At 06:57 PM 16/03/2013, you wrote:
On 15/03/2013, at 5:12 PM, Adam Woolley wrote:
Have you got any rough 'rules of thumb' that you use in order to
decide if the short term deviation is worth it or not?
Better air within 30 degrees either side of track is worth deviating for.
It is more complicated than that. Keep in mind the extra distance you
would fly to get to the next turnpoint. if you end up abeam the
turnpoint by flying a track 30 off the direct one you will fly 50% further
Also plot the achieved cross country speed vs the average climb rate.
It is not a linear function. It may be worth greater deviations from
track on weak thermal days than strong ones.
You can get these numbers (and a lot of other interesting
information) using a ruler, from the polar plotted on a piece of
graph paper and a few simple geometric constructions.
Your highly trained and experienced GFA instructor should have
explained this to you before you try to go cross country.
(Pig squadron on the grid, ready for first launch).
Yes, staying out of sink is very important. Most of us do it poorly.
It is extremely important when trying to center weak and broken
thermals which is why I like a vario with a sink sound as it provides
full information on the bad air as well as the good air while doing this.
Byars and Holbrook said this in their book "Soaring cross country
" 40 years ago - "never fly through the same bad air twice".
Mike
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