The concept behind the VANDAL-5 or VILLAN-5 is to create a cheap, repairable, modular and durable 5in Adversarial Trainer.
The basic frame layout is inspired by the Prince Vandal of Novgorod, a Russian fiber-optic FPV loitering munition developed by the Ushkuynik center for the Russian Armed Forces. It’s commonly abbreviated KVN and was first reported in 2024.
KVM Frame Design
Initially I scoffed at the crudeness of the frame in both its design and construction. The frame itself consists of only a single piece of FR-4 (yes, the same material as used for PCB's) and a FDM 3D printed canopy that houses the camera and flight controller/ESC stack. While it seems quite improvised, where it shines in it's ability to be manufactured in large quantities very rapidly.
Traditionally, FPV frames tend to be Carbon Fiber. Higher stiffness, but higher price and lower availability than the FR-4 fiberglass. While carbon fiber is the peak of performance and FPV industry standard, FR-4 offers a substantially cheaper option with decent enough performance for an attritable quadcopter.
Traditional FPV frames also generally consist of 4 replaceable arms, a bottom plate, a crush plate, 6-8 aluminum standoffs and a top plate. At a minimum (not including camera plates which are sometimes present if not 3d printed, as well as arm reinforcements) we are looking at a minimum of 7 carbon fiber components with 2-3 different thicknesses of carbon fiber sheet (the arms are substantially thicker than the body plates).
The KVN uses one single piece. Yet unibody frames are not at all a new idea and are usually not recommended due to repairability. If you break an arm, which is one of the most common forms of frame breakage by far, the entire frame must be replaced which means the VTX, flight controller and camera all need to be re-mounted onto a new frame.
Toothpick Frames and Frame Geometry
These unibody frames are most often seen on Toothpick frames (pioneered by Dave.C FPV) and are mostly under 3in prop size. Bellow is a generic SkystarsRC toothpick and it shares the simple 2 part layout of the KVN, A plate and a printed canopy to cover the FC and house the camera.
One of the larger examples of a unibody that is somewhat popular is the Happymodel Crux-35 frame
The main downside is that eventually, arms like this will still break at any point where not reinforced (generally at its thinnest point)
More robust reinforcement tends to fair a bit better
But ultimately, having full reinforcement is the best insurance for a unibody design as seen on these printed Micro Oblivion frames. 
3D printed unibody frames
This tends to be a taboo in FPV circles, for good reason. Early 3D printed frames were ineffective for one of two reasons as far as I can tell.
The first reason was due to a lack of stiffness, mainly because 3D printed frames tended to just be regular thickness FPV frames, but 3d printed. 3D prints are capable of nearly equal stiffness to Carbon Fiber simply by increasing the thickness to 3-4x the original Carbon Fiber thickness, given the correct slicer settings.
The second issue once you can get it stiff enough to fly, is durability. Usually one good crash and a 3D printed frame is inop. This again can be remedied to some degree by ensuring the design is 3-4x thicker than equivalent CF as well as having as many reinforcement points as you can without sacrificing too much airflow.
Here is an example of a printed Crux 35 frame that meets/exceeds the durability and stiffness of the original CF frame, as you can see, it needs to be substantially beefier.
My though process is if you make the frame design thick enough and you have side and front arm bar supports, you can get excellent durability out of even printed frames. Now is FDM 3D printing the best solution? No, generally not, but that is what is great about it. If you can rapidly iterate using 3D printed frames, see where it breaks, and reinforce it enough for the design to be survivable, imagine how it will perform at half to a quarter the thickness using the correct materials.
If performance is the goal though, simply use an existing freestyle or race frame, those are as optimized as they can get for their respective performance expectations. This design on the other hand is not perusing pure flight performance, it is attempting to to prioritize and balance durability, economy and repairability.
With that in mind I plan on experimenting with 3 variants,
- FDM 3D Printed for it's unit level print-on-demand/overnight replacement capability (ASA/ASA LW printed with a 0.4mm nozzle at 3-6 wall thickness and under 10 percent gyroid infill)
- FR-4 Fiberglass for low cost mass manufacturing (any PCB manufacturer can pump these out in 500+ piece quantities without much issue.
- Carbon Fiber frame as a baseline just to compare the performance and ensure that the FDM and FR-4 are acceptably comparable.
Prop and Motor Selection
The KVM is estimated to be 8in in prop size and more recently speculated to be running 10in props although I have not been able to verify this. For our trainer, I believe 5in and 2207 motors will be the best option due to the wide availability, low cost due to popularity, and well documented performance.
Battery Selection
As we have established, this is not meant to be a freestyle ripper, it only has to fly as well as a 8-10in quad with payload therefore 4S1P 18650/21700 Lithium Ion packs will probably be the best choice based on my tests so far.