Propeller Cupping????

[Rick Doane]

Jim:

What I have found concerning cupping numbers is that is does not mean very much when it is related to full blade pitch. I too have found that is possible to measure the trailing edge cup as accurately as the gauge will allow with more difficulty defining/measuring the tip cup. Either number means nothing when trying to quantifying the pitch vs. MPH, at least for me. Cup measurements are obtained from very short distances up the prop face and can be plotted to give a visual shape of the edge. I have found that neither blade is exactly the same. I agree with Charles Perdue that mapping a prop is the best way to gain information to better understand what the prop is doing. I perfer to pitch up a prop and test on the boat prior to annealing/hardening. Approximately 0.5 inches of pitch can be added without deforming the blade and drastically changing the rake value. I measure three places on each blade from the hub to the outer edge and average the measurements for the pitch. Most prop blades come within 0.1-0.2 inches of pitch stock.

I have only used tip cup as a means to make an average/high roostertail prop smoother. I perfer to roll inward the outer edges of a prop to control lift. If a boat hops in a turn, then you can bet that one blade is not the same pitch/entrance angle as the other.

The attached photos are of my old pitch blocks from 1976 and 2005. Even the crude one worked.

I wonder if I can get any thoughts or discussion on the pitch difference between the front side vs. the back side of the prop and how it determines the speed of the boat?

 

[Jim Allen]

Excellent post Rick. Your pitching blocks are identical to mine except all of mine have pre-installed 1/4" dowel pins to insure perfect alignment. I always anneal the props because this makes working easier.

I make sure the blades have the same pitch & the same rake angles. When I find a prop where the blade orientation (180 or 120 deg) or the blade tracking is off, I do not use it. Props with these types of errors can be difficult to balance & may cause unwanted vibrations & oscillations, even when balanced.

I measure at many points from the blade's root at the hub, out to the blade's tip. I want all of the helical angles to be correct from the hub to the tip. This means the blade has true pitch everywhere on the blade. Comparing identical props that have varying true pitches & the same progression amounts, knowing the engines RPM, the speed of the boat, easily tells what propeller of that type is the optimum. I control lift with different prop depths & thrust angles.

From many years of testing, I am convinced that the information that Andy Brown discovered & posted is 100% correct. I have used & tested his ideas about progression on X462,467,448,450,452; 1667; 1967; 2267; V-967-3B; 2170; 2175; 2167-3B Octura props & 2718; 2718-3B; 2818; 2918; 3016 ABC props. All props listed were tested as a group with several blades varying by 1/8" of pitch. All props are magnetically balanced & hardened.

Hell of a lot of work here.

Jim Allen

 

[Rick Doane]

Thank you Jim. I failed to mention that my blocks have locating pins also and I machined the fixture with a roughing end mill. This gave the sides ridges that when the mold is made, it locks the piece into the sides of the fixture. This allows me to make many molds with just one fixture. You might be able to see this in the attached photo.

Rick

 

[Jim Allen]

Thank you Jim. I failed to mention that my blocks have locating pins also and I machined the fixture with a roughing end mill. This gave the sides ridges that when the mold is made, it locks the piece into the sides of the fixture. This allows me to make many molds with just one fixture. You might be able to see this in the attached photo.

Rick

Good idea. I made individual blocks for each propeller type. Still have many that I will probably never use again.

 

[Christian Lucas]

Hi,

what about a tool like this described in the artikel , http://www.hydrocompinc.com/knowledge/publications/PropellerCup.pdf .

I often do not cup ,i use a grindig tool doing similar at the Training edge belong to the powerdiagram of a motor not al the trailing edge from the hub to the tip . Less for IC. motors and all the way for high torque electric motors.

 

[hugh hargett]

That tool would be great. Whos gonna make it for you? coz you wont find it out there for rc boat props. I posted a link to that pdf earlier in the thread. Theres some good info in there.

only one person I know that can supply you with these type progressive pitch anvils

"These anvils are used to make different amounts of progressive pitch. They are held rigidly in a machinist vise & a dead blow rubber mallet is used on the back side of each blade. NO NICKS OR DINGS to be removed on the inside or outside of blade surfaces with this method!"

-Jim Allen-

 

[Christian Lucas]

Hi Jim,

i have currently not such thing.maybe i will make one for me to test it.i have a lot of messuring tools as i learnd flight instrument mechanik .i meet Jimmy Gale 30 years ago and he show me a lot of intresting ways to messure all what you want to know from a propeller. He has also a very practical way to rise or lower the pitch .He makes a brick of epoxi with one propellerblade stick in ,Set a hard shaft in the hub and bend the blade to the right pitch.

I learnd to make geometric propellers with same pitch of le and te.But for best efficancy the blade has to meet the water at an angel of attac of 4degree. Also i do no cupping i grind some material of the pressure surface right at the trailing edge. this Is called the Johnson 5 term in the book from Peter du Cane "High Speed Small Craft" he was the designer of the John Cobb Crusaeder.

 

[dwilfong]

You need to think of the blade as a super cavitating hydrofoil.

Because that is what it is.

When removing thickness from the trailing edge it will remove some lift from the prop.

This way more trailing edge cup can be used with out adding lift.

David

 

[John Beardslee]

Jim here is a sample of the 2818 prop I am running stock pitch and cup.

This is how I map the prop.

The % are from the point where the blade meets the hub out to the tip.

The Deg are from the trailing edge to the lead in.

This is how I get the measurements.

Now how do you determine the progression? in 5 deg increments? or the average of 10 deg at different sections? or 15 Deg at different sections.

As you See there are many ways to interpret this info.

So what matters?

With this mapping you can break the prop down to any segmentation you want for interpretation.

David

David,

Look carefully at the two pictures on the right hand side. The top blade in the photo has 0% progression. The leading edge pitch, the middle of the blade pitch & the trailing edge pitches are are all the same, 21". When I attempted to use blades pitched this way, in a surface piercing setup, they had very high slip numbers.

The bottom blade has a total progression amount of 21%. 23"-19"=4"; 4"/19"=.2105 or 21%. What Andy Brown was saying in the post that I previously quoted is; the progression amount changes with the type of hull; the amount of blade area; the blade shape; the blade rake & the amount of drag the hull in question has.

The pitch gage I use measures the progression amount directly, at any radius point, from the leading to the trailing edge. This cannot be done with this type of gage design unless a minimum arc of 72 deg can be swung at one time. The Prop Tracker, prop gage, can read in an arc of 360 deg. (http://www.proptracker.com/contact.asp) The gage I use is this same design in reverse. The propeller is stationary & the mounted arm is rotating on the same 1/4" OD center post that the prop is mounted on. At the base, fastened to the center post, is a stationary drive dog. Since my blade is mounted on a stationary drive dog, readings taken at any radius, after rotating the blade must start & stop at the same points (blade orentation) & at the same depth (blade rake angle).

Jim Allen

Any of you old enough to have run full sized outboard hydros when we used tru pitch props from Michigan Wheel? When I first started those props would have actual shift points - after you got them on plane you would feel a shift, usually around 35 - 50 mph. It actually was finally hooking up after slipping through a couple of stages while coming on plane and moving up to racing speeds. Cupping and progressive pitch changed all that.

Thanks, John

 

[Jim Allen]

"Any of you old enough to have run full sized outboard hydros when we used tru pitch props from Michigan Wheel? When I first started those props would have actual shift points - after you got them on plane you would feel a shift, usually around 35 - 50 mph. It actually was finally hooking up after slipping through a couple of stages while coming on plane and moving up to racing speeds. Cupping and progressive pitch changed all that."

John,

I'm very familiar with the true helical pitch propellers used by Ed Kalfus. They had no progressive pitch at all. The prop blades were shaped like airplane props, blades had zero rake & they would slip badly as they were accelerated. Later tests showed them to be very inefficient.

Jim

 

[Norm Doerr]

Jim here is a sample of the 2818 prop I am running stock pitch and cup.

This is how I map the prop.

The % are from the point where the blade meets the hub out to the tip.

The Deg are from the trailing edge to the lead in.

This is how I get the measurements.

Now how do you determine the progression? in 5 deg increments? or the average of 10 deg at different sections? or 15 Deg at different sections.

As you See there are many ways to interpret this info.

So what matters?

With this mapping you can break the prop down to any segmentation you want for interpretation.

David

David,

Look carefully at the two pictures on the right hand side. The top blade in the photo has 0% progression. The leading edge pitch, the middle of the blade pitch & the trailing edge pitches are are all the same, 21". When I attempted to use blades pitched this way, in a surface piercing setup, they had very high slip numbers.

The bottom blade has a total progression amount of 21%. 23"-19"=4"; 4"/19"=.2105 or 21%. What Andy Brown was saying in the post that I previously quoted is; the progression amount changes with the type of hull; the amount of blade area; the blade shape; the blade rake & the amount of drag the hull in question has.

The pitch gage I use measures the progression amount directly, at any radius point, from the leading to the trailing edge. This cannot be done with this type of gage design unless a minimum arc of 72 deg can be swung at one time. The Prop Tracker, prop gage, can read in an arc of 360 deg. (http://www.proptracker.com/contact.asp) The gage I use is this same design in reverse. The propeller is stationary & the mounted arm is rotating on the same 1/4" OD center post that the prop is mounted on. At the base, fastened to the center post, is a stationary drive dog. Since my blade is mounted on a stationary drive dog, readings taken at any radius, after rotating the blade must start & stop at the same points (blade orentation) & at the same depth (blade rake angle).

Jim Allen

Any of you old enough to have run full sized outboard hydros when we used tru pitch props from Michigan Wheel? When I first started those props would have actual shift points - after you got them on plane you would feel a shift, usually around 35 - 50 mph. It actually was finally hooking up after slipping through a couple of stages while coming on plane and moving up to racing speeds. Cupping and progressive pitch changed all that.

Thanks, John

Jim here is a sample of the 2818 prop I am running stock pitch and cup.

This is how I map the prop.

The % are from the point where the blade meets the hub out to the tip.

The Deg are from the trailing edge to the lead in.

This is how I get the measurements.

Now how do you determine the progression? in 5 deg increments? or the average of 10 deg at different sections? or 15 Deg at different sections.

As you See there are many ways to interpret this info.

So what matters?

With this mapping you can break the prop down to any segmentation you want for interpretation.

David

David,

Look carefully at the two pictures on the right hand side. The top blade in the photo has 0% progression. The leading edge pitch, the middle of the blade pitch & the trailing edge pitches are are all the same, 21". When I attempted to use blades pitched this way, in a surface piercing setup, they had very high slip numbers.

The bottom blade has a total progression amount of 21%. 23"-19"=4"; 4"/19"=.2105 or 21%. What Andy Brown was saying in the post that I previously quoted is; the progression amount changes with the type of hull; the amount of blade area; the blade shape; the blade rake & the amount of drag the hull in question has.

The pitch gage I use measures the progression amount directly, at any radius point, from the leading to the trailing edge. This cannot be done with this type of gage design unless a minimum arc of 72 deg can be swung at one time. The Prop Tracker, prop gage, can read in an arc of 360 deg. (http://www.proptracker.com/contact.asp) The gage I use is this same design in reverse. The propeller is stationary & the mounted arm is rotating on the same 1/4" OD center post that the prop is mounted on. At the base, fastened to the center post, is a stationary drive dog. Since my blade is mounted on a stationary drive dog, readings taken at any radius, after rotating the blade must start & stop at the same points (blade orentation) & at the same depth (blade rake angle).

Jim Allen

Any of you old enough to have run full sized outboard hydros when we used tru pitch props from Michigan Wheel? When I first started those props would have actual shift points - after you got them on plane you would feel a shift, usually around 35 - 50 mph. It actually was finally hooking up after slipping through a couple of stages while coming on plane and moving up to racing speeds. Cupping and progressive pitch changed all that.

Thanks, John

Yup.. Loopers and Megaphones....

 

[Norm Doerr]

"Any of you old enough to have run full sized outboard hydros when we used tru pitch props from Michigan Wheel? When I first started those props would have actual shift points - after you got them on plane you would feel a shift, usually around 35 - 50 mph. It actually was finally hooking up after slipping through a couple of stages while coming on plane and moving up to racing speeds. Cupping and progressive pitch changed all that."

John,

I'm very familiar with the true helical pitch propellers used by Ed Kalfus. They had no progressive pitch at all. The prop blades were shaped like airplane props, blades had zero rake & they would slip badly as they were accelerated. Later tests showed them to be very inefficient.

Jim

"Any of you old enough to have run full sized outboard hydros when we used tru pitch props from Michigan Wheel? When I first started those props would have actual shift points - after you got them on plane you would feel a shift, usually around 35 - 50 mph. It actually was finally hooking up after slipping through a couple of stages while coming on plane and moving up to racing speeds. Cupping and progressive pitch changed all that."

John,

I'm very familiar with the true helical pitch propellers used by Ed Kalfus. They had no progressive pitch at all. The prop blades were shaped like airplane props, blades had zero rake & they would slip badly as they were accelerated. Later tests showed them to be very inefficient.

Jim

Interesting.. I know not a lot but some of the best props I ever had for heat racing would cavitate and boil the water on launch. Even slowing down to a crawl for the start they would not do it. but on the launch I would have to "feather" the RPM range and off it would go. No clue why... I even bent some of them myself and don't know enough to figure it out.

 

[Christian Lucas]

Hi,

do you have some old Octura Competion serie Propeller dia 1,6 to 2,8 ,pitch ratio 1,8 . They have a round trailing edge on the pressure side witch make the prop less bite during start . want moore grip ,tool a campfer/ cannel on the pressure surface at the trailing edge and wonder wy your motor is unable to start with this prop . Do the cannel with soft way to the leading edge and a sharp line at the trailing egde .This prop work great with outrunner high torque motors .

 

[John Beardslee]

"Any of you old enough to have run full sized outboard hydros when we used tru pitch props from Michigan Wheel? When I first started those props would have actual shift points - after you got them on plane you would feel a shift, usually around 35 - 50 mph. It actually was finally hooking up after slipping through a couple of stages while coming on plane and moving up to racing speeds. Cupping and progressive pitch changed all that."

John,

I'm very familiar with the true helical pitch propellers used by Ed Kalfus. They had no progressive pitch at all. The prop blades were shaped like airplane props, blades had zero rake & they would slip badly as they were accelerated. Later tests showed them to be very inefficient.

Jim

"Any of you old enough to have run full sized outboard hydros when we used tru pitch props from Michigan Wheel? When I first started those props would have actual shift points - after you got them on plane you would feel a shift, usually around 35 - 50 mph. It actually was finally hooking up after slipping through a couple of stages while coming on plane and moving up to racing speeds. Cupping and progressive pitch changed all that."

John,

I'm very familiar with the true helical pitch propellers used by Ed Kalfus. They had no progressive pitch at all. The prop blades were shaped like airplane props, blades had zero rake & they would slip badly as they were accelerated. Later tests showed them to be very inefficient.

Jim

Interesting.. I know not a lot but some of the best props I ever had for heat racing would cavitate and boil the water on launch. Even slowing down to a crawl for the start they would not do it. but on the launch I would have to "feather" the RPM range and off it would go. No clue why... I even bent some of them myself and don't know enough to figure it out.

Hi Norm,

All of my best cupped and progressive pitched wheels on full size hydros were the hardest to get on plane. On the fuel boats the merc quickie lower unit gears would shear if you hit it to hard heading out of the pits, so most of us in the 60's would run Koenig or Anzanii lower units on our Loopers. When I started running toy boats it was fun to by 24 Octura props the same size and just go crazy cutting and twisting to find something to run better. Always did think if I could find a giant to pick up my full size boats and launch me that I could make some huge moves on record speeds with bigger props. Oh well, it was hard enough in those days just to get a crew that could lift the boats out of the water to start those monsters!

Thanks, John

 

[John Beardslee]

Hi,

do you have some old Octura Competion serie Propeller dia 1,6 to 2,8 ,pitch ratio 1,8 . They have a round trailing edge on the pressure side witch make the prop less bite during start . want moore grip ,tool a campfer/ cannel on the pressure surface at the trailing edge and wonder wy your motor is unable to start with this prop . Do the cannel with soft way to the leading edge and a sharp line at the trailing egde .This prop work great with outrunner high torque motors .

Hi Christian,

That was the only series available when I started playing with model boats. The first boat over 60, 70 & 80 mph were the 2.4, 2.6 & 2.8's that I had turned into elephant ear props and heat treated. I've been wondering if anyone has been trying those old series props. I've got many of those and the ABC copies.

Thanks, John

 

[Christian Lucas]

Hi John,

these are also the one and only props i can get when i was young .My first surface pircing boat was a self build tunnel with also a self build outbord with brass tube and flexcabel using the black plastic 1,6 . It takes me much time to start and rob a lot of reare energie from the batteries,that was the starting point for me to find a propeller that is not first cooking water surging 30% of the batteries .I like also the 12xx serie Octura with cupping .I drove a 7,5ccm K&B outbord with a 1255 cupped on a tunnel acclerates good doing some wheelies when i trow it in the water .But sometimes the motor reves under this load and the boat comes back on the shore.

Have fun. Christian

 

[hugh hargett]

At least with fe some of the esc's offer a softstart . That may help with cavitation launch problems. My brother asked me is it possible to get an overall faster straightline speed if you keep the launch cavitation to a minimum?

 

[Christian Lucas]

Hi John,

show a pic of my first tunnel with outbord and a 20 Octura Wing Ding electric .tunnel was 1978 and Wing Ding 1984 with straight propshaft and spoiler to prevent the rear from jumping work well.

The pic in the midle show the Johnson 5 term profil for surface propeller . The pic show only the pressureside without the suckingside . The waterflow on the bladeface will get slower,building up pressure in the middle and be forced to acclerate at the end to leave the blade at the trailing edge with high speed . I do this all on not to thin wegde shape propeller without any cupping of the blade. This pic is from the book " High Speed Small Craft " written from Comander Peter Du Cane ,cheef engenier at Vosper Thoncraft in England .In his book he also show solid roket powered models of the Cruasader at 100 mph where he test riding stability of the revers triangle design.

 

[John Beardslee]

At least with fe some of the esc's offer a softstart . That may help with cavitation launch problems. My brother asked me is it possible to get an overall faster straightline speed if you keep the launch cavitation to a minimum?

Hi Hugh,

From what I know about electric motors (not much) you get all the torque from the start so feathering the throttle on launch to get up to speed might work better than full throttle launches. Just thinking out loud - my approach would be to find a prop design that would launch good and not have a negative affect on hull attitude at speeds. Then, like we used to do in the early 60's slot car drag racing toys - start using motors with lower number of windings on the armatures and max out the rpm's. Is it the battery pack voltages that determine the classes?

Thanks, John

 

[Christian Lucas]

Hi Hugh , John ,

John ,don´t forget ,the slotracer has no batteries onbord with limited capacity .I Hugh will go for a record he has to use every mAh out of the batteries .For this he need a prop that bit from the first rev . The German JAG s team start with there owen propeller that bit less.Result was that the rigger acclerates and at the moment when the prop gets the right inputflow of water ,the prop get full grip and sent the boat in a propwalk right turn in the shore. Somtimes it worked out and they set the record ,but it´s a game to react fast enough.

Next year they grind a little Johnson 5 Term in the blade and the game was easyer and the record rise as the boat acclerates faster as the grip starts from begin.Not they start from stand still.

If i would look for a record i would go like a ic boat not from stand still .Better to come out a corner with good speed and acclerate than .

Hugh,

You have the right boat here with the Eagle SCX from Andy . This boat is proven to do it . So you need the best motor for this projekt.

My advise is the Scorpion 4225 that can go for a run with about 7 kw power as it does in the record speedheli the Banshee copter.

The motor weight 400 g turning 520 kv .If you like higher kv is no problem .Up to 30000 rpm it is possible to go with outrunner and esc,without having to much stress for them.At this high revs the motor is able to do up to 10 kw for a run.Thats pretty enough i think you need much less. Aske Andy how much power a 2170 prop will take at 28000 rpm ,you need 30000 to break the record or moore revs ,all possible.

For the esc you can go different ways.Simple to use a YGE 360 esc that will control the power ,it´s the esc that the airplane guys use.

It´s also possible to wire the motor with to seperate coils each feed by a seperate controller.Can be done halve side each esc or quarter of the stator wired seperate and connect q 1 and 3 other esc q 2 and 4 . If you want the last watt from the motor you can wire a double LRK wind of to seperate sps system so the motor run as a 6 phase motor .

John , for records there are different classes for 2S , 4S , 6S and 10S allowed up to 2P of 5000 mAh cappasity as i know so max 10000 mAh cappacity to store.