Sovereign Tech Tandem-5 Chinook to ACH-47A Conversion

New project! This will be the build of a Sovereign Technologies Tandem-5 (500 size Chinook. Couldn’t believe it made the journey from Taiwan in just over a week..

Initial impressions: Box was well-packed and everything was undamaged. All parts are bagged as individual assemblies. The gears and drive system appear to be excellent quality. The motor is included, as is a tandem mixer module to allow use of a conventional FBL. They also emailed me a VBar profile, however I don’t plan on using it.

However, it isn’t all positives. The fuselage is vacuformed plastic. While the toyish look wasn’t a surprise, I really expected a fiberglass fuselage for the price. And while the heads appear to be decent quality, they have little to no flapping travel or damping. Instead, they appear to rely on tip weighted, flexible plastic blades. More to come after initial assembly is completed.

Got the mechanics assembled. Overall quality is pretty good with minimal lash between the 2 rotors. Not much clearance on the back side of the servo arms, so any excess thread length on the ball links needs to be trimmed, especially for the servo closest to the motor.

Besides the vacuformed fuselage, my only real gripe is the rotor heads. While the spindles are independently damped, they don’t allow much movement in flapping at all. They have stiff dampers and very little movement before running into mechanical interference.

I attempted to swap out Goblin 570 3 blade heads to fix this, but that proved to be impractical without excessive custom parts. For now, I’m planning on modifying the stock heads to allow more flapping movement.

Ok, lots of small mods completed since I last posted. The biggest one was modifying the rotor head to get more flapping travel. This involved removing ~2mm of material from the outer edge of the hub. Even with softer dampers, the stock head could barely move without hitting a hard stop. This mod expands the travel significantly. I also tossed the stock dampers and used some 70 shore O rings instead.

The mod did get me concerned about the Delta-3 offset in this head design though. The ball link for pitch control is very far inboard of the flapping axis. This results in an unstable system for leading edge control (e.i, a flap up results in increased blade pitch). I consulted with Jim Davy on what he learned from his TwinRexx and decided to switch both my heads to trailing edge control. This should result in a stable system.

For the flight controls, the stock heli includes a special mixer board to allow the 6 servo setup to interface with a conventional FBL. Setup was done with a PC app over Bluetooth and was pretty straightforward. I used an ikon2 with a srxl2 so I could get telemetry to my Spektrum radio. Only one photo today, but a lot of progress!

Maiden flight complete on the mechanics. Needs some significant gain tuning, but it flew ok. No shortage of power, and it had no shortage of yaw authority.

In addition to the head changes mentioned previously, I also switched out the stock blades. The stock blades have large masses molded into the tips that look ridiculous. Instead, I used these plastic blades which I’ve used on many of my 500 projects: