2 blade vs 3 blade

[jany77]

i wonder if anyone can give me straight answer ,im looking for thrust data for rotax 447 with 60x38 2 blade wood prop ,or smaller 3 blade prop around 52-54" thank you

[phantom]

the bigger the prop the more thrust you will have as long as your gear drive can keep the tip speed down to a reasonable level but when taken to extreme you will lose top speed, a 447 with a gear to turn a 96 inch prop will have more thrust than a 582 with a 60 inch prop.

Norm

[NoWingsAttached]

I don't recall seeing a 3-blade wood prop. The giant, small-radius spoons ya see at Mentone on the AeroStars are 2-blade. THe bigger prop diameter the better. I went from a 3-blade IVO to a 2-blade IVO, same prop and diameter. I tuned the pitched, and there was no appreciable difference in performance. If anything, it worked better as a two blade, but vibration increased just a tad. I should get one of those $70 prop balancers...

[PW_Plack]

Originally Posted by NoWingsAttached

...If anything, it worked better as a two blade, but vibration increased just a tad. I should get one of those $70 prop balancers...

Gerg, there will be more vibration with a two-blade, even if the balance is perfect.

[kiwidesign79]

Is there a big difference in hp required to spin a three blade vs a two blade?

[REDHORSE556CES]

Originally Posted by NoWingsAttached

I don't recall seeing a 3-blade wood prop

3-Blades, etc.
http://www.arrowprop.com/low.htm

[BEN S]

Save your money Gerg, they look cool other than that, no appreciable difference.
Ben S

[Chuck Roberg]

I don't recall seeing a 3-blade wood prop.

FYI: Tom Milton has one hanging on his shop wall. Think he said it used to be on a Rotax.

[jany77]

i meant 3 blade adjustable such as gsc

[WHY]

Hi Jan

That would depend on the room for diameter and the hp available. Theoretically, the 2 blade is more efficient due to more space between the blades to get a clean bite on the air,----BUT, when you are restricted on diameter, then you would add another blade to soak up the hp.

The old Corsair in WW11 had the inverted gull wing to give it more prop clearance and still had to go to 4 blades to soak up the hp.

Tony

PS with todays composites, I think the wood prop is best limited to 2 blades

[scottessex]

I tried my IVO prop in 2 blade mode, pitched to limit RPM of course, all it did was make more noise and have a longer take off run, went back to the 3 blade. But I am limited to 60".
Sure a large prop will move more air and provide more thrust, but it also will act like a parachute once it hits its max forward speed. A PPC can use a much larger prop because it flys very slow.
Of course if you have a light weight gyro with a huge prop, and large rotors, it can lift a fair amount of weight and fly just fine, but it will fly slow. (Gyronimo)

Kiwi, what soaks up the power is the pitch, you can spin a 2 or 3 or 4 blade at 6400 eng rpm with the same engine just fine. The 2 blade would be at a courser pitch. the 4 blade much shallower. My problem was that the 2 blades were at such a course pitch to soak up the power at 6400 RPM, the tips were stalling and making noise and not producing thrust. Each application is different.

[RICK MARTIN]

Jany77,

To answer your original question:

I have no figures for a 2 blade prop on a 447.

But I'm pretty sure you are looking for about 260 lbs of thrust from a single carb 447 with a 60" 3 blade prop. I had this set up on my Gyrobee and used an Ivo. I flew the crap out of that machine for five years of great fun.

By the way, I originally used the 60x38 wooden prop (Tennessee) specified in the Gyrobee plans and could not get enough thrust out of it. It seemed to have too much pitch and would only let the engine develop 5800 rpm static. Once I got the 3 blade Ivo I just dialed it in for about 6250 rpm static which seemed to be the sweet spot for max thrust which was 260 lbs.

I hope this helps.