C-180 on floats 2 blade vs 3 blade prop

[ScandySky]

We have a 1959 C-180B on floats with a 230hp O-470 and 88 in McCauley seaplane prop. To reduce noise on take-off we consider to echange the 2 blade with a 3 blade prop.
Any suggestions which 3 blade works fine for a C-180 on floats?
Is there a noticable reduction of noise on take off?
Is there any decline in performance vs the 2 blade seaplane prop?
Any advantages /disadvantages to consider?

Thx, Daniel

[PilotDAR]

I installed an MTV9 three blade reversing on my client's 550 powered 182 amphibian, we were very happy with the results. I did the formal Transport Canada/EASA noise test, as the plane was exported to it's owner in Norway. With the prop RPM at 2500, and at 3350 gross weight, the noise was 88.5 dBA. At 2700 it was too loud to pass EASA requirements, though it is FAA STC'd that way. Interestingly, during my testing (36 overflights of the microphone), I found that all other things being equal, the difference in altitude in a Vy climb after takeoff, 2 km from brake release, was 60 feet. The extra 200 RPM was making a lot more noise than altitude. I chose the nickel leading edges for my client, and after more than 400 hours (including his son learning to fly in it) there is zero damage to the leading edges, and it is water based.

The reversing feature is excellent for water maneuvering, I have a reversing MT on my flying boat also, though check to assure it's STC'd in Canada, I'm not sure that's been done for the 180. Select a propeller which has an STC (FAA or TC) which TC will accept. At present, serialized STCs for propeller changes are a little problematic, particularly for an increase in number of blades....

[ScandySky]

I know the plane, but a 550 is quite a different engine. Looking for a good 3 blade option for a O-470 on a floatplane.

[Big Pistons Forever]

A guy I know put a Hartzell "top prop" 3 blade prop on his C 180. Said it was much quieter but he thought takeoff performance was slightly reduced, although not bad enough to be a problem. No 3 blade prop will equal a 88in 2 blade seaplane prop.

[digits_]

No 3 blade prop will equal a 88in 2 blade seaplane prop.

Do you know why that is?
Theoretically, one would assume that you could get the same performance with more shorter blades. There are a lot of variables you can play with. But ut doesn't seem to work that way in reality.

I'm curious to learn the reason for that.

[Big Pistons Forever]

No 3 blade prop will equal a 88in 2 blade seaplane prop.

Do you know why that is?
Theoretically, one would assume that you could get the same performance with more shorter blades. There are a lot of variables you can play with. But ut doesn't seem to work that way in reality.

I'm curious to learn the reason for that.

There is more blade in the clear air away from the cowling due to the greater prop diameter.

[PilotDAR]

And..... simply making a bigger footprint in the air. Think bigger prop is like bigger snowshoes, lower [snow] pressure. For the same airplane power and drag, a lower propeller disc loading with a larger diameter prop. But, as noted, noise becomes a problem, and that's a hot button topic with TC these days...

[fish4life]

Not a 180 but 2 blade prop performance vs 3 blade was also explained a bit on Mike Patey’s video of why they chose a 2 blade for the burj helicopter pad landing / takeoff

[photofly]

No 3 blade prop will equal a 88in 2 blade seaplane prop.

Do you know why that is?
Theoretically, one would assume that you could get the same performance with more shorter blades. There are a lot of variables you can play with. But ut doesn't seem to work that way in reality.

I'm curious to learn the reason for that.

Propeller theory produces the result that increasing the number of blades increases the drag (torque) and decreases efficiency. A three bladed prop has exactly the same drag issues as a triplane where each airfoil interferes with the airflow around the others - making it less efficient than a biplane. Each blade of a propellor is flying in the combined upwash/wake/pressure pattern of all the previous blade passages, and the more blades there are per rotation the closer to the effects of the previous blades is the next.

The most efficient number of blades on a prop for generating thrust is one - for the same reasons that a monoplane is the most efficient way to generate lift. Single bladed props can be done (I'm told) but the counterweighting is an engineering challenge. They do occur in nature, however - think of sycamore seeds.

Leaving aside single-bladed props as a curiosity, to absorb the same power, a three bladed prop can be shorter than a two bladed one generating the same thrust, in the same way that the wingspan of a biplane is shorter than a monoplane of the same weight. This has the benefits of better ground clearance, and lower tip speed, therefore less noise. With high RPM the mach number at the blade tip gets high and supersonic effects cause a lot of additional drag. At that point the efficiency of the two bladed prop drops in comparison with the equivalent (shorter) three bladed one.

So for best conversion of torque into thrust you should have very large, very slow propellors with very few blades. Looking at the video, the Gossamer Albatross had something like a 7' two blade prop turning at 70 rpm.

Any engineering decision to move from two to three or more blades is likely forced by one or more considerations of ground- or inter-engine spacing and inability to produce power at sufficiently low rpm, and blade tip speed.

Here's a video about a one-bladed prop, which turned out not to be more efficient, after all:
https://www.youtube.com/watch?v=fhzWd2Ld12s

[rigpiggy]

I installed an MTV9 three blade reversing on my client's 550 powered 182 amphibian, we were very happy with the results. I did the formal Transport Canada/EASA noise test, as the plane was exported to it's owner in Norway. With the prop RPM at 2500, and at 3350 gross weight, the noise was 88.5 dBA. At 2700 it was too loud to pass EASA requirements, though it is FAA STC'd that way. Interestingly, during my testing (36 overflights of the microphone), I found that all other things being equal, the difference in altitude in a Vy climb after takeoff, 2 km from brake release, was 60 feet. The extra 200 RPM was making a lot more noise than altitude. I chose the nickel leading edges for my client, and after more than 400 hours (including his son learning to fly in it)

Had all blades separate at the trailing edge. I don't recommend MTs

[PilotDAR]

Yes, all three blades on my MT separated at the trailing edge for about 1.5". The manual explains how the repair is done with five minute epoxy and fiberglass cloth. I repaired the delamination as the MT manual said a few year back, and have not had any problem since. There are plusses and minuses to both metal and wood composite. Yes, I've done blade repairs on my MT, though I've never had to dress out a nick!

[rigpiggy]

nope, 3 months for the repairs, and good luck getting MT to answer/call you back with a timeline

[PilotDAR]

Hmmm... I think that Hope Aero in Toronto could repair it, and certify the work. Certainly, the repair I did was an easy do, though O/M so not certified.

[all_ramped_up]

Canadian Propeller in Winnipeg is MT certified too I believe.