3-Blade or 2-Blade Prop on a Single (200 HP) Engine?

How many blades are better on a single 200 HP propeller engine?

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Alex Batista

Alex Batista

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Here’s something else I’ve been curious about while looking at airplanes to buy. What is the difference between a 3-Blade and a 2-Blade prop? Many of you know I’m in the market for a Piper Arrow II or III; I’ve seen some with 3-Blade Props and others with 2-Blades. What’s the simple (and/or detailed) answer in your opinion?
 
3 blades is sexier. They are usually smoother.

Drawback might be maintenance cost if you're 3 Blade CS. Mine is fixed pitch so mx is near zero, just re-torquing the bolts at each oil change.
 
3 blades are purportedly smoother and quieter, give better ground clearance since in any application they’re generally shorter, and look sexier - - -

Generally more expensive, worth it? - YMMV.
 
3 blades tend to be quieter. You lose a little in cruise, gain a little in climb/take off performance. On Comanche's one of the 2 blade props has an AD on it that requires something to be done every 500 hours. The 3 blade does not. 3 blade is heavier and could affect forward CG on the W&B.
 
3 blades tend to make lower cowl removal more complicated and requires 2 persons. 3 blades cost more than 2 when it comes time for servicing.


Tom
 
On the Arrow the best mod is the Hartzell Model HC-C2YR-1BFP/F7497 Constant Speed (Scimitar) prop...My 180 with all available speed mods/speed tips, and this prop was 140knt airplane at 6500-8500...often questioned till people flew it...smoother, lower noise and 3-5 knots faster than stock prop and no rpm limitations...modern prop tech and my 68 short body Hershey bar Arrow is was the fastest of any I have flown...others seemed to be 125-135knt range and long bodied tapered wing III three blade being the slowest...
 
3 Blade.............Heavy, expensive, slow.........and no quieter than a 2 blade. The sound depends on length.........and many, like the 3 blade 401 86" for the Cessna 185 are MUCH louder.
Besides, they don't look "sexy!" They look ridiculous!!
 
For most spam cans added weight at the prop is a double negative. Added weight is bad enough, putting it at the forward most part of the aircraft is even worse in most cases.
 
kgruber said:
3 Blade.............Heavy, expensive, slow.........and no quieter than a 2 blade. The sound depends on length.........and many, like the 3 blade 401 86" for the Cessna 185 are MUCH louder.
Besides, they don't look "sexy!" They look ridiculous!!
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I won't trade my C401-86 for any 2-blade!
 
bnt83 said:
For most spam cans added weight at the prop is a double negative. Added weight is bad enough, putting it at the forward most part of the aircraft is even worse in most cases.
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It allows me to put more stuff in the back, which is the point of having a "Wagon." No CG problem on my plane, even when on retracted wheel skis.
 
Stewartb said:
It allows me to put more stuff in the back, which is the point of having a "Wagon." No CG problem on my plane, even when on retracted wheel skis.
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Right except many spam cans have the CG so far forward as it is that its practically impossible to load it out of the aft CG anyway.

Then they flare & land like crap when flying solo with little in the back.
 
As part of my unplanned engine and prop event on my Mooney I'm switching back to a 2 blade. Oddly the Mooney 2 and 3 blades(except the MT Composite) are the same length so there's not really any other gains there. Now, if I had known the engine shop was going to take so long I probably would have gone with the the MT.
 
MooneyDriver78 said:
3 blades tend to make lower cowl removal more complicated and requires 2 persons. 3 blades cost more than 2 when it comes time for servicing.


Tom
Click to expand...

That's going to depend on the airplane. The lower cowl on the Comanche isn't affected by it being 2 or 3 blade the way it goes on or off.
 
Warlock said:
On the Arrow the best mod is the Hartzell Model HC-C2YR-1BFP/F7497 Constant Speed (Scimitar) prop...My 180 with all available speed mods/speed tips, and this prop was 140knt airplane at 6500-8500...often questioned till people flew it...smoother, lower noise and 3-5 knots faster than stock prop and no rpm limitations...modern prop tech and my 68 short body Hershey bar Arrow is was the fastest of any I have flown...others seemed to be 125-135knt range and long bodied tapered wing III three blade being the slowest...
Click to expand...

Wow! That’s very interesting! How much did that upgrade cost you? Or did you buy it like that?
 
EdFred said:
3 blades tend to be quieter. You lose a little in cruise, gain a little in climb/take off performance. On Comanche's one of the 2 blade props has an AD on it that requires something to be done every 500 hours. The 3 blade does not. 3 blade is heavier and could affect forward CG on the W&B.
Click to expand...

You're not welcome to offer advice here any more. You sold your plane. ;)
 
Alex Batista said:
Well I’m sure there’s more to them than That, no?
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Thrust vs. drag for a given power setting.

For a given blade geometry: At cruise, as power increases, more blades are needed to keep each blade delivering thrust in an efficient performance band. But each blade generates additional drag.

Below 200 HP or so, the equation tends to favor 2 blades for max cruise performance. 3 blades will generally fly slower.

Above 300 HP, 2 bladed props can be loaded beyond their aerodynamic sweet spot. 3 blades can share the thrust better, outweighing the drag losses from one more spinny thing.

In between, it depends. In climb, 3 blades can often provide better performance even in lower HP engines.
 
When shopping for airplanes, the propeller on the front of it is pretty far down the list of criteria that would make me buy one over another. Of course this assumes that the prop that is on the plane is airworthy, has no burdensome ADs against it, and is legal for the airplane.

The rest of the posts here have the specific differences covered.
 
If you happen to have gobs of HP, more blades are more better.

cw-news-dowty-propellers.jpg;width=550;quality=60


With wee bits of HP, sometimes only one will do.

J2-Cub-Single-blade-prop.jpg
 
mondtster said:
the propeller on the front of it is pretty far down the list of criteria that would make me buy one over another.
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Yeah, I figured. I started this thread just as an educational piece to learn both some “facts” and some “opinions”.
 
The scimitar prop stc is about 9k...for the arrow only if you need a new prop does it make sense...
 
Alex Batista said:
Is this still true if we’re talking about a CS propeller?
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I think it varies by plane and by prop but generally yes. The thing to keep in mind is while 3 blade are generally slower, we're not talking big differences in speed in most cases. A couple knots usually. Close enough any number of other factors could all but make the difference non-existent when comparing any two similar planes. A bigger factor is probably the weight difference and cost difference in most cases.
 
The benefits have all been covered above already. I'll add that most of the things stated are generalizations and they are typically true, the specifics do matter. On the 414, going to 4-bladed props improved performance in all phases of flight. However the old props were junky original McCauleys. I would get PIREPs from people who have done both to see what the pros and cons are for your specific application and how you intend to use the plane before making a decision one way or the other.

MT props are usually lighter weight being composite. So I went from 3 blades to 4 blades and gained performance while losing weight. The same would occur on the MU-2 if I went from 3 blade (Hartzell) to 5 blade (MT) - less weight. The performance of the MTs on the MU-2 is more debated.
 
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