ARTICLE DATE: August 1974

Herr Limbach’s Flying Beetles

SICHER, ZUVERLAESSIG, SPORTLICH, and sparsam, which translates from German into safe, reliable, sporting, and economical. This not only describes the engines built by Herr Peter Limbach (EAA 75951) in his motorenbau, or engine plant, near Bonn, West Germany, but it seems to be the motto of his whole operation.

When that issue hit the newsstands in Europe, I had just completed initial contact with Mr. Limbach in the hope of writing an article for SPORT AVIATION. Obviously, a day late and a Deutsch Mark short!

Mr. Cox, Editor-in-Chief of SPORT AVIATION, still wanted to provide additional information that might be of interest to the home builder movement, and Peter Limbach will have a display at Oshkosh this year, so he gave me two weeks to complete this article as he had a deadline to meet for this issue.

The Army has become liberalized recently, but spare time for a Lieutenant Colonel is still precious. All of this to say, please accept what may appear as a true amateur effort which, after all, is the idea of EAA.

Mr. Cox said that ideally the article should include historical information, development experiences on the engines, a listing of various aircraft that use them, a good description of each model with specific details, and any other info I consider significant.

As I’m no Hemmingway, Dick Bach, or Ernest K. Gann, that is probably as good an outline as any, so here goes. Peter Limbach was born in the same building he now uses for a factory. He says the family dates back a thousand years and used to be robber barons in this area.

As you’ll see later in the article, his engines are expensive, but I’m certain not for this reason. He got into the VW engine business by doing VW engine rebuilding. As Volkswagen didn’t appreciate his competition and he enjoys a good working relationship with them now, he asked that I not get into this subject.

I remember many of my dreams included flying my Mooney Mite with a turbocharged and geared VW that I’d built from a reconditioned short block bought from mail order catalogues and blasting non-stop California to New York for a new light aircraft record.

Little did I know that Peter Limbach might have been right in there with me. I can speak with authority that the weakened U.S. dollar which used to buy four German Deutsch Marks (DM) now only buys around 2.50 DM, and the cost of labor in Germany has gone up at least as rapidly as it has in the U.S.

After Peter delivered about 25,000 rebuilt engines, the basic law of economics caught up and the U.S. market for rebuilt engines disappeared. He hasn’t done any of this work since 1969.

Rebuilding an engine is a tremendous education, and when you’ve done 25,000 you pretty well know everything that can go wrong: which parts suppliers build less expensive yet reliable spares, and what basic design weaknesses must be corrected.

Now, if you want to eat and engine building/rebuilding is your business, you’ve got to find a new outlet. Peter admittedly had no knowledge of the airplane business in 1969, but has learned an amazing amount since.

After listening to him describe in detail some of the mistakes they’ve made, the costs involved in initial design and engineering development and testing, redesign, construction, and assembly, the thought of depending upon continuing life flying behind a converted VW the way most homebuilders do sort of sickens the stomach, while making dreams of converting a VW engine from the local junk yard bankrolled by the quarters stolen from the wife’s cookie jar fade rapidly.

Without the kind assistance of Volkswagen, it would be impossible for the Limbach engines to exist. The cost of development and manufacture of a new engine from scratch which meets the FAA requirements either in Germany or the U. S. is prohibitive for the small-time operator.

Volkswagen provides a short block “kit” from the industrial engine line, one hundred units at a time. By buying a minimum of one hundred, Peter gets a discount. The “kit” includes the housing or block, crankshaft, camshaft, heads with valves installed, connecting rods, and assorted bearings and hardware.

This is a bulk shipment and not from the spare parts department. In return Peter must guarantee that none of these components or assemblies will ever be put in a car.

The cooperation with Volkswagen is sufficient to permit Peter to specify which parts he wants in the “kit” and a combination of parts from several engine models will be supplied if he specifies them. Once the short blocks are at the Limbach factory, they are completely checked for airworthiness by a qualified inspector on Peter’s staff or himself.

Since 1969 he has not only learned a lot about aircraft needs, but he has obtained the aircraft engine inspector license from the LBA, which is the German equivalent of the FAA. Then the modification process begins. Peter prefers mounting all accessories on the flywheel end of the engine and has designed a mounting plate for this purpose.

He believes better cooling can be achieved this way and the engine looks more streamlined. He machines a taper for the propeller hub, installs a thrust bearing, and magnafluxes the crankshaft.

Volkswagen had previously magnafluxed the shaft prior to shipment and in the future Peter hopes to get approval from the LBA and the FAA for Volkswagen to accomplish all the required inspections on the parts they supply before shipment, thus saving him this expense.

The accessory case receives several components from several manufacturers around Europe and in the U. S. The magneto for the single ignition engines is a Slick No. 4030, which costs only about $65.00 with the shielded harness.

If he is making a double ignition engine, then he uses a Bendix D2000 magneto and high temperature harness which has one drive for two siamesed magnetos and costs approximately $400.00 in Germany.

Depending on the installation required or power output desired, Zenith 28RXZ, two Stromberg-Zenith 150CD, or, on the big engine, two Stromberg-Zenith 175CD carburetors are used.

Use of an American aircraft carburetor under the engine could eliminate the need for a fuel pump, but, again, the cost would be excessive, and as Peter says, “when you are asking for ten at a time, they won’t even talk about a discount”.

So, an APG 17.09.001A fuel pump is adopted. The starter is usually placed on the accessory pack and is a Fiat 76-0.5AP (12V/130 Amp) unit chosen for reliability and light weight. If he mounts a starter gear behind the propeller hub, then a .4HP Bosch Aircraft unit is installed.

The alternator is either a Ducati Type 610-12 Volt/150 Watt or a Ducellier Type 7522-12 Volt/22 Amp and, again, either driven from the accessory panel or by a belt at the fan pulley end. As they are German engines, Bosch Aircraft spark plugs are used.

Unlike Continental, Lycoming, Franklin, etc., Peter must engineer his engines to work in aircraft already flying or on the drawing board. The manufacturer shows him a drawing and says, “this space is for the engine”, and then it’s up to Peter to rebuild a VW to fit.

As a result, Peter has a large number of different models licensed for installation. There is a code system like that used by German auto manufacturers to designate car models which is used to describe each of the eight engines presently licensed.

Since Sport Avia, a general aviation manufacturer of powered gliders and sport aircraft, initially encouraged his efforts and assisted him in development of an engine for their RF5-powered glider, the first letter designation is S.

The second is L for Limbach. The numbers following generally indicate displacement; the next letter is either E for ein, meaning one, or D for double, signifying single or double ignition.

The next letter is the alphabetical series of the line and, finally, if it has a Roman numeral I, it is designed to accept a variable pitch propeller. Example: The SL2400 EBI is the 2368 cc single ignition engine which is the second development of this series and can handle a variable pitch prop.

The series includes to date:

Model	Take Off Power	Continuous Power
SL 1700 E and E	68 HP at 3600 RPM	61 HP at 3200 RPM
SL 1700 EA and EA	60 HP at 3550 RPM	56 HP at 3300 RPM
SL 1700 EB and EBI	72 HP at 3600 RPM	66 HP at 3200 RPM
SL 1700 EC and ECI	68 HP at 3600 RPM	61 HP at 3200 RPM
SL 1700 D	65 HP at 3600 RPM	60 HP at 3200 RPM
SL 1900 D and DI	74 HP at 3600 RPM	65 HP at 3200 RPM
SL 2400 EB and EBI	85 HP at 3000 RPM	85 HP at 3000 RPM

That last figure is not a misprint as he limits the RPM due to the long 2.79 inch stroke, but feels it can maintain this power setting indefinitely. The SL2400 modified with double ignition has been built and is the engine Peter thinks would have the best chance for volume sales in the U.S.

It is based on the VW 411/412 series engine that is also used in the two liter Porsche 914 and has inherently better cooling characteristics. It has not been certified by the LBA at this time, but should have no problem meeting the specifications.

Peter will have this engine along with another experimental model, the SL 1700 EF, that can be mounted inside the fuselage of an aircraft using a squirrel cage blower for cooling, (BD-5 builders take note, it only needs a dry sump) and two of the LBA certified models at his Oshkosh display booth.

Two of the engines will be fitted with the Hoffman propellers especially designed for this installation. One of the certified models is considered by Peter to be perfect for the Evans VP-2 and an installation in an immaculate VP-2 is being engineered with a complete cowling by Sport Avia at this time.

The requirement to develop so many different models has a positive spin-off in the effective elimination of all competitive VW modifiers and other engine builders, less Rolls Royce, in Europe.

At this point I think a comparison chart between two of the normally recognized U. S. competitors is appropriate. I chose the Continental A65 and Franklin 2A-110 with statistics from a 1965 edition of Janes — All the World’s Aircraft.

	Continental A65-8F	Franklin 2A-110	Limbach SL 2400 EB
Displacemen t Y	171 cu in – (2800 cc)	118 cu in – (1935 cc)	2368 cc
Weight	167 lb	130 lb	188 lb
Compression	6.3:1	10.5:1	8:1
H.P.	65 at 2300 RPM	60 at 3000 RPM	85 at 3000 RPM

The Limbach engines are inherently quiet and vibrationless as they are derived from automobile engines that require closer tolerances to keep mechanical noises to a minimum. Presently, Peter has approval for 800 hours between overhauls on all the LBA certified models and is striving for 1000 hours.

He goes into great lengths to explain why his engines, which are almost all used on powered gliders, require more stamina than a standard aircraft model. A man used to getting into his beetle, starting the engine, and immediately driving off will expect to do the same in his Volkswagen-powered glider.

He starts the engine, applies full power, climbs out at maximum rate of climb and often maximum angle of climb so that minimum cooling air is available. Upon reaching his desired altitude just as the valves are becoming molten, he shuts down to soar with the birds. If the engine should begin to diesel at this point, he pulls up into a stall to force the engine to stop.

When he gets so low that one more turn will put him into the base of an alp, he initiates a re-start and expects, in fact, demands, that the engine immediately start and provide maximum power to extricate him from his predicament and initiate a new climb.

Powered glider pilots who have engine failures and land in some farmer’s field are not required to file a report, and often, if they forget to put the wheel (gliders only have one) down and cause the engine to make a rapid stop, merely install a new propeller and fly on. Peter has overhauled some of his engines after their experiencing several of these “stops”.

To get 800 hours out of any engine with this kind of treatment is certainly commendable and a demonstration of his engineering ability. Peter feels that 300 hours between rebuilds may be OK for the homebuilder, but 1000 hours is mandatory for an FAA licensed commercial product.

What will an engine cost? Peter believes he can produce a basic single ignition engine without electrics and a Slick magneto suitable for a powered glider and sell it in the States for $1,000.00 if demand is high enough. The SL 2400 with dual ignition and all electrics would cost 5000 DM or about $2,000.00 in Germany.

If some of the U.S.-made parts were installed there, saving the 125% duty and markup, and a fairly large production run of several thousand units were manufactured, this price could be reduced considerably. Peter has invested two hundred thousand dollars in the project and sold only five hundred engines.

Obviously, the price must remain high at such low volume. Not to be overlooked at this point is the fact that most of the moving parts needing replacement at overhaul time are derived directly from Volkswagen.

What causes such high costs when every EAA member knows you merely bolt a prop on the fan pulley end, stick a magneto where the distributor was, and go flying? Peter showed me a welder at work on a novel (as Mechanics Illustrated would say) heat exchanger which cools the oil while warming the fuel air mixture.

He is paid 20,000 DM ($8,000.00) per year. Peter also pays into the German version of Social Security and has a participation-type shop with profit-sharing features. So, if the man works on the development of one part through several stages of testing, redesign, and construction, he may spend 2 years before they have a satisfactory solution.

The labor alone costs Peter $20,000.00. The movement of the outlet for the balance tube on the intake manifold only two inches from its original location costs $200.00.

Peter has to pay $84.00 per hour to run his engines on the Sport Avia test stand. What have all these costs bought in the way of providing a reliable aircraft engine? Basically, so many modifications that the engine can in no way be considered a VW.

To stay cool, VW heads require 500 liters of air blowing past them each second. Merely placing them out in the airstream will not accomplish this requirement because the way they are finned the air must blow down over them, not horizontally along them.

To complicate matters there is only one head on each side instead of one per cylinder so that the area between the cylinders gets a bit warmer (makes one wonder about a Corvair engine). When modifying for double ignition, Peter casts a new head with extra metal around the second spark plug hole.

Merely having an additional hole results in only three threads holding the plug and no assurance that he didn’t drill through a crack. Again, on the double ignition heads a special, complex valve housing is cast with the intake manifold reversed to come up from underneath and pass through it.

This removes all manifolding from above the engine to allow maximum flow of cooling air over the heads. Peter manages to keep the head temperature s around 250° and obtains very tight seals, deploring any oil leakage.

In fact, while touching one of his engines he got a drop of oil on his hand and exclaimed, “What’s that?”, to. which his son, a budding engineer, said, “Oil”!, after which followed a heated exchange with one of the workers in rather expressive German.

Peter presently builds engines for the full line of Sport Avia motor gliders and sport aircraft, Alexander Schleicher’s new ASK 16 motor gliders and some interesting experimental designs that offer outstanding performance. The future appears even brighter for Peter if the file of interested letters representing a virtual Who’s Who of Aviation is any indication.

The File included –

• Champion Motors (Israel) Limited;

• Caproni of Italy, for motor glider Calif A-21;

• SAAB Aerospace Division of Sweden for a helicopter study;

• Pilatus of Switzerland for a motor glider project;

• Rene Fournier of France for a new motor glider project;

• Karl Yager of Australia, conducting experimental aircraft work;

• Eligiro of Italy, who wants to continue development of the Finnish JT-5 Autogyro;

• Technoimport of Romania, planning a motorized sailplane;

• LTC Windover, a friend of mine from Canada, who is in charge of the Canadian Air Cadet Training Program and plans to build 200 Pazmany PL-4’s for use by the Air Cadets. (He will do an aerobatic demonstration with the PL-4 at Oshkosh.)

Avia export of Russia, inquiring on prices and delivery times; and Ladislao Pazmany, T. Claude Ryan, W.S. Evans, Ernest Schweize and James R. Bede, who need no further introduction to the readers of this article.

Peter wants to concentrate on finishing certification of the model he has developed at this time before embarking on any new projects. His mind is constantly active, and I saw in his drafting room plans for geared and belt-driven reduction systems.

Peter prefers gears for less bulk and weight. He thought the use of the second gear from a VW would give just the reduction he needed until Volkswagen said it only had a life of 50 hours at 75% power.

How many experimenters with reduction systems know the design life of their components? He also had drawings for additional mounts, flanges, tighteners, electronic ignition, mechanical fuel injection, turbochargers, etc.



He showed me a color photo of an experimental turbocharged, fuel injected, and dual ignition engine he has built, but considers the cost of certification, coupled with expected demand, to be prohibitive. I asked him why he didn’t use Volkswagen’s electronic fuel injection instead of carburetors.

He said he did try it, but the engine quit every time they used the radio transmitter. Volkswagen knew this, but forgot to mention it to him. He has an interesting solution for shock loads associated with starting a geared engine.

A clutch which is always engaged, but capable of slipping slightly eliminates transmission of the shock load to the engine. He hopes to get financial help from the German government and the Hoffman Propeller Company to develop his geared engine, because reduced propeller speed will greatly reduce noise pollution.

His engines are down to 60-68 DB at 3000 RPM, but the propeller tip speeds are too near sonic velocity. All of his experiments have been greatly helped by Herr Wagner of the German LBA, and Peter asked that I mention his welcome assistance in this article.

I hope I have generated some interest in Peter Limbach’s work, and that many of you, especially the Pazmany, Aerosport, Evans-VP, Monnett, Teenie Two and maybe even the BD-5 types lucky enough to attend this year’s fly-in will take the time to visit with him at his display.

Now, if Peter would let me have his experimental, dual ignition, and injected turbocharged model, and I could buy back my old Mooney Mite.

Limbach SL 1700 EB EBI



LIMBACH SL 1700 EB & EB I
Type	Four cylinder, horizontally opposed air cooled engine, with single ignition
Maximum HP (5 min.)	72/3600 rpm
Continuous HP	66/3200 rpm
Bore	88 mm/3.46 inch
Stroke	74 mm/2.91 inch
Displacement	1800 cm3
Compression Ratio	8:1
Firing Order	1-3-2-4
Spark Plugs	Bosch WB 240 ERT 1
Magneto	Slick No. 4030
Harness	Slick High Temperature
Propeller Drive	1:1 (anti clockwise)
Fuel Min Octane	90
Carburetor	2 Stromberg-Zenith 150 CD
Fuel Pump	APG 17.09.001
Starter	Fiat 0.5 HP
Alternator	Ducellier 250 W
Oil Capacity	2,5 1/2.64 quarts
Dry Weight approx	74 kg/164 lbs
Propeller Flange	EB: for solid propeller – EB I: for Hoffman variable pitch propeller
LBA Type Certificate No. (for use in "Powered gliders")	4582

Sportavia Limbach SL 1700 E & EI



SPORTAVIA — Limbach SL 1700 E & E I
Type	Four cylinder, horizontally opposed air cooled engine, with single ignition
Take Off HP	68/3600 rpm
Continuous HP	61/3200 rpm
Bore	88 mm/3.46 inch
Stroke	69 mm/2.71 inch
Displacement	1680 cm3/102.51 cubic inches
Compression Ratio	8:1
Firing Order	1-3-2-4
Spark Plugs	Bosch WB 240 ERT 1
Magneto	Slick No. 4030
Harness	Slick High Temperature
Propeller Drive	1:1
Fuel Min Octane	90
Carburetor	Stromberg Zenith 150 CD
Fuel Pump	APG 17.09.001
Starter	Fiat 0.5 HP
Alternator	Ducellier 250 W
Oil Capacity	2,5 1/2.64 quarts
Dry Weight approx	73 kg/161 lbs.
Propeller Flange	E: for solid propeller – E I: for Hoffmann variable pitch propeller
LBAType Certificate No. – (for use in "Powered gliders")	4582

Limbach SL 1700 EA & EA I



Limbach SL 1700 EA & EA I
Type	Four cylinder, horizontally opposed air cooled engine, with single ignition
TakeOff HP	60/3550 rpm
Continuous HP	56/330 rpm
Bore	88 mm/3.46 inch
Stroke	69 mm/2.71 inch
Displacement	1680 cm3/102.51 cubic inches
Compression Ratio	8:1
Firing Order	1-3-2-4
Spark Plugs	Bosch WB 240 ERT 1
Magneto	Slick No. 4030
Harness	Slick High Temperature
Propeller Drive	1:1
Fuel Min Octane	90
Carburetors	Zenith 28 RXZ
Fuel Pump	APG 17.09.001 A
Starter	Bosch 0.4 HP
Alternator	Ducati 150 W
Oil Capacity	2,5 1/2.64 quarts
Dry Weight approx	68 kg/150 lbs.
Propeller Flange	EA; for solid propeller – EA I: for Hoffmann variable pitch propeller
LBAType Certificate No. (for use in "Powered gliders")	4582

Limbach SL 2400 EB & EB I



Limbach SL 2400 EB & EB I
Type	Four cylinder, horizontally opposed air cooled engine, with single ignition
Maximum HP	85/3000 rpm
Continuous HP	85/3000 rpm
Bore	103 mm/4.06 inch
Stroke	71 mm/2.79 inch
Displacement	2368 cm3
Compression Ratio	8:1
Firing Order	1-3-2-4
Spark Plugs	Beru ED 225/14/3 m 5
Magneto	Slick No. 4030
Harness	Slick High Temperature
Propeller Drive	1:1
Fuel Min Octane	90
Carburetor	2 Stromberg-Zenith 175 CD
Fuel Pump	APG 17.09.001
Starter	Fiat 0.5 HP
Alternator	Ducellier 250 W
Oil Capacity	2,5 1/2.64 quarts
Dry Weight approx	85 kg/188 lbs.
Propeller Flange	EB: for solid propeller EB I: for Hoffmann variable pitch propeller
LBA Type Certificate No. (for use in "Powered gliders")	Not certified
(Note: the picture is of a dual ignition model, the SL 2400 D, otherwise specifications are identical with the EB and EB I.)

Limbach SL 1700 D – DI & 1900 D – DI



Limbach SL 1700 D & D I and 1900 D & D I
Type	Four cylinder, horizontally opposed air cooled engine, with double ignition 1700	Four cylinder, horizontally opposed air cooled engine, with double ignition 1900
Take off HP: (5 min.)	65/3600 rpm	74/3600 rpm
Continuous HP	60/3200 rpm	65/3200 rpm
Bore	88 mm/3.46 inch	90 mm
Stroke	69 mm/2.71 inch	74 mm
Displacement	1680 cm3/102.51 cubic inches	1883 cm3
Compression Ratio	8:1	8:1
Firing Order	1-3-2-4	1-3-2-4
Spark Plugs	Bosch WB 240 ERT 1	Bosch WB 240 ERT 1
Magneto	Bendix D 2000	Bendix D 2000
Harness	Bendix High Temperature	Bendix High Temperature
Propeller Drive	1:1	1:1
Fuel Min Octane	90	90
Carburetor	Stromberg Zenith 150 CD	Stromberg Zenith 150 CD
Fuel Pump	APG 17.09.001	APG 17.09.001
Starter	Fiat 0.5 HP	Fiat 0.5 HP
Alternator	Ducellier 250 W	Ducellier 250 W
Oil Capacity	2,5 1/2.64 quarts	2,5 1/2.64 quarts
Dry Weight approx.	74 kg/164 lbs.	74 kg/164 lbs.
Propeller Flange	D:for solid propeller – D I: for Hoffman variable pitch propeller	D:for solid propeller – D I: for Hoffman variable pitch propeller
LBA Type Certificate No. (for use in "Powered gliders")	Not certified	Not certified

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Random Rotors



Ken Brock is a real ambassador for sport flying activities. After completing his spectacular air show routine, he is being interviewed for area T.V. Ken is president of the Popular Rotorcraft Association.



LEFT: The rotary wing lineup at Oshkosh 74.
RIGHT: Herb Krause of St. Paul and his modified Bensen. Notice the mufflers. The gyro gang is taking the lead in developing mufflers to quieten their aircraft. All of us will be down in their area looking for ideas soon.



Dutch Roembke of Las Vegas makes a minor adjustment to his mighty Mac before thrashing off on another flight.

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Summary

Article Name
History Of The Limbach Engine
Description
From one of the most recognizable engines comes one of the most reliable homebuilt aircraft engines. The Limbach has made it's place in history and continues as a viable aircooled aircraft engine.
Author
John F. Crater (EAA 65356)