Archive for 2008

What Is a UAV

The term UAV is an abbreviation of Unmanned Aerial vehicle, meaning aerial vehicles which operate without a human pilot. UAVs are commonly used in both the military and police forces in situations where the risk of sending a human piloted aircraft is unacceptable, or the situation makes using a manned aircraft impractical.

One of the predecessors of today’s fully autonomous UAVs were the “aerial torpedoes”, designed and built during World War One. These were primitive UAVs, relying on mechanical gyroscopes to maintain straight and level flight, and flying until they ran out of fuel. They would then fall from the sky and deliver and explosive payload.

More advanced UAVs used radio technology for guidance, allowing them to fly missions and return. They were constantly controlled by a human pilot, and were not capable of flying themselves. This made them much like todays RC model airplanes which many people fly as a hobby. It is interesting to note that the government considers all aircraft UAVs, if they are unmanned and used by a government or business.

After the invention of the integrated circuit, engineers were able to build sophisticated UAVs, using electronic autopilots. It was at this stage of development that UAVs became widely used in military applications. UAVs could be deployed, fly themselves to a target location, and either attack the location with weapons, or survey it with cameras and other sensor equipment.

Modern UAVs are controlled with both autopilots, and human controllers in ground stations. This allows them to fly long, uneventfully flights under their own control, and fly under the command of a human pilot during complicated phases of the mission.

What Are UAVs Used For?

Since their creation, UAVs have found many uses in police, military, and in some cases, civil applications. Currently, UAVs are most often used for the following tasks:

• Aerial Reconnaissance – UAVs are often used to get aerial video of a remote location, especially where there would be unacceptable risk to the pilot of a manned aircraft. UAVs can be equipped with high resolution still, video, and even infrared cameras. The information obtained by the UAV can be streamed back to the control center in real time.
• Scientific Research – In many cases, scientific research necessitates obtaining data from hazardous, or remote locations. A good example is hurricane research, which often involves sending a large manned aircraft into the center of the storm to obtain meteorological data. A UAV can be used to obtain this data, with no risk to a human pilot.
• Logistics and Transportation – UAVs can be used to carry and deliver a variety of payloads. Helicopter type UAVs are well suited to this purpose, because payloads can be suspended from the bottom of the airframe, with little aerodynamic penalty.

Types Of UAVs

There are many different types of UAVs, designed for different purposes. The US air force is one of the most prominent users of UAV technology, and classifies UAVs by dividing them into tiers. To get a general idea of the different types of UAVs used, here is an abbreviated version of the US air force specification:

• Micro UAVs – small, extremely portable units.
• Low altitude, long endurance UAVs
• High altitude, long endurance UAVs employing a conventional design.
• High altitude, long endurance UAVs using a low observable design.

Some UAVs use a blimp design, and are well suited to carrying large amounts of cargo.
Some of the first UAVs were called “drones” and were not autonomous, because
they required constant control input from a remote human pilot. Computer technology now allows UAVs to make their own decisions, or fly autonomously. Autonomous flight involves the UAV making decisions as it flies.

Generally, autonomous flight consists of the following operations:

• Interpreting sensor input, and merging the input of multiple sensors
• Communicating with ground stations, satellites, and other UAVs and aircraft
• Determining the ideal course to fly for a given mission, based on sensor input.
• Determining the best maneuvers to perform for a given task
• In some cases, cooperating with other UAVs to accomplish a common task.

The Swarm Project by MIT is an excellent example of cooperation between UAVs. Autonomy is an area of rapid development, with the ultimate goal of replacing the human pilot entirely.

Conclusion

UAVs represent an area of rapid development in both military and civilian applications. UAVs unique capability of flying dangerous, long, or precision missions give it a unique advantage over conventional aircraft. This article has only briefly introduced UAVs and their applications.

Introduction

Aerial photography has been used since the first hot air balloons to give a new perspective to the objects and landscapes in our world. With the modernization of both aviation and camera technology, a new type of aerial photography was born. RC aerial photography uses ordinary to advanced RC aircraft to carry a camera payload and obtain aerial pictures. RC aerial photography has evolved into both an exciting hobby, and a thriving business.

RC aerial photography can add a new perspective to images of large objects. by showing the large scale relation between different objects. Many engineering, mapping, and surveying projects depend on a clear understanding of the large scale properties of an area of land, making aerial photography the perfect tool for obtaining this information. Traditionally, aerial pictures were obtained by sending a human photographer on a flight in a full scale aircraft, usually either an airplane or helicopter. This is a time consuming and inconvenient, because aerial photography is affected by rapidly changing weather and lighting conditions.

RC aerial photography is a simple and cost effective solution. You can rapidly deploy and recover an RC aircraft, and get aerial pictures of equal to (and in many cases better) quality than those taken from a full scale aircraft. Conventional aircraft are limited by altitude regulations, so they can fly at a minimum of 500 feet above ground level. RC aircraft are free to maneuver at any altitude, giving you the freedom to decide which altitude is best for your aerial photographs.

Not only is RC aerial photography a valid business, it’s also a great hobby. What better way to get aerial pictures of your house, or pictures of your street than with your own RC aircraft?

This article will introduce you to RC aerial photography, show you how to get great aerial pictures, and demonstrate some of the many applications of available technology.

The Basics Explained: Light and Angle

Light is one of the primary factors affecting any aerial photo. Unlike indoor photography where several sources of light are available, RC aerial photography depends entirely on the light provided by the Sun. Use sunlight to your advantage by following these guidelines:

Ground based photography is best done in the morning or evening, because the of the favorable lighting and because shadows are hidden behind the subject. Aerial photography exposes these shadows, so try to take your aerial pictures when the Sun is highest in the sky. This is usually between 10:00 AM and 2:00 PM, but will vary from season to season. Taking aerial photos when the Sun is high will minimize the shadows that appear in your aerial pictures, increasing clarity and reducing “visual clutter”.

There are three main angles or styles from which aerial photos are taken. Each produces a different visual effect, and is used for different applications. They are listed as follows:

1. Vertical – Vertical images are taken with the camera pointing straight down. This is a great angle for surveying, because it gives the photo a scale that you can use to measure the distance between objects. You can calculate the scale of an aerial photo by dividing the focal length of the lens by the altitude of the RC aircraft. For example, an aerial picture taken from a camera with a focal length of 1 inch at an altitude of 50 feet (600 inches) would have a sca1e of 1/600. This means that one inch measured on the image corresponds to 600 inches on the photo. This calculation will work with any units (kilometers, meters, yards etc.) as long as both the focal length of the camera and the height above ground are expressed in the same units. Because the camera refocuses to keep the image sharp, this method will provide only a rough estimate of the scale factor of the image. Fortunately, software is available to calculate and measure distances on aerial photos precisely.
2. Low Oblique – Low oblique photos are taken from an angle of 40 degrees from vertical. They provide a large view of the ground, but don’t show the horizon.
3. High Oblique – High oblique photos are taken at least 70 degrees from vertical, and include the horizon. High Oblique photos will provide a very large overview of an area, and can show varying amounts of sky in the image depending on the angle from the ground.

Atmospheric Effects

There are several atmospheric affects which influence the look of your aerial photos:

1. Haze – Haze is caused by particles and water drops suspended in the air. Haze severely limits the contrast of your pictures, because the light emitted from them had to travel through hundreds of feet of haze before reaching the camera. Haze is most common in metropolitan areas, where there is significant pollution, and during the summer months. Even if atmospheric conditions aren’t perfect, you can minimize their effects on your pictures by shooting with the sun at the back of the camera. This avoids showing haze or smoke in the atmosphere.
2. Clouds – Clouds can also hinder RC aerial photography, by diffusing light and casting large shadows on the ground. In general cumulus clouds (large, low clouds) are the most obscuring, but even thin cirrus (high and wisp like) clouds can cause a loss of lighting. Try to take aerial pictures on days with a minimum amount of cloud cover.
3. Smog – Smog has a similar effect as haze, reducing the clarity of your aerial pictures. Smog is caused by excessive air pollution, and is most common in large cities.

Effects Caused By Motion

Cameras work by letting light hit a photosensitive material for a set amount of time. If the camera or subject are moving relative to one another, then image blurring will occur during the exposure time. By reducing the exposure time (increasing the shutter speed) you can minimize blurring in your aerial photos. You can also minimize image blurring by matching speed and direction with the target.

Planning The Flight

The most important factor that you need to consider when planning an RC aerial photography flight is the weather. As previously discussed, cloud cover will lower available light and reduce the contrast of the aerial pictures. Wind also has an adverse effect on RC aerial photography – creating unwanted motion between the camera and the subject being photographed. Also, RC become difficult to control in high wind conditions, increasing the chances of an accident.

An ideal day for RC aerial photography would be windless, completely clear of clouds, and free of any atmospheric interference (smog, haze etc.) Because this is rarely the case, you will have to listen to weather reports and use your own judgment to determine the best days to fly. There are several excellent sources of weather information available, including radio reports, television, and the internet. You can find weather information and forecasts at the Weather Network and (for Canadian locations) at Navcanada. By clicking on the METAR/TAF button on the Navcanada forecasts and observations page, you can browse frequently updated weather data, used every day by pilots of full scale aircraft. Unless you are familiar with METAR/TAF abbreviations, we suggest that you select plain English forecasts and reports. The METAR is a weather report taken at a current time for a certain location, and the TAF is a forecast predicting the at the location.

Weather reports outside North America can be found on BBC Weather.

Conclusion

RC aerial photography can provide a new perspective on everyday objects and places. New platforms, such as the Tango aircraft (for long range applications) and the Draganflyer X6 open new possibilities for this exciting business and hobby. A full exploration of RC aerial photography is beyond the scope of this article, we suggest reading some of the excellent books on the subject available.