Two Blades Versus Three Blades

praterdj · #1 07-19-2006, 09:17 AM

There are discussions ongoing about props but they are typically related to a specific engine. I don?t recall a question specifically around two blade vs. three blades so please don?t feel the need to slam me for asking a prop question even if you think it has already been addressed.

I plan to use a 360 on my 8, not sure if it will be an o-360 or an IO-360 as I am still weighing the advantages/disadvantages of each.

My question is two blades versus three blade props.

I have always preferred the looks of a 3 blade over a two blade (Personal opinion) but I am questioning the performance. I know in RC flying a 3 blade has some drawbacks if not properly applied. (Size ? Pitch)

Does anyone have any experience with both that can offer an assessment of the performance qualities of a 3 blade versus a two blade? I would like to know comparisons for climb, cruise, and what the disadvantage would be of using a fixed pitch three blade.

I really wanted a constant speed prop and the costs alone may prevent me from using a 3 blade. Any information would be greatly appreciated. This is one of the critical decisions that can have a significant impact on performance.

pierre smith · #2 07-19-2006, 09:31 AM

Hi Donald,
I have the three-bladed fixed Catto on my -6A and I can cruise at 204 TAS at WOT and 8000 and it is sooooo smooth, the main reason I went with it. It is also quieter on the ground and in the air. From what I gather, a good two bladed prop is better in climb and cruise (a little faster), but the smoothness and comfort is worth the coupla MPH loss.
Regards,

Steve Sampson · #3 07-19-2006, 10:29 AM

Don - I thought about this a bit back and summarised my thoughts on my build log here . It might give you a couple of data points to add to your list. Scroll down to the May 26th entry. No one has come back with hard data to say I am wrong on any of my asertions though it is why I wrote it to see if I would flush any more info out.

Cheers!

Yukon · #4 07-19-2006, 10:37 AM

Don,
I've been trying to decide between 2 or 3 bladed MT. From what I've been told by distributors, 3 blade is a little quicker for takeoff and climb, but 2-3 mph slower in cruise. 3 blade is somewhat smoother, but I understand that even a 2 blade is quite smooth (composite).

mandm1516 · #5 07-19-2006, 10:58 AM

Not speaking from experience nor do I like speaking for others, but Randy Lervold did a pretty long write up on props on his web site www.rv-8.com comparing a few 2 blade and one 3 blade for climb rate, top speed, noise and cruise.
Mike

Low Pass · #6 07-19-2006, 11:03 AM

1. If you have the $$, get the injected engine. IMO, the efficiency alone makes it worthwhile. Carbs have lots of pieces, don't work upside down and are fairly inefficient at vaporizing fuel evenly.

2. Prop choice - very generally speaking (with comparable blades/airfoils/ mfgr/matls) 2-bladed props are more efficient, more noisy, more vibration prone, less expensive, lighter, less complex.

Does anyone make a FP 3-blade for 180-200-HP GA applications? IMO, I would go with the performance of a 2 blade CS over the smoothest FP prop.

Also, doesn't mean that the best available 3-bladed prop isn't better in these areas than the best available 2-bladed prop. It's just general characteristics of propellers.

alpinelakespilot2000 · #7 07-19-2006, 11:17 AM

Do you want to hand prop a 3-blade if you ever need to? Just something else to add to the equation.

penguin · #8 07-19-2006, 11:34 AM

Hartzell blended airfoil 2 bladed c/s seems to be a pretty good option right now. There has been plenty of discussion on this topic before - I would suggest a search of the archives will produce plenty of hits.

Pete

Davepar · #9 07-19-2006, 12:01 PM

Another data point for nose gear planes is that the bottom cowl is slightly more difficult to install/remove with a 3-blade. You have to extend the slot for the nose gear leg.

glenn654 · #10 07-19-2006, 03:09 PM

I have a -4 w/ a Catto 3-blade FP on an O-320-D1A, 160 HP and have been very happy w/ it's performance. Very smooth and quite...like Pierre says. I had a Pacesetter 200 before and had no idea how noisy it was until installing the Catto. Climb inproved slightly (about 100-150 fpm), just as fast as Pacesetter, light weight, simple and no maintaince. My climb and take-off distances are not as good as my C/S buddies but they can't ourrun me except w/ more horses. I've read somewhere (can't remember) that the drag penalty of the third blade is very minor. I'd recommend the 3-blade for the smooth, quiet operation and especially the Catto.

Glenn
N654RV @ OKZ

P.S. I'm not really on commission....I just like the prop.