Propeller Question for Andy Brown

[Jim Allen]

Andy,

I know you have tested Octura 2167 props in the past. I have two identical 2167 propellers , one with 5.000" leading edge pitch X 7.000" trailing edge pitch. One with 5.125" leading edge pitch X 7.500" trailing edge pitch. The first blade runs 78+ MPH at 20,000 RPM & is very smooth on the oval course. The higher pitch blade causes the tail of the boat to hop up & down slightly. Do you have any ideas as to what would eliminate this problem? The thrust angle is zero for both & both are running at the same strut depth.

Jim Allen

 

[John Beardslee]

Hi Jim,

If you don't hear from Andy, Marty Davis may know someone who can help you. Good to see you back on here.

Thanks, John

 

[shoboat]

Jim,

What is diameter of all six blades out from the hub to the blade tips?
These blades have all been heat treated?
Both propellers have the exact same diameter?
I would put them on a lathe and see if all the blades are the same diameter.
One of the blades could be bent ever so slightly causing the frequency hop.
Sounds like you need a new "Game Changer" for that set up, they already

have more pitch in them.

Good Luck,

Mark Sholund

 

[Jim Allen]

Mark,

The diameter & blade area is the same for both propellers. Propeller blade tips are always checked in the lathe for the same distance from the hub before magnetic balancing, The Octura C-20 berrilium copper alloy has been carefully annealed, pitched in my pitch gauge, annealed & re-pitched several times before hardening. Annealing & re-pitching several times eliminates any stresses placed in the blades from the pitching process. This allows heat treating of the blades to give the ultimate tensile & yield strengths possible for the C-20 alloy. Terry suggested a reduction in strut depth might eliminate the problem. I'm in the process of stroking the engine plus adding my connecting rod, crankshaft & a machined piston. I'm looking for more high end HP & RPM above 22, 000. I would like to try even higher leading & trailing edge pitches if that is possible.

JA

 

[dwilfong]

You need to take the ski ramp out of the blade.

Look at the lead in of the troth in the prop and you will see what I am talking about.

I put mine in a vice and used a deep 1/4" drive socket the right size to press it out.

It will bounce up on this ramp if not removed.

Just what I found from testing with this prop on my SGX.

 

[Mike Rappold]

You need to take the ski ramp out of the blade.

Look at the lead in of the troth in the prop and you will see what I am talking about.

I put mine in a vice and used a deep 1/4" drive socket the right size to press it out.

It will bounce up on this ramp if not removed.

Just what I found from testing with this prop on my SGX.

Can you further explain where in the blade you are referring to for the ski ramp and troth?Mike

 

[dwilfong]

when you look at a blade from the tip towards the hub at the front of the prop it looks like a troth.

If you have one in your hand you will see what I mean about a ramp in the troth.

The RCMK H767 prop had the same problem.

Hopped like crazy till I removed it.

 

[Eric Canto]

Dave means trough, not troth. Just trying to help ;-)

 

[Jim Allen]

I have questions & thoughts about what could be happening.

David,

What is the leading edge pitch & trailing edge pitch after you have reduced the ski ramp? Is the blade your showing heat treated?

When attempting to increase propeller pitch by twisting or bending the blades, one method used to correct the hub insertion angle for the new pitch amount is by hand grinding the correct angle at this point. Could pitch changes of a large amount up or down from the original pitch cause the hopping problem? Another method, thought up by a modeler here, used a jig to position each blade after it was separated from the hub with a very thin metal coping saw . The blades were re-attached with silver solder (1150*F) annealed & then heat treated. I don't know if these blades stood up to surface piercing use. Does a large amount of pitch change cause some other blade characteristics to change between blades that are identical, except for their pitch.

JA

 

[Christian Lucas]

Hi Jim,

do you remember when we talk about propellerblade pisition on the hub and effect . Are you shure that all the blade stay at the same position looking from the trailing edge side ? can you shot a photo from both propellers side by side like in my drawing , than we can have a closer look .All samll difference in angle or position can have a big effect adding lift or not.

 

[Jim Allen]

Hi Christian,

I still have this information in my file & I considered it in trying to determine what was different between the two propellers. The photos show the same two blades positioned right to left & left to right because the camera angle makes them look different. I also re-cut the drive dog slot after indexing both blades to the same position. My pitch gauge tells me they have the same rake angle but different pitches as stated.

JA

 

[dwilfong]

Jim

5" of pitch at the leading edge measured at the 70% out from the hub mark. This is with 15% of blade rotation from the leading edge.

With 10 deg of rotation from the trailing edge it is 6.9" at the same mark. Using a Orlic gage

I have a small kiln with a controller on it and do the best I can on the heat treating.

Use a recipe Stu gave me, heck its his old kiln .....LOL

Thanks Eric the spell check gets me all the time........never could spell worth a crap..................

You have to have more input than just a spell check being my prop mentor and all..................

 

[Andy Brown]

Andy,

I know you have tested Octura 2167 props in the past. I have two identical 2167 propellers , one with 5.000" leading edge pitch X 7.000" trailing edge pitch. One with 5.125" leading edge pitch X 7.500" trailing edge pitch. The first blade runs 78+ MPH at 20,000 RPM & is very smooth on the oval course. The higher pitch blade causes the tail of the boat to hop up & down slightly. Do you have any ideas as to what would eliminate this problem? The thrust angle is zero for both & both are running at the same strut depth.

Jim Allen

Hi Jim,

The answers to your questions are simple.

#1. The increased pitch at the L.E. will increase the lift.

#2. The increased pitch on the T.E. will increase lift.

#3. The increased lift can be reduced, to a certain degree, by cupping the tip of the prop.

Basically make the tip feel like a spoon when you run your thumb over the face of the blade toward the tip.

This cupping is like adding a "fence" to the tip of the blade which helps keep the water from spinning off the end,

which there by reduces lift. This "fence" is actually rake that is added to the tip of the blade only.

Rake added to the complete blade will also reduce lift as many are now learning by using the new high rake ABC props.

Rake can be partially added to a prop by bending, but the blade must be cut loose to add rake to the complete blade.

Back cutting does not add rake. Back cutting can have the effect of reducing lift, but only because the operation simply reduces high pitched areas at the T.E.

Jim, You should be able to stop the hopping without modifying the prop by simply raising the strut. Keep the same zero degree angle but raise the strut about 2mm. You should see a difference. If not try another 2mm. There will be a point that the prop will stop lifting too much.

I recently tested a 3 blade prop that I had to raise 10mm before it stopped lifting too much. Once I got it that high it ran perfectly all around the course. The tub was running perfectly level, which meant less than 50% of the blade was in the water.

P.S. Pressing the convex out of the trough as David suggested is a method of increasing the rake to about the outer 50% of the blade. I said the same thing in more simple terms, simply "bending" , which I do with a very large set of cupping pliers.

 

[Jeff Lutz]

Andy,

I know you have tested Octura 2167 props in the past. I have two identical 2167 propellers , one with 5.000" leading edge pitch X 7.000" trailing edge pitch. One with 5.125" leading edge pitch X 7.500" trailing edge pitch. The first blade runs 78+ MPH at 20,000 RPM & is very smooth on the oval course. The higher pitch blade causes the tail of the boat to hop up & down slightly. Do you have any ideas as to what would eliminate this problem? The thrust angle is zero for both & both are running at the same strut depth.

Jim Allen

Hi Jim,

The answers to your questions are simple.

#1. The increased pitch at the L.E. will increase the lift.

#2. The increased pitch on the T.E. will increase lift.

#3. The increased lift can be reduced, to a certain degree, by cupping the tip of the prop.

Basically make the tip feel like a spoon when you run your thumb over the face of the blade toward the tip.

This cupping is like adding a "fence" to the tip of the blade which helps keep the water from spinning off the end,

which there by reduces lift. This "fence" is actually rake that is added to the tip of the blade only.

Rake added to the complete blade will also reduce lift as many are now learning by using the new high rake ABC props.

Rake can be partially added to a prop by bending, but the blade must be cut loose to add rake to the complete blade.

Back cutting does not add rake. Back cutting can have the effect of reducing lift, but only because the operation simply reduces high pitched areas at the T.E.

Jim, You should be able to stop the hopping without modifying the prop by simply raising the strut. Keep the same zero degree angle but raise the strut about 2mm. You should see a difference. If not try another 2mm. There will be a point that the prop will stop lifting too much.

I recently tested a 3 blade prop that I had to raise 10mm before it stopped lifting too much. Once I got it that high it ran perfectly all around the course. The tub was running perfectly level, which meant less than 50% of the blade was in the water.

P.S. Pressing the convex out of the trough as David suggested is a method of increasing the rake to about the outer 50% of the blade. I said the same thing in more simple terms, simply "bending" , which I do with a very large set of cupping pliers.

. Andy, I revisited your abc S 40 just a couple of summers ago. Lifted the strut .060" and made a tweak to the tips of the prop, boat hauled the mail. Some people think that prop won't run because the blade diameter is only around 62mm , but the radar gun said other wise.

 

[Jim Allen]

Andy,

The information you posted is right on according to this weekends testing. I may have misstated the pitch of these two 2167 propellers. The one that doesn't hop is 5.000" leading edge pitch X 7.500" trailing edge pitch. The blade that was hopping slightly is 5.125" X 7.500". Raising the strut up .1250" with the depth gauge as Terry Keeley suggested & you have stated, at the 0* thrust angle, eliminated the hopping. The boat was 2 to 3 MPH faster according to the Stalker Radar gun. All the propellers I'm testing run at the 0* thrust angle with some propellers running with their center line's 5/8" above the water line at speed. The boat's gas engine is turning 20, 000+ RPM (Tiny Tach reading). I should tell you that the engine's mounting position in my SG gas rigger has been moved forward approximately 2" & the distance between the sponsons increased to 17 3/16". There is 3 lbs of weight on the tail at the prop & the distance from the sponson's trailing edge to the propeller is 32 ". As you know I have changed the skid fin's thickness from .0625" to .0938" & that eliminated the flexing, bending problem. Now the boat really hooks up in the turn!

I'm trying to find where this propeller will stop working. Should I increase both the leading edge & trailing edge pitches or should I increase the leading edge pitch & keep the trailing edge pitch the same?

Thanks Much,

Jim Allen

 

[Andy Brown]

Andy,

I know you have tested Octura 2167 props in the past. I have two identical 2167 propellers , one with 5.000" leading edge pitch X 7.000" trailing edge pitch. One with 5.125" leading edge pitch X 7.500" trailing edge pitch. The first blade runs 78+ MPH at 20,000 RPM & is very smooth on the oval course. The higher pitch blade causes the tail of the boat to hop up & down slightly. Do you have any ideas as to what would eliminate this problem? The thrust angle is zero for both & both are running at the same strut depth.

Jim Allen

Hi Jim,

The answers to your questions are simple.

#1. The increased pitch at the L.E. will increase the lift.

#2. The increased pitch on the T.E. will increase lift.

#3. The increased lift can be reduced, to a certain degree, by cupping the tip of the prop.

Basically make the tip feel like a spoon when you run your thumb over the face of the blade toward the tip.

This cupping is like adding a "fence" to the tip of the blade which helps keep the water from spinning off the end,

which there by reduces lift. This "fence" is actually rake that is added to the tip of the blade only.

Rake added to the complete blade will also reduce lift as many are now learning by using the new high rake ABC props.

Rake can be partially added to a prop by bending, but the blade must be cut loose to add rake to the complete blade.

Back cutting does not add rake. Back cutting can have the effect of reducing lift, but only because the operation simply reduces high pitched areas at the T.E.

Jim, You should be able to stop the hopping without modifying the prop by simply raising the strut. Keep the same zero degree angle but raise the strut about 2mm. You should see a difference. If not try another 2mm. There will be a point that the prop will stop lifting too much.

I recently tested a 3 blade prop that I had to raise 10mm before it stopped lifting too much. Once I got it that high it ran perfectly all around the course. The tub was running perfectly level, which meant less than 50% of the blade was in the water.

P.S. Pressing the convex out of the trough as David suggested is a method of increasing the rake to about the outer 50% of the blade. I said the same thing in more simple terms, simply "bending" , which I do with a very large set of cupping pliers.

. Andy, I revisited your abc S 40 just a couple of summers ago. Lifted the strut .060" and made a tweak to the tips of the prop, boat hauled the mail. Some people think that prop won't run because the blade diameter is only around 62mm , but the radar gun said other wise.

Jeff, I have been working with very small blade areas recently and seeing very good results.

Andy,

The information you posted is right on according to this weekends testing. I may have misstated the pitch of these two 2167 propellers. The one that doesn't hop is 5.000" leading edge pitch X 7.500" trailing edge pitch. The blade that was hopping slightly is 5.125" X 7.500". Raising the strut up .1250" with the depth gauge as Terry Keeley suggested & you have stated, at the 0* thrust angle, eliminated the hopping. The boat was 2 to 3 MPH faster according to the Stalker Radar gun. All the propellers I'm testing run at the 0* thrust angle with some propellers running with their center line's 5/8" above the water line at speed. The boat's gas engine is turning 20, 000+ RPM (Tiny Tach reading). I should tell you that the engine's mounting position in my SG gas rigger has been moved forward approximately 2" & the distance between the sponsons increased to 17 3/16". There is 3 lbs of weight on the tail at the prop & the distance from the sponson's trailing edge to the propeller is 32 ". As you know I have changed the skid fin's thickness from .0625" to .0938" & that eliminated the flexing, bending problem. Now the boat really hooks up in the turn!

I'm trying to find where this propeller will stop working. Should I increase both the leading edge & trailing edge pitches or should I increase the leading edge pitch & keep the trailing edge pitch the same?

Thanks Much,

Jim Allen

Jim, L.E. pitch is King! You currently have about 50% progression. That is more than enough. A prop with 5.3" L.E. and 7.3" T.E. could gain more top end speed with out increasing the load on the engine. 5.3" to 7.3" will give you 38% progression which is still plenty to get good bite and acceleration.

 

[Jim Allen]

Andy,

Thank you for your sharing your vast knowledge about propellers. I'll be testing the 6545 props this summer.

Thanks again!

Jim Allen

 

[Terry Keeley]

Hey Jim, is this for SAW or heat racing?

Just curious, you say you're turning 5.125" LE at 20K, I figure you should be running mid 80's, is that about right?

 

[Jim Allen]

Hi Terry,

I'm using these props on my SG heat racing rigger. I'm using this boat as a test bed even though it is a little heavy at 15 lbs 12 ounces ready to run, but I'm running right at 80 MPH. The engine makes its peak hp at 21,000 to 22,000 RPM & it shows good over rev HP at 23,000.

JA

 

[Terry Keeley]

Hi Terry,

I'm using these props on my SG heat racing rigger. I'm using this boat as a test bed even though it is a little heavy at 15 lbs 12 ounces ready to run, but I'm running right at 80 MPH. The engine makes its peak hp at 21,000 to 22,000 RPM & it shows good over rev HP at 23,000.

JA

I see, cool.

A little more slip than I figured, or you measure LE pitch differently than I do which is completely possible. Could also be due to the heavier boat...