All, thanks for your replies.

I should clarify that this is about depreciation for valuation and
price calculation in our club and not for tax purposes.

What I am trying to come up with is a tariff for our club gliders.
The goal is to charge enough in glider rental to maintain the assets
of the club. Conceivably, this would mean not just to keep a fleet in
the air, but to replace gliders as they age so we have reasonably
recent gliders to fly. Depreciation may be a major component. How do
other clubs deal with such issues?

(To give more of a background: The club in question currently has a
Schweizer 2-33 as training glider, and then a 1-26, a Pilatus B4 and a
Grob 102 Astir, and a Piper Super Cub. I think this is somewhat
typical for a number of smaller clubs in the US, and worth
discussing. While I love the club and enjoy flying there, you will
probably all agree with me that a reasonable forward-looking plan has
to include an update of the fleet. That is why I'd like to figure
out reasonable rental charges for those a/c, but also for potential
upgrades.)