In this letter, we propose an energy-efficient 3-
dimensional placement of multiple aerial access points (AAPs),
in the desired area, acting as flying base stations for uplink
communication from a set of ground user equipment (UE).
The globally optimal energy-efficient vertical position of AAPs
is derived analytically by considering the inter-cell interference
and AAP energy consumption. The horizontal position of AAPs,
which maximize the packing density of the AAP coverage
area, are determined using a novel regular polygon-based AAP
placement algorithm. We also determine an accurate upper
bound on the maximum number of AAPs that could be
deployed in a given circular area. The effect of the AAP energy
consumption on the optimal placement and the analytic findings
are verified via numerical simulations