It's a Brodak profile P-40 ARF that I'm just finishing up. Sorry, I forgot to weigh it before leaving the shop tonight, but I think most people's are in the 40s. I always used an APC 12x4 when the same LA.46 was on my 52 oz. Cardinal. I haven't used a 3-blade prop on anything since I was 12 and flying my plastic Stuka.

I just now went eBay shopping and didn't see an APC 11x5 3-blade, so I dropped a Master Airscrew 11x5 and 11x6 in my shopping cart. I haven't clicked the Buy button yet.

Any thoughts on my 3-blade prop choice would be appreciated.
Thanks,
Rusty

I've got a 3 blade prop on my Brodak P-40 ARF,  although electric.  If nothing else it looks so much better than a 2 blade.  good luck.

Hello Rusty!  Generally I try to avoid sharing my experiences / opinions because there are so many variables between models, environments, equipment and even modelers themselves but I can say "give it a try", you may be pleasantly surprised.  A few years ago and even until now, I have been building a Claus Maikis model called the Big Tiger.  Honestly I endorse the design without question.  One of mine uses an OS 40FP with a 2-blade 11x6 and two of them used Fox 40's r/c, with the throttles locked open, and Master Airscrew 10x7 props with greater than expected performance.  Recently, because I accidentally broke one of the props and subsequently I mounted an APC 11x6 four blade prop.  I was pleasantly surprised and have not regretted the change.  Now, that's my experience, for what it's worth.  So, in conclusion, my suggestion is try it  !!

It's a Brodak profile P-40 ARF that I'm just finishing up. Sorry, I forgot to weigh it before leaving the shop tonight, but I think most people's are in the 40s. I always used an APC 12x4 when the same LA.46 was on my 52 oz. Cardinal. I haven't used a 3-blade prop on anything since I was 12 and flying my plastic Stuka.

I just now went eBay shopping and didn't see an APC 11x5 3-blade, so I dropped a Master Airscrew 11x5 and 11x6 in my shopping cart. I haven't clicked the Buy button yet.

Any thoughts on my 3-blade prop choice would be appreciated.

   How many blades it has is probably less important than the pitch, and you are adding 25% more pitch (with a corresponding drop in the RPM and horsepower). It's an open question whether it will draw fuel sufficiently at the much lower revs. The only thing you have going for you is the reduced diameter, which will cut the efficiency and maybe permit you to run it faster than the difference in pitch would suggest. If you end up flying the airplane faster, that will certainly increase the line tension in level flight.

     I would be a bit surprised if this was better (assuming you match airspeeds) but there's only one sure way to find out. It is a pretty drastic change, so you might have to make other changes, too (like a narrower tank, a smaller venturi, or many more layers of pantyhose to recover some fuel draw). I would strongly discourage you from adding head gaskets or other modifications, like the people who will descend upon you to change the exhaust duration and/or "drop the liner".

   If you can get it working otherwise, and then you find that you are running a 4-2 break, and the power change at the break is excessive, THEN, add a head gasket about .005 at a time, and reevaluate.

   If it was me, I would try about an 11.5-3.75 "flat back" Eather three-blade, specifically, the prop I ground down in the flyoff in 2006, since it's already about 11 7/8 and fuzzy! That would maintain the RPM at near the current value, so fuel draw would be unaffected.

     Brett

Thanks for the replies, guys. I'll let you know what I finally choose.

I'd planned to maiden it today, but we'd have had to use the mild morning time to mow, and then fly in the heat. So we blew it off till Thursday. I would've had to pull an all-nighter to get it ready anyway, so it's just as well. I think I have another thread on it, so I'll do a show and tell over there.

I've never tried the wood Master Airscrews, so I might try one.

Hi Gerald, good to hear from you, I don't believe I've ever seen you post before. Gerald is one of my regular
Video Hangout guests. I'd love it if some of you other guys would drop in or just watch.

That's a cool looking prop you posted, Fred. Cool is low on my list, but it's my first Warbird pattern ship, so... I do like Cool. I'll read that link. Got another couple of replies on it, so I'm interested.

Brett, weakening fuel draw is something that hadn't occurred to me, good tip. As you said, I'll just try and see. I usually use muffler pressure, mainly to close the loop and keep grass seeds and debris out of the tank, so maybe that'll help boost it. Randy says pressure makes them stupid, but I seem to get along with it... give or take a half second.

I plan to use the new Sullivan 6 oz. clunk I bought for my Cardinal kit. I do have a couple of narrower metal tanks, but they're only 4 oz., and maybe a 4.5. Not enough since it might be cool in Huntersville in October. Probably not enough in the summer either. I donated my other good 6 oz. tank to my club's plane, a really old Tutor I flew so successfully this spring and also fixed up before returning it.

With the LA(or any other engine that wasn't originally meant to) I don't care to run a significant 4-2 break. When I plant and pull up for that first wingover, I like knowing it's got the authority to power up and over without worrying if it's going to delay breaking and flutter in the wind.

If I try a few 3-bladers and am still not happy with it, I'll bolt my old reliable 2-blade on it and never look back. Cool be-damned, I'm here to fly, not look good. I just like looking good when it works out.

I'll report back after its maiden flights.
Rusty

& dont forget 60% nitro .

Lol, y'all don't tempt me, I have all the stuff to slap a bladder on it.

Thanks, Brent. My LA has the same venturi/NV as yours. I have heard the same about MA's pitch.

A local flier beats me regularly in Classic with an overweight USA-1 powered by an LA-46. He uses a 12x7 Master Airscrew 3 blade cut down to 11 inches. As stated above, MA props are underpitched. He runs a fast 2 stroke, not a 4 x 2 run. Just FYI and might be worth a try. 

Yeah, that sounds worth trying. I probably don't need all that pitch for my 40something oz. plane, but at their price I can try an assortment. I need one for my Yak-9 Fox.35 too. I have a 10x5 or thereabouts for it but haven't ever bolted it on.