Prop Technical Discussion

[Marty Davis]

Marty,

Take .006" off the bottom of your disc and that should zero you in.

I am sure Steve will do it for you if needed.

I am not a big fan of T.E. cup as it does kill RPM and that does hurt

the ultimate speed of the boat and the acceleration rate.

I think you need to work more on the middle of the blade to increase

the C.O.B. and then I think you will have less progression and I think

that will work better on hydro set ups. The Monos I think like more

pitch progression in the blade than the hydros do. I can pass on some

results with the Mono pitch progression. As we increased the C.O.B. and

the T.E. cup together we started to go a whole lot faster with the 1614/3.

I can go back though my propeller boxes and measure the progressions on my

best hydro propellers and see what I find. I remember a few years back I had

a range that I liked to stay in with the progression rate on my hydros, I will

have to look back though some notes to find it all. I have been working on the

new propellers for the twin set ups and I have found the higher COB really helps

the big blocks with the acceleration and top end.

Thanks,

Mark Sholund

Interesting....

What got me started in this recent analysis was a prop that I bought that Andy did for his Borther-in-law. Probably a very special prop.

It ran 90 mph on my new 67 boat and launched well and milled well, etc.

Funny thing the COB pitch was fairly low and the pitch progression VERY high 10%+

Prop was amazing... I say was because it got trashed in Charleston. Good thing though, I had documented it thoroughly and can duplicate it fairly easily.

What I am thinking is that pitch progression is an area that can yield BIG dividends. The way that I have been pitching props for a long time is similar to this prop. I have always wanted a prop that would launch easily, mill well and run really fast. That is a tricky thing to accomplish.

I bent a couple props for a twin 91 (for Larry Beals) that were exceptional and had all these characteristics. The way that I did them was to use low COB pitch and high progression.

This is a neat area that deserves careful analysis and testing.

Marty,

when it had low CENTER OR BLADE pitch was the leading edge greater than the trailing edge?

chris

Chris:

Sorry to say, I didn't measure the tongue area. My bad....

 

[Marty Davis]

Great Post!... Hit at exactly the right time..... 70% is just the unwritten "rule of thumb" we all, currently use, with that area of the blade in theory, doing the grunt work..... Mark has taken it down to 50-55 i'm sure in the past... results maybe?... and why?..

I had, a paper by possibly Brian Callahan, that had some serious water dynamics and formulas per prop testing on it given to me by K Bulifant years ago, maybe it's around in ether limbo..... I cant regain it, along with the other 10 years of literature I had compiled.. so... graciously, I appreciate the information here easily.

Mysteriously, I had completed rough in, and was starting to install cup in a few....

Apples to Apples: Marty, explain to figures: 3.1 2.8 2.4 2.1-(stock) with nominally a .3 jump,across the span... what %.... Formula for the lost?

Bad thing is, this is a tunnel hull prop, and with possible hull characteristics entering into the equation, it is almost guaranteed to cavitate and does, until that fateful moment the planet aligns and we're off...( tunnel gaining air, and balance, possibly) changing the percentage possibly over the span might be interesting....

Throw an orange in: best hydro propellor ( Mark did years ago) 3.4 3.1 2.8 2.4..... same nominal .3 progression?.... for the most part. Again on theory, maybe that allowing it to drop to stock easing the water off (back cut, aiding also?)....and yet easier reentry for another bite of water......

The current "ski style" hydros have amazed me, factly, as pulling previously thought off the chart cup and progression thought on other traditional style hull testing, it's fun to search out, and have a boat ask for more...( I didnt find it last year!)looking into percentage may allow me use of a few of the "duds" sitting around.....

Progression is just another deal, along with back, and barr cutting..... knowing the effects say of higher progression, possibly, would you see the need to in theory: back cut more with the higher leading edge progression?.. barr cut more, if you have serious boat pukin' cup on the trailing?..... ( hopefully the nomenclature is correct)..... where does overall diameter come into play?

I watch thrust cone,motor harmony, and overall speed gain.... searching for THE ONE, and then.... the machine will aid me to take it up from there... maybe.... 2 1/2 months to wait, and a beryllium pile. Only the water, the boat, and inherent variables, will tell.

Mentor and classic: Are you, testing to burn nitro, or are you making changes and learning?

Thanks for the winter stimulation... lets keep it going.... Mike

Mike:

One side point that you mentioned. I ALWAYS use Barr Back Cut on my best props. That is unrrelated to the progression I think. Might be able to pull a little more prop with the BBC.

I have no idea what the optimum progression is other than to look at my best props and see what they are.

For example: I have 6 props that ran 80 or better on a friends .21 JAE. The really ranged in progression from 5,5,3,3,7,11 Does seem to be a pattern here, but not enough data points.

The 67 prop that was so good had a progression of 12 from the 2nd to 3rd step which is a LOT. No cavitation, hooked up immediately.

I modified my prop documentation spreadsheet so that I can analyze some more spread on the prop. Will start to analyze my best props when I get my 21 prop box back from loan.

That prop technical article is still posted at http://rcboat.com/past.htm

 

[mtruex]

Great Post!... Hit at exactly the right time..... 70% is just the unwritten "rule of thumb" we all, currently use, with that area of the blade in theory, doing the grunt work..... Mark has taken it down to 50-55 i'm sure in the past... results maybe?... and why?..

I had, a paper by possibly Brian Callahan, that had some serious water dynamics and formulas per prop testing on it given to me by K Bulifant years ago, maybe it's around in ether limbo..... I cant regain it, along with the other 10 years of literature I had compiled.. so... graciously, I appreciate the information here easily.

Mysteriously, I had completed rough in, and was starting to install cup in a few....

Apples to Apples: Marty, explain to figures: 3.1 2.8 2.4 2.1-(stock) with nominally a .3 jump,across the span... what %.... Formula for the lost?

Bad thing is, this is a tunnel hull prop, and with possible hull characteristics entering into the equation, it is almost guaranteed to cavitate and does, until that fateful moment the planet aligns and we're off...( tunnel gaining air, and balance, possibly) changing the percentage possibly over the span might be interesting....

Throw an orange in: best hydro propellor ( Mark did years ago) 3.4 3.1 2.8 2.4..... same nominal .3 progression?.... for the most part. Again on theory, maybe that allowing it to drop to stock easing the water off (back cut, aiding also?)....and yet easier reentry for another bite of water......

The current "ski style" hydros have amazed me, factly, as pulling previously thought off the chart cup and progression thought on other traditional style hull testing, it's fun to search out, and have a boat ask for more...( I didnt find it last year!)looking into percentage may allow me use of a few of the "duds" sitting around.....

Progression is just another deal, along with back, and barr cutting..... knowing the effects say of higher progression, possibly, would you see the need to in theory: back cut more with the higher leading edge progression?.. barr cut more, if you have serious boat pukin' cup on the trailing?..... ( hopefully the nomenclature is correct)..... where does overall diameter come into play?

I watch thrust cone,motor harmony, and overall speed gain.... searching for THE ONE, and then.... the machine will aid me to take it up from there... maybe.... 2 1/2 months to wait, and a beryllium pile. Only the water, the boat, and inherent variables, will tell.

Mentor and classic: Are you, testing to burn nitro, or are you making changes and learning?

Thanks for the winter stimulation... lets keep it going.... Mike

Mike:

One side point that you mentioned. I ALWAYS use Barr Back Cut on my best props. That is unrrelated to the progression I think. Might be able to pull a little more prop with the BBC.

I have no idea what the optimum progression is other than to look at my best props and see what they are.

For example: I have 6 props that ran 80 or better on a friends .21 JAE. The really ranged in progression from 5,5,3,3,7,11 Does seem to be a pattern here, but not enough data points.

The 67 prop that was so good had a progression of 12 from the 2nd to 3rd step which is a LOT. No cavitation, hooked up immediately.

I modified my prop documentation spreadsheet so that I can analyze some more spread on the prop. Will start to analyze my best props when I get my 21 prop box back from loan.

That prop technical article is still posted at http://rcboat.com/past.htm

marty,

before you get too wraped up in all these measurements you need to make sure your guage is right, on mine if i take a measurement on the 1/16 step and compare it to a measurement taken on the .059 step there is a big difference..you say your second step is .134 , thats a big deal..

 

[Marty Davis]

Great Post!... Hit at exactly the right time..... 70% is just the unwritten "rule of thumb" we all, currently use, with that area of the blade in theory, doing the grunt work..... Mark has taken it down to 50-55 i'm sure in the past... results maybe?... and why?..

I had, a paper by possibly Brian Callahan, that had some serious water dynamics and formulas per prop testing on it given to me by K Bulifant years ago, maybe it's around in ether limbo..... I cant regain it, along with the other 10 years of literature I had compiled.. so... graciously, I appreciate the information here easily.

Mysteriously, I had completed rough in, and was starting to install cup in a few....

Apples to Apples: Marty, explain to figures: 3.1 2.8 2.4 2.1-(stock) with nominally a .3 jump,across the span... what %.... Formula for the lost?

Bad thing is, this is a tunnel hull prop, and with possible hull characteristics entering into the equation, it is almost guaranteed to cavitate and does, until that fateful moment the planet aligns and we're off...( tunnel gaining air, and balance, possibly) changing the percentage possibly over the span might be interesting....

Throw an orange in: best hydro propellor ( Mark did years ago) 3.4 3.1 2.8 2.4..... same nominal .3 progression?.... for the most part. Again on theory, maybe that allowing it to drop to stock easing the water off (back cut, aiding also?)....and yet easier reentry for another bite of water......

The current "ski style" hydros have amazed me, factly, as pulling previously thought off the chart cup and progression thought on other traditional style hull testing, it's fun to search out, and have a boat ask for more...( I didnt find it last year!)looking into percentage may allow me use of a few of the "duds" sitting around.....

Progression is just another deal, along with back, and barr cutting..... knowing the effects say of higher progression, possibly, would you see the need to in theory: back cut more with the higher leading edge progression?.. barr cut more, if you have serious boat pukin' cup on the trailing?..... ( hopefully the nomenclature is correct)..... where does overall diameter come into play?

I watch thrust cone,motor harmony, and overall speed gain.... searching for THE ONE, and then.... the machine will aid me to take it up from there... maybe.... 2 1/2 months to wait, and a beryllium pile. Only the water, the boat, and inherent variables, will tell.

Mentor and classic: Are you, testing to burn nitro, or are you making changes and learning?

Thanks for the winter stimulation... lets keep it going.... Mike

Mike:

One side point that you mentioned. I ALWAYS use Barr Back Cut on my best props. That is unrrelated to the progression I think. Might be able to pull a little more prop with the BBC.

I have no idea what the optimum progression is other than to look at my best props and see what they are.

For example: I have 6 props that ran 80 or better on a friends .21 JAE. The really ranged in progression from 5,5,3,3,7,11 Does seem to be a pattern here, but not enough data points.

The 67 prop that was so good had a progression of 12 from the 2nd to 3rd step which is a LOT. No cavitation, hooked up immediately.

I modified my prop documentation spreadsheet so that I can analyze some more spread on the prop. Will start to analyze my best props when I get my 21 prop box back from loan.

That prop technical article is still posted at http://rcboat.com/past.htm

marty,

before you get too wraped up in all these measurements you need to make sure your guage is right, on mine if i take a measurement on the 1/16 step and compare it to a measurement taken on the .059 step there is a big difference..you say your second step is .134 , thats a big deal..

I agree, maybe I will talk to Steve and see if he will correct this problem.

 

[Marty Davis]

I decided to help this discussion, that I would upload a spreadsheet that will be part of the new Engine Analysis Software coming version. It is free for all and should be an invaluable tool for those with the Woods Pitch Gauge.

Be sure to look at the drawing that is in the zip file. It shows how to automatically set the pointer so that it is at 70% of the measured prop diameter. It will make it easy to use a set of calipers to measure between the Dubro Collar and the Pointer to set this 70%.

At the top of the sheet there are 3 RED BOXES to imput your steps if your gauge is not machined on 1/16" increments. Steve told me that for anyone that has one of this Gauges that is not the correct thickness, he will replace the disk with the blocks on it. The inputs in the red boxes are the correct ones for the 1/16" increments that the Gauge was designed for.

The Green Columns at the far left show the pitch progression automatically in percentage as you input the data.

I am open for suggestions if you don't like something on the sheet.

Here is the link to download the sheet: http://engine-analysis-software.com/Woods_Gauge.zip

 

[shoboat]

Marty,

Interesting information, but this is what I have come up with.

I have (10) H-32's here in stock and I have measured them all.

I have the duplicator here also, so I measured the stock propeller first.

I used two of my three Wood's Gauges to measure them, so it is very accurate.

Stock H-32 from ABC Propeller in Columbus, Ohio

1st step at .7 radi = 4.74" trailing edge cup measurement (1/16 on the chart)

2nd step at .7 radi = 4.50"

3rd step at .7 radi = 4.29" this is the C.O.B. pitch measurement (3/16 on the chart)

If you go up .250" or a 1/4" up from .7 radi and measure you will get 4.29" C.O.B.

stock pitch from ABC = 4.30" pretty accurate don't you think?

So the first step will give you T.E. cup, third step will show you C.O.B. pitch

I will continue the duplicator H-32 tomorrow. I work at 3AM at the Airport for Delta

Air Lines and I need some sleep. To be continued tomorrow.

Thanks For Sharing,

Mark Sholund

 

[Marty Davis]

Marty,

Interesting information, but this is what I have come up with.

I have (10) H-32's here in stock and I have measured them all.

I have the duplicator here also, so I measured the stock propeller first.

I used two of my three Wood's Gauges to measure them, so it is very accurate.

Stock H-32 from ABC Propeller in Columbus, Ohio

1st step at .7 radi = 4.74" trailing edge cup measurement (1/16 on the chart)

2nd step at .7 radi = 4.50"

3rd step at .7 radi = 4.29" this is the C.O.B. pitch measurement (3/16 on the chart)

If you go up .250" or a 1/4" up from .7 radi and measure you will get 4.29" C.O.B.

stock pitch from ABC = 4.30" pretty accurate don't you think?

So the first step will give you T.E. cup, third step will show you C.O.B. pitch

I will continue the duplicator H-32 tomorrow. I work at 3AM at the Airport for Delta

Air Lines and I need some sleep. To be continued tomorrow.

Thanks For Sharing,

Mark Sholund

Be sure to measure the tongue area too. That is the control.....

 

[Terry Keeley]

Terry:

I am not sure as all the markings were removed. It was a stainless prop that had a diameter of 2.425 and looks like an H32. Just a little smaller in diameter than an H32.

H-32's a good prop, think Andy started with a 1667 on that one...

 

[Ian Inverarity]

Ian,

Most propeller information available out there will tell

you that .7 radi is where most of the water comes off the blade.

You can cup anywhere you would like, but @ .7 is the most effective.

Ian,

Do you ever Google propellers? and read any technical articles?

HydroComp.com is a good one and there are all kinds of articles on

cupping.

Happy Reading,

Mark Sholund

Mark,

I have done a little Googling, perhaps not as much as you! Do you have a link to that information regarding the 0.7 radi? On the Hydrocomp Inc site the article I could find about cupping suggested cupping in the range of 40 to 90% radi, also suggesting increasing cup moving out towards the tips may be better. From other research I have done I have seen the 70% used for the rating and measuring of pitch of aircraft props. Has the 70% or 0.7 radi been arbitrarily adopted for our props, or has it been verified as the most important pitch location on our high speed surface piecing props?

The research I did on aircraft props suggest the thrust cone narrows after the prop, while clearly for model boat props the thrust cone expands moving away from the prop. That is what applies for aircraft props may not be that relevant for our model boat props. The surface speed of any part of the prop is directly proportional to the diameter of that part, that is the surface speed (or tangential velocity) is highest at the tips and least at the hub. So 90% diameter has a 20% greater surface speed than 70% diameter. Also the amount of water that any part of a prop will travel thru will also be proportional to the diameter. To me this would suggest that diameters greater than 70% may have more influence? :huh:

Thanks,

Ian.

 

[shoboat]

Ian,

I will dig up some notes for you soon. We have been pretty busy at work.

Thanks,

Mark Sholund

 

[Ian Inverarity]

Let's talk on the same level with pitch measurement.

I use a Steve Woods Pitch Gauge and the way that I measure my props is with the First and Second Steps on the gauge. On mine the first step is .072" and the second step is .134". This gives me the cup and the root pitch further down the blade. For my H32 the measurements are 8.25 degrees at .134" and 3.75 degrees at .072" Oh, I forgot, I use .134" on the tongue area of the prop.

I haven't used a Steve Woods pitch gauge, so I am not entirely sure I understand how they work. But looking at the above examples is the realistic resolution of the degree measurement 0.25 degrees? As I calculate it 3.75 degrees at 0.072" step is 6.912" pitch, is that correct? So with a 0.25 degree resolution and the 0.072" step the adjacent resolvable pitches would be 3.5 degrees and 4.0 degrees, which I calculate as 7.406" pitch and 6.48" pitch. That seems pretty coarse resolution? :huh:

Ian.

 

[Jim Caldwell]

I have the Dial Indicator system (VooDoo gauge)but no conversion chart.

Can any one help me out??

 

[Rick Doane]

Jim:

With any pitch gauge........Pitch = Distance X 360 divided by Degrees.

Regards........Rick

 

[Marty Davis]

Great Post!... Hit at exactly the right time..... 70% is just the unwritten "rule of thumb" we all, currently use, with that area of the blade in theory, doing the grunt work..... Mark has taken it down to 50-55 i'm sure in the past... results maybe?... and why?..

I had, a paper by possibly Brian Callahan, that had some serious water dynamics and formulas per prop testing on it given to me by K Bulifant years ago, maybe it's around in ether limbo..... I cant regain it, along with the other 10 years of literature I had compiled.. so... graciously, I appreciate the information here easily.

Mysteriously, I had completed rough in, and was starting to install cup in a few....

Apples to Apples: Marty, explain to figures: 3.1 2.8 2.4 2.1-(stock) with nominally a .3 jump,across the span... what %.... Formula for the lost?

Bad thing is, this is a tunnel hull prop, and with possible hull characteristics entering into the equation, it is almost guaranteed to cavitate and does, until that fateful moment the planet aligns and we're off...( tunnel gaining air, and balance, possibly) changing the percentage possibly over the span might be interesting....

Throw an orange in: best hydro propellor ( Mark did years ago) 3.4 3.1 2.8 2.4..... same nominal .3 progression?.... for the most part. Again on theory, maybe that allowing it to drop to stock easing the water off (back cut, aiding also?)....and yet easier reentry for another bite of water......

The current "ski style" hydros have amazed me, factly, as pulling previously thought off the chart cup and progression thought on other traditional style hull testing, it's fun to search out, and have a boat ask for more...( I didnt find it last year!)looking into percentage may allow me use of a few of the "duds" sitting around.....

Progression is just another deal, along with back, and barr cutting..... knowing the effects say of higher progression, possibly, would you see the need to in theory: back cut more with the higher leading edge progression?.. barr cut more, if you have serious boat pukin' cup on the trailing?..... ( hopefully the nomenclature is correct)..... where does overall diameter come into play?

I watch thrust cone,motor harmony, and overall speed gain.... searching for THE ONE, and then.... the machine will aid me to take it up from there... maybe.... 2 1/2 months to wait, and a beryllium pile. Only the water, the boat, and inherent variables, will tell.

Mentor and classic: Are you, testing to burn nitro, or are you making changes and learning?

Thanks for the winter stimulation... lets keep it going.... Mike

Mike:

That article that Brian Callahan found is still posted on my http://rcboat.com/past.htm technical notes area.

 

[Marty Davis]

Great Post!... Hit at exactly the right time..... 70% is just the unwritten "rule of thumb" we all, currently use, with that area of the blade in theory, doing the grunt work..... Mark has taken it down to 50-55 i'm sure in the past... results maybe?... and why?..

I had, a paper by possibly Brian Callahan, that had some serious water dynamics and formulas per prop testing on it given to me by K Bulifant years ago, maybe it's around in ether limbo..... I cant regain it, along with the other 10 years of literature I had compiled.. so... graciously, I appreciate the information here easily.

Mysteriously, I had completed rough in, and was starting to install cup in a few....

Apples to Apples: Marty, explain to figures: 3.1 2.8 2.4 2.1-(stock) with nominally a .3 jump,across the span... what %.... Formula for the lost?

Bad thing is, this is a tunnel hull prop, and with possible hull characteristics entering into the equation, it is almost guaranteed to cavitate and does, until that fateful moment the planet aligns and we're off...( tunnel gaining air, and balance, possibly) changing the percentage possibly over the span might be interesting....

Throw an orange in: best hydro propellor ( Mark did years ago) 3.4 3.1 2.8 2.4..... same nominal .3 progression?.... for the most part. Again on theory, maybe that allowing it to drop to stock easing the water off (back cut, aiding also?)....and yet easier reentry for another bite of water......

The current "ski style" hydros have amazed me, factly, as pulling previously thought off the chart cup and progression thought on other traditional style hull testing, it's fun to search out, and have a boat ask for more...( I didnt find it last year!)looking into percentage may allow me use of a few of the "duds" sitting around.....

Progression is just another deal, along with back, and barr cutting..... knowing the effects say of higher progression, possibly, would you see the need to in theory: back cut more with the higher leading edge progression?.. barr cut more, if you have serious boat pukin' cup on the trailing?..... ( hopefully the nomenclature is correct)..... where does overall diameter come into play?

I watch thrust cone,motor harmony, and overall speed gain.... searching for THE ONE, and then.... the machine will aid me to take it up from there... maybe.... 2 1/2 months to wait, and a beryllium pile. Only the water, the boat, and inherent variables, will tell.

Mentor and classic: Are you, testing to burn nitro, or are you making changes and learning?

Thanks for the winter stimulation... lets keep it going.... Mike

Mike:

One side point that you mentioned. I ALWAYS use Barr Back Cut on my best props. That is unrrelated to the progression I think. Might be able to pull a little more prop with the BBC.

I have no idea what the optimum progression is other than to look at my best props and see what they are.

For example: I have 6 props that ran 80 or better on a friends .21 JAE. The really ranged in progression from 5,5,3,3,7,11 Does seem to be a pattern here, but not enough data points.

The 67 prop that was so good had a progression of 12 from the 2nd to 3rd step which is a LOT. No cavitation, hooked up immediately.

I modified my prop documentation spreadsheet so that I can analyze some more spread on the prop. Will start to analyze my best props when I get my 21 prop box back from loan.

That prop technical article is still posted at http://rcboat.com/past.htm

marty,

before you get too wraped up in all these measurements you need to make sure your guage is right, on mine if i take a measurement on the 1/16 step and compare it to a measurement taken on the .059 step there is a big difference..you say your second step is .134 , thats a big deal..

I agree, maybe I will talk to Steve and see if he will correct this problem.

Got my new step wheel for the Woods Pitch guage. It is perfect and now I will convert all my previous measurements to the new wheel.

THANKS STEVE....

 

[steve wood]

Great Post!... Hit at exactly the right time..... 70% is just the unwritten "rule of thumb" we all, currently use, with that area of the blade in theory, doing the grunt work..... Mark has taken it down to 50-55 i'm sure in the past... results maybe?... and why?..

I had, a paper by possibly Brian Callahan, that had some serious water dynamics and formulas per prop testing on it given to me by K Bulifant years ago, maybe it's around in ether limbo..... I cant regain it, along with the other 10 years of literature I had compiled.. so... graciously, I appreciate the information here easily.

Mysteriously, I had completed rough in, and was starting to install cup in a few....

Apples to Apples: Marty, explain to figures: 3.1 2.8 2.4 2.1-(stock) with nominally a .3 jump,across the span... what %.... Formula for the lost?

Bad thing is, this is a tunnel hull prop, and with possible hull characteristics entering into the equation, it is almost guaranteed to cavitate and does, until that fateful moment the planet aligns and we're off...( tunnel gaining air, and balance, possibly) changing the percentage possibly over the span might be interesting....

Throw an orange in: best hydro propellor ( Mark did years ago) 3.4 3.1 2.8 2.4..... same nominal .3 progression?.... for the most part. Again on theory, maybe that allowing it to drop to stock easing the water off (back cut, aiding also?)....and yet easier reentry for another bite of water......

The current "ski style" hydros have amazed me, factly, as pulling previously thought off the chart cup and progression thought on other traditional style hull testing, it's fun to search out, and have a boat ask for more...( I didnt find it last year!)looking into percentage may allow me use of a few of the "duds" sitting around.....

Progression is just another deal, along with back, and barr cutting..... knowing the effects say of higher progression, possibly, would you see the need to in theory: back cut more with the higher leading edge progression?.. barr cut more, if you have serious boat pukin' cup on the trailing?..... ( hopefully the nomenclature is correct)..... where does overall diameter come into play?

I watch thrust cone,motor harmony, and overall speed gain.... searching for THE ONE, and then.... the machine will aid me to take it up from there... maybe.... 2 1/2 months to wait, and a beryllium pile. Only the water, the boat, and inherent variables, will tell.

Mentor and classic: Are you, testing to burn nitro, or are you making changes and learning?

Thanks for the winter stimulation... lets keep it going.... Mike

Mike:

One side point that you mentioned. I ALWAYS use Barr Back Cut on my best props. That is unrrelated to the progression I think. Might be able to pull a little more prop with the BBC.

I have no idea what the optimum progression is other than to look at my best props and see what they are.

For example: I have 6 props that ran 80 or better on a friends .21 JAE. The really ranged in progression from 5,5,3,3,7,11 Does seem to be a pattern here, but not enough data points.

The 67 prop that was so good had a progression of 12 from the 2nd to 3rd step which is a LOT. No cavitation, hooked up immediately.

I modified my prop documentation spreadsheet so that I can analyze some more spread on the prop. Will start to analyze my best props when I get my 21 prop box back from loan.

That prop technical article is still posted at http://rcboat.com/past.htm

marty,

before you get too wraped up in all these measurements you need to make sure your guage is right, on mine if i take a measurement on the 1/16 step and compare it to a measurement taken on the .059 step there is a big difference..you say your second step is .134 , thats a big deal..

I agree, maybe I will talk to Steve and see if he will correct this problem.

Got my new step wheel for the Woods Pitch guage. It is perfect and now I will convert all my previous measurements to the new wheel.

THANKS STEVE....

thanks for letting me know there was a problem

 

[Marty Davis]

Great Post!... Hit at exactly the right time..... 70% is just the unwritten "rule of thumb" we all, currently use, with that area of the blade in theory, doing the grunt work..... Mark has taken it down to 50-55 i'm sure in the past... results maybe?... and why?..

I had, a paper by possibly Brian Callahan, that had some serious water dynamics and formulas per prop testing on it given to me by K Bulifant years ago, maybe it's around in ether limbo..... I cant regain it, along with the other 10 years of literature I had compiled.. so... graciously, I appreciate the information here easily.

Mysteriously, I had completed rough in, and was starting to install cup in a few....

Apples to Apples: Marty, explain to figures: 3.1 2.8 2.4 2.1-(stock) with nominally a .3 jump,across the span... what %.... Formula for the lost?

Bad thing is, this is a tunnel hull prop, and with possible hull characteristics entering into the equation, it is almost guaranteed to cavitate and does, until that fateful moment the planet aligns and we're off...( tunnel gaining air, and balance, possibly) changing the percentage possibly over the span might be interesting....

Throw an orange in: best hydro propellor ( Mark did years ago) 3.4 3.1 2.8 2.4..... same nominal .3 progression?.... for the most part. Again on theory, maybe that allowing it to drop to stock easing the water off (back cut, aiding also?)....and yet easier reentry for another bite of water......

The current "ski style" hydros have amazed me, factly, as pulling previously thought off the chart cup and progression thought on other traditional style hull testing, it's fun to search out, and have a boat ask for more...( I didnt find it last year!)looking into percentage may allow me use of a few of the "duds" sitting around.....

Progression is just another deal, along with back, and barr cutting..... knowing the effects say of higher progression, possibly, would you see the need to in theory: back cut more with the higher leading edge progression?.. barr cut more, if you have serious boat pukin' cup on the trailing?..... ( hopefully the nomenclature is correct)..... where does overall diameter come into play?

I watch thrust cone,motor harmony, and overall speed gain.... searching for THE ONE, and then.... the machine will aid me to take it up from there... maybe.... 2 1/2 months to wait, and a beryllium pile. Only the water, the boat, and inherent variables, will tell.

Mentor and classic: Are you, testing to burn nitro, or are you making changes and learning?

Thanks for the winter stimulation... lets keep it going.... Mike

Mike:

One side point that you mentioned. I ALWAYS use Barr Back Cut on my best props. That is unrrelated to the progression I think. Might be able to pull a little more prop with the BBC.

I have no idea what the optimum progression is other than to look at my best props and see what they are.

For example: I have 6 props that ran 80 or better on a friends .21 JAE. The really ranged in progression from 5,5,3,3,7,11 Does seem to be a pattern here, but not enough data points.

The 67 prop that was so good had a progression of 12 from the 2nd to 3rd step which is a LOT. No cavitation, hooked up immediately.

I modified my prop documentation spreadsheet so that I can analyze some more spread on the prop. Will start to analyze my best props when I get my 21 prop box back from loan.

That prop technical article is still posted at http://rcboat.com/past.htm

marty,

before you get too wraped up in all these measurements you need to make sure your guage is right, on mine if i take a measurement on the 1/16 step and compare it to a measurement taken on the .059 step there is a big difference..you say your second step is .134 , thats a big deal..

I agree, maybe I will talk to Steve and see if he will correct this problem.

Got my new step wheel for the Woods Pitch guage. It is perfect and now I will convert all my previous measurements to the new wheel.

THANKS STEVE....

thanks for letting me know there was a problem

Steve:

No problem.....

I love the gauge and use it all the time. Wonder how I got by with the old Hughey Gauge.