Micro Drones
September 19, 2002, updated on
September 21, 2002
Updated on June 18, 2005
Source:
http://www.aerovironment.com/area-aircraft/prod-serv/bwidpap.pdf
I discovered with some astonishment on the web, thanks to my friend Christophe Tardy, the development of mini-drones. Interested readers will find an article (in English) in PDF format titled "Development of the Black Widow Micro Air Vehicle." In English, MAV stands for "micro air vehicle." The performance of such devices leaves you... speechless. Indeed, new things are discovered every day on the web. These objects resemble toys but are far from it. The Black Widow has a wingspan of 15 cm. The article refers to tests conducted in August 2000, i.e., two years ago. The ultimate purpose is obviously military.
The Black Widow
These tests mark the conclusion of a four-year development program. The specifications for this device are astonishing:
- Wingspan: less than 15 cm
- Weight: less than 100 grams
- Payload: 12 grams
- Embedded 2-gram video camera transmitting color images remotely
- Speed: 55 km/h
- Flight duration: 30 minutes
- Electric propulsion powered by battery
- Operational range (regarding communications): 2 km
- Onboard autopilot enabling untrained personnel to operate the device. Flight control via embedded microprocessor
- Flight control and radio communication management system weighs 5 grams
- Micro-motors actuating two control surfaces—a horizontal plane and a central vertical fin—each weighing half a gram
It was the Rand Corporation that launched a feasibility study on flying micromachines in 1993. It is noted that military planners envision developing devices reaching such a degree of miniaturization that they could be the size of a flying or crawling insect. Given that our era is defined by nanotechnology, how can we be surprised by the emergence of "nanobots" and "nanoaeronautics"? There is no theoretical limit to the miniaturization of objects, except molecular and atomic dimensions. For someone capable of creating "nano-pumps" just a few microns in diameter, devices measuring a few millimeters are "gigantic."
Several universities participated in this development program for micromachines and "microaeronautics," including those in Florida and Arizona. The defined objectives were to deliver a 30-gram payload to a target 600 meters away, with the machine remaining airborne for at least two minutes. At the end of this program, a prototype was successfully tested in August 2000, achieving the following performance:
- Mass: 80 grams (...)
- Wingspan: 15 cm
- Electric motor directly driving the propeller (carbon fiber; efficiency of 83%, while the motor itself has an efficiency of 70%)
- Flight duration: thirty minutes (...)
- Speed: 55 km/h, yielding a theoretical range of 27 kilometers and an operational radius of 13 kilometers
- Capable of transmitting acquired data up to 1.8 kilometers (current limit of its operational range), across sixteen channels
- Flight altitude: 250 meters. This is a typical operational altitude, not a ceiling
- Video signal transmitter mass: 1.4 gram. Color resolution: 510 by 488 pixels
- Power required by this transmitter: 550 milliwatts
- Signal power: 100 milliwatts at 2.4 gigahertz
- Remote control frequency: 433 MHz
- Payload: 12 grams
- Low overall cost
Lithium batteries are low-cost and extremely reliable. The aircraft flies at a constant speed for nine-tenths of the time, simplifying aerodynamic optimization. The electric motor weighs 7 grams. The motor-propeller unit delivers 10 grams of thrust at 5,000 rpm. Wind tunnel tests in a 50 x 50 cm diameter tunnel yielded a propeller efficiency of 83%, matching the computer simulations' prediction of 82%. The wing is made of expanded polystyrene, plus a covering and structural elements, all glued together. The coverings are made of Kevlar. The vertical fins are made of balsa. The data acquisition and transmission system, connected during flight, was designed for sixteen channels. In storage mode, the entire device fits into a briefcase (one might think of James Bond).
The "mini-airplane builder," the model aircraft constructor (which I once was), will be surprised by the craft's shape. No ailerons, a wing with very low aspect ratio. The explanation is simple: compactness was prioritized over pure aerodynamic performance (which would require a high aspect ratio). The absence of a tail: purely aerodynamic stabilization systems are kept to a bare minimum. This machine is
not manually piloted.
But this should not surprise anyone and is simply a consequence of advances in "servo systems" and automatic attitude control. Human performance in this domain is very limited. Their "sensors" are poorly performing and have long reaction times. You know the trick with the banknote placed as in Figure A, dropped, and the subject unable to catch it—simply because the delay between detecting the signal "bill in motion" and the command "close hand" arriving exceeds the time it takes for the bill to fall.
Next image, in
Ba speedboat maintaining constant altitude and high speed on its ailerons: unmaneuverable by a human.
In C, a robot built ten years ago by a friend, controlled by a simple PC of the time. Two degrees of freedom. On the mobile platform, a PVC tube supporting a pétanque ball or a tray filled with glasses. Returns to a stable position ultra-fast, without oscillations. Capable of enduring atmospheric turbulence up to a certain point. Detail: this robot was originally designed for the pastry industry, to write people's names in cream on birthday cakes ordered by customers. "Happy birthday, Marcel," with choice of font, etc.
Lacking support, the company went bankrupt ten years ago (normal: it was too simple and too inexpensive).
You yourself, during your airplane travels, unconsciously occupy machines that are not man-piloted or only poorly so. A Boeing 747 has a horizontal stabilizer with a surface area equivalent to that of the wings of a normal-sized aircraft. In "aerodynamic stabilization" mode, this stabilizer acts as a "downforce," compensating for the pitching moment generated by the wing. This unnecessarily increases fuel consumption. To understand all this, refer to my comic strip "L'Aspirissoufle" (formerly "Si on volait?"), available on
the CD containing over fifteen comics from the series "Les Aventures d'Anselme Lanturlu"
(18 euros from J.P. Petit, Villa Jean-Christophe, chemin de la Montagnère, 84120 Pertuis. Shipping included).
A normal wing, when loaded, develops a pitching moment. The horizontal plane (tail), acting as a downforce, compensates for this...