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Re: [Phys-l] unusual areodynamics



We could determine the power-to-weight by looking at the dip angle of the fuselage while it's flying with the wings oriented vertically. I suppose that we need to know the lift from the (usually) vertical tail section to do it (any ideas on doing that?), but it seems like the plane didn't have to tip much to get enough vertical force on the propeller to keep it flying.

jg

--
Joshua Gates
Physics Faculty
Tatnall School (Wilmington DE)
JHU Center for Talented Youth
_____

From: John Denker [mailto:jsd@av8n.com]
To: Forum for Physics Educators [mailto:phys-l@carnot.physics.buffalo.edu]
Sent: Sun, 11 Dec 2011 23:35:23 -0500
Subject: Re: [Phys-l] unusual areodynamics

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.
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