I would like to know the name and the usefulness of this piece that covers the top of the tire of some planes, such as some Cessnas.
"Wheel pants" is a common term for these wheel fairings, at least in US usage, which serve to reduce drag. They have also been called "spats", though that term has traditionally been reserved for something much larger, at least in US usage.
How can drag induced by the landing gear be reduced?? -- see all answers
What is "spatted undercarriage"? -- see all answers