Boeing B-52 Stratofortress Wing Dihedral

 

 

And now for something completely different but it's a rabbit hole I've explored fairly thoroughly so I thought I'd share. Thanks to Ron VanDerwarker, Rob de Bie, and Haydn Hughes for information.

The B-52 is rightly famous for the bending of its high-aspect-ratio wing in flight as well as on the ground, the amount varying considerably with aerodynamic and fuel loads.

  

Note that the airplane is restricted in g loading to lower numbers operationally but during initial development it was taken to at least 3.5 gs.

Some believe based on three-view drawings and pictures of the airplane on the ground that the B-52 wing has anhedral (wing angled down, also known as cathedral) rather than dihedral (wing angled up).

However, the appearance of anhedral when on the ground is deceptive, a combination of a swept wing viewed at an angle of incidence from the front (also see https://tailspintopics.blogspot.com/2014/03/anhedraldihedral-and-wing-sweep.html) exacerbated by the significant droop of the B-52's wing when fully fueled and stationary.  

This B-52D three-view drawing appears to be both Boeing-generated and accurate, although the top view has slightly greater wing span than the front view, not unusual and resulting from differential sizing of the views.

 

Based on this drawing, I’ve verified that the wing has dihedral:

The blue line is the wing's angle of incidence (6°) relative to the fuselage; the red line is along the wing leading edge. The difference between the two indicates dihedral (I don’t know what definition was used for measuring it, but it was possibly the trailing edge).

 

This Boeing illustration also depicts the dihedral present at the wing root with the scan distortion corrected with red lines:

 

Note that the clearance depicted on the Boeing three-view under the engine pods, external tank, and wing tip is dependent on fuel load in the wing and tip tank.

I’m pretty sure that “jigged" means that the three-view drawing does not show wing droop, i.e. the wing is drawn with a dihedral of 2.5°, which is possibly the case when the wing and tip tank are empty of fuel.

 

With no fuel in the wing or the tip tank, the auxiliary landing gear out on the wing tip would be well off the ground with no wing droop.

 

When generating lift, of course, the wing bent upward along its span.

 

For modelers building a B-52, there are two ways of incorporating wing bending if desired: 1) bending the wing and 2) modifying the angle of the attachment of the wing to the fuselage. The latter is incorrect and doesn't accurately represent the bending of the wing itself along its span but is an easier way of positioning the wing tip correctly with respect to the ground for a given fuel load. Nevertheless, Haydn Hughes did the former successfully: "Back in 2002 I made a couple of saw cuts in each wing of slightly different widths and inserted strips of plastic card until I got what I thought was a reasonable 'bend' in the wing. This did mean I had to replace the vortex generators though!"

 

My guess is that it would be more accurate to make the saw cuts perpendicular to the leading edge.