Ex 18 Diversions - Wind Spider

Today was my first double lesson. Very lucky with the weather as it turns out, the weeken before had been awfull,
and the rest of the weekend wasnt much better, but our 9am slot Saturday morning worked out great. Weather got a bit poor
by the time we headed back in, had to dip down below 2K feet from the 3K we were at but hey, got 1:45 mins flying time in.

We started the day of with a ful brief (my first with Doug) and we went through Doug's wind spider, which he wants me to draw
on the map for every lesson from now onwards.

Drawing the wind spider:

1) Get the wind for the altitude say 3000ft , 250/20 knots.
2) On the basis that we are travlling at 100knots airspeed, in 1/10 minute we should travle 10 miles
i.e. airspeed / 10, so whatever speed we are travelling at in 6 mins we travel 1/10 (move dec place to the left)
so 258 knots in 6 mins would cover 25.8 miles.
3) Calculate Max drift angle so put in t 100 knots and 90 degrees track off the wind, so giving full crosswind, the flight
computer will then give you your max drift angle, write this on the map.
4) for each 45 degree increment, use the whizwheel to calc ground speed with the wind, so N, NE, E, SE,S,SW,W,NW
which gives you 8 legs values - hence the spider. we know that from the groundspeed, we divide by 10 at it gives us the distance
5) Draw a point on the map somewehere not being used, for the center of the spider.
6) draw the 8 distances legs outwards in the correct direction for each of the legs of the spider.

Once completed, you then have 8 lengths in 8 directions which i indicate how far you can travel in that direction in 6 mins


Using the wind spider:

So youre flying along, and need to divert (for weather etc), you plot where you are now, look at the place you want to land,
and draw a line to it. You estimate in your head what that angle is - lets say 050 degrees. The closest spider to that is the NE
spider at 45 degrees. Using the end of pen of whatever hold then pen up to this spider line and put your finger on its length.
The go back to your new track, and measure how many of the lengths are on the track (roughly). This gives you your time, i.e. 2.5
lengths = 15 mins (2.5 * 6). We have calulated the max drift for today as being 15 degrees. and the wind is coming from 140 degrees
so we have a full crosswind from the right - so we add the full max drift.
Hence we need to fly 065 degrees for 15 mins to get to our destination.
Flyihg along, we constantly check we are tracking that our guess is right, and when we start the turn, start the watch, and gross error
check.

Anyway, we did 4 of these in our lesson today and the first 3 worked out perfectly, the last one a little less accurate on the timing,
but heading was correct, and i adjusted half way for the new times, so we got there exactly on time (2mins added to a 20 mins flight
time)