RE: Propeller crash course!
 

A lot of flyers wind up with the idea that there is one and only one best prop for an engine. And that belief usually settles down to the belief that it's about the only thing to use.

The 12x6 prop on a 46AX suggestion is an excellent one. Why? Because it's tempered with the information about what airplane was hooked to the engine/prop. Because the real deal is what airplane is being dragged around more than anything else.

I've been running 46AXs for a year now and have pumped out jeez, 8 or 9........ ok, I just went to the shop and counted..... 12 for me and two for friends...... pumped out a BUNCH of 46size ARFs in the last year. And I've experimented like crazy with props. And the experiments have been on different airframes.

Trust me, your 46AX will pull almost anything and do it with almost any prop. OK, that's too broad..... If the airplane is from a 30 size to a 60 size the 46AX can do it. But it needs the right prop for the job. And it'll swing from a 10" to a 13" diameter prop and do it like a bull, but you've got to make sensible choices for the pitch. The choice of pitch is dictated by the weight and drag and purpose of the airframe after you've decided on the diameter. If you decided you need to change diameter or pitch, you'll need to revisit the appropriate pitch. This ain't soundbite simple.

And you will have to set engine rpm for the prop load and the needle for the right fuel flow with whatever prop you're using.

The 46AX will turn a number of 12x6 props excellently well. The "extra" inch of diameter turns the power system into a steady PULLING thing. Don't get lost in the idea that the engine delivers some theoretical horsepower max at whatever awesome rpm the advertising says. That doesn't apply to your airframe EVER.

I've adjusted prop diameter to get the max fan (diameter) working for the pitch that I wanted from the power system. With one much flown airplane, the best prop has been a 11.4x5 sorta wide blade, that I make out of purchased prop. The airplane and engine are excellent with that. What's the rpm? Don't remember 'cause it means so little. That prop won't work as good on another of my 46size beauties. But a 12x6 does excellent. That rpm? Don't remember 'cause.............. But believe it, both engines are putting out close to max power for the needs of that airplane.

RE: Propeller crash course!
 

Darock, I feel more confident now into keeping the 12x6 on my trainer :)
Will fly with it for a week or so and then see how confortable I am with it...

RE: Propeller crash course!
 

With experience, you can learn to tune an engine without a tach but you won't be able to tell how fast it is turning with out one. I am not impressed when flyers say that there engine is really strong because "it screams!" Much more useful is rpm numbers to go with the the info on what prop they are using. The tachs have dropped in price by 2/3 over the last couple of years. I am currently using a Globee which I really like and is priced at under $25.00 at Tower. Well worth having! [8D]
[8D]

RE: Propeller crash course!
 

G'day Darock,
Thanks a heap mate, I have been trying to get people to forget about "Maximum Horspower" & stuff like that, & get em to try various props to suit, not only their aircraft, but also the way they fly that aircraft.
In this world not all planes are created equal.

RE: Propeller crash course!
 

Unless I missed it, noone mentioned it/this. Once in the air and flying your rpms will go up, by how much depends on factors already stated.
And air temp has alot to do with how high a motor will spin up, motors make less power in the heat. Hot air/less hp.
And to a lesser extent props are affected by the air temp. Cold air is more dense than hot, therefore the prop will be getting a slighter better bite and may not turn up as high as it would in hot air.
Most of this will not matter squat to most of us. But to anyone squeezing everthing possible out of their plane, it starts to ad up.

RE: Propeller crash course!
 

G'day JD,
Your statement may be true, but the I think you notice a difference in engine speed when cool, as opposed to hot, is the air density, true. But I think you will find it has to do with combustion, more than prop. When the air is cooler, more density, you can run your motors slightly leaner, as the air warms up, gets less dense, you have to richen the mixture or it will be too lean & stop.