2 Blade vs 3 Blade?

OK Guy's I need some general info on the pro's an con's of why/were we would want to use 3 Blade Prop vs 2 Blade.
Happy Holiday's,
SteveC.

First advantage would be to use a smaller diameter prop for more ground clearance. Read one time that the formula was to multiply the diameter of the 2 blade prop by 90%.

The 3 blade uses more power than a similar size 2 blade which will load the engine more. Useful if the engine needs a larger propeller but you are limited in clearance.

Hi,
Can I just butt in here with a related question of my own. Would
using a multi-bladed prop. also tend to dampen vibration more than a
2 blader,due to greater "flywheel effect",or is that just horsefeathers ? Thanks.

Bob Allan

Ive personally seen a three blade cure an erratic engine run on a plane after 70 + flights trying to correct this using the changing of fuels, plugs,tanks ect.
The installation of the three blade was to check on difference in
turning capability vs. 2 blade.
this absolutly cured the run problem and is repeatable both ways.
We don,t know if it was a reasonation change causing tank foaming to
cease due to rpm difference or what; but changing back to different
pitch and dia. 2 blades causes the problem to return.
Let me add , all props were well balanced.
Also ;this occured on a profile model( I hate profiles )
Charlie Pate

sounds like a classic case of fuel foaming in the tank due to a vibration harmonic.

Part of the reason 3 blade props run smoother is the airflow. With an even number of blades two blades generate a vibration from the airflow- one blade hits its highest Angle of Attack at the same time the opposite blade hits its lowest angle, adding a side to side vibration. Read a story once where the RAF nearly lost a test pilot to this. They were trying soak up more power and went to a 4 blade prop, from a 3 bladed one.

Hi,

I prefer the 3 blade over the 2 blade because from what I have observed the 3 blade has better vertical performance than a 2 blade. If you keep the CG in a good spot the turn rate isn't hampered to any degree either.

>OK Guy's I need some general info on the pro's an con's of
>why/were we would want to use 3 Blade Prop vs 2 Blade.
>Happy Holiday's,
> SteveC.

Bob Hunt said once that the 3 blades gave him better overall tension, that his Saturn flew as if it was "nailed to the hemisphere".

But he said also that on bad wind the 2 blades gave him better corners.

Paul Walker is opposed to large diameters, saying that they hurt the turn. For 2C engines, 12.3" diameter is his max, but I think he runs more on the Saito .72, like 14" 3 blades. My only experience with props over 12" was to change from 12-6 APC to 12.5-6 APC on my 2Star .60bb. While I liked the 12.5", that doesn't mean much. I can't recall ever using a 3 blade.

On boats, I know what more blades does, and yes, the more blades make it run smoother. I run a "Hi-Five" 5 blade on my bass boat. Hole shots are much better, it will stay on plane at a lower speed, it's much better in rough water, always easier to drive, and it's just as fast as both the 3 blade Laser II's I have. This is on a "small" lower unit, XR-4 Merc 150. Steve

>OK Guy's I need some general info on the pro's an con's of
>why/were we would want to use 3 Blade Prop vs 2 Blade.
>Happy Holiday's,
> SteveC.

I have found threw experience that I like the three blade better on the bigger motors ST 60's Os 46VF and PA's. Threw my experience they have always-improved vertical and overhead performance especially on heavy airplanes. On the smaller, lighter planes I've built I've always liked the performance of the two blade.

Trying propellers is part of trimming a plane just like lead out position and tip weight. My advice is try them both, never be afraid to try a different prop on a plane. Sometimes you get a pleasant surprise from the prop you didn't think would help. I trim my planes with both and go with what I like the best. On the average it takes me about 40 flights to get an airplane where I like it and some have taken three times that. Don't be afraid to make small changes one at a time you can always put it back if you don't like it and if your flying a pattern you most likely will fly a pattern every time you make a change.