Aircraft can build up static electric charge as they fly through rain, snow, dust, or even dry air. This charge collects on the outer metal skin and composite surfaces, especially near sharp edges such as wingtips and trailing edges. If the charge is not controlled, it can create electrical noise that interferes with radios, navigation receivers, and other antennas.
Static dischargers, often called static wicks, help protect communication by giving charge a safe path into the surrounding air.
A static discharger is a small conductive device mounted near the trailing edge of a wing, stabilizer, or control surface. Its thin, pointed end creates a strong local electric field, which ionizes nearby air molecules and lets charge leak away gradually. This process is called corona discharge, and it reduces sudden arcing that could produce stronger radio interference.
Static wicks do not protect the airplane from lightning, but they help keep electrical systems clearer during normal flight through charge-producing conditions.
Key Facts
- Static charge builds up when friction and particle impacts transfer electrons to or from the aircraft surface.
- Electric field strength near a sharp tip is high, so static dischargers release charge more easily from their pointed ends.
- Basic charge relation: Q = It, where Q is charge, I is current, and t is time.
- Electric current is charge flow rate: I = ΔQ/Δt.
- Corona discharge occurs when a strong electric field ionizes air and allows charge to leak away gradually.
- Static dischargers reduce radio noise but are not designed to conduct a lightning strike.
Vocabulary
- Static electricity
- Static electricity is an imbalance of electric charge that can build up on an object's surface.
- Static discharger
- A static discharger is a small conductive wick on an aircraft that releases accumulated charge into the air.
- Corona discharge
- Corona discharge is the gradual release of electric charge through ionized air near a strong electric field.
- Trailing edge
- The trailing edge is the rear edge of a wing or control surface where airflow leaves the surface.
- Radio interference
- Radio interference is unwanted electrical noise that disrupts communication or navigation signals.
Common Mistakes to Avoid
- Thinking static wicks prevent lightning strikes. They bleed off normal static charge but cannot stop a lightning attachment or replace lightning protection systems.
- Placing static dischargers anywhere on the aircraft in a diagram. They are usually mounted on trailing edges and tips where charge can be released efficiently into the airflow.
- Assuming static electricity only builds up in storms. Charge can accumulate in dry air, dust, snow, rain, and cloud particles, so the system matters in many flight conditions.
- Confusing static discharge with grounding to Earth. An aircraft in flight is not connected to the ground, so static wicks release charge into ionized surrounding air instead.
Practice Questions
- 1 A static discharger releases an average current of 8.0 microamperes for 25 seconds. How much charge leaves the aircraft? Use Q = It.
- 2 An aircraft accumulates 0.060 C of charge during a flight segment. If its static dischargers remove charge at a combined average current of 12 microamperes, how long would it take to remove that charge? Use t = Q/I.
- 3 Explain why static dischargers are shaped with thin pointed ends and placed near trailing edges instead of being made as large smooth plates on the middle of the wing.