No Over-Under Puffball

Now for the third puzzle in this three-part series introduced by The Plane of the Shadow Wedge. Here we will get a better perspective on the shadow wedge with the help of the two "puffballs". This puzzle is called "The Over-Under Puffball" and is shown below.

The puzzle is fairly obvious: how is it that the left puffball in the Fairbanks video appears to be behind or above the wing? Could the shadow wedge be responsible for this anomaly as well? Is the shadow hiding part of the left puffball so it only appears to be behind the wing? To cut to the chase, yes, it's the shadow wedge again and this will be explained below in some detail.

In addition to the shadow effect, there is another contributing factor in this illusion. If you look closely, you'll notice that the CNN Ghostplane video is slightly ahead of the Fairbanks video, which you can tell by comparing the last frame of both. Notice that only a small tip of the right wing is visible in the CNN Ghostplane video. This time delay makes it appear that the Fairbanks puffball is covered and thus not visible when it is really just a little later in becoming visible.

To better understand this shadow wedge, and how it explains the puffball illusion, I have put together a visualization of the shadow wedge. We will use this visual of the wedge to see how it affects each frame of the video.

Here is the shadow wedge overlaid on the first frame where the left puffball is partially visible.

There are two planes represented in the shadow wedge. The darker plane is on the surface of the wall, and the lighter plane is the outer edge of the shadow. The dark triangle is a cross-section of the wedge in the area where the plane passes through the wedge.

This image also shows an outline of the airplane. The nose cone is actually too short because the first frame of the animation sequence starts with part of the nose cone already in the wall.

It is difficult to make out all of the details in this composite image, so I will decompose it into its parts. I am also starting with a better quality video, from the History Channel program, "102 Minutes that Changed America". This video unfortunately chops off the top of the full size video a bit, but the essential details are still visible.

This first frame is just after impact, and I have drawn a line through the shadow of the fuselage on the tower wall that is just barely visible in this video.

Some people claim this shadow of the fuselage on the wall is physically impossible, but there is a reasonable explanation for it, though I won't go into great detail here. The shadow of the fuselage on the wall is due to the brighter sky in the area around the sun as compared to the rest of the sky.

The angle of the shadow is not parallel to the floors, but it is about the same as the sun angle of 27 degrees. The whitish area just below where the plane impacts is from the mechanical floors of the tower.

I extended this line through the shadow up to the corner of the tower, and then drew another line back through the plane at the point where the edge of the shadow is visible on the fuselage. This upper line is in the direction of the sunlight. The next image is the same frame with an overlay plane showing where the edge of the shadow wedge would lay.

Having shown this angle of the shadow wedge parallel to the sunlight, this is not the same angle we will want to examine in other frames because we really want to see the roll angle of the plane impacting with the wall which is slightly different.

So next we will jump forward to the puffball frame to draw that intersection angle and return to see where it lines up on this frame.

(under construction)