Hi guys.
I´ve got a question about the diffrence betweenn, say a 12x6 original prop and a 12x6 prop cut from a 13x6 original. Would it perform the same?? If not what would be the diffrences?
Thanks
Marcos

Unless the tips on the shortened prop are reshaped to the shape on the 12x6, it won't be as effecient.
It might be more noisy.
The differences for all intents should be small though, nothing "plane-threatening".

Hi Marcos,

It should perform more or less the same, if the tips are rounded as the original 12*6. Nevertheless I must said that the angle at which the prop ends at the tips would be not flat at all, given a little bit more extra torque.

Como esta todo en Puerto la Cruz?, que envidia, puedes volar todo el tiempo!!.Por aqui no puedo todavia. Estamos bajo cero. Un cordial saludo de un otro Venezolano.

Thanks Tall Paul, thanks Alejandro B. I´ve just read your notes and as you say it seems to perform about the same.
The only diffrence I notice is a small reduction in RPM(very small)

Por aqui volamos casi todos los dÃ*as(mientras el trabajo lo permita) Saludos y espero voñver a saber de ti

Marcos

What you get with the clipped 13X6 prop (to make it 12 inch dia) is larger blades than the unclipped 12X6. More blade area = more load on the engine... until you hit max static thrust (or max thrust for the airspeed)

Assuming you have shaped the tips appropriately... you get the same top static thrust, but at a slightly lower rpm. (because static thrust will max out based on dia, more than blade shape or pitch.)

It is rue that just chopping it off square ended is a bad idea.

The comments thus far are for the most part valid, and as you have already found out there isn’t much practical difference. However one point was overlooked. In addition to a little larger area than a 12-6, it will also have a little greater pitch. The pitch of a propeller varies from pretty steep near the hub to much flatter toward the tip. This is so that when moving through the air, the blade angle of attack at each radius remains close to the same. By convention, the specified pitch is the pitch at a specific radius (usually 75%). By shortening the propeller you cut away some of the flatter pitch, and the pitch at 75% of the new radius is a little greater than that point on an original 12-6 prop. I suspect as much or more of the additional load on the engine comes from this pitch increase as from the increased area.

LouW...this isn't exactly true. Most common propellors have a helical pitch, meaning that the pitch is the same at any point along the blade. The ANGLE of the blade varies but the PITCH remains the same. Imagine cutting a 4 TPI (threads per inch) thread in a lathe. Cut one on a small diameter rod and the the angle the thread lays over will be very apparent. This is the equivalent of the prop pitch close to the hub. Now cut another 4TPI on a large diameter (say 12") and the thread will appear to be almost vertical, or flat. So the ANGLE the thread lays over at is equivalent to the angle you see at different points along a prop blade even though the PITCH remains the same.

So if you had a helical pitch 13" prop and cut it down to 12" then the pitch at the tips would still be the same. Some props do vary their pitch BY DESIGN towards the tip. Depending on the application they either increase or decrease towards the tip. In this case the 75% point will change as you said.