Gearbox for the aeronautical industry Mark 15

gear trainparallel-shaft2 - 5 kNm

Overview
The Mark 15 Propeller Speed Reduction Unit (PSRU) from Aerosport Engineering is a geared reduction unit for experimental and advanced-category aircraft propulsion installations. It is offered in Single Mesh (two-gear) and Dual Mesh (with idler gear for same-direction propeller rotation) configurations and supports multiple engine/adaptor combinations and propeller sizes.

Main design and purpose
The Mark 15 is intended to match large piston engines to appropriate propeller diameters by selecting optimized gear ratios. Variants accommodate propeller rotation direction and different engine-to-propeller interfaces. The PSRU can operate with a stand-alone lubrication package or use an engine oil system when compatible.

Key features

• Available as Single Mesh (input gear + prop gear) or Dual Mesh (idler for same-direction prop rotation).
• Hydrodynamic (fluid-film) journal bearings on input and propeller shaft ends for high load capacity in compact packaging.
• Provision for integrated propeller governor drive with vibration-isolated drive and internal control plumbing; supports Beta/reverse-prop functionality and two integrated governor solenoids for Beta mode and flat-pitch stop.
• Bellhousing/adaptor options machined from 7075-T6 aluminium with ~8 mm average wall thickness; includes alternate mounting flanges and an integrated alternator provision for electrical redundancy.
• Multiple propeller flange options: SAE ARP-880 (8-bolt/2-dowel) and SAE ARP-502 (6-bolt/2-dowel).
• Shortest engine-to-prop flange distance 14 in; prop shaft extension increments available up to +2 in where required.
• Designed gear ratios: 1.724, 1.821, 1.926, 2.038, 2.160, 2.292, 2.435, 2.478, 2.591, 2.762, 2.950, 3.158.

Lubrication and oil system
The Mark 15 can use the engine scavenge/pressure system or a dedicated stand-alone lubrication system when engine oil capacity/pressure is unsuitable. Stand-alone systems include pump(s), cooler, dry-sump tank, filter adapter and plumbing. The gearbox includes provisions for condition monitoring: chip detector, inlet/outlet oil temperature sensors and an oil-pressure sensor location (1/8" NPT). Filtration is inspected after run-in testing.

Bellhousing and adaptors
Bellhousings are machined to suit a range of engines (examples: Chevrolet small-block & big-block, GM LS/LT, Ford Windsor, Chrysler Hemi, ASE-650 Saga V12). Features include direct engine mounting options, alternator mount for redundancy, governor pad and multiple mounting locations. Typical bellhousing weight ~10 kg (22 lb).

Testing program
Aerosport conducts start-up checks, extended run-in and endurance tests (examples: 60+ hour endurance runs as part of verification). Tests monitor oil pressures/flow, inlet/outlet temperatures, governor functionality, prop pitch cycling, chip detection and filter inspections. Load runs vary up to full-rated input for break-in and verification on custom test rigs that replicate installation conditions.

Transmissibility, resonant frequency & torsional isolation
Documentation details excitation/pulse rate concepts, resonant frequency, transmissibility and torsional isolation measures. Matching excitation to resonance increases transmissibility; operating sufficiently above resonance reduces transmitted torque spikes. Mark 15 design and installed torsional isolation address resonant amplification and torque-pulse transmission to the driven load.

Propeller and thrust handling
The propeller shaft includes pressure-lubricated thrust interfaces and generous thrust surfaces to center and stabilize the shaft under axial load. Propeller thrust capacity is rated to 3000 lb in either direction (tractor or pusher) depending on configuration.

Testing & quality control
Parts and materials are traceable; vendors are ISO-certified and material certificates are obtained. Aerosport performs independent material/hardness checks when required. PSRUs undergo full functional testing and inspection, including filter inspection and leak checks, before delivery.

Technical specifications

• Commercial denomination: Mark 15 PSRU
• Brand: Aerosport Engineering
• Configurations: Single Mesh and Dual Mesh (idler for same-direction propeller rotation)
• Rated input torque capacity: exceeds 1600 lb-ft (depends on configuration and safety margin)
• Propeller axial (thrust) capacity: 3000 lb (both pusher and tractor)
• Typical single-mesh weight (assembled with bellhousing & governor): ~39 kg / ~88 lb (varies with ratio and options)
• Bellhousing material: 7075-T6 aluminium; typical bellhousing weight ~10 kg / 22 lb
• Vertical offset (crankshaft centerline to prop centerline): 200.66 mm (7.90 in)
• Available gear ratios: 1.724, 1.821, 1.926, 2.038, 2.160, 2.292, 2.435, 2.478, 2.591, 2.762, 2.950, 3.158
• Propeller flange options: SAE ARP-880 (8-bolt/2-dowel), SAE ARP-502 (6-bolt/2-dowel)
• Bearing type: hydrodynamic fluid-film bearings (input and propeller shafts)
• Governor integration: AND-20010 pad, vibration-isolated gear drive, internal control plumbing; Beta/reverse capability supported
• Alternator: bellhousing provision for secondary alternator (electrical redundancy)
• Lubrication: engine scavenge/pressure system or stand-alone dry-sump with pump(s), cooler, filter adapter and plumbing
• Monitoring: chip detector, inlet/outlet oil temperature sensor locations, oil pressure sensor location
• Testing: component break-in, continuous run-in at variable loads (up to full throttle), endurance testing (examples up to 60+ hours)
• Installation allowances: prop shaft extension increments available up to +2 in if needed for cowling/clearance