title: Hirth F-23
text: # Hirth F-23
  
  The Hirth F-23 is a twin cylinder, horizontally-opposed, two stroke, carburetted or optionally fuel injected aircraft engine designed for use on ultralight aircraft. It is manufactured by Hirth of Germany.
  
  ## Development
  
  The F-23 is intended to compete with the 50 hp (37 kW) Rotax 503 and is differentiated from the Rotax powerplant by offering a horizontally-opposed cylinder layout. The F-23 uses free air cooling and piston-ported induction, with dual Bing 34mm slide or optional diaphragm type carburetors. The cylinder walls are electrochemically coated with Nikasil. Standard starting is recoil start. A belt reduction drive system, fuel injection, tuned exhaust and electric start are optional.
  
  The engine runs on a 50:1 pre-mix of unleaded 93 octane auto fuel and oil. Recommended time between overhauls is 1000 hours.
  
  The F-23 produces 50 hp (37 kW) at 6150 rpm and 40 hp (30 kW) at 5500 rpm.
  
  ## Applications
  
  * Aeronix Airelle
  * Air Sports AIRector 120
  * Aurore MB 02-2 Mini Bulle
  * DAR-23
  * Fisher FP-303
  * Monnett Moni - motorglider
  * Rotorschmiede VA115
  * Sadler Vampire
  * Solid Air Diamant LP
  * Spacek SD-1 Minisport
  * TechProAviation Merlin 100
  * Team Mini-Max AeroMax
  * TeST TST-1 Alpin
  * Wings of Freedom Phoenix 103
  
  ## Specifications (F-23)
  
  Data from Recreational Power Engineering
  
  ### General characteristics
  
  * Type: Twin cylinder, two-stroke, aircraft engine
  * Bore: 72 mm (2.8 in)
  * Stroke: 64 mm (2.5 in)
  * Displacement: 521 cc (31.8 cu in)
  * Length: 247 mm (9.7 in)
  * Width: 570 mm (22.4 in)
  * Height: 338 mm (13.3 in)
  * Dry weight: 84 lb (38.1 kg) including reduction unit, full exhaust system and electric start
  
  ### Components
  
  * Valvetrain: piston-ported
  * Fuel system: 2 X Bing 34mm slide or optional diaphragm type carburetor or fuel injection
  * Fuel type: unleaded 93 octane auto fuel
  * Oil system: 50:1 fuel/oil premix
  * Cooling system: free air
  * Reduction gear: cog belt with 1.8:1, 2.2:1 and 2.5:1 ratios optional
  
  ### Performance
  
  * Power output: 50 hp (37 kW) at 6150 rpm
  * Compression ratio: 9.5:1
  