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This file, from NICAP and CUFOS, collects US Air Force Office of Special Investigations records from 1949 on a Project Grudge special inquiry into a sighting at Rogue River, Oregon, on 24 May 1949. NACA Ames Laboratory employees Gilbert Rivera and Don Heaphy described a silvery pancake-shaped object about 30 feet across that sped off like a jet. An annotated analysis that follows rejects the radar kite explanation and concludes that the case must remain unexplained.
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1/2 to 1 minute of arc, and the object was apparently resolved by the eyes of five people. The 8-power binoculars would have made details down to 1/8 or so of the diameter of the object apparent to the viewers using binoculars (Mr. B and Mr. C). $ ^{*} $
An object that is 1 minute of arc in angular size would be 1/60 of a degree or (1/60) of 0.017 radians or 0.00028 radians in angular size. This corresponds to 0.28 feet in linear size if 1000 feet away,about 1 1/2 feet if 1 mile away, and about six feet if four miles away.
These sizes calculated above are based upon the minimal expected angular size for resolution of the object into a circular shape with the naked eye. However, if the estimates of Mrs. D and Mrs. A are more nearly correct, then we should use an angular size comparable to 0.1 degree or 0.0017 radians. The linear size estimates are now about 1.7 feet if 1000 feet away, 8.4 feet if 1 mile away, and 33 feet if about 4 miles away. This last size estimate agrees with the numbers given by Mr. B and Mr. C, and probably with the fuselage length estimate given by Mr. D. However, their estimates were purely qualitative since they had no distance estimates to work from. It is unfortunate that the interviewers didn't think to obtain rough angular size estimates (such as the size of a pea at arms length, etc.) from the witnesses
Despite the difficulty (or impossibility) of obtaining size estimates from the data presented in the OSI files, it seems clear that the object seen by five people was not an ordinary aircraft and, moreover, the detail reported by two observers who used binoculars (not just one as implied by the BB#14 summary) rules out other readily identifiable aerial phenomena. Thus I believe that this case must remain unexplained.
Note: Relatively recent studies by military investigators specializing in visual detection and recognition of military targets and other studies concerned with the presentation of visual information on TV type displays have shown that detection of a target against a somewhat "contrasty" background requires that the angular size of the object subtend roughly one "eye resolution element", which is about 1 minute of arc or about 1/3 of a milliradian. For the shape of an object to be barely recognizable requires about 1.5 - 2 resolution elements along any major axis of the object (if it is square or circular it has no major axis; in any other case the orientation of the object will be barely detectable with 1.5-2 resolution elements along its major axis). For objects with non-simple surfaces (e.g., projections, etc.) it is barely possible to differentiate between classes of comparable non-simple surfaces if there are about 4 resolution elements along any major extension. Thus, for example, to distinguish between a plane and a blimp seen at great distances would require that the plane be seen in such a way that the Document, cited by the archive. The PDF is mirrored here; the original link is above. The text was read from the page images by GLM-OCR; expect the odd misread word. 28 pages are in the text index: search them above, or from the library's search.