Originally Posted by
Glowgeek
You likely will see even more vertical performance with an 18x6 and may not lose much if any air speed as compared to the 17x8, Dan. All depends on how draggy the airframe is. At a given peak rpm a larger prop diameter creates more thrust, whereas greater prop pitch creates more air speed. Thing is, if the airframe has a lot of drag, a higher prop pitch/smaller diameter prop may not have enough thrust to drag the plane through the air any faster. I'd definitely try an 18x6, it may just tickle your fancy.
Originally Posted by
Rcplanedan
thanks..well im definitely thinking about it. Got some nice 10mph winds to go fly with today,
IF.... IF you go to an 18 x 6, then at least make sure it's either a good woody (I particularly like the ones JustEngines supplies and have a bit of a dislike for for example MenzS), or better, the APC 18 x 6
W... That is the one I run.
Mind you, it COULD be necessary to reduce servo-speed a touch on the upstroke of the throttle, due to the larger inertia of the prop: With gasoline, if the throttle opens TOO quick for the acceleration of the engine, mixture temporarily gets out of whack and that can lead to trouble. No biggie, do NOT adjust acceleration problems with the idle mixture, just reduce servo travelling speed to say, 0,5 ~ 0,7 sec, that usually does the trick.
The downside of an 18 x 6 prop is that at idle it functions as a huge airbrake, and you MUST come in on the throttle at landing. My BigLift (the plane in the vid I posted) can maintain a 45 degree dive without exceeding 60 kph at idle, and WILL stall over the runway threshold if I hold idle at landing. I need about 3~3,5K RPM for landing.
Chances are, for your particular plane, the 17 x 8 is the better choice due to the wider speed envelope.