On Sep 16, 11:44*am, mattm wrote:
On Sep 16, 8:46*am, Nick S wrote:

Ok, so this has sparked a curiosity for me. Who has a list of WAGs
(Mental math calculations) that can be used in the cockpit for glide
distances with wind and such? Is there a resource right now listing
them? Obviously I know it depends on glider performance, but what are
some starting points?

-Nick S

I like to keep a simplified whiz wheel in my cockpit in case of gadget
failure (I have flown cross country with them). *You can construct one
with great ease by getting your favorite computer graphing program
(such as Excel) to print a chart with logarithmic scales. *Make one
with suitable distance numbers (e.g. 2-60 for miles or 3-120 for km)
and another with corresponding alititudes (e.g. 200-6000 feet or
100-4000m).
The trick is to get the scales the same length and to get the ratio
between
the low and high numbers the same. *Cut them out and paste them to
some lightweight cardboard (a manila folder works great) and hold them
together with a paper clip. *Scribble some notes as to what your
best speed and resulting glide ratios at various MC settings on the
contraption and you're all set. *If you want to get fancy you can
paste
the distance ruler from your chart onto the thing and use it as a
chart
ruler.

-- Matt

I forgot to add: in order to use it, put a mark on the altitude scale
that corresponds to the "1" unit on the distance scale (e.g. mark
5280 feet if you're using statute miles or 1000m if using km). To
set the contraption to a particular MC setting line up the mark
with the glide ratio from your table. Read your required altitude
directly by looking next to the distance you have to fly. If you have
a headwind or tailwind you can fudge a few points in the right
direction using the basic (S-H)/S ratio. E.g. at MC=2 you have
a best speed of 60 kts and a glide ratio of 30 (I'm picking a
medium performance plane to make it easy). With a 10kt
headwind you only get 5/6 the performance, so use 25 for
your glide ratio.

When I was a student pilot a long time ago everyone used fancy
whiz wheels because GPS hadn't (quite) arrived. My textbook
had a picture of a whiz wheel, so I applied my programmer/math
geek mind to the issue for a while and eventually programmed
a whiz wheel I could print on my laser printer. When I started
flying more that just a couple of miles from the airport I found
out how easy the thing was to use. Unfortunately my program
is lost (last version I had was on a diskette that my computer
wouldn't read) so I've just gone for the easy design.

-- Matt