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Strange Shapes in the Sky: Stealth and Flying Wings

XB-35

XB-35 (United States Air Force, Wikimedia Commons)

XB-35

XB-35 (United States Air Force, Wikimedia Commons)

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Learn about how and why engineers designed and built some very unique aircraft.

Some of the coolest shapes you will see in aircraft are the work of engineers who were looking for innovative solutions to different challenges. Sometimes they were looking for better ways to make planes fly farther, faster, and higher. But sometimes those designers were trying to do something really different, like making an airplane harder to detect with radar. Here are a few examples of out-of-the-box thinking by aviation engineers.

Being Stealthy

During the early 1960s, the United States and the  were engaged in what is known as the . Although these countries were not attacking each other with guns and bombs, they were at war. Each side in the conflict put a lot of effort into finding out what the other side was up to. This is better known as .

One way to gather information was by looking down from the sky. To do this, the US Central Intelligence Agency (CIA) developed secret spy planes to fly around and over the Soviet Union. These planes used cameras and other instruments to gather data about Soviet military activities.

These aircraft had to stay safe from enemy fighters and   while they flew near or over enemy territory. There were several ways they could do this. One way was to fly so high and fast that the enemy could not catch them and shoot them down. Another was to not be detected by enemy . This is called '.'

In the late 1950s, the CIA wanted a secret aircraft that would fly higher and faster than any plane before it. They also wanted it to be hard to detect by radar. The CIA asked the engineers at Lockheed’s Advanced Development Projects (ADP) group to design this plane. The ADP, better known as the “Skunk Works,” was led by Clarence L. “Kelly” Johnson. Johnson and his Skunk Works engineers designed and built some of the most important planes in history.

Entrance of the Lockheed Skunk Works in Palmdale, California
Entrance of the Lockheed Skunk Works in Palmdale, California (Source: Alan Radecki [CC BY-SA 3.0] via Wikimedia Commons).
Image - Text Version

Shown is a colour photograph of an aerial view of the front entrance area of the Lockheed Skunk Works in California on a sunny day. To the upper left is a driveway. In the upper right, lower left, and lower right are grey, square buildings, with grass and cement in between the buildings. In front of the main entrance are two planes on posts. To the left of the door is a light grey P-80 jet with straight wings and to the right of the door is a triangular black F-117 jet. Round tables with umbrellas and Joshua trees dot the nearby landscape.

To meet the CIA’s needs, Johnson and his team created the A-12/YF-12/SR-71 Blackbird. The Blackbird was a huge leap forward in aviation. Johnson said that designing and building the Blackbird “was no easy task. Everything about the [Blackbird] had to be invented from scratch...the design, the technology, even the materials.”

Lockheed SR-71 Blackbird in flight
Lockheed SR-71 Blackbird in flight (Source: Public domain image by the United States Navy).
Image - Text Version

Shown is a photograph of a sleek black jet plane flying towards and below the viewer over a rocky desert. The plane has a long, wide, pointed nose and triangular wings with large, pointed engines mounted in the wings midway between the fuselage and the tips of the wings. On top of each engine is a tailplane that angles towards the middle of the plane. White contrails are streaming from the wings behind the plane.

 

Radar works by sending out . When these waves hit something, they are reflected back to the radar receiver. This is called a radar echo. It is much like the echo you hear when you yell in a large empty room. In the room, the sound waves that you send out bounce back after hitting the walls of the room. When radar waves hit an object, they also bounce back. The farther away the target is, the more powerful the radar must be. If the power is not strong enough, the signal won’t make it back. By calculating how long the waves take to return to the radar receiver, the distance to the target can be determined. By determining where the signal bounced, the position of the target can be figured out.

Did you know?

Large radars can detect large targets several hundred kilometres away.

Like sound waves, radar waves bounce better off some things than others. The engineers at Lockheed wanted the Blackbird to have what is called a low . This would make the Blackbird appear smaller on radar than it actually is. With a smaller RCS, radars would not detect a Blackbird until it was much closer than a non-stealthy aircraft. The engineers did this in several ways.

Radar cross-sections from various animals and aircraft
Radar cross-sections from various animals and aircraft (Let’s Talk Science using images by Anhelina Lisna via iStockphoto, Gyzele via iStockphoto and LNM via iStockphoto).
Image - Text Version

Shown is an image showing overhead drawings in black on a white background of different airplane types with red dots of different sizes representing their radar cross-sections, or RCS. In the upper right is the label Radar Cross-Sections. In the right is an A380, a large jet airliner with a very large red dot underneath representing a 100 square metre RCS. In the lower left is a 737-8, a medium-sized jet airliner with a large red dot representing an 11 square metre RCS. In the top centre is an F-16, a small jet fighter with a small red dot representing a 4 square metre RCS. In the left centre is a B-2, a triangular jet stealth bomber with a very small red dot representing a 0.01 square metre RCS. In the upper left is an F-117, a triangular jet stealth fighter with a very small red dot representing a 0.003 square metre RCS. To the left of that is a small bird, with a very small red dot representing a 0.01 square metre RCS. Finally, in the top left is a winged insect, with a tiny red dot representing a 0.0001 square metre RCS.

The shape of the Blackbird has lots of curves and very few flat surfaces. These curves were designed to reflect radar waves away from the radar, not back towards it. If you look at the Blackbird from the side, there are no flat surfaces at all - even surfaces that have to be flat, like the vertical tails, are angled.

Special  were used in parts of the aircraft that were most likely to point in the direction of enemy radars.This included parts like the edges of the fuselage and wings.

Did you know?

Even the black paint on the Blackbird absorbed radar waves!

All of this meant that very little of the radar energy that hit the aircraft was reflected back to the radar receiver. This made the Blackbird a very difficult aircraft for radars to detect.

An actual Blackbird was taken out to  , a secret facility in the Nevada desert, to test how small its radar cross-section was. The Blackbird was mounted on a pole in the middle of a large flat area. Radars were aimed at the aircraft from different distances and angles.

These tests helped Lockheed engineers adjust the design of the Blackbird so that it had as small an RCS as possible.

Lockheed A-12 Blackbird reconnaissance aircraft mounted on a pole for radar cross-section (RCS) testing in Area 51, Nevada, 1962
Lockheed A-12 Blackbird reconnaissance aircraft mounted on a pole for radar cross-section (RCS) testing in Area 51, Nevada, 1962 (Source Public domain image from the Central Intelligence Agency via Wikimedia Commons).
Image - Text Version

Shown is a black and white photograph of a flat desert, with a large pole sticking up from the desert floor. On top of the pole is a large, grey jet airplane, with a long, pointed nose, two engines in a triangular wing, and two tails sticking out of the engines. The airplane is upside down on the pole. A jeep is parked at the bottom of the pole, and some scientific instruments and a shack are visible near the left side of the photo.

 

This test facility, and ones like it around the world, are still used by military aircraft designers. The designers measure the RCS of airplanes, drones, and missiles to figure out how stealthy they are.

Even though the Blackbird first flew in 1962, it still looks futuristic and it still holds many world records for speed and . On top of that, Kelly Johnson and his Skunk Works designers also designed the world’s first stealth aircraft.

A Lockheed YF-12 Blackbird at Area 51 in Nevada, with Clarence L. “Kelly” Johnson standing in the left foreground
A Lockheed YF-12 Blackbird at Area 51 in Nevada, with Clarence L. “Kelly” Johnson standing in the left foreground (Source: Smithsonian Institution).
Image - Text Version

Shown is a black and white photo of a large, silver and black jet airplane, with a long, pointed nose, two engines in a triangular wing, and two tails sticking out of the engines sitting on a runway in a flat desert. On the left side of the photo, a clean-shaven, middle-aged Caucasian man with dark hair in a dark suit stands in front of the plane.

 

One of the things engineers always try to do is make things better. In the 1970s, the engineers at the Skunk Works wanted to make a plane with an RCS even smaller than that of the Blackbird.

Ben Rich, who worked on the Blackbird, was now in charge of the Skunk Works. They were not interested in making a plane that would fly higher or faster. They wanted a plane that would be “invisible” to radar. 

Ben Rich with F-117 Nighthawk
Ben Rich with F-117 Nighthawk (Source: National Portrait Gallery, Smithsonian Institution).
Image - Text Version

Shown is a black and white photo of a black jet airplane with a pyramid-shaped nose sitting on a runway in a flat desert. On the left side of the photo, a clean-shaven, older Caucasian man with grey hair in a dark suit stands in front of the plane.

 

The plane that Rich and his team designed was code-named Have Blue. Its shape was totally different from the Blackbird’s. The Blackbird has lots of curves, but Have Blue didn’t have any curves at all. The whole plane was made up of flat surfaces designed to reflect radar waves away from the radar receiver. Both of the Have Blue prototypes were destroyed in crashes.

Have Blue
Have Blue (Source: Public domain image by the United States Air Force via Wikimedia Commons).
Image - Text Version

Shown is a colour photo of a small, triangular-shaped grey jet airplane with irregular black, green, and tan spots, with a long, pointed nose, pyramid-shaped fuselage, two tails at the rear, and triangular wings sitting on a runway in front of a corrugated metal wall. The airplane is facing toward the left of the viewer.

 

The lessons learned from Have Blue led to the F-117 Nighthawk. The F-117 is like the Blackbird in some ways. It is black, and it is covered in radar-absorbent materials. Its shape is like Have Blue’s, though. The F-117 was so difficult to fly, one of its nicknames was the “Wobblin’ Goblin.” But it worked. To a radar, the F-117 looks the same size as a hummingbird! The F-117 became the first stealth fighter.

F-117 Nighthawk in flight
F-117 Nighthawk in flight (Source: Public domain image by the United States Air Force via Wikimedia Commons).
Image - Text Version

Shown is a photograph of a sleek black jet plane flying towards and below the viewer over a rocky desert. The plane is boxy, made up entirely of flat surfaces. The plane has a long, wide, pointed nose and triangular wings. The pilot has three triangular windows at the front and two The tail is shaped like a small V and is at the very back of the plane.

 

The F-117 is truly one of the strangest shapes in the sky!

The Blackbird and the Nighthawk are great examples of how even the same engineers can come up with very different solutions to an engineering challenge.

Flying the Flying Wing

One of the most unusual aircraft designs is the ‘’. A flying wing is an aircraft that has no  or tail. In a flying wing, the engines, , landing gear and all other parts of the aircraft are actually inside the wing. The advantage of the flying wing design is that it has much less   than a conventional aircraft of the same weight. This means that it can fly farther on less fuel.

The key problem of the flying wing design is that it is unstable. The lack of a tail makes it hard to fly. But this did not discourage designers. The advantages of the flying wing concept attracted several aerospace engineers to try to solve the problem.

Jack Northrop was the biggest supporter of the flying wing. During his long career he built many flying wing designs in an effort to prove how good the concept was. Northrop’s dream was to build large flying wing aircraft, such as airliners and bombers. But before he could do that, Northrop had to solve the control and stability problems that flying wings posed.

Jack Northrop in front of an XB-35
Jack Northrop in front of an XB-35 (Source: Public domain image by the United States Air Force via Wikimedia Commons).
Image - Text Version

Shown is a black and white photograph of a older Caucasian male wearing a white shirt, medium pants, and a white hat standing in front of the nose wheel of a large, silver, boomerang-shaped airplane sitting on a desert runway. The crew's windows are behind the man's head, and a group of men are standing underneath the airplane to the right of the picture.

 

In 1940, the Northrop Company was ordered to build a huge flying wing , the XB-35. Now Northrop had to make the flying wing concept work for real!

Northrop chose to build four flying scale models of the XB-35. They would help engineers and test pilots learn more about how the flying wing would perform in the air and hopefully solve any problems that they encountered.

The scale model, called the N-9M, had a wingspan of 18.3 metres (60 feet). This was about 1/3 the size of the XB-35. The first N-9M flew on December 27, 1942, 3½ years before the first XB-35.

The N-9Ms were a useful part of the B-35 program. A number of control and stability issues were discovered and solved as a result of their flight tests. The flight test data also helped to verify wind tunnel and other data. 

There were still problems with the big bombers, though. After several crashes the Northrop flying wing bombers were cancelled. All of the Northrop flying wings were scrapped in the early 1950s. One of the N-9Ms survived as part of the collection of the Planes of Fame Museum in Chino, California for many years. Tragically, it crashed in 2019.

The last surviving Northrop N-9M model in flight
The last surviving Northrop N-9M model in flight (Source: public domain image by Malfita via Wikimedia Commons).
Image - Text Version

Shown are a series of four colour photos of a boomerang-shaped airplane flying. The airplane is yellow on the top and blue on the bottom. Two propellers protrude from the rear of the middle of the wing, and the pilot sits under a clear teardrop-shaped dome in the middle of the wing. The top left photo shows the plane from the right bottom. The top right photo shows the plane directly from the side, where it appears very small. The bottom right photo shows the airplane banking to the right, towards the viewer. The bottom left photo shows the airplane banking towards the left, towards the viewer. The boomerang shape of the airplane is clearly shown in this photo.

 

For 30 years, Jack Northrop thought that his dream of a flying wing was dead. But in 1980, a seriously ill Jack Northrop was taken to a secret room at the Northrop company headquarters. The company president and its top designers got special security clearance to show Jack a model of the top-secret aircraft that they were building.

This was a huge flying-wing stealth bomber that became the B-2 Spirit. The B-2 happens to have exactly the same wingspan as the XB-35!

When Jack Northrop died in 1981, he was happy to know that his flying wing would finally be a reality.

B-2 Spirit bomber in flight
B-2 Spirit bomber in flight (Source: Public domain image from the United States Air Force via Wikimedia Commons).
Image - Text Version

Shown is a colour photo of a large dark grey airplane from above and to the right flying over a desert. The plane is flying towards the right of the photo. The plane is shaped like a large triangle, with four triangular shaped sections cut out of the rear. There is a smooth bulge in the front of the plane, with tinted windows in the front of it. On either side of the bulge are two smaller bulges for the engines.

 

Did you know?

The XB-35 and the B-2 both have the exact same wingspan: 52 m (172 feet)!

So remember - the next time you see an unusual airplane, it has that shape for a reason! It can be fun to try to figure out what challenge the designers were trying to solve. 

Learn More

Lockheed Martin: Blackbird
Lockheed Martin’s website has a page with good information and images about designing and building the Blackbird.

F117 Development
The Stealth Fighter Association’s website has a page with lots of information on the development of the F-117 and the prototypes that led up to it.

Northrop Bombers
These pages on the Century of Flight website have good information with photos of both the N-9M and the big Northrop flying wing bombers, the XB-35 and the later B-49 jet flying wings.

References

Crickmore, P. (1997). Lockheed A-12/YF-12/SR-71. Wings of Fame, 8, 30–93.

Crickmore, P. (2004). Lockheed Blackbird: Beyond the Secret Missions. Osprey.

Dorr, R. F. (1994). Lockheed F-117: The Black Jet. World Airpower Journal, 19, 48–107.

Miller, J. (1990). Lockheed F-117 Stealth fighter: America's Most Secret Warplane Revealed! Aerofax.

Miller, J. (1985). Lockheed SR-71 (A-12/YF-12/D-21). Aerofax, Inc.

Pape, G. R., and Campbell, J. M. (1995). Northrop Flying Wings: A history of Jack Northrop's Visionary Aircraft. Schiffer Pub.