The T-Rex 550E DFC is Align’s latest edition of its very successful 550 series of electric helicopters. When I learned about the availability of these kits, I knew I had to add one to my fleet, as the previous T-Rex 550 was already one of my favorite. I had high expectations on what Align did to improve upon an already excellent design, and the new features certainly did not disappoint:

• DFC flybarless head with matching DFC swashplate. DFC (Direct Flight Control) system is a design which streamlines the rotor head assembly by eliminating the washout mixer, allowing blade grips to connect directly to swashplate. This allows for a lower head that is not only aerodynamically efficient, but also brings the head closer to helicopter’s lateral CG line. The DFC system results in noticeably faster forward flight, as well as quicker control response, yet is supposed to reduce energy consumption at the same time.
• The frame is constructed with 2mm thick 3K carbon plates, along with CNC metal reinforcement plate and mounting blocks. Together these pieces form an extremely rigid, yet light weight frame system.
• The new 550E DFC kits now come standard with T-Rex 600 tailboom and torque tube drive train. This allows the use of 600mm blades on this helicopter without interfering with tail blades. The included stock carbon blade is 520mm.
• Tail control is through a 5mm carbon tail pushrod with metal tail control arm, and a precision CNC dual pivot tail pitch slider assembly. This assembly alone contains 6 ball bearings to ensure excellent precision.
• The T-Rex 550E DFC comes with module 1, CNC machined 112 tooth helical main gear, and a 11 tooth matching steel helical pinion gear.
• Rudder servo is mounted in between frame for protection, and to bring lateral CG closer to center line.
• Brand new Align DS615 swashplate digital metal gear servos, as well as Align DS655 rudder digital metal gear servos.
• Brand new 600MX brushless motor with 1220KV, with heat sink can and built in cooling fan
• New Castle Creations Talon 90 brushless ESC, 6S 90amps max, BEC 9A continuous with 20A burst, BEC adjustable output 6V-8V
• New, larger, airbrushed fiberglass aerodynamic canopy
• The kit arrived in the typical Align boxes within box packaging, neatly labeled with its contents. All the individual pieces are logically grouped together per the building steps to eliminate any confusion.

Construction sequence begins with rotor head, with most pieces already dry-assembled for quick re-assembly (remember to use Loctite/threadlocker). The main blade grips are the typical dual radial bearings type, with thrust bearing for lateral support on the 6mm spindle shaft. Head dampener is of the hard type, as required by the lower DFC rotor head design. The swashplate is a DFC specific design where the balls in upper piece are oriented perpendicular to the center. Most of the pieces here are taken directly from T-Rex 600E DFC, and are labeled as such. Note the direction of main shaft during assembly, with tapered end going down into the main gear.


The frame assembly is done by attaching 6 CNC metal blocks holding the 2mm thick carbon side plates to the bottom plate. Together with CNC aluminum bearing blocks and motor mount, the finished frame is very rigid, capable of withstanding some extreme forces. Care should be taken when tightening up the frame mounting bolts; place the assembly on glass surface per instruction to ensure plumpness of the finished assembly.


The DS615 and DS655 servos in the super combo kit are updated version of the proven DS610 and DS 650. The DS615 cyclic servos are rated at 12.8 kg/cm torque, and 0.07 sec/60° when powered with 6 volts source. The DS655 rudder servos are 5.5 kg/cm and 0.05 sec/60°, also at 6 volts. Both models are digital driven, with coreless motors transferring power through their metal gear transmission. On the test bench, both types of servos seem quieter and less chattery than their predecessors.


With the servos mounted into the frame, now we move onto tail assembly. The dual-pivot tail pitch control assembly is extremely smooth; care should be taken when applying Loctite to the screws to ensure the smoothness is maintained. Should there be any type of binding, remove screws from one pivot point at a time to pinpoint the rough spots. Time spent here will be rewarded with a solid rudder control in flight, and should not be skimped.


The 600 size tailboom is a welcome feature to the 550. Longer tailboom not only allows for the option of longer blades, it also provides more leverage for the tail assembly to increase tail control authority and stability. Follow the instruction and carefully glue the bearing to torque tube, lube it up and install in tailboom using the supplied installation tube.


The helical main gear rides on a new and improved one way bearing hub assembly. This is similar design to most other modern T-Rexes and has proven to be extremely reliable. The gear itself is very high quality, with perfectly machined mod 1 tooth and clean finish. No noticeable warp was observed on the gear, a typical benefit of machined gear over molded one.

The power system consist of Align’s new 660MX brushless outrunner motor, with a 6s friendly rotation/voltage value of 1220kv. The motor’s ribbed casing acts as cooling fins, while the top of the motor has integrated fan to provide active cooling. Also included in the super combo kit is the brand new Talon 90 amps ESC from Castle Creations. While lacking the data recording capability of ICE series, it has a beefy BEC that’s capable of 20 amps peak current, strong enough to handle even the most demanding digital servos. An ingenious mounting system provides a base for the ESC to latch on to, allowing for quick release should you want to swap this ESC between models. Software seems similar as the other Castle ESC’s, with similar features such as direct entry government mode, as well as standard throttle modes. Together they form a very potent power system for the T-Rex 550E DFC.


If there is one thing I had to pick on the original T-Rex 550, I’d have to say the shape of its canopy. Fortunately the new T-Rex 550E DFC comes with a totally redesigned canopy with a brand new color scheme. The canopy is longer and larger than its predecessor, making the 550E DFC look bigger and more streamlined. The airbrushing graphics are typical of Align’s high quality canopies, beautiful lines with vivid colors. Mounting is done with a lower latch that attaches to the front landing bow, and two rudder padded holes for the rear mounting ears.



Setup

With all servos connected to the Align 3GX flybarless system, a single servo wire was used to connect it to the Futaba S-Bus receiver for a very clean install. Setting of the 3GX system consists of a few steps done with the 3GX push button and transmitter stick:

• DIR mode basically bypass the flybarless system, so you can check for proper control direction, cyclic pitch (must be set to 8 degrees), and collective pitch (set to +/- 12 degrees).
• Set the elevator travel limit and gyro direction
• Set the aileron travel limit and gyro direction

Then go through the rudder gyro setup which sets the servo type, frame rate, travel limit, reverse, etc. All steps are clearly explained in the manual, and should be followed carefully to ensure proper setup.
I have a habit of flying electric helis only in idle-up 1 mode. So with the Talon ESC set to fixed end points as default, my idle-up 1 throttle curve is 100-85-80-85-100, with a straight pitch curve of 0-25-50-75-100. Normal throttle and pitch curves are 0-25-50-75-100. No surprises here.
At this time the heli is ready and can be flown. Further tuning of the flybarless system can be done with the Flight Mode settings and gain dial, but I left everything default for the maiden flight.


Flight
Allow the 3GX system to initialize after power up, which is indicated by a rapid up-down-up motion of the swashplate. Proper initialization is represented with green LED on the 3GX. As I flipped the idle up switch, the Talon ESC smoothly spun up the rotor with its excellent soft start function. As it reaches full speed, a gentle push of collective stick brought the helicopter into a stable hover. As expected, no trim adjustments were needed if 3GX was setup properly. The 550E DFC just sat there in a comfortable hover.

A quick circuit around the field exhibited increased forward flight speed, as expected from the low drag DFC head and improved 600MX motor. The 550E DFC tracked perfectly through the corners, with noticeably higher control precision. Similar to other DFC equipped T-Rex helicopters, the collective and cyclic response are noticeably quicker. Stationary flips and rolls are fast and stable, with no noticeable wobbles. Tic-tocks are crisp and precise. The new 2.1 software in 3GX contains improved pirouetting compensation routine, which results in stable pirouetting maneuvers at all orientations.



Conclusion
As a midsized helicopter, the T-Rex 550E DFC provides the stability of larger helicopters, while maintaining portability and economical operation. These benefits make the 550 class helicopters a top choice for the weekend fliers, as well as a practice machine for the serious competition pilots. With the excellent performance and value of the T-Rex 550E DFC, the competitions have just seen the bar being raised.