2 Stroke vs. 4 Stroke
11-24-2005 | 04:23 PM
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From: SMITHTOWN, NY
2 Stroke vs. 4 Stroke
Im currently putting together a Showtime 4D and dont know which engine to use. I have a 91 FX that im thinking about using. I was also thinking about using a Saito 125 or possibly a small gas engine like the Evolution 26 GT. Ive heard that the 4 stokes are not as reliable as the 2 strokes. I will be using the plane for 3d and more slow flying than anything. Any insight will be a great help also what prop size to use.
11-24-2005 | 05:04 PM
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From: STOCKHOLM Akersberga, SWEDEN
RE: 2 Stroke vs. 4 Stroke
Both these glow engines should work good for you. Forget gas for small 3D planes unless the wingarea is HUGE or if you need the extra weight for the balance. Reliability should also be equal between these two if you follow the engine manual regarding the settings and fuel requirements. IMO the modeller is responsibel if an engine is not reliable unless you go and buy an cheap low quality engine with known carburation problems. Just my thoughts!
11-25-2005 | 12:22 AM
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RE: 2 Stroke vs. 4 Stroke
Jim,
With a good carburettor that has linear fuel metering, a two-stroke engine running at a part throttle setting, is not much different from the same engine running with an extra small carburettor.
It is true that most carburettors supplied on two-strokes, like those from current OS and most clones, cannot be adjusted for a perfect part throttle mixture and they do tend to load up in the mid-range, around 1/4-1/3 throttle, when adjusted for a perfect idle mixture.
Dave Gierke found this behavior in the .61FX, in that MAN 05/03 'engine shootout'.
Engines that have a more precise low-speed needle taper (like MVVS and Webra), or that have a means of adjusting the mid-range mixture, like on some older F3A carburettors from OS, Enya, Etc., or the current Super Tigre rotating fuel sleeve, will not suffer from a bad part throttle, after adjustment is done.
Four-stroke engines actually use the same carburettors as two-strokes, yet don't suffer from this loading-up (unless it is a YS, there is no raw fuel under the piston), so they are less sensitive to an overly rich mixture, at part throttle settings.
With a good carburettor that has linear fuel metering, a two-stroke engine running at a part throttle setting, is not much different from the same engine running with an extra small carburettor.
It is true that most carburettors supplied on two-strokes, like those from current OS and most clones, cannot be adjusted for a perfect part throttle mixture and they do tend to load up in the mid-range, around 1/4-1/3 throttle, when adjusted for a perfect idle mixture.
Dave Gierke found this behavior in the .61FX, in that MAN 05/03 'engine shootout'.
Engines that have a more precise low-speed needle taper (like MVVS and Webra), or that have a means of adjusting the mid-range mixture, like on some older F3A carburettors from OS, Enya, Etc., or the current Super Tigre rotating fuel sleeve, will not suffer from a bad part throttle, after adjustment is done.
Four-stroke engines actually use the same carburettors as two-strokes, yet don't suffer from this loading-up (unless it is a YS, there is no raw fuel under the piston), so they are less sensitive to an overly rich mixture, at part throttle settings.
11-25-2005 | 04:38 AM
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RE: 2 Stroke vs. 4 Stroke
ORIGINAL: DarZeelon
Jim,
With a good carburettor that has linear fuel metering, a two-stroke engine running at a part throttle setting, is not much different from the same engine running with an extra small carburettor.
It is true that most carburettors supplied on two-strokes, like those from current OS and most clones, cannot be adjusted for a perfect part throttle mixture and they do tend to load up in the mid-range, around 1/4-1/3 throttle, when adjusted for a perfect idle mixture.
Dave Gierke found this behavior in the .61FX, in that MAN 05/03 'engine shootout'.
Engines that have a more precise low-speed needle taper (like MVVS and Webra), or that have a means of adjusting the mid-range mixture, like on some older F3A carburettors from OS, Enya, Etc., or the current Super Tigre rotating fuel sleeve, will not suffer from a bad part throttle, after adjustment is done.
Four-stroke engines actually use the same carburettors as two-strokes, yet don't suffer from this loading-up (unless it is a YS, there is no raw fuel under the piston), so they are less sensitive to an overly rich mixture, at part throttle settings.
Jim,
With a good carburettor that has linear fuel metering, a two-stroke engine running at a part throttle setting, is not much different from the same engine running with an extra small carburettor.
It is true that most carburettors supplied on two-strokes, like those from current OS and most clones, cannot be adjusted for a perfect part throttle mixture and they do tend to load up in the mid-range, around 1/4-1/3 throttle, when adjusted for a perfect idle mixture.
Dave Gierke found this behavior in the .61FX, in that MAN 05/03 'engine shootout'.
Engines that have a more precise low-speed needle taper (like MVVS and Webra), or that have a means of adjusting the mid-range mixture, like on some older F3A carburettors from OS, Enya, Etc., or the current Super Tigre rotating fuel sleeve, will not suffer from a bad part throttle, after adjustment is done.
Four-stroke engines actually use the same carburettors as two-strokes, yet don't suffer from this loading-up (unless it is a YS, there is no raw fuel under the piston), so they are less sensitive to an overly rich mixture, at part throttle settings.
Actually, it depends upon how the two-stroke engine is timed/ported as to how well it will handle partial throttle operation. Such factors as crankcase stuffing, lower piston fit to the liner, compression ratio, the amount of nitromethane being used in the fuel, glow plug heat range, etc., all play a significant role in tractability.
Smaller throat carbs keep the gas velocity high, which aids in atomization, hence keeping the fire lit. This is particularly important at partial throttle settings, especially when used with larger, higher mass, propellers, as in 3D applications.
The superior exhaust scavenging of a four-stroke engine aids in the four-stroke's ability to recover from a partial throttle setting and return to high speed operation with increased reliability (less hesitation/stumbling). Four-strokes are clearly superior to two-strokes for 3D flying because of this trait. This is especially so when higher percentages of nitromethane are used in the fuel.
11-25-2005 | 10:06 AM
#7
Senior Member
RE: 2 Stroke vs. 4 Stroke
ORIGINAL: Ed Cregger
Actually, it depends upon how the two-stroke engine is timed/ported as to how well it will handle partial throttle operation. Such factors as crankcase stuffing, lower piston fit to the liner, compression ratio, the amount of nitromethane being used in the fuel, glow plug heat range, etc., all play a significant role in tractability.
Smaller throat carbs keep the gas velocity high, which aids in atomization, hence keeping the fire lit. This is particularly important at partial throttle settings, especially when used with larger, higher mass, propellers, as in 3D applications.
The superior exhaust scavenging of a four-stroke engine aids in the four-stroke's ability to recover from a partial throttle setting and return to high speed operation with increased reliability (less hesitation/stumbling). Four-strokes are clearly superior to two-strokes for 3D flying because of this trait. This is especially so when higher percentages of nitromethane are used in the fuel.
Actually, it depends upon how the two-stroke engine is timed/ported as to how well it will handle partial throttle operation. Such factors as crankcase stuffing, lower piston fit to the liner, compression ratio, the amount of nitromethane being used in the fuel, glow plug heat range, etc., all play a significant role in tractability.
Smaller throat carbs keep the gas velocity high, which aids in atomization, hence keeping the fire lit. This is particularly important at partial throttle settings, especially when used with larger, higher mass, propellers, as in 3D applications.
The superior exhaust scavenging of a four-stroke engine aids in the four-stroke's ability to recover from a partial throttle setting and return to high speed operation with increased reliability (less hesitation/stumbling). Four-strokes are clearly superior to two-strokes for 3D flying because of this trait. This is especially so when higher percentages of nitromethane are used in the fuel.
This is correct, Ed.
A radically timed engine will be somewhere between 'very hard to tune' and 'impossible'...
However, in a moderately timed engine, intended for mid-high performance level, the carburettor's fuel curve will make all the difference in the world.
With the suitable carburettor (#3219/R from MVVS, which sadly, is no longer made), I managed to make Rossi .45/.53 engines' part throttle behavior, good enough for 3-D flying.
