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While the operation of radio control models as a hobby is a relatively recent event, the technology behind the hobby dates back to the nineteenth century. During the course of this blog, we’ll trace the evolution of rc model transmitters and their applications.
The first use of radio control technology dates back to 1898, when Nikola Tesla built a pair of radio controlled boats, demonstrating them to a shocked crowd at Madison Square Garden. Though only able to cruise a short distance, the boats showed the potential of radio control. During World War I, Archibald Low designs an aerial drone plane for the Royal Flying Corps for use as a radio-controlled guided bomb. By the 1930s practical rc planes were available to hobbyists, with Walter and William Good building and flying the first fully-functional rc aircraft in 1937. As a result of progress in radio control technology during World War II, the use of rc models increased dramatically during the 1950s, though the battery capacities were limited and needed frequent rechargings until transistors became available.
Transistors also reduced the voltage requirements of a battery, virtually eliminating the older high voltage batteries. One channel rc radio kits were introduced in the 1950s with preassembled units offered later. In both tube and transistor radios of the era, the rc planes control functions were operated by an electromagnetic escapement utilizing a rubber- band loop system from which the rc pilot could control rudder and speed functions. By the 1960s, crystal-controlled superheterodyne receivers became available. These offered a true three-dimensional control of rc aircraft (yaw, pitch and motor speed). Heterodyne receivers also provided a more sensitive signal selection coupled with a more stable rc model control. After World War II commercial rc planes control signals were limited to two or three channels using amplitude modulation. More channel choices were added in the 1960s using frequency modulation, which offered twenty or more operating channels.
The next generation of rc model transmitters was developed in the mid-1970s. A Pulse Width Modulation (PWM) Signal is a method by which an analog signal is produced using a digital source. PWM signals consist of two primary components that define its behavior: a duty cycle and a frequency. The duty cycle is the amount of time the signal is in a high (on) state as a percentage of the total time it takes to complete one cycle. The frequency determines how fast the PWM completes a cycle, and consequently how fast it switches between high and low states. By cycling a digital signal on and off at a fast enough rate, and with a certain duty cycle, the output will appear to behave like a constant voltage analog signal when providing power to devices. These signals transmitted in a rapid succession could control multiple functions on the rc model.
On the heels of PWM signal technology Pulse Code Modulation (PCM) was developed. While analog technology uses continuous signals, digital technology encodes the information into discrete signal states. With two states assigned per digital signal, they are called binary signals, while a single binary digit is termed a bit. While PCM is an efficient means of signal transmission, it is by no means foolproof due to the proliferation of radio control devices in both the hobby and industrial markets. To overcome this problem, some late model FM receivers which still use PWM coding can be modified by the use of advanced computer chips to detect the individual signal characteristics of a particular Pulse Width Modulation without needing a designated code, as required with PCM coding.
By the early 2000s, Spread Spectrum rc contol systems came into use. A Spread Spectrum rc control system uses a variable frequency of operation, usually in the 2.4 gigahertz band, in which the rc transmitter stays on a given frequency for a minimal amount of time. With the enhanced security offered by Spread Spectrum systems, an increasing number of radio manufacturers are offering the units to hobbyists at a price from $3,000 to as low as $30. A number of manufacturers are now selling conversion kits for older digital 72 MHz radios and receivers, providing even more options for the rc model operator.
Though flying an rc model can be a fun activity, certain safety considerations must be observed in order to make the flight both a safe and enjoyable experience. During this blog, we’ll take a look at buying an rc plane or helicopter from the safety standpoint, as well as techniques to promote safe flying.
Real aircraft must undergo a pre-flight checklist, which is also a good philosophy for radio control aircraft. The pilot must make sure the rudder, ailerons, and elevators are functioning properly, with both the receiver battery and radio fully charged. The problem with rc planes, as opposed to rc helicopters, is the center of gravity. The center of gravity is a point at which the plane needs to balance in order to fly well. The center of gravity for a plane with a tail can be as far back as 32% from the nose of the plane of the plane, though the operator may still have to make it balance. While placement of the battery and radio can compensate for any CG imbalance, it’s always desirable to have both a light nose and tail section of the aircraft, with adjustments made at the center of the fuselage. A properly balanced plane will be more responsive to commands and use less fuel/battery charge. Flying wing designs have a common center of gravity at 23% back from the nose.
Before launching the plane, be sure the correct propellers are installed. The thickest section of the prop should be facing toward the front, The rc pilot can determine the front of the blade by manufacturer lettering. The plane will still fly with the prop(s) mounted backward, though at about a third of the power of a front mounted blade since the thicker front section displaces more air. Better quality props are more rigid, and thus more stable in flight – especially at high rpms. They are also less likely to flatten out over extended use. Getting a good launch of the aircraft is more difficult than it appears. Inexperienced rc pilots have a tendency to spin the plane, often a cause of crashes. If one wingtip is moving faster than the other, it will have more air over the wing, so the plane will roll towards the slower wing. The correct procedure is to release the plane when both wings are level and moving in the same direction at the same speed. If the model is launched at too steep an angle, it will experience an immediate stall.
Transmitters are an important element of rc flight. Many rc pilots have a tendency to fly their planes by their thumbs. Clutch the transmitter sticks on the side with the elevons or elevator-ailerons control. This offers the rc pilot more than one orientation to the controls and prevents accidental maneuvers of the rc plane. Don’t jerk the control sticks, but rather use a gradual motion from which to control the model. Proper antenna angle is another factor, since there may be local interference, which affects signal quality. Fly the plane at a close distance, using different antenna angles to determine the optimum signal. While more recent rc planes are equipped with a homing device, which returns the plane to the transmitter if the model experiences signal or line of sight interference, it’s always best to fly your rc plane no farther than your field of view. A three channel transmitter with throttle, rudder and elevator controls is usually the best for a beginner. Speaking of planes, the most important decision facing beginning rc pilots is choice of aircraft. The hard fact is the plane will experience a number of crashes until the pilot becomes more proficient. Foam is a relatively inexpensive material and easy to repair if the rc plane is damaged. While a foam aircraft construction is not the most pleasing to the eye, it provides the rc model beginner with a practical means of getting into the air. RC models may be purchased in either ready to fly (RTF) or in kit form, which must be assembled. Building your own model has the advantages of learning the parts and operating systems of the plane, as well as a lower cost. RC model planes may be powered by either gasoline engines or lithium polymer (LIPO) batteries. The use of lipo batteries has increased drastically in radio control use over the last ten years. They offer near gasoline engine performance while being more compact, with little or no maintenance.
The use of radio control aircraft, quadcopters and drones have increased exponentially over the last fifteen years. Near collisions between drones and passenger aircraft now run into the hundreds each year, with the FAA receiving in excess of 100 reports per month. While most drones weigh less than ten pounds and have a limited altitude, heavier and more capable machines are the rise. For example, even a collision between a lightweight drone and a jetliner could result in millions of dollars if the jetliner sustained damage to either the engine or control surfaces. Though the FAA has a regulation in effect for four years making it illegal to fly a drone within five miles of an airport and limiting the altitude to 400 ft., many operators who use drones in their business pay scant attention. A year later the FAA enacted a five dollar registration fee for all drones weighing more than half a pound. While ineffective at tracking drones, it may get the attention of some operators. For all the electronics and regulations, perhaps the best source of rc model safety is common sense in their use.
During the last five years, the use of and uses for drones have increased exponentially. In this blog, we’ll trace the employment of drones in a number of industries.
While much of the current drone technology isn’t new, recent investments in both capital and technology have made drones a practical tool in a number of industries. The agricultural sector is one in which drone applications are on the rise. With the global population projected to reach about 9 billion by 2050 and agricultural consumption to increase by 70 per cent during the same period, the use of drones in agriculture has the potential of revolutionizing that sector of the economy. Such drones are high-tech systems which perform many tasks a farmer can’t, such as conducting soil scans, monitoring crop health, applying fertilizers and water, even tracking weather and estimating yields, as well as collecting and analyzing data. With the FAA currently streamlining regulations for agri-drone use, the market for such systems has the potential for approximately 80% of all drones produced, according to a recent study by Bank of America Merrill Lynch.
A number of construction companies are exploring the possibilities of utilizing drones or UAVs (Unmanned Aerial Vehicles) in that industry. Drones have a number of roles in the construction industry: among them are marketing, surveying, inspection, progress reporting, safety and monitoring workers at multiple sites. In the survey role, drones allow contractors to get detailed information about a job site, as well as conditions on surrounding properties. While site surveyors are necessary in some situations, drones can perform essentially the same function at a fraction of the cost. In the realm of construction inspection, drones offer a high degree of flexibility. For example, drones can effectively scan the roof of a skyscraper, revealing any possible construction faults. They are also useful at sites such as tunnels and bridges, which may be inaccessible from the surrounding land. The contractor can even use the drone to compare the construction to the actual plans of a project. Drone photography can be utilized to show aerial views of a site from different angles to determine feasibility of construction. These photos can be sent to a number of potential contractors during the bid process. The same capability is also useful to show job progress to developers, who may not be able to visit the site on a regular basis. Finally, drones provide a means of monitoring the safety of workers at multiple sites, keeping the contractor informed of any safety issues on a real time basis, requiring a fraction of the manpower and cost of on site supervisors.
Drones also have potential in the commercial sector. For example, Wal Mart is currently utilizing drones comparable to those used in agriculture to scan warehouse inventory, checking for missing or misplaced items. Drones flying through a warehouse are able to complete an inventory in a day – a task that would take an on site warehouse crew a month. Though in its early stages, a few major companies are using drones for delivery purposes. Dominos Pizza began a delivery service in Britain, in which a drone was able to deliver two pizzas per trip. This service has the obvious advantage of avoiding traffic jams. In Philadelphia, a dry cleaning service is using drones to make emergency deliveries of laundry to customers. Though weight restrictions are a problem, they are capable of flying a freshly cleaned suit to a customer’s front door. The latest evolution is party drones, which fly over an outdoor party, playing prerecorded music.
While drones haven’t been adopted on a mass scale, they have increased the functionality of a number of key industries, breaking through the traditional barriers. From quick deliveries, to monitoring construction progress to agriculture, drones increase work efficiency and productivity, improving customer service, safety and security – with little or no manpower. According to a recent Price Waterhouse Coopers study, drone related activity provides an economic boost of more than $127 billion globally. With the relaxed FAA flight rules approved in 2016, drone operators have more flexibility from which to operate. As it becomes cheaper to develop industry-specific drones, subsidiary niche markets will emerge. A recent study indicates the use of commercial drones could add $82 billion and 100,000 jobs to the national economy by 2025 – not bad for a young industry.
After my grandson flew his newly purchased quadcopter a few weeks ago, I was stunned by the quality of video produced by its camera. During the course of this blog, we will trace the development of compact cameras, as well as their effect upon the radio control models.
The evolution of drone cameras began in 1901, when renown photographer George Lawrence conceived the idea of attaching a camera to a balloon to take photos of banquet halls and outdoor ceremonies. Lawrence developed a panoramic camera with a relatively slow shutter speed, which proved idea for area photographs. While his first balloon pictures were a success, both he and the balloon crashed, with Lawrence surviving a 200 ft. fall without injury. He then developed a camera platform using a series of kites connected by bamboo shafts to support the weight of the camera and ran a steel piano wire from the ground up to carry the electrical current that would trip the camera shutter. The photos were retrieved by parachute. This system was so successful, Lawrence used it to photograph San Francisco after the 1906 earthquake – from which he earned $ 15,000.
However, it wasn’t until the advent of digital technology in the 1970′s, which allowed photography to become more adaptable, that compact cameras became feasible. A digital camera is a hardware device, which takes pictures like a conventional camera, but stores the image to data instead of printing it to film. Most digital cameras are now capable of recording video in addition to taking photos. Perhaps the earliest precursor to digital photography occurred in 1957 in which Russell Kirsch, a pioneer of computer technology, developed an image scanning program utilizing a rotating drum to create images, the first scanned image a picture of Kirsch’s son. By 1969 a charge-coupled semiconductor was created by ATT Bell Labs, in which a semiconductor was capable of gathering data from photoelectric sensors, then transferring that charge to a second storage capacitor. Analog data could be transferred from a light sensitive chip, which could be converted into a digital grid, producing an image. In 1974 Bell Laboratories developed a charge transfer system, which could store and transfer charge carriers containing pixel data in serial order. This system was further refined by Bell in 1978, in which a charge transfer imaging device was produced using solid state technologies. This system was both more cost-effective, as well as preventing smearing aberrations created by similar image capture devices.
In 1973 Eastman Kodak took a gamble and hired Steve Sasson, a young electrical engineer. Sasson was one of a small cadre of electrical engineers employed by Kodak, a company well known for its chemical and mechanical engineering projects. Sasson was directed to capitalize on the capabilities of a charge-coupled device created by Fairchild Semiconductor, which could transmit and store images of 100 by 100 pixels. In 1975 Sasson completed a prototype camera incorporating a charge-coupled device, adapting a lens from an eight millimeter film camera, an analog -to-digital converter from a Motorola digital voltmeter, and a digital-data cassette recorder for storing image data. With this combination, Sasson and other Kodak technicians could capture an image and record it to a cassette in a mere 23 seconds.
By 1990 several companies began to enter the digital photography market, creating a new segment for consumer cameras. The first digital camera ready for sale in the US market was the Dycam Model 1, which came out the same year. The Model 1 was capable of recording images at a maximum resolution of 376 pixels by 240 pixels. Two developments in the 1990′s further enhanced the marketability of digital cameras. The first was a codec, utilized for image compression, the precursor to the JPEG image file format of today. This system exponentially increased the storage capacity of digital cameras over prior magnetic tape and floppy disc storage systems. By the mid 1990′s Apple began to market the Quick Take 100, the most widely marketed digital camera in the United States. The Quick Take had a maximum resolution of 640 by 480 pixels and could store up to 24 images in 24 bit color. In 1995 Casio released the QV-10, the first consumer digital camera to include a to include a liquid crystal display (LCD) screen, which quickly allowed camera owners to review newly photographed images. Other developments in the 1990′s included a pocketable imaging device with an LCD screen capable of displaying images from a camera storage device, as well as a single- lens digital reflex camera, which could reproduce camera images in 35mm film quality. By the end of the decade, digital cameras had a resolution of 2,000 pixels by 2,000 pixels.
In the early 2000′s a merging of digital camera and lithium polymer battery technologies took place. In the latter case, the flexible polymer battery began to deliver near gas engine performance with the attributes of less weight and volume on the rc model frame. Digital cameras were now both lightweight and efficient, capable of both still photos and video covering a relatively wide area. By 2010 a number of drones and smaller quadcopters carried flash drive units, which could be inserted into the rc model camera to record flight video. Once on the ground, the rc pilot would then insert the drive unit into the USB connection of a personal computer, playing the video of the quadcopter flight on the computer monitor screen – a far cry from pulling piano wire to trip a camera shutter.
Within the past fifteen years there has been a revolution in both types and capabilities of rc model batteries. During this blog, we will attempt to analyze current types of batteries on the market and their best uses.
The NICAD or nickel cadium battery was the first battery in use for rc models and has served the radio control pilot for decades. NICAD batteries were first developed in Sweden, with the first practical batteries produced in 1906. Nickel cadium batteries were first produced in the United States in 1946 and radio control enthusiasts began to use them in the 1950s. They were popular because they had a higher power to weight ratio than gasoline engines in use on rc models of the time, although they had a limited endurance. Nickel cadium batteries offer the advantages of a low internal charge resistance, producing high currents. These batteries also have a relatively low self discharge (retaining its charge while stored) and their performance is not drastically affected by fluctuations in temperature. Some of the disadvantages of NICADS are they are both heavier and bulkier than newer technology batteries, are not environmentally friendly, as well as gradually losing their charge capacity if not periodically drained and recharged. Despite the availability of newer battery types, some rc hobbyists continue to use them when extremely fast performance Is required.
Nickel-metal hydride (NIMH) batteries are chemically similar to nickel cadium cells while utilizing a hydrogen-absorbing alloy instead of cadium. An NIMH battery has two to three times the capacity of an NICAD battery. Nickel-metal hydride batteries were first tested in 1967 using a lanthanum alloy, which was both expensive to produce in addition to having a limited charge life. After extensive testing in the 1970s and 1980s a practical battery using a mischmetal alloy was developed in 1987. NIMH batteries have the advantages of a higher capacity than NICAD batteries, in addition to retaining more of their charge capacity over time and being more environmentally friendly. Nickel-hydride batteries can lose their charge faster than other types, and require an outside charger for peak efficiency, unlike NICAD batteries. NIMH batteries are lighter than nickel-cadium units and more subject to breakage with imported batteries often running below stated capacity. NIMH batteries are most often used in transmitter and receiver packs of rc model units.
A lithium polymer or LIPO battery is a rechargeable battery of lithium-ion in a soft pouch type structure, unlike NICAD or NIMH batteries. The cells of the LIPO batteries contain liquid electrolytes with the polymer barriers used to separate the battery cells. The electrolytes may also be gelled by a polymer additive to conduct current. Lithium polymer batteries have been in use since the mid 1990s and have a very high power to weight ratio. They retain much of their charge in storage and are resistant to temperature changes. However, they are sensitive to overcharging and rapidly discharging, posing a fire hazard due to the polymer chemicals. RC models such as quadcopters now routinely use LIPO batteries attaining performance and endurance greater than many gas powered units. There are two recent variations of LIPO technology which overcome some of the basic LIPO battery limitations. The LifePO4 is more resistant to overcharging and discharging than the basic LIPO battery, as well as being less flammable . The LifePO4 has an ever higher power to weight ratio than a regular lithium polymer battery. The A123 battery, a modified LifePO4 utilizing nano technology, is able to deliver current at an even faster rate than the LifePO4 with greater safety. Such batteries give the rc pilot revolutionary advantages of weight, performance and safety.
My grandson and I were looking at pictures of rc helicopters online and we saw the picture of a strange looking craft. Unlike a conventional helicopter, which has a large main rotor centered above the cabin with a smaller rotor mounted at the tail, this unit had its rotors mounted at the end of four bars, extending from the center. The helicopter in question is called a quadcopter and is one of the fastest growing types of rc models. During the course of this blog, we will trace the development of quadcopters, as well as some of the reasons for their current popularity.
While manned quadcopters were first tested in the 1920s, rc model applications began in Japan in the early 1990s. Although the tests were successful, the quad units were never marketed internationally. During the early phases of the wars in Iraq and Afghanistan, the military was in need of a means of conducting reconnaissance in support of ground operations. These missions were first conducted by small rc planes mounted with cameras. While the rc aircraft were effective camera platforms, the need for a hover capability became apparent. Experiments were conducted with a number of designs, with a practical rc quadcopter developed by the late 2000s.
Radio control quadcopters have only recently come into use due to the processing power required to not only keep all four rotors turning, but at a synchronized speed. RC quadcopters represent the merging of several technologies. The first being a solid state gyro system from which to steer the craft, followed by high capacity batteries to provide increased flight endurance, along with digital camera technology for video and still photo observation. Many of them are constructed of a carbon-fiber material, similar to that on the Boeing 787 Dreamliner. These copters are quite durable, with some test units surviving crashes in excess of 100 ft.
The quadcopter is a popular rc vehicle for a number of reasons. To begin with, it has fewer moving parts than a conventional rc helicopter and is easier to fly. While a conventional rc copter may need pitch adjustments to its main rotor while in flight, the quadcopter runs via four flat-bladed rotors. To control the quad in flight is merely a matter of controlling the power to each of the rotors. Quadcopters are also relatively safe from wind conditions due to their balanced structure. Quad units are simplier to build and repair than conventional rc helos. A number of quads are equipped with multi-colored led lights, enabling night flights. With current battery and engine technology, many quadcopters can fly in excess of 30 min. Finally, the quads are built around the ever present camera, an afterthought on a conventional rc copter.
In 2010, a radio controlled aircraft collided with a small private plane during a charity airshow at a Colorado airport. While there was no visual damage to the private plane, the incident reflected a growing trend in rc aviation – the use of FPV planes. During the course of this blog, we will discuss the current problems surrounding their use.
We first need to define an FPV plane. An FPV (First Person View) plane is a radio controlled model aircraft, which utilizes a small onboard video camera and transmitter sending imagery to a ground receiving unit in the form of video goggles or a portable LCD screen. The view from such flights is the same as a pilot would have from the plane. Because of this, the rc pilot on the ground need not maintain line of sight (LOS) contact with the model, limited only by the reach of the radio signal and the power supply of the aircraft. While a number of rc aircraft are built with FPV capability, kits are available to install video cameras on virtually any rc plane. The rc pilot using goggles or head tracking gear usually has an exciting flight experience.
The capability of FPV aircraft to fly beyond visual contact range (some have a radius in excess of thirty miles), as well as an altitude ceiling above 3,000 ft., may sometimes cause problems when the pilot loses the video signal. For example, private planes often make their landing approaches at altitudes within the envelope of the FPV model. A loss of signal at the wrong time could result in a collision between the two craft and pilot error due to the distraction. Collisions with communications towers, power lines and other ground obstacles pose an equal threat. Though there are currently no laws or regulations governing control of FPV planes, the Academy of Model Aeronautics has proposed several guidelines to make FPV flight safer.
The first is the use of a buddy box system, in which two pilots, one in sight of the rc and the other monitoring the flight by video are able to direct the plane using independent flight controls. Another proposal requires an FPV pilot to fly their craft within line of sight at an altitude of no higher than 400 ft. Some models utilize autopilots, which automatically fly the plane back to its controller upon loss of video power. For all of the safety concerns, there has never been a recorded incident of an FPV plane causing major property damage or injuries, due to the majority of FPV models being constructed of styrofoam, which is lighter and less rigid.
In 2001, two events occurred which shaped the military and law enforcement applications of UAVs( unmanned aerial vehicles), or more commonly called drones. The first event happened on April 1 of that year, in which a U.S. Navy EP-3A signals intelligence aircraft collided with a Chinese J-811 interceptor approximately seventy miles off the coast of Hainan Island. While the Chinese aircraft was destroyed, the EP-3A was able to land safely on Hainan Island with the crew eventually released and the plane shipped back to the U.S. in sections aboard a Russian freighter. On September 11, the World Trade Center towers were destroyed by terrorists crashing jetliners into the towers. Both situations underscored the need for an unmanned aircraft. In the case of the Hainan Island incident, a means of gathering signal intelligence without the vulnerabilities of having a crew forced down over hostile territory. In the September 11 case, a means of destroying and neutralizing the leadership of terror cells without direct military intervention.
While such aircraft have been successful in the war on terror, drones are being considered for use in domestic operations such as homeland security, disaster relief and law enforcement. Although relatively few drones are currently flown over U.S. soil, the Federal Aviation Administration (FAA) predicts that about 30,000 drones could be flown domestically within 20 years. Both members of Congress and the public have expressed concerns about privacy and other civil liberties. While ground-based law enforcement must have a search warrant to enter an individual’s residence, there is currently no such restriction for drones. This is because the airspace above a home is considered a public space. Two approaches under consideration to correct this are to obtain a search warrant detailing the specific use of the drone and the filing of a data collection sheet, stating the time, date and property to be photographed. Another aspect of this is previous court rulings allowing manned aircraft to collect evidence above a residence, in which a 1989 Supreme Court ruling allowed imagery of marijuana growing in a greenhouse taken by a helicopter. With drones getting ever smaller, nosy neighbors could pose a similar threat.
Drones are currently regulated by the FAA, which prohibits people from using them commercially and requires public institutions to apply for authorization to use them. However, all of this will change in 2015, when the agency is directed by Congress to open domestic skies to commercial drones, and to integrate the use of both manned and unmanned aircraft. Based on existing law, surveillance of an individual while in their home, using technology not in general public use, would be in violation of their rights without a search warrant. Perhaps the key factors are whether the drone was flying over a public place or private residence and was the search considered active (crime in progress) or continuous surveillance. While Congress has shown a willingness to debate the issue, much of the privacy battles may be fought at the local level, with each state developing standards for law enforcement use of drones and how to regulate the use of drones by individuals.
The successful transcontinental flight of the Solar Impulse has drawn renewed interest in the use of renewable fuels for aviation. As we progress through this blog, we will trace the development of solar fuel technology, as well as explore its potential.
The first successful flight of a solar- powered aircraft was performed by the Sunrise, a small radio control aircraft weighing 27 lbs. with a 32 in. wingspan. The Sunrise was powered by 1,000 solar fuel cells located in both wings, producing approximately 450 watts of power, which gave the aircraft a surface ceiling of 20,000 ft. The Sunrise was built by Astro Flight, formed in 1969 to build a radio controlled sailplane for use in AMA certified competitions. The funding for the flight of the Sunrise in 1974 was the result of a government contract with Lockheed to begin research on solar powered aircraft, subcontracting the project to Astro. In 1979, DuPont sponsored a project led by Dr. Paul MacCready to develop a solar- powered plane capable of carrying a human. This effort resulted in an aircraft called the Gossamer Penguin, which first flew the following year. The Penguin used a 600 watt solar panel similar to the Sunrise, along with a production version Cobalt 40 motor. This aircraft could achieve passenger flights of short distances, which gave DuPont an incentive to build a solar plane capable of crossing the English Channel. It took three months to construct the Solar Challenger out of 16,128 cells. These cells yielded 2,500 watts at sea level with approximately 4,000 watts at cruise altitude. The Solar Challenger successfully crossed the English Channel in 1981.
While the early flights of solar aircraft were successful, interest declined during the 1980s. In 1993, a project known as Pathfinder was restored for the purpose detecting ballistic missile launches . The new project known as HALSOL (High Altitude SOLar aircraft) had both high- altitude and long- endurance capabilities. However, after several test flights in 1993 and 1994 the project was cancelled. That same year NASA established the Environmental Research Aircraft and Sensor Technology (ERAST) program, in which additional solar cells were added, covering most of the upper wing surface. After a series of tests were conducted in 1995, Pathfinder achieved an altitude of 50,500 ft. – a record for a solar-powered aircraft. In 1997, Pathfinder was tested at the U.S. Navy Ballistic Missile Test Center in Barking Sands, Hawaii. This site was selected due to its ideal climatic conditions from which to test the solar panels. After additional modifications, the Pathfinder was able to set two new world altitude records at 71,530 ft. and 80,201 ft. for both solar-powered and propeller-driven aircraft.
While the Solar Impulse is not the first plane to fly under solar power, nor the first aircraft of its kind to cross the United States, it represents a quantum leap over previous designs. The plane already holds three records for manned solar flight, altitude (30,300 ft.), length (26 hrs.) and distance (693 miles). The plane is capable of overnight flight with solar charged batteries. The carbon-fiber construction of the aircraft adds to its efficiency. Although the Impulse’s wings are as long as an Airbus A340, the weight of the aircraft is only 3,527 lbs. – less than the average sports car. With both improvements in batteries and solar panels over the last ten years, we may soon reach a point when solar-powered passenger service becomes a reality.
During a recent visit to a local hobby store, I got an education about an important but often ignored tool of rc modeling – antennas. During the course of this blog, we will provide an overview of antennas and their applications for rc planes.
For all of the sophistication of antenna theory, the techniques for the successful operation of an rc model antenna are relatively simple. To gain further insight, we must define an antenna and how it operates. A transmitter antenna is a straight wire or telescoping pole device which converts an electric signal in the form of a radio frequency into an electromagnetic field. For successful operation, the antenna must be connected to the transmitter device at one end with the other end connection free. In the case of rc model planes, a receiver antenna is also necessary. A receiver antenna is usually a straight wire, which converts the transmitter radio signal and its associated electromagnetic energy into an electrical signal, which controls the aircraft. As with transmitter antennas, one end is connected to the aircraft, while the other is free from contact. Frequencies denote the number of times an event occurs within a given time period. Radio frequencies are stated in Megahertz, or cycles per second with one hertz expressed as one cycle per second. A radio band is a spectrum or range of frequencies designated by the Federal Communications Commission for a particular purpose. Most rc models operate in the 27MHz, 35MHz, 40MHz, 72MHz and 75MHz bands. Electromagnetic fields can be explained in the form of static electricity creating energy. However, the electrical charge traveling from the rc model transmitter contains more energy, traveling through space at the speed of light. The magnetic and electric fields change as the transmitter antenna frequencies change.
Directing the antenna for the best performance is another issue. When the hobbyist points the antenna in either a forward or direct vertical position, the antenna is often pointed at the model. If the model flies straight, there is usually no problem, but if the aircraft is performing a manuever it could result in a pause, from a temporary loss of signal. Some hobbyists even point their antennas toward the ground. By doing so, they lose the strongest part of the signal and limit the distance from which they are able to control the plane. An advantage of pointing the antenna to the side other than constant signal strength is pointing the antenna toward the plane results in more stress on the antenna from being continually flexed, which causes both more breakage and repair bills. There are also several troubleshooting procedures to make sure your rc plane is responding properly. The first and perhaps most obvious is to check the on and off switches, not just to make sure they are on or off, but to determine if they are in working order. Next, be sure the transmitter is set to the right frequency for the plane. Often this can be corrected by merely changing the crystals in the transmitter. Be sure both your transmitter and receiver batteries are at a full charge before flying. Ideally, they both should have an equal charge. Next, inspect the receiver antenna for proper installation with the transmitter antenna fully extended. Based upon prevailing rc radio frequencies, a transmitter antenna length of 28″ and a receiver antenna of about 40″ provide optimal performance for most rc models. Switching rc model and transmitter combinations is another way to isolate problems. These are but a few procedures to make sure the rc pilot has a trouble free flight.