Hirth 3701
German two-stroke aircraft engine
title: "Hirth 3701" type: doc version: 1 created: 2026-02-28 author: "Wikipedia contributors" status: active scope: public tags: ["hirth-aircraft-engines", "two-stroke-aircraft-piston-engines", "straight-three-engines"] description: "German two-stroke aircraft engine" topic_path: "general/hirth-aircraft-engines" source: "https://en.wikipedia.org/wiki/Hirth_3701" license: "CC BY-SA 4.0" wikipedia_page_id: 0 wikipedia_revision_id: 0
::summary German two-stroke aircraft engine ::
::data[format=table title="infobox aero engine"]
| Field | Value |
|---|---|
| name | Hirth 3701 |
| engine_type | Three-cylinder two-stroke aircraft engine |
| manufacturer | Hirth |
| national_origin | Germany |
| :: |
| name=Hirth 3701 | image= | caption= |engine_type=Three-cylinder two-stroke aircraft engine |manufacturer=Hirth |national_origin=Germany |first_run= |major_applications= |produced= |number_built= |developed_from= |variants_with_their_own_articles=
The Hirth 3701 is an in-line three-cylinder, two-stroke, carburetted aircraft engine, with optional fuel injection, designed for use on ultralight aircraft and small homebuilts. It is manufactured by Hirth of Germany.
Development
The 3701 was developed as a liquid-cooled and narrower installation alternative to the four-cylinder Hirth F-30 air-cooled engine of 85 to.
The 3701 features triple Bing 34 mm slide carburetors or optionally fuel injection. The cylinder walls are electrochemically coated with Nikasil. Standard starting is electric start and recoil start is not available as an option. The reduction drive system available is the G-50 gearbox, with reduction ratios of 2.16:1, 2.29:1, 2.59:1, 3.16:1, or 3.65:1.
The engine runs on a 50:1 pre-mix of unleaded 93 octane auto fuel and oil, or optionally 100:1 oil injection.
Variants
;3701 high-torque/low-rpm engine :Three-cylinder in-line, two-stroke aircraft engine with three Bing 34 mm slide carburetors or fuel injection. Low piston port timing produces 84 hp at 4950 rpm with a very flat torque curve. ;3701 high-performance engine :Three-cylinder in-line, two stroke aircraft engine with three Bing 34 mm slide carburetors or fuel injection. High piston port timing produces 100 hp at 6000 rpm with a steep torque curve.
Applications
- Alliant Destiny Fusion
- Alliant Destiny XLT
- CGS Hawk II Arrow
- Eagle Helicycle
- Earthstar Thunder Gull II
- Quicksilver MX II
- Pietro Terzi Lucy THM
- InterPlane Skyboy
- Rans S-9 Chaos
- Zenair CH 601 Zodiac
Specifications (3701 high performance)
and start a new, fully formatted line with -- |ref=Recreational Power Engineering |type=Three-cylinder, two-stroke, in-line, aircraft engine |bore=76 mm |stroke=69 mm |displacement=939 cc (57.3 cu in) |length=490 mm |diameter= |width=280 mm |height=420 mm |weight=108 lb, including electric starter and exhaust system. With optional gearbox total weight is 127 lb, plus radiator. |valvetrain=piston ported |supercharger= |turbocharger= |fuelsystem=3 X Bing 34 mm slide type carburetors or fuel injection |fueltype=unleaded 93 octane auto fuel |oilsystem=50:1 fuel/oil premix or oil injection |coolingsystem=liquid |power=100 hp at 6000 rpm |specpower= |compression=9.5:1 |fuelcon= |specfuelcon= |oilcon= |power/weight=
|designer= |reduction_gear= G-50 gearbox with reduction ratios of 2.16:1, 2.29:1, 2.59:1, 3.16:1, or 3.65:1
|general_other= |components_other= |performance_other=
References
References
- Recreational Power Engineering. "3701S – 2 cycle 100hp".
- Ultraligero.Net. "3701–2 cycle – 100hp".
- Von Koschier, Angelo. (November 2003). "Helicycle".
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