Hirth – Archive

Hirth Engines general information:

Hirth Logo medium

Hirth has been in the engine manufacturing business since before World War 2. They made engines for the Luftwaffe during the war. After the war they were no longer allowed to make aircraft engines. To stay in business they began making two stroke engines for non aircraft purposes. Eventually as the ultralight aircraft industry began to take off they began to make engines for that market, and soon the UAV market as well. To this day, Hirth manufactures many models of two stroke engines for aviation, both manned and unmanned, but they still have no interest in the four stroke market. Hirth uses many modern designs, one of which is Nikasil cylinders. Nikasil has several advantages over the old steel sleeve design that Rotax uses. First of all, Nikasil wears far better than steel sleeves and will out last a steel sleeve many times over. Another huge advantage of using Nikasil in a two stroke is that it expands at the same rate as the piston making a piston seizure far less likely.  Another advance in two stroke technology pioneered by Hirth is  carbon fiber reed valves in place of piston porting or rotary valve porting. Reed valve porting is far more efficient than other forms of porting. It increases engine torque and reduces fuel burn. In the past reed valves were made of stainless steel and would eventually fatigue and crack or break off. With the advent of carbon fiber reed valves, that is no longer is an issue. We now can have all of the advantages of reed valves without compromising reliability. Another modern design that Hirth has developed for the two stroke aviation market is electronic fuel injection. Many of the problems that two stroke engines suffer from are related to improper jetting and prop loading. The fuel injection eliminates those issues by using an ECM to continually monitor the operating parameters of the engine and adjusting the fuel rate accordingly. The fuel injection also compensates for altitude and weather changes to keep the engine operating at peak performance in all conditions. Not only does fuel injection help the performance, but it also keeps the engine cleaner, reduces fuel burn by about 10% and eliminates the possibility of carb ice. Other Hirth features include 4130 chrome moly crankshafts with a three year factory warranty, viton crank seals and more. Because of these modern design innovations Hirth is able to rate their engines at a 1000-1200 hour TBO. But keep in mind that it is still necessary to do a teardown, de-carbon and inspection at 500 hours. All of these Hirth engines are available with Electronic Fuel Injection (EFI) or carbs. Oil injection is also available on all of these engines except the 3002/3003 models. However, I personally do not recommend oil injection. While it is conveinent, it is a mechanical device that can fail. It also does require the pilot to monitor the oil usage and make sure it is working properly. Also, it is my suspicion that oil injected engines have a higher failure rate and do not last as long as pre-mix engines. I do not have hard data to prove that, so it is just an opinion. So far in nearly 10 years of selling Hirth engines, the only one that has failed was an oil injection failure (although that may have been an installation error)

Warranty:  The Hirth factory warranty is one year from the date of purchase for the entire engine.  The crankshaft is warranted for 3 years from date of purchase.  For new Hirth engines purchased from Heavenbound Aviation we offer a limited warranty for an additional 4 years, giving you a total of 5 years of warranty.  Our limited warranty covers all labor fully and parts at our cost for any failure, not including operator error, abuse, or routine maintenance.  We do this for two reasons.  First, there seems to be a skepticism about Hirth engines and their reliability among the Rotax crowd.  I will put my money on Hirth engines.  Secondly, if there is a failure in any engine I sell, I want to know about it, and to be the one to find out what failed and why so we can prevent it in the future.  Often when an engine fails in the experimental world it simply gets repaired without finding the original cause.  That means that it may happen again to that engine, or to someone else.  At Heavenbound Aviation, our goal is to make ALL engines as reliable as absolutely possible.  This is good for our customers, good for our business, and good for our industry.

Hirth F33F33-pic

The Hirth F33 is a single cylinder, 28 HP engine that is uniquely suited to the part 103 ultralight category. Weighing only 40 lbs including the belt reduction drive it is in most cases the only engine that can actually make weight on a Part 103 ultralight. Using all of the same technology that the larger Hirth engines use, even including dual ignition, this is a high quality aircraft engine from the drawing board up. It can even be equipped with electronic fuel injection if desired. In many cases the F33 can even make ultralight weight with electric start! The F33 is the only engine I am aware of currently that can make ultralight weight on a Challenger. It is also used on the Aerolite 103 to make Part 103. The F33 is a very versatile, good performing and reliable engine.

Hirth 27022702 pic

The Hirth 2702, 40 HP is the smallest inline twin that Hirth produces. The 2702 is a very reliable and economical engine. It produces its HP at a lower rpm and with higher torque than most two stroke engines with it’s peak power being produced at 5500 RPM. The engine is very robustly built for a 40 HP engine, using many of the same components as the 65 HP 3203. Like all Hirth aviation engines it includes dual electronic ignition. The 2702 is a great replacement for the 447 in many applications. It’s only disadvantage is that compared to a 447 it is approximately 10 lbs heavier. In an application that requires a gearbox, the 2702 is fitted with the G50 gearbox. While the G50 gearbox is a excellent gearbox and rated for up to 100 HP, it does increase the weight even more.  However, the 4V belt drive can be used on the 2702 which saves weight and is less expensive.  For an aircraft that does not need to meet part 103, it is an excellent option. However, when considering all of the options, for a little more money and nearly the same weight you could opt for a 3202 at 55 HP.  Or, if your airframe is compatible with it, you could use the F23 which is 50 HP and considerably lighter.

Hirth F23F23-picthumb

The Hirth F23, 50 HP engine is an incredible design. It is a horizontally opposed twin cylinder, free air cooled engine. This engine is a boxer engine with both cylinders firing at the same time. This makes an exceptionally well balanced and smooth running engine. The real beauty of this engine is that it puts out an honest 50 HP and weighs in at only 71 lbs complete including the belt redrive! That is 15 lbs lighter than a 447 with B box, and 10 more horsepower! The F23 should be the most popular engine in the single seat and light two seat market. The only real challenge for the F23 is the installation. Since most airframes were designed around inline twin cylinder engines, it can be challenging to work out a good installation. To further complicate things, it uses dual exhaust. But once the installation is worked out, it is an extremely reliable and durable engine. It is also a very economical engine. We have already completed an F23
installation on a Kolb Firefly, and will soon be working on a Challenger installation. There is an installation available for the Aerolite 103, and one is being developed for a
Quicksilver as well. Kolb F23 picIt appears that the F23 will also be the first of the Hirth line to achieve ATSM certification for Special Light Sport Aircraft.  Skycraft is working with Hirth to get the F23 certified for their SD-1 aircraft.  You can see those flying on youtube.  The F23 is also gaining popularity in the paragliding and powered parachute world.  I expect the F23 will be one of the most popular light sport engines in the future.  Check out our videos page to see the F23 Kolb in action.

Hirth 3202

3203-picThe Hirth 3202, 55 HP engine is a low rpm, high torque engine, making it’s peak power at 5500 RPM. It is a very powerful engine that works very well on many two seat light sport aircraft. This is an ideal engine for most of the Challenger line of aircraft as well as many of the Quicksilver models. The 3202 makes an excellent replacement for the 503. It will install easily in nearly any application that the 503 was used in, and will out perform it with no weight gain. Compared to the 503, the 3202 is the same weight, or if comparing both with electric start, the 3202 is little lighter. The 3202 offers a much higher TBO than the 503, and will burn less fuel, especially with fuel injection. The 3202 often looses out to the 3203 however, because for a little more money and no weight gain, it is possible to have an additional 10 HP.

Hirth 3203

The Hirth 3203, 65 HP, is nearly identical to the 3202, but is ported and tuned differently to make peak horsepower at 6500 RPM rather than 5500. This gives it a very respectable power to weight ratio. The 3203 is a direct competitor of the Rotax 582 in many applications. Since it is an air cooled engine it does not suffer from the downfalls of liquid cooling. Also, because it is air cooled it is far lighter installed than a 582. Not only that, but it costs less than a 582 when all of the installation components are factored in, and is far less complex to install. Really, the only installation where a liquid cooled engine has an advantage is when the engine is located in a tight cowl that cannot get enough airflow to the engine. That is not an issue in any of the airframes we sell however, and therefore an air cooled engine is superior in every way for our application. Honestly, the only valid reason I can come up with for using a liquid cooled engine on a ChallIMG_9930enger or GT Quicksilver would be for better cabin heat. But I think a good snow suit would be a much better option when considering all the negative tradeoffs.  Another category where the 3203 trumps the 582 is fuel burn. The 3203, especially with fuel injection, will use noticeably less fuel. The 3202 and 3203 are my favorite engines for most Challenger models, as well as two seat Quicksilver models and the GT400.

Hirth 3502/3503

350X-picThe Hirth 3502, 60 HP and the 3503, 70 HP are liquid cooled versions of the 3202 and 3203. They share the same crankshaft, pistons, and the same bore and stroke. They were created primarily to be a drop in replacement for the 582. They use the same bolt pattern on the crankcase and can therefore use the same mount, as well as the same radiator system as a 582. Unlike the 582, these engines have all of the modern advances Hirth engines are know for such as reed valve porting, nikisil cylinders, viton seals, and electronic fuel injection if desired. While I would choose a 35 series engine over a 582, I would still not recommend it for our application in most cases. The 3203 is simply a better choice and more cost effective. However, if someone has an existing aircraft with a dead or dying 582, this would be a simple change out and might make a lot of sense.

Hirth 3702/3703

3701-pic3The Hirth 3702, 84 HP, and 3703, 100 HP engines are three cylinder inline water cooled engines. These engines certainly have a place in the light sport aircraft world, allowing a lot of power to be put into a narrow cowl, and with an amazing power to weight ratio. In the airframes that we sell, the only one that could possibly make use of this engine would be a GT500, but to my knowledge it has never been done. The 3002/3003 engine would probably be a better choice for that application.

Hirth 3002/3003

300X picThe Hirth 3002, 80 HP, and 3003, 110 HP engines are unique in the industry. The are a four cylinder horizontally opposed air cooled engines. The 3002 is tuned for high torque, low rpm, and the 3003 is tuned for high horsepower. These engines are a great alternative to the Rotax 912 series engines. The installed weight of a 3002/3003 engine typically comes in at about 45 lbs less than a Rotax 912.  The thrust from the 3003 will leave a 912 in the dust.  Not only that, but it also comes in at about half the cost! The fuel burn of the 3002/3003 will be slightly more than a 912.  But the trade off is that you get exceptionally better performance. With a 1000 hour TBO, much less up front cost, and similar fuel burn, the overall cost of operation is much less.  Should you happen to fly enough hours to reach TBO, you will find that for around $4000 you can have a full overhaul completed with new pistons, crank and all.  If you hit TBO in a 912 you are going to find that it is more economical to sell the engine on ebay and buy a new one.  It is cost prohibitive to overhaul in most cases.   Along the way, you will spend a small fortune keeping up with the AD’s and maintenance of the 912, with parts prices that are off the chart and often not readily available.  Keep in mind also that when comparing the cost of a 912 to other options, the price of the 912 does not include a lot of necessary parts for the installation such as exhaust, radiator, oil cooler, etc…

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