3 blade props. What do you think?

[Larrynoel]

I have a McCauley 3 blade prop on my 67C.  I got the airplane this way and it seems work fine.  Are any advantage to it or dose it just look cool? Or, is there some disadvantages? What do you think. Thanks, Larry

[Parker_Woodruff]

It runs a bit slower in cruise, but will help climb performance.

Some 3-blade props have this goofy harmonic/vibration when installed on the front of a 4 cylinder engine, but some don't.  I've flown in one that didn't have an issue, and one that gave me a headache from the noise/vibration.

They also weigh  more and cost more to overhaul.

[Kevin]

I agree with Parker on all counts, especially on the "goofy harmonic/vibration" count. I don't know why it is, but you can install the same prop on 5 identical Mooneys and it will be fine, and on the 6th one it will vibrate.

[Earl]

Also I believe the 3-blade props are a bit shorter than the 2-balde so you get one more porpoise before a prop strike.......OK, that's probably not a mental image we want to have.  How about more clearance when operating off a grass field?

[fantom]

We have one engineer around here who recently put an MT 3 blade composite prop on his J. Evaluation and pictures to come soon, I hope. ;-)

[KSMooniac]

Jim and Gary are correct...the existing metal 3-blade props for Mooneys are the same diameter, so all you get is more weight, more cost, slower cruise speed and more vibration to go with better takeoff and climb.

I did install an MT last month but haven't gotten my free time to line up with a clear, smooth day yet!  I've flown one quick test flight, one trip and a BFR/IPC but haven't done my performance testing yet.  First impression is definitely better takeoff and climb, but I'm not sure yet on cruise.  I'm pretty sure I haven't lost any cruise speed, but I was hoping for a 2-3 knot improvement over my square-tipped McCauley.  We'll see...

[kortopates]

There is one other significant difference. When you pull the power to land, a 3 bladed prop has so much more drag its truly amazing how the plane slows up more quickly compared to the 2 bladed prop. Its really much more forgiving to the pilot that comes in a bit hot and otherwise would float a great deal more. However, if you loose that engine and become a glider that additional drag is going to work against you. Maybe after pulling the prop control all the way back for best glide the difference is minimal - I don't know of any data either way. But given the loss in cruise performance, at least for metal 3 blade props, and additional weight hit on useful load, the only real reason to get one is ramp appeal. A few years back, one of the manufacturers was selling 3 blade props discounted to a price less than 2 blade props and thats when we saw a lot of 3 blade props put on 4 cyl Mooneys.

[Earl]

Quote: JimR

I believe that that is only the case with the 3 blade MT prop.  The other 3 bladers are the same length as the two bladers, so they offer no ground clearance improvement.

Jim

[scottfromiowa]

All comments you made (last post) and were told appear CORRECT (regarding a 3-blade prop)  I'm just back from vegas and in a betting mood.  I don't know what you two blade prop guys are reading...cause my prop...that is METAL is definitely shorter than a stock two blade prop providing more ground clearance and definitely improved climb and ground roll.  The cruise penalty is NOT significant...and my prop definitely LOOKS better than a two blade prop.  The two vs three debate reoccurs about every three months.  It's like bladders...I value the climb and aesthetics/ground clearance.  Some feel the price cruise penalty makes two blade the better pick.  I have ZERO regrets on my prop through 300 hours.  Vibration is a NON-factor...

[scottfromiowa]

In a two blade prop the blades are aligned, right?...to diameter "'s both blades plus spinner for your 74" or 71"?  I'm talking individual blade length and ground clearance from tip of blade to ground.  What is your individual blade length and distance to ground?  I'll measure mine and I'm betting my three blade has a shorter blade and more ground clearance...if I'm wrong, I'm wrong, but I don't think I am.  My blades don't "line up" so diameter would be different with a 3-blade.

Also, in the event of a gear up whether through gear or pilot failure the three-blade will hold the aircraft up on two blades reducing potential damage to belly, wings/tail.

[sleepingsquirrel]

Cats an dogs flying in airplanes , now grown men measuring,  and one of them betting his is SHORTER ! 

Scott makes a good point about the three blade prop holding the plane off the ground. Forgot to mention the reduced wear on the nose wheel and mains as a matter of practice.

[Lood]

I don't have any knowledge of the other makes, but Hartzell's default diameter is 74 inches - for both the two- and the three blader props for vintage Mooney's. Thus, no difference in ground clearance here.
If the diameter is the same, the radius and cross sections are both equal on either prop and as a result, also the ground clearance. However, there is a diameter reduction allowed down to 73 inches on the three blader and to 72.5 inches on some two bladers. So, it comes down to what's currently installed and with what you aim to, or have repaced it with and whether you've opted for the diameter reduction...

[Earl]

I just went to the Hartzell website and their top prop conversion allows a diameter reduction from 74" for the 2-blade to 73" for the 3-blade.  What is interesting is they show the diameter of a 3 blade as 76" but it can somehow be reduced to 73", which is not allowable on the 2 blade.  Not sure haow that works.  Harder to find specs on the McCauley site but they have some goofy pdf with Professor Propeller telling you that one of the advantages of a 3 blade prop is more ground clearance.  Maybe the hub where the blades are mounted is smaller and you get the reduction there?

 

As for me, I went with the longer, cheaper 2-blade blade and my wife loves it!

[scottfromiowa]

Going to measure clearance today.  An excuse to go out to hanger on another overcast Iowa winter day...

My propeller model is B3D36C524-E Model is 74SA-0 so there is a "74" in the blade model.  My prop is a McCauley.

Hmmmm...may be eating some humble pie, but I will have tip down and measure from end of tip to ground to see what clearance is.  Understand varience based on biscuits.  I wonder what difference in actual blade length/hub/spinner there are between props to get this "74" diameter?  My spinner is "BIG"...perhaps that offsets my short blades squirrel  To hard to measure this as I can't measure straight through because three blade individual props are NOT lined up.

[scottfromiowa]

Glad I had better luck in Vegas (3/4 on red) humble pie eaten Jim.  My prop is 9 3/4" right at top of your range for clearance...might be a little more as nose gear settles into a depression, but no more than 1/2 inch.  Apparently there is NO real difference in ground clearance between a 2 and 3 blade prop.

[fantom]

Guys....don't neglect to keep checking the nose gear tire pressure. Don't want to lose ANY clearance from an uninflated tire.

[sleepingsquirrel]

That was one question I asked my instructor on my Mooney check ride. If the nose wheel blows should I expect a prop strike? He said no.

[eaglebkh]

The 3-blade McCauley came on my E when I bought it.  The only real advantage I have experienced is the elimination of the Hartzell 2-blade AD.  I really can't say that climb performance is all that great, because at max gross I can barely acheive 500fpm out of my 628' home base.  Just the wife and me, and I can usually get 800-900fpm no problem.  Solo is 1000fpm+.

I don't believe the extra weight and cruise speed penalty are worth the potential gain in climb performance and ramp appeal.

[KSMooniac]

The MT 3-blade prop is the only one that has a smaller diameter than all of the other metal 2- and 3-blade props that are approved for our planes.  Other airframes have 3-blade options that are shorter than 2-blade options, but not our Mooneys.

[clh]

Quote: sleepingsquirrel

That was one question I asked my instructor on my Mooney check ride. If the nose wheel blows should I expect a prop strike? He said no, but don't land it like a wheelbarrow!

[DaV8or]

Quote: KSMooniac

The MT 3-blade prop is the only one that has a smaller diameter than all of the other metal 2- and 3-blade props that are approved for our planes.  Other airframes have 3-blade options that are shorter than 2-blade options, but not our Mooneys.

[KSMooniac]

Dave, do you know which STC they are approved under?  I didn't think there was a 2-blade McCauley approved on the IO-360 AIA Mooneys, but I could be mistaken.

[kerry]

Has anybody heard of a one blade propeller.  Not for a mooney, but for other aircraft.  Years ago someone was telling me about one bladded aircraft propellers.  This came up when we had a discussion of 2 vs. 3 blade propellers.  I tried to find info on it but came up empty.

[sleepingsquirrel]

I think model aircraft running for speed use a one blade counter weighted prop. I don't think that it's practical for a one bladed prop to be used on larger aircraft because of power density. I always thought that the number of blades had to do with the horsepower of the engine and power density. There is something to do with the effeciency of the blade and it's percentage of the area of the propeller disc and the strength of materials the prop can be made from in the existing technology. One blade transmitting 280 HP to the air is closer to limits of  material failure than 3 blades sharing the load. The Sea Fury had five blades to handel the HP , keep the tips subsonic ,and give ground clearance without cranking the wings like the Corsair. I think that propeller technology really needs the tips below supersonic speeds to be effecient, for a given RPM then there is a maximum diameter, for a given HP there needs to be the right number of blades to turn HP into thrust without exceeding the stength of the material the prop is made from. Too many blades gets into more blades = more tips=less efficient just due to tip losses.(there are other losses when lift is generated as well)  This is what gave birth to the jet age. We are just the orphan children of technology that reached its peak around 1945.

There have been advancements in propeller design, recip engines, and material. However, the gains are not quantum leaps. I have read that our propellers are not more than 5% more efficient than the Wright's  props.

  OK I'm out on a limb now, but squirrels are good at that.

http://en.wikipedia.org/wiki/Single-blade_propeller   example of a low power application.

[LT4BIRD]

My friend has a three blade on his 201. Same year as mine only I'm running the two blade. We did flights of two several times with almost the exact performance. I had maby two knot's on him. Climb was about the same.

Two bade is faster but the three blade is so sexy...