Source: https://oliviercouthaud.com/picotalon · Status: In progress · 2026 · Tags: 3D printing, LW-PLA, AeroSandbox, FluidX3D

# PicoTalon

A 3D-printed RC plane, assembled and waiting for its electronics, plus a computer model I use to check decisions before it flies.

[Image: The assembled orange plane on a light blue-grey tablecloth, seen from the front. The wings and the V-shaped tail are attached. The nose has an open camera hole with vents above it, and a black rod sticks out from each side of the nose. A few spare orange printed bits, a carbon rod and some glue bottles lie on the table.]

Figure: The plane assembled, with the wings and V-tail on and the nose open at the front for the camera. It weighs 400 g with the battery. The motor, controller, servos, flight controller and FPV gear are not in yet, and it has not flown.

## What I wanted

The part of printing I enjoy most is the material itself: how different infills feel, how strong they turn out to be, what kind of force each one holds against, and how the printer lays them down. A plane is a good place to use all of that. The goal is one 3D-printed plane flying, before anything fancier. The longer idea, several aircraft working together without a ground link, is parked on purpose. This one is a hand-launched pusher with FPV video from a DJI O4 Air Unit Pro, an ExpressLRS receiver, and a TBS Lucid H7 Wing flight controller, which I'll most likely run ArduPilot on.

The airframe is the Pico Talon by [Flightory](https://flightory.com): 905 mm wingspan, 640 mm long. It is not my design. I bought the file pack, so I am not sharing its STLs, plans or renders. The photos, diagrams and plots here are mine. Every part that can be printed is printed and it is assembled; the electronics are next, and I am waiting for them to arrive. With the battery in and no other electronics it weighs 400 g.

Almost every part is Prusament PLA Lightweight, a foaming filament, printed on a Prusa CORE One+. The slicer estimates all the LW-PLA parts at about 260 g together. The parts that carry load are Prusament PETG.

**What is LW-PLA?**

A PLA filament with a foaming agent in it. When it melts in the nozzle it swells, so a printed wall is mostly tiny bubbles and much lighter than ordinary PLA. Because it swells, the slicer has to push out less of it (an extrusion multiplier of about 0.45 here), and it is fussy about stringing.

Figure: Diagram. Two tracks. The build is the printed plane; the 400 g is the assembled airframe with the battery and no other electronics. The model is a set of scripts that answers questions about it before the electronics go in. Orange: what the model hands back to the build.

## How it is built

I slice the LW-PLA parts one at a time in PrusaSlicer 2.9.6, starting from Prusa's own settings for the filament: 230 °C, extrusion multiplier about 0.45, one wall, sparse infill. Flightory's manual calls for a lattice infill that PrusaSlicer doesn't have, so I chose the wing infill from slicer estimates on one panel (adaptive cubic at 3%: 24.9 g, about 4 hours). All four wing panels were printed with it. None has flown.

Orientation matters for a part with thin walls, so I check each one against the manual's pictures by slicing the first layers. Slicing the first layers caught one orientation that eyeballing a render had misjudged: the FUS 2 part as supplied has about 1550 mm² of overhang, and 64 mm² flipped, which is how the manual shows it.

The 21 PETG pieces are laid out on plates (two, plus a third that redoes the wing roots and adds a spare set of locks). The first two come to about 82 g by the slicer, and the single-part slices added up to about 83 g.

[Image: Top view of the printed parts laid out on a white board in the shape of the plane: fuselage sections down the middle, wing panels left and right with a dark carbon rod through them, the tail pieces at the bottom, and a bundle of thin carbon rods in the top right corner.]

Figure: The printed parts laid out on a white board next to the carbon rods, before assembly.

## How strong the parts are

I put spare, broken and misprinted parts under load, nothing drastic, and they are surprisingly strong. Even a single layer with minimal infill is still really good. I find it hard not to enjoy this: how different the infills feel, how much each one can take, which direction of force it takes it from, and how they are put down line by line. These were informal hand tests, not a proper test, so I have no numbers.

## A model of the plane

While the parts were printing I built scripts that rebuild the plane from the CAD meshes, so I could ask questions before anything was wired. Where does the centre of gravity land, is it stable, what does the powertrain draw. The chain is in the diagram above: a 1:1 assembly checked against Flightory's 640 mm length, a mass budget, a vortex-lattice model with a fuselage term, then a motor, speed controller, battery and propeller model.

**What is a vortex-lattice model?**

It covers the wing and tail with a grid of small panels, each carrying a vortex, and solves for the lift pattern that makes the air flow along the surface. It is fast and good at lift and balance, but it ignores thickness and friction. So I feed each wing strip's result to NeuralFoil, a network trained on XFoil results, to add the drag and the point where each section stalls.

Figure: Diagram. The mass budget, each line starting where the one above ends, so the staircase finishes at the 824 g estimate. The vertical line is 800 g. Power is the battery, motor, speed controller and propeller. Orange: the budget assumes about 32 g of PETG and the slicer says about 83 g, a gap that is not included in the total. The weights are a mix of shop weights and estimates, not scale weights.

## What the model says

**Model outputs for an 800 g aircraft, CG at X 275.4 mm (X is mm aft of the nose tip), sea level, 15 °C.**

| Quantity | Value |
|---|---|
| Neutral point | X 295 mm (range 285 to 297) |
| Static margin at the manual's CG | 11.6% MAC (plausible 6 to 13%) |
| Stall speed | 31 km/h (33 with a more cautious CLmax) |
| Best L/D, trimmed | 13.1 at 46 km/h (12.0 at 43.5 with extra drag) |
| First stall | Wing root; the tips keep a large margin |
| Cruise endurance, 80% of the pack | 41 to 49 min at about 41 km/h (about the slowest speed I allow, roughly 1.3 × stall; in practice I would fly about 45 km/h and lose only about 2 min), 33 to 39 min at 55 km/h |
| Same, with climbs, turns and wind | about 24 to 31 min at 55 km/h. A planning estimate that assumes 25 to 35% extra energy |

Endurance rows: HQProp 7.5x5. The range is P10 to P90 of 1500 runs with my uncertain inputs varied, so it shows how much my guesses matter, not how much flights will vary. The propeller data is the biggest guess: it is computed data, calibrated on a different prop. None of these numbers is measured on the real plane.

**What do centre of gravity and static margin mean?**

The centre of gravity (CG) is where the plane balances. The neutral point is the spot where its own pitch stiffness cancels out. The static margin is the gap between the two, as a fraction of the wing's average chord (MAC). A bigger gap is calmer and a little sluggish. A CG at or behind the neutral point means the plane is unstable and would pitch away from you.

The mass budget is 824 g, and I made it before weighing anything. The bare airframe with the battery now weighs 400 g on the scale, lighter than the budget has for the same parts, so the budget is probably too high. I will redo it from real weights once the electronics are in, and the 700 g curves below show what a lighter plane does. In the other direction, at 900 g the same model gives a stall of about 32 km/h and 38 to 45 min best endurance.

I compared the aerodynamics with the polars in Flightory's manual. My lift at zero angle of attack and my lift slope agree with those polars to within 2%. That checks my model against their calculation, not against a plane. Their curves look like a wing-and-tail calculation without the fuselage (they don't say what it contained). In my model the fuselage costs roughly 20% of L/D and about 6% MAC of static margin.

It stalls at the wing root first, next to the fuselage, and the tips keep a large margin, so the stall should be gentle.

[Image: Local lift coefficient along the half wing at the moment the first section stalls, for the 800 gram aircraft. The blue curve starts near 1.31 at the root and falls to about 0.5 near the tip. The dashed orange line, the maximum each section could reach, stays flat near 1.32. The two touch at about 58 mm from the centreline, so the root stalls first. A grey band marks the curled wingtip, which is not used.]

Figure: Where the wing stalls first: local lift (blue) against what each section can give (dashed). They meet at about 58 mm from the centreline.

[Image: Lift to drag ratio against airspeed for the 800 gram aircraft. It peaks at 13.1 near 46 kilometres per hour and falls to about 4 at 119. A red dotted line marks the stall speed near 31 kilometres per hour and a grey band marks 50 to 70.]

Figure: Trimmed flight at 800 g: lift to drag against airspeed. The red dotted line is the stall speed, the grey band 50 to 70 km/h.

[Image: Glide sink rate against airspeed for the 800 gram aircraft, lowest at about 0.83 metres per second near 35 kilometres per hour, rising to 8 at 119. Same stall line and grey band.]

Figure: Glide sink rate against airspeed, same lines.

[Image: Power against airspeed for the 800 gram aircraft: aerodynamic power from about 7 watts to 63 watts, and a dashed estimate of electrical power. Same stall line and grey band.]

Figure: Power against airspeed. The dashed electrical curve is a rough early assumption of 45% efficiency. The real motor and prop model is in the endurance plots below.

[Image: Trim angle of attack falling from 11 degrees at 32 kilometres per hour to about minus 2, and elevator trim between minus 7 and plus 1 degrees, against airspeed for the 800 gram aircraft. Same stall line and grey band.]

Figure: Trim angle of attack and elevator trim against airspeed, same lines.

### Endurance by weight and speed

In cruise the battery supplies about 40 W, and about 13 W of that is avionics, mostly the O4 Pro. Without it, cruise endurance would be about 25% longer. DJI doesn't publish the O4 Pro's power draw. I use 9 W, with 7.5 to 10.5 W as the range. The 10.5 comes from one third-party page and I haven't measured any of it, so treat the 13 W and the 25% as soft.

**What is a Monte Carlo band?**

I ran the endurance calculation 1500 times, each time drawing every uncertain input (prop efficiency, avionics power, drag, battery capacity) at random from a plausible range. P10 to P90 is the middle 80% of those runs. It shows how much my guesses matter. It says nothing about how the plane will really do.

[Image: Endurance in minutes against airspeed for 700, 800 and 900 gram aircraft with an HQProp 7.5x5, 80 percent of a 2000 mAh 4S pack, sea level. All three curves fall from about 43 to 51 minutes near 35 km/h to about 10 minutes at 108 km/h. Shaded bands show the 10th to 90th percentile of a Monte Carlo over uncertain inputs. Dotted verticals mark 1.3 times stall speed for each mass.]

Figure: Endurance against airspeed for 700, 800 (orange) and 900 g (dark); 700 g is teal.

[Image: Still-air range in kilometres against airspeed, same three masses and bands. Range peaks around 31 to 34 km at roughly 50 km/h and falls to about 17 km at 108 km/h.]

Figure: Still-air range, same colours. The dotted verticals mark 1.3 × stall speed, the slowest speed used.

[Image: Battery power in watts against airspeed, same three masses. Power rises from about 30 W at the slowest speed to about 145 W at 108 km/h; the three curves nearly coincide.]

Figure: Battery power against airspeed, same colours, including about 13 W of avionics. The bands are the 10th to 90th percentile of 1500 Monte Carlo samples. No flight has validated any of it.

## What I ran into

**The fifth fuselage section took three tries.** First with retraction off, which had worked on simpler parts: ooze piled up. Then with retraction, wipe and avoid-crossing, which left a mess inside. G-code measurements showed the trade. The settings that worked on FUS 2 and 3 put about 12 m of travel across the hollow bore, and avoiding that made the nozzle follow the walls with 4355 retractions, smearing strings inside. The third attempt went back to the FUS 2 and 3 settings and came out fine.

**The camera needed a different nose.** The O4 lens would sit about 12 mm behind a 16 mm window, so only about 67 degrees of its 155 degree view gets out. It needed a different front, one that loads from the rear, leaves the cables plugged in and puts the antennas left and right. Revision 3.3 was printed, and when I checked it, a slot stopped short, so the camera could not go in. It and 3.4 were replaced by a rear-loading nose (RL1e) that takes the whole unit from behind. That nose is printed and on the plane, and it works. The camera has not run in it yet, so cooling is untested, and the antennas end up about 16 mm from the video transmitter, where DJI asks for 50 mm.

**The airflow simulation is not grid-converged.** I ran the whole plane through FluidX3D, a lattice-Boltzmann solver, on my GPU, at 15 m/s. It is not grid-converged: the answers keep changing as the cells get smaller, and they stay far from the lifting-surface model. Drag comes out four to six times higher than my model gives. Pick a cell size below to see it. I leave those numbers out of everything else here.

### Finer grid, different answer

**The mass budget is soft.** It was built from slicer weights, shop weights and guesses, it sits well above what the scale says for the airframe, and its PETG weights are lower than the slicer's. An earlier budget put the CG at X 296.6 mm, behind the neutral point, which would be unstable. Moving the battery forward fixed it on paper (X 275.4 mm now).

**The powertrain is oversized for its speed controller.** On paper the 7.5x5 propeller at full throttle draws 56 to 61 A from the battery, against a 40 A controller and a motor rated 36 A peak. The model says to cap throttle near 72%. Cruise only needs 25 to 40%, so the cap costs nothing in normal flying.

## Where it stands

Every part that can be printed is printed, so what is left is the electronics, and they have not arrived yet. When they do, the motor, speed controller, servos, flight controller and FPV gear go in. I will weigh the finished plane and redo the mass budget, since 824 g is an estimate and the airframe came in at 400 g with the battery.

Before the first power-up I will do a bench thrust and current check with the plane restrained and the propeller on. Before the first flight, simulator practice. The first flight log will tell me how close the model is, and I will fit it to that.

In France a plane with a camera needs operator registration and the online open-category exam. Flying in goggles needs a second person who keeps the plane in sight, and 800 g or more adds aircraft registration and a signalling beacon, which is one more reason to weigh it with everything on board. I will check airspace and local restrictions before any outdoor flight.

- **Design**: Flightory Pico Talon, purchased; not mine
- **Mine**: The print setup, the slicing checks, the mass budget and the model of the plane
- **Stack**: Prusa CORE One+, PrusaSlicer, LW-PLA and PETG; Python, AeroSandbox, NeuralFoil, [FluidX3D](https://github.com/ProjectPhysX/FluidX3D) (lattice-Boltzmann solver, free for non-commercial use), APC and UIUC propeller data
- **Stage**: Fully printed and assembled; waiting for the electronics to arrive; not flown
- **Weight**: 400 g with the battery and no other electronics
- **Status**: In progress
- **Code**: Not public