2, 3, or 4 blades vs smaller prop diameter

Homebuilt Aircraft & Kit Plane Forum

Help Support Homebuilt Aircraft & Kit Plane Forum:

Air Trikes

Well-Known Member
Joined
Dec 21, 2015
Messages
106
Location
Montreal Canada
I'm rebuilding a Woody's Pusher and need a prop for it. I have space for a maximum prop diameter of 68 inches to clear the fuselage. I'd like to lower the engine to keep the CG lower and the engine mount shorter is possible without sacrificing too much thrust. I'm looking for take-off/climb performance, not speed (too much drag - open cockpit etc.).
Would a 3 bladed 68" prop give more thrust than a 3 bladed 68" prop?
Would a 4 bladed 60" prop give the same thrust as a 3 bladed 68" prop?

Engine is an O-320-E2D - stock, 150 HP.
Do not try to use smaller diameter prop, no advantages for your draggy plane. I think your optimal prop is 68" 3-blade. Scimitar blade will provide more thrust and higher efficiency for 150 HP at 2700 RPM max engine. I can supply you an optimal prop.
 

OKDon

Well-Known Member
Supporting Member
Joined
Feb 25, 2022
Messages
54
Would a 3 bladed 68" prop give more thrust than a 3 bladed 68" prop?
Huh? No ,Yes, maybe?
Duh! Don't know how I typed that! Meant would a 3 bladed 68" prop give more thrust than a 2 bladed 68" prop?

I'm trying to get a handle on how changing diameter and number of blades can be used to optimize thrust when the max diameter is constrained.
 

TFF

Well-Known Member
Joined
Apr 28, 2010
Messages
17,941
Location
Memphis, TN
If everything is the SAME except adding one blade, you will loose performance by a lot. You have 150 hp divided by two blades. Divide by three and there is a lot less horsepower per blade, all things being equal. The engine isn’t strong enough to make up for that third blade.

A Sensenitch and a Warp Drive prop are not equals. With props comparisons really only work within a family close together. A Cato 3 blade has nothing to do with an Ivo 3 blade; they might as well be from different solar systems, if you want an apple to apple comparison. That’s where the superstition of props comes in.

You have to pick a type and work within that narrow band. If you change, you start over. The manufacturers have some level of knowledge of crossover. Sensenitch is a standard, so everyone is going to compare up or down with something like that. What prop do you have now? Makes all the difference in where you can go. Usually smaller is not as good, but has other qualities so you have to make the good and bad list, and see where it all lands.
 

c_m_bouis

Member
Joined
Oct 1, 2022
Messages
9
Location
Washington
We were almost there.
For the AM 15, 147HP engine on a Powered Parachute, 64 inch blade .
The type and number of blades recommended would be?

THANK YOU for sharing your expertise!

Chuck
 

c_m_bouis

Member
Joined
Oct 1, 2022
Messages
9
Location
Washington
Apologies.
Not sure if the 4 blade wide or six blade standard reply was for my PPC \ AM 15 HP or not.
Want to be sure.
Thank you
Chuck
 

OKDon

Well-Known Member
Supporting Member
Joined
Feb 25, 2022
Messages
54
If everything is the SAME except adding one blade, you will loose performance by a lot. You have 150 hp divided by two blades. Divide by three and there is a lot less horsepower per blade, all things being equal. The engine isn’t strong enough to make up for that third blade.

A Sensenitch and a Warp Drive prop are not equals. With props comparisons really only work within a family close together. A Cato 3 blade has nothing to do with an Ivo 3 blade; they might as well be from different solar systems, if you want an apple to apple comparison. That’s where the superstition of props comes in.

You have to pick a type and work within that narrow band. If you change, you start over. The manufacturers have some level of knowledge of crossover. Sensenitch is a standard, so everyone is going to compare up or down with something like that. What prop do you have now? Makes all the difference in where you can go. Usually smaller is not as good, but has other qualities so you have to make the good and bad list, and see where it all lands.
My constraint is the max 68" prop diameter and the engine I have. I want take-off and climb performance. I'm leaning towards 3 blades for smoother operation, less pounding on the vertical stabilizer if nothing else.

Any PIREPS on Warp Drive props?
 
Top