Feeling the Need for Speed
Written by Chris Mulcahy RC Helicopters Column As seen in the July 2018 issue of Model Aviation.
The R5 looks fast in a hover. Its fuselage is bright and easy to see.
One aspect of the hobby that I have never tried is building and flying a dedicated speed helicopter. There aren’t many purpose-built speed machines to choose from, but we certainly have a few more than we used to. During the winter, I had a chance to start on my own speed machine, the Gaui R5. At first glance, the R5 has a stunning appearance. It is extremely slim, with a full-body fuselage and no visible signs of any landing gear. It just looks fast. When you lift the hood, you start to get a glimpse of the passion and creativity that went into cramming a 700-size powerplant into a 550-size helicopter. The kit came with Halo 550 mm main and 80 mm tail blades. Although I used the tail blades, I decided to use Rail Blades 626 main blades at the recommendation of other R5 owners. The kit is made of aluminum and carbon fiber. The fuselage is prepainted fiberglass with carbon-fiber reinforcements and a bright, glossy finish. It came with a printed instruction manual and the screws, nuts, and bolts were grouped together in labeled bags. This made it easy to find each bolt needed during the build.
The beginning of the build. Everything was packaged well!
The build went smoothly, and I was impressed with the quality of the parts. Tolerances were perfect, finishes were immaculate, and every part went together smoothly and accurately. It was a joy to build. There were a few subassemblies that I took apart to apply threadlocker. Sometimes parts are put together at the factory during packaging to ensure that everything is included. The R5 features a belt and pulley system to drive the rotorhead. The motor is connected to a pulley, which in turn meshes into the main gear (see my June 2018 column about gear ratios). To carry all of that power, Gaui made the main gear taller than most. The tail is also belt driven, with a cool sprung tensioner on the side. The tail servo drives a bellcrank, which then drives the tail rotor pushrod. It is a smooth operation. The tail rotor hub is a beautiful piece of aluminum, made from a single piece with merely a small cap to complete the assembly. There is ample room up front for any type of ESC. I chose to install a Castle Creations Edge HV 160. I installed a Scorpion HKII-4235-630KV LE motor, Futaba CGY750 gyro, Futaba BLS272/274 cyclic/tail servos, and a Futaba R7008SB receiver guided by my Futaba 16SZ transmitter. I made a 12S stick pack from two Pulse 6S 3,700 mAh LiPo batteries and used a 2S 2,250 mAh receiver pack. The R5 has a removeable battery tray that slides in easily, with a good, solid retaining latch. I had to cut the motor shaft because it was too long and intruded into the battery area. But wait. What about that landing gear? The R5 uses a unique rotating bar at the base of its fuselage. When deployed, it sits perpendicular to the longitudinal axis of the helicopter (it sticks out sideways). When in flight, it rotates 90° and becomes flush with the fuselage, practically disappearing. Gaui includes a small servo with a voltage regulator to drive the landing gear.
The video shows the landing skid rotation in action.
The landing skid is deployed and the R5 is ready to land.
One thing that I learned during the build was to plan out my electronics installation before putting it into the rear half of the fuselage. I spent some time exploring mounting options for my receiver and gyro before permanently attaching them and tidying up all of the wiring. After this was complete, I slid the mechanics into the fuselage and finished attaching the tail hub. Using Castle Creations Castle Link programming software, I programmed the ESC so that I had three head speeds to experiment with: 2,280 rpm, 2,510 rpm, and 3,018 rpm. The gyro was set up as stock, although I later decreased the tail gyro gain quite a bit.
2 comments
r5
Awesome article
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