brett65

My Feedback: (18)

I am currently running a 55ax with bisson pitts muffler on my extra 300 and its turning a 13x7 wood prop. I am pleased with the performance, and expect that an APC would be even better. What would a good size be for a 3 blade? I was thinking of 12x6. Thanks for any recommendations, and I do plan on experimenting with different ones.

Mr67Stang

While 3 blade props look great on these types of planes you may not like it's performance in the air. Slowwer flight more speed braking at idle. It deppends how you fly. To me a 13x7 seems large for a .55ax but you obviously have it working. The 12x6 3 blade should work if you can swing a 13x7 now. They say to go to 3 blade go down one inch in diameter.

PSL: I use an APC 13x4 wide with my 55 AX for 3D flying.

mscic-RCU

My Feedback: (6)

Rule of thumb for a 3 blade is down one size in diameter and pitch. A 12X6 sounds right.

MinnFlyer

My Feedback: (4)

Actually, the rule of thumb is down one size in length OR pitch

So if you're using a 13x7, a 12x7 or 13x6 would be the appropriate size.

That said, a 13x7 is the uppermost size for this engine. I run a 12x7 Graupner on my 55AX and the performance is outstanding, so going to a 12x6 should be great.

brett65

My Feedback: (18)

I have the upper recommended limit prop 13x7 because I wanted to limit the rpm's during break in. I think that it will perform the slow flight maneuvers better with something like a 13x4 like mr67stang said.

MinnFlyer

My Feedback: (4)

You've got that backward.

Use the smallest size prop for break-in. Limit the RPM with the needle valve by running it rich.

The smaller prop will put much less strain on the engine while it is breaking in. A big prop will put much more strain on it.

brett65

My Feedback: (18)

Oops! Do you think that I may have hurt it at all?

MinnFlyer

My Feedback: (4)

Probably not as long as you kept it on the rich side

da Rock

I'm actually running a 3 blade on an OS55AX. I don't fly it a lot, but have worked out the favorite 2blade and 3blade on the airplane. The model is the Phoenix ARF Decathlon that Tower sells.

It turned out heavy for a 46size model at 6 pounds 5 ounces. I flew it for awhile with an OS46AX in it and sorted out which 2blades worked best, but wanted a more nimble flyer. When the 55AX came out, I tried one on a TigerII and liked it. The Tiger didn't need it at all, so I swapped it into the Decathlon. The 55 didn't like the same props from it's time in the Tiger so I "had to" run some tests. I love this hobby. You're all the time having to do things. Like run prop tests. hehehe....

Turned out the 55AX ran almost as good on a Master Airscrew 12x6 3blade as it did with the best 2blade. It pulled almost as good vertical, but seemed to be on the back of the torque curve. It took a second to wind up but once there it stayed. So when I nicked one of the tips one day, I took the prop home and turned it into an 11.7x6. I do so much blade work that I've got a jig setup for my band saw and belt sander. Makes for accurate and uniform blade lengths. The engine really liked the new length. It's the favorite prop for that plane/engine now. Trouble is, the plane still doesn't get much air time. Pudgy airplanes seem to be less fun.

I've wanted to try the MA 11x8 3blader, but never seen one to buy. And I wish MA made a 12x5, but they don't. We simply don't have any real variety in 3bladers.

brett65

My Feedback: (18)

That's cool to know, thanks! I have the phoenix extra, and I love flying it. I would love to get one of their decathalons too, I love scale airplanes. I guess it comes from building model cars for so long. I have a 1/24 scale ford mustang that has almost every wire and line and hose that you would see on the real thing. I built it when I was seventeen, and I don't think I could replicate it today.

ChuckW

I'd try an APC 12x7 2-blade or even an 11x8 2-blade. They will perform a lot better than that big 13x7.

The 3-blades look nice and keep noise down but I have been disappointed with the performance in most cases.

da Rock

That's a shame, because my OS61 does very well on the Skybolt with a MA 12x6 3-blade. The OS75AX on my Tiger60 does exceptionally well with a MA 13x8 3-blade. And the OS91FXs on my Sukhoi, P47, and Corsair all run really good with MA 14x7 3-bladers. All those planes work very well with 3bladers on those engines.

I've found that the thing that makes it hard to find 3bladers that work with all models is the lack of selection. For example, there is only one 3blade available from MA in a 13" prop, the 13x8.

And Master Airscrew's own literature seems to be behind the times. The engines they suggest for those props I'm using are all way larger than the engines I'm using those props on. The engines nowadays can easily turn props much larger than MA suggests. I'd bet their advice stops lots of people from trying their props and finding good performance. I first tried their suggested 10x7 on a .61 and the engine almost blew itself up. Sounded like a ratrace engine. That .61 wound up turning the prop MA suggests for .90-1.08 engines. And flying better than good with it.