Bolly brolga

[BrendAn]

Hi. Wondering if anyone is using a bolly made brolga magnum prop and what their thoughts on it are. 

And how much loss of top.speed can I expect from a 4 blade compared to a 3. I have an ancient warp drive 3 blade atm.  It's for a 912 ul 80hp.

[RFguy]

you wont necesssarily lose any top speed because its a four blade, it all depends on the drag and the prop blade profile. 

four blades, in general, are more lightly loaded per blade, and at slow speeds (like during TO roll)  , wont be cavitating so much which leads to shorter TO rolls.

I dont expect to lose any top speed with my E-PROPS four blade fast jab-rotax prop backed up by maths an graphs and simulations by the manufacturer.....

Edited October 13, 2022 by RFguy

[RFguy]

and cavitating is not technically quite right - that's more a water ship hydrostatic phenom. but with fewer blades , they will be operating with a higher AoA. (all things being equal- which they are not- this is a complex topic).

 

[facthunter]

The only reason I would use more blades is where the prop has limited diameter requirements and tip speed issues.  Nev

[BrendAn]

7 hours ago, RFguy said:

you wont necesssarily lose any top speed because its a four blade, it all depends on the drag and the prop blade profile. 

four blades, in general, are more lightly loaded per blade, and at slow speeds (like during TO roll)  , wont be cavitating so much which leads to shorter TO rolls.

I dont expect to lose any top speed with my E-PROPS four blade fast jab-rotax prop backed up by maths an graphs and simulations by the manufacturer.....

Good to know they don't lose top speed. I have switched from 3 to 4 blade on my outboards and inboards a few times because they are so smooth . The outboards definitely lost a knot or 2 but the benefits outweighed that .

Who sells E props in aus. I can't find much on Google.

 

[BrendAn]

6 hours ago, facthunter said:

The only reason I would use more blades is where the prop has limited diameter requirements and tip speed issues.  Nev

I like the smaller diameter for ground clearance.  The warp drive looks huge on my little 55.

Isn't the most efficient prop a single blade.

 

[facthunter]

They were used for a brief time but died a natural death. Scale effect (Reynolds number) would favour a larger section.  Water and air don't behave the same. Nev

Edited October 14, 2022 by facthunter
spelling

[RFguy]

Some will lose speed due to high drag. there are blades, and there are blades. I'm very much generalizing. 

 

Most props at their best cruise, IE matching pitch with airspeed etc and RPM in the right region, have  nearly identical efficiency.

 

Go look at all the prop comparisons, there is usually nothing in it, despite the very different blade looks.....

They're usually compared with at climb (usually suboptimal efficiency compared to cruise)  and cruise. 

Edited October 14, 2022 by RFguy

[facthunter]

Wood has an efficiency deficit due to not being fine enough at leading and trailing edges. A well matched fixed pitch metal prop will have very good efficiency.  Any CS prop will be a compromise at all but one speed also but has a better flexibility. I don't see the need if you don't cruise above say 125 Knots. Chance of failure should dictate a lot which props you use. A blade off usually shakes the engine out. or damages it somehow. Nev

[Blueadventures]

31 minutes ago, BrendAn said:

Good to know they don't lose top speed. I have switched from 3 to 4 blade on my outboards and inboards a few times because they are so smooth . The outboards definitely lost a knot or 2 but the benefits outweighed that .

Who sells E props in aus. I can't find much on Google.

 

Mark Kyle on this forum

[BrendAn]

39 minutes ago, Blueadventures said:

Mark Kyle on this forum

Thanks blue.

[facthunter]

There's got to be a place for composites. Metal is pretty weighty and if you get stone nicks a crack will start from it if you don't blend it in. Wood's no good in rain. Nev

[spacesailor]

Metal props ?.

WW2 scrap metal,

We had lots of ' Duralumin ' alloy props go through the smelter .

Very strong & flexible, suprisingly so .

spacesailor

[facthunter]

Used it for model plane undercarriages and engine mounts. Springy enough as it is supplied. Nev