Re: [Phys-L] Video Analysis of Album Cover Flight and Glider Stall

[John Denker <jsd@av8n.com>]

On 2/6/20 9:22 AM, Steinert, Jeff wrote:

> This is likely a question for JD, but all responses are appreciated:

:-)

> My students are using video analysis in Logger Pro to explain the flight of
> a projectile of their own choosing. One has flown an album cover and
> produced a rather complicated trajectory that can be viewed here:
> https://docs.google.com/document/d/1FCZhpNazYJajSGyo8tdHiWpq1mXD-kw3rHfC7Wi7Vsg/edit?usp=sharing

OK.

> I searched the net for a graphical depiction of the trajectory for a
> stalling glider with no luck and I'd like to give my student a place to
> start in her search for an explanation using the forces acting on her album
> cover. Does the above plot resemble what you'd expect to see for a stalling
> glider?

Short answer: Yes, that's pretty much exactly what you
see in a stall, followed by stall recovery.

 Note that "glider" is not particularly relevant to
 the story.  Searching for /aerodynamic stall/ will give
 better results than "glider stall".

To answer a slightly different question:  That is not
the only behavior you might expect to see from a flying
album cover. You're lucky that the data is not very
much more complicated.  You are not guaranteed to get
a stall followed by stall recovery.  You could get a
stall followed by another stall, followed by some sort
of spin.

Suggestion:  When plotting the data, join the plotting
symbols with lines.
 -- The lines give us information about the ordering of
  the points, especially near the peak where things get
  messy.
 -- Keep the symbols, since they provide timing information.
 -- Prepare a separate plot, zoomed in on the messy region.
 -- If the video analysis tool permits it, keep track of
  the *attitude* of the flying object.  The aerodynamics
  (including stall) depends super-strongly on the angle
  of attack, which in turn depends on both attitude and
  direction of flight.  Measuring the attitude would
  require separately tracking the front and back of the
  object.

===============

The basic physics of lift is explained here, with lots
of diagrams and only the simplest of equations:
  https://www.av8n.com/how/htm/airfoils.html

Don't restrict attention to a square album cover.  Also
fly something with a greater aspect ratio, perhaps a
thin plastic ruler or other long thing slat, and throw
it with a tumbling motion, as shown here:
  https://www.av8n.com/how/htm/airfoils.html#fig-tumble

Then you will understand what I mean when I say that a
stall followed by stall recovery is not the only thing
that could happen.  Also you will learn something
tremendously important about the physics of lift.

The physics of stalls is discussed in detail here,
possibly more detail than you need at the moment:
  https://www.av8n.com/how/htm/vdamp.html

Yet more detail about stalls -- including (!) spins --
is discussed here:
  https://www.av8n.com/how/htm/spins.html