⚡ Key Takeaways
- Four product families: rivet-type parts, screws, anti-loosening washers, and bonded nut plates with aluminium sleeves.
- Bonded nut plates join composite structure without drilling, without loss of strength and without damaging the laminate.
- Two-piece wedge-locking washers: the cam angle between the two faces exceeds the thread helix angle, so removal torque exceeds installation torque and transverse vibration cannot loosen the joint.
- Single-sided toothed conical washers compensate clearance and add friction under vibration and alternating load.
- High-strength aluminium sleeves cut weight in the eVTOL airframe.
- Sealing: IP68 water resistance for a machine that flies through rain.
- Every kilogram removed from the airframe adds kilometres of range — lightweighting is the first metric in aerospace.
1. Why eVTOL pushes fasteners to the limit
2. Bonded nut plates for composites
3. Washers: two-piece versus single-sided teeth
4. Aluminium sleeves and lightweighting
5. Selection logic and FAQ
1. Why eVTOL pushes fasteners to the limit
Electric vertical take-off aircraft demand lightweighting and reliability at the same time:
- Weight: each kilogram removed from the airframe adds kilometres of range;
- Vibration: multirotor motors vibrate constantly, so nothing may come loose;
- Composites: carbon fibre airframes cannot simply be drilled;
- Safety: one loose bolt is a flight incident.
2. Bonded nut plates for composites
Drilling carbon fibre cuts the fibres and robs the laminate of strength. A bonded nut plate avoids that:
- No hole: bonded to the composite surface, so no fibres are cut;
- Non-destructive: the laminate structure is left intact;
- High strength: plate dimensions are sized to the joint load;
- Lightweight: the stud-to-plate attachment is chosen to suit the requirement.
3. Washers: two-piece versus single-sided teeth
| Type | Principle | Best for |
|---|---|---|
| Two-piece wedge-locking washer | The cam angle between the two washer faces is greater than the thread helix angle, so removal torque exceeds installation torque | Joints with heavy transverse vibration |
| Single-sided toothed conical washer | Compensates clearance and increases friction at the contact face | Vibration with alternating load |
Why the two-piece washer holds
An ordinary washer relies on friction, and under transverse vibration the thread pair rotates relative to each other and preload bleeds away. In a two-piece wedge-locking washer (the Nord-Lock principle) the two halves interlock, and the cam angle on their inner faces is steeper than the thread helix angle. Turning the bolt in the loosening direction actually increases tension, so removal torque is higher than installation torque — loosening is blocked mechanically, not by friction.
4. Aluminium sleeves and lightweighting
High-strength aluminium sleeves and spacers replace steel parts in the eVTOL airframe:
- More than 60% lighter (aluminium 2.7 versus steel 7.8 g/cm³);
- Galvanically matched to ZT68 aluminium bolts (see the ZT68 guide);
- Produced by a combination of cold heading and CNC machining.
5. Selection logic and FAQ
Three questions
- Is the part carbon fibre composite? Then a bonded nut plate, no drilling.
- Is vibration severe? Then a two-piece wedge-locking washer.
- Is weight critical? Then aluminium sleeves plus ZT68 aluminium bolts.
FAQ
Q: Can a bonded nut plate be removed? The bond is permanent, but the stud thread can be unscrewed.
Q: Should a wedge-locking washer be lubricated? No — lubrication reduces the wedging effect.
Q: Do eVTOL bolts need non-destructive testing? Yes. Flight-critical parts are 100% dye-penetrant inspected.
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