How do I convert pitch of a Grim prop?

[Meniscus]

I know the Octura props such as Y535 has a pitch of 1.5.

So what pitch is the Grim L38 x 55? Is this really a simple conversion from metric to standard? In which case it would have a pitch of 2.165? That just doesn't seem right.

Once again, I'm admitting I'm an idiot with props, LOL! :rockon2:

[Jesse J]

That's how I've done it, but then :stupid: :beerchug: I will be watching to see what people say. It always sounds like a super high pitch prop calculated that way. But it would be some funky-ness if it weren't right....

[egneg]

The Y535 has a pitch of 2.125"

[Meniscus]

Thanks Egneg for clarifying. Is that the total pitch? as calculated times the diameter?

I'm thinking the pitch of the Grim is 1.4473, so the total pitch is 55mm or 2.1654?

I'm so confused!

[D. Newland]

Here's what I know:

The 40/52 3 blade Grim prop acted just like an Octura X442/2 both in speed and amp draw.

With that limited example, I'd bet the 38/55 (2 blade?) would act like an Octura X438/2...that's at least the prop I would run to compare it.

[Fluid]

In general it is as simple as a normal metric conversion. The diameter of the 38x55 prop is 38mm or 1.496". The pitch is 55 mm or 2.165". The pitch ratio is 1.44:1. What the numbers do not tell you is the lifting characteristics of the prop or its blade area. So, comparing props of similar dimension but of different manufacturer can be problematic.



.

[Meniscus]

The Grim 40/52 is not a lifting prop, or at least the website doesn't identify it as such.

LOL, I'm still confused. Thanks for the input Dave!

[Darin Jordan]

Is that the total pitch? as calculated times the diameter?

I'm thinking the pitch of the Grim is 1.4473, so the total pitch is 55mm or 2.1654?

I'm so confused!

It's pretty simple on this series of prop... The prop is 38mm in diameter, and 55mm pitch... that's AVERAGE pitch, I believe... If you measure it at the trailing edge, it'll likely read higher, and toward the leading edge lower... Advertised pitch is usually the average for the blade.

[Meniscus]

In general it is as simple as a normal metric conversion. The diameter of the 38x55 prop is 38mm or 1.496". The pitch is 55 mm or 2.165". The pitch ratio is 1.44:1. What the numbers do not tell you is the lifting characteristics of the prop or its blade area. So, comparing props of similar dimension but of different manufacturer can be problematic.



.

OK, so I think I'm getting it. So my guess at the pitch ratio is close, even though I didn't refer to it with that term, keeping in mind the the different characteristics from different manufacturers.

Thanks Jay.

[Jesse J]

At least it is simple for SOMEbody.... What does the pitch ratio have to do with anything?

[z400]

you can simply type in the number in google.

For example.

55mm to inches.


This is what google says.
55 millimeters = 2.16535433 inches

[Meniscus]

Thanks guys. I appreciate everyone input! :thumbup1:

[egneg]

It's pretty simple on this series of prop... The prop is 38mm in diameter, and 55mm pitch... that's AVERAGE pitch, I believe... If you measure it at the trailing edge, it'll likely read higher, and toward the leading edge lower... Advertised pitch is usually the average for the blade.

Exactly most props have a progressive pitch versus a flat pitch. Average has different meanings depending on the criteria used. Different manufacturers do not use the same progression, blade shape, etc. The same is true with full size props as these are often defined as low, medium, and high pitch. I had an article downloaded that wanted to have this data quantified and standardized (based on mathematical measurements and formulas). I will look for it as it made more sense to me than having to guess what prop would do what. If this data is recorded and applied to different applications it would help a great deal in the long run as there would be few questions as to what prop to use with what setup.


The math never lies if the correct data is used!

[Flying Scotsman]

Ben, I think you have lost it mate, my recovery method is at least a huge gulp of scotch

Douggie

[detox]

Buy yourself a tape measurer that measures in both millimeters and inches. It is very easy to convert pitch using one. I bought a cheap Husky brand at Homedepot.

[Meniscus]

LMAO! I know, I know. I figured I'd get heckled, but I did get some good insight. Thanks everyone.

And for the record, I'm a Rum drinker ;)

[785boats]

Here's my take on it.
If you know the pitch ratio & the diameter you can work out the pitch. It's the diameter multiplied by the pitch ratio.

1) An Octura X440 has a pitch ratio of 1.4 & a diameter of 40mm.
1.4 x 40mm = 56mm pitch.

2) An Octura X640 has a pitch ratio of 1.6 & a diameter of 40mm.
1.6 x 40mm = 74mm pitch.

If you know the pitch & the diameter you can work out the pitch ratio. It's the pitch divided by the diameter.

1) A Grimracer 40 x 52 prop has a diameter of 40mm & a pitch of 52mm.
52mm divided by 40mm = 1.3 pitch ratio.

2) A Grim racer 40 x 57 prop has a diameter of 40mm & a pitch of 57mm.
57mm divided by 40mm = 1.42 pitch ratio.
Does that help?

Maybe someone could answer a question for me.
How do you tell the prop size, pitch or pitch ratio from the Prather ident numbers? They seem to bear no relationship to the actual prop statistics. Or am I missing something here.
Cheers.
Paul

[egneg]

I can't answer how the numbers work for Prather props so I use this chart.

http://www.offshoreelectrics.com/propeller-chart.php

[785boats]

Thanks man.
I thought there'd be a table somewhere.
Much appreciated.
Paul.

[egneg]

I found the information but to correct myself it was meant to quantify prop cupping and not progressive pitch. Even though it is not directly on subject it may help some folks if I can get it to load as it is a PDF file.

I am sorry but It won't let me upload - if you want it send a PM with email addy and I will send it to you. :confused:

[Meniscus]

Here's my take on it.
If you know the pitch ratio & the diameter you can work out the pitch. It's the diameter multiplied by the pitch ratio.

1) An Octura X440 has a pitch ratio of 1.4 & a diameter of 40mm.
1.4 x 40mm = 56mm pitch.

2) An Octura X640 has a pitch ratio of 1.6 & a diameter of 40mm.
1.6 x 40mm = 74mm pitch.

If you know the pitch & the diameter you can work out the pitch ratio. It's the pitch divided by the diameter.

1) A Grimracer 40 x 52 prop has a diameter of 40mm & a pitch of 52mm.
52mm divided by 40mm = 1.3 pitch ratio.

2) A Grim racer 40 x 57 prop has a diameter of 40mm & a pitch of 57mm.
57mm divided by 40mm = 1.42 pitch ratio.
Does that help?

Maybe someone could answer a question for me.
How do you tell the prop size, pitch or pitch ratio from the Prather ident numbers? They seem to bear no relationship to the actual prop statistics. Or am I missing something here.
Cheers.
Paul

That makes sense. I just couldn't get my head wrapped around going the other way with the Grim props. LOL :laugh: :doh: