The Hirth 2704 and 2706 are a family of in-line twin 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 (up and down movements) of the piston during one power cycle, this power cycle being completed in one revolution of t ...

, carburetted aircraft engines, with optional

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

, 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 especially two seat ultralight trainers, single seat gyrocopters and small homebuilts. It was 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.Cliche, Andre: ''Ultralight Aircraft Shopper's Guide'' 8th Edition, pages G-3 and G-4 Cybair Limited Publishing, 2001. Purdy, Don: ''AeroCrafter - Homebuilt Aircraft Sourcebook'', page 72. BAI Communications. The series is out of production and were replaced by the

Hirth 3202 The Hirth 3202 and 3203 are a family of in-line twin cylinder, two stroke, carburetted aircraft engines, with optional fuel injection, designed for use on ultralight aircraft, especially two seat ultralight trainers, gyrocopters and small h ...

and 3203 in May 2002.

Development

The 2706 was developed as a competitor to the

Rotax 582 The Rotax 582 is a two-stroke, two-cylinder, rotary intake valve, oil-in-fuel or oil injection pump, liquid-cooled, gear reduction-drive aircraft engine manufactured by BRP-Rotax GmbH & Co. KG. It is for use in non-certified aircraft operating ...

and is similar to the

Rotax Rotax is the brand name for a range of internal combustion engines developed and manufactured by the Austrian company BRP-Rotax GmbH & Co KG (until 2016 BRP-Powertrain GmbH & Co. KG), in turn owned by the Canadian Bombardier Recreational Produc ...

powerplant in being a two-cylinder in-line engine, with dual

capacitor discharge ignition Capacitor discharge ignition (CDI) or thyristor ignition is a type of automotive electronic ignition system which is widely used in outboard motors, motorcycles, lawn mowers, chainsaws, small engines, turbine-powered aircraft, and some cars. It ...

, although it is air-cooled, compared to the 582's liquid cooling. The 2704 was developed from the 2706 as a de-rated version to compete with the

Rotax 503 The Rotax 503 is a , inline 2-cylinder, two-stroke aircraft engine, built by BRP-Rotax GmbH & Co. KG of Austria for use in ultralight aircraft.Raisner, William: ''LEAF catlog'', pages 6-105. Leading Edge Airfoils, 1995. As of 2011 the Rot ...

. Both the 2704 and 2706 use free air or fan cooling, with dual Bing 34mm 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 initially developed to allow Wank ...

. Standard starting is

recoil start Rope start (also called pull start or ''rewind start'') is a method of starting an internal combustion engine, usually on small machines, such as lawn mowers, chainsaws, ultralight aircraft, small outboard motors and portable engine-generators. A ...

with electric start 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 engines run on a 50:1 pre-mix of unleaded 93 octane auto fuel and oil, or optionally 100:1 oil injection.

Variants

;2704 :Twin-cylinder in-line, two stroke, aircraft engine with a single or dual Bing 34mm slide carburetor or fuel injection. Produces at 5500 rpm and has a factory rated TBO of 1200 hours. Still in production. ;2706 :Twin-cylinder in-line, two stroke, aircraft engine with dual Bing 34mm slide carburetor or fuel injection. Produces at 6200 rpm and has a factory rated TBO of 1000 hours. The 2706 was replaced in production in May 2002 by the Hirth 3203.

Applications

;2704 ;2706

Specifications (2704)

References

External links