The US Navy has tested a spy-in-the-sky glider 30cm across made from circuit boards.
"Its lack of a motor and small size make it nearly undetectable in flight," said the US Naval Research Laboratory.
Called Close-In Covert Autonomous Disposable Aircraft (CICADA), the planes landed within 5m of their targets, despite being released 17km high more than 50km away. 
"The mission profile is straight forward," said test flight coordinator Chris Bovais. "The CICADA is dropped from another airborne platform, flies to a single waypoint, and then enters an orbit. It descends in that orbit until it reaches the ground."
In this case, two CICADAs were held under the wings of a larger (Uasusa Tempest, 3m span) powered autonomous aircraft, and all three were dropped from a high-altitude balloon.
"The Tempest mother ship was released from the balloon, autonomously executed a pull-up manoeuvre, and then carried the two CICADAs to a drop location," said the Lab. "Each CICADA vehicle was then released from the mother ship and autonomously flew to the pre-programmed target waypoint."
The airframe of the Mark III CICADA is also the autopilot PCB: "the first known multi-purpose airframe-avionics implementation of its kind", said the Lab. "This novel construction method significantly reduces assembly time, minimises wiring requirements, and enables the manufacture of low-cost and rugged micro air vehicles."
Various payload sizes and sensors can be accommodated by making bigger or smaller airframe-PCBs and attaching an appropriate wing - also made from flat sheet.
Proposed sensors include: acoustic, magnetic, chemical, biological and signal intelligence (sigint).
CICADAs can spy on the way down, or replace sensors manually positioned on the ground.
On the test CICADAs, the only flight sensors were a 5Hz GPS receiver and a two-axis gyroscope, joined by a computer running custom software
"Although having minimal sensors, the navigation solution and the flight controller proved to be quite robust during in-flight testing, routinely recovering from tumbling launches," said the Lab. "The flight controller also included a custom algorithm that accurately estimated wind speed and magnitude, despite having no air data sensors onboard."