On Friday, May 15, 2020 at 7:18:47 PM UTC+2, Charles Ethridge wrote:
Hi, all.

When racing a typical 1-2 hour flatland race in, say, a Diana2 or Ventus3-15 (15 meter ships with water ballast and flaps), are there any guidelines or formulas for how much water to dump, particularly when thermals are weak or narrow?

Here are the parameters I'm thinking would apply (but I'm no expert yet- thus the question):

1. Average thermal strength
2. Average thermal width
3. Average distance between good thermals
4. Height band for the day

I was hoping to find something on this subject in a glider racing book or the Diana2 flight manual, but no luck so far finding either googling.

Ben Ethridge

The designer of the Diana 2, Krzysztof Kubrynski, covers this in his paper "HIGH PERFORMANCE SAILPLANE DESIGN STRATEGY USING INVERSE DESIGN AND OPTIMIZATION TECHNIQUES", and the results can be summarized with:
3kts, tank it
2kts, empty it