The Hirth 3701 is an in-line three-cylinder,

two-stroke A two-stroke (or two-stroke cycle) engine is a type of internal combustion engine that completes a power cycle with two strokes of the piston, one up and one down, in one revolution of the crankshaft in contrast to a four-stroke engine which re ...

, carburetted aircraft engine, with optional

fuel injection Fuel injection is the introduction of fuel in an internal combustion engine, most commonly automotive engines, by the means of a fuel injector. This article focuses on fuel injection in reciprocating piston and Wankel rotary engines. All c ...

, designed for use on

ultralight aircraft Ultralight aviation (called microlight aviation in some countries) is the flying of lightweight, 1- or 2-seat fixed-wing aircraft. Some countries differentiate between weight-shift control and Aircraft flight control system, conventional three-a ...

and small homebuilts. It is manufactured by

Hirth Hirth Engines GmbH is an engine manufacturer based in Benningen, Germany. It is currently a part of the UMS Aero Group. Hirth began manufacturing aero engines in the 1920s, was taken over by Heinkel in WWII to develop the Heinkel-Hirth jet en ...

of Germany.

Development

The 3701 was developed as a liquid-cooled and narrower installation alternative to the four-cylinder

Hirth F-30 The Hirth F-30 is a horizontally opposed four-cylinder, two-stroke, carburetted aircraft engine, with optional fuel injection, designed for use on ultralight aircraft and homebuilts. It is manufactured by Hirth of Germany.Cliche, Andre: ''Ul ...

air-cooled engine of . The 3701 features triple Bing 34 mm slide carburetors or optionally fuel injection. The cylinder walls are electrochemically coated with

Nikasil Nikasil is a trademarked electrodeposited lipophilic nickel matrix silicon carbide coating for engine components, mainly piston engine cylinder liners. Development Nikasil was introduced by Mahle in 1967 and was initially developed to allow W ...

. Standard starting is electric start and

recoil start Rope start (also called ripcord , ''pull start'', or ''rewind start'') is a method of starting an internal combustion engine, usually on small machines, such as lawn mowers, chainsaws, grass trimmers, ultralight aircraft, small outboard mo ...

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 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 at 6000 rpm with a steep torque curve.

Applications

Specifications (3701 high performance)

References

External links

* on

Archive.org The Internet Archive is an American non-profit organization founded in 1996 by Brewster Kahle that runs a digital library website, archive.org. It provides free access to collections of digitized media including websites, software applic ...