Pitch progression on 19 degree rake 38% BAR AMC props

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Ian Inverarity

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Joined
Nov 2, 2002
Messages
2,662
I have a 2717-19-38 ABC prop (raw) and have measured the pitch at 50% diameter, using an Orlic pitch gauge at 5 degree sweep at various places from the leading edge to the trailing edge.

See the picture, the LE pitch is 4.32, the next measurement is 4.1, about 4/5th's of the blade chord from the LE the pitch gets up to 4.39", then the TE cup is 7.5"

Has anyone else measured one of these props? Do they get similar results?

2717 pitch.jpg
 
Ian are you calculating between each 5 deg sweep?

That's very close to what I have seen.

Flip the prop over and see what you get.
 
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I have a 2717-19-38 ABC prop (raw) and have measured the pitch at 50% diameter, using an Orlic pitch gauge at 5 degree sweep at various places from the leading edge to the trailing edge.

See the picture, the LE pitch is 4.32, the next measurement is 4.1, about 4/5th's of the blade chord from the LE the pitch gets up to 4.39", then the TE cup is 7.5"

Has anyone else measured one of these props? Do they get similar results?
Ian:

Are you finding that the measurements are skewed because it is so difficult to find the trailing edge of the prop with any degree of consistently. Maybe your approach, measuring various 5 degree segments, is because of this difficulty?
 
Did you get that needle point for your indicator?

That'a a huge amount of cup and won't make the prop go any faster that the 4.32" of LE pitch, probably why most guys are cutting most of it off.

Odd that the pitch would decrease in the 2nd segment. What does it measure when you go 75% out from the C/L?
 
Her is what I got at 50% of the blade on a cleaned up one with the cup reduced. Thy have 7.5 cup stock.

deg rotation from leading edge the pitch is referenced from each 5 deg to the next one not over all.

When I get the time will make a spread sheet so you can se the pitch from any 5 deg point to any other 5 deg point.

deg lift pitch

55 .696 5.62

50 .618 5.25

45 .545 4.82

40 .478 4.10

35 .416 4.18

30 .359 4.03

25 .301 4.32

20 .245 4.32

15 .185 4.32

10 .125 4.53

5 .062 4.46

No need to grind any off the lead in thy pull it just fine.

Just take some TE cup out to unload the eng some to let it rev.

You are loading the eng with TRUE pitch not cup.

I always check the lead in at 15 deg for a reference.
 
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I probably should have explained better, I use a 5 degree sweep and check the blade in multiple places, not increasing the sweep from the LE. The indicated positions on the blade are where I start measuring the 5 degree sweep, except at the TE.

Terry, yes I did get the needle point, awesome idea!!
default_cool.png
And I think every ABC cleaver I have ever measured has a higher LE pitch than just behind that area on the blade, its not unusual. I don't measure at 75%.

Marty, before I clean them up there is a bit of difficulty getting a consistent TE cup measurement, but normally I can get it pretty repeatable, particularly using the needle tip on the dial! I always measure small segments, I have never measured more than 5 degrees. One day I will build my own (when I get time), it will measure in 3.6 degree sweeps.

David, what my measurements show is most of the blade is only 4.1-4.3" of pitch (at 50% diameter). What I was wondering is if this progression (or lack of it) is typical in the 19 degree rake series?
 
at 15deg from the leading edge you have .185 this is about 4.39 pitch.

at 30deg from the leading edge you have .359 this is about 5.52 pitch that is about 26% progression?

How much progression dose a prop need?

I guess it all comes down to how you check the pitch and from what point to what point.

If we take a chunk from the middle it will tell a different story.

Now take from the lead in to 15 deg it is 4.44 and from 15 deg to 30deg it is 4.2

Now that shows negative progression.

I was told by a wise man to think about how the water flows over the prop.

It is forced out to the end on the blade by centrifugal force. It dose not travel from leading edge to trailing edge on the same path we measure with the gauge.

it runs a skewed path threw the trough as I call it down the middle of the blade.

Once you see this in your head it will give you a different way at looking at the prop.

Once the light was turned on in my head I never looked at a prop the same way.
 
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How much progression dose a prop need?
The million dollar question David! I was asking about the distribution of pitch. Most props gradually increase pitch from the LE to the TE. The ABC cleavers do not (in my experience), they are mostly relatively constant pitch, with a significant TE cup. This 19 degree rake prop that I have seems to follow that trend, I was wondering if that was generally true of the series, or just my particular prop.
 
You would have to check them all to find out I guess.

Or may be Jim will chime in and answer that for you.

I have a 2517 and a 2519 both 38 bar 19 rake I will be doing this week will let you know what I see.
 
I probably should have explained better, I use a 5 degree sweep and check the blade in multiple places, not increasing the sweep from the LE. The indicated positions on the blade are where I start measuring the 5 degree sweep, except at the TE.

Terry, yes I did get the needle point, awesome idea!!
default_cool.png
And I think every ABC cleaver I have ever measured has a higher LE pitch than just behind that area on the blade, its not unusual. I don't measure at 75%.

Marty, before I clean them up there is a bit of difficulty getting a consistent TE cup measurement, but normally I can get it pretty repeatable, particularly using the needle tip on the dial! I always measure small segments, I have never measured more than 5 degrees. One day I will build my own (when I get time), it will measure in 3.6 degree sweeps.

David, what my measurements show is most of the blade is only 4.1-4.3" of pitch (at 50% diameter). What I was wondering is if this progression (or lack of it) is typical in the 19 degree rake series?
I am interested in how and where you measure the 5 degree segments. How far out from the hub, are the 5 degree segments connected? Just the method of measuring the segments.
 
How much progression dose a prop need?
The million dollar question David! I was asking about the distribution of pitch. Most props gradually increase pitch from the LE to the TE. The ABC cleavers do not (in my experience), they are mostly relatively constant pitch, with a significant TE cup. This 19 degree rake prop that I have seems to follow that trend, I was wondering if that was generally true of the series, or just my particular prop.
What you are asking is: Is the prop "true pitch" or is it "progressive pitch". And are all the segments increasing from the tongue all the way to the trailing edge? Are there any 5 degree segments on the path that are less than the previous segment?
 
Marty

The only way to see is to map the whole prop at say 10% increments from the blade attaching point on the hub to the tip.

I have done this on the old style 2818 a few years back. It takes some time to do.

Then again I have bin told the maps Jim will provide may give all the info you would need.

Then again some can just rub there thumb down the trough and tell..............you know who you are.....LOL

Terry

Marty made a good point. If there is progression in the trough leading to the tip this is the progression that will keep the water in contact as it flow down the trough to the tip.

Think about the centrifugal force pulling the water to the tip in this trough.

Look at the prop from the back of the hub towards the tip and you will see what I mean. The roll up on the leading edge (rake) holds the water in This trough and sends it over the back edge and out the tip.

So you are not seeing the progression the way we measure the prop.
 
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Guys,

All you need is the design pitch report from Jim.

And see if it matches the blueprint of the propeller design.

They are usually pretty close if you can measure accurately.

I will warn you that the design pitch report is pretty interesting.

You will learn more about propellers once you learn to read them

and measure a few dozen of them. It will help you understand the

design of the blades much better also.

Good Luck Testing Fellas,

Mark Sholund
 
Guys,

All you need is the design pitch report from Jim.

And see if it matches the blueprint of the propeller design.

They are usually pretty close if you can measure accurately.

I will warn you that the design pitch report is pretty interesting.

You will learn more about propellers once you learn to read them

and measure a few dozen of them. It will help you understand the

design of the blades much better also.

Good Luck Testing Fellas,

Mark Sholund
Mark, going back to my original picture, do you get similar measurements on that prop or others in the series? Reports aside, what do you get when you check a prop?
 
I probably should have explained better, I use a 5 degree sweep and check the blade in multiple places, not increasing the sweep from the LE. The indicated positions on the blade are where I start measuring the 5 degree sweep, except at the TE.

Terry, yes I did get the needle point, awesome idea!!
default_cool.png
And I think every ABC cleaver I have ever measured has a higher LE pitch than just behind that area on the blade, its not unusual. I don't measure at 75%.

Marty, before I clean them up there is a bit of difficulty getting a consistent TE cup measurement, but normally I can get it pretty repeatable, particularly using the needle tip on the dial! I always measure small segments, I have never measured more than 5 degrees. One day I will build my own (when I get time), it will measure in 3.6 degree sweeps.

David, what my measurements show is most of the blade is only 4.1-4.3" of pitch (at 50% diameter). What I was wondering is if this progression (or lack of it) is typical in the 19 degree rake series?
I am interested in how and where you measure the 5 degree segments. How far out from the hub, are the 5 degree segments connected? Just the method of measuring the segments.
The Orlic pitch gauge can have the sweep angle set in 5 degree increments, I use the 5 degree sweep. It works by moving the blade 5 degrees and measuring the height difference between two points. Thus it actually only gives the average over 5 degrees (or whatever angle you choose) and cant tell you about what happens between those points. I generally measure at 50% diameter and out near the tip (exactly where depends on the prop tip shape). Are the segments I meansure connected? No.
 
How much progression dose a prop need?
The million dollar question David! I was asking about the distribution of pitch. Most props gradually increase pitch from the LE to the TE. The ABC cleavers do not (in my experience), they are mostly relatively constant pitch, with a significant TE cup. This 19 degree rake prop that I have seems to follow that trend, I was wondering if that was generally true of the series, or just my particular prop.
What you are asking is: Is the prop "true pitch" or is it "progressive pitch". And are all the segments increasing from the tongue all the way to the trailing edge? Are there any 5 degree segments on the path that are less than the previous segment?
As per my picture, the section of blade I measured after the TE of the prop had less pitch the the LE. This is normal on ABC cleavers from what I have measured.
 
Ian,

I will check one tonight and see what I come up with.

The design pitch report will show the mapping of the blades.

If it was me I would just reduce the cup a little at a time and go

test it. The on- the- water- testing is what is all about anyways.

I have some pretty good numbers that seem to work rather well

on most Road Runner Twin set ups. I have been working with a

few of the Team Road Runner Twin Pilots recently and we are

starting to get more performance out of their boats. I will share

with you to possibly lower the strut settings a little deeper into the

water so the angle of attack is more neutral on your set up. A lot

of people are leaving the strut angle and depth how they had it with

another propeller and then the boat gets very light at the end of the

straightaway and sometimes blows off the water. This is due to the

blade design not lifting the transom as much as some other propellers

have in the past. If you adjust the angle of attack with the new ABC

propellers I think you will see better handling and lower lap times if you

are heat racing them.

Thanks,

Mark Sholund
 
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