Re: [Phys-l] unusual areodynamics

[John Denker <jsd@av8n.com>]

On 12/11/2011 09:35 PM, I wrote:
> > its power-to-weight ratio is greater than 1. 

D'oh!  That's not even dimensionally correct.
I should have said "thrust-to-weight ratio".
Sorry.

On 12/12/2011 05:23 AM, Josh Gates wrote:
> 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. 

No.

The weight is being supported mainly by the lift of the 
*fuselage*.

The thrust-to-weight ratio during this maneuver is (to a 
good approximation) equal to the lift-to-drag ratio of the 
fuselage.  The engine in this aircraft is so powerful that 
it can fly this maneuver at nowhere near full power ... 
closer to 25% than to 100%.

You can get a much tighter lower bound on the max thrust-
to-weight ratio from the maneuver where the airplane hangs
on the prop, at zero airspeed.

>  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.

Again: In knife-edge flight, the weight is being supported mainly 
by the lift of the *fueslage*.
  a) You can get lift from things that don't look airfoil-shaped.
   Even a barn door will develop a goodly amount of lift.  
    -- The lift-to-drag ratio might not be very good.
    -- The maximum coefficient of lift might not be very good,
     but this just means the stall speed will be high.
  b) The fuselage of an aerobatic aircraft is optimized to be
   a fairly decent airfoil ... /intentionally/ so, with this
   maneuver in mind.

During knife-edge flight, the lift from the rudder has got to 
be *negative* (or at most very slightly positive).  We know this,
because otherwise there would be no stability of the angle of 
attack:
     http://www.av8n.com/how/htm/aoastab.html

To say almost the same thing another way, if the distribution of
mass in the airplane is consistent with stability, you will need
"top rudder" to control the angle of attack of the fuselage and 
maintain equilibrium of the torques in the XY (yaw) direction.

We need to have both equilibrium and stability.
  http://www.av8n.com/how/htm/equilib.html

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

Since the lift and drag you get from the fuselage are very 
unlike what you get from the wings, you can imagine that the 
slow /aileron roll/ is harder than it looks.
  http://www.youtube.com/watch?v=tzowQtqOM_I&t=2m58s
Anybody can do it badly, but making it look nice and smooth
is hard.