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Author Topic: Propeller Pitch - GT Sitek  (Read 550 times)

DBS88

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Propeller Pitch - GT Sitek
« on: October 10, 2020, 06:41:30 pm »

I have a pair of 2 inch WW2 Style props for my Black Swan Sloop and am trying to find out what pitch they are. I believe they are from GT Sitek and having read many posts on this forum, George of GT Sitek is highly regarded. So if you are able to help with the following it will be appreciated.


1) Do you know what pitch the props are that come from GT Sitek?
2) Is there a way to work out the pitch for these props?
3) Is there an alternative contact for GT Sitek other than the website? Have not been able to contact him through the website.


The reason its important is because this is a steam powered build and a response on this forum on 4th Sept 2010 by MONAHAN STEAM MODELS explains very clearly why this matters.Re: TRV1A Prop size.


Any assistance in this matter will be greatly appreciated, thank you, Kind Regards Dave



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Des

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Re: Propeller Pitch - GT Sitek
« Reply #1 on: October 10, 2020, 09:32:31 pm »

If your props are a "standard" design from a commercial model prop supplier, you will probably find that they are either 50 mm dia x 52 mm pitch, or 52 mm dia x 54 mm pitch.
Des
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mudway

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Re: Propeller Pitch - GT Sitek
« Reply #2 on: October 11, 2020, 12:27:47 am »

Didn't Black Swans all have regular commercial props not warship propellers?
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RST

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Re: Propeller Pitch - GT Sitek
« Reply #3 on: October 11, 2020, 01:05:32 am »

Quote
I have a pair of 2 inch WW2 Style props for my Black Swan Sloop and am trying to find out what pitch they are. I believe they are from GT Sitek and having read many posts on this forum, George of GT Sitek is highly regarded. So if you are able to help with the following it will be appreciated.
...Silly question but have you tried Sitek first?
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davidjt

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Re: Propeller Pitch - GT Sitek
« Reply #4 on: October 11, 2020, 09:27:07 am »



Image: boats.comThe pitch station is the middle of the propeller or the part of the propeller that the blades are connected to. Measure the pitch angle or the angle of the propeller's blades at a horizontal plane. The protractor should be at a flat 180 degrees on the pitch station. Look through the protractor to see what angle the propeller's blade goes through.


http://features.boats.com/boat-content/files/2015/05/Prop-Pitch.jpg
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chas

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Re: Propeller Pitch - GT Sitek
« Reply #5 on: October 11, 2020, 09:36:53 am »

Hi Dave, the reason you couldn't contact George is because retired some years ago. I last had one of his props about 7 years ago, and he was only doing a few then. It's a shame he's stopped, but it happens to us all, and retirement was well earned.
Chas

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DBS88

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Re: Propeller Pitch - GT Sitek
« Reply #6 on: October 11, 2020, 10:08:32 am »

Great photo of Wild Goose, I guess this is where a working model departs from the original boat and true scale model, so the props I need are steeper pitch steam props, not standard props. The website for GT Sitek still seems to be working, just that after several attempts at emailing over the last four months no reply received. I got the props last year from Fleetscale and I believe Fleetscale get them from GT Sitek. So wondered if there was an alternative contact or if anyoneís had recent contact?
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TheLongBuild

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Re: Propeller Pitch - GT Sitek
« Reply #7 on: October 11, 2020, 05:50:13 pm »

Although a different manufacture they might be able to help you out at PropShop.

Jerry C

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Re: Propeller Pitch - GT Sitek
« Reply #8 on: October 12, 2020, 02:13:27 am »

Going back to basics but Iíll give it a go. At its simplest the pitch of a propeller is the theoretical distance it will travel forward in one complete revolution ( on a model prop this is measured in inches). If correctly made any point on a blade will travel forward the same amount in one rev. Consequently the pitch angle of a blade is course close to the propeller boss, fining out as you move towards the prop tips. Any point on a blade will cover an increasing rotating distance in one rev as you move away from the boss (pi x d) where d is the distances nce from the centre axis of the prop shaft. If you suspend the shaft with the propeller mounted so the shaft is vertical with prop to the bottom, now suspend a piece of cotton with small weights on each end, over a blade the angle the cotton makes with the normal to the shaft (plane of the prop)  is the pitch angle for that pointís distance from the shaft axis. Course near boss fine near tip. The straight line between the contact points on the leading and trailing edges of the blade is called the chord angle. Using the chord angle and the circumference of the circle the chord travels in a bit of trigonometry  (Pitch/circumference = tan chord angle) will enable you to find the pitch in inches.
To add a slight complication, the section through a blade is similar to an aerofoil section of an aircraft wing effectively giving lift towards the bow when turning ahead. This is one of the reasons a propeller is less efficient when turning astern. Hope Iíve made sence with this.
Jerry C.

Baldrick

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Re: Propeller Pitch - GT Sitek
« Reply #9 on: October 12, 2020, 08:52:43 am »

  Perhaps if you got a plastic bowl of porridge to a medium/stiff consistency. Filled to the brim and floated it in the washing up bowl full of water, then you could get your prop, fitted on the prop shaft, embed it to its halfway point horizontally in the porridge, hold the shaft stationary then one full  turn of the shaft would lead a track in the porridge the length of which would equal the pitch of the propeller minus the length of the centre boss . Simples  O0
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Tug Fanatic

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Re: Propeller Pitch - GT Sitek
« Reply #10 on: October 12, 2020, 09:25:21 am »

To add something to Jerry C explanation.

Think of a prop as a series of wings that go round in circles. The airfoil section of a blade creates a low pressure area ahead of the blade which means that not only does the propeller thrust water backwards but it creates a suction ahead of the prop that drags the model forward. That is the same suction that creates most of the lift in an aeroplane wing. All this means that the curve shape on the front surface of the blade is as important as the pitch. This explains why props don't work as well astern.

One of the other important, often overlooked factors is the sharpness of the leading edge. Again using the aircraft wing as an analogy it is clearly important what the leading edge of a wing looks like. You wouldn't expect a blunt leading edge because of the enormous drag that it would create. The same is true of you model boat prop where the leading edge of each blade is cutting a path through the water. Keep them sharp. The sharpness of the leading edge, or rather the lack of, is a big problem for cheap plastic props.

This shape (airfoil section) is what largely distinguishes a good prop from a poor one & why some props generate much more thrust than others which superficially look the same. It also suggests that a well designed cast prop, where a good airfoil shape can be used, could outperform a prop made from curved sections of sheet material if the potential of the production method was full utilised in the design.
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chas

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Re: Propeller Pitch - GT Sitek
« Reply #11 on: October 12, 2020, 10:12:51 am »

You've had some very interesting options to measure the pitch, but I favour a simpler method. If they came from Fleetscale, just email them and ask, they are very nice to deal with.
Chas

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