Prop pitch

Advertise with us
Shop deals on ebay
shop deals on amazon
Intlwaters

Help Support Intlwaters:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.
dwilfong

dwilfong

Well-Known Member
Joined
Jul 1, 2008
Messages
5,968
I have bin playing with my new pitch gage and was wondering. When changing the trailing edge cup of a prop is there a point where the difference in leading edge pitch and the progression of pitch to the trailing edge will not be beneficial. Is there a amount of progression that is more efficient. And in how many degrees should you keep the progression to a certain amount.

David
 
David,

I have the tech articles you are looking for.

NAMBA website, go to news, and propwash past issues.

may 2004

dec 2005

There may be others, these were the ones I saved in my cabinet.Lohring Miller has one on propeller geometry, the other on propeller pitch measurments.

Happy Hunting. email me if you need me to scan and send them.

Randy
 
Here's something Andy Brown posted on Marty's old RC Boat forum, I thought it was so imortant I printed it:

Andy_on_props~0.jpg
 
I like to think that the leading edge pitch should come close to matching the boat speed and engine rpm. That is, the water should enter with very little angle to the bottom of the prop (the pitch surface). That means low slip on the leading edge pitch at the design speed and rpm. The pitch then should increase until it gives the desired slip when calculated at the trailing edge. Different boats run best with different slips. Light SAW riggers may only need 10% more pitch to create the desired thrust, while monos need more. The standard prop mods do much more like changing the lift, reducing the blade area, and controlling the thrust cone. There is no substitute for bending a lot of props and seeing what happens.

Lohring Miller
 
Thanks every one for the help.

Have bin playing with x series props for my 40 mono and up till now it's bin a guessing game. The new pitch gauge has opened my eyes to what is going on. I know what the speed at RPM was but only had a prop chart to figure with. The progression of the prop especially the leading edge was what has bin holding me back. I can see this now with the calculations I have made with the new info. I hope the new props will do what I hope. will test this weekend and see if the numbers add up.

I am still a little confused about what imparts lift in the prop. Any help would be appreciated.
 
David,

I always understood it as trailing edge pitch decreases ventilation of the blade, therefore causing less slippage and providing lift.
 
dwilfong said:
Thanks every one for the help.

Have bin playing with x series props for my 40 mono and up till now it's bin a guessing game. The new pitch gauge has opened my eyes to what is going on. I know what the speed at RPM was but only had a prop chart to figure with. The progression of the prop especially the leading edge was what has bin holding me back. I can see this now with the calculations I have made with the new info. I hope the new props will do what I hope. will test this weekend and see if the numbers add up.

I am still a little confused about what imparts lift in the prop. Any help would be appreciated.
Click to expand...
Mike Nowicki gave me a simple explanation that makes sense, the greater the pitch the more the prop wants to stay on the surface and not penetrate it. Imagine a paddlewheel (like some of our SAW props). :blink:

I know from experience that de-tonguing adds lift and cupping reduces it, and of course the greater the pitch the greater the lift.
 
Last edited by a moderator:
lohring said:
I like to think that the leading edge pitch should come close to matching the boat speed and engine rpm. That is, the water should enter with very little angle to the bottom of the prop (the pitch surface). That means low slip on the leading edge pitch at the design speed and rpm. The pitch then should increase until it gives the desired slip when calculated at the trailing edge. Different boats run best with different slips. Light SAW riggers may only need 10% more pitch to create the desired thrust, while monos need more. The standard prop mods do much more like changing the lift, reducing the blade area, and controlling the thrust cone. There is no substitute for bending a lot of props and seeing what happens.

Lohring Miller
Click to expand...
"I like to think that the leading edge pitch should come close to matching the boat speed and engine rpm."

Lohring, That is what I was saying in my post from 2003. And really it should be the average of the face and back pitch added together. The back being the surface of blade that is toward the front of the boat. That surface may have 10% -15% less pitch than the face surface that we normally measure.
 
Andy Brown said:
lohring said:
I like to think that the leading edge pitch should come close to matching the boat speed and engine rpm. That is, the water should enter with very little angle to the bottom of the prop (the pitch surface). That means low slip on the leading edge pitch at the design speed and rpm. The pitch then should increase until it gives the desired slip when calculated at the trailing edge. Different boats run best with different slips. Light SAW riggers may only need 10% more pitch to create the desired thrust, while monos need more. The standard prop mods do much more like changing the lift, reducing the blade area, and controlling the thrust cone. There is no substitute for bending a lot of props and seeing what happens.

Lohring Miller
Click to expand...
"I like to think that the leading edge pitch should come close to matching the boat speed and engine rpm."

Lohring, That is what I was saying in my post from 2003. And really it should be the average of the face and back pitch added together. The back being the surface of blade that is toward the front of the boat. That surface may have 10% -15% less pitch than the face surface that we normally measure.
Click to expand...
OMG :eek: A GHOST
 
TUNLBOTR said:
David,

I always understood it as trailing edge pitch decreases ventilation of the blade, therefore causing less slippage and providing lift.
Click to expand...
Yes David, It brings the last part of the blade into contact with the water instead of air as I mentioned in my post from 2003. Thereby reducing ventilation of the blade and reducing slippage.
 
Ray Sametz said:
Andy Brown said:
lohring said:
I like to think that the leading edge pitch should come close to matching the boat speed and engine rpm. That is, the water should enter with very little angle to the bottom of the prop (the pitch surface). That means low slip on the leading edge pitch at the design speed and rpm. The pitch then should increase until it gives the desired slip when calculated at the trailing edge. Different boats run best with different slips. Light SAW riggers may only need 10% more pitch to create the desired thrust, while monos need more. The standard prop mods do much more like changing the lift, reducing the blade area, and controlling the thrust cone. There is no substitute for bending a lot of props and seeing what happens.

Lohring Miller
Click to expand...
"I like to think that the leading edge pitch should come close to matching the boat speed and engine rpm."

Lohring, That is what I was saying in my post from 2003. And really it should be the average of the face and back pitch added together. The back being the surface of blade that is toward the front of the boat. That surface may have 10% -15% less pitch than the face surface that we normally measure.
Click to expand...
OMG :eek: A GHOST
Click to expand...

LOL @ Ray!!!!
 
So let me see if I understand this now the amount of pitch on the last 5 to10deg of the trailing edge will make the prop want to push up the back of the boat. So the weight of the boat over all and the weight on the tail will determine how much ramp you need on the trailing edge to lift the back.

So a prop with a progression in the pitch spreed out over more deg will lift less than a ski ramp on the end?

David
 
For reasons I don't understand, monos seem to like the low rake octura X series props that have a lot of cup at the trailing edge. The SAW riggers like a gradual pitch progression on props like the 2100 series. A lot of what I know about that came from the props Andy modified for us to set the gas records.

Lohring Miller
 
lohring said:
For reasons I don't understand, monos seem to like the low rake octura X series props that have a lot of cup at the trailing edge. The SAW riggers like a gradual pitch progression on props like the 2100 series. A lot of what I know about that came from the props Andy modified for us to set the gas records.

Lohring Miller
Click to expand...

I think that has to do with the amount of drag each has.

Pretty sure most of the mono SAW records were set with what would normally be hydro props, just takes a long time for them to hook up!

Hard to go real fast (ultimately) with a prop that has that much progression, as Andy told me a long time ago it's like a brake. ;)
 

Similar threads

A
Mixing Fuel
2
Replies
26
Views
4K
Timbo Whalen
Timbo Whalen
C
Custom propeller - Do you want to test it?
Replies
4
Views
2K
John Beardslee
John Beardslee
Jake Ellwood
Is my OS 21 Outboard worn out?
Replies
3
Views
1K
Rokieboater
Rokieboater
Chris Wittrig
Sponsorship vs. Donations | How to Get the Most Value as a Business | Give it a Try with the 2022 NAMBA Nationals
Replies
15
Views
2K
Chris Wittrig
Chris Wittrig
B
Future of RC's
2 3
Replies
45
Views
7K
Samuel Hagan JR
Samuel Hagan JR

Latest posts

Back
Top