ORIGINAL: Mr67Stang
ORIGINAL: ArmedZagi
I also thought 4-stroke proiduced more torque than 2-strokes?
Ding! Ding! Ding! We have a winner. The biggest difference I have found as far as performance of the two engine types is torque. If you get a OS .46 FX/AX and a Saito FA-82 you can swing a bigger prop on the Saito due to the increased torque. Everyone says the Two Strokes have more "horse power" but look at the numbers. On the Tower site an OS .46 AX puts out "Power Output: 1.65ps@16000 RPM" But I challenge you to tune this engine to spin 16,000 RPM with any prop you would actually use on this motor and expect it to live. I bet you will find yourself spinning closser to 11,000 to 12,000 RPM and who knows what the HP is at that RPM. Now practical aplication says fit a motor that fits your plane. Example. I have a Sig Something Extra and us an OS .46 FX even though a Saito FA-82 would probably be more fun I don't have the clearence for a bigger prop than the 12x4 Zinger on it. I am pretty much restricted to 3 point landings with this prop. I would have to hand launch with a 13x4 and 3 point it if I had the Saito 82. Hmm now I could get longer main gear but it would look silly.
Um, excuse me, but isn't a Saito .82 a much larger engine than a OS .46 . If you are going to compare two stroke torque to four stroke torque, shouldn't you compare the OS .46 to a four stroke that displaces approximately .46 cubic inches? Yes, the two stroke horsepower claims are highly inflated, that's because a lot of people make buying decisions based on the advertised numbers.
The torque needed to turn a prop is proportional to the RPM squared. Because of this, it actually takes more torque to turn a 10x6 at 14,000 rpm than it does to turn a 12x6 at 9000 rpm. Not understanding the exponential nature of prop load leads to the fallicy that 4 stroke engines make more torque than 2 stroke engines.