Rutan Boomerang Behold the Boomerang: the extraordinary
brainchild of aviation pioneer Burt Rutan, this is not just an aircraft; it's an airborne enigma.
The number one question people constantly ask whenever they see this plane is “Why
is it so unconventional?” It's not merely the aircraft's aesthetic that turns heads;
it's the genius engineering that sculpted its form. The mission was as clear as the skies
it was destined to conquer: forge a vessel that epitomizes efficiency and safety. The ingenious
resolution? To place the engines in a proximity unlike any typical twin-engine craft, giving rise
to the Boomerang's distinctive, asymmetrical architecture. A marvel that is as visually
captivating as it is technologically remarkable. Designed by Burt Rutan, an aeronautical maestro,
whose academic journey culminated with a Bachelor of Science in Aeronautical
Engineering from California Polytechnic State University San Luis Obispo in the year 1965.
During the '70s and '80s, Burt's professional period was marked by remarkable productivity,
during which he conceived several distinctive, swift, and high-performance designs for homebuilt
aircraft. He was at the forefront of innovating a streamlined construction technique for crafting
sleek airplanes using molded foam and fiberglass, eliminating the necessity for traditional molds.
He established Scaled Composites with the aim of advancing the design of pioneering aircraft
for business and defense clients. Before this venture, and while at Rutan Aircraft Factory,
Burt was responsible for designing the Voyager, which made history as
the first airplane to circumnavigate the globe non-stop without needing to refuel.
In the late 1980s and early '90s, Burt was extensively engaged at Scaled Composites,
yet he managed to carve out time to work on the Boomerang, a project that was particularly close
to his heart. Despite the initial doubts from colleagues about his unconventional concept, Burt
felt free to trust his creative instincts since the Boomerang was a personal endeavor. His aim was
to design an aircraft that didn't compromise on safety or efficiency, traits he had successfully
realized individually in previous designs — with efficiency in the Catbird and safety
in the Defiant. His vision for the Boomerang was to embody both attributes simultaneously.
To appreciate the innovative nature of the Boomerang, one must consider the prevailing
aircraft design standards of the era. Twin-engine aircraft, largely unchanged since the 1930s,
typically featured an engine on each wing, with a symmetric airframe on both sides of
the aircraft's centerline. The main advantage of this design was its redundant systems for safety;
if one engine failed, the other could continue to power the aircraft, a critical feature for
over-water flights or nocturnal travel where engine failure in a single-engine
plane would pose significant risks. Nonetheless, the standard twin-engine
configuration is not without its drawbacks. Should one engine of a conventional twin-engine plane
fail, the aircraft faces challenges not just from the loss of power, but from uneven thrust
as well. The farther the engines are placed from the aircraft's center, the more severe
the effect of this asymmetrical thrust becomes. To combat the issue of uneven thrust and the
problems related to the 'critical engine,' some aircraft designers have turned to a 'centerline
thrust' configuration, aligning one engine in front and another at the rear in a push-pull
setup. This arrangement centralizes the thrust line, but it introduces other problems; the noise
level inside the cabin can be significantly higher, and vibrations can be more pronounced
compared to conventional twin-engine designs. The Cessna Skymaster exemplifies this push-pull
design, yet it falls short in terms of efficiency because of several design shortcomings. The cabin
of the Skymaster is notorious for its loud and vibratory environment. Additionally,
the aircraft suffers from a lack of adequate baggage space, as the prime location for
luggage is occupied by the rear engine. While the centerline thrust design of the Skymaster
addressed certain safety concerns, it did so at the expense of comfort and overall performance.
In response to the limitations of conventional aircraft designs, Burt Rutan introduced the Rutan
Defiant in the late 1970s. This push-pull aircraft featured a canard configuration and was later
available as a homebuilt kit. While it mirrored the Skymaster in enhancing safety during engine
failure, it did not achieve optimal efficiency. When conceiving the Boomerang, Burt Rutan
established foundational design goals: to surpass the interior space of the Long-EZ,
accommodate five passengers, match the Catbird's impressive speed and efficiency,
and feature dual engines for the safety benefits during nocturnal or over-water flights, akin to
the Defiant. He aimed to maintain the favorable flight characteristics of his centerline thrust
Defiant without inheriting the shortcomings typical of existing push-pull configurations.
Starting with a clean design sheet, Rutan explored innovative solutions to minimize
the distance that engines were traditionally mounted from the aircraft's centerline. His
solution was to reposition the right engine onto the fuselage, bringing both engines closer to the
aircraft's center of gravity. This design choice led to reduced drag by decreasing
the frontal area compared to traditional twin-engine aircraft, which usually have
two engine nacelles plus the fuselage. He then altered the rest of the airframe to mitigate
the adverse effects of an engine failure on either side. His approach included several
unconventional adjustments to ensure the aircraft remained balanced across various fuel loads,
passenger numbers, and cargo configurations. Burt Rutan's tenure at Scaled Composites
positioned him at the forefront of the shift towards utilizing carbon fiber in the creation of
strong, yet lightweight, structures. The Boomerang capitalized on this advanced material. However,
the substantial weight reduction it offered also presented a challenge in maintaining
the aircraft's balance with the placement of engines, fuel, and passengers. To counteract this,
Burt ingeniously designed the aircraft's wings with a forward sweep, lending the Boomerang its
distinctive look. The forward-swept wings weren't just for aesthetics; they strategically shifted
the aerodynamic center forward to balance out the weight of the engine mounted at the
front. The strength of carbon fiber addressed the potential issues of aeroelasticity that such an
unconventional wing design might encounter—a feat less feasible with older, conventional materials.
Remarkably, the Boomerang weighs 1,367 pounds less than a pressurized Baron, representing an
exceptional reduction in weight. Part of this weight saving comes from employing smaller
4-cylinder engines, which are viable options precisely because the airframe itself is lighter.
The strength of the carbon fiber composition further allows for the Boomerang's cabin to
be pressurized to 4.6 psi, outperforming the Baron's 3.8 psi pressurization capability. This
pressure differential means that at an altitude of 25,000 feet, the internal cabin altitude of
the Boomerang feels like 10,150 feet, compared to the Baron's 12,300 feet, enhancing comfort
and reducing passenger fatigue. Although the Baron can accommodate up to six seats, its cargo space
is somewhat constrained. On the other hand, the Boomerang not only offers seating for five but
also retains ample baggage space in the left-side boom, facilitating the storage of elongated
items without impinging on passenger space. The Boomerang is equipped with a pair of Lycoming
TIO-360 (Lycoming; lie coming, 360 is pronounced three sixty) 4-cylinder turbocharged engines,
each with a slightly different power output—one at 210hp and the other at 200hp. This disparity might
appear to be a deliberate engineering decision, but it was actually driven by Burt Rutan's
economical approach. The engines were simply the ones he had available and accessible at the time,
which explains their incorporation into the aircraft. To further economize, the Boomerang
was constructed during off-hours by Burt and a small team of Scaled Composites volunteers,
who dedicated their time to bring his vision to life. Despite its advanced and innovative design,
the Boomerang has a fundamentally grassroots origin, reflecting Burt's characteristic approach.
The aircraft's design allows it to fly with either engine at full throttle without requiring rudder
adjustments, yet it still maintains the ability to perform a controlled stall. The forward-swept
wings are designed so the roots will stall first, preserving aileron effectiveness at the wingtips,
thus allowing the pilot to maintain roll control. The aircraft's design causes it
to naturally lower its nose, gain speed, and recover flight. If the pilot intentionally
maintains a nose-high attitude, the Boomerang will continue this stall-and-recover sequence while
still keeping directional control. In traditional twin-engine aircraft, during an engine failure,
full rudder input may not be sufficient to avoid the plane turning towards the inoperative engine,
leading to a potential loss of control before stalling. Moreover, the Boomerang
features a tail behind each engine to ensure airflow over one of the tails for improved
rudder and yaw control at lower speeds. For access, the Boomerang boasts two doors:
a small airstair located behind the wing on the right side for the three rear passengers, and a
unique windshield door on the right for front seat entry. The pressurized cabin necessitates
the windshield door to open inward before sliding back, complemented by a pop-out step to facilitate
boarding and alighting. This door design also allows for a continuous wing spar, enhancing
structural integrity and reducing weight. The construction of the fuselage employs a
manual filament-winding technique to produce crosswise longerons that are cleverly placed
to distribute loads effectively and outline the framework for the doors and windows. The wing spar
is designed to be a single, uninterrupted piece for enhanced durability and to minimize structural
weight. This spar crosses through the cabin area just behind the two front seats at an incline,
influenced by the unconventional shape of the wings, which cleverly explains why Burt
Rutan arranged the front seats in a staggered formation. The pilot is seated to the right,
slightly ahead, while the co-pilot's seat is offset to the left and behind, allowing
for more comfortable spacing of shoulders and elbows, diverging from the standard side-by-side
arrangement. The additional three seats are situated aft of the wing spar, each angled
to afford individual space for each occupant. In the cockpit, both front seats are equipped
with a side-stick for control; however, only the right seat is fitted with rudder
pedals. These pedals are split into right and left components, each governing its own braking system,
offering independent control. The Boomerang's design forgoes traditional nose wheel steering,
instead relying on differential braking for maneuvering on the ground. Each main gear leg
hosts a pair of wheels, with each wheel tied to its own brake system, connected to the respective
side of the split rudder pedals, providing a dual system for braking and steering reliability.
The aircraft's landing gear design is also quite distinctive. The nose wheel is asymmetrically
mounted on the left side of the fuselage, optimally positioned between the two main
gear legs for better balance. When retracted, the nose wheel tucks neatly just ahead of the left
seat occupant's feet, maximizing use of space and maintaining the aircraft's sleek design.
The positioning of the main gear legs is strategic; the one attached to the fuselage
is set back further than the one on the boom. This design choice prevents the aircraft from
tipping backward onto its tail if passengers board through the rear door before anyone is seated at
the front. The gear leg on the fuselage retracts forwards, while the boom's main gear leg retracts
backwards. Despite the uneven weight distribution on the main gear and their varying distances
from the nose wheel, the aircraft maintains stable handling during takeoffs and landings.
In flight, the Boomerang excels whether it is powered by both engines or just one. It has a
high wing loading of approximately 41 pounds per square foot, which affords the aircraft a very
steady feel in the air. This aspect also plays a role in achieving a high maximum cruising speed
of 264 knots (304 mph). The wing is engineered with ailerons that extend almost the full span
and double as flaperons, enhancing control and efficiency. For better high-speed performance,
the ailerons are designed to deflect upwards, adjusting the wing's camber.
The Boomerang exhibits remarkable resilience to the effects of asymmetrical thrust in case one
engine fails, mainly due to the proximity of the two engines to one another. When observed
from the front, the distance between the propeller discs is less than a foot,
a stark contrast to the nearly six-foot gap on an aircraft like the Baron. Rutan's other design
features are more subtle but equally crucial. For instance, he positioned the left engine
farther from the plane's centerline, which helps balance the thrust lines at high angles of attack,
mitigating P Factor issues. Additionally, the dual tail design positioned to catch
the prop wash provides excellent yaw control. At a casual look, the Boomerang's unconventional
design might be mistaken for a flight of fancy, but in reality, it embodies what Burt Rutan
considers his crowning accomplishment in General Aviation. This aircraft excels in both efficiency
and practicality, all the while neutralizing the perilous effects of asymmetrical thrust commonly
associated with twin-engine planes. What heightens its remarkable stature is that it came to life
without the aid of wind tunnel experimentation or sophisticated computer-aided design. The
success that Burt achieved in realizing his vision marks an extraordinary feat,
and the Boomerang stands as a testament to the innovative essence of experimental aviation.
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