I was recently flying HLG in Sedona Arizona. As I recall the density
altitude was easily above 10,000 feet. I noticed a few things.
First, my launches were noticeable higher. I have a pretty good launch that
is completely natural (i.e.. requires no thought of technique), and very
consistent. I would guess that my launches in Sedona were on average 10
feet higher than normal sea level launches. The Encore just kept going and
going on the up line. I was amazed. These launches were to the moon. (No
I was not channeling like all the granola flakes who commonly visit Sedona)
The second thing I noticed was that the approach to hand catch was
frustratingly difficult to get correct. Again, I fly enough HLG that I
normally don't have to think about getting home for the hand catch. In
Sedona, I was either too fast, requiring a wave-off, or I was short and
failed to make it home. This drove me crazy. I normally never miss the
hand catch. It's hard on the glider to land it on rocks and parking lots
and stuff. This was maddening.
The third thing I noticed was that the glider wasn't any harder to thermal.
The disadvantage of having to fly at higher ground speeds was off-set by the
fact that you were covering more ground with the glider zipping around at
that higher speed. When lift was located, the glider thermalled just like
normal.
In conclusion, I like flying at high density altitudes (other than needing
to learn to catch all over) and would like to attend a contest up in the
mountains to see how others deal with the differences.
Timothy E. Cone
[EMAIL PROTECTED]
http://www.NightOps.com
----- Original Message -----
From: "Don Stackhouse @ DJ Aerotech" <[EMAIL PROTECTED]>
To: <[EMAIL PROTECTED]>
Sent: Friday, April 28, 2000 10:39 AM
Subject: Re: [RCSE] Does Altitude cause bad air?
> Glenn R. Whitcomb asks:
>
> >...Does high altitude affect lift and the way gliders
> >fly?
>
> In addition to the increase in true airspeed caused by the lower air
> density, as discussed by Oliver Wilson, and the associated increase in
sink
> rate and turning radius, there is also a decrease in Reynolds number. This
> usually reduces the max lift coefficient, and increases drag.
>
> The reduction in air density causes an increase in speed, but since lift
is
> proportional to the square of the velocity, that speed increase is
> inversely proportional to the SQUARE ROOT of the air density change.
> Meanwhile, since Reynolds number is LINEARLY proportional to density (and
> because air viscosity at our altitudes is approximately constant with
> altitude), the change in Reynolds number follows a linear function.
> Therefore, the increase in airspeed due to the thinner air at higher
> altitude cannot compensate completely for the loss of air density, and the
> Reynolds numbers go lower. This usually hurts performance over the entire
> operating envelope, althoiugh the exact extent of that loss depends on how
> well the design of the specific model in question handles the decrease in
> Reynolds numbers.
>
>
> Don Stackhouse @ DJ Aerotech
> [EMAIL PROTECTED]
> http://www.bright.net/~djwerks/
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