A APPLIED TECHNOLOGY LABORATORY U. S. ARMY RESEARCH AND TECHNOLOGY LABORATORIES (AVRADCOM)Foet Eustis, Va. 23604
APPLIED TECHNOLOGY LABORATORY POSITION STATEMENTReconnaissance and target detection RPVs that use piston engine driven propellers are highly susceptible to ground detection due to propulsion system noise.This report examines the noise and detectability aspects of designing propellers for RPVs using piston engines in the 25 horsepower category.Results of this work, although preliminary, cover design variao)les considered essential to selecting best choice minimum detection propeller configurations. Future R&D in this area is desired to develop performance/noise data from small-scale propellers to a level that compares with that of large-scale propellers.Bill W. Scruggs, Jr., of the Aeronautical Systems Division served as project engineer for this effort.
DISCLAIMERSThe findings in this report are not to be construed as an official Department of the Army position unless so designated by other authorized documents.When Government drawings, specifications, or other data are used for any purpose other than in connection with a definitely related Government procurement operation, the United States Government thereby incurs no responsibility nor any obligation whatsoever, and the fact that the Government may have formulated, furnished, or in any way supplied the said drawings, specifications, or other data is not to be regarded by implication or otherwise as in any manner licensing the holder or any other person or corporation, or conveying any rights or permission, to manufacture, use, or sell any patented iniention that may in any wa be related thereto.Trade names cited in this report do not constitute an official endorsement or approval of the use of such commercial hardware o. software.
DISPOSITION :NSTRUCTIONS
Destroy this report when no longer neededDo not return t to the originator. Several small-scale propeller configurations applicable to a conceptual Remotely Piloted Vehicle (RPV) aircraft were designed, fabricated, and tested to determine their performance, acoustic, an~d detectability characteristics.The tests were conducted in static and simulated forward flight conditions in a wind tunnel. Propellers tested included tractor, pusher, and ducted configurations. The accustic data obtained was used to determine the slar' It is concluded that the acoustic and detectability characteristcsa of small-scale RPV propellers are, in general, significantly different from those of the large-scale propellers. It was found that the forward velocity has a significant effect on the acoustic characteristics as well as the detection distances (slant range and altitude of no detection) of most of the RPV propeller configurations tested. An increase in forward velocity resulted in a significant drop in the SPLs at higher harmonics (beyond 4th or 5th) of the blade passage frequency in the forward direction as well as in and about the plane of the propeller. In fact, for most of the propeller configurations tested, an...
