I sold all I had. Can't really find a viable use for them.

3-blade props are for ground clearance and good looks. i have an electric turbo porter i plan on using a three bladed master on purely for the looks. i don't have any planes that need the additional clearance. altogether i probably have 20 3-blade props of varying sizes. so far used? none. BUT it won't be for long. the turbo porter (running gear) looks to be my christmas present :-)

Sounds like they need to brush up on engine mounting techniques, and reinforce the firewall. I know it's to dramatically describe there was more thrust discovered by the change, I just wished these exaggerations would be avoided.
In my experience the plane was slower. I don't want it to move slower. 2 blade props have their application and so do 3 and 4 blade props. I avoid going over 2 blades, it's a personal choice, like avoiding some fuels, glow plugs, batteries, servos, etc. and I enjoy the speed my planes are flying at, and the more noise, the better. To each his own.

hyflyer9 a 2 blade fixed pitch prop is more efficient and one that has less pitch makes a better climb prop. the more the pitch the better top speed but this is base on full size planes. but this is a very crude answer..

While my DA-100 is definetly quieter with a Mejzlik 3 blade, there is one significant difference all of you have missed. When hand proping the engine, the trailing blade is 60 degrees closer to your fingers than with a two blade prop. Ask me how I know, It's been two weeks now and it still smarts....

First off, the rule when converting from 2-bladed to 3-bladed props is reduce diameter by 1 and increase pitch by 1. Example, I have an 11x7 prop on my 2-stroke .61 engine I'd then use a 10x8 3-blade for this set-up. Master Airscrew has a complete line of 3-blade props in conventional and pusher orientations. They are a bit pricey as you move to the larger diameter end of the spectrum. Also, Dubro offers an array of 3-blade compatible spinners to accompany the prop. Nothing like good 'ole experimentation to determine whether the move to 3-blade offers any improvement in thrust. Good luck!

Yes but there is only one pitch that works well and does not over rev the engine, and the pitch that works well with a6 blade prop is higher than with a four blade prop. Thus it is better for high speed and high altitude.

Secondly, if that rule is to apply to the sizes we've just covered a bit here, then it should consider 22" props differently from the 10" ones for example. None of the "rules of thumb" really ever consider that model airplanes have come a long way since Master Airscrew first offered their line of 3-blade props and wrote up their recommendations. Back then, the recommendations on the back of the packaging suggested a 12x6 for a .90-1.08. No mention of 4strokes ('cause there were none) and the power output back then must have been a lot less than nowadays. Because what you see on most OS91FXs today will be a 14x7(3) and that's a prop that's significantly more load on an engine than one with 2" less diameter AND less pitch. Moreover, that comparison is 3-blade versuse 3-blade.

Also, Master Airscrew's line hasn't been increased to include props for 100cc, 150cc, and larger engines, which are fast becoming the popular sizes for a lot of IMAC flyers, both competitive and sport flyers. MAS's recommendations are significantly wrong, and they're printed right beside the "general rule for converting from 2 blades to 3......"

What would you guess for applying that rule to the big engines that're the ones you're most apt to see sporting a 3 blade? "Reduce diameter by 2 and increase pitch by 2"? That actually would be a shortfall in both dimensions if actual power were properly corrected for.

The best advice nowadays is to ask around to find someone using your engine and and a plane like your plane. And better advice would be to take that advice and try anything you can find the next step up and the next step down in diameter while you're trying the suggested one. But expect to hear a lot of confrontational conjecture about taking that advice.

Trial and error. Eventually you will have a drawer full of props and you can try them on all your engines/airplanes.

Trial and error sounds like the best advice so far.

CCF FLYER

In one case at least, it is a car trunk that's not full (or the airplanes couldn't get to the field) but has a plentiful pile to one side. And when I can convince them, the guys at the field will have a good selection to try on their own models. (And of course, I get to try them on mine.)

It works better than your wildest expectations. And works even better if you ignore the rules of thumb and most conventional "wisdom."

The only failing is that most guys seldom try more than a 2nd one.

True.

Is cowl width much of a consideration? On my EF Yak....the 2 blade doesn't stick out past the cowl very much. I'm saying maybe 3-4 inches on both sides. Obviously, a 3 blade (smaller diameter) would stick out less. Is this of any concern that the 3 blade wouldn't make the thrust past the cowl?
Thanks
Barry

Not usually much of a consideration.

If your Yak is an electric, chances are there isn't a 3 blade made in the size you need.

People who've tested 3 blades on their Yaks and Sukhois often wind up flying them. If you can find one to test, it's worth the try.

What is behind the prop, like cowl, has been proven to be whatever problem it would be anywhere on the plane. Being directly behind the prop has never been a big deal. P-47, Corsair, Hellcat, FW190, La-5, Hawker Tempest II and Fury, etc were all exceptionally fast and had big, radial cowls... and multi-bladed props.

Even if you go down 1" in diameter, the blades still reach past the cowl as far minus just 1/2". And with a 3 blader, there is an extra blade to make up for the lack of radius with a whole extra blade of area.

Not really. I got used to 3-blade props on my Extra300 where I have a 22x10 Biela on a 56cc engine.
After having used this combination, I changed the prop on my YAK from a 2-blade 23x8 to a 3-blade 22x10. Despite the YAK having a relatively wide cowl opening, my assessment is that I have improved prop efficiency.
Some people like to increase slightly the spacing between the front of the cowl and the back of the prop on planes like YAKs with wide cowls.

da rock, 100%. Trial and error and leave the conventional wisdom behind is the best advise.

This all sounds very promising. I'm gonna try one I think. I'm thinking probably a 22x10 3 blade. Maybe a 21x10.
What kind of RPM would I see? About the same as I see with the 2 blade? (7050 RPM on my 23x8 NX)
Thanks
Barry

sounds expensive! more so when you gotta buy nice carbon fiber props for your 100cc plane. or even a 50cc.

Yeah, the costs add up! Spread out over a lifetime, it's not so bad.

If you study the situation in IMAC for example, where the majority of flyers are using 50cc, 100cc, 150cc, and larger engines, it appears that there are two fairly obvious situations. The range of 3 blade props is huge in the sizes those engines require. The engine retailers have solid experience and knowledge of which of those 3 blades work best on their engines. After all, those engines are expensive, prices go into the thousands of dollars, and not high retail volume items. The prop manufacturers are the same. So you've got two things, decent selection and good advice for matching prop to engine/plane. That results in fewer props in those guys stockpiles.

Compare that to the glow engine guys and the alky burner boys have basically one mfg of 3 blade props and that company advises matchups from the 70s and whose props few LHS keep on hand.... but plenty of $5 to $10 two blade props. It isn't a financial hardship to have a double handful of those 2bladers.

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Concerning the methanol/nitro burning engines your statement, "Compare that to the glow engine guys and the alky burner boys have basically one mfg of 3 blade props and that company advises matchups from the 70s ....", is not altogether accurate; APC along with M.A.S. provide offerings and the recommended mathups are tried and true. The 2-blade to 3-blade conversion as previously stated does work but as noted is a starting point from which to experiment from if so inclined. Speaking for myself, the cool factor and mystery behind running more than a standard 2-blade is the lure. Also, given the availablity of small 3-blade spinners allows increased safety to those with an elec starter[8D].

Personal observation seldom is altogether accurate for the whole country.

I've seen those you mention being for sale, but only on Tower. They don't ever seem to be stocked in any LHS ever. MAS and Graupners are often in LHSs I've been in. A Tower search shows 2 and looking up both for the engine size recommendations gets just diameter, pitch, hub thickness and hole diameter.

What is kewl is that searching through the props it turns out that Tower has four 4-bladers for sale. Same deal, no engine size mentioned. But the size could match up with my engines and they are cheap enough to be worth testing on a chance they'll work.

What is more surprising is that the APC website only lists 2 three bladers and they're not the size Tower has. And quite disappointing is they do have a section that is titled "Propeller Size Recomendations[sic]" but it tells you they aren't going to do it. Have you seen them make specific recomendations somewhere? As for MAS's recommendations, they are the ones I mention being basically from the 70s. and my observations made earlier give the reasons I think they are pretty much out of date:

Another thing to consider when chosing a 3 blade prop , or any prop for that matter , is at what tip speed is the prop most effective, i.e. at speed speed is the thrust to drag of the blade delivering optimum thrust.
always, conventional wisdom dictates that the engines rpm is the driving force between deciding on the prop but some props may not like being spun at that rpm.
Its for this reason that I seldom take heed of prop rpm data posted on websites and fora. I am building myself a thrust rig to measure the force each prop is capable of delivering on a given engine and checking rpm data alongside that.
Ultimately, what we want is thrust first, low noise second and perhaps fuel economy third.
Any noise the prop produces is a loss of thrust.
every prop design has an optimum rpm range. matching tis to the engine is the holy grail. Currently I think we go about prop selection in a very arse about face way.

Listening to forums I fitted a 12x6 APC to my OS55AX. At full throtle the prop is signing an opera, indicating that I could benefit from more  pitch, diameter or blades.
trial and error is best but measuring thrust is where we need to be.

while doing my training I had asked my instructor what prop to put on my plane..  he started with a general recommendation and then said "if you dont like how it flies with that prop, use a different one"  So yeah I have 3-4 different props for an engine, but hey I can change how my plane flies by changing out the prop.  I feel like i want a gentle day... large diameter small pitch.... if i feel like hey i want to zip around....  small diameter larger pitch.  Works so far