Asymetric Beauty
First Impressions: Whether it is the first or the one-hundredth time you’ve seen the Boomerang, it still evokes a “how does it fly?” wonderment. This iconic flying machine is a spectacular departure from conventional aircraft. Its stunning design is recognized by all, including non-pilots. I know I shouldn’t be surprised, but the Rutan Model 202 flies even more beautifully than it looks.
Background: This year, 2024, marks 50 years of Rutan aircraft production, which began with the VariViggin design. Burt Rutan has never been accused of not thinking outside the box. Yet, as unconventional as his designs are, his objective is not to produce uniquely remarkable creations. They are purpose-built both to serve as a proof of concept and to solve problems and/or deficiencies faced by conventional aircraft.
The Model 202 Boomerang was designed to solve the control problem that non-centerline thrust, multi-engine aircraft have when encountering an engine failure. The primary advantage of a multi-engine aircraft is redundancy. In theory, a multi-engine aircraft should be safer. Multi-engine pilots require specialized training and proficiency. For this reason, the FAA requires a separate “class” rating for your airman’s certificate. At the heart of multi-engine training is the concept of Vmc (minimum controllable airspeed). Every multi-engine pilot knows that maintaining Vmc or greater, is crucial to prevent the plane from experiencing a Vmc “rollover” should an engine fail. During an engine failure, the operating engine continues producing thrust, while the inoperative engine is only producing drag. With the operative engine producing full power (such as during a takeoff or go-around), the slower the plane’s speed, the more rudder input is required, until eventually the rudder’s effectiveness reaches its limits (below Vmc), which will cause the airplane to yaw into the “dead” engine and rapidly roll over. Trained and proficient multi-engine pilots can counteract this fatal scenario with both rudder and some aileron input, while maintaining Vmc or greater. Many lives and airplanes have been lost by pilots who did not maintain Vmc during an engine failure. The Boomerang serves as a proof of concept which demonstrates that this does not have to be the case. How Burt Rutan solved this problem with the Model 202 is pure genius and a lot of math.
The sole Boomerang is now in the care and custody of Tres Clements, owner of Aerocrafted. He and the Model 202 now reside in San Luis Obispo, CA, which is also where Burt Rutan studied at California Polytechnic State University in the 1960s.
Design Characteristics: The Boomerang is a composite, 5-seat turbocharged light twin. Very little in the design is symmetric. The offset fuselage, different sized-wings with different wing-sweeps, lopsided elevator, and the twin engines mounted in echelon look like a sci-fi artist’s rendering that could not possibly work in real life. Even the cockpit seats are offset, with the pilot’s seat on the right and slightly forward of the co-pilot on the left, allowing for more shoulder room. Amazingly, all these unusual features cohesively work together to form a beautifully crafted, very functional flying machine.
The calculated design of the main cabin includes contoured seating for three. The forward seat faces aft and the rearmost seat cants slightly to allow additional legroom. An empty cabinet/shelf, once used for testing equipment and a cumbersome 90’s computer, now provides the perfect place for stocking snacks and beverages. The interior is grey with maroon accents. It was completed by Oregon Aero and includes ultra-comfortable memory foam cushions, which is important since the Boomerang can remain airborne up to ten hours with a 2,200-mile range.
Emergency main landing gear extension is accomplished mechanically by connecting a ratchet to a ¼” drive fitting immediately behind the copilot’s left shoulder. The nose landing gear is mechanically extended with an over-center handle in the floor pedestal between the pilot’s and copilot’s legs.
There are two options for baggage; check-in and carry-on. Check-in bags are loaded in the rear portion of the left engine nacelle, which can accommodate items up to eight feet long. Naturally, they are inaccessible in flight. In the cabin, “carry-on” baggage is stowed behind the aft seat.
Powerplants: The carbon fiber airframe is, of course, lightweight, allowing for the use of smaller engines which are, in fact, slightly different models with differing horsepower. The right engine (a TIO-360-C1A6D), delivers 210 horsepower, and the left engine (a TIO-360-A1B), produces 200 horsepower. Both engines turn counterclockwise, spinning 75-inch, three-bladed Hartzell propellers. The Boomerang has three 57-gallon fuel tanks, for a total of 171 gallons. There is one tank in each wing and the third is located in the center wing and forward section of the boom, behind the left engine. Both engines use electronic ignition. The 12-volt DC electrical system consists of two 70-amp alternators and independent left and right busses, which can be tied together. Either buss can handle the entire electrical load of the aircraft, including all four electronic ignition modules.
Preflight/Takeoff: Preflight begins with cockpit checks…but how to access the cockpit? There is no need for anti-theft devices because cockpit entry is not obvious! First, find a small step recessed in the fuselage just below the front right window. Second, flip this hidden step down to unlock the forward right window. Third, slide the entire window aft along a composite track inside the cabin. [Footnote: the top track is actually a golf club shaft!].
After cockpit checks, work your way around the airplane counter-clockwise. There are two pitot tubes on the right wing and two airspeed indicators in the cockpit. Rutan’s original pitot tube is on top of the right wing toward the trailing edge where it, incidentally, won’t accumulate ice. This pitot source doubles as an AOA indicator of sorts in that the airspeed rapidly drops off as airflow begins to separate from the top of the wing before a stall. Pilots seeing this rapid drop in airspeed will instinctively lower the nose. The second pitot tube is an extended flight test tube that protrudes from the leading edge of the right wing to provide for more accurate data collection.
Each main landing gear has two tires and are actuated mechanically by means of a slip clutch, sprockets, chains and torque tubes. Uniquely, the left gear swings aft and the right gear swings forward, which together cancels out any change in moment during extension and retraction. The nose gear swings aft with a mechanical lever in the cockpit.
Passengers access the main cabin via Eisenhower steps that swing out from the right aft cockpit fuselage. The pilot and copilot climb into the cockpit by stepping on the small swing-out step (better stretch first!) and then entering through the right front “eyeball” window. The window can then be slid forward and latched closed, which will also stow the step. The free-castering nosewheel requires the use of differential braking at low taxi speeds. Each main landing gear has two tires with two independent brakes. This feature doubles braking power; more importantly, it provides redundancy for directional control in the event of a single brake or hydraulic failure. Each brake pedal is split, and both sides of each pedal should be tested during taxi. The throttles, prop controls, and mixtures are small horizontally-mounted levers located between the seats. These engine levers, which are outside of your normal field of view, so they require tactile familiarity in the case of an engine emergency.
Taxiing on centerline is a strange sight picture. The longitudinal axis of the Boomerang is about one foot to the left of the cabin fuselage. This means the pilot is about five feet right of centerline. After engine run-ups, lower the full span flaperons until fully down. Complete the take-off checks and line-up on centerline. Holding the brakes, push the left and right throttles up to 25” and 35” of manifold pressure respectfully. The right engine (which is incidentally out of the Model 81 Catbird) has a manual waste gate, so when the brakes are released, and the airplane accelerates, it will boost to 42” of manifold pressure. At sea level, on a standard day, fully opening the left throttle (which has an automatic waste gate) will provide even acceleration.
Flight Characteristics: Bottom line up front; the Boomerang flies beautifully. After gear retraction, my first reaction was surprise at its agility. It does not fly like other light twins. Although I have never flown a P-38, I can imagine the agility would be similar, especially in the P-38L with its hydraulically-boosted ailerons. The side sticks offer smooth roll control with a surprisingly high roll rate. Aileron rolls are effortless, even with feet on the floor.
The right flaperon is connected to the right stick and the left flaperon is connected to the left stick. Flaperon droop position is set with a toggle switch on the stick that electrically controls a linear actuator to lengthen and shorten the connection between the sticks, which equally extend or retract the flaperons on each side. Thus, as the flaps are retracted, the pilot and copilot sticks move outboard. There is no speed limitation for the flaperons and with them fully retracted (-2˚ reflex), the roll rate is naturally less than fully extended (8˚ down) due to the reduced stick range of motion.
With only two souls onboard, the airplane will exceed a 2,000-foot-per-minute climb rate. The Boomerang was designed to have a pressurized cabin, but since the pressurization system was never completed Tres typically cruises at 16,000 to 17,000 feet at 205 True Air Speed (TAS), while only burning 16 gph at 50% (about 240 TAS at 75%). With 171 gallons on board, the max range is an impressive 2,200 nautical miles! Not only does the Boomerang have astounding speed and efficiency for a light twin; its carrying capacity is more than 400 pounds greater than planes with 130 additional horsepower!
Another unique capability of the Boomerang is the ability to synchronize the propellers visually. You can look out the left window and see the reflection of the right propeller in the chromed spinner of the left engine. Thus, you can adjust either the left or right prop control until the reflection is in phase with the left spinner.
If you are not already impressed with the Boomerang, you will be during the engine failure demonstration. To replicate a failed engine with the prop feathered, Tres set the left engine 10-inches of manifold pressure and the propeller to fine pitch. With the right engine at take-off power, he told me to stall the plane. With full confidence in Burt Rutan’s design and Tres’ coaching, I gently slowed the Boomerang to about 71 knots indicated on the conventional airspeed indicator. The non-conventional airspeed rapidly dropped to around 50 knots, indicating airflow separation at the wing root. Incredibly, not only did the Boomerang not roll upside down into the dead engine, it wouldn’t even stall. This inability to execute an unaccelerated stall is because, with only two of us onboard, we were at the forward CG limit, which demonstrates the wide CG range and large carrying capacity that is available.
After lowering the nose and gaining airspeed, Tres instructed me to be more aggressive in the pull up, attempting an accelerated stall. With an aggressive pitch up, the Boomerang finally stalled, but was more benign than even the most forgiving single-engine trainer, without even a slight wing drop. Thanks to the forward-swept wings, the wing roots stall first, retaining full aileron control. There was no wing drop-off whatsoever and no rudder input required. The myth of the non-centerline thrust, multi-engine plane without a Vmc is true!
So, how does the Model 202 seemingly break all the rules of multi-engine flying considerations? The Pilot Operating Handbook says it best . . .
“There is one twin-engine airplane, which is not centerline thrust, which does not have a VMC. It is called the Boomerang and was designed and built by Burt Rutan. It has one engine mounted on the fuselage, and the second engine on the boom. Both engines are much closer together than on a conventional twin-engine airplane. The Boomerang has two vertical tails, each directly behind the engine. So whichever engine fails, the other one continues to provide extra slipstream over a vertical tail and rudder to increase directional stability. The center of gravity is not within the fuselage, but somewhere between boom and fuselage. Both engines rotate the same way, so that at high angles of attack the P-factor offsets both thrust lines to the right. The figure below shows that this puts each thrust line at almost equal distance to the center of gravity. Whichever engine may fail, the moments created by the remaining engine are small. Even though the Boomerang looks totally asymmetric, it is more symmetric in its flying qualities than any twin with wing mounted engines.”
Landing: Manage your airspeed to decelerate below 130 knots for the gear speed. Manipulating the landing gear is a two-step process. Lower the gear handle for the mains and swing the nose gear lever up to place it in the down position. After confirming three green lights, ensure the full-span flaperons are fully down. Check boost pumps on and verify prop and mixture positions. Maintain 120 knots in the pattern and slow to 115 knots on final. Don’t forget – you are not trying to place the cabin and nose gear on centerline. Line-up about four feet right of runway centerline and execute a normal flare while pulling the throttles to idle.
Wrap-Up: In the world of aircraft, most things are symmetrical. A pilot’s brain seems wired to immediately question anything that isn’t. Burt Rutan, however, has proven that aircraft asymmetry doesn’t equate to imbalance. On the contrary, the Boomerang is the most well-balanced propeller-driven twin I have ever flown. It’s ability to maintain balance with only one operative engine makes it a true marvel. No, Burt Rutan did not write the laws of physics, but he certainly has learned to apply and harness them in uniquely inspiring ways. His Boomerang is indeed an asymmetric beauty.
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