I am trying to find a 14x4 Four blade prop. Would somebody know who might make one ?
I have found 11x6 and 14.5x11, both APC.
The 11x6 is working for me but I really would like larger diameter, but will need lower pitch.
Thanks.

Hi!
You will not find one because no glow engine is going to be able to swing that big prop with any performance.

What engine do you have in mind ...a .40-.46 engine? Stay with a 11x6 or 12x4 APC..that is the prop that works best for those engine sizes in a sport airplane.

The 3 and 4 blade props you see on the planes in various photos are for STATIC only. They are replaced with a 2 blade for flying. In addition, 3 and 4 blade props are VERY ineffecient.

Question - when the engine is running, can you tell how many blade prop is on it ?

Would you be so kind as to supply some numbers?

Or just a source that describes what the efficiencies are?

Inefficient?

These two airplanes fly great on the props they are pictured with. They also happen to fly great on 2bladers. They also fly not so great on the 2bladers they don't like and the 3bladers they don't like. But there is almost nothing to choose from between the best 2 and the best 3. As for "efficiency"........ the engines don't seem to notice any difference and perform equally well with either, the spectators can't tell which is on the airplanes, and the airplanes don't show any difference in flight performance.

da Rock, while I have no specific site to send you, you could try the search function on RCU. I have read on many threads here where a 3 blade will not perform like a 2 blade, and 4 blades are for static only. It has something to with the Reynolds number, which has something to do with the size of air molecules and their effect on full scale vs models (rough definition). This month's RC Report had an article explaining how to make a four blade for static.

And therein lies the rub.
As much as we would like to think otherwise, the wisdom we find on the internet sometimes isn't really a good reflection of the truth.

Sometimes what everybody says has gone through a number of interpretations. And the fact is that this efficiency idea is getting out of hand.

For example, the Reynolds numbers each blade of a prop sees is going to be virtually the same for each blade, no matter how many blades are on the hub. And a reduction in scale isn't going to apply differently from a 2 to a 3 to a 4blade prop. And whomever backed his argument on efficiency with Reynolds numbers really laid it on.

I included pictures of two popular airplanes that fly excellently with 3bladers up front. If there is a difference in their performance from the 2bladers that've been on those same airplanes, it beats me what it is. As for a difference in efficiency, whatever that is, I've not even noticed a difference in fuel usage. But haven't actually done anything to test that as that aspect of "efficiency" is totally irrelevant to my choice of props.

It actually appears that the only real problem with choosing a 3blade or 4blade prop for our engine/airplanes is the lack of those props in different sizes and pitches.

da Rock,
I rarely counterpoint, but I think your post isn't quite accurate, no offense. I've done a considerable amount of research on the Reynolds number, and it does hold water. Think about the repeated phrase that 'bigger flys better'. It is true, and I have first hand experience with that theory (flying .40 size to big gassers). We simply don't have small enough air molecules to make a 4 bladed prop spinning in a 15 inch diameter at 10,000 RPM (for example) work efficently. The air is too big, so to speak. The prop will cavitate on it's own prop wash. Air molecules will not be able to fill the void fast enough. It's just too much turbulence.

That's the way I understand the Reynolds number theory, in layman's terms. Please correct me if I am wrong.

This is what I've always heard as well. The prop doesn't travel forward far enough to get the next blade into "clean" air. However I have seen plenty of scale warbirds fly just fine on 4 bladed props.

Ok guys, sorry to get everybody worked up over my foolish quirk. That being, a Mustang is suppose to have a 4 bladed prop.
Just to fill in the blanks, she's a 40 size with a .46 Evo. Flys good with the 4-11x6 but was hopeing to find larger diameter w/less pitch for scale.
Thanks for all your imput and I appologize again for getting people all cranked up for my sillyness.

You're not silly. You want what a bunch of modelers have wanted.

There really aren't a lot of 4bladers around. Never have been.

I just spent an hour or so searching the internet. Again. I looked really hard a month ago when I was trying 3bladers on my P47 and wanted to try 4blades. And was wanting the same for my 61engines. The problem we have is basically that there are only a very, very few available. I had to settle for a 3blade on the P47 because there wasn't even one 4blade in an appropriate size.

There does happen to be one manufacturer that offers a possible solution for larger engines and modelers with deep pockets. They offer a prop system that has 2, 3, and 4 blade hubs. Their hubs take the same blades (about $8 a blade depending on size) but take different numbers of them. The hub adjusts the blades to whatever pitch you want. You choose the number of blades, and buy the diameter you want. Then test and adjust the pitch to suit your application.

Is it a realistic solution? Not for me right now.

I've tested and found that my P47 works great with the 3blader, as good as with the best 2blader. And it looks better scale wise. "Better" is about all I can do right now. But 2 blades really look wrong. Three blades doesn't look bad. And they fly great.

You're absolutely right that the prop on the fullscale P47 works in better Reynolds than the prop on a 60size model P47. But that's not the issue and wasn't the issue to begin with.

It was stated that a 2blade works better than a 3 or 4blade. For example, "I have read on many threads here where a 3 blade will not perform like a 2 blade" and "In addition, 3 and 4 blade props are VERY ineffecient."and it was stated that it's because of the Reynolds numbers, "It has something to with the Reynolds number,"

There are a couple of different concepts that've been balled into one idea. And it'd be good for newbies to understand a couple of things about the differences between 2bladers and 3 and 4bladers.

Noone should avoid trying out a 3 or 4 blade prop on his model "because 3 and 4 blade props really are not very inefficient". While it's been proven that they are less efficient, the jury is out on how much. And modelers have proven without doubt that 3s are often as good or better than 2s. Precision aerobatics flyers use them by choice. To produce the extreme performance required, they work great. They're required because they are also quieter. But if they were VERY inefficient, those guys couldn't even consider them for their demanding event.

As to why more blades are less efficient that less. One of the strongest arguments it simply tip loss. More tips, more percentage of working blade lost.

And a 7" blade sees very close to the same Reynolds effect that a 7.5" blade sees. Almost identical chords, and after the engine reacts to the load, the speed also compensates. Chord and speed are major players in Reynolds. And if they're about the same and the scale effect is almost identical, there isn't a Reynolds difference.

Thank you for clarifying that for me.