 Lancair crash at SnF
On Apr 24, 6:41 pm, tman <inv@lid> wrote:
> Hold on while I try to correct some nits in what Bertie said and see
> what happens :)
>
> Bertie the Bunyip wrote:
> > There is no inertia involved in making a downwind turn. None.
>
> Here's why I wonder about that. Let's suppose 65 KAS before and after a
> 180 turn from a 10 KT headwind. OK, before the turn, your groundspeed
> is 55KTS and after the turn your groundspeed is 75KTS. Your intertial
> frame of reference is tied to the g/speed, not the a/speed. So -- the
> kinetic energy of the aircraft and contents is about 33% higher
> (75/55)^2. That energy is only going to come from one place with no
> power -- trading in altitude (potential energy) for kinetic energy.
See the previous post. There's a change in kinetic energy, but
very, very little. Many people make the mistake of thinking that the
earth has an effect on the airplane. It does, but only vertically, by
gravity. Gravity has no horizontal Component. Like a gyroscope, which
is rigid with respect to space and cares not one bit about the earth,
the airplane's mass, as it moves in the horizontal, is affected only
by its relationship to space and the air it flies in.
That isn't to say that the earth isn't going to get in the
way a little harder. Landing downwind, as with landing into the wind,
involves transferring the weight from the wings to the wheels, and
downwind means much more groundspeed and maybe loss of control as the
roll continues at higher speed while the flight controls feel a
decreasing airspeed, or maybe the airplane will run out of runway.
Bang.
We do illusions created by drift turns with students, usually
in a strong wind and at around 500 feet, so that they can see that the
ball stays centered in the turn while they get the visual impression
that the airplane is skidding or slipping on the downwind and upwind
sides of the turn. The airspeed does not change. Not so's you could
read it. If we put the student under the hood and make him fly on
instruments while we do this, he can't tell us when he's turning into
the wind or out of it. Can't feel anything, can't see any performance
changes on the gauges.
Dan |