Expert: Paul Soderman - 5/10/2008

Question
In the F-4 Phantom flight manuel it describes the wing tips with obvious anhedral and stabilator with obvious cathedral.  I can understand the horizontal stabilator as being cathedrallike but shouldn't the wingtips be described as obvious "dihedral" since they are angled upward from the horizontal as opposed to downward as anhedral would be?  Thanks for any assistance.  

Rick Dixon

Answer
Rick
Like almost all aircraft the F-4 has wing dihedral for lateral stability.  Side slip to the right and the right wing raises.  However, the F-4 dihedral is somewhat complicated as explained in Wikipedia:

"Wind tunnel testing had revealed lateral instability requiring the addition of five degrees dihedral to the wings.[28] To avoid redesigning the titanium central section of the aircraft, McDonnell engineers angled up only the outer portions of the wings by 12 degrees which averaged to the required five degrees over the entire wingspan. The wings also received the distinctive "dogtooth" for improved control at high angles of attack. The all-moving tailplane was given 23 degrees of anhedral to improve control at high angles of attack while still keeping the tailplane clear of the engine exhaust"

So I don't quite understand the manual you have.  Perhaps it is talking about the main inboard section.  It seems that the inboard section of the wing has anhedral, the outboard section has 12 deg dihedral, and the average is 5 deg dihedral over the wingspan. Photos of the F-4 show the wing tip dihedral and tail anhedral.  I don't know what cathedral is.

If you can get the following report, it should describe the aircraft aerodynamics in detail:

Loftin, Laurence K. Quest for Performance: The Evolution of Modern Aircraft, SP-468. Washington, DC: National Aeronautics and Space Administration, History Office, Scientific and Technical Information Branch, 1985. Retrieved: 19 November 2007.

Paul