Hello,

i intend to buy an OS 75 AX for a Four Star 60.

what is more suitable propeller for this plane and engine?

my options are master airscrew 14x6 or 14x8, i'de be glad to hear other options.

i see that RCKen did brake in with 14x8 for this engine, i really dont need speed on this plane.

thanks
Alex.

I'm running an APC 13x6 on my super sportster and it seems to work well. I really need to experiment with a few different props though.

It will handle more prop than a 60 size engine without a problem. Mine is a 14-6 APC and it flys great. It peaks at about 9800 RPM and pulls vertical with it like there is no tomorrow.

CGr.

I've run mine with a Graupner 14 x 7 and 13.5 x 8 and both are excellent

thanks guys,
14x6 it will be, just wanted to hear opinions.
props i'm changing fast and at this size its not cheap.
Alex

I started using Graupner props about the middle of last summer and found I really like them alot.

Back when I got my 75AX it was in the upper 90s for a month. I did about a weeks worth of swapping props around to see what it liked best while I dialed in the new airplane. One test was the "unlimited vertical" test. Timing the vertical climb until the model stops climbing. (Virginia, no there isn't a Santa, and there are very few models with unlimited vertical.) Turns out the engine/airplane would go 10seconds with a bunch of different props. There happens to be lots more tests I do when I'm testing props, but the limit of vertical one seems to grab most people the hardest. And 10 seconds is a good time, because thankfully, the model is still within sight.

Anyway, one prop I happened to try was still going decently strong at 10 seconds. Usually got to 11.something. Here's a picture of it.

BTW, during the week of tests, the DensityAltitude was between 3,250 and 3,520 the entire time. Close enough to consider all test days as relatively significant.

I also tried a 12x6(3) and it allowed the engine to run past what must have been optimum rpm in the air.

The 12x8(3) in the picture works better on our grass field than the engines next favorite prop (and EVO 14x6). The 2blade 14x6 did the vertical every time just over 10sec. So for some reason the MA12x8(3) seemed to have hit the sweet spot for that engine. If you have the chance to try one, it wouldn't be wasted money. I also use 10%nitro fuel. Never saw a reason to run higher nitro for what I do. This winter, the 3blade is pulling even better, but I haven't bothered to put a watch on any climb, nor have I even tached it. In the summer it tached a couple hundred over 9k on the ground when needled to fly (not max ground rpm for tach wars, but set to fly without meltdown).

Rock: I've never tried the three blade props. I've seen some people here on RCU (via pictures posted) using them but few at the field. The Pattern folks seem to use them a lot, but for some strange reason, they don't recommend them to those of us that are working our way up in experience levels.

I have a Goldberg Progege with the OS 75 AX engine and use the 14-6 prop I mentioned above and it seems to give me good, consistent performance with that 'unliminted vertical' we all seem to strive. But it does climb vertically with out 'effort' with that prop. I just wonder how it will do with the three blade you recommend.

I may give that a try and see. Can't hurt, that's for sure.

CGr.

Can't hurt for sure, and will give you some excellent entertainment. And the best thing about a prop that didn't do good on the engine you thought it'd bring alive.......... To keep from having wasted the money on that prop, you NEED TO buy a new engine that uses it. And then an airplane to suit that sucker. It's a never ending quest, but somebody's gotta do it.

What I found with my 75 was it performed very much the same with about 5 props. Most were 14x6's That 3 blade appeared to perform the same with just a bit of an edge. What was interesting was that other than the ground rpm (which really doesn't matter much for anything) the 3blade, with it's 8" pitch, performed very much like it was a 6" pitch. I really couldn't tell any difference in fuel consumption, to show how close the total performance was. I'm still using it because it was close to the best 2bladers, but was ahead. AND it's smaller diameter sprays less grass crud on the airplane. That airplane comes down with very little oil on it, and if I can keep the green stuff off, it's worth the price. And since the price included extra performance.......... win win

Hope it works as good for you. But remember my guarantee...........
If you are not entirely satisfied, there will be no additional charge.

I love that guarantee!! How can a guy lose with assurances like that !!

I was at the LHS yesterday afternoon and he had a MAS three blade sitting there looking for a home. My thoughts were pretty much on the same as yours. That grass stain is a pain. If I had a prop with a smaller disk diameter, perhaps that would pick up less grass on take off and landing. Hey, for the $12.00 price tag he had on that thing, it will be worth it to try it out. Don't recall the exact size, but I do recall that it would probably work on my OS 75 AX.

Thanks for the input.

CGr.