Lets just say....

If im able to get 8400 rpm using a 15x6 prop, and 9500 rpm using a 14x6 prop.... for say the same amount of thrust - Which prop would be better for 3D?

well, IF they are the same thrust the 15" would be a better choice. It will give you a little more control during high alpha/stalled manuevers. This is because it has a tad more air over the ailerons and stab.....However, I would be willing to guess that the 14 x 6 is actually giving you a tad more thrust. I'm guessing the extra 1,100 rpm will outweigh the extra 1" of prop. But it all depends on which engine/plane/weight combo.

Saito 91 on showtime 50 at about 6.5lbs.

Wondering if static thrust is equal...or just about.... is there a benefit to the higher rpm range?

So far ive run:

an apc 14x7 at 9000 rpm(calculated 9.77 lbs of thrust) ,,,

and 15x6 xoar at 8400 rpm(calculated 11.22 lbs of thrust)


also wondering if i should be looking for higher peak rpm - am i putting too much load on engine with 15x6?

I fly a lot of 3D and I like to have my engines revving on light props. Why, I want a faster spool up time. You rarely use full throttle except on pull outs and the odd vertical manouvre but you want that engine running at or near peak torque.

Try a 15 x6 Zinger or a APC 16 x 4 wide. Maybe even a 15 x 4 Zinger.

try 15x4 apc if you wanna 3d your ST or 15x6 wood .... that 14x7 would make a decent imac type prop for some speed

the 14x7 was excellent for more pattern type flying-used it for 2 seasons. But after trying a Xoar 15x6...all I can say is WOW!!!! What took me so long! Ive flown a 15x4 apc before...I honestly didnt like it. It was just too slow. Maybe I should give it another shot. Im guessing everything is a little easier when its slower.

maybe you should keep the 15x6 xoar....even though it is not on the "reccomended" props list........... you cant go smaller or else you'll have to increase your pitch, and you cant go bigger than 15 ....now that you have discovered the wood 15x6 are best now its time to experiment with different brands.....performance is what you want so dont even try a power point or zinger..........

So back to the original question...if i stay at 15 im at 8400 rpm..... if i go lower to 14.... I would gain in rpm. Now LETS say im able to achieve enough rpm with a 14 to have same amount of thrust..... whats better low rpm or higher at equal thrust? Im guessing higher.

i would go with 14x4W

My take on this is:

IF and I mean IFF! the thrust was exactly the same on both props and the lower RPM didn't overheat the engine I'd go with the lower RPM. My reasoning would be a larger airflow for one and the second and more important would be that the "feeling" of quicker spool up would be with the slower RPM. It takes less time to get to a lower RPM than a higher one. Also the larger prop would probably give more thrust earlier in the RPM range thus quicker pull out.

Thanks
Barry

Personally I would go for the bigger diameter over higher RPMs. The bigger the diameter of the prop the more air is moving the control surfaces to control the plane. Go with a light wood prop to make up for some RPMs and make spool uo speed quicker and also have less torque roll. Or another option is throw that monster 91 on the Pro Yak.

Of those two props, I would use the shorter one. The throttle response should be better for 3D. I would personally not use either one and go to a 15x4W. But that may just be me.

david

[quote]ORIGINAL: beachbrada


[quote]ORIGINAL: ro347


LOL!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

I think you're comparing apples to oranges- apc = plastic/ heavier to xoar = wood/lighter.. If you and your motor like the spool up of wood then stick with it. I would compare wood to wood. Try some [link=http://www.vesspropellers.com/servlet/the-Sport-Series-Props/Categories]Vess[/link] props. I run 6 pitch props on 4 strokes because they torque up more than 2 strokers. If you want a durable prop look at [link=http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXZ981&P=SM]MAS K[/link] or my favorite has been [link=http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXNGU4&P=SM]MAS S2[/link] lately. I run 14x6s on my saito 91. It's your decision though.

I have my Saito 91 on an AeroWorks Extra 260 weighing 6.5 lbs. The APC 15X4W pulls good but the spool-up is so slooooow that it is hard to get a stable hover. The woods, 14X6 MA Scimitar is pretty good but the XOAR is better, give a much much much faster spool-up and make for a much easier hover. Go to Paul Swanny's website (google it) and he highly recommends the XOAR props. He also makes one of the best 3D profiles on the planet (Mojo). I have yet to find anything that works better on my 50cc Extra than XOAR.

How do you like that Extra with the .91? You think it needs more?

Yes sir, I do. It will hover and also will pull out but the pull-out is sooo sloooow that most times I just rock it over and fly it out. Don't get me wrong, the old 91 has treated me well and it's still strong considering it's 11 or 12 yrs old but the 260 is roughly 6.5 lbs and that's just a wee bit much for a 91 to hover. The 100 at only 1 more oz would be a better choice if one is buying an engine for this plane. If you already have the 91 like I did it will get the job done but that's about it. I know one fellow in my neck of the woods that runs a Saito 125 on his and likes it a bunch. I think the 125 is only like 2 or 3 oz heavier but I don't know that for sure. Good luck with yours.

Hey ro347 every body's flying style is different. When I finish a new plane engine combo .I go test fly the plane after the first two or three flights and have the plane flying the way I want, CG, and control throws then The next day out, I will grab 7 or 8 props, a variety of wood and composite props with different Pitches and dia. and keep flying and changing the props until I find the perfect prop for my flying style. I know your like the rest of us and have a 5 gallon bucket of props LOL!!! The Higher altitudes that we fly compared to the lower alt. you fly, requires we have at least 20% more power due to density alt. and our naturally aspirated engines to make the plane fly the same. At the higher alt. we loose out due to the lighter air causing lose of lift and power.
jerrysu29 Call Sign Wild Man