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Our monthly update for April is out now! The remaining ground tests on the DarkAero 1 prototype continued in April, with the team focused on the main landing gear drop tests. Additionally, the recent acquisition of a new CNC mill increased machining capability for current contract manufacturing projects and upcoming kit production. Read the full update here:  https://darkaero.com/updates-files/april-2024 

Our next video will discuss our new CNC mill! Here’s a preview of some stainless steel landing gear parts we recently machined with it. 

Beyond composite parts, we have also manufactured countless machined metal parts for the DarkAero 1 prototype. Our machining journey began nearly 10 years ago when we started out with a common Tormach PCNC 1100. We used this mill to create the majority of machined metal parts in the prototype aircraft which ranged from simple brackets to complicated landing gear components like the nose gear fork. Recently, we parted ways with our 1100 and progressed to a completely new machine that will dramatically increase our CNC machining capability. Our next video will dive into the details of the new machine along with what parts we will be making on it. Stay tuned! 

One of the remaining tasks on the control system involved revising the armrest covers so they extend to the floor of the cabin. Although the new design offered improved aesthetics, the change was implemented primarily to protect the controls against interference from occupants and loose objects in the cabin per FAR 23.685. This became especially important after installing the outboard seatbelt attach brackets as these are positioned particularly close to the flap controls. A pocket was recessed into the new cover so the seatbelt connection had room to rotate and remain separated from the flap actuation mechanism.

The revised cover was CNC cut from a flat pattern of infused sandwich panel stock, and the recessed pocket was folded into its final shape rather than being molded. A machined HDPE jig was used to hold the folded structure in its correct shape and allow bonding in a single operation. Installing the new cover in place has really made the cabin feel more complete and less like a prototype. 

An important part of validating a new aircraft design like the DarkAero 1 is proving that the control system is able to produce the desired response throughout the full flight envelope. 

In our last post (part 1), we discussed measuring the stiffness of the aileron controls. You can read the full post here:  https://www.youtube.com/post/UgkxLCma_8Psat-Oqo3qauTt1hrQaxEU0B90  In this post (part 2), let’s discuss how compliance, or lack of stiffness, can arise in a control system structure commonly assumed to be stiff: carbon fiber torque tubes. 

Carbon fiber torque tubes are used extensively throughout the control system of the DarkAero 1 for their combination of low weight and high stiffness. Off-the-shelf filament wound tubes were selected for the prototype control system. In testing, a fair amount of system compliance was traced to these torque tubes as their torsional stiffness proved to be much less than expected. Despite being made of carbon fiber and sourced from a reputable tube manufacturer, these tubes were not specifically optimized for torsional loading. To achieve maximum torsional stiffness, the fibers in a carbon fiber tube must be oriented at positive and negative 45 degree angles relative to the axis of the tube. Off-the-shelf carbon fiber tubes are generally not built like this. Filament wound tubes often use a wide range of fiber orientations and roll-wrapped tubes commonly use fibers at 0 and 90 degrees to the tube axis.

This led us to manufacture torque-specific carbon fiber tubes in-house with the fibers aligned at the optimum 45 degree orientation. The new tubes were also designed to be easily retrofitted to the existing torque tubes to eliminate the need to remake any control system hardware that interfaces with them.    

To prove just how big of a difference this makes in the torsional stiffness, we took two tubes, one off-the-shelf and one made in-house and applied the same torsional load to each. The torsionally-optimized tube we made in-house was over 50% more stiff in torsion than the off-the-shelf tube. 

We will now be implementing these higher shear modulus tubes into the control system of the prototype in high compliance areas. Moving forward, all production control system torque tubes will be manufactured from the more rigid design. 

Our monthly update for March is out now! 

In March, the team worked through remaining control system tasks on the DarkAero 1 prototype including modifications to increase stiffness in the aileron, flap, and rudder controls. The armrest covers were also revised to better enclose the control system hardware. Session 22 of the Aerospace Composites Course was held and new team members were onboarded. 

Check out the full update here:  https://darkaero.com/updates-files/mar-2024