Frequently asked questions about the L 275 E / L 550 E
In which positions can the L 275 E / L 550 E be mounted?
The L 275 E can be mounted in any position:
• Tractor
• Pusher
• Helicopter
• Carbs up
• Carbs down
How is the L 275 E / L 550 E packaged? Does it have shrouding all around?
The L 275 E / L 550 E do not have any shrouding.  The type of cooling system necessary will very much depend on your installation situation,  (pusher, tractor – propeller, high-speed aircraft or low speed paramotor)
What is the maximum service altitude?
The operating manual for the L 550 EG states 6600m.  Whether you can fly as high as that depends on your power requirements for the altitude desired.
Are the engines available with fuel injection?
We have working L 550 E engines with the electronic engine management system used on our certified L 2400 DF / DT line of engines.  The engine management system feature automatic altitude compensation and reduces fuel flow in midrange significantly.  Do you have silencers for the L 275 E / L 550 E engines?
No – we don't.  Simple silencing systems will reduce power,  most of our customers were not willing to sacrifice power in their application.  A silencer that does not reduce resp enhances power will require a length of roughly 1200 – 1500mm.  I could be engineered on request.
What are the engines electrical requirements, ie. 12v, 24v?pulleys
The L 275 / L 550 E have magneto ignition and do not need electrical power for running.  If equipped with an electrical starter, a 12V battery capable of delivering 80-100 A is needed.  For the L 550 E a 24
V battery was also successfully used.
Can the L 275 handle a belt-reduction?
The L 275 E is designed for direct drive and will not take bearing side loads other than those generated within the engine itself.  For a belt reduction system you will have to devise a strut between the two pulleys that eliminates side loads on the crankshaft. What is the life of the engine?
The L 275 E / L 550 E  were specifically designed to be very lightweight – thus sacrificing longevity.  Customers using the engine report service lives between 150h and 250h.  Depending on condition the engines may be overhauled.
What conditions does the engine life depend on?
Two stroke engines in general do not like continuous operation.  In this mode of operation the piston ring grooves tend to fill up with carbon deposits and at a time the piston ring might stick.  A sticking piston ring will definitely lead to engine failure.  The L 275 / L 550 series engines feature a tapered piston ring to prevent sticking rings but depending on temperatures, type of fuel and oil, the possibility of ring sticking cannot be excluded.  Limbach Flugmotoren recommends to remove pistons and cylinders and to decarbonizes the pistons, rings and cylinders every 75h.
Another limiting factor are vibrations, which can lead to worn carburetor linkages, premature coupling failures etc.
In which direction do the engines rotate – can I change it?
Viewed from the propeller hub, the engines rotate clockwise.  Changing the direction of rotation would incorporate changes to:
• the magneto rotor
• the coil mounts
• the starter
• the starter ring gear
The change could be engineered providing adequate quantity is purchased.
What is the weight of accessories?
Following a weight breakdown:
L 275 E Basic engine
Incl.  ignition system and heat sinks
Without: exhaust stacks ca. 7.8kg
Parts and accessories:
Propeller hub (included as standard) 0.36 kg
Exhaust stacks (option) 0.20 kg ca.
Electric starter (option)  0.3kW    1.36 kg
Starter mount (option) 0.3 kg
Starter ring gear (option)  0.56 kg
L 550 E Basic engine
Incl.  ignition system and heat sinks
Without: exhaust stacks ca. 18.3 kg
Parts and accessories:
Electric starter (option) ca. 1.9 kg
Without heat sinks ca. –1.0kg
Is a generator/alternator available for the L 275 E / L 550 E
Yes, we have a 28V/1200W alternator with an integrated voltage regulator.  It is a low cost unit, derived from an automotive alternator.  It can be supplied with the necessary couplings. For the L 275 E there is no mounting adapter available.  The adapter needs to be 60mm thick and usually incorporates an airframe-specific engine mount.  For the L 550 E we have a mounting adapter also serving as engine mount.
The weight is approximately 5kg including the coupling.
Do you have a hand starter?
No,  during initial development we experimented with hand starters, but found that they were quite heavy and did not reliably start the engine.  Some of our customers have fitted the engines with decompression valves to allow for easier hand starting.
The change could be engineered providing adequate quantity is purchased.
Can you recommend a propeller?
Definitely no.  Propeller design depends on many factors that we don't know of (aircraft weight, cruise- and climb speed etc.).  Best is to contact a propeller manufacturer: MT PROPELLER ENTWICKLUNG GmbH
FLUGPLATZ STRAUBING-Wallmühle
94348 ATTING
GERMANY
sales@mt-propeller
<-propeller
HOFFMANN GmbH & Co. KG
KÜPFERLINGSTR. 9
83022 ROSENHEIM
GERMANY
info@hoffmann-prop
www.hoffmannprop
HELIX-CARBON GmbH
DUESERHOFSTRASSE 20
52074 AACHEN
GERMANY
info@helix-propeller.de
www.helix-propeller.de
HELICES HALTER
05300 SALEON
France
halter@uav-propellers
www.uav-propellers
Does the L 275 E / L 550 E need a fuel pump.
The L 275 E / L 550 E feature all-position diaphragm carburetors with integrated fuel pumps.  If the fuel tank is located close to the engine (200 – 300mm difference in height) the fuel pumps work well.  For applications with a fuel tank aft of the engine, acceleration forces during take-off must be considered.  They could disturb the function of the integrated pumps.  It is possible to overboost the integrated pumps with an electrical fuel pump (0.3 bar).
How can I measure the rpm
You have two possibilities to measure rpm.
a) The ignition coils feature a cut-wire (red) to switch off the engine.  Those lines
carry a pulse that may be used to generate an rpm signal.  Caution however is
necessary because the voltage on those lines can be as high as 400V and any
short circuit to ground will switch off the engine.
b) The ignition flywheel has two magnets inside.  Using an inductive sensor, you
may generate an rpm signal each time the magnets pass the sensor.
Which type of oils do you recommend?
We recommend a high quality synthetic two-stroke oil. Castrol RS2T or ELF HTX 909 appear to be good choices.  Synthetic oils reduce the amount of deposits and contribute to engine reliability.  The tendency to build deposits may vary with locally available fuels.  It might be necessary in such cases to decarbonize the engine before it reaches 75h.
Why do I need to decarbonize th e engines?
Two stroke engines in general have a higher amount of un- or partially burnt fuel in their exhaust gases.  That will form solid deposits.  Additives such as lead or bromide might accelerate formation of deposits.  Fuels with a high sulfur content also show this behavior.  Deposits will eventually reduce the cross-section of the exhaust and reduce power.  Deposits also may disturb piston ring function and cause engine damage.

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