Equation question from Reichmann X-C Soaring

[Tim Taylor]

I am working with a fourth printing (1988) and the equation presented
for Optimum Average Cruise Speed does not make sense. It is equation
VI in the book, but it gives a very slow speed to fly compared to the
graphical approach of just finding the tangent to the line.

Plugging in zero for the sink rate in equation V gives the same result
as plotting the tangent on the polar, I am not sure what equation VI
is finding.

Any one have some insight?

Thanks,

Tim

[Jack Glendening[_2_]]

On Feb 19, 10:36 am, Tim Taylor > wrote:
> I am working with a fourth printing (1988) and the equation presented
> for Optimum Average Cruise Speed does not make sense. It is equation
> VI in the book, but it gives a very slow speed to fly compared to the
> graphical approach of just finding the tangent to the line.

That equation gives what might be called the average "travel" speed of
a leg (Reichmann calls it a "cruise" speed), which includes the time
spent thermalling - it is not a "speed to fly". Jack

[[email protected]]

On Feb 21, 8:09 pm, Jack Glendening > wrote:
> On Feb 19, 10:36 am, Tim Taylor > wrote:
>
> > I am working with a fourth printing (1988) and the equation presented
> > for Optimum Average Cruise Speed does not make sense. It is equation
> > VI in the book, but it gives a very slow speed to fly compared to the
> > graphical approach of just finding the tangent to the line.
>
> That equation gives what might be called the average "travel" speed of
> a leg (Reichmann calls it a "cruise" speed), which includes the time
> spent thermalling - it is not a "speed to fly". Jack

Right - Be a bit careful, as the English translation has many
unfortunate names for the terms in these equations...

[Tim Taylor]

On Feb 21, 6:33 pm, wrote:
> On Feb 21, 8:09 pm, Jack Glendening > wrote:
>
> > On Feb 19, 10:36 am, Tim Taylor > wrote:
>
> > > I am working with a fourth printing (1988) and the equation presented
> > > for Optimum Average Cruise Speed does not make sense. It is equation
> > > VI in the book, but it gives a very slow speed to fly compared to the
> > > graphical approach of just finding the tangent to the line.
>
> > That equation gives what might be called the average "travel" speed of
> > a leg (Reichmann calls it a "cruise" speed), which includes the time
> > spent thermalling - it is not a "speed to fly". Jack
>
> Right - Be a bit careful, as the English translation has many
> unfortunate names for the terms in these equations...

Jack and Dave,

Thanks, I finally realized it meant "Average" speed, then found it
written that way in "Competing in Gliders".

Thanks,

Tim