Tachometer settings on 4-cycle engines
07-14-2002 | 10:18 PM
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Tachometer settings on 4-cycle engines
The tachometers count prop blades... they don't measure tip speed, so blade length is irrelevant.
The tah will have a setting for 2-blade and for 3-blade. Very few people make use of the 3 blade function. And the (even fewer) people who use 4-blade props simply divide the indicated rpm in half.
There is no difference in how you use the tach on the 4-stroke vs the 2-stroke. Turn it on, point it at the engine through the prop arc... or point it through the prop arc from behind... It does help to have a good light source on the poosite side of the prop from the tach, though they can usually read the reflection of the light off the blades, at any angle when outdoors on a sunny day...
The rpm will vary with each individual engine, and with each individual prop on a given engine. The tach is needed because its harder to hear when a 4-stoke is running at peak rpm, than it is with a 2-stroke. Find the peak rpm, and richen the fuel mix about 1/4 turn durring break-in.
You should see the exhaust as wispy white trails behind the plane in flight. If you can't see any exhaust trail against a clear blue sky, SHUT DOWN AND LAND. 4-strokes will run WAY lean, and burn themselves up. 2-strokes will die from fuel starvation long before they will get as hot as a 4-stroke will get durring a lean run.
The tah will have a setting for 2-blade and for 3-blade. Very few people make use of the 3 blade function. And the (even fewer) people who use 4-blade props simply divide the indicated rpm in half.
There is no difference in how you use the tach on the 4-stroke vs the 2-stroke. Turn it on, point it at the engine through the prop arc... or point it through the prop arc from behind... It does help to have a good light source on the poosite side of the prop from the tach, though they can usually read the reflection of the light off the blades, at any angle when outdoors on a sunny day...
The rpm will vary with each individual engine, and with each individual prop on a given engine. The tach is needed because its harder to hear when a 4-stoke is running at peak rpm, than it is with a 2-stroke. Find the peak rpm, and richen the fuel mix about 1/4 turn durring break-in.
You should see the exhaust as wispy white trails behind the plane in flight. If you can't see any exhaust trail against a clear blue sky, SHUT DOWN AND LAND. 4-strokes will run WAY lean, and burn themselves up. 2-strokes will die from fuel starvation long before they will get as hot as a 4-stroke will get durring a lean run.
08-23-2002 | 11:27 AM
#2
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Tachometer settings on 4-cycle engines
The easy answer to your questions is. It dosent matter what engine/prop/fuel/plug ect...ect..... To get the most out of that
4-cycle lean it to max rpm on the tach. Then richen it till it loses about 400rpm. This should be a good setting if you are in your recomended prop range. Be sure to post how it works.
Later, daveo
4-cycle lean it to max rpm on the tach. Then richen it till it loses about 400rpm. This should be a good setting if you are in your recomended prop range. Be sure to post how it works.
Later, daveo
09-20-2002 | 03:39 AM
#3
Tachometer settings on 4-cycle engines
I've owned three (3) OS .70's and it's OS's "crown jewel" of 4C engines as far as I'm concerned. Wonderful engine!
Your questions however....
Who could possibly know the "proper" RPM for a 14-6 prop installed on that engine? (PS: It's TOO BIG!)
If everybody had the same fuel, the same plug, the same atmospheric pressure, temperature, humidity...then a number could be arrived at.
Are all .70's the same? I guess so...since OS is the only company making one. Even so...there are unit-to-unit variations that would impart differences in the actual measured RPM.
Setting the "MAX" rpm for the engine is easier if you have ever adjusted an engine. 4C engines are very unlike 2C engines in that they have a large-ish "plateau" in the engine output as the needle is leaned. Usually... one starts out rich, and then slowly turns the needle in until the engine "smoothes out" at high power. That's about the spot....don't keep turning the needle in hoping for some miracle...it'll never happen.
Huber makes a good point...if you aren't seeing a nice exhaust plume in flight, AND getting a nice clean oil deposit on your model....you're fixin' to ruin something.
Learn to LISTEN to your engine...not "measure" it.
Your questions however....
Who could possibly know the "proper" RPM for a 14-6 prop installed on that engine? (PS: It's TOO BIG!)
If everybody had the same fuel, the same plug, the same atmospheric pressure, temperature, humidity...then a number could be arrived at.
Are all .70's the same? I guess so...since OS is the only company making one. Even so...there are unit-to-unit variations that would impart differences in the actual measured RPM.
Setting the "MAX" rpm for the engine is easier if you have ever adjusted an engine. 4C engines are very unlike 2C engines in that they have a large-ish "plateau" in the engine output as the needle is leaned. Usually... one starts out rich, and then slowly turns the needle in until the engine "smoothes out" at high power. That's about the spot....don't keep turning the needle in hoping for some miracle...it'll never happen.
Huber makes a good point...if you aren't seeing a nice exhaust plume in flight, AND getting a nice clean oil deposit on your model....you're fixin' to ruin something.
Learn to LISTEN to your engine...not "measure" it.
