final glide estimates

bagmaker wrote:
Newbie help required!
Lets suppose I am on a shallow final glide, 60k out in my 40:1 ship,
cruising at 60 knots. Recent thermals have been at least 5 knots and I
am coming into some big lift. For the discussion rough air Vne is 100
knots.

Best not to confuse "rough air" speeds with Vne, which is the "never
exceed" speed. The "rough air" limit (I'm not sure this is used any more
- only my very old gliders had it) is quite a bit lower, and the newer
gliders don't have it, but do state "maneuvering speed", lower yet.

And, practically speaking, you certainly don't want to be going Vne when
there are thermals bigger than 5 knots in your way! If the glider hangs
together, it will be a very rough ride.

What strength thermal should I take to increase finishing speed to Vne

You need your gilder's polar to determine what strength thermal is
needed for any McCready speed determination - nothing else needed.

and how much (if any) time will this save me?

It will save you time, but without the polar, your altitude above the
finish, and the distance to the finish, we can't give you a number.

How do I estimate this at the time?

You don't have to estimate it. A chart of speed vs McCready settings is
made up ahead of time. The less thinking you have to do while flying,
the more time you can spend flying the glider.

What is the latest point on track
to take such a thermal?

I'm guessing, but I'd say about where you need to stay in the thermal at
least one full turn to get high enough to use the 100 knot speed. Any
closer, and you'd waste time getting unneeded altitude.


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Eric Greenwell - Washington State, USA

www.motorglider.org - Download "A Guide to Self-launching Sailplane
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