Thanks for the response. I don't know if the Tach is accurate. Do
you have a good suggestion how I might check?

Ask your maintanance guy. A tach check may be part of the annual or the
100 hour. If you have access to a strobe and an accurate flash rate,
you could use that on the prop too. Use a partner, for obvious reasons.
"Kids, don't try this at home!"

Headwinds, of course, can't be calculated in the abstract, but
I do add this consideration when I plan actual flights.

You can figure a break-even point for winds.

You also need to include taxi time in your figuring. On the hobbs, you
taxi at full price. On the tach, it's less than half price. An
unexpected ground delay or early release could also swamp your calculations.

Now, do you actually have a choice, per flight, as to what method you'll
be using (tach or hobbs)? Can you decide after the flight?

Jose
--
Quantum Mechanics is like this: God =does= play dice with the universe,
except there's no God, and there's no dice. And maybe there's no universe.
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