Spring
Balance
Horizontal
Pivot Mass Balance Weight Axis
Mass Balance Weight
Figure 7: Wing Flap Static Balance
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Section 51-80
Electrical Bonding
1. General
The bonding system gives the airplane good lightning protection. A special bonding system is necessary for the composite structure of the DA 40. Without this special system, the composite structure would not sufficiently conduct electricity.
Refer to Section 21-60 for details about the static discharge wicks.
2. Description
Figure 1 shows a simplified bonding system schematic.
The lightning conductor system is the main part of the bonding system. High capacity aluminum alloy tubes and strips make the lightning conductor system.
The lightning conductor system has a longitudinal branch and a lateral branch. The longitudinal branch runs from the engine block via engine truss, firewall, cabin, aft fuselage and empennage to the elevator. The horizontal branch connects the left wing tip with the right wing tip. It is connected with the longitudinal branch at the cabin floor under the forward seats.
Metal braiding and strips connect all conductive components (for example: wing skin, fuel tanks, control systems, landing gear, engine, etc.) and antenna ground plates to the lightning conductor system.
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AMM
Engine Mount Landing
Figure 1: Airplane Lightning Protection and Bonding System Schematic
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Structures
The following design features also give lightning protection: ) The aluminum tubes of the lightning conductor system are also used as conduits for electric wires. ) Carbon fiber material is used for the lower wing skin and parts of the fuselage skin, canopy frame and rear door frame. Carbon fiber material is conductive. ) Carbon fiber material with interwoven aluminum fibers is used for the upper wing skin and the engine cowlings. Carbon fiber material with interwoven aluminum fibers is conductive. ) The forward wing spar separates the lightning conductor system from the fuel tanks. ) A lightning conductor strip is integrated in the horizontal stabilizer. ) The tail skid has an aluminum bar on the lower edge. ) The propeller is non-conductive (except for the erosion sheath), therefore currents cannot flow in structural parts of the propeller. The propeller spinner is made from aluminum and is connected to electrical ground.
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Maintenance Practices
1. General
This Section tells you how to do a test of the electrical bonding system.
2. Test the Electrical Bonding System
The resistance measurements on the DA 40 are divided into three categories: ) Very low resistance measurements for conduits in the direct lightning path and electrical power grounds. ) Low resistance measurements for bondings of controls. ) High resistance measurements for the static discharge wicks.
Do the low resistance bonding measurements with a milliohmmeter and Kelvin probes. The test current must be approximately 2 amps. Do the high resistance measurements with a high voltage megaohmmeter. Measure the static
% discharge wicks and the precautions against static charge of the airplane. % All measurements are referenced to the negative pole of the main battery. The airplane must be in a serviceable condition during the tests, except that the engine cowlings must be removed.
% A. Very Low Resistance Measurements (Lycoming version)
Item Attachment Point max. allowable [mù] measured [mù] passed 中国航空网 www.aero.cn 航空翻译 www.aviation.cn 本文链接地址：钻石40飞机维护手册 DA 40 SERIES AMM 4(42)
