Evo mojih iskustava.
na osnovu ovih uputstava sam razradio OS46ax i radi perfektno
originalno uputstvo:
http://www.osengines.com/manuals/index.htmlkao drugo
izvor
http://www.masportaviator.com/clanak
http://www.masportaviator.com/ah.asp?CatID=8&ID=46 (I deo)
http://www.masportaviator.com/ah.asp?CatID=8&ID=47 (II deo)
(ovde dajem "kratak" izvod jer je tamo tekst mnoooogo dugacak pa da se ne bi lutalo)
With the engine properly and securely mounted on the plane, we are ready to start the break-in.
Well, not just yet. You’ll need fuel, the right propeller and a glow plug, also a glow plug igniter,
and starter – electric or hand. Glow plug igniters and starters will come later as will detailed glow
plug and fuel selections. For now, just assume you have the best of each.
Break-in propellers however, are important. The size propeller used during break-in depends
upon the engine type – ringed or ABC (AAC). For ringed engines, use a propeller one inch less in
diameter than will be used in flight. ABC engines need the exact same propeller as will normally
be flown. Type construction, wood, fiberglass, etc. should also match for ABC engines but is not
critical for ringed engines. ABC engines should be broken-in exactly as they will be flown, except
for the high-speed mixture setting.
In an ABC type engine, the cylinder’s bore (diameter) tapers from a larger diameter at the bottom
to a smaller diameter at the top. The piston has a constant diameter that is almost equal to the
diameter of the cylinder at its very top. As the piston travels upwards, the bore becomes smaller
until, at the very top of its stroke, the piston is almost the same size as cylinder’s diameter.
However the piston and cylinder react to the heat generated when the engine runs by expanding
differently. The cylinder expands more than the piston.
Since the piston is nearly the same size as the cylinder, at the top, in an ABC engine, break-in
involves the cylinder’s wearing away to become an exact fit to the piston when both parts are hot.
But most ABC engines are built with the cylinder slightly too tight. Therefore, when the engine is
first run and heats up, the cylinder remains too small. During the break-in, the cylinder loses
material until it exactly fits the piston when hot. How much wear occurs depends on the engine’s
RPM and propeller load. Using the same propeller for break-in and normal running insures that
the initial wear pattern will match the run pattern. The only difference is that the engine will be run
slightly richer than normal during break-in for extra cooling and lubrication. ABC engines normally
have short break-in periods averaging 5-10 flights.
Ringed engines do not need to turn the same rpm during break-in as during flight, but do need to
run cooler than normal. Therefore, ringed engines require a richer fuel mixture during initial
flights. Using a propeller one inch less in diameter reduces the engine load, and heat generated,
while allowing the engine to achieve enough rpms for break-in on the ground with a rich mixture.
Ringed engines usually require more break-in time, averaging 15-20 flights.
Before running any engine, use common sense and take every precaution. The plane must be
immobile, the propeller tight, all obstacles cleared, no smoking and do this outside. Wear eye and
ear protection and never, repeat never, stand to the side in the propeller arc or make any
adjustments at all from in front of the engine. DO NOT REACH AROUND THE SPINNING
PROPELLER TO MAKE NEEDLE ADJUSTMENTS, TO REMOVE THE GLOW DRIVER OR FOR
ANY OTHER PURPOSE. Always make all adjustments standing in the rear of the engine.
ALWAYS, PLEASE.
I have taken far too many friends to hospitals over the years, watched too many micro-surgeries
and hoped far too many times that they could re-attach nearly severed fingers to not to warn
anyone reading this to be careful. There is no “reset button” once that propeller hits you.
Break-in procedures for ringed engines vary by individuals but you should consider this one.
Open the high-speed needle valve one-half turn more than the engine directions state. Have the
throttle wide open and the plane properly secured. Prime the engine by holding one finger over
the venturi, hold the propeller securely and rotate it counter-clockwise until fuel moves through
the fuel line and nearly into the carburetor. Do not have the glow driver attached.
Connect the glow driver, making sure any wire is clear of the propeller arc, and start the engine.
Remove the glow driver. The engine will run full at throttle but very, very rich. If the engine falters,
close the needle valve, (while standing behind the engine), just enough to insure a steady run.
The engine should be spitting raw, un-burnt fuel out of the muffler and running about 2,000 rpms
slower than normal (photo 15). Run the engine this way for 5 minutes then shut down to cool.
Repeat this procedure once more. On the third run, let the engine run rich for 2 minutes, then
begin to “lean” the mixture, turn the needle valve clockwise or “close it”, until the engine sound
changes from a low pitched tone to an alternating low-pitch / high-pitch sound. Stop there and let
it run for 30 seconds. Then return to the rich setting for 2 minutes and then stop it again.
Restart, then lean to that alternating sound and run for 1 minute. Then richen the mixture again
(open the needle valve) but only to one-half turn less than the initial rich setting. Engine rpms
should now be about 1,500rpm lower than normal. After 1 minute running rich, lean to the
alternating sound point and run for 1 minute. Continue alternating the needle valve settings for 5
more minutes. Stop and let cool. Restart and set the needle valve to the alternating sound point.
Run the engine at this point for 3-5 minutes. If the engine holds rpm and doesn’t appear to slow
down, it is ready to finish the break-in while flying. Install the flying propeller. Total ground time is
usually 30 minutes.
Before flying, the idle-mixture needs adjusting. Most forty size engine use a separate idle needle
valve (photo 16). The idle adjustment screw or needle valve meters the amount of fuel that flows
into the carburetor during idle. Before adjusting the idle mixture, make sure this valve is set as per
the engine’s instructions. Clockwise adjustments lean the idle mixture while counter-clockwise
turns richen it.
Some engines use an air-bleed hole located in the carburetor’s top front section (photo 17). A
screw meters the amount of air admitted through this hole at idle, adjusting the idle mixture.
Initially, the screw should cover just half the air inlet hole (see photo). This may be too rich but the
idle mixture can be leaned by turning the screw clockwise. Turning the screw past the hole
continues to adjust the idle mixture, despite appearances.
There is little purpose adjusting the idle mixture on the test stand since fuel pressure, air intake
volume and airflow will be very different once the engine is installed in the airplane. The idle
setting will just have to be readjusted again. Mount the engine in the airplane if that has not
already been done. Then run the engine at full throttle and set the needle valve just slightly leaner
than the alternating sound point. Stop, attach the glow driver and restart.
Slow the engine to about 3,000 rpm (a tachometer helps here). Watch the rpms. If the engine
gradually slows, then stops, the mixture is too rich. Once the engine stops, lean the idle mixture
one-quarter turn. If the engine rpms increase, the mixture is too lean. Richen the idle mixture,
again once the engine is not running, one-quarter turn. Check each new setting by running the
engine at full throttle then reducing to 3,000 rpm. This “clears” the previous incorrect idle setting.
Even if the engine does not quit, but needs final adjusting, always stop the engine before making
any idle adjustments. Take every opportunity to stay away from a spinning prop with hands or
screwdriver.
Continue adjusting until the engine holds a steady 3,000 rpm. Disconnect the glow driver and
make any final idle adjustments. Why have the glow driver connected during the initial idle
settings? Incorrect idle mixtures often dampen an unconnected glow plug so quickly that there is
no time to determine just what is wrong with the setting. Keeping the plug “lit” helps ease the
adjustment process. After the initial settings, disconnect the glow driver, idle the engine for 30
seconds, then quickly advance the throttle, If the engine just stops, richen the idle mixture just
slightly. If the engine stumbles and quits, won’t accelerate or accelerates very slowly, lean it a bit.
During the first few flights, 3,000rpm provides a reliable idle for most engines. Slower idle settings
are possible, but run the risk of the engine’s quitting due to the high internal friction present during
break-in. Set the initial throttle trim on the transmitter for a 3,000 rpm idle at full “up” throttle trim,
while full “down” throttle trim stops the engine.
Landing patterns are flown at high idle. Once the field is “made” (the plane can glide to the
runway without engine power) reduce the trim to half. If the engine quits, landing is no problem. If
it runs more slowly, you’ll make a very pretty landing. This half-trim setting will be around 2,200 to
2,400 rpm and is the target idle speed once the engine is fully broken-in.
Breaking in an ABC engine is somewhat easier. Only one ground run of 10-15 minutes is required
using the flying propeller. Set the high-speed needle valve to the most open setting given in the
instructions. Start the engine at full throttle. The exhaust sound should be slightly lean of the
alternating low and high-pitched sounds. If only a very high-pitched sound is heard, richen the
mixture. If only a low pitched sound, lean the mixture to just past the alternating point. Run for 5
minutes, alternating full throttle and half throttle. Continue running for 5 minutes at a slightly
leaner mixture setting, again alternating full and mid throttle. During the final five minutes, lean
the high-speed mixture until rpms peak and start to drop. Immediately richen the mixture to 1,000
rpms less than that peak (about ½ turn). This is the initial flying high-speed mixture. Adjust the
idle mixture just as for ringed engines.
After about 10 flights for ABC engines, 20 flights for ringed engines, the high-speed mixture can
be leaned to 500 rpm less than peak. Never run leaner than this. In flight, a trainer’s engine turns
about 500 rpms faster than on the ground. The mixture tends to lean as rpm’s increase. In steep
climbs and while inverted, fuel feed rates are reduced. Most importantly, fuel pressure drops as
the tank empties, even with muffler pressure, as the weight of the fuel pushing itself into the fuel
outlet (tank head pressure) gets lower. The slightly rich ground mixture compensates for all these
possible problems. 500 rpms rich is the leanest run setting without a fuel pump. 600 is better and
will greatly lengthen engine life.
