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Wings - The Aerospace Age

(1958 - Present)

  ACHIEVEMENTS IN AERONAUTICS

At the end of this block of study, you should be able to:

5.94 Discuss the X-15 and XB-70.
5.95 Discuss the various types of airfoils.
5.96 Discuss the importance of composite materials.


The X-15 was a joint Air Force, Navy, and NACA project aimed at building an aircraft that could fly at a speed of 4,500 mph and reach am altitude of 250,000 feet. To accomplish this, the aircraft would have to withstand a temperature of 1,200 F. In September 1955, the X-15 contract was awarded to North American Aviation.

The X-15 was 50 feet long and had a 22-foot wingspan, and it weighed about 33,000 pounds of which 18,000 pounds was fuel. The X-15 was rocket-powered and was carried under the wing of a specially modified B-52.

Three X-15s were built, and between them, they flew over 200 total flights. The first flight, June 8, 1959, was a powerless glide to Earth. Flight-testing of the X-15 continued through 1967. Before flight-testing ended, the X-15 had exceeded both of its design goals. It had reached a speed of 4,534 mph (Mach 6.72) at an altitude of 314,750 feet.

In 1954, the Air Force requested bids on a contract to build a supersonic replacement for the B-52.
This aircraft would have to fly three times the speed of sound and at an altitude of 70,000 feet. North American Aviation won the contract to build three, later reduced to two, prototypes. The first flight took place in September 1964.

The XB-70 had a delta wing with a span of 105 feet, two vertical stabilizers, and a 185-foot-long fuselage. There were several design features which were unique to the aircraft. The very thin delta wings were constructed of welded stainless steel honeycomb and were designed so that at supersonic speeds the wing rode on its own shock wave. The fuel tanks were blanketed with nitrogen so the fuel could not ignite when the skin temperature rose due to frictional heating. The six turbojet engines were mounted side by side and buried within the fuselage/wing structure. Each engine produced about 30,000 pounds of thrust. The wingtips folded down in high-speed flight to provide for better stability.

In 1964, Congress decided the Air Force did not need a supersonic bomber and canceled the program. One aircraft was destroyed in 1966 and the other is at the Air Force Museum in Dayton, Ohio.

Research into airfoils in recent years has produced some revolutionary new concepts and with new technology revived old ideas. The list contains forward-swept wings, oblique wings, joined wings, mission-adaptive wings, supercritical wings, winglets, and canards.

Sweeping wings forward goes back more than 100 years to pre-Wright experiments of the 1870s. The concept was flight-tested earlier in this century and has theoretical advantages. Its use has been overshadowed by rearward-swept wings, since forward-swept wings needed to be structurally stronger in high-speed night. In the past, this meant making the wing heavier using conventional metal alloys. The forward-swept wing is now practical as the result of advances in composite-material technology. This technology enables the wings to be made lighter, smaller, and less costly than equivalent performance planes with rearward-swept metal wings. The forward-swept design also reduces weight, cost, and drag. Test data shows this technology provides an aircraft that can weigh less, fly longer ranges with given fuel loads, and turn very tight at supersonic speeds.

The X-29A test plane with forward-swept wing.

The oblique-wing changes form during flight for optimum lift under different circumstances and can be rotated to different positions for the best aerodynamic characteristics. The ability to change the wing angle provides efficiency at both low and high speeds. For takeoff, landing, and low-speed cruise, the wing is perpendicular to the fuselage; at high speeds, the wing is pivoted to different oblique angles.

An airfoil produces lift by creating pressure differences on its upper and lower surfaces. At the wingtips, this difference in pressure produces wingtip vortices. This swirling air increases drag, decreases lift, and can produce potentially dangerous air turbulence around airports. The winglets, placed in a vertical position at the end of the wings, eliminates the vortices thereby improving the efficiency of the wing.

Canards are horizontal surfaces forward of the main airfoils and are used for trim and control. The use of canards increases maneuverability and can allow the main wings of an aircraft to be smaller and lighter.

The mission-adaptive wing maintains its best efficiency under most conditions. Unlike flaps, slats, ailerons, etc., which are add-ons to the wing, the wing will change to create its most efficient shape for a variety of conditions.

An aircraft using a joined wing would have its main wing swept upward and backward connected at the tips to the rearward wing which would be swept forward and downward, resembling the shape of a diamond. The advantages of this type of wing would be its greater strength, lighter weight, lower drag, increased lift, and unique maneuverability.

Even though an aircraft may be flying at subsonic speeds, portions of it, especially the wing, may reach supersonic speeds. When the wing reaches supersonic speeds, it can be accompanied with a sudden increase in drag. The supercritical wing is designed to delay the point at which it reaches supersonic speeds, thus delaying the increased drag.

Research direction in the past has always been limited by weight and structural-stress limitations. Many designs that look good on paper could not be tested because the aircraft would be too heavy and/or incapable of withstanding the in-flight stresses. However, advances in construction materials in the 1970s have overcome some of these limitations. Super strong, but lightweight, nonmetallic, epoxy graphite composite materials have been developed that are stronger than many common metals used in aircraft construction.

REVIEW EXERCISE


COMMERCIAL AVIATION

At the end of this block of study, you should be able to:

5.97 Discuss the advancements in civil aviation.


By the mid-1960s, jet airline travel was growing so fast that it looked like there was no end in sight to its growth. With this in mind, in April 1966, Pan American World Airways approached Boeing with an order for 25 giant jet airliners With this firm order, Boeing announced they would begin production of the Boeing 747. This jumbo jet had a wingspan 65 feet longer than the 707, and its fuselage was nearly 90 feet longer and almost twice the diameter. While the 707 weighed 250,000 pounds, the 747 weighed nearly 800,000 pounds fully loaded. The 747 first flew in February 1969 and flew its first commercial flight for Pan American on January 22, 1970.

Both Lockheed and Douglas entered the jumbo jet field in 1966 with announcements of intent to build a medium-haul jumbo jet. The Douglas DC-10 first flew in August 1970 while the Lockheed L-1011 flew In November 1970.

Improvements of the basic models of the 747, DC-10, and L-1011 have continued to keep these aircraft in the marketplace. In just looking at the 747, there have been seven different models. The newest, the 747-400, which was rolled out in January 1988, employs many aerodynamic improvements that increased the range and fuel efficiency.

Before 1978, the United States had the technological edge over foreign aircraft manufacturers, with 85 percent of ail the world airliners being designed and built by the United States. By 1978, the technology gap had been narrowed to the point that American manufacturers began to feel a threat from abroad. This threat gave rise to the introduction of a new family of advanced-technology jetliners for the 1980s and 1990s. The DC-9 Super 80, the Boeing 767, and the Boeing 757 are three aircraft which were developed to improve efficiency through the use of advanced technology. The newest high-technology airliner, which first flew in early 1990, is the McDonnell-Douglas 11 (MD-11).

REVIEW EXERCISE


  THE VIETNAM CONFLICT

At the end of this block of study, you should be able to:

5.98 Discuss the policy that was applied to American air power in Vietnam.


From 1950 to 1973, the United States was involved in its longest armed conflict. Rather than discussing the entire war, this section will only deal with America's use of air power in Vietnam.

America's initial use of air power in Vietnam was used to raise the morale of the South Vietnamese Armed Forces and to contain the military advances of the Viet Cong until ground troops could arrive.

As the United States became more deeply involved in the conflict, the doctrine of gradualism governed the use of air power. President Lyndon B. Johnson wanted air power to support the ground troops, deny the Communists areas of sanctuary, punish the North Vietnamese, and limit the flow of supplies into South Vietnam.

The proper use of air power in Vietnam was hampered by the gradualistic policy and the politicians in Washington, D.C., who controlled its day-to day employment. Gradualism took away the two principles of war that air power must have to be successful—mass and surprise. Under this policy, the politicians committed American Air assets piecemeal, restricted certain targets from attack, dictated the frequency and level of attacks, and even limited certain types of tactics. As a result, this allowed North Vietnam to study American strategy, weapons, and tactics. The government in Hanoi was able to build up its air defenses and disperse its people, supplies, and industries.

In 1972, the policy of gradualism wits modified under President Richard M. Nixon as a result of the North Vietnamese invasion on April 2, 1972. Nixon authorized senior field commanders to make day-to-day decisions, and he lifted restrictions on many targets that had been off-limits. In reaction to the invasion, Operation Linebacker I was launched. It ran from May through October 1972 and was designed to isolate North Vietnam from external supply sources.


In mid-December 1972, the peace talks in Paris broke down. In an attempt to get North Vietnam back to the negotiating table, President Nixon launched Linebacker II. This operation was the only true strategic bombing campaign of the war. Air power was swiftly and massively applied to the heart of North Vietnam. Although it is not known for sure, this proper application of air power may have encouraged North Vietnam to sign the cease-fire agreements on January 28, 1973.

REVIEW EXERCISE

 


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Updated: 12 March, 2004