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2 blade v 3 blade prop

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2 blade v 3 blade prop

Old 5th Mar 2016, 20:47
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2 blade v 3 blade prop

Anyone want to take a stab atthe pro's and cons of a 2 blade over 3 on the same model aircraft
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Old 5th Mar 2016, 21:05
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With no more specifics, only a generality: all other parameters equal, less blades will give better efficiency but will require larger diameter, and will produce more noise.

There's a thousand things more to be said though, a propeller blade is like a wing, it has angle of attack and chord and aspect ratio and thickness, perhaps even warp, and what not.

Not even to begin about constant speed vs. ground adjustable vs. whatever else.
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Old 5th Mar 2016, 22:47
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Originally Posted by Jan Olieslagers View Post
less blades will ... produce more noise
Which is why, if I've remembered this right from decades ago (and it hasn't changed), the Beavers with three blades are operating on the east, populated, side of Vancouver Island, and the Beavers with two blades are operating on the west side where nobody much lives or worries about the noise.
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Old 6th Mar 2016, 00:12
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Originally Posted by piperboy84 View Post
Anyone want to take a stab atthe pro's and cons of a 2 blade over 3 on the same model aircraft
Typically on a small aircraft 2-blade prop is better for higher cruise speed, 3-blade for better climb.

These are some observations from an owner of Piper Arrow:

I recently fitted a new three blade to my Arrow. I'm still in two minds about it but some observations so far are:

Smoother operation and less vibration at all power settings

Less cockpit noise

Better initial climb performance (around 1200fpm at mtow) up to about 3000 feet after which it drops off significantly

Much better go-around climb rate

Marginally better ground performance - around 5% shorter take off roll

About a 6% LOSS in overall cruise performance which does seem to increase with altitude, although at max continuous power in straight and level it's actually a few knots faster

Only limitation is to avoid continuous operation below 1950 RPM and less than 15" MAP

Slightly more fuel efficient, although I can't figure out why

Slightly cooler engine operation probably due increased cooling airflow through the cowling

Added drag of the extra blade helps when trying to slow down - steeper approaches and quicker deceleration are very noticeable

No change in glide performance - Arrows glide like man-hole covers with rough edges anyway

The only thing I'm not entirely happy about is the reduced cruise performance, but hopefully with a repaint and speed kit fitted, I might get a bit back.

Let me know if there's any specific questions you have
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Old 6th Mar 2016, 09:07
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If you ever have to hand-prop it a three blade makes that a lot of work and demands a lot of care.
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Old 6th Mar 2016, 09:22
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I started out with a two blade McCauley C23 on my Bonanza, seven years later switched to a C76 with prop deice (3 blade). Less noise, less vibration, less top cruise, slightly better take-off performance, higher overhaul costs. I am now on a Hartzell 3 blade Q-tip, much less noise, even less top cruise, low landing fees when in Germany.
My friend switched from a C76 3 blade McCauley to a 3 blade Super Scimitar, unable to tell because he added a turbonormalizer at the same time. Very good prop.
Another friend switched from a Hartzell 3 blade to a C406 3 blade; Very bad decision because it moved the CG aft a lot because the new prop was lighter, needing lots of lead in the nose to get it right.
Depending on aircraft type, prop weight needs to be considered as well.
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Old 6th Mar 2016, 11:57
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In the early 1980s, I instructed on PA-44 Seminoles. We had two blades per engine on the first two aircraft and then took delivery of a new aircraft with three blades on the props. This was a new option introduced by Piper for that year's model.

The AFM had data for both two-blade and three-blade props. I remember being surprised that the three-blade data showed, in comparison with two blades:

1. Noisier;
2. Slower; and
3. Heavier.

Having spoken with the Piper dealers, the only reason we could come up with for the three-blade option was that it looked better on the ramp! I suppose there was a small benefit from the smaller diameter prop as well, being less prone to ground strikes and stone damage when taxying between grass/tarmac.
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Old 6th Mar 2016, 15:49
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Several of the differences mentioned (especially performance, cruise vs. climb) have to do with blade pitch rather than with number of blades, so they are not really relevant in this discussion. On the other hand I would never have thought of the difference regarding hand propping.
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Old 6th Mar 2016, 16:19
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The reason I ask is I have an opportunity to change out the 2 blade CSP for a 3 blade CSP for free if I agree to use my aircraft for noise tests as part of the certification process . I use the plane for off field landings so the higher ground clearance would be nice but the plane is slow enough without losing more cruise speed with the 3 blades, it's a composite prop and is supposedly lighter than the 2 blade one currently installed.
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Old 6th Mar 2016, 17:21
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If CSP stands for Constant Speed Propeller, I have no more to say: that kind of hai-tech does not belong to my world of flying.
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Old 6th Mar 2016, 22:23
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If you have the chance to get it for free as part of the certification process you could try saying yes, as long as they let you change back if you are not happy.

From what I have seen of this there are too many variables to reliably compare 2 and 3 blades.

The only differences that seem fairly reliable are that 3 bladers are more expensive and smoother.

I have a 3 blade MT that gets a very bad press sometimes. The anti camp say its slower in cruise and top speed. All I know is mine makes book speeds.

I can confirm it climbs pretty well. But it should with 200 Hp in a light RV.

The Ravens aerobatic team use both 2 and 3 blade props. They say they cant tell the difference in performance.
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Old 6th Mar 2016, 23:45
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Props are a trade off of many points. The larger the air mass a prop can throw back the better, with the smallest of added velocity, this means large diameter low rpm as per first war1 fighters. So in theory a smaller diameter 3 blade can not perform better than a larger 2 blade it replaces. A 3 blade also seems to have higher drag per speed curve so may be better on slower cruising aircraft.

My experience is with 200hp Cessna Cardinal F177RGs put a Hartzell 3 blade on one and everything is bad. Take off, climb, cruise and max speed.

The only improvement is lower noise and better ground clearance. Take the same prop put it on an Arrow 200hp same engine and it performs better.

So the only way to find out is try it, but don't expect to much and as said if a reduction in performance will they put the 2 blade back on then, you have nothing to worry about.
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Old 7th Mar 2016, 00:21
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Gliders can manage quite adequately in one blade.

https://en.m.wikipedia.org/wiki/Single-blade_propeller

And glider tugs with four blades.

http://www.fly13.co.uk/Tug/
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Old 7th Mar 2016, 02:14
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The problem with this kind of comparison, is that you can't change just the number of blades and nothing else to get a realistic result.

In reality the differences will be due to variations in blade length, aerofoil, control of the pitch management, and, interaction with the airframe/engine/spinner combination, to name just a few.

The only way to make a real comparison, is to fit the new prop, and carry out objective, back to back tests, under the same conditions.

As someone said earler, if you're going to get the 3 blader for free, and you can keep the old one, you have very little to loose.


MJ
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Old 7th Mar 2016, 11:53
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I had a friend who installed an MT composite 3 blade prop on his Mooney. There seemed to be a lot less flywheel effect when stopping the engine. This must also be noticeable in flight, less gyroscopic effect of the prop on the engine mounts. I don't know if this is good or bad.
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Old 7th Mar 2016, 12:02
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The problem with this kind of comparison, is that you can't change just the number of blades and nothing else to get a realistic result.

In reality the differences will be due to variations in blade length, aerofoil, control of the pitch management, and, interaction with the airframe/engine/spinner combination, to name just a few.

The only way to make a real comparison, is to fit the new prop, and carry out objective, back to back tests, under the same conditions.
Very true. Although some general assumptions can be made about the affects of a changed propeller, it is not as simple as number of blades, all of the foregoing characteristics must also be considered, and correctly applied.

In general: More blades = less noise, smaller diameter = less low speed thrust, but you'll get it back with speed.

Floatplanes tend to like large diameter two blade props, as they aid acceleration at low speed (needed to "get on the step"), and the planes don't go that fast anyway! But those props make a racket, and are banned in some places - yes, even in Canada!

I am a very strong proponent of the MT three blade props, they are magnificent! I have tested and approved many, on different aircraft types, and have always been pleased with the outcome. Like any non metal prop, they do have a lower "polar moment of inertia", which can make them more difficult to start, for lesser flywheel affect, but with a good stater, they work fine.
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Old 8th Mar 2016, 01:03
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I used to fly a 1967 PA12R-180. When I got there it had a 3 blade prop. Never flew it with the two blade. Looking at the old and new CG it was too far forward with the 3 blade. Had to ballast in the baggage compartment or reduce fuel to stay in limits with two adults in front.
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Old 8th Mar 2016, 02:36
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1967 PA12R-180....... with two adults in front.
Several things do not add up...

Looking at the old and new CG it was too far forward with the 3 blade.
Using the MT three blade, you might be able to move the CG back, which can be a great advantage sometimes.
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Old 8th Mar 2016, 10:34
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On some aircraft you may want to shift the CG rearward, on others (F33A) you may want to shift it forward. This would be a major consideration if I would change props for any reason. Since the prop is about as far forward as you can go, even 10lbs difference will have a major effect on CG. On the TN Bonanzas a new composite prop helps compensate for the 70 lbs weight of the turbo installation. One aircraft I fly needed a very large 110 cuft O2 cylinder in the back to compensate the weight of the turbo. With a lighter composite prop this O2 cylinder could have been several sizes smaller, leaving a higher useful load.
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Old 8th Mar 2016, 23:14
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Whoops! PA28R-180. Must have been a fit of nostalgia that crept in. I learned to fly in a PA12 and of course the two (thin) adults go in the back.
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