A glider is just like any other asset: you must pay capital gains taxes on any gains. Losses on personal use items such as cars are not deductible (
https://www.irs.gov/taxtopics/tc409.html). The basis (cost) for the gain calculation includes such things as:
1. Amount paid to seller.
2. Import duties, if any.
3. Transportation costs.
4. Inspection costs.
5. Costs to make the glider airworthy.
6. Sales tax.
Costs to maintain the glider after purchase are not a part of the basis or the capital gains calculation. Installation of new equipment, like a transponder, are.
PS the AOPA article, which is quite good, does not address capital gains taxes at all.
Tom