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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.
While watching the recent movie Sully, I was amazed at the sophistication of current flight simulators available to the major aircraft producers. During the course of this blog, we will trace the development of flight simulators from mere mechanical devices to the virtual reality electronics of today.
A flight simulator is a mechanical or electronic device, which attempts to duplicate both aircraft flight and the environment in which it flies. Current simulators can replicate factors such as flight controls, wind, moisture and electronic system interaction. While flight simulation is used primarily for pilot training, it may also be used to design aircraft, as well as identify effects of aircraft properties.
The earliest flight simulators were used during World War I to teach gunnery techniques. This involved a static simulator with a model aircraft passing in front to aid both pilots and gunners to develop correct lead angles to the target. This was the only form of flight simulation for nearly ten years. The Link Trainer, developed by Edwin Link in the late 1920′s, capitalized on the use of pneumatic devices from player pianos and organs from the family musical instrument business. The first trainer was patented in 1930 with an electrical suction pump boosting the various control valves operated by stick and rudder action while another motor simulated the effects of wind and other external disturbances. These actions could be manually adjusted to provide a variety of flight characteristics.
While the Link Trainer provided a quantum leap in capability over previous flight simulators, many in both the military and civil aviation communities believed the live flight experience offered a better training environment. However, by the early 1930′s, the United States Army Air Corps had a need for flight simulator applications which could train mail pilots to fly by instruments for long distances. An enhancement to the Link Trainer was a device called the course plotter, in which a self-propelled tracker could remotely trace the trainer position from an inked wheel with communications between pilot and instructor facilitated by the use of simulated radio beacons.
It was during the late 1930′s, when flight simulation began to be based on electronic applications. The Dehmel Trainer, developed by Dr. R. C. Dehmel of Southwestern Bell, coupled a Link Trainer with an advanced radio simulation system, which could accurately duplicate navigation signals transmitted to a receiving aircraft, providing a state of art simulation of radio navigation aids. The Aerostructor, developed by A. E. Travis, utilized a fixed base trainer with a moving visual presentation, as opposed to radio and electronic signals. This presentation was based on a loop of film which depicted the effects of course changes, pitch and roll. While the Aerostructor was never mass produced, a modified version of it was in service with the US Navy.
During World War II advances in aircraft design such as retractable landing gear, variable pitch propellers and higher speeds created a demand for more realistic forms of flight simulation. In response to this, the Hawarden Trainer was developed, which used a cutaway center section of a Spitfire fuselage, which allowed training in all aspects of operational flight. In 1939, the British were in need of a simulator which could train it’s navigators who were ferrying US aircraft across the Atlantic. The navigator was supported by a number of radio aids, as well as a celestial dome corresponding to changes in the position of the stars relative to changes in time, longitude and latitude. The Celestial Trainer, designed by Ed Link and P. Weems was also modified to train bomber crews, in which simulated landscapes gave the bomb aimer target sightings as they would appear from a moving aircraft. Redifussion (Redifon) produced a navigation device in 1940, which simulated existing radio direction equipment allowing two stations to take a fix on an aircraft’s position. By the end of the war, aircraft crews were trained by the simulation of radar signals to acquaint them with new types of radar developed during the war.
While the science of flight simulation had progressed dramatically over the past thirty years, they were unable to accurately duplicate performance characteristics of a plane. This changed with the arrival of subsonic jetliners in the 1950′s. Aircraft manufacturers began to produce more complete data and extensive flight testing. This data was stored on analogue computers, making the data transferable, but requiring more hardware as aircraft testing became more sophisticated. By the early 1960′s, digital computers began to replace the aging analogue units due to the increased data capacity and speed of the digital units. The most successful of these, the Link Mark I, operated with three parallel processors functional, arithmetic and radio selection, using a drum memory for data storage. By the 1970′s the majority of computer systems could be adapted for flight simulation.
During that decade computer image generation or CGI technology became available for flight simulation models. This technology, adapted from the space program, used a ground plane image, supplemented by three dimensional graphics. This technology became more sophisticated in recent years, mating it to advances in digital computers – a far cry from the rolling ground plane pictures of the 1940′s. Today, flight simulation is a colossal industry, spanning the globe with a wide range of high tech applications for both aircraft users and producers, enhancing the safety of both crew and passengers.
In 1947, the U.S. military was in a state of transition. Just two short years after the end of World War II, the USAF was established as a separate service, as well as the OSS or Office Of Strategic Services of World War II being replaced by the Central Intelligence Agency or CIA – an agency with much broader powers and resources. With the onset of the Cold War, some of the traditional roles performed by the armed services were being revised to meet the new environment in which they were to operate. We will examine the role of Army aviation from its earliest days to the dedicated ground support role of today.
Army aviation actually began during the Civil War, in which both Union and Confederate forces used balloons for communications and artillery observation. While such missions could be hazardous at times, the balloons were effective in both roles. By World War I aircraft were used in direct ground support, along with other duties such as observation and establishing air superiority over the battlefield. While the ground support role of aircraft was proven during World War I, the Air Corps leadership lost interest in the concept between the wars in favor of large strategic bombers. However, this began to change as the United States entered World War II, due to a series of large scale ground exercises in 1940 and 1941. In June 1942 the War Department authorized the Field Artillery to maintain a small unit of spotter planes organic to the ground forces and independent of other Air Corps units. Small planes, such as the L-4 Grasshopper proved their worth in every theater of operations.
In 1947 the National Defense Act was passed, in which the Air Force was created as a separate service, equal to the Army and Navy. This left Army aviation with a narrowly defined mission of providing limited ground support and logistics to ground units and to disrupt enemy supply lines and communications near the line of battle. As a result of the Key West Agreement in 1948, Army aviation assumed the responsibility of transport and dispersion of troops under conditions of a nuclear battlefield. While the National Defense Act stripped the Army of most of its fixed wing aircraft, this proved to be a blessing in disguise, as it allowed the Army to devote more research toward rotary wing aircraft, or helicopters. During the Korean War the Army made significant advancements in its helicopter fleet, making it an essential item of the modern battlefield. Medical evacuation in Korea was particularly successful, with approximately 600 helicopters evacuating more than 23,000 casualties.
Although helicopters were successful in support roles, the Army was slow to develop them for a ground attack role. Part of this was due to the philosophy of massive retaliation during the Eisenhower Administration, in which USAF strategic bombers played the dominant role. Also, as tactical nuclear weapons were developed in the mid 1950s, the Army began to restructure its organization around them in the belief that large scale conventional wars were obsolete. However, as the Soviets began deploying tactical nuclear weapons of their own, the Army leadership realized the potential of a limited conventional war and began to prepare both hardware and doctrine for it. Due to experience in the Korean War, the Department of Defense authorized the Army to modify and test existing helicopters as attack platforms. While the tests were partially successful, it was clear larger helicopters with more capable engines were necessary for sustained fire support.
By 1960 the United States was finding itself more deeply involved in Southeast Asia and needed a means of providing close ground support, the helicopter being the ideal weapons platform. As a result of a Pentagon study that year, a new generation of helicopters was authorized. Purchase of the Bell UH-1 “Huey” and the CH-47 Chinook helicopters were approved, the Huey arguably the most important aircraft the Army ever procured, with many still in service today. The extensive use of helicopters during field exercises in 1963 and 1964 validated the concept of the airmobile division. However, when the 1st Air Cavalry (Airmobile) Division began operations in Viet Nam, there was a shortage of artillery support with Air Force and Navy ground support lacking accuracy. To surmount this problem, the Army developed the AH-1 Cobra, the first dedicated ground attack helicopter. The Cobra, armed with 2.75 in. rockets, was so effective that many ground commanders requested fire support from Cobra units, as opposed to regular tube artillery. Viet Nam proved that helicopters were both survivable and effective. Operational statistics revealed for a maximum force level of 2,600 helicopters in country, one copter was hit for every 1,147 sorties with one shot down for every 13,461 sorties flown with one aircraft lost every 21,194 sorties.
Army aviation had proven its value again as a vital part of the combined arms team. With both the airmobile and aerial field artillery concepts validated and the subsequent use of helicopter gunships as anti-armor weapons, Army aviation has truly progressed from the days of mere artillery spotting – becoming a separate branch of the Army in 1983. In the Gulf War, as well as Iraq and Afghanistan, Army aviation has proven itself a force to be reckoned with.
The history and development of medical transport closely parallels developments in both aviation and medical technology, since physicians have sought to use aircraft in patient care from the earliest days of flight. During the course of this blog, we will trace the progress of in-flight care from the trainer aircraft of World War I to the turbine helicopters of today.
Ironically, the need for in-flight medical care arose from pilot training injuries during World War I. To support expansion of the Air Corps, a number of new airfields were constructed in remote areas of the country. If a student pilot were injured in a crash, it could be several hours to the closest hospital. Therefore, the Air Corps undertook a novel approach and converted a number of Curtiss JN-4 “Jenny” trainers to flying ambulances. Although several versions were built, the patients were enclosed in the fuselage without the benefit of in-flight care. In spite of the limitations of the aircraft, the USAAC system became a prototype for other air ambulance services.
By World War II the emphasis was on long range medical evacuation, involving the use of large cargo planes. These aircraft were large enough to accommodate in-flight care while transporting the injured to theatre hospitals, where they could receive more comprehensive care. While the cargo planes were a quantum leap in both service and technology, there was still a pressing need for small aircraft capable of flying from the forward areas to small field hospitals in the rear. The Cessna Birddog and other small fixed wing aircraft were modified to carry stretchers and medical supplies. Sikorski YR-4B helicopters were first used in Burma in 1944 to evacuate soldiers from isolated areas behind Japanese lines. Although the early helicopters had a limited capacity, their missions were successful. By Korea, dedicated helicopters such as the Bell 47 and Sikorski R-5 were able to provide timely evacuation of the wounded, reducing the fatality rate from the 4.5% of World War II to 2.5%. In Viet Nam, with the use of the Bell UH-1 Huey, the fatality rate was further reduced to less than 1.5%.
The success of military medevac programs inspired civil efforts, as well. Project CARESOM was initiated in Mississippi in 1969, in which several military helicopters were provided to the state by a federal grant to transport patients in underserved areas of the state. The city of Hattiesburg continued the program and became the first civilian medical air unit in the United States. Another experiment, the Military Assistance to Safety and Traffic (MAST), was formed in 1969 at Fort Sam Houston to use military helicopters to supplement civilian providers. The program was highly successful and spawned services such as Flight For Life Colorado, which began in 1972, along with the Air Ambulance program in Canada, which was established in 1977 by the Ontario Ministry of Health. The Ontario program also transferred patients between facilities. One of the first helicopter services independent of any hospital, Mercy Flight WNY was formed in 1981 in New York state and is one of a few not-for-profit providers. Today, there are more than 200 medical transport firms in the United States with the number growing. The scope of their services has grown, as well. Medics can now perform emergency procedures done by ER doctors, just a few years ago.
The use of seaplanes dates back to 1910, when French aviation pioneer Henri Fabre performed the first successful launch of a seaplane from water. Fabre’s plane, Le Canard or Duck, was powered by a 50 hp. engine and flew a course of about 1,650 ft. The following year, Glenn Curtiss, the renowned American aviator and racing enthusiast modified a biplane with attached floats and successfully took off and landed from water. During World War I seaplanes played a limited but important role in protecting convoys from prowling German U boats. However, it was not until after the war when a Curtiss NC-4 became the first aircraft to fly across the Atlantic from New York to Lisbon that their potential was recognized by both the civil and military aviation communities.
In order to gain a better understanding of seaplanes, we must first define them by their subcategories – amphibians, float planes and flying boats. An amphibian is an aircraft which can take off from both land and water, having both floats and /or a boat shaped fuselage with retractable wheels. Float planes are essentially land based aircraft with flotation pontoons attached underneath the plane corresponding with the landing gear position, as these are often interchangable with landing wheels. Floatplanes either have a large central float located underneath the fuselage with additional floats near the wingtips for lateral stability or a catamaran arrangement placing two equal sized floats below the inner wing to provide buoyancy. Flying boats are seaplanes which have a boatlike shape to their fuselage and usually land in water, although the employment of beaching gear, a temporary dolly on wheels, may be used to move the plane from water to land.
During the 1920s a number of float planes competed in the international racing circuit. By the 1930s seaplanes were being developed for use as commercial airliners. The advantages were twofold: early aircraft engines were still relatively unreliable, so a plane which could land on the sea offered a measure of protection in the event of engine failure, while the capability to land on water made such aircraft accessible to remote areas of the globe. By the mid 1930s seaplanes such as the Sikorsky S-42 and the Martin M-130 were flying transoceanic routes on a regular basis, connecting North America with both Europe and Asia. Flying boats, amphibians and float planes were used extensively during World War II for reconnaisance, transport and bombardment missions, the Consolidated PBY Catalina a prime example.
However, after the war interest in amphibian aircraft began to wane for several reasons. By the late 1940s enough commercial airliners with intercontinental range became available to cover the routes flown by the seaplanes, while newer land based aircraft offered more passenger capacity, speed and range than flying boats. Military use of seaplanes declined as well, as a result of their being superceded by more efficient land based patrol and transport aircraft and the more cost effective helicopters in the air-sea rescue role.
Despite their decline in commercial and military use, amphibians are extremely well suited for operations in remote areas of the globe, providing vital links to the outside world. The current trend toward light sport aircraft has renewed interest in them, with a number of high tech designs such as the Privateer, Donier S-Ray and Petrel. The common thread among these aircraft are lightweight composite materials, fuel efficient engines, as well as the latest electronics. These planes are both versatile and fun to fly. Instead of fishing on one lake with a boat, why not fish from several with an amphibian?