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. The base price in 2009 was US$4423.

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:
Air Sports AIRector 120
Aurore MB 02-2 Mini Bulle
DAR-23
Fisher FP-303
Monnett Moni - motorglider
Sadler Vampire
Spacek SD-1 Minisport
TechProAviation Merlin 100
Team Mini-Max AeroMax
TeST TST-1 Alpin
Wings of Freedom Phoenix 103

Specifications:
F-23
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
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
Power output: 50 hp (37 kW) at 6150 rpm
Compression ratio: 9.5:1