HK 450TT Pro
The HK 450TT Pro is a low-cost clone of the Align T-Rex 450 Pro marketed and sold by Hong Kong-based internet discount marketer HobbyKing. It is also available as the EXI 450 Pro TT and as the Skya 450 PRO 3D.
The kit with its torque tube tail rotor drive system features a pre-assembled main rotor head built of machined aluminum parts and is identical to the optional Pro head from Align. The carbon fiber frame with its machined cyclic servo block and main rotor support frame is pre-assembled as well, but should be disassembled prior to construction to ease the installation of the servos. HobbyKing claims that the 450TT Pro is a fresh design and shares no parts with previous T-Rex-based clones.
Like the model it is patterned after, the 450TT Pro is made from such materials as carbon fiber and aluminum alloy. According to customer reviews on HobbyKing's website and on internet discussion boards, the 450TT Pro seems to be of better quality than what is generally found on clones, but problems with hardware and bearings still occur on occasion.
There are a few differences in materials, most notably the 325mm fiberglass main rotor blades, composite tail rotor blades and flybar paddles and the painted plastic canopy. While the 450 Pro comes standard with a composite tail servo mounting frame, the 450TT Pro comes standard with a machined aluminum alloy frame.
A notable variation is the machined one-piece tail slider assembly used on the 450TT Pro. It slides over the tail boom and is secured with a machined aluminum pin retained by the vertical tail fin. The Align utilizes a two-piece design with a retaining pin machined in one of the halves.
A comprehensive hardware package is included with the 450TT Pro, but the M2 washers which should be used to help secure the servos are not included. As with most clones, no assembly manual is provided either, requiring the download of the 450 Pro assembly manual from Align's website. Linkage balls are based on an older Align design, but the studs might not be long enough to fully engage certain servo arms. Use of Align's linkage balls backed by M2 nuts is recommended; the assembly manual makes the same recommendation.
When assembled with name-brand electronics, the 450TT Pro flies much like the 450 Pro. It is in no way intended or designed for a raw beginner, but if properly set up by an experienced user and fitted with training skids, the 450TT Pro would be an inexpensive way to learn the basics of R/C helicopter flight with the aid of an instructor. Use of HobbyKing's electronics will work for all but aggressive 3D flight; any application where aggressive flight is expected should be upgraded with a name-brand tail servo and gyro. HobbyKing's inexpensive HK401 gyro will work well for most applications, but there is a risk of tail blowout if this gyro is used in aggressive manuevers.
A potential weak spot on this and the original is the front tail drive gear assembly with its beveled "umbrella gear." This is the shaft and gear driven directly off of the main drive gears and may be stripped if the tail rotor comes in contact with the ground either during a crash or a landing.
The shaft and gear are listed under Horizon Hobby part number AGNH45040.
- Main rotor diameter: 27.95" (710mm)
- Tail rotor diameter: 6.22" (158mm)
- Length: 25" (635mm)
- Weight (airframe only/flying weight): 15.8 oz./27.5 oz. (450g/780g)
- Main drive gear: 150t
- Autorotation/Tail drive gear: 106t
- Tail drive gear: 25t
- Motor drive gear: 14t
- Carbon fiber and aluminum alloy main frame
- Aluminum alloy main rotor head
- Aluminum alloy torque tube
- Aluminum alloy tail rotor slider
- Carbon fiber and aluminum tail reinforcement rods
- Fiberglass main blades with brass reinforcement mounting grommets
- Composite flybar paddles
- Composite tail rotor blades
- Nylon landing skids
- Painted polycarbonate canopy
- Recommended electronics: 3550Kv helicopter motor, 2200mAh 3S lithium polymer battery, 40A ESC, metal-geared digital micro servos for cyclic/collective/pitch control, analog or digital gyro-compatible servo for tail control, piezoelectric or MEMS gyro
- Skill level: Intermediate/advanced
- Bare airframe price as of November 2011 (USD): $59.99 via the Hong Kong warehouse
- Review at RCGroups.com
- Discussion forum at RCGroups.com
- Comprehensive assembly thread of the EXI 450 Pro TT at RCGroups.com
- Photos and description of the Skya 450 PRO 3D at RCGroups.com
- Product page at Hobbyking.com
- Product page of the Align replacement drive gear set at Horizonhobby.com
- Link to the downloadable .pdf file of the Align 450 Pro assembly manual at Align.com.tw
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