Logic means the teaching of the principles for the correct thinking. Such thinking is considered logically correct, if a true assumption leads to a true conclusion.

A true assumption for the optimal engine in an airplane is for example: a light, reliable and low fuel-consumption engine. Requirements that since the beginning of powered flight haven’t changed and their performance decided what an efficient airplane engine is and what it is not. This is reason enough to take the performance of those three assumptions and scrutinize them closely.

From the principles, the lightest engine with a pretense power is the one with the more favorable quotient of power and weight, Kg/HP.

Without a doubt, next to the turbine, it’s the two-stroke gasoline engine. Today, 2 cycles with the usage of modern technology, power of 110 HP (81KW) with an engine installation weight of approximately 60Kg can easily be reached. This results in approximately 2 HP per kilogram of engine weight without reaching the boundaries of the feasible; the modern four-stroke engine without the turbine charger shows in comparison a ratio of 1.1 HP per Kg. A four stroke with an installation weight of approximately 70 Kg, was only 66 percent of the power of a two stroke of equal weight. Because of this, almost all of the bigger automobile manufacturers have started to research the two-stroke engine with injection again.

From the principle, the most reliable engine is the one with the lesser moving parts in thermal and mechanical strain (load) and a lesser probability of failure.

The two-stroke engine with regard to one cylinder has only 3 parts with relative movement: crankshaft, connecting rod, and piston. A Four-stroke engine with simple design has a minimum of 9 moving parts: crankshaft, connecting rods, pistons, camshaft, 2 push rods, 2 levers, 2 valves and the necessary oil pump. Four-cylinder four stroke engines in comparison have a ratio of 9 to 35 moving parts, in favor of the two-strokes.

Also the two-stroke has per crankshaft turn one powerstroke, the four-stroke only on every second turn. At the same rpm and power, the powerstrokes in a four-stroke have to be more intensive. With that, the two-stroke has a much more harmonic power output with less vibration. The four-cylinder two stroke is almost turbine-like.

The engine with the optimal fuel consumption is the one which has the least specific fuel consumption at the most used power setting.

Since four-stroke engines are heavier than two-stroke engines, they use only 75% of the possible power in the cruising RPM range. An 80 HP (59Kw) standard four-cylinder-four-stroke engine with two-piston technology has a cruise power of 60 HP (44Kw) at a fuel consumption of approximately 16 liters per hour. At full take-off power, they have 20 HP of reserve available.

A modern two-stroke engine with similar piston displacement performs with 10 to 15 Kg less installation weight between 100 Hp to 120 HP (74Kw-88Kw). At 50 to 60% of the possible power, you already achieve the necessary cruise power of 60 HP (44Kw). The specific engine load is 15% less than the comparable four-stroke. In this partial load area, the two-stroke with an automatic fuel injection consumes approximately 15 liter per hour. With that, the two-stroke is also more favorable in the fuel consumption. For the take-off power the two stroke has an additional 40 to 60 HP available. This is at least double of what the comparable four-stroke has for usable reserves.

The most efficient engine for ultralight airplanes is the one with the least weight, highest reliability, moderate fuel consumption, and lowest operating expense.

The proportion for price comparison is the ratio of cost per HP (Kw). With the modern two-stroke engines, depending on the model, the cost per HP is usually one half the cost of 4-strokes.

The result of our logical consideration of an engine:

The modern two stroke engine is not only an alternative to the costly four stroke, the use of two cycle engines corresponds more with principles of the correct logical thinking. And logic in the area of technology is always the most important argument.


The new generation. We are proud to present you our new engine series. We have a total of 15 different engines from 15 HP (11 KW) to 110 HP (81 KW), air cooled 1-2 and 4 cylinders as well as water-cooled 2- and 3-cylinder will cover all applications. Light and high power engines with top quality. Special timing programmable ignition system, programmable fuel injection, new high temp resistant alloy and new gearboxes provide today a longer lasting and more reliable engine, which in the past seemed to be unattainable.

Hirth has made a substantial investment into the future. A young, innovative engineering team, a new development department, new research department, two new engine test stands for simulation of all applications, improved quality control and a special developed oil just for HIRTH engines.
“Future now” has been our motto for the past two years. Today we deliver more high power engines worldwide than ever before. The enthusiasm of our customer for our new generation engine shows us that our strong effort was worth it.


Tech’s, an abbreviation for technical specifications, means a particular technical layout, with which the engine puts their principle advantages in practice. In the past 2 years Hirth has set new standards and some of those standards you should be aware of.



In the past, due to weight limitations, the ultralight airplanes used the lightest two-stroke engine which still has the required power for a two-seater ultralight. The necessary conclusion: those engines often were running at 80 to 90 percent of the maximal power. That type of performance results in the two-stroke being very intensive in fuel consumption.

Today, Hirth presents a large model selection of extremely light two-stroke engines whose performance reaches from 15 HP (11 KW) to 110 HP (81 KW). This is the first time that a dealer or end consumer can choose from different engines, whose travel performance ranges from 50-60 percent of the load area. With a four-stroke, typical travel consumption and enormous start and climbing reserves, the engineering team from Hirth will advise you to get the perfect engine to fit your needs.

The combination makes it possible

In the past, the small, high performance two–stroke manufacturers suspended production of these engines due to the piston seizure. The cause in most of these cases was that in high thermal demand the pistons expand faster in size than the cylinder walls. This is a common problem when aluminum pistons are used in combination with steel sleeved cylinders.

Today at Hirth we have new material combinations which eliminates such failure. The light metal piston is made of a special alloy that expands slower under thermal load than the light metal cylinder walls. An engine seizure even under extreme conditions is nearly impossible. Beyond that, Hirth uses a new alloy for the cylinder heads which allow the engines to run for long durations at maximum power.


In the past, for example, military airplanes used oil, which even at a complete oil loss would guarantee an emergency run. That became famous under the name Mathy-Oil.

Today at Hirth we have our own oil with compatible quality for our engines developed in the USA-BlueMax. With that oil, it’s impossible to get corrosions, deposits on cylinder heads and carbon on piston rings. More than one dozen engines were destroyed on the test stands during the oil selection process.


In the past, the light crankshaft on the two-stroke engines couldn’t handle the load from the big and heavy propeller.

Today at Hirth we use only steel with the grade of 42 CroMo 4 to manufacture our own crankshaft. An extremely hard but also tough alloy. Costly in the processing but unrivaled in stability! That’s the only reason why Hirth offers a 3-year warranty on the crankshaft-independent of the hours of usage, the warranty still covers where others already require an exchange of the expensive parts.

Also, we have a tempering procedure for the cylinder walls on our two-stroke engines. With this procedure, the wear and tear on the cylinder walls is minimized. In reality, the new engines with the combination of all the measurements, after 1000 hours of usage the wear and tear on the cylinder wall is only two thousandth of a millimeter. Cylinder and piston exchange is usually not required for 1,000 hours.


In the past, a needle jet in the carburetor controlled the fuel supply to the two-stroke engines. Simply by the pilot moving the gas lever, a method that in the high powered sports leaves much to be desired.

Today at Hirth we developed a programmable fuel injection for our engines with that the following operating parameter will be established, air temperature, air pressure, engine temperature, exhaust temperature, RPM and throttle position with the recording of all those measurements it will be feasible to get the exact fuel-air-mix for each engine, only what the engine really needs. As much fuel as necessary and as less a possible. Up to 40% less than in the past.

With this procedure, it’s impossible to run the engine too rich or to overheat it. Temperature compensation and altitude compensation is completely automatic. It’s impossible to ice-up the carburetor.

Today the map-controlled injection from Hirth guarantees the optimal operating conditions which is automatically regulated and much more adaptable than a pilot could ever do with readjusting. All of that is possible because the not “thinking” needle jet was substituted with a natural feedback-regulation system. High performance at it’s best.


In the past everyone assumed that with an electronic double ignition the engine received the optimal ignition supply. An adjustment of the ignition point timing mark for each RPM did not happen-in favor of non-advancing adjustments.

Today at Hirth high performance engines have a double ignition where the timing mark can be adjusted depending on the RPM range. An engine will get the best parameter with the help of a laptop to set an optimal ignition in each case, no matter if you are a dealer or the end consumer. A service that seems to be exceptional, but it is not anymore, it’s what an airplane manufacturer or airplane dealer can require.


Early on a 2-seat Ultralight could not exceed maximum empty weight so it could be considered legal with a full gas tank and was within the boundaries for registration and insurance limits.

Today, very often 15Kg decide if a 2-seat ultralight obtains their registration as a 2-seater or can keep the registration. The modern four-cylinder engine with injection 3002/03 from Hirth has at 100 to 110 HP (81Kw) an optimal installation weight of only 60 Kg, the typical 5 Kg for oil and water are inapplicable. , also the costly installation of radiator, etc. Even with more power the 3003 is perfect for ultralights, with its inline fan cooling to decrease the weight and increase the power. An engine which reminds you of a turbine with it’s ride qualities.


Early on, the exhaust system of two-strokes was often black, sooty and even contained oil matter.

Today at Hirth the oil consumption of our engines was decreased by approximately l: 100 due to the described innovations. The cold trail of smoke and the bad exhaust emission data belong to the past, because of that the F-30 injection passed the ICOM-Test without any problems in 1998. Exhaust, which deserves a special exhaust system, the new, light-grade steel exhaust system from Hirth fulfills the wishes for a quiet and brilliant solution.


In the past, it was believed that the two-stroke engine was a temporary solution until a light build four-stroke engine would corner the market.

Today it’s different, our light and small four-cylinder two stroke engine with injection from Hirth can stand up to any four-stroke engine on the ultralight market. With power and sturdiness that can’t be reached by a four-stroke engine due to the principles. That’s the reason why the engineers in the ultralight and microhelicopter development believe that in the future, the majority of the sport airplanes will be equipped with a new generation of two-stroke engines.

Hirth is a pioneer in this development, with their new engine generation. Fit to take on any challenge in the future, with a 3-year warranty on the crankshaft and a 1-year on the complete engine-without limitations.