Rotax 503

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Aircraft engine

title: "Rotax 503" type: doc version: 1 created: 2026-02-28 author: "Wikipedia contributors" status: active scope: public tags: ["air-cooled-aircraft-piston-engines", "rotax-engines", "two-stroke-aircraft-piston-engines"] description: "Aircraft engine" topic_path: "general/air-cooled-aircraft-piston-engines" source: "https://en.wikipedia.org/wiki/Rotax_503" license: "CC BY-SA 4.0" wikipedia_page_id: 0 wikipedia_revision_id: 0

::summary Aircraft engine ::

::data[format=table title="infobox aero engine"]

FieldValue
name503
imageRotax 503 display.JPG
captionRotax 503 trade show display
engine_typePiston aero-engine
manufacturerRotax
national_originAustria
major_applications
produceduntil 2011
::

| name=503 | image=Rotax 503 display.JPG | caption=Rotax 503 trade show display |engine_type=Piston aero-engine |manufacturer=Rotax |national_origin=Austria |first_run= |major_applications= |produced=until 2011 |number_built= |developed_from= |variants_with_their_own_articles= ::figure[src="https://upload.wikimedia.org/wikipedia/commons/6/68/Flightstar_II_C-IGRH_Rotax_503_engine_03.JPG" caption="Flightstar II]] ultralight"] ::

::figure[src="https://upload.wikimedia.org/wikipedia/commons/a/aa/Blue_Yonder_EZ_Flyer_Twin_Engine_03.JPG" caption="The prototype [[Blue Yonder Twin Engine EZ Flyer]] is powered by two 503s in pusher configuration"] ::

::figure[src="https://upload.wikimedia.org/wikipedia/commons/8/8c/Air_Creation_RACER_503_SL_C-IECN_08.JPG" caption="[[Air Creation Racer]] [[ultralight trike]] with Rotax 503 mounted up-right. Below the muffler is the smaller after-muffler."] ::

The Rotax 503 is a 37 kW, inline 2-cylinder, two-stroke aircraft engine, built by BRP-Rotax GmbH & Co. KG of Austria for use in ultralight aircraft.

For decades the engine was one of the most popular and reputedly reliable aircraft engines in its class (two-stroke, under 60 horsepower), and it remains widely used and supported.

As of 2011 the Rotax 503 is no longer in production. However, a Russian manufacturer has developed an approximate reproduction, the RMZ 500. Rotax subsequently offered only one other two-stroke engine for aircraft, the partially water-cooled Rotax 582.

Design and development

The Rotax 503 is piston ported with air-cooled cylinders and heads, utilizing either an engine driven fan and cowl, or free air cooling. Lubrication is either by use of pre-mixed fuel and oil or oil injection from an externally mounted oil tank. The 503 has dual independent breakerless, magneto capacitor-discharge ignition (CDI) systems. It can be equipped with either one or two piston-type carburetors. It uses a manifold-driven pneumatic fuel pump to provide fuel pressure. An optional High Altitude Compensation kit is available.

The engine's propeller drive is via a Rotax type B, C, or E style gearbox. The standard engine includes a muffler exhaust system with an extra after-muffler as optional. The standard starter is a recoil start type, with an electric starter optional. An integral alternating current generator producing 170 watts at 12 volts with external rectifier-regulator is optional. The engine includes an intake air filter and can be fitted with an intake silencer system.

Limitations

Rotax recommends teardown and inspection every 150 hours, and overhaul every 300 hours.

The manufacturer acknowledges the design limitations of this engine, warning pilots:

Applications

Specifications (503)

|ref=OPERATORS MANUAL FOR ENGINE TYPES 447, 503 & 582 |type=two-stroke air-cooled aeroengine |bore=72 mm (2.84 in) |stroke=61 mm (2.4 in) |displacement=503cc 30.69 (cu in) |length= |diameter= |width= |height= |weight=31.4 kg (69 lb) (dry, no exhaust system) |valvetrain=piston ports |supercharger= |turbocharger= |fuelsystem=pneumatic pump pressurized |fueltype=regular autofuel |oilsystem=premixed in the fuel at 50:1 or oil injection |coolingsystem=fan or free air |power=37 kW (50 hp) at 6800 rpm |specpower= |compression=10.8 (theoretical) |fuelcon=15 L/hr (4 US gph) |specfuelcon= |oilcon= |power/weight=1.18 kW/kg (0.72 hp/lb)

|designer= |reduction_gear=Rotax 'B' gearbox: 2.00, 2.24 or 2.58 ratios; Rotax 'C' or 'D' gearbox: 2.62, 3.00, 3.47 or 4.00 ratios

|general_other= |components_other= |performance_other=

|see also= |related= |similar aircraft= |lists=

References

References

  1. [[Rotax. (2006). "OPERATORS MANUAL FOR ENGINE TYPES 447, 503 & 582".
  2. Raisner, William: ''LEAF catalog'', pp. 6-105. Leading Edge Airfoils, 1995.
  3. Johnson, Dan: [https://bydanjohnson.com/whats-affordable-in-2022-a-new-503-wheeled-carriages-and-two-place-ppgs/ "What’s Affordable in 2022? A New “503,” Wheeled-Carriages, and Two-Place PPGs,"] February 3, 2022, ByDanJohnson.com, retrieved June 29, 2023
  4. Prizio, Dave: [https://www.kitplanes.com/firewall-forward-rotax-service-training/ "Firewall Forward: Rotax service Training,"] July 19, 2013, ''Kitplanes,'' retrieved July 5, 2023
  5. "Rotax Website - Aircraft Overview". Brp-powertrain.com.

::callout[type=info title="Wikipedia Source"] This article was imported from Wikipedia and is available under the Creative Commons Attribution-ShareAlike 4.0 License. Content has been adapted to SurfDoc format. Original contributors can be found on the article history page. ::

air-cooled-aircraft-piston-enginesrotax-enginestwo-stroke-aircraft-piston-engines