Re: [Phys-l] unusual areodynamics

[John Denker <jsd@av8n.com>]

On 12/11/2011 07:46 PM, Aburr@aol.com wrote:
> It  would be interesting to have jsd explain the aerodynamics of this 
> y0utube  clip 
> _http://www.youtube.com/watch_popup?v=tzowQtqOM_I_ 

The short answer is:   When I look at that video, all I see 
is that the pilot is really good.

The aerodynamics is "unusual" by the standards of hopping
into Grandma's Cessna-172 and flying off to get Sunday brunch 
... but it is not unusual by airshow standards.

The long answer would be very long:  There are entire books
on basic aerodynamics, and additional books on how to perform
airshow maneuvers.

As for the medium answer, I don't know where to begin.
  1) The pilot is very skilled.  That's the real story.
  2) It's a high-performance airplane.
   -- You can tell that its power-to-weight ratio is
    greater than 1.  That's an order of magnitude more 
    than what a C-172 has.
   -- You can see that it has lots of aileron authority.
    I estimate the roll rate exceeds 1000 degrees per 
    second.  That's about two orders of magnitude more
    than what a C-172 can do.  Personally, I don't fly RC
    planes and I've never flown a full-size plane that 
    could roll more than 400 degrees per second ... but 
    I have no problem imagining what 1000 degrees per
    second is like, and the physics is prosaic:  big
    ailerons and lots of aileron deflection.
   -- Ditto for rudder authority and elevator authority.
    If you skip to 
      http://www.youtube.com/watch?v=tzowQtqOM_I&t=5m26s
    you can see roughly 90 degrees of rudder deflection
    and 90 degrees of elevator deflection.  IIRC that's
    about six times more than what a C-172 has.

So, this is a world-class aerobatic RC plane ... but you
can understand it by application of prosaic aerodynamic
principles.

Also note that at small scale, everything happens faster,
which is one of several reasons why an RC plane is /harder/ 
to fly than a full-sized one.  So the bottom line is the
same as the top line:  The kid's got some talent.

==========

If there is anything in particular that looks "unusual"
to you, please ask a more specific question.