ORIGINAL: KC36330
ORIGINAL: MJD
Quite possibly but not always true - which .46 two stroke? Some are timed for more power at lower rpm, the OS .46AX is an example..........................................
like some of the people you mentioned you're missing the forest because you think the trees are blocking your view. the timing and porting of the engine have nothing at all to do with getting more speed from the same said engine, when you drop prop diameter you increase pitch to
match the load on the engine so you keep the engine in its power band producing max performance. the AX torquer engines do not respond well to tuned pipes/ultra thrust/Jett stream systems but they respond to propping the same as any other engine and as mentioned above the airframe is the limitation. don't confusing propping with trying to get more RPM.
when propping always use the sum of
Diameter x Diameter x Diameter x Pitch and keeping that as close as possible you'll keep the same load on the engine, and the same peak RPM. propping for RPM is a different ballgame and is engine specific.
kc
I can see the forest and the treess quite well, thank you.
Timing and porting of the engine define the performance curve of the engine. There are numerous .46 engines out there and his original message did not say which he had. Nor did I suggest changing any of these things or adding tuned exhaust systems or the like. Nor did he say he is already propping the engine for best pwoer output. If you are assuming he is already propping that engine for best power output you may be mistaken. Or you may not. Irrelevant in any case.
Yeah, if you are trying to match the load of the baseline prop then the general rule is drop diamter and increase pitch. Most of us know that already.
I suggested that in many cases the baseline from which people start when trying to increase speed is not at or near the peak horsepower regime of the engine. This depends on the engine and the prop you start with - that's obvious. All he said was what do you do to increase speed, increase or reduce pitch. Apart from the scenario you are discussing above which assumes the engine is at the best area in it's power curve already, or that you don't want to run it in a different rpm range for some reason, I am saying that he may want to look at the horsepower curve of the engine he's using (which we didn't know yet) because it may be advantageous to unload the engine. These two considerations go hand in hand when you are figuring out what to do to increase performance.
- I never argued that the general rule of dropping diameter and increasing pitch was not valid. It assumes you are content with where you are in the pwerband of the engine involved. Keeping the same load on the engine is also engine specific if top speed is the goal, because it assumes the rpm is where you want to begin with.
- The rule about diameter cubed times pitch is somewhat crude and doesn't match a lot of empirical data. But it is a rough guideline, yes. Some argue that the load formula works better using diameter to the 4th power. And as soon as the prop blade layout, airfoil etc. changes at all the rule goes out to lunch in many cases. In the end the tach tells the tale.
- I did not suggest that all engines respond by jumping up rpm. I said that some will, some will not, depending on the engine and the prop you start with. I specifically referred to the AX as an example where that might not help due to it's peak horsepower being at lower rpm than many other .46's.
That's all - you're reading stuff into my post that was not there.