How to Choose eVTOL and Drone Fasteners: The Selection Logic of Lightweighting, Anti-Loosening and Airframe Joints
Executive Summary
Electric vertical take-off and landing (eVTOL) aircraft plus industrial/consumer drones push both weight saving and reliability to the forefront of fastener selection: the airframe and arms use aluminum and even carbon-fiber composites, prop hubs and motor mounts bear continuous vibration, and the traction battery pack must be serviceable. A wrongly chosen M5 bolt in material or anti-loosening method can cause an airframe-level accident. Following the product line of the low-altitude-economy handbook, this article explains the few things engineers must settle first.
Table of Contents
- Three Special Constraints Low-Altitude Aircraft Place on Fasteners
- Material Selection: Balancing Strength and Weight
- Anti-Loosening: Joint Reliability under Vibration and Alternating Load
- Soft Materials and Composites: Where Threads Must Not Be Tapped Directly
- Sealing and Protection: IP Ratings and Salt Spray
- Selection Checklist
Three Special Constraints Low-Altitude Aircraft Place on Fasteners
Unlike ground equipment, fasteners on eVTOL and drones simultaneously bear three superimposed working conditions. The first is continuous vibration: rotating propellers and high-speed motors transmit high-frequency vibration to every joint, and ordinary threads readily self-loosen under transverse vibration. The second is weight-saving pressure: every extra gram converts directly into range and payload, so designers want thinner bosses and lighter bolts. The third is long-term maintenance-free: OEMs do not want users to re-tighten bolts after every flight; the joint must hold clamping force for the design life.
With these three constraints stacked, the selection logic is completely different from an ordinary cabinet: you cannot only ask "can it be screwed in," but must simultaneously answer "will it loosen, will it be too heavy, can the base bite the thread."
Material Selection: Balancing Strength and Weight
The light-metal fasteners common on low-altitude aircraft almost all revolve around "specific strength." Real grade combinations commonly used in engineering are shown below; during selection, match the position's load, temperature and corrosion environment to the table:
| Material / Grade | Typical Strength Class | Relative Weight | Suitable Positions |
|---|---|---|---|
| Carbon steel 8.8/10.9 | ISO 898-1 / GB/T 3098.1 | Baseline | Motor mounts, load-transfer points; needs anti-corrosion coating |
| Stainless A2-70 / A4-80 | ISO 3506 / GB/T 3098.6 | Close to carbon steel | Exposed parts, humid environments; lubricate to prevent galling |
| High-strength aluminum (e.g. 7075-T6 type) | Custom cold heading | ~1/3 of steel | Weight-saving joints, lifting bushings |
| Titanium Ti-6Al-4V | High specific strength | ~60% of steel | Critical load-bearing, low-magnetic, temperature-sensitive positions |
Anti-Loosening: Joint Reliability under Vibration and Alternating Load
The low-altitude-economy handbook treats anti-loosening as the core of the screw product line. In practice, three routes are commonly used, alone or in combination:
- Mechanical / wedge lock washers: double lock washers rely on the wedge angle of the contacting faces exceeding the thread lead angle, so removal torque always exceeds installation torque—the definitive treatment for positions with strong transverse vibration; single-face serrated conical washers provide clearance compensation and friction resistance when vibration stacks with alternating load.
- Pre-applied thread-locking adhesive: a chemical or physical layer pre-applied to the threads cures after assembly into a reversible locking torque, suiting batch installation where washer thickness is not desired.
- Structural anti-loosening: captive screws mounted on panels stay put after removal, both anti-loosening and anti-loss; ideal for battery compartments and service covers.
Soft Materials and Composites: Where Threads Must Not Be Tapped Directly
The airframe makes heavy use of aluminum die castings and carbon-fiber composites. Directly tapping M5/M6 threads in aluminum strips after only a few disassembly cycles; composites, in principle, should not be directly drilled for load bearing. The industry handbook gives two engineering countermeasures:
- Thread-insert reinforcement: press or heat-stake thread inserts into aluminum/magnesium die castings, replacing soft base threads with hard internal threads; after reinforcement, engagement strength reaches 8.8 class and even 12.9 class.
- Composite bonded joints: for carbon-fiber composite plates, bonded plates achieve hole-free, non-damaging high-strength joints; the bond plate can be lightweighted by required joint strength, avoiding fiber cutting and stress concentration from drilling.
Sealing and Protection: IP Ratings and Salt Spray
eVTOL and drones often operate in open-air, rain and salt-spray environments. Joints needing protection can be pre-coated with adhesive under the bolt head or on the threads, or fitted with O-rings; the handbook sealing grade can reach IP68. Exposed steel parts, meanwhile, need zinc-flake or Dacromet-type anti-corrosion coating, with corrosion life verified through neutral salt-spray testing.
Selection Checklist
- Prop hub / motor mount (high vibration, load-bearing): 10.9-class steel bolts + double lock washer + pre-applied adhesive, tightened by torque or torque-angle method.
- Airframe cover / battery compartment (serviceable): captive screws; exposed stainless or black anodized.
- Aluminum die-cast boss (repeated disassembly): reinforce with thread inserts before installing standard bolts.
- Carbon-fiber composite joints: prefer bonded plates, avoid direct drilling; where drilling is unavoidable, use sleeves to distribute load.
- Outdoor / salt-spray positions: A4-80 stainless or carbon steel with long-life anti-corrosion coating; seal to IP67/IP68 where needed.
Low-altitude fastener selection is essentially balancing four variables—weight saving, anti-loosening, base strength and protection. First divide working conditions by position, then settle material grade, anti-loosening method and thread reinforcement one by one; this is far more reliable than picking a size number off the shelf.
Conclusion
Choosing fasteners for eVTOL and drone airframes balances three competing demands: minimum weight, maximum reliability, and provable repeatability. Material selection is the first lever—high-strength aluminum for non-critical skin joints, titanium for rotating and high-load positions, and corrosion-resistant steel only where strength-to-weight is less important than toughness. Anti-loosening is specified by the joint's vibration environment: rotor-mount and motor-adapter joints get the most aggressive locking, while static avionics mounts can use lighter solutions. Soft materials demand special care: honeycomb and carbon composite must not be tapped directly, because threads in laminate delaminate under load; bonded inserts, sleeves, or rivet nuts are used instead, with pull-out strength validated. Sealing and protection follow the operating profile—IP-rated penetrations for amphibious or high-moisture drones, and salt-spray-tested finishes for coastal or maritime use. The selection checklist should end with a consistency check: can the supplier deliver the same torque–preload, coating thickness, and lot traceability across the production run? In low-altitude aviation, a single off-spec bolt is not a warranty claim—it is a flight-safety event.
eVTOL and drones turn fasteners from "standard parts" into "part of structural design": steel at load points, aluminum at weight-saving points, stainless at corrosion-prone points, titanium at critical nodes; wedge washers or pre-applied adhesive at vibrating positions; thread inserts in soft bases and bonded plates in composites. YF Zhichengjia, founded in Shenzhen in 2005, is a fastener manufacturer able to provide customization and selection support for anti-loosening/sealing/captive screws, self-clinching and rivet nuts, lock washers, high-strength aluminum bushings and thread inserts. For more technical material see the technical document library, or contact our technical engineers for one-on-one evaluation.
