History Of Hirth Engines – Gobler-Hirthmotoren GmbH

September 1990: Ask most ultralight manufacturers what Rotax needs most and you’ll get the same answer — competition. Even though Rotax has made tremendous strides in the design, development and marketing of their engines; even though they have increased reliability substantially; even though they are increasingly responsive to the needs of their distributors and users; there is something unsettling about having only one engine manufacturer for ultralight airplanes.

The eggs of the industry as well as the financial future of all ultralight manufacturers are indeed in one basket. Hirth Engine Company, technically known as Gobler-Hirthmotoren GmbH & Co., KG, has been in the airplane engine business for a long time. Throughout their long history they have displayed an uncanny knack for being in the wrong place at the wrong time and involved with the wrong partners.

Hellmuth Hirth began making airplane engines back in 1930. In 1940 the company was forcibly absorbed by Ernst Heinkel. From the dates and circumstances of this “transaction” it can be safely inferred that old Hellmuth was paying too much attention to his engineering, and not enough attention to the staying on Der Furher’s good side.

After Adolph lit his last fire, the com­pany reformed in 1948 with a lot of the old talent and a lot of new. The company went into the manufacture of small engines for agricultural and industrial uses and gradually worked their way toward engines for snow mobiles and all-terrain vehicles. In 1975 the company was purchased by Hans Gobler and has since labored under the pon­derous moniker mentioned earlier.

Through marketing agreements with Rolls Royce and Continental Engines, as well as through their own efforts, Hirth engines in their various models from 3.5 to 75-horsepower have been spread across the globe.

In the late 70s Jim Bede — aviation’s answer to Tammy’s Jim Baker — ordered 5000 Hirth F-20s for his anticipated sales of the BD-5. He didn’t use Hirth manifolds though, but elected to design his own.

Furthermore, he didn’t do much testing on the torsional loads and resonance of his drive line. The end result was an engine which didn’t put out enough power and broke crank shafts after 75 hours. Once again, Hirth was on the ropes.

In 1987 Hirth made substantial changes to the design and manufacturing of their engines. They removed the steel-sleeved cylinders and replaced them with Nikasil-treated aluminum cylinders; they switched to chrome steel crankshafts and they changed the design and alloy of their pistons. They changed the design of their heads to provide more pre-combustion compression.

In fact, the post-1987 engine is a completely new product. Since the introduction of these new en­gines, they have received mixed reviews. Some of the engines ran for a long time, while others burned the number-one cylinder out in a few hours.

The heat problem was traced to the fact that the en­gines are very critical in cooling system de­sign and airflow. If you can keep enough air around the engine, and if the airflow is cor­rect, the engine runs okay.

In airplanes with cowlings and formal cooling systems, where some thought needs to be put into the baffling, the engines thrive. But it seems that when the engines are just hung on the airframe, as is the case in many ultralights, problems develop.

Hirth Reduction Drive Solutions

The fix for the cooling problems involves the orientation of the cylinder heads. Unlike many engines, the heads on the Hirth engines can be removed and turned to change the direction in which the cooling fins point.

The Hirth 263 and 2703 engines are fan cooled so the heads should be installed with the cooling fins perpendicular to the crank­ shaft. Cooling air is then drawn in at the magneto end by the cooling fan, routed into a cooling chamber and then through the fins via an air guide on the exhaust side of the engine.

A small but very important vane attached to the air guide directs the correct amount of air over cylinder number one. If this vane is missing, or misaligned, things are going to get quiet. After passing the cylinders and their heads the cooling air is expelled on the carburetor side of the engine.

The “other two-stroke engine flies all the way to Florida from Moline, Illinois in only 23 hours”.

In pusher con­figurations this air exhausts past the propeller. In tractor installations the cowl­ing and baffling must be so shaped as to en­ courage the discharge of air. If the engine cooling air exhausts into a high pressure area of the fuselage or cowling, it’s glider time again.

Of course, the cooling fins on free-air cooled engines should be aligned with the airflow. But considering the cooling difficul­ties inherent in the engine, it would seem prudent to use a fan-cooled engine and the latest edition of the Sky Prints Atlas, these will get you across the country in fine shape.

Furthermore, they don’t go out of date, if you keep updating the charts as soon as you receive them from Sky Prints every eight weeks. In addition to the reprint of the WAC charts, there’s also a list of all the MOAs and Restricted areas, with times closed and altitudes affected.

These are keyed by chart number so they’re very easy to find. Every type of chart and graph is in this manual, including a chart of the mileage between major cities.
Some of the information is repeated in both Atlases, but I’d rather have it with me in two places, rather than not at all.

The other book in the package is the IFR Atlas which has all the Low Altitude En­ route Charts from coast to coast. These meet FAA specifications for IFR use, but directives in the current update bulletin must be observed. Updates will arrive every 56 days.

These charts are all spiral bound and are very easy to use in the cockpit. Their use eliminates the endless folding and refolding of huge NOS charts which seemed to take forever, and never came out right. Howie’s charts are not printed in two colors, as are the FAA charts, but this doesn’t seem to cre­ate any difficulty in locating any of the in­ formation which was color coded.

The IFR Atlas starts off with an eight- page chart of the US, complete with terrain depiction. This is the chart to use to avoid the high-altitude areas during your cross­ country flight. Major terminal areas are presented in blown-up detail that make them very easy to read, and the information sim­ple to interpret.

The charts are coded so that you can go from one area to the next. For example, there are charts for TL, LL, TR, LR — which means Top Left, Lower Left, Top Right and Lower Right. Vertical charts are marked T, TC, LC, L — Top, Top Center, Lower Center, Bottom. IFR pilots who are accustomed to using Low Altitude charts will feel right at home with these, and VFR pilots will appreciate their simplicity.

During the month of July, I’m scheduled to fly from Apple Valley, California to Arlington, Washington, and I’ll use my new Sky Prints Air Chart Systems from Howie Keefe to plot my course. I’ll start by drawing a line between the two points, then determine which VORs along the route are closest. I’ll use charts 1, 3, 5, and 7.

Because my trip starts from a lo­ cation laced with MOAs and restricted areas, I’ll deviate from the straight-line approach and fly Palmdale, over the Tehachapis, and up the San Joaquin Valley.

Although this route is a few miles longer, flying over 500 miles of flat terrain is much smarter than flying in a straight line which would take me mostly over the Sierra Nevadas.
At the top of the San Joaquin, in Red Bluff, we run out of nice valley and must navigate the mountains.

We then head for Klamath Falls, Portland, Oregon, and on to Arlington, Washington which is just a little north of Seattle. If we were flying in a Lear or a Citation, we might choose a slightly different route, but since we’ll be flying in a 285-hp Navion, the valley route is much safer and smoother.

Now that I know my route of flight, I can transfer it to the closest VORs, and the charts will give me my headings and distances. In four hours, we’ll be needing fuel, so I’ll plan to stop at Redding, Red Bluff or Klamath Falls, depending on whether we’re getting headwinds, tailwinds or calm skies.

The charts indicate that there’s a tower at Redding, and that it’s operating on 119.8, ATIS on 124.1, Ground on 121.7, and Approach Control on 132.2c. The little “c” on the Ground Control frequency indicates that this Approach Control is via Center.

Hirth UAV starter generator

I would then list my VORs and courses, the first being to Palmdale direct 114.5, then a small dog-leg around a few restricted areas near Edwards AFB, over the Tehachapis to Shafter VOR, Visalia etc. — all the way to Arlington, Washington.

If you make each leg a separate flight, and list all the information needed for that section; before you know it, your whole flight plan will be complete. Because I’m familiar with the route of my proposed flight, having flown it quite a number of times, I chose not to take the direct route which would have taken me over some rocky terrain.

There’s no reason to have a rough flight over high mountains when a few extra miles of flying will take you over smoother, more accessible areas. It’s well worth the peace of mind we’ll get from knowing there’s a good place to land.

Individual manuals are also available: Sky Prints Aviation Atlas, East or West versions, IFR Atlas, East or West, GRAC Atlas and the Loran Atlas.

If you’ve priced charts lately, you know that Howie’s Air Chart Systems is definitely a good buy. What’s more, Sky Prints has been in business for 29 years, and they’ve always been very well respected by every­ one in the aviation industry.

early hirth two stroke engine


Hirth Engines International Inc. has announced the models F23 and 2703 engines are now available with twin Capacitor Discharge Ignition (CDI) systems. This feature has been long awaited by many ultralight and kit plane manufacturers and designers. Now, the already excellent reliability record of the CDI ignition is enhanced by a second compOlete system of spark plugs, coils, and CDI units.

In the unlikely event that one system should fail in flight, the second system functions to ensure flight completion. There are additional bonuses of extra power by the two simultaneous sparks and the fact that CDI produces a better, hotter spark. There being no points, almost no radio interference is produced. CDI improves quick starting. HIRTH engines have remarkably good starting whether in the heat of summer or in bitter winter cold.

The twin carb, twin CDI equipped HIRTH model 2703 produces a good 55 hp with automotive premium gasoline at a 50 to 1 mix with any brand name oil for 2 stroke air-cooled engines. Provided spark plugs are changed for next hotter rating, Aviation 100LL can be used. If plugs are not changed, they may collect lead beads in about 10 hours.

Many pilots of Quad City Challengers favor the HIRTH 2703 for its electric starter neatly tucked beside the engine instead of protruding forward. They also like the lighter weight, extra power and fuel economy of the HIRTH. So far, HIRTH engines in the Challengers have been almost trouble free. The engine has a 1000 hour rating before overhaul. A number of engines have exceeded 1000 hours with only regular servicing.

The HIRTH 2703 can be direct drive or equipped with a reduction drive. Several cogbelt, grooved belt, and gear boxes are available. The Challengers use a 2.2 or 2.4 to one cogbelt redrive. A cabin heat box is available for those wanting cabin comfort for winter flying. Most 2703 engines are installed with cylinders down. However, Falconar Aviation Ltd makes a remarkably efficient “Dynamount” for a cylinders-up configuration. By proper alignment, it ensures minimum thrust line deflection with application of power.

The other twin CDI engine is the 2 cylinder opposed F23. This engine weighs only 60 lbs. complete with electric starter. It used the same cylinders as the 2702 or 2703. The HIRTH CDI engines provide 1240 watts of electric power for lights, radio, etc. HIRTH engines use NIKASIL in the treatment of cylinder walls which makes the engine very resistant to seizure.

History Of Hirth Engines - Gobler-Hirthmotoren GmbH
Article Name
History Of Hirth Engines - Gobler-Hirthmotoren GmbH
A two stroke engine manufacturer with a history way back to World War 2.

Be the first to comment on "History Of Hirth Engines – Gobler-Hirthmotoren GmbH"

Leave a comment

Your email address will not be published.