Does any one know what size 4 blade prop is equal to a stander 2 blade 27x10 prop and a 26x12 prop

Right... well general rule of thumb for four-bladers is to go down in both diameter and pitch speed. I'd try 25x8 or 24x10 if those are sizes you can get in 4-bladers.

To be honest though, I do not have much experience with four blade props. I personally think they're 'a bit of a wank' because they are less efficient than a conventional two-blader. Once in the air you won't be able to see the difference!

Cheers - boingk

To keep the same load on the motor and go from 2 blades to 4 blades you want to reduce the diameter by 15% and keep pitch the same (see Propellers in http://www.mh-aerotools.de/airfoils/index.htm if you want the detailed reasoning).

So ideally you want 27 x 0.85 = 23 x 10 or 26 x 0.85 = 22 x 12. But since there aren't all that many 4-bladers around I guesss you just get as close to those sizes as you can find .

Steve

There we go, didn't know there was a thought out formula for it! Top stuff, Steve.

- boingk

boingk can you tell me what make 4 blade prop less efficient then 2 blade prop if your keeping the same load on the engine

its way more tech. then I can get inta!

but it has something ta do with pitch and speed, a model engine dosn't make enough torque ta turn a 4 blade prop with enough pitch ta get the air out of its( the air) own way!

with a 2 bladed prop, you can use more pitch!

ok think of it as tailgating! the secound car don't hafta work as hard cuase the lead car is moving the air! with a 4 bladed prop, the extra 2 blades are basicaly tailgating!

hope that helps!

what i am think is that a 4 blade prop would be more efficient in a ducted fan because Ducted fan reduce propeller blade tip losses, the ducted fan is more efficient in producing thrust than a conventional propeller, especially at low speed and high static thrust level

you can't compare a ducted fan ta a normal prop!

as soon as you add a duct ta the equation, it makes the fan more efficiant!

try running a fan without a shroud! all you get is alot of air tumbling around with no directional thrust!

spose I should mention the old byron reduction drive 4 bladed set-up! that worked ok for a big scale warbird!

with the 50% gear reduction, you could keep the prop big enough, with enough pitch ta still be able ta move the air outa of its own way!

don't know if your familure with marine applications, but when you over spin a prop you get cavitaion!(water just bubbling instead of pushing) same thoery with a 4 blaed prop!

the only reason full size airplanes use them(4 bladed props) is ta keep the size down! and still be able ta get the thrust at 30 ta 40 thousand feet! spinning twice the pitch at 1/2 the speed of our models

unless you are wanting that scale look!(on the ground) a 2 bladed prop works alot mo better on a model! and actualy look more scale in the air, as you can keep the prop disc looking scale

no i am not going to use the prop for model airplane i am trying to make a VTOL like the Honeywell RQ-16 T-Hawk i ask what 4 blade prop is equal to a 2 blade 27x10 prop because i wanted to keep the size down

sounds like fun! as I think I mentioned earlier, I'm no expert!

so wish ya luck! heres a post from scale warbird thread, might have some better info!https://www.rcgroups.com/forums/show....php?t=1510053

hey whisky thank you alot for the helpful info. i found a good 4 blade prop to here is a link to it http://www.troybuiltmodels.com/items/BP2410-4.html i well soon make a build log on it

I just googled that T-HAWK! dude thats gonna be a sweet project, definitaly wanna see that!

thank you right now i am working on the turning system