The most common mistake in choosing sheet material is treating "carbon fiber is strongest" as a universal rule and building the whole aircraft out of carbon sheet. But at least one class of drone part must never be carbon fiber: the antenna mount. Carbon fiber's conductivity along the fiber direction is 3.6 × 104 S/m; FR4's is about 3.3 × 10-13 S/m. That is a gap of 17 orders of magnitude. At GPS and video-link frequencies, carbon fiber behaves like a metal shield.
The One-Minute Summary
- Use CFRP for structural parts. 3K plain-weave carbon sheet has a specific stiffness of 42.2 GPa·cm³/g, 1.65 times that of aluminum 6061-T6 (25.5); specific strength is 467 vs. 115, a 4x difference.
- Keep carbon fiber away from antenna mounts and GPS brackets. The conductivity gap is 17 orders of magnitude; at those frequencies carbon fiber is a conductor.
- Use FR4/G-10 for insulating and heat-resistant parts. G-10's maximum service temperature is 140°C; high-Tg FR4 reaches a glass transition temperature of 180°C.
- Don't mix data for woven and unidirectional laminates. 3K plain-weave sheet has a modulus of 64.1 GPa; unidirectional CFRP is 135 GPa, more than twice as high.
- G-10/FR4 vendors publish only flexural modulus, not tensile modulus, so it cannot be compared directly with CFRP's tensile modulus. This is a common trap in the literature and in catalogs.
Manufacturer Data for Four Materials
Every value in the table below comes from a manufacturer datasheet or a materials database, not a secondhand summary. Pay particular attention to the test method noted in each column, because it determines whether the numbers can be compared with each other.
| Property | 3K plain-weave CFRP | G-10 / GFRP | FR4 (high Tg) | Aluminum 6061-T6 |
|---|---|---|---|---|
| Density | 1.52 g/cm³ | 1.80 g/cm³ | 1.82 g/cm³* | 2.70 g/cm³ |
| Tensile strength | 710 MPa | 310 MPa | 385 MPa | 310 MPa |
| Modulus | 64.1 GPa (tensile) | 18.6 GPa (flexural) | 25.8 GPa (D790) | 68.9 GPa (elastic) |
| Shear strength | — | 131 MPa | — | 207 MPa |
| Max. service temperature | Depends on resin | 140 °C | Tg 180 °C | — |
| Dielectric constant @ 1 MHz | Conductor | 5.0 | 4.24 @ 100MHz | Conductor |
| Water absorption, 24 hr | — | 0.10 % | 0.15 % | — |
| Flame rating | — | UL 94 V-0 | UL 94 V-0 | — |
| *The high-Tg FR4 datasheet (Isola 370HR) does not list density, so the NEMA G-10/FR4 value of 1.82 is used here. The G-10 and FR4 moduli are flexural moduli (ASTM D790), while the CFRP value is a tensile modulus (ASTM D3039). The test methods differ, so they are shown side by side for order-of-magnitude reference only and must not be treated as an equivalent comparison. CFRP data are from the Rock West Composites 401-3KP-11 product specification (Toray T300 fiber + epoxy, resin infused). | ||||
Specific Stiffness and Specific Strength: What Drones Really Care About
A drone is a weight-sensitive vehicle, so strength alone tells you little. What matters is how much strength and stiffness you get per gram. Divide the numbers in the table above by density:
Specific stiffness vs. specific strength of four materials
Horizontal axis: specific strength. Vertical axis: specific stiffness. The farther up and to the right, the better for lightweight structures.
Why Antenna Mounts Must Never Be Carbon Fiber
This is the most important section of the article. Carbon fiber is not just "slightly conductive"; it is a conductor.
| Material / direction | Conductivity (S/m) | Behavior |
|---|---|---|
| CFRP along the fiber, σxx | 3.6 × 10⁴ | Conductor |
| CFRP in-plane transverse, σyy | 1.145 | Weakly conductive |
| CFRP through-thickness, σzz | 3.9 × 10⁻³ | Weakly conductive |
| Single carbon fiber filament (converted, T300) | 5.88 × 10⁴ | Conductor |
| FR4 (converted, Isola 370HR) | approx. 3.3 × 10⁻¹³ | Insulator |
| CFRP conductivity tensor from Zhu et al. (2021); T300 filament value converted from the manufacturer's resistivity of 1.7 × 10⁻³ Ω·cm; FR4 converted from the Isola 370HR volume resistivity of 3.0 × 10⁸ MΩ·cm. Along the fiber direction, CFRP and FR4 differ by about 17 orders of magnitude. | ||
Material conductivity across orders of magnitude
Horizontal axis in powers of 10, spanning 17 orders of magnitude
One study measured an EMI shielding effectiveness of 45–70 dB for continuous carbon fiber composites at 0.03–3 GHz (2 or more layers), with absorption accounting for 80–90%. But the specimens in that study were 3D-printed Onyx with continuous carbon fiber, not standard prepreg laminate, and not a measurement of a drone antenna mount.
We could not find any reliable source giving "specific attenuation in dB for a carbon fiber drone antenna mount at GPS L1 / 2.4 GHz / 5.8 GHz"; everything we found was forum posts and vendor marketing pages. So this article claims only the fact backed by manufacturer and journal data, a conductivity gap of 17 orders of magnitude, and does not offer made-up dB figures.
Matching Parts to Materials
| Part | Recommended material | Typical thickness | Deciding factor |
|---|---|---|---|
| Main frame plates (top/bottom) | 3K CFRP | 2–3 mm | Highest specific stiffness; weight-sensitive |
| Arms | 3K CFRP | 5–6 mm | Bending stiffness scales with thickness cubed; 5mm is mainstream for 5″, 6mm for 7–10″ |
| Side plates / camera mounts | 3K CFRP | 1.5–3 mm | Stiffness first; not an electronic interface |
| GPS / antenna mounts | FR4 or G-10 (never CFRP) | 1–2 mm | Must be RF-transparent; carbon fiber blocks signals |
| ESC isolation plates / insulating pads | FR4 | 0.5–1 mm | Insulating, flame retardant to UL 94 V-0 |
| Heat-resistant spacers | G-10 / FR4 | 1–2 mm | G-10 is usable up to 140°C |
| Battery plate | CFRP or G-10 | 1.5–2 mm | Choose G-10 if it sits close to the battery and shorts are a concern |
| End tabs (for test coupons) | G-10 / glass-epoxy | 1.5–1.6 mm | ASTM standards explicitly advise against tabs of the same material as the coupon |
| Thicknesses are taken from the official specification pages of frame makers such as iFlight, GEPRC, and Armattan. Thickness varies with wheelbase: 5-inch arms are mostly 5mm and 7–10-inch arms 6mm; bottom plates are 2.5–3mm and top plates 2mm. | |||
Carbon fiber is conductive. If a battery plate directly touches the battery's positive and negative contacts or exposed solder joints, it could in theory create a conductive path. In practice most designs add an insulating pad or use carbon sheet with a film layer, but if you are designing your own parts, this must be dealt with at the drawing stage. Don't wait until after assembly to find out.
Two Easy-to-Miss Data Traps
Trap 1: Woven and Unidirectional Laminates Differ by 2x in Modulus
Toray T300 unidirectional composite (60% fiber volume fraction) has a tensile modulus of 135 GPa and a tensile strength of 1,860 MPa. But 3K plain-weave sheet made from the same T300 fiber is only 64.1 GPa and 710 MPa.
The reason is that a woven sheet splits its fibers between interlaced 0° and 90° directions, so only half the fibers carry load in either direction, and the fiber waviness from weaving (crimp) lowers efficiency further. The vast majority of carbon sheet used on drones is woven, so always confirm which type a figure refers to when you cite data. Using 135 GPa to calculate your 3K plain-weave arm would overestimate it by more than 2x.
Trap 2: Flexural Modulus Is Not Tensile Modulus
Vendor datasheets for G-10 and FR4 give only flexural modulus (ASTM D790), not tensile modulus. Comparing 18.6 GPa directly with CFRP's 64.1 GPa (tensile modulus, ASTM D3039) is, strictly speaking, not valid: the test methods and stress states differ.
The specific-stiffness scatter plot in this article already flags this. For order-of-magnitude comparisons in practice it is fine, but if you are doing structural calculations, always go back to the original datasheet and confirm the test standard behind every number.
Machinability: Three Materials on One Machine
| Item | CFRP | GFRP / G-10 | FR4 |
|---|---|---|---|
| Tool wear | Most severe; dominated by abrasive wear | Equally severe; glass fiber is also abrasive | Severe |
| Cutting parameters | Tool makers' datasheets mostly group Carbon/Glass Fiber together; parameter ranges can be shared | Close to GFRP | |
| Dust conductivity | Conductive; a threat to electrical equipment | Non-conductive | Non-conductive |
| Dust irritation | Irritates skin and respiratory tract | Glass fiber mechanical irritation is more pronounced | Same as GFRP |
| Delamination tendency | High; exit side needs backing support | Moderate | Moderate |
| Dust collection | Required for all three, along with P100-rated respiratory protection | ||
| Harvey Tool's composite speeds-and-feeds datasheet already groups "Carbon/Glass Fiber" into one category and differentiates recommended cutting speeds by fiber content (5–20% and 21–40%) rather than by material type. In practice, parameters do not need big changes when you switch materials, but we still recommend a test cut on scrap first. | |||
FAQ
What is the difference between 3K, 6K, and 12K? Which should a drone use?
The number is the count of filaments per tow (3K = 3,000 filaments). The higher the K count, the thicker the tow, the more visible the weave pattern, and the lower the price, but fiber waviness also increases and mechanical efficiency drops slightly. 3K plain or twill weave is the mainstream choice for drone parts. Also note that ASTM D5379 explicitly states that its standard specimen dimensions do not apply to large-tow fabrics of 12K and above, so if you will be doing material qualification, choosing 3K saves trouble later.
Can carbon fiber sheet directly replace aluminum parts?
Yes, where the part sees bending and tension, and the advantage is clear (1.65x the specific stiffness and 4.06x the specific strength). But there are three situations where a direct swap is not recommended: areas that need threads (tapped threads in carbon sheet are weak; use threaded inserts instead), areas that need to conduct heat (aluminum's 167 W/m·K is far better than composites), and areas subject to local crushing or impact (interlaminar strength is the weak point of composites).
Are FR4 and G-10 the same thing?
Very close, but not identical. Both are glass-fiber epoxy laminates; FR4 is G-10 with a flame retardant added (FR = Flame Retardant) and meets UL 94 V-0. In practice, NEMA specifications often list G-10/FR4 together, and the data are nearly identical (density 1.80–1.82, dielectric constant 5.0–5.2). If your application requires flame retardancy, choose FR4; for purely structural or insulating uses, either works.
Why do some frames still use carbon fiber antenna mounts?
Usually because that part is not the surface the antenna itself mounts to, but a mechanical support arm for the antenna, with the antenna body held a certain distance away by plastic or FR4. Carbon fiber severely affects an antenna in the near field, but the effect drops once there is enough distance. This has to be verified by testing; it is not something you can decide by feel. When designing your own parts, the safest approach is still to keep carbon fiber out of every structural part around the antenna.
If one CNC cuts all three materials, do I need to change tools?
You do not need a different type of tool, but you should track tool life separately. Harvey Tool's datasheet groups Carbon/Glass Fiber into one category and gives parameters by fiber content rather than by material type, so the same composite end mill can cut all three. What really needs to be separated is the dust collection and protection setup: carbon fiber dust is conductive, so always clean the machine after cutting carbon sheet before cutting other materials, so that carbon dust does not remain on the linear guides or in the electrical areas.
Sources
- Rock West Composites, 401-3KP-11 product specification (3K plain-weave carbon sheet: modulus 9.3 Msi ≈ 64.1 GPa, tensile 103 ksi ≈ 710 MPa, density 0.055 lb/in³ ≈ 1.52 g/cm³), accessed September 3, 2026 — https://www.rockwestcomposites.com/401-3kp-11.html
- Toray Carbon Fibers America, T300 Technical Data Sheet No. CFA-001 (fiber 3,530 MPa / 230 GPa, density 1.76 g/cm³, resistivity 1.7 × 10⁻³ Ω·cm; composite 1,860 MPa / 135 GPa), accessed September 3, 2026 — https://media.easycomposites.co.uk/datasheets/T300DataSheet.pdf
- Laminated Plastics, G-10 Technical Data Sheet (density 1.80 g/cm³, flexural modulus 18.6 GPa, max. service temperature 140°C, dielectric constant 5.0 @1MHz), accessed September 3, 2026 — https://laminatedplastics.com/g-10.pdf
- Professional Plastics, NEMA G-10/FR4 Data Sheet (specific gravity 1.82, dielectric constant 5.2 @1MHz, shear strength 131 MPa), accessed September 3, 2026 — https://www.professionalplastics.com/professionalplastics/PhenolicG-10FR4DataSheets.pdf
- Isola, 370HR Data Sheet Rev C (Tg 180°C, Td 340°C, Dk 4.24 @100MHz, volume resistivity 3.0 × 10⁸ MΩ·cm), accessed September 3, 2026 — https://www.isola-group.com/wp-content/uploads/data-sheets/370hr.pdf
- ASM / MatWeb, Aluminum 6061-T6 Material Data Sheet (density 2.70 g/cc, UTS 310 MPa, elastic modulus 68.9 GPa), accessed September 3, 2026 — https://asm.matweb.com/search/specificmaterial.asp?bassnum=ma6061t6
- Zhu, Ming, Wang, Duan, Xiao, Zhang, Sun & Tian (2021), Materials 14(18):5210 (CFRP conductivity tensor σxx 3.6 × 10⁴, σyy 1.145, σzz 3.9 × 10⁻³ S/m) — https://pmc.ncbi.nlm.nih.gov/articles/PMC8467610/
- Martins, Silva, Fernandes, Sampaio & Pontes (2023), Polymers 15(24):4649 (continuous carbon fiber composites, 45–70 dB shielding effectiveness at 0.03–3 GHz; specimens were 3D-printed Onyx with continuous carbon fiber) — https://pmc.ncbi.nlm.nih.gov/articles/PMC10748082/
- iFlight / GEPRC official frame specification pages (plate thickness by model: bottom plate 2.5–3mm, top plate 2mm, arms 5–6mm), accessed September 3, 2026 — https://shop.iflight.com/Chimera7-ECO-Frame-kit-Pro2079
- Harvey Tool, Speeds & Feeds — End Mills for Composites (Carbon/Glass Fiber grouped together; parameters by fiber content), accessed September 3, 2026 — https://harveyperformance.widen.net/content/lp2peneiuc/original/SF_785200.pdf
One Machine Cuts All Three Sheet Materials
Carbon-CNC is designed specifically for composites. CFRP, GFRP, and FR4, as well as thin non-ferrous sheet, ABS, PMMA, and PC, are all within its capabilities. To check your mix of parts and sheet thicknesses, bring your drawings and talk with us.
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