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Re: Campbell's even crazier than a MANIAC? (archeopteryx climbing)
Im pretty sure this isn't true due to the exponential nature of drag forces
relative to velocity, but rather is a good approximation for small % changes in
The vertical descent rate, delta h, has a linear relationship with the delta
energy, obviouslyby the factor mg.
However, to maintain the same glide, if the vertical rate doubles, the
horizontal must double as well.
This results in 4x as much drag, with only 2x as much change in potential
energy to make up for that drag, the aircraft will decelerate, and its glide
will be worse(at that angle of attack).
For lower values, like 10% more weight, the glide doesn't change appreciably.
For a given angle of attack(AoA)
10% more weight needs 10% more lift, which is a factor of airspeed squared, so
it must fly ~3.16% faster, but will have 10% more drag, as work done is
proportional to force (over a distance), 10% more "work" is done, and it must
use up 10% more PE, and thus sink 10% faster.
103.16/110 = .9378 -> call it 94% the previous glide for a 10% increase in
For something getting a 20:1 glide, a 10% increase in weight only brings that
down to about 18.76:1 for the same AoA.
This could possibly be increased by flying at a higher AoA to decrease
parasitic drag, however this AoA will be higher than optimum AoA of the lighter
As most designs don't get best glide right above stall speed, there is some
"slop" such that a 10% increase in weight doesn't mean a sqrt(10%) increase in
best glide speed(with an accompanying 10% increase in descent rate).
Still, glide is reduced somewhat
--- On Tue, 9/30/08, jrc <email@example.com> wrote:
> From: jrc <firstname.lastname@example.org>
> Subject: Re: Campbell's even crazier than a MANIAC? (archeopteryx climbing)
> To: email@example.com
> Cc: firstname.lastname@example.org
> Date: Tuesday, September 30, 2008, 8:38 AM
> That energy can also come from atmospheric shears as well as
> from delta h.
> As an aside, one of the interesting things about gliding
> flight is that
> glide angle and glide range are not decreased with
> increasing weight. For a
> given planform, increasing the weight increases both the
> sink rate and the
> airspeed by exactly the same amount, so the glide angle and
> range remains
> ----- Original Message -----
> From: "Erik Boehm" <email@example.com>
> To: "DML" <firstname.lastname@example.org>;
> Sent: Monday, September 29, 2008 10:40 AM
> Subject: Re: Campbell's even crazier than a MANIAC?
> (archeopteryx climbing)
> > More generally regarding powered flyers and gliding
> .... if their minimum
> > energy output to maintain level powered flight is X
> watts, then when it is
> > not powering its flight(flapping, a propellor, etc),
> those X watts are
> > coming from a change in potential energy, ie delta h
> (height in: PE =
> > mgh).
> > The more energy intensive the flying must be, the
> faster it will sink
> > while gliding, but it can still glide.