There is interesting progress being made to develop a nanoair vehicle that weighs less than 10 grams and is shorter than 3 inches. A promising design is using electricity and plasma jets.
Plasma micro thruster powered UAV the size of a cigarette
The Nano Air Vehicle (NAV) Program will develop and demonstrate an extremely small (less than 7.5 cm), ultra-lightweight (less than 10 grams) air vehicle system with the potential to perform indoor and outdoor military missions.
Technical Area Figures of Merit -Phase I targets
1. Aerodynamic Performance and Airfoil/Wing/Rotor Design and Manufacture Develop computational aerodynamic modeling tools to design a high performance airfoil at a low Reynolds number.
Demonstrate reliable wing manufacturing principles and achieve wing loading of > 0.1 kg/m2.
Demonstrate airfoil section steady lift to drag capability over 8 at low Reynolds number (Re < 15,000). 2. Propulsion and Power Demonstrate system electrical power to mechanical transduction conversion efficiency of at least 20 percent. Demonstrate an ability to meet power requirements for a notional mission of 1 kilometer with a total hover time of over one minute.
19 page pdf, Santhanakrishnan, A. and Jacob, J.D., “On Plasma Synthetic Jet Actuators,”
Plasma actuators, also known as dielectric barrier discharge actuators (or OAUGDPTM, one atmosphere uniform glow discharge plasma1) typically refer to an asymmetric arrangement of two electrodes separated by dielectric material. Back in Jan 2006 they were creating 10,000 pulses of 1 m/s jets.
Hydrodynamics & Aerodynamics Laboratory at Oklahoma State University is working on novel applications of fluid mechanics, particularly to aerospace, including flow control, UAV design, and bio-fluid mechanics.