A good friend of mine designed the on-board electrical systems and is now performing breadboard testing of the components.

Although the total power draw of the vehicle avionics and ignition system is only about 10W, during a long flight this would require an unacceptable battery mass fraction without an on-board power generation system.

The alternator used only weighs ounces, but can produce 120V AC at high engine RPM. This power is then rectified and regulated down to 12V DC. Some of the power is regulated further to ~5V DC to power the autopilot and servo rail. The system has been tested at 6,000 engine RPM and 30+ Watts power output and is performing well so far.

In the event of alternator/regulator failure, the autopilot will switch over to the VTOL lift motor batteries and an alarm will sound. The lift batteries are large and can power the systems for a very long time.

Now the fun part: packaging!

GB engine and propeller testing has started!

One of my 3 engines is shown above during its mostly "stock" first run. Custom parts are being added one at a time so as to isolate potential problems.

The engine has been fitted with a Walbro WYL barrel-type carburetor with a small throat. This carburetor is somewhat sensitive to needle adjustments and requires a larger main jet. Although using a carb will not enable us to reach the lowest BSFC numbers possible, they should be good enough to set records. If initial powered flights and record attempts are successful, it is possible fuel injection will be added in the future.

In the future, I may increase the compression ratio. Option 1 is machining an offset hole for the piston pin. Option 2 is TIG welding on an additional ~1mm of piston height to increase the the compression ratio and efficiency of the engine. The success or failure of that experiment may be contingent on the exact alloy of the piston. It will be fixtured in water such that the side skirts will not be annealed. The final piston crown shape would be turned on my lathe.

Either way, with a piston stroke of only 26mm, it won't take much pin offset or filler rod!

After going on hiatus for a couple years, the project is back!

Many parts have been designed, 3D printed, CNC machined, TIG welded, and turned on my trusty Atlas 618 lathe over the past 2 years of working the occasional evening and weekend.

These include:

• 3D printed engine cooling shroud with integrated cooling flap and servo mounts.
• 3D printed ignition timing ring and machined aluminum alternator adapter.
• 3D printed VTOL motor mounts and VTOL boom mounts.
• CNC machined aluminum VTOL propeller locking mechanisms.
• Welded aluminum exhaust.
• CNC machined aluminum propeller hub and spinner back

The all-carbon 4-meter-span polyhedral wing has been removed in favor of an off-the-shelf 6-meter glider wing. Although flight simulation of the original polyhedral wing indicated that the vehicle would be controllable (somewhat) with the VTOL booms mounted to them, it was decided to use a wing with ailerons instead.

The picture above was taken during indoor hovering tests. The PID loops were tuned and the airframe was checked for adverse dynamic interactions with the autopilot. Wiring was run externally during these tests so as to minimize the need for rework if the boom placement was unacceptable. Control characteristics were deemed acceptable, so the wings and booms will soon be fitted with the final lightweight mil-spec wiring.