Bronze Badge question

Greg Arnold wrote:

When you are thermalling, a headwind tends to move you
upwind in relation to the airmass.

Why then does my GPS record very nice little loops, the centers
of which parallel the movement of the average wind during thermaling
and move DOWNwind?



Jack

To quote page 116 of Reichmann's "Cross-Country Soaring" 7th edition,

"The problem is definitely a different one from that of greatest
distance described above. Then we were optimizing for distance; now we
are optimizing for cruise speed: how fast should we fly from thermal to
thermal to realize the best average speed. Since the best cruise
airspeed will result in the best ground-speed as well, there is no need
to calculate the effects of wind."


Tony Verhulst wrote:
.... Best avg XC speed
will be achieved through answer c.

Ok, answer C says "The best lift/drag speed with no regard to wind
velocity.".

So, my best lift/drag speed is 50 knots and I'm flying into a 50 knot
headwind at 50 indicated. And, I'm going ... where? "A" is the correct
answer, IMHO. Answer "A", in the above example, would get you a ground
speed of 25 knots (75 - 50)- you're not going to do much better than
that. The question, though, is poorly worded.

Tony V.

Hi,

I agree with Helmut Reichmann on this topic. Thermals move with the wind.
Optimizing speed between them has nothing to do with the wind speed. If you
were flying downwind between thermals would you slow down? No.

Of course it is all different when you are on final glide. At that point
you do want to factor in the effect of wind if you are trying to optimize
distance. All the final glide computers that I am aware of have no way to
tell them than you are on final glide and always give speed to fly commands
for interthermal flying. That is because they are helping you optimize
speed around a task, not distance from a given point. They also work well
to help you determine at what altitude to leave the last thermal. Just set
the MacCready setting on the final glide computer or software to your actual
climb rate in the last thermal. When it says you can make it home you
should leave. That will optimize your final glide time. That is also from
Reichmann's excellent book.

Good Soaring,

Paul Remde
Cumulus Soaring, Inc.
http://www.cumulus-soaring.com

"John Cotter" wrote in message
ups.com...
To quote page 116 of Reichmann's "Cross-Country Soaring" 7th edition,

"The problem is definitely a different one from that of greatest
distance described above. Then we were optimizing for distance; now we
are optimizing for cruise speed: how fast should we fly from thermal to
thermal to realize the best average speed. Since the best cruise
airspeed will result in the best ground-speed as well, there is no need
to calculate the effects of wind."


Tony Verhulst wrote:
.... Best avg XC speed
will be achieved through answer c.

Ok, answer C says "The best lift/drag speed with no regard to wind
velocity.".

So, my best lift/drag speed is 50 knots and I'm flying into a 50 knot
headwind at 50 indicated. And, I'm going ... where? "A" is the correct
answer, IMHO. Answer "A", in the above example, would get you a ground
speed of 25 knots (75 - 50)- you're not going to do much better than
that. The question, though, is poorly worded.

Tony V.

This is like asking: What is the air-speed velocity of an unladen
swallow?

There are many more questions to ask before you can give an answer.
All the answers are wrong that are given on the exam. But there are
many more factors that would need to be answered:

1. Is this an intermediate leg or the final leg?
2. How strong is the average thermal?
3. If it is the final leg how close am I to final glide?
4. How strong is the wind?
5. Is there a wind gradient?

If this was meant to assume an intermediate leg, you need to climb back
to altitude at the end of the glide, no appreciable wind gradient, and
the wind is less than speed to fly then the correct answer is the
MacCready speed for the next expected thermal.

Tim

Correct Test Answer is A)

You'd better consider winds throughout flight, as well as inter
thermal..

You'd be smart to use MacCready (correct spelling of Paul's name by the
way) speed estimate plus 1/2 headwind component. If not, I'll beat you
around the course. My Cambridge computer factors in wind component.

Kansas Example:

Winds 40K at altitude / 1-26 sailplane.. L/D of 45K for argument..

c) if I fly at L/D of 45K - I'm going forward at 5K.
b) Min sink of lets say 40K.. plus 1/2 of 40K headwind - I'm going
ahead at 20K.. better
a) L/D speed of 45K plus 1/2 of 40K (20K) equals 65KIAS - I'm going
ahead at 25K .. best.

Best answer for the question.. yet should still use MacCready speed
estimate plus 1/2 headwind component.

Reference FAA Glider Flying Handbook, FAA-H-8083-13; pge 7-34



wrote:
80) What is the approximate proper airspeed to use when flying between
thermals on a cross-country flight against a headwind?

a) The best lift/drag speed increased by one-half the estimated wind
velocity.
b) The minimum sink speed increased by one-half the estimated wind
velocity.
c) The best lift/drag speed with no regard to wind velocity.

The SAA safety site gives the correct answer as "A". I have alway
heard that when flying between clouds you did not consider the wind in
your calculations. Maybe the tricky part of this question is the word
"Thermals".

I'm curious to know your contest record. Also curious to know what
Cambridge computer you use. I thought I had the latest one.

Andy (GY)

Here is the clue guys......."BRONZE BADGE"...... meaning, I just
learned how to fly a glider and Im trying to get to the destination
airport.

Lets start with best L/D because Im trying to not land out and time is
not an issue, and then add 1/2 the windspeed, since most gliders will
do this and still be on a reasonably decent part of the polar in terms
of sink...and get some better penetration.

I say "A" is the correct answer for a Bronze Badge level pilot since
they base their knowledge on a lot of generalizations about performance
to make inflight calculations relatively easy...

...of course the contest level pilot will have a much more refined
answer with his vast knowledge of his own glider and intimacy with its
performance specs, along with his computer instruments that he can
program for optimum results.

Ray