Features intro
The TREX 250 features the same great features that we see in the entire Align product line. A full metal head, pre-painted fiberglass canopy, and carbon fiber pieces lace the tiny 250 throughout. The combo kit that we are reviewing also includes three digital cyclic servos, brushless ESC, motor, and a heading lock gyro with a digital tail servo.

MAIN FRAME
COMPONENT LAYOUT: The three cyclic servos are arranged around the head with two up front and one behind the main shaft. The brushless motor sits below and in front of the main gear. A battery tray is located in the nose of the mechanics and in line with the tail boom. The receiver is located on the bottom frame support. Above the receiver, a mounting tray for the gyro is sandwiched between the frames and extends out and under the boom.
DESIGN: The frame is designed similarly to the TREX 450. The stacked carbon fiber frames are spaced by metal spacers and plastic bearing blocks.
SWASH CONTROL: The 120° CCPM swashplate is controlled using three direct linkages from the included digital micro servos. No bellcranks or additional linkage rods are needed. This design provides a slop-free connection for the ultimate in control.
CANOPY: The included canopy is made from fiberglass and is pre-painted. The canopy mounts to the frame by means of two canopy standoffs that attach through the frame into the anti-rotation bracket. The bottom of the canopy is held in place by slipping under the bottom frame stiffener.
LANDING GEAR: The landing gear on the TREX 250 looks like miniaturized TREX 500 gear. The landing gear attaches to the plastic bottom frame stiffener using four self-tapping screws. The skid tubes slide into the plastic struts and are secured by a drop of thin CA.

DRIVE TRAIN
MOTOR MOUNT: The brushless motor is secured to an aluminum mount that is attached to the lower frames and also acts as a spacer. The mount has two elongated holes to provide enough room to adjust the gear mesh for different sized pinions.
PINION: The small brass pinion is press fit onto the motor shaft. A small drop of green thread lock is used to ensure that the pinion does not slip.
MAIN GEAR: The small white plastic main gear attaches to the main shaft using a single screw that threads into the bottom of the main shaft. This holds the gear in place. The main gear also drives the secondary gear for the tail belt.
AUTOROTATION DRIVE: The one-way bearing is pressed into the main gear and allows the main rotor to spin freely. The tail is not driven during an autorotation.
TAIL DRIVE: The tail is driven by a secondary gear mated to a pulley. A belt runs through the boom and over a second plastic pulley that is attached to the tail shaft.

ROTOR HEAD
WASHOUT ARMS: The CNC aluminum washout arms are dual ball bearing supported and attach to the washout base with a machine screw. The washout arms do not have any output options. The plastic link is attached with a single machine screw.
BELL/HILLER ARMS: The aluminum Bell/Hiller arms are also ball bearing supported and are attached to the seesaw with a single machine screw. No mixing options are available.
MAIN BLADE GRIPS: The CNC aluminum main blade grips on the TREX 250 use two ball bearings each to provide smooth operation. The grips have only one attachment point on the pitch arms. The rotor blades are attached to the grips with a single machine screw that threads into the opposite side of the grip.
HEAD BLOCK: The head block is made from a solid piece of aluminum. The damping is performed by a single rubber damper. The head block is held to the main shaft using a single Jesus bolt that threads into the backside of the head block.
PHASING: The phasing is accomplished by two steel pins that are pressed into the headblock. The phasing is not adjustable and is slop free.
SWASHPLATE: The 120° CCPM swashplate is made entirely of aluminum. The swash is bearing supported and no slop is noticed between the two swashplate halves.

TAIL
BOOM: The aluminum boom is 8.5mm in diameter and 240mm in length. The boom is black anodized and an Align 250 helicopter logo is etched on both sides.
TAIL CASE: The tail case is similar to the TREX 500 but scaled down. An aluminum clamp slides over the boom and is secured using the screws that mount the vertical tail fin. Towards the rear of the case, two aluminum plates attach to the clamp and provide a bearing support for the tail shaft.
TAIL BLADE GRIPS: Each of the aluminum tail blade grips are supported by a single ball bearing. The grips are mounted to the tail rotor hub using a single machine screw that threads into the hub. Like the main rotor blades, the tail rotor blades are held to the grips with a single machine screw that threads into the backside of the grip.
TAIL PITCH ACTUATOR SYSTEM: A single arm attaches to the tail case with a single machine screw and a pin that locks it in place. This allows for a mounting point for the control arm bellcrank. The plastic control arm is bushing supported and attaches to the single-point tail pitch slider. The plastic slider is supported by two ball bearings and is attached to the metal T-type arm with an aluminum slider shaft. Two aluminum links attach to the fork and the blade grips with small machine screws.

Testing
We tested the TREX 250 Super Combo with everything that was included with the kit. In addition to the kit, we used carbon fiber blades from Align, and an 850mah 11.1V 20C Align battery pack. We set the pitch range to +10.5 and -10.5 degrees and set the cyclic servos to 60%. Initially, I tested the heli per the manual and set the cyclic servos to 45%. After the first flight, I felt this was too slow to get the true feel for the helicopter. I decided to see how far I could increase the throw, making sure that the swashplate and linkages didn't bind.

Hovering • I was somewhat skeptical about how this small helicopter would hover. To my surprise, hovering the TREX 250 was much like hovering its bigger brother, the TREX450se V2. Although not as stable, the hover was very manageable (how else do you think we get those crazy close-up pictures?) After raising the headspeed a bit, the 250 seemed to lock into a hover much better than at the lower head speed. The cyclic felt a bit touchier, but overall the 250 hovers much better than you'd think.
Rating: 4

Forward Flight • The Trex 250 is a small, agile machine that does not like to just stay in a hover. This thing was made to move. The forward flight speed was moderate and felt touchy. With this size of helicopter, it's a bit difficult to keep the helicopter from moving around, and small inputs seem to change the flight path pretty drastically. This was a bit tricky to get used to, but after a dozen flights or so I had the TREX 250 flying gracefully through the air without any noticeable pitching effects.
Rating: 3.5

Cyclic Pitch Response • After increasing the cyclic rate from the transmitter, the TREX 250 came alive. The cyclic was fast and responsive, allowing stationary flips and rolls. Transitioning from forward flight into a vertical climbing roll was easy and fun; I never felt like the cyclic was too slow to complete a full rotation. After adding some expo and low rates, the TREX 250 was very easy to fly around in a scale like manner. The Align TREX 250 was designed to perform 3D out of the box with the included power and control system, and that is exactly what it does. After flying several other helicopters in this class range, the cyclic response is beyond my expectations.
Rating: 5

Collective Pitch Response • With the carbon fiber blades and a screaming head speed (which reaches close to 4500 rpm), the 250 had no problems performing full collective climb outs. I felt that the collective was a bit touchy around center stick, but once you have a few flights under your belt this feeling is almost unnoticeable. Quick stops and changes in direction felt a little mushy, but nothing that would scare you if you had to change directions in a hurry. The collective, with the use of the carbon fiber blades, easily handled Tic-tocks and collective pops. Overall, the TREX 250 handled very well in 3D flight and felt very precise.
Rating: 4

Tail Rotor Response• We tested the TREX 250 using the stock gyro and tail servo. This combo seems to work very well with this size of helicopter. It may not lock in or feel like a high-end gyro, but it gets the job done. I had a bit of wag that was a little difficult to get rid of, but once I took some time and set the gyro up properly the tail held just fine. The tail had plenty of authority to correct for full collective punch-outs and quick direction changes. The tail would move around a small amount compared to other helicopters with included heading lock gyros. I set the dual rates to 100% and the tail continued to piro consistently, even when applying a moderate amount of collective.
Rating: 5

Autorotation Capabilities• Even though the TREX 250 uses a one-way bearing and has a non-driven tail rotor, the 250 would be very hard to successfully perform a high altitude auto. The weight and size of the rotor disc does not allow the 250 to retain much energy. Keeping the throttle hold activated for last minute bail outs - or bleeding off the head speed when your about a foot off the ground - is about the only thing that will be useful for this size of helicopter.
Rating: 3

Post Flight Inspection • While going over the 250 and making sure that everything is in good working order, I noticed that the tail belt was releasing some fibers from the sides. This was normal wear and tear as the belt was breaking in. The main rotor and tail rotor both remained slop free. The landing gear seemed to take some heavy abuse, including a 3-foot auto.
Rating: 5

Conclusion
The Align TREX 250 has made its way into the world and it is here to stay. This miniaturized helicopter flies very well and parts are easily obtained from any local hobby shop or online dealer. This helicopter is perfect for those who don't have space to fly or can only fly at small fields or parks. The 250 can be setup for both the 3D pilot in mind or a beginner that is not use to the sensitive controls. Overall, this rugged little helicopter will surely be a big hit for 2009.

When You Open the Box
Opening the box to the TREX 250 is quite a treat. The small yellow box contains everything that is needed to get the helicopter in the air except for the transmitter. The 250 comes partially assembled, which includes the tail case, head, and frames. The parts are all locked into a plastic tray that is perfectly molded for the servos, frame and canopy, and bags of hardware. The kit also includes both a small Phillips head screwdriver, and a small hex driver. Align also included two bottles of thread locking compound to finish off the build. The ESC, gyro, and servo horns are in a plastic bag that is taped to the inside of the cover. The manual and other printed material is found underneath the plastic tray.

Manual and Build
Building this small helicopter takes a little patience. The parts are small and very easy to lose in the carpet abyss. The manual does a great job showing you how the parts are installed. It even shows how to build the kit even if it weren't an ARF. Be careful when you tighten down the screws with the supplied hex driver. Too much force can cause the head of the screw to strip out. When tightening the tail belt, slide the servo mount all the way to the frames. This will help prevent the belt from loosening up during flight.