ALX-8421LS - Hartzell Engine Technologies 12 Volt 70 Amp Alternator Replaced By ALX-8521LS

ALX-8421LS – Hartzell Engine Technologies 12 Volt 70 Amp Alternator

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Overview

The Hartzell Engine Technologies ALX-8421LS is a flight-critical, FAA-PMA approved 12-volt, 70-amp lightweight alternator, which has been superseded by the current production model, ALX-8521LS. This legacy unit was an industry-standard power generation source for a wide range of Lycoming engines, designed to provide reliable electrical power for aircraft avionics and systems. As a high-efficiency, gear-driven alternator, the ALX-8421LS was engineered by Kelly Aerospace (now part of Hartzell) to deliver durable performance in the demanding firewall-forward environment.

While this part number is no longer in production, serviceable units are sought after for direct replacement on aircraft where the newer model is not yet installed. This unit provides a powerful, lightweight solution for maintaining the certified configuration of many popular general aviation aircraft.

Key Features

• High-Output, Lightweight Design: Delivers a powerful 70 amps of continuous power in a compact and lightweight package. This high output is essential for supporting the electrical loads of IFR panels and other electronic systems.

• Gear-Driven Reliability: Driven directly by the engine's accessory gear train. This design provides a positive, slip-free mechanical connection that is significantly more reliable than belt-driven systems, eliminating the risk of a thrown or broken belt causing a complete loss of generated power.

• Durable Construction: Built with high-quality copper windings and robust bearings, designed to withstand the high temperatures and constant vibration of the engine compartment.

• Direct Legacy Replacement: Engineered as the original direct, bolt-on replacement for many factory-installed alternators, guaranteeing perfect fitment and electrical compatibility on specified Lycoming engines.

• Superseded by ALX-8521LS: This model has been officially superseded by the improved Hartzell ALX-8521LS, which is the current-production replacement.

Technical Specifications

• Part Number: ALX-8421LS

• Component Type: Engine-Driven Alternator

• Manufacturer: Hartzell Engine Technologies (Kelly Aerospace)

• Voltage Output: 12 VDC (for 14-volt systems)

• Current Output: 70 Amps

• Drive Type: Gear-Driven

• Cooling: Integrated Fan, External Ventilation

• Superseding Part Number: ALX-8521LS

• Certification: FAA-PMA

Aircraft Compatibility

The Hartzell ALX-8421LS was the specified PMA alternator for a vast range of aircraft powered by Lycoming's most popular 4- and 6-cylinder engines. It is imperative to consult the specific aircraft's Illustrated Parts Catalog (IPC) or the current Hartzell application guide for final verification and to confirm eligibility for the superseding part.

• Common Lycoming Engine Series:

  • O-320, IO-320, LIO-320, AIO-320, AEIO-320

  • O-360, IO-360, LIO-360, AIO-360, AEIO-360

• Common Aircraft Platforms:

  • Piper: PA-28 (Archer, Arrow), PA-44 Seminole

  • Mooney: M20 Series

  • Grumman: AA-5 Series

  • Numerous experimental aircraft, especially the Van's RV series.

Why Choose ALX-8421LS?

For aircraft specifically requiring a like-for-like replacement of an existing ALX-8421LS, a serviceable unit provides a way to maintain the aircraft's original configuration without the need for additional logbook entries or paperwork associated with a supersedure. It is the proven, certified component that was the standard for years, offering reliable power generation. For new installations or overhauls, the superseding ALX-8521LS is the recommended part.

The Hartzell ALX-8421LS is a synchronous AC generator that produces three-phase alternating current. This AC output is then passed through an internal, solid-state rectifier bridge, which consists of six heavy-duty diodes. This bridge converts the three-phase AC power into smooth, usable direct current (DC) for the aircraft's 14-volt electrical bus. The alternator's output voltage is controlled by varying the small amount of DC current supplied to its rotor, known as the "field current." This is managed by the aircraft's separate voltage regulator, which senses the bus voltage and adjusts the field current as needed to maintain a constant output under all electrical load conditions. The supersedure to the ALX-8521LS typically involves evolutionary improvements in internal components, such as more efficient stator windings or more robust diode technology, to enhance durability and performance.

Note: This is a flight-critical component. This part number has been superseded by P/N ALX-8521LS. Installation of either this part or its replacement must be performed by a certified A&P mechanic. Proper gear backlash must be checked and set upon installation to prevent damage to the engine's accessory drive train. All electrical connections must be clean and torqued to the specified value.