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4.2 Propeller Blockage Research Needs R. R. Tumlinson Beech Aircraft Corp.
If the general aviation industry is to produce the most efficient airplanes, it is important that the best technical tools which can be economically used be employed. That is the business of this workshop. One of the technical tools that is needed and which is currently not available is a means to accurately determine propeller blockage.
Propeller blockage refers to the effect of mutual propeller-nacelle or fuselage interference on the propulsive efficiency. The interference of the body on the propeller arises from the retardation of the airflow through the propeller disk and the resulting change in advance ratios. The interference of the propeller on the body stems from additional drag on the body because of the slipstream effect on local pressure and boundary layer. This effect has been understood for many years, and there are many reports in the literature. In the Tnterest of brevity, the present body of information will not be explored in this presentation except for the biblio- graphy included and to note the important parameters of advance ratio, body shape, and the propel ler-dlameter-body-diameter rat io.
However, while the sources of the propeller body interference have been understood for some time, the experimental data available to allow accurate estima- tion is long out of date. Current configurations with horizontally opposed engines outdate the data available which was determined with radial engine and in-line engine configurations as well as RAF -6 and Clark -Y propeller blades.
Performance data prav]ded by propeller manufacturers is elther provided on the basis of an isolated propeller, or at best, with approximate correction factors based on experimental data on data of 20-year old configurations. The most recent propeller efficiency computer program compiled by Hamilton Standard under NASA contract (References 8 and 9) provide only isolated propeller information. Thls view is understandable for a propeller manufacturer; but for the airframe manufacturer, an important gap remains.
Current information is needed to provide a basis to determine accurate drag levels from fllght-test data. The drag determined from flight can be only as accurate as the installed power basis. Improvement over the presently available data would also provide an improvement in accurately estimating installed thrust and drag and the resulting aircraft performance. Finally, improvement would provide a rational
basisto determinean accurate trade off betweennet propeller thrustand body drag
in determiningnewconfigurations.
So• specifically• what is needed? First• a current body of empirical data is
neededwhich coversthe importantparameters -- on current configurationswlth
asymmetricshapes. Second•a mathematicalmodel of this data with current compu-
tational fluid mechanism techniquesis neededto providea way to easily generalize
data for specific cases.
Test programs could be conducted in a large-scale wind tunnel where thrust and drag can be accurately separated. As an alternate• flight test programs could also be used with special englne-propeller installations so that independent deter- mination of installed thrust can be made. One such program has been proposed utilizing a separately driven propeller in the nose of a twin-englne airplane. With different nose body shapes and separately determined thrust, propeller-body interference effects could be determined. Perhaps a by-product of a flight test pro- gram would be a practical thrust-meter. Thls may be a little wishful thinking• but these recommendations for large-scale wind-tunnel tests and flight tests were proven practical by the testing performed many years ago on the obsolete configurations. So it is felt that these can be improved upon today, and I hope that such a program will be seriously considered.
References • McHugh• J.G., and Derring• E.H.• "The Effects of Nacelle-Propeller Diameter Ratio on Body Interference and on Propeller and Cooling Characteristics•" NACA TR 680• April 1939.
.
Glauert• H., "Airplane Propellers, Vol. IV of 'Aerodynamic Theory, d_v.
k' _" W.F. Durand, ed.
3.
Anon., "Hamilton Standard Method of Propeller Performance Calculation," (Black Book), Hamilton Standard, 1941.
4.
Anon., "Generalized Method of Propeller Performance Estimation" (Red Book), Hamilton Standard PDB 1601 • Revision A, June 1963.
5.
Anon., "S.B.A.C. Standard Method of Propeller Performance Estimation," Society of British Aircraft Constructors• Ltd.
6.
Fage• A., Lock, C.N.N., Boteman• H., and Williams• D.H., "Experi- ments with a Family of Airscrews including Effect of Tractor and Pusher Bodies; Part I! Experiments on Airscrews with Tractor and Pusher Bodles•" British A.R.C. R & M No. 830, November 1922.
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Boteman, H. • Townsend, H .C.H. • and Kirkup, T .A., "Experiments with a Family of Airscrews, including Effect of Tractor and Pusher Bodies; Part IV On the Effect of Placing an Airscrew in Various Positions within the Nose of a Streamline Body," British A.R.C. R & M No. 1030, February 1926.
Q Worobel, R., and Mayo, M.G., "Advanced General Aviation Propeller Study," NASA CR 114289, April 1971.
9.
Worobel, R., and Malyco, M.G., "Advanced General Aviation Propeller Study," NASA CR 114399, December 1971.
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