size of 4s compared to 2s
12-07-2009 | 06:57 PM
#2
RE: size of 4s compared to 2s
Generally, most people consider that a 4-stroke needs to be 1.5 times larger to get the equivalent performance of a 2-stroke. Using that, the .52 would be roughly equal to a .35 2-stroke.
That isn't a set in stone rule though. It depends which 2-stroke and 4-stroke you are talking about. They are not all created equal. For instance, a general rule is that you need a .70 4-stroke to replace a .46 2-stroke which very often is the case but I've seen and flown 40 size planes with good .52 4-strokes or the OS .56 2-stroke though and they performed great. Something like a YS-63 will perform as good or better than something like a .55-AX. Experimenting with props on a 4-stroke can get some very nice results to.
So the 1.5 times the displacement is a fairly good rule of thumb but not true in every case.
That isn't a set in stone rule though. It depends which 2-stroke and 4-stroke you are talking about. They are not all created equal. For instance, a general rule is that you need a .70 4-stroke to replace a .46 2-stroke which very often is the case but I've seen and flown 40 size planes with good .52 4-strokes or the OS .56 2-stroke though and they performed great. Something like a YS-63 will perform as good or better than something like a .55-AX. Experimenting with props on a 4-stroke can get some very nice results to.
So the 1.5 times the displacement is a fairly good rule of thumb but not true in every case.
12-07-2009 | 07:18 PM
#4
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From: Berthoud,
CO
RE: size of 4s compared to 2s
ORIGINAL: ChuckW
Generally, most people consider that a 4-stroke needs to be 1.5 times larger to get the equivalent performance of a 2-stroke. Using that, the .52 would be roughly equal to a .35 2-stroke.
That isn't a set in stone rule though. It depends which 2-stroke and 4-stroke you are talking about. They are not all created equal. For instance, a general rule is that you need a .70 4-stroke to replace a .46 2-stroke which very often is the case but I've seen and flown 40 size planes with good .52 4-strokes or the OS .56 2-stroke though and they performed great. Something like a YS-63 will perform as good or better than something like a .55-AX. Experimenting with props on a 4-stroke can get some very nice results to.
So the 1.5 times the displacement is a fairly good rule of thumb but not true in every case.
Generally, most people consider that a 4-stroke needs to be 1.5 times larger to get the equivalent performance of a 2-stroke. Using that, the .52 would be roughly equal to a .35 2-stroke.
That isn't a set in stone rule though. It depends which 2-stroke and 4-stroke you are talking about. They are not all created equal. For instance, a general rule is that you need a .70 4-stroke to replace a .46 2-stroke which very often is the case but I've seen and flown 40 size planes with good .52 4-strokes or the OS .56 2-stroke though and they performed great. Something like a YS-63 will perform as good or better than something like a .55-AX. Experimenting with props on a 4-stroke can get some very nice results to.
So the 1.5 times the displacement is a fairly good rule of thumb but not true in every case.
12-07-2009 | 08:13 PM
#5
My Feedback: (-1)
RE: size of 4s compared to 2s
Todays four strokes have gotten a lot better too, more power, more RPMs and bigger props. Some of our thinking is a bit off these days. I tend to go with the old rule of thumb and discover I have really over powered a plane, not that that's a bad thing!!!!!! I would like to see an honest torque test using the new two and four stroke engines to get a better handle on the power differences. Hear that RC Report!!!!!!!!!!!
12-07-2009 | 10:36 PM
#6
Senior Member
RE: size of 4s compared to 2s
I think you will find that equivalent sized 4 strokes can turn a much larger prop with a lot more pitch. My Magnum 52 with the right prop demonstrates about the same power as a good .40. Using the high ptich props makes a good idle even more important in order to keep landing speeds down so a good quality 4 stroke is preferred. My Magnum did not exibit good idle quality until it was returned and repaired. Ifind it acceptable now.
12-07-2009 | 11:40 PM
#7
RE: size of 4s compared to 2s
The biggest difference is the torque curve between a 4 stroke and.2 strokes, 4 strokeshave a much higher torque curve ,at a lower rpm, where as a 2 stroke develops it torque at thehigher rpm,s
A 46 ax has more power then a Saito .56 but only when the rpm,s are way up , drop the rpm,s down to mid range and the .56 will out pull it.
A 46 ax has more power then a Saito .56 but only when the rpm,s are way up , drop the rpm,s down to mid range and the .56 will out pull it.
