THE HIGH SPEED
- Chapter 4: The High-Speed
- HIGH-SPEED FLIGHT TESTS OF
-  Throughout the
forties the Flight Research Division at Langley measured propeller
performance on several piston-engine fighter aircraft at speeds in
excess of 400 mph. The test propellers were generally typical of
advanced service practice and they provided useful data on
compressibility effects as they were encountered in actual
operating conditions (refs. 160, 161). The results were invariably consistent with
expectations based on the wind tunnel programs, but were rarely
directly cornparable because of differences in the test
propellers. Principal figures in the flight work were T.
Voglewede, A. Vogeley, and J. Hammack.
- The successes of the high-speed research
airplanes in the late forties had led to thinking at Langley about
a possible "propeller research-airplane," and the
flight division eventually succeeded in promoting such a
project. Aimed primarily at potential long-range military
applications,  it was developed as a joint effort with the
services; the Air Force provided the XF-88B airplane and the test
propellers and associated equipment, and the Navy provided the
turbojets and the T-38 turboprop engine which was installed in the
nose of the XF-88B to power the test propellers. Unfortunately,
this program did not start to produce results until the
mid-fifties when interest in high-speed propellers had almost
disappeared. Three propellers were eventually tested at flight
speeds up to slightly above Mach 1 on the XF-88B (fig. 36). By the time the results were analyzed in 1957,
the Subcommittee on Propellers for Aircraft had been disbanded,
eliminating a main heading on this subject in the NACA Annual
Report. Thus, we find in the 1958 (Final) NACA Annual Report only
an obscure reference to these interesting data, the crowning
achievement of a difficult and costly project, under the heading
"Low-Speed Aerodynamics." Peak efficiency of 80 percent had been
measured at Mach 0.95 on a thin "supersonic" propeller, generally
confirming the levels indicated in the Langley high-speed wind
tunnel programs (ref. 162).
- Taken as a whole, the high-speed propeller
program is clearly one of the more substantial NACA contributions.
The magnitude of the undertaking was well beyond anything that
might realistically have been expected from private industry, and
this was another example of NACA fulfilling its proper
- There were occasional noteworthy flashes
of inspiration. The impressive blade pressure distribution surveys
afford perhaps the best example. Several innovative developments
had to be brought together to make these measurements possible.
These unique data still have been only partially analyzed and
remain available to enterprising future researchers.
- Like several other NACA programs,
high-speed propellers has its mythology. Evidence of this can be
found, for example, in the writings of G. W. Gray whose book
163) states, "Almost everything in
the way of improving propeller efficiency for high-speed flight
rests on the utilization of the 16-series airfoils. "The principal
source of his education in high-speed propellers and the NACA
reviewer of this material was.....
-  FIGURE
36.-Supersomic propeller (feathered) driven by T-38 turboprop
engine mounted on XF-88 propeller research airplane.
-  .... Stack, a
man who had outstanding talent for technical salesmanship. Any
qualifications or words of caution which Stack probably included
were undoubtedly lost in his effusive account of how NACA had
created efficient 500-mph propellers. He often used the term
"16-series" to encompass all the improvements embodied in the NACA
propellers, including the all-important reduced thickness ratios,
a usage which Gray evidently misunderstood.
- The progress in high-speed propeller
technology made in the NACA
program took place in an
environment of dwindling user interest. In 1949 T. B. Rhines of
the Hamilton Standard (Propeller) Division of United Aircraft
complained poignantly that ". . . . various representatives of the
aircraft industry imply that even if the [high-speed] propeller is
good it is not wanted" (ref. 155). There was still hope that 500-600-mph transports
might need transonic propellers, especially for long range, but
with the advent of the Comet and the 707 this application also
faded and the NACA high-speed propeller program ended with the
transition to NASA.
- The oil crisis is now forcing new
considerations of high-speed propellers, and we may see a
renaissance for both military and commercial applications.