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3 blade vs 2 blade

A

almarsh

Well Known Member
WOULD LIKE SOME INPUT ON PROP SET UP FOR FIXED PITCH 0320 160HP CARBURATED ENGINE SET UP . PLEASE CAN ANYONE GIVE ME THE PROS AND CONS FOR EACH, AND WHAT THE PRICE DIFFERENCE MIGHT BE ??????? THIS IS A RV6A SET UP

THANKS

[email protected]
 
almarsh said:
WOULD LIKE SOME INPUT ON PROP SET UP FOR FIXED PITCH 0320 160HP CARBURATED ENGINE SET UP . PLEASE CAN ANYONE GIVE ME THE PROS AND CONS FOR EACH, AND WHAT THE PRICE DIFFERENCE MIGHT BE ??????? THIS IS A RV6A SET UP

THANKS

[email protected]
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I cant comment on your specific setup, but as far as the general question of 2 vs. 3 blade prop, I have asked the same question before and if you do a search you should find more than a few posts on that topic.

good luck
 
3 blades: better ground clearance, smoother operation, about 1000.00 more than a 2 blade. cool factor:cool:
2 blades: lower cost, around 1500.00 for the prop.

Hope this helps. I prefer the three.
 
Two vs Three

Two blade is much noisier but more efficient and gives you more of everything including vibration.

I upgraded to a 3 blade CATTO and found it to be much smoother that the 2 blade, but my takeoff and climb performance was certainly a little less.

H.
 
hughfi said:
I upgraded to a 3 blade CATTO and found it to be much smoother that the 2 blade, but my takeoff and climb performance was certainly a little less.
H.
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That's interesting. Typically 3 blades improve take off and climb performance. I went from Sensenich wood 2-blade to Catto 3-blade. My take off roll shortened 17% and climb went up 15%. Cruise stayed the same.
 
With the "A" model an advantage of 2 blade over 3 blade is cowl removal.

It is a PITA to drop the lower cowl with the 3 blade.
 
3 blade good

Have the 3 blade fixed on 160 lyc. for 400 + hours
pitched for 2600 rpm cruise
the new 2 blade Sensenitch(50 hours) has been in the box a few years and I cant imagine going back to it for all the reasons you can read about here on the threads.
Anyone looking for a 2 blade Sensenitch?
Keith
 
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Mel said:
That's interesting. Typically 3 blades improve take off and climb performance.
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I'm surprised to hear that, as a two blade prop is more efficient than a three blade prop. Variations in design between manufacturers can play a significant role, of course. I once flew a 182 that went from a two blade to a three blade, then back to the two immediately due to the decrease in performance.
 
Flyfalcons said:
I'm surprised to hear that, as a two blade prop is more efficient than a three blade prop. Variations in design between manufacturers can play a significant role, of course. I once flew a 182 that went from a two blade to a three blade, then back to the two immediately due to the decrease in performance.
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It just seems like the performance is better due to all the vibration....:)

The fastest fighters in WWII had 3 and 4 blade props, not 2.
 
Apples-to-apples proof positive that three blades are both smoother AND faster: A guy was flying his 182 with a three blade, lost part of a blade and he said vibration went up and speed went down;)

Bob Kelly
 
David-aviator said:
The fastest fighters in WWII had 3 and 4 blade props, not 2.
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Apart from lowering tip speeds, this also allowed them to make the prop blades short enough that the tips didn't prevent a wheel landing. And keep in mind that the fastest fighters in WWII also had extremely high power to weight ratios... There's no replacement for displacement, as they say...
 
YES

videobobk said:
Apples-to-apples proof positive that three blades are both smoother AND faster: A guy was flying his 182 with a three blade, lost part of a blade and he said vibration went up and speed went down;)

Bob Kelly
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Now, that there is funny, I don't care who you are!

Chuck
 
re

i once flew with a guy who had two blade prop he lost one blade in flight and noticed that vibration picked up as speed was significantly decreased
 
Skylane POH excerpt

This is straight from the 182S "information manual"/POH:
"Performance above is based on a 2-bladed propellor. Performance with the 3-blade propellor is essentially the same as shown above."

FWIW
 
I can deal with the slight difference in speed (if there is any), for a smoother ride and they look better. Here's another question, which company is showing the best performance on a 3 blade prop?
 
2 vs 3 blade

I suspect that specifics of the installation in a given airframe are more meaningful than generic 2 vs. 3 blade differences. Nevertheless, I've been very disappointed by the performance of two 3 blade props on our airplanes. After an AD requiring replacement of the Hartzell 2 blade on our Lance we couldn't get a new 2 blade prop for at least 6 months from Hartzell. They would however immediately sell us a three blade for the same price, supposedly a newer design that gave better climb and same cruise as the 2 blade. We bought it to get flying again and found it didn't perform. The climb is not noticeably better and cruise is at least 5 mph slower. Prop tip clearance, a factor with the Lance, is better. Maintenance access is much worse and you can't safely hand prop it now (in my opinion - ymmv). Similar findings on our Pitts S-2A. After a prop strike we were able to get an MT 3-blade (the only other prop certified for the airframe) for a similar price as a new Hartzell and thought we'd get better performance. In the real world it may hang on a bit better at the end of up lines, but cruise climb is no better. Cruise speed is again about 4 or 5 mph less that the Hartzell 2 blade. A huge difference with the MT is power off drag, very much higher than with the Hartzell. This makes power off approaches from downwind by the runway end extremely short but exciting! Whether it's due to 3 vs. 2 blades, pitch limits or blade airfoil characteristics I don't know. The composite 3 blade was actually slightly heavier than the metal 2 blade but didn't affect cg much. I won't hand prop the 3 blade for safety reasons although I did hand prop the plane many times with the 2 blade. Prop tip clearance is very slightly better, but this was not an issue at all with the 2 blade on the Pitts. Maintenance access is worse with the 3 blade. The MT is smoother but not dramatically so. Both 3 blade props will be more expensive to overhaul than a 2 blade when that time comes. I'll never again get a three blade prop on a light aircraft without convincing objective evidence of its performance edge. I must admit that the 3 blade looks cool, so that could be a factor for some buyers - just not for me. Hope all this is helpful.
 
Flyfalcons said:
What is the climb penalty?
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There is no real climb penalty. The two blade as slightly more static thrust than the three but at a common climb to cruise they are near the same. If you are climbing at max climb the two will be slightly better. Choosing between the two is all about your mission for the aircraft.
 
props interchangeable?

If an RV7A has it's cowl built around the Sensenich prop/spinner, can a Catto 3 blade prop/spineer be installed later without having to redo the cowl (or anything else)? and vice versa?

Bevan
 
Hi Beven,

Obviously the spinner would need to be changed. The cowl "slot" for the nose gear would also have to be lengthened if you had the minimum required for your two balde. This, in turn, may require some rework of you intersection fairing (or a cover plate) to cover the slot extension forward of the nose gear.

As mentioned, getting the cowl off, even with the extended slot, is more difficult than with a two blade. However, after a couple of times, you will have the procedure down!

If I had it to do over again, I would still go with the 3 blade Catto. Performs well, looks great, is quite, and really smooooootthhh!!


Hope this helps.

Cheers,

db
 
It depends ...

almarsh said:
WOULD LIKE SOME INPUT ON PROP SET UP FOR FIXED PITCH 0320 160HP CARBURATED ENGINE SET UP . PLEASE CAN ANYONE GIVE ME THE PROS AND CONS FOR EACH, AND WHAT THE PRICE DIFFERENCE MIGHT BE ??????? THIS IS A RV6A SET UP

THANKS

[email protected]
Click to expand...

On the same plane (O-320, 160HP, RV6) I have flown:

1. Ed Sterba, 2-blade, Fix Pitch Wood
2. MT, 2-blade, Fixed Pitch Composite
3. Craig Catto, 3-blade, Fixed Pitch Composite
4. Hartzell, 2-blade, Variable Pitch Metal


Have also flown an RV9A (O-320) with the same 3-blade Catto and a 2-blade Sensenich.

[And I have a NEW Sensenich, 2-blade Fixed Pitch Metal if anyone is interested. By the way, my buddies with same engine and the Sensenich would outclimb me and outrun too unless I turned high RPM with the wood and composites]


Summary of all of this ...
The Sterba is the best value (lowest cost to get in the air). It was the original prop and gave good performance.

The MT was a bit smoother and yielded a few more knots of speed. Not sure if the take-off roll was better or worse (may have been a few feet more ... I am doing this from memory now)

The Catto 3-blade "felt" lighter on the plane for some reason. Again maybe a little more performance on the top end. Maybe the shorter blades made the initial cranking feel quicker. (As noted, the 3-blade is a little more work if you have an "A" model RV)

With the Hartzell, I obviously climb faster but to my surprise, I tend to fly faster (several knots). What I **think** is happening is that I will naturally run more MP at a controlled RPM than with the fixed pitch props.

With some of the props, I did Phase one tests of up to 2850 (NOT WITH METAL PROPS).

What this means is that depending upon on how well tuned your prop is for YOUR plane and the way YOU fly, any of them will be just fine.

If you want the best WEATHER protection, go metal.
If you want the smooth and light and sexy, go 3-blade Catto
If you want smooth and light and pretty good looking consider 2-blade composite
If you want economical, go Sterba
If you want best acceleration, braking, climb and maybe top speed go CS

This did not answer your question directly but I do not think there is an absolute answer.

There was something I liked about ALL of the above props.


Your Mileage May Vary.

James
 
Why multi-blade props?

Ok, Guys; here's the straight skinny! You may not believe this since so much mis-information has been floating around for years, but a multi-blade prop, IF PROPERLY DESIGNED FOR THE PLANE, will be just as efficient in converting horsepower to thrust as a two-blade, but, if it's the same diameter as the two-blade, it will have better static thrust and climb performance. Here's how it works: Each blade sweeps out a volume of air that is a tube of the prop's diameter and as long as the forward speed. 'Got that? EACH blade! More blades, more volume! Thrust is mass times induced velocity, just as on a wing, lift is mass times downwash velocity. BUT, the velocity term is a loss; it's wasted energy! To get the most efficient wing or prop, you want the most mass and the least induced velocity. How is it that Tom Aberle in his Phantom biplane at Reno qualified at 220mph with a two-blade prop in 2003, then, with the same engine and at 7.7% lower rpm, qualified at 240mph in 2004 with a three-blade, and with a four-blade and the same rpm as the two-blade for slightly more power, went 252mph in 2008? How does that fit in with the "less blades are better" folly? Now since the area a blade sweeps out is proportional to diameter-squared, when going from a two-blade to a three blade you can reduce the diameter by sq. rt.(2/3) and still sweep the same volume but have a lower tip Mach and its high tip drag. You will actually have slightly better cruise efficiency but the same climb and static thrust at the same rpm. Take it a step further and go from a two-blade to a four-blade and you can reduce the diameter to 70.7% of the two-blade and, again, get slightly better cruise efficiency but the same static and climb. But reduce the diameter to about midway of the ratio, 91% rather than 82% for the three-blade or 85% instead of 71% for the four blade, and you'll have better static and climb, and better cruise efficiency. The biggest loss in most propeller designs is the non-aerodynamic root shape which makes lots of rotary and forward drag and impedes engine cooling flow, and the wide tip chord which makes incredible tip drag but produces no thrust. So with more root drag on more blades you get less cruise speed. So add a streamlined cuff on your blade roots, as they did on some planes in WWII, reduce the tip chord to zero, and enjoy the better speed and climb! And also better engine cooling!
 
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elippse said:
Ok, Guys; here's the straight skinny! You may not believe this since so much mis-information has been floating around for years, but a multi-blade prop, IF PROPERLY DESIGNED FOR THE PLANE, will be just as efficient in converting horsepower to thrust as a two-blade....SNIP!
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So when is someone going to design a CS three-blade PROPERLY DESIGNED FOR THE RV? So far, the available options are a disappointment.
 
3 vs. 2

It would be nice if somebody would actually design and manufacture a three blade CS prop that would produce these gains in my real world. Regardless of design, maintenance and overhaul costs go up with the three blade. Blade designs on those racers looks wild!
 
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