The Boeing Bird of Prey was a trailblazing stealth aircraft secretly developed by the US military between 1992 to 1999 at Area 51. Its extraterrestrial appearance would no doubt be responsible for UFO sightings occurring at the time.
Named after it resembles a Klingon spacecraft from Star-Trek, the ‘black budget’ project was also applauded for the effective management of its small $67 million funds.
In Frankenstein style, the Bird of Prey was fashioned out of a medley of aeronautical parts borrowed from other aircraft at the same time as being at the forefront of clandestine military technology.
The Bird of Prey had its origins in the US black programs of the previous decade, which aimed to explore the phenomenon of stealth flight.
Boeing X-32 – So Ugly it Failed
In October 1983, the Lockheed F-117 Nighthawk became the first ever stealth plane issued by the US military. Its ‘F’ initial designated it as a fighter, however the craft itself was not designed with this in mind.
It possessed no radar system and onboard guns, and only had space for two 2,000 pound bombs. However, it was incredibly effective at dodging radar, having a radar cross section of just 0.11 inches, making it practically impossible for the enemy to see it.
As the 1980s came to a close, the US military announced that a new Advanced Tactical Fighter contract, which aimed to surpass the F-117, was up for grabs. Vying for the prize were Lockheed, Northrop, and McDonnell Douglas.
McDonnell Douglas in partnership with Boeing came out on top because they had managed to poach the brilliant Alan Wiechman from Lockheed to run their new Phantom Works division. He was a respected aeronautical engineer who had contributed enormously to the F-117 as well as to the Lockheed Shadow, an experimental stealth warship.
Wiechman’s contributions to stealth aviation were enormous, and he would go on to receive a Technical Achievement Award for his work on the Bird of Prey in the late 1990s before the program was even declassified. It read:
“Because of Wiechman’s work, the United States gained a 15-year lead over potential adversaries that it has not relinquished, and the effectiveness of his designs and products has been thoroughly proven in combat operations”.
Being a private firm, McDonnell Douglas had to be stricter with money than their other competitors such as Lockheed or Northrop, who were funded by taxpayers money a lot of the time. As a result, they thought of a variety of creative ways to stretch their $67 million budget.
One of these was their implementation of a revolutionary new technique that took advantage of the latest advances in 3D computer graphics.
It allowed them to ‘rapid prototype,’ which meant they could program and test virtual Bird of Prey prototypes instead of physically building them. It also meant that when the time came to create a real-life version they could construct a Bird of Prey that was closest to the finished product.
In another initiative that also cut costs, Wiechman and his team pioneered single-piece composite designs, which were fabricated without the body panels that often helped reveal clandestine craft. 4 years into the program, in 1996, the first and only version of the Bird of Prey was made, with its test flight booked for September 11th, 1996.
Bird of Prey
The Bird of Prey, weighing 7,400 pounds and having a height of 9 feet, was also 47 feet long and had drooped wingtips that were 23 feet. It was propelled by a Pratt & Whitney JT15D-5C engine which gave it 3,190 pounds of thrust and gave it a top speed of 300 miles per hour.
It was flown at a maximum altitude of 20,000 feet, rising 3,000 feet per minute at peak performance. It was controlled by a hydraulically powered irreversible flight control system, an older model that was favored over the more modern and pricier digital fly-by-wire controls.
Roll control was achieved by linking a series of pedals and a stick to 4 control surfaces located on the inner wings and outer wing panels.
Because of budget constraints, the Bird of Prey was patched together with the components of other planes. The engine was the same model used in the Cessna Citation business jet, the modified landing gear came from a Beech King and Queen Air twin-prop commuter craft, and a Gulfstream II business jet was scavenged for the wheels, tires, and elevon actuators.
Elsewhere, the throttle and stick were from an F-18 Hornet, and the rudder pedals from an A-4 Skyhawk. One of the test pilots, Doug Benjamin, would later comment on the mishmash of pieces seemingly flung together to produce the Bird of Prey:
“The clock was from Walmart and the environmental control system was essentially a hair-dryer”.
On the other hand, its stealth capabilities were much more state-of-the-art and helped cloak the Bird of Prey from being detected by radar, infrared, visual, and acoustic signatures.
A low-radar profile was achieved by its sleek, low body, and the gaps in its structure were concealed by flexible covers. For this purpose also, the canopy, landing gear, wings, and fuselage were all carefully aligned to stop anything from jutting out.
In an effort to make it even more invisible, the engine intake was completely hidden from the front.
The power plant was placed deep within the fuselage and camouflaged by the canopy and inlet duct, and the engine exhaust was tinkered with so that it reduced the acoustic signature of the airplane.
Finally, the color scheme, consisting of several shades of grey, helped lessen its visual impression.
Testing
Even before testing, there were concerns that the alien-looking prototype wouldn’t even be able to fly. Phantom Works chief aviator Rudy Haug illustrated his worries by folding a sheet of paper to the exact dimensions of the Bird of Prey before throwing it in the air, his paper model flipping onto its back because of the downturned wingtips.
Nevertheless, assured by the 3D models which demonstrated that the Bird of Prey wouldn’t crash, the planned test flight went ahead.
First, however the Bird of Prey was required to undergo a static engine test, which exposed some underlying structural snags. It was discovered that inlet flow distortion was stopping airflow to the compressor and significantly increasing the thrust-to-weight ratio.
Next, its speed was tested on the runway, with high-speed taxi runs coming in at 3% slower than predicted because of high thrust. Compiling a best-case and worst-case scenario, planners were not perturbed by the data, which seemed to suggest that it would be sufficiently safe to operate the aircraft and that there was enough time to perform an emergency maneuver if necessary.
Just in case, mechanics added a nine-square-foot ventricle fin that would help with directional stability for the first 7 test runs, although this had the major drawback of preventing the Bird of Prey from flying in the necessary conditions to test some of its more advanced faculties.
This was changed to a five-square ventricle fin for the rest of the program which allowed the plane to meet the experimental flight requirements.
With no more obstacles, Rudy Haug took the Bird of Prey for its first spin in September 1996. He reported experiencing significant drag coming from the open wheel-well cavity 3 times greater than forecast.
The 15% scale model they had used to test the aerodynamics had been too small to take into account how smaller details like the inlet, exhaust, or gear wells would affect performance. To counteract this, engineers added what they termed ‘Cadillac fins’ to the main landing gear struts, an addition that decreased unwanted drag.
By the 3rd test flight, the team was aware that the Bird of Prey met all of its stability derivatives apart from directional stability due to roll rate or CnP, which was reading negative about conventional fighter aircraft readings. It was making the airplane jerk in an undesired yaw direction after performing roll movements.
The team’s fixes, which included extending the ARI gearing between the elevon and rudder, made the problem worse until it became such a recurring symptom that it was causing the plane to wildly roll around in an overextended dihedral effect.
Equally troubling was the time delay between the pilot’s commands and the roll producing the yaw motion, causing bouts of oscillation. A redesign of the ARI solved everything, allowing the Bird of Prey to meet over 90% of the stability derivatives.
By the fifth flight, the Bird of Prey was finally able to consistently operate, permitting the team to start rounds of low observable testing leading to a couple of close shaves. While figuring out gear retraction and extension sequences, a faulty landing gear failed to fully retract, compelling Haug to press the electrical override switch.
It enabled him to input an alternative sequence, saving him from being potentially impaled by a flight boom attached to the nose that threatened to snap.
Disaster nearly struck a second time after the nose of the craft jerked in an awkward yaw direction as soon as it left the ground during high-speed taxi runs.
The wheel’s center of pressure in combination with the poor resistance of the center spring had caused the Bird of Prey to jar, and the plane was only saved from obliteration when the nose wheel luckily centered itself before touchdown.
Afterward, the nose was torn off and replaced with the same part from an F-100 Super Sabre because of its sturdier center-of-pressure characteristics.
This had the unfortunate side-effect of limiting turning radius, and from then on a tow bar would have to be manually used by the ground crew for sharp turns in a process that was called ‘Steerman’.
Throughout the trials, pilots had to contend with the unusual design of the small craft, which had a thrust-to-weight ratio similar to a cargo airplane. It had a reference lifting area of only 366 square feet, and because the fuselage possessed half the load it had 20 pounds of wing-loading per square foot.
Overall, the Bird of Prey undertook 38 missions between September 1996 and April 1999.
The Bird of Prey’s Legacy
The Bird of Prey was ultimately a triumph, representing a quantum leap forward in stealth technology that was later incorporated into many of Boeing’s future projects.
The Boeing X-45A, unveiled in November 2000 for example, utilized many of the features that helped reduce its imprint on radar such as the smooth body shape. It was also an impressive example of how a company could create a cutting-edge aircraft with very little money, and a testament to the inexpensiveness of new manufacturing approaches.
The project was declassified in 2003 because many of its novel designs had become standard issue by that time. The Bird of Prey is now exhibited at the National Museum of the US Air Force at Wright-Patterson Air Force Base, Ohio.