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Lose 5-10 knots with a 3 blade prop on a 10?

rv6ejguy said:
Just another point of interest in this discussion about numbers of blades- the Phantom biplane racer at Reno gained over 30mph going to a 4 blade Paul Lipps design compared to the original 2 blade. Absolutely huge.

This shows that with proper design, more blades does not always have to be slower.

I submit that some of the 3 blade props available for RVs could be improved on.
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Assuming the prop is properly designed and optimized for the aircraft.....

I believe the theory is that less blades are optimal because each blade has more time to clear the turbulent air from the previous blade sweep. This works up to the point where the blades cannot support the power of the engine. They either have to become too thick or too long or run too fast. Then you have to shift up to more blades to effectively absorb the power.

Because the RV-10 is a relatively fast aircraft with a powerful engine, I suspect that the 2 vs 3 blades argument is finely balanced.
 
paul330 said:
Assuming the prop is properly designed and optimized for the aircraft.....

I believe the theory is that less blades are optimal because each blade has more time to clear the turbulent air from the previous blade sweep. This works up to the point where the blades cannot support the power of the engine. They either have to become too thick or too long or run too fast. Then you have to shift up to more blades to effectively absorb the power.

Because the RV-10 is a relatively fast aircraft with a powerful engine, I suspect that the 2 vs 3 blades argument is finely balanced.
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At 150 knots, each blade describes its own helix through the air so no blade is in the turbulent air from the preceding one. Running up on the ground, yup, blades are in disturbed air.
 
Because I know none of us are patient, and I have not had the chance yet for side by side, same day same location tests yet, here is what we found yesterday.

Bare in mind this is subject to some validation, but nothing beats a side by side test, because that takes out a lot of variables.

Observation yesterday is at least 4 knots, I am edging towards 5 maybe 6. Certainly not 10 knots as someone originally was fearing.

Another observation (no real data here), but the take off distance I would have expected to be a bit shorter, but when flown from my home airfield, where markings are available for reference, it appeared to be the same. Maybe it felt quicker, but there ya go. Thats why data beats what it feels like every day.

As we know more I will share it, especially if we get a comparison with an almost identical air-conditioned plane we have that is two blade, that we do have on hand :)
 
I have the MT prop. My aircraft has two radios and two GPS antenna. But is generally fairly smooth apart from that. As long as she is clean and the air filter is clean with clean plugs etc she will almost meet the VANS performance numbers for top speed and for cruise. However the one area where she really impresses is the take off and climb. One up and lightly loaded she will easily hold 3000ft min climb. Fully loaded she will do over 2000ft min.

So I would agree with the general feeling that she is down a touch on top speed and maybe on cruise, but that's less easy to be sure of. However the performance benefit is great take off and fantastic climb.

Over all she is quite light and the prop helps with that of course. She is also smooth and quiet. These are less easy to quantify but people often mention how smooth she is, but that comes after amazement at the performance.

EDIT to add: If top speed is your priority then 2 blade is probably best. If climb is more important I would say go for the MT 3 blade. BUT ALL THIS IS SPLITTING HAIRS, THESE ARE ALL GREAT AIRCRAFT WHATEVER THE PROP.
 
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Cold

You can have my 3 blade prop when you pry it from my cold, dead hands. VNE at sea level, 4K fpm when light on a cold day, 170 knots abeam the numbers on the downwind, a 180 degree turn to the runway, and off at the first taxiway. I?ll give up the few extra knots at top speed because I would be over VNE anyways. 2350 Rpms, wot, 10,500 gives me 167 ktas, 7.8gph. Oh, it looks darn good just sitting there too.
 
Same plane comparison

To throw my 2 cents into this fray, here's my experience with a move from a 2 blade to a 3 blade on the same airplane. (Sorry, no MT info here though...)

- Engine - custom built balanced components I/O-390 210Hp
- Original 2 blade prop - Hartzell HC-E2YR-1B/7666A-2R (common on many Vans)
- New 3 blade - Harzell "Top Prop" scimitar HC-E3YR-1RF/F7392

Performance result - noticeable climb performance improvement, as expected, with the 3 blade AND (the big surprise) exactly the same cruise speed. So, this is a demonstration of how efficiency and design come to play - the scimitar 3 blade is apparently a significant design improvement over the older 7666 blades, compensating for the usual cruise performance reduction of a 3 blade. Interesting also was that the dynamic balance delivered some exciting news - 0.02"/sec. right out of the box, no balance weights required at all! Speaks well for both Hartzell and Lycoming. And I also have to heap praise on the Hatzell customer support. Since this was a Top Prop meant for a Commander, the spinner was wrong, and the customer support folks were incredible in finding me a spinner in their line that fit.
 
Took a while.

Using an otherwise identical airframe (same builder) at similar weights etc, the only difference was the prop.

The three blade composite Hartzell was 5 knots slower (side by side so to speak) when comparing GPS ground speed in the same parcel of air. This was suing the same WOT, 2400 RPM and the same LOP fuel flows (both very accurate K factor).

This was at 1500 and 6500 feet. We did not get to do say 9500' however I suspect based on numbers seen at those heights the loss might even be 7 knots.

Hope that helps! :)
 
I have been flying it on my RV-10 for over 10 years and have been extremely happy with it. The propeller is very smooth, looks amazing and is very rugged. I have flown my RV-10 side by side with a number of other RV-10's with the stock 2 blade Hartzell, it is faster then some and slower then others.

48544513901_263be31635_b.jpg


This is a picture from this years trip to Oshkosh at 15,000ft with 4 people and lots of baggage, 172 kts TAS
48544514066_13da25e803_b.jpg


Rob Hickman
N402RH RV-10
 
N402RH said:
I have been flying it on my RV-10 for over 10 years and have been extremely happy with it. The propeller is very smooth, looks amazing and is very rugged. I have flown my RV-10 side by side with a number of other RV-10's with the stock 2 blade Hartzell, it is faster then some and slower then others.
This is a picture from this years trip to Oshkosh at 15,000ft with 4 people and lots of baggage, 172 kts TAS
48544514066_13da25e803_b.jpg


Rob Hickman
N402RH RV-10
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And you have it pulled way back! 67% power and 11 GPH!
 
Subwaybob said:
And you have it pulled way back! 67% power and 11 GPH!
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Flew to Oshkosh with a Bonanza A36 and V35 and had to make sure I left last and passed them both before every stop....
And to be fair I was hauling the same amount of people as both Bonanzas combined.

"If You Ain't First, You're Last!"

I did suggest on one of my passes that maybe they should try putting the gear down like the RV-10.

The ground speed was 252 MPH

Rob Hickman
N402RH RV-10
 
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It looks like you're using significant advance on the timing to recover some of the power you'd otherwise lose due to the high density altitude/low MP. Poor man's turbo. Is that an accurate statement?
 
BobTurner said:
It looks like you're using significant advance on the timing to recover some of the power you'd otherwise lose due to the high density altitude/low MP. Poor man's turbo. Is that an accurate statement?
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Running a single Light Speed Plasma III , you can see the advance in the picture 36.5 deg and full throttle.

Rob Hickman
N402RH RV-10
 
Can't have your cake and eat it too....

I have flown my RV-10 side by side with a number of other RV-10's with the stock 2 blade Hartzell, it is faster then some and slower then others.
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That goes to what Vic said. But take the airplane variation out if it.

Three blade wide cord will be the king of take off and climb over 2 blades but the theory says you will lose some HIGH SPEED efficiency. It is baked into the cake (aero, physics, math). Two blades for lower power engines (say under 250-300HP) has advantages, one being higher top speed, all other things being equal.

Three blade, you have more ground clearance, lower tip speed, less noise, less gyroscopic inertia.... however more cost, weight, lower top speed (typically) in apples to apples comparison .

Same airplane, one with 2 blade Hartzell vs three blade wide cord MT/HC, the 3-blade will be slower in theory. I must say HC 3 blade has done an amazing job mitigating any cons of the three blade... There is no free lunch. 3 blades are awesome and so are 2 blades, but neither do everything better than the other.
 
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most of these pat generalizations about 2 vs 3 blade props are urban legends, like better climb but lower top end with the 3 blade. In all the cases in this discussion a 2 blade from one brand with one diameter is being compared with a 3 blade of another brand with another blade design of another diameter. There are just too many variables. Is the 2 blade optimized for a specific airframe? Could its efficiency be beter tuned to a given RV by changing the blade diameter by 1/4" either way? Hartzell is trying to make a prop for a wide range of airplanes so there are compromises - no way around that unless they design a prop for your airplane/engine combo. Could the 3 blade be optimized via diameter and blade design to equal the 2 blade, or come very close? Well that depends how optimal the design is of the 2 blade and its match to a given airframe - if it is off point, then there is more performance to be had, so a perfectly optimized 3 blade might catch it or pass it. It is extremely complicated so when the coffee shop aero experts say this or that about 2 blade or 3 blade their opinions are worth less than the coffee they are drinking. Usually they are based on no data and very little understanding of the optimization exercise. I am an aero engineer but I have never done that exercise but I think I have an appreciation of how challenging it would be. Craig Catto probably understands it.

I think the only things you can say definitely are: 3 blade is more expensive and it has less vibration. Some think it looks cooler, but when it is flying you can't really see it. 3 blade must be way more expensive to ship because of the awkward box. Beyond that to make a pat rule without specifics is useless.
 
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