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Written by Josh Bernstein
A finely tuned aerobatic biplane
Product review
As seen in the July 2017 issue of
Model Aviation.



Bonus video


Specifications

Model type: Electric 3-D/aerobatic biplane
Skill level: Intermediate to advanced
Wingspan: 40.7 inches
Wing area: 691.3 square inches
Length: 43.4 inches
Wing loading: 11.2 ounces per square foot
Cube loading: 5.1
Weight: 54 ounces
Power system: Brushless electric outrunner
Radio: Six-channel computer radio
Construction: EPO foam with plywood subframing
Street price: $309.99


Test-Model Details

Motor used: Potenza 10 1,400 Kv brushless outrunner (included)
Speed controller: Hobbywing Skywalker 50-amp ESC w/SBEC (included)
Battery: Turnigy 2,200 mAh 3S 40C LiPo; Zippy Compact 2,700 mAh 3S 35C
Propeller: 11.5 x 4.5 custom-tooled SR (included)
Receiver: Spektrum DSM2 Satellite
Servos: Six Potenza DS15 15-gram digital metal-gear submicro servos (included)
Ready-to-fly weight: 54 ounces
Flight duration: 3.5 to 5 minutes


Pluses

• Lightweight, rigid, and durable EPO foam w/internal plywood structure.
• Wide flight envelope includes sport, precision, and 3-D.
• Aura 8 Advanced Flight Control System provides large-scale stability.
• Configurable for the famous Quique biplane Crow feature.


Minus

• Short flight times with recommended 2,200 mAh 3S battery pack.

Don’t let the fact that Flex Innovations hasn’t been around for long fool you. It’s far from being the new kid on the block. After three decades spent winning worldwide competitions and honing his skills as a top designer/engineer of many well-known RC airplanes, Quique Somenzini and an equally accomplished David Ribbe took their decades of experience and started Flex Innovations in 2013.

With the design and engineering chops of well-known, competition-winning pilot Seth Arnold, and former aerospace engineer Joseph Burch, Flex Innovations has developed a loyal following of enthusiasts who appreciate the quality of design and engineering that comes from a wide base of experience.

Having been impressed by what this team was able to do with a large, foam, general-aviation airplane such as the Premier Aircraft Cessna 170 PNP, I was excited to try out its latest offering: the Mamba 10.

A scaled-down version of the company’s popular monster biplane, the Mamba 70CC, the Mamba 10 squeezes a tremendous amount of sophistication into a durable 54-ounce package. With a wingspan slightly less than 41 inches and just over 43 inches long, this 3-D capable, aerobatic biplane provides a whopping 691.3 square inches of wing area.

This results in a wing loading (the proportion of total wing area to flying weight) of 11.2 ounces per square inch. What do all of these numbers mean? In short, the Mamba 10 feels floaty and stable, particularly during low-and-slow post-stall maneuvers such as hovers and harriers. Despite its low wing loading, the included Aura 8 Advanced Flight Control System (AFCS) works to stabilize the Mamba 10 and provide a level of precision uncommon in an airplane of this size and weight.


Assembly

The Mamba 10 arrived tightly and protectively packed with each part separated and supported. The Mamba 10 is sold only in a Plug-N-Play (PNP) configuration, so the parts bag is small and the build steps are few.




With few parts and an easy-to-follow manual, the Mamba 10 can be unboxed and built within an hour.


The manual suggests a 1-hour build time, and this was my experience. The wire landing gear pops into its receiving slot in the bottom of the fuselage and is secured by screwing in a rectangular plastic support. With the landing gear in place, I installed the tail wheel and the tail section.

After sliding the stabilizer tube through the fuselage, I slid both stabilizer/elevator halves over the tube and into their corresponding plastic receivers. It might be helpful to slightly compress the edges of the foam on the stabilizer halves before trying to fully seat them. After doing so and adding a small amount of silicone lubricant to the foam and the elevator joiners, I was able to slide both stabilizer/elevator halves together for a tight and secure fit.

Because rigidity is a plus on an aerobatic model, I appreciate an airframe that takes some elbow grease to assemble. It’s important not to force these installation steps, however, because it’s easy to bend or break the foam. A little lubricant or creative compressing of edges will work wonders.

Instead of proceeding to the wing attachment, the manual diverts your attention to the Aura 8 AFCS setup. This is important because if you want to take advantage of the stabilization system’s Crow speed-brake function, you’ll need to add servo extensions.




As the only biplane in its class with four aileron servos, the Aura 8-equipped Mamba 10 can utilize the remarkable Crow speed-brake function.


Access to the airplane’s fuselage is enhanced if the lower wing isn’t attached. This is also a good time to decide which receiver configuration to use. Although the Mamba 10 can be flown with a wide range of receivers, I opted to utilize a simple satellite receiver. With eight channel ports (and advanced programming and mixing capabilities), the Aura 8 can manage all of your servo connections, allowing a satellite receiver’s connector (a small white plug with three wires) and a six-channel radio to control features including Crow that otherwise would require advanced programming with an eight-channel radio system.

After you’ve installed your chosen receiver, you’re left with an important setup decision: Use the stock stabilization settings or dive into the advanced features of the Aura 8? With a computer and the supplied USB cable, the Aura 8 allows users to customize a range of parameters. Practically speaking, there are two upgrades from which pilots can choose. First is the flight mode setup, which determines which rates, exponential, and stabilization gain settings are used.

Users can choose the Stock setup, which has three flight mode settings:

• Flight Mode 1: Gyro off—sport/precision rates, low exponential.
• Flight Mode 2: Sport mode—sport/precision rates, low exponential, low gains.
• Flight Mode 3: 3-D mode—high rates, moderate exponential, high gains.

The other choice is the Expert setup which also has three flight mode settings:

• Flight Mode 1: 3-D high airspeed mode—rates are high (but for ailerons at 70%), high exponential, medium gains. (“For half to full throttle … ideal for tumbling or high-energy aerobatics.”)
• Flight Mode 2: Sport mode—sport/precision rates, low exponential, low gains.
• Flight Mode 3: 3-D slow airspeed mode—rates are maximum, moderate exponential, highest gains. (“Ideal for harriers, torque rolls, hovering, etc., or any other slow-speed maneuvering. As the gains are at their highest, control surface oscillation may occur at high speeds which may lead to a potential crash.”)

The second upgrade that can be programmed using the Aura 8 is the use of what Flex Innovations refers to as, “the world-famous QQ biplane Crow.” Crow is a flight function often used on sailplanes, which, on the Mamba 10, involves both lower ailerons deflecting down, both upper ailerons deflecting up, and some elevator deflection. This results in tremendous drag, dramatically reducing airspeed.




Vortex generators at the wings’ leading edges reenergize the airflow, improving slow-speed control and reducing tip stalls.


As one of the RC world’s top biplane designers, Quique utilizes this Crow feature to both allow pilots to make dramatic short field landings and, perhaps more importantly, to perform slow and controlled downlines. Completing the Crow setup requires some programming steps as well as some configuration changes to the Aura 8’s physical servo plug locations.

You will need to remove the Y-adapter for the upper wing servos, install the extensions, and plug each of the four aileron servos into its own channel. This process took roughly 10 minutes.

Because of the Aura 8’s advanced preprogramming, not only can your Crow feature be set to any available radio switch, it is also proportional to the throttle. When Crow is activated, it will increase as throttle is lowered and decrease as throttle is raised. Fully proportional-to-throttle Crow! It works brilliantly in flight.

With the receiver bound and the Aura 8 programmed, I moved on to attaching the wings. Biplane cabanes (top wing-to-fuselage bracing) come in all forms and are often the most involved part of the build process. The Mamba 10 utilizes four small carbon-fiber tubes that are set into rigid plastic cups on the underside of the upper wing and the top of the fuselage.




Removing the lower wing and aft hatch provides access to the tail servos and the Aura 8 AFCS.


This approach is low-tech, lightweight, and incredibly strong. The manual walks builders through the process of securing the tubes to the fuselage with 15-minute epoxy and, after the epoxy has cured, attaching the tubes to the upper wing with small screws. Foam and plastic struts are set into corresponding bases and lock top and bottom wings together toward the wingtips.

Having built and flown many biplanes in this class, I can say that the Mamba 10’s wings are as locked together as any I’ve seen. With a wingspan of slightly less than 41 inches, the Mamba 10 should fit in the backseat of most vehicles, but two minutes with a screwdriver can have the wings removed.

After attaching the wings, I installed the included hand-tooled Somenzini-Ribbe (SR) 11.5 x 4.5-inch propeller and spinner. With the build process complete, I bench-tested the power system, and then took the Mamba 10 to a local flying field.


Flying

After range testing, bind-free servo deflection checks, and confirming the proper center of gravity (CG) and propeller tightness, I selected the Expert Flight Mode 2 (sport/precision) and taxied the Mamba 10 to the runway. The tail wheel spring absorbed any imperfections, so ground handling was stable and responsive.

Heading into a slight headwind, I brought power up to full and watched the Mamba 10 launch itself skyward. Leveling off and reducing throttle to half, I applied a few clicks of trim and began my standard in-flight testing.

Most stabilization systems prefer that after trimming you reset trims to neutral and mechanically adjust your control surfaces. This avoids a trim-shift issue when switching flight modes. The Aura 8 has a quick-trim feature that allows users to handle this process electronically, negating the need to disconnect and adjust multiple clevises.

After trimming the airplane to fly straight and level upright, I rolled it inverted to get a sense of its CG. With the recommended 2,200 mAh 3S battery pack set 3/4 inch from the front of the battery compartment, the Mamba 10 required only a breath of pressure on the elevator stick to maintain level inverted flight.

This is the sweet spot for 3-D planes—slightly nose-heavy will result in a good balance of 3-D, precision, and balloon-free landings. With CG testing completed, and given the Mamba 10’s excellent inverted mannerisms, I kept it wheels-up and performed some inverted circles and Figure Eights.

If, like me, you’re a big fan of inverted flight, don’t fly the Mamba 10 upside down. It can be addicting. Because this was a test flight, I rolled it back to upright and explored some sport maneuvers such as Hammerheads, loops, and rolls. If you enjoy the Hammerhead maneuver (or stall turn), the Mamba 10 might be the perfect airplane. The rudder authority is incredible.

With this much yaw control, transitioning into knife-edge flight was a no-brainer. As someone who has owned and flown many biplanes, I’m intimately familiar with the coupling issues biplanes are known for. Approaching from the right and rolling the Mamba 10 on its side, I applied top rudder and waited for the expected pitch and roll coupling. The airplane locked into a knife-edge without a hint of coupling, and only the slightest amount of rudder input was necessary to maintain altitude.

Given these factors, I had no choice but to finish out the battery transitioning through knife-edge passes, circles, and Figure Eights. (The Aura 8 has been conveniently preprogrammed for the necessary rudder-to-aileron/elevator mixing.) With this level of precision and absence of coupling, I was able to perform clean point rolls and slow rolls without constantly fighting to keep the Mamba 10 on its centerline.

With a fresh battery (a slightly larger 2,700 mAh 3S battery pack), I explored the Mamba 10’s 3-D mannerisms. Starting with the high-speed 3-D mode, I threw the airplane into Pop-Tops, blenders, aggressive snaps, and anything else that came to mind. Although the Mamba 10 is capable of a wide range of 3-D maneuvers, with its lower wing loading and the fact that it’s a biplane, I would describe its tumbling abilities as strong, but not extreme.

However, that same low wing loading, when combined with the Aura 8’s advanced stabilization makes the Mamba 10 cry out to be flown low and slow. With confidence-inspiring stability, the Mamba 10 is a dream to harrier (upright or inverted) and hover.

Hovering a short-coupled (the distance between the wing and the tail section) biplane is usually a task best left to advanced pilots. The Mamba 10, however, with its massive rudder and elevator, plus the Aura 8, could be used as a hovering trainer.




The combination of the Aura 8, low wing loading, massive control surfaces, and ample power results in hovering mannerisms rarely seen in biplanes of this size.


Not only does the airplane lock into hovers, but with four huge ailerons—each controlled by its own dedicated servo countering the effects of motor torque (torque roll)—is as simple as holding in a bit of right aileron. Of course, should you be a pilot who has learned to embrace the beauty of the torque roll, hovering while holding in full left aileron will result in your Mamba 10 transforming into a spinning top.

Speaking of ailerons, the Mamba 10’s roll rate is something to see. Rolls are not only drill fast, but surprisingly axial. One of my complaints about 3-D-capable biplanes of this size is that during slow, high-alpha (the angle of attack) rolling harriers, the roll rate is often so slow that the maneuver falls apart.

With the Mamba 10’s extreme roll authority, I found myself performing those same rolling harriers at remarkably slow airspeeds, all the while keeping a high roll rate. For an advanced pilot who’s comfortable with all of the various rolling maneuvers, the Mamba 10 is just what the doctor ordered.

During bench testing, the Mamba 10’s 120-gram Potenza 1,400 Kv motor drew roughly 45 amps for a total of 500 watts. With a claimed flying weight of 54 ounces, this results in approximately 150 watts per pound. Although economical for 3-D (particularly when compared with the 200 to 250 watts per pound found in higher-end dedicated 3-D machines), it is in the ballpark for foam 3-D/aerobatic airplanes in this class.

Watts per pound is one thing, but what we care about is thrust. The combination of the Mamba 10’s 1,400 Kv motor and its lower-pitched propeller results in a fast spool-up rate and respectable vertical performance. Although not rocketlike, the Mamba 10 has sufficient thrust to get off the deck in a hurry.

I had never utilized the Crow feature on anything other than a sailplane, so I was eager to try out this advanced programming feature on a park-flyer-size biplane. With Crow, it felt like at least a 40% reduction in airspeed. Crow-enabled downlines felt nothing like the usual knee-shaking experience of watching your beloved airplane plummet to earth.

I found myself incorporating downlines into my flight patterns with increasing regularity. Likewise, flipping on Crow before landing has an effect that reminds me of a fighter plane catching the wire during a carrier landing. You’re moving, and then you’re not.

During subsequent flights with the Mamba 10, I found myself conflicted between wanting to spend the entire flight enjoying the airplane’s stable low-and-slow characteristics or its precise higher-speed mannerisms. With the Mamba 10’s ability to transition cleanly between stable post-stall, tumbling, and higher-speed precision maneuvers, pilots can begin choreographing routines, as opposed to stumbling around without a plan.

That’s not to say the Mamba 10 doesn’t make a good throw-it-into-the-backseat-for-a-quick-flight-at-the-park airplane, just that its stability and precision can inspire confidence for pilots looking to take their progress a little more seriously.

Along with all of the positive things I have to say about the Mamba 10, there is one unavoidable negative: flight times. Although the Mamba 10 is touted as being able to use the widely owned 2,200 mAh 3S LiPo battery, 3.5 minutes of aggressive flying feels like only a small serving of your favorite dish.

There’s an easy fix, however. Either upgrade to a Flex Innovations 4S power system and subsequent 2,200 mAh 4S battery pack or simply use a larger 3S battery pack (up to 3,100 mAh) and pilots can increase their flight times to 5 minutes. This would be nearly the industry standard for an airplane in this class.

During initial testing, using a 9-ounce 2,700 mAh 3S battery pack provided 5 minutes of mixed-throttle flight while sacrificing little, if any, of the Mamba 10’s floaty, post-stall performance.


Conclusion

Building on the success of the 70cc Giant Scale Mamba, Quique and his team have created a park-flyer-size biplane that celebrates the marriage of modern technology and expert engineering. Take a lightweight, stiff airframe, design it for light wing loading, throw in some fine tuning with vortex generators, run the whole system through an advanced flight control system such as the Aura 8, and what you end up with is a truly multidimensional airplane.

Is it 3-D-capable? You bet. Stable and precise? No doubt about it. A comfortable sport flier? Of course. Durable, repairable, can go from unboxing to flyable in an hour and able to fly with a commonly owned 2,200 mAh 3S LiPo battery pack? Yes, indeed.

With the Mamba 10 Super PNP biplane, Flex Innovations has released an absolute winner.

—Josh Bernstein
joshbernstein2@yahoo.com


Manufacturer/Distributor:

Flex Innovations/Premier Aircraft
(866) 310-3539
www.flexinnovations.com


Sources:

Spektrum
(800) 338-4639
www.spektrumrc.com






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