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praterdj

Well Known Member
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. :p

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. :confused: 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.
 
Fixed Catto

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, :)
 
2 blade or 3

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!
 
2 vs 3

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).
 
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
 
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.
 
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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
 
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.
 
2 blade-vs-3 blade

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.
 
Another one of those hard choices

Don

If you don't mind advice from a Longhorn..... :eek:

This is one of those hard choices that really depend on your wallet and personal priorities. I too am still debating (been debating for over a year of course) since I am not going to be able to put it off much longer. You have to decide which advantages are most important for you. Also keep in mind the -8 can be nose heavy, especially with the 200hp which I have, so that was my number one issue, since the 15lb difference would be more when you add in the ballast I would have to compensate with. Since lightness and smoothness are my priorities and I would rather fly upside down than fast, I have pretty much decided on the MT, but I don't know if my accountant will allow it. ;)

Oversimplified quick points on the props that I thoroughly researched:

2 blade Hartzell
- Certified, Very good prop, faster, cheaper (by about $2500 new), metal easier to care for many service station, much heavier, more vibration, RPM limits (except for the just recently announced blended prop with no limits).

3 blade MT
- Certified, also very good prop, 2-5kts slower depending on who you ask, composite limited service stations, much lighter (15lbs), much smoother and quieter in vibration and perceived noise, no restrictions, less prop inertia due to lighter mass.

The WW left me a bit uneasy and the AeroComp is way out of my budget.



Steve Sampson said:
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!
Click to expand...

I hate to be the first :) , but actually Steve, the 3-blade is lighter.
 
Forgot

Oh yeah I forgot one other point.

You have a couple inches more ground clearance with the 3 blade. And if you ever put the prop into the ground it will splinter and you will not have to tear the engine down.

Not that I plan on putting mine in the dirt, but you never know. A hanger neighbor with a -4 was taxiing at Houston intl and an MD90 whipped by by, turned and blew his tail off the ground and put his -4 on its nose. He said "I had the stick back, but there was nothing to do but hang on and kill the engine."
 
Generally, 2-blade is more efficient in cruise and 3-blade has better climb, ALL OTHER THINGS BEING EQUAL. Problem is, all other things are never equal.
My Catto 3-blade (set up for climb) increased my climb and shortened my take-off roll by 17% and my cruise is the same (201 mph true at 75%) compared to my Sensenich wood. Plus I gained quietness, smoothness, ground clearance, and appearance.
Every situation is unique.
 
And if you ever put the prop into the ground it will splinter and you will not have to tear the engine down.


Not true, the current definition of prop strike by the feds includes even a slow down of the prop precipitated by things such as long grass.

If you plinter a prop blade you have to do a teardown to be compliant. I would bet however, that the probability of an engine passing the inspection without repair is much greater if the blade simply shatters.
 
Guys, I really appreciate all of the information you provided. This was exactly the type of dialog I was hoping for. More than some money is always a factor in the decisions I make but it is just one of the criteria. I really wasn?t aware of a few things:

-Consensus is that 3-Blade props are smoother and quieter. That is a definite plus. Smoother means lest vibration related damage to the airframe down the road.

-More expensive. I kind of expected this since I was leaning towards a 3-blade because I prefer the looks. Someone mentioned that the difference was around $2,500.00. That?s certainly enough to make it a consideration but all things considered it did not put it out of reach.

-Mel?s post was encouraging and if I choose the three blade I will definitely set mine up for climb. I am with most everyone else in that I have the desire for speed but I would certainly give up 2-3 knots to maximize climb. After all the 8 is a fairly fast ship anyway so I?ll still be very happy with the top end speed.

-I actually like the fact that if a prop strike occurs it will in theory do less harm to the engine.

-Weight. I have mentioned in several posts that I am 250 pounds in a tandem airplane so weight is a major consideration. I like the fact that the three blade is lighter.

Thanks again. Each of you offered constructive information that will assist me in my decision making process.
 
Don - I have said my bit so I wont repeat, but in your summary, you said the 3 blade is lighter. Not sure which manufacturer you are looking at but if you look at the spec for 2 and 3 blade props from MT, the 2 blade is lighter. I think this is true throughout their range. You can check on MT's web site.

Good luck!
 
I think that was 3 blade composite vs. 2 blade metal. I'm not sure, but I think I remember the 3 blade being lighter.

-John
 
jcoloccia said:
I think that was 3 blade composite vs. 2 blade metal. I'm not sure, but I think I remember the 3 blade being lighter.

-John
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Depends on CS versus FP as well. My 3 blade Catto FP is, I think, 18 pounds. A 2 blade metal Sensenich is in the neighborhood of 34 lbs. A CS 2 blade Hartzell (with governor) is around 55 lbs.

I have an IO-360-A3B6D, but put my battery in back and I don't have the forward CG issue that a lot of guys do in the -8.

And at $1850, you can't beat the price !!

Cheers
 
I'll check the mfg.

Steve Sampson said:
Don - I have said my bit so I wont repeat, but in your summary, you said the 3 blade is lighter. Not sure which manufacturer you are looking at but if you look at the spec for 2 and 3 blade props from MT, the 2 blade is lighter. I think this is true throughout their range. You can check on MT's web site.

Good luck!
Click to expand...
Steve?.Thanks for the heads up. I?ll certainly check the numbers from the manufacturer before I make the decision. I will be comparing a three blade composite against a metal two blade constant speed propeller. This is why I assumed that there would be a weight savings.
 
rv8bldr said:
Depends on CS versus FP as well. My 3 blade Catto FP is, I think, 18 pounds. A 2 blade metal Sensenich is in the neighborhood of 34 lbs. A CS 2 blade Hartzell (with governor) is around 55 lbs.

I have an IO-360-A3B6D, but put my battery in back and I don't have the forward CG issue that a lot of guys do in the -8.

And at $1850, you can't beat the price !!

Cheers
Click to expand...
Mark,

Thanks for the post. I was typing my last response when you entered yours. I'm pretty excited about the opportunity to save around 37 pounds on the nose. I'm planining on putting my battery in the back as well so this should help a lot.

Mel mentioned he was running a Catto as well so I'm certainly going to check them out. The price alone may have made the decision. Not that it was the only factor but considering I was wanting a three blade anyway it was the icing on the cake. :cool:

Thanks to all for their input.
 
Constant speed

praterdj said:
Steve?.Thanks for the heads up. I?ll certainly check the numbers from the manufacturer before I make the decision. I will be comparing a three blade composite against a metal two blade constant speed propeller. This is why I assumed that there would be a weight savings.
Click to expand...

Good, I mentioned only the CS props in my post, because that was what I thought you were lookng for. So, in that case the composite MT is lighter (about 15lbs) than the Hartzell. The WW is even lighter, so you may want to research that. I stopped looking at it after I read a few things.

Good Luck,
 
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