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Report No. 389. The effect of small angles of yaw and pitch on the characteristics of airplane propellers
398
BOOK R E V I E W S .
[J. F. I.
Satisfactory air flow has been a t t a i n e d with a velocity t h a t is uniform over the jet to within :t= 0.5 per cent. The turbulence present in the tunnel has been compared with t h a t of several other tunnels by means of the results of sphere drag tests and was found to average well with the values of those tunnels. Included also in the report are comparisons of results of stable autorotation and of rollingmoment tests obtained both in the vertical tunnel and in the old horizontal 5-foot atmospheric tunnel. Report No. 388. Investigation of the Diaphragm-Type Pressure Cell by Theodore Theodorsen, I8 pages, illustrations quarto. Washington, Government Printing Office, I93I , price ten cents. This report relates to various improvements in the process of manufacture of the N. A. C. A. standard pressure cell. Like most pressure recording devices employing thin diaphragms, they would in general show considerable change in calibration with temperature and also some change of calibration with time or aging effect. Some instruments exhibited considerable internal friction. It was established t h a t the temperature dependency of the stiffness was due to difference in the thermal expansivlty between the diaphragm proper and the supporting body of the cell, and convenient methods for its compensation have been developed. The diaphragm is furnished with a small central bushing of a different metal, and it is possible to determine a size of this bushing which gives the diaphragm exactly the same thermal expansivity as the cell body. It was further established t h a t the internal hysteresis in the diaphragm was of a negligible magnitude a n d t h a t the observed lag was due, primarily, to the force of the hairspring on the stylus point. The resultant adoption of weaker hairsprings made it possible to extend the useful range of the instrument considerably downward. Satisfactory instruments having a range of less t h a n 3 inches of water were made possible. It was found t h a t the tendency to change calibration with time was caused, to a great extent, b y insufficient clamping of the diaphragm. The adoption of double copper gaskets improved this condition. T h e required diaphragm thickness and the desirable rate of mechanical magnification have been determined on the basis of several hundred tests. Report No. 389 . The Effect of Small Angles of Yaw and Pitch on the Characteristics of Airplane Propellers, b y Hugh B. Freeman, I I pages, illustrations, quarto, Washington, Government Printing Office, I93I , price ten cents. T h e subject tests were carried out in the 2o-foot wind tunnel of the National Advisory Committee for Aeronautics to determine the effect on the characteristics of a propeller of inclining the propeller axis at small angles to the relative wind. Tests were made of a full-scale propeller and fuselage combination a t four angles of yaw (o °, q- 5 °, -b Io °, a n d -}- I5°), and of a model propeller, nacelle, and wing combination at five angles of pitch (-- 5 °, o °, -I- 5 °, q- Io °, and -4- I5°). T h e results of the full-scale tests of a propeller and fuselage, without a wing, show t h a t the effect on the propeller performance is small. Similar results are shown by the model test data except t h a t where the propeller is directly in front of the wing there is a n appreciable decrease in effective t h r u s t and propulsive efficiency with increase of angle of pitch.
BOOK R E V I E W S .
[J. F. I.
Satisfactory air flow has been a t t a i n e d with a velocity t h a t is uniform over the jet to within :t= 0.5 per cent. The turbulence present in the tunnel has been compared with t h a t of several other tunnels by means of the results of sphere drag tests and was found to average well with the values of those tunnels. Included also in the report are comparisons of results of stable autorotation and of rollingmoment tests obtained both in the vertical tunnel and in the old horizontal 5-foot atmospheric tunnel. Report No. 388. Investigation of the Diaphragm-Type Pressure Cell by Theodore Theodorsen, I8 pages, illustrations quarto. Washington, Government Printing Office, I93I , price ten cents. This report relates to various improvements in the process of manufacture of the N. A. C. A. standard pressure cell. Like most pressure recording devices employing thin diaphragms, they would in general show considerable change in calibration with temperature and also some change of calibration with time or aging effect. Some instruments exhibited considerable internal friction. It was established t h a t the temperature dependency of the stiffness was due to difference in the thermal expansivlty between the diaphragm proper and the supporting body of the cell, and convenient methods for its compensation have been developed. The diaphragm is furnished with a small central bushing of a different metal, and it is possible to determine a size of this bushing which gives the diaphragm exactly the same thermal expansivity as the cell body. It was further established t h a t the internal hysteresis in the diaphragm was of a negligible magnitude a n d t h a t the observed lag was due, primarily, to the force of the hairspring on the stylus point. The resultant adoption of weaker hairsprings made it possible to extend the useful range of the instrument considerably downward. Satisfactory instruments having a range of less t h a n 3 inches of water were made possible. It was found t h a t the tendency to change calibration with time was caused, to a great extent, b y insufficient clamping of the diaphragm. The adoption of double copper gaskets improved this condition. T h e required diaphragm thickness and the desirable rate of mechanical magnification have been determined on the basis of several hundred tests. Report No. 389 . The Effect of Small Angles of Yaw and Pitch on the Characteristics of Airplane Propellers, b y Hugh B. Freeman, I I pages, illustrations, quarto, Washington, Government Printing Office, I93I , price ten cents. T h e subject tests were carried out in the 2o-foot wind tunnel of the National Advisory Committee for Aeronautics to determine the effect on the characteristics of a propeller of inclining the propeller axis at small angles to the relative wind. Tests were made of a full-scale propeller and fuselage combination a t four angles of yaw (o °, q- 5 °, -b Io °, a n d -}- I5°), and of a model propeller, nacelle, and wing combination at five angles of pitch (-- 5 °, o °, -I- 5 °, q- Io °, and -4- I5°). T h e results of the full-scale tests of a propeller and fuselage, without a wing, show t h a t the effect on the propeller performance is small. Similar results are shown by the model test data except t h a t where the propeller is directly in front of the wing there is a n appreciable decrease in effective t h r u s t and propulsive efficiency with increase of angle of pitch.