Hirth F-23
# 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
