri's work to undertake in 1945 a series of tests
of a small airfoil in a 1 by 3-inch jet to evaluate constriction
effects in both the closed and semi-open configuration
53). At about the same time, W. F.
Lindsey wrote a memo to Stack suggesting a more thorough
investigation at a more adequate scale, utilizing the 4 x 18-inch
tunnel equipment. Stack rejected the proposal, telling Lindsey
that Ames was planning to undertake a similar study (perhaps the
work of Allen and Vincenti (ref. 84) ). But about a year afterward, in 1946, Stack
approved tests of a 9 x 9-inch open-throat configuration in
connection with studies then in progress of various wind tunnel
designs for the so-called "NACA Supersonic Center." Lindsey and
- FIGURE 18.-Schematic drawings of the
Annular Transonic and the 4 x 19-Inch tunnels.
- ....that the flow
pulsations near Mach 1in the 9 x 9-inch throat could be reduced by
improved design of the diffuser entrance, but satisfactory
conditions for testing at conditions for testing at low supersonic
speeds could not be obtained (ref. 54).
- A few weeks after becoming division chief
in the summer of 1947, I called Lindsey and suggested that we
convert the 4 x 18-inch airfoil tunnel into a semi-open facility
to extend our airfoil testing to Mach 1. Recalling his earlier
rejected proposal along these lines, Lindsey was naturally happy
to proceed. In addition to applying the diffuser design criteria
he had developed in the 9 x 9-inch throat work, Lindsey
incorporated a very effective adjustable choking device located in
the diffuser section to prevent downstream disturbances from
affecting the test section (fig. 18). The rather small "open" sides of this 4 x 19-inch
tunnel (17 percent open in contrast to Ferri's 43 percent)
undoubtedly also contributed to the reduction of pulsations.
Preliminary runs in 1948 revealed that testing up to Mach 1 was
possible with negligible pulsations and transient disturbances
54). A comprehensive airfoil test
program (reviewed in ref. 51) was initiated and the first results for Mach 1.0
(figs. 4, 5, 6, and refs. 54, 56) were published in 1949.