anhedral

The opposite of dihedral is called anhedral, and, of course, refers to a wing that is angled down.

[flight dynamics] twist, dihedral and wingtips 2009

Sorry for going off topic, but I would appreciate some more aerodynamics posts: the one on anhedral and dihedral was especially good.

[propaganda] predators, women and the ahl 2009

A good example of an aircraft with geometric anhedral is the Sea Harrier:

[flight dynamics] twist, dihedral and wingtips 2009

To counteract this large amount of dihedral, some geometric anhedral is required.

[flight dynamics] twist, dihedral and wingtips 2009

This is why most aerobatic planes and military fighters utilize some amount of anhedral.

[flight dynamics] twist, dihedral and wingtips 2009

All this talk of anhedral and dihedral leads to the question of why one would want use either of these on an aircraft.

[flight dynamics] twist, dihedral and wingtips 2009

DHC DeHavilland Canada (aircraft manufacturer) dihedral upward or positive slope of the wings or tail flats (anhedral is the downward or negative slope)

FM 44-80 Visual Aircraft Recognition - Glossary United States Army 1993

Features of the CH-53K helicopter include: a joint interoperable glass cockpit; fly-by-wire flight controls; fourth generation rotor blades with anhedral tips; a low-maintenance elastomeric rotor head; upgraded engines; a locking cargo rail system; external cargo handling improvements; survivability enhancements; and reduced operation and support costs.

The Earth Times Online Newspaper 2010

The GE38-1B engine planned for the CH-53K is a derivative of the Oct 30 / 06: Sikorsky Aircraft has submitted test results for its 4th Generation ™ rotor blade, which builds on the work done for the Growth Rotor Blade ™ (GRB) currently used on their new UH-60M and S / H-92 helicopters, using anhedral tips.

Defense Industry Daily 2009

… and was a fighter but almost all modern fighters use anhedral, e.g. the F18:

[flight dynamics] twist, dihedral and wingtips 2009