Progress was made on the DarkAero 1 prototype in May, with major efforts focused on the engine installation, electrical system wiring, and the nose gear retract mechanism. Our intern Ryan rejoined with us at the end of May and put in many hours on the seat fabrication and testing.

Engine Installation 
The biggest challenge with installing the engine has been keeping the engine and its accessories tightly packaged underneath the cowling while balancing serviceability, function, and system safety. All the pieces fit together like a three-dimensional puzzle with fluid hoses and electrical wires connecting the components. The specifics on each system are detailed below.

Ignition System - The ignition system was finished after we installed the proper end connectors on the ignition lead cables and then established optimal routing of the leads from the spark plugs, through the airboxes, and to the ignition coils. Labeling each lead on both ends helped to keep everything organized during installation.

Fuel System - The fuel pumps were installed behind the firewall on the copilot fuselage side wall. We are using a dual fuel pump setup for redundancy. Firesleeve was added to the stock fuel lines that come with the UL Power engine and the fuel return line was replaced with a custom line with integrated firesleeve.

Oil Cooling - Progress on the oil cooling system continued with the installation of the hardware we purchased in April. Our initial set of oil hoses were swapped out for lighter hoses that utilize an integrated fire sleeve, shaving a pound of weight compared to the original set. The initial fit up of the oil cooler was accomplished with just through holes in the firewall sandwich panel but hardpoints were added in to allow the oil cooler to be bolted in place. We also updated the oil thermostat to comply with the most recent UL Power service bulletin which dictates upgrading the springs in the thermostat.

Cylinder Cooling - Completing the air cooling system for the engine was relatively easy since we were able to use the stock airboxes supplied with the UL Power engine as a starting point. The air boxes were trimmed to their final dimensions and they were closed out on top with covers made from aluminum sheet metal. We made the tops of the airboxes removable for service by fastening them in place with screws and nutplates. We received the first 3D printed intake diffuser and installed it as well. The intake diffusers were initially planned as a molded component but we decided to make them 3D printed to give ourselves more flexibility with the design and to make iterating on them faster.  

Electrical - The batteries and alternator regulator were installed on the pilot side of the firewall using Click Bond studs and brackets. The batteries will be actively cooled to protect them from high engine temperatures and keep them within acceptable operating temperature limits. This will be accomplished by enclosing the batteries in an airbox with forced air cooling supplied by a bleed line from the nearby cylinder cooling plenum.

Oil Separator - The oil separator removes oil from blow-by air that escapes from the crankcase breather and returns the oil back to the oil sump. This helps reduce oil consumption and keeps the belly of the airplane clean. Hardpoints were added to the firewall to allow the oil separator to be bolted in place. Hoses were sized and installed to connect the oil separator to the crankcase breather and the separator exhaust was interfaced with the engine exhaust through a check valve.  

Instrument Panel 
In May, we worked through the majority of the instrument panel wiring and connected it to our previously completed center tunnel avionics box for bench testing. This allowed us to confirm the function of our Garmin engine interface system, both ECUs, and our ADS-B transponder. Next month we will be building and wiring our last avionics section, which sits aft of the cockpit. This section includes our comm radio, ADAHRS unit, and backup ADAHRS unit. This will be the last modular unit in our avionics architecture to complete. Following this, we will be installing all three sections in the aircraft and interconnecting them. 

Canopy work 
In May we worked through improving the manufacturing process of our canopy to reduce “webbing” distortions in our formed plastic and improve demolding of the canopy. By studying the footage from each of our formed canopies, we narrowed in on technique adjustments that we will be implementing next month to further improve the webbing distortions we have been seeing in our canopies.

In the interest of expediting progress on the DarkAero 1 prototype, we are looking at contracting out the manufacture of its canopy. We are in talks with a couple contractors already, but are open to any interested parties who would like to work with us to get the prototype canopy developed faster and better in quality than we can currently achieve. 

Knowledge Base
We have released the first version of the DarkAero knowledge base! As we mentioned last month, the intent of the knowledge base is to better assist builders of the DarkAero 1, or those that want to design and manufacture around the same processes by consolidating the information needed on our website. We will continue to add information to the site as time permits. 

You can view the knowledge base here: darkaero.com/knowledge

Nose Gear Design 
In reviewing the retract mechanism for the nose gear, we realized we had a solution, but not an optimal solution we were satisfied with. We wanted something that could check all the boxes for safety, builder simplicity, cost, weight, serviceability, and redundancy. Although painful to backtrack, we determined that it was the right, long-term decision to redesign it. Our previous nose gear configuration incorporated a stepper motor and planetary gear system that was fixed to the back portion of the engine mount. It required heavy gears, coupled shafts, and several components that would prove challenging to machine. It was a compact and unique solution but would likely prove difficult for builders and require additional manufacturing on our end that didn’t add up. 

We have designed a new system that is an all-around better solution. It is simpler, lighter, and easier for builders to install. It moves away from the stepper motor and instead utilizes a robust, IP66 rated linear actuator. The new design improves over the existing design in that it includes an integrated method for lock-up and lock-down and a way to easily disengage to allow the gear to drop in case of a complete system failure. We are very excited about this new design given its safety, weight savings, and simplicity. We only have a few small details to finalize, and we have already ordered the linear actuator and started to machine out the new components necessary for the design. 

June and Beyond
Looking ahead to our goals in June, we are planning to finalize the engine installation, complete the seats, install the instrument panel, assemble and actuate the nose gear, and move on to building the control system.