Turning Clock or anti clock wise

Discussion in 'Props' started by BertKu, Dec 28, 2012.

  1. BertKu
    Joined: May 2009
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    Location: South Africa Little Brak River

    BertKu Senior Member

    MikeJohns, I am making a 480 mm twin prop. I still have to shape it slightly better, although the weight of each piece is 574 gram , thus I should not have too much balancing problems after welding. I also made an experimental 3 bladed prop as an experiment and to learn. I may use it one day on a small motor.

    I like to bend the edge of the twin blade the same way as I made the 3 bladed experimental prop. For anti clock wise propulsion, is it correct that I use 005.jpg and bend the right edge A of 006.jpg to the front and the left edge B to the back. Your comment is appreciated. Bert
     

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  2. BertKu
    Joined: May 2009
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    Location: South Africa Little Brak River

    BertKu Senior Member

    Thanks MikeJohns (Mike?) Yes I have fun. If it does not give the correct result, we have to make another one again. That keeps me busy and happy.
    I have transferred your reply from Sailor000 thread to my thread "Turning clock or anti clock wise".
    I am busy in making the edges concave. Also twisting this 3 mm stainless steel 316 to the correct angle. I will be mister world strongest man, by the time it is twisted. To concave the edge I need a 10 pounder, some hard wood and some round bars, in the hope that I will not make pits/cuts/dents in the blade. For strengthening I will have small angel parts (8 of them) to ensure stiffness. Bert
     
  3. BertKu
    Joined: May 2009
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    Location: South Africa Little Brak River

    BertKu Senior Member

    Hi Mike,

    Geeh, one can get quickly confused. I nearly bend the blade in the wrong direction and like to confirm that I am doing it the right way.
    a) anti clockwise propulsion , thus my motor turns from right to left.
    b) lets forget about all the angles, I will get that right at a later stage
    c) The drawing I made, is that now correct for the anti clockwise propulsion ?.
    Why anti clockwise?, while everybody's propulsion is clockwise. Just trying to see what is better.
    Bert
    P.s. the boat has to move from left to right, looking at the propellor center part.
     

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    Last edited: Dec 28, 2012
  4. daiquiri
    Joined: May 2004
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    Location: Italy (Garda Lake) and Croatia (Istria)

    daiquiri Engineering and Design

    Hi BertKu,
    I have modified your pics to explain the blade orientation for an anti-clockwise prop:

    Pitch.jpg

    The above pic tells you that you need to reverse the blade position on the shaft/hub, in order to get an anti-clockwise prop. The dotted line shows the correct position of the blade root.
    The below pic shows what it should look like at the end. As you can see, the correct blade setting is a mirrored image of what you have shown in your pic.

    Cheers
     
  5. BertKu
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    BertKu Senior Member

    Thanks so much Daiquiri, I should have explained whether the red part of the shaft/hub is facing in the direction the boat is going or in the direction of the transom. Your arrow is thus the direction the boat has to move. i.e. forward with anti clockwise shaft turning. You see Daiquiri, if I look at the information of Dave Gerr, it does not tell me and therefore I like to thank you very much. Also after I have calculated the angles, one can get very easy bending the blade in the wrong direction. Why ? Your 32 degree may be for me 58 degrees, although it is also 32 degrees, (90 - 58)but I take it probably from the wrong centerline. Thus am I right in saying, if I get any software telling me that the angle has to be 68 degree, I take it at 70% of the blade length. 68 degrees related to the center line of the shaft. Or I can take the 68 degrees in two ways. From the center line of the shaft or from the imaginary front line. One of the two is very wrong. Lucky most programmes gives me the pitch and therefore I project it in the direction the boat has to move, thus shaft centerline is my basis for my calculation.
    For people who know it , it is easy. However for people like me, we seem to be able to implement the wrong answer. No harm in helping me, I am grateful.
    Bert
     
  6. daiquiri
    Joined: May 2004
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    daiquiri Engineering and Design

    The blade angles on propeller constructive drawings are not referred to the centerline, but to a plane perpendicular to the centreline. I'll re-use one of previous pics to explain it better:

    Blade angle.jpg

    It can be comprehended also by looking at this drawing of an aeronautical propeller: http://woodenpropeller.com/Blade_outline.html, where airfoil section angles (blade angles) are indicated along the blade length. The geometrical definitions and parameters are the same as for marine props, only the dimensions and the chord/blade proportions are different.

    In fact, now that I look better at these pics, your prop appears to have a very high pitch. If it is a prop for a high-speed boat, then it could be reasonable. If not, then it could be due to a misunderstanding of how to read the angles given by the prop software you use, or in the technical drawing you're using as a reference. Is it possible that you might have wrongly referred the blade angle to the centreline instead of measuring it relative to the plane perpendicular to the centreline?

    Cheers
     
  7. Frosty

    Frosty Previous Member

    Pitch is not constant through its diameter.

    Pitch is a an average. do yourself a favour and learn from me that you cant make a prop.
     
  8. midnitmike
    Joined: Apr 2012
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    midnitmike Senior Member

    From Prop 101
    "Pitch is the distance, in inches, a particular prop would theoretically travel in one full revolution, as if traveling through a solid."

    In the OP's case his blade (at least until he bends it) has a constant angle from root to tip and does not vary. From the looks of his handy work up to this point I'd say he has fair chance of making a workable prop, so long as it's not subjected to too much horsepower. Using thicker stock will give him a stronger root section and the potential to produce a stronger weld in this critical area, but again his requirements are dependent on the application.

    Having just finished reading the entire Weedwhacker conversion thread I'm reminded of the many posts where hand made props were quite the norm, at least until they found suitable alternatives. I will agree with you on one point Frosty making a prop is not for the unskilled or faint of heart...failure is an option. But on the other hand saying that just because you couldn't make one doesn't mean he can't.

    MM
     
  9. BertKu
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    BertKu Senior Member

    We know, a number of people have explained that very well.
    Fully agree and therefore it is so much more fun to make something what works reasonable well or even exceeded expectations. Who knows. But Frosty, why not a little positive and help me to come up with the information I need. i.e. semi displacement 4.6 meter, 520 kg, 1Hp, single engine, cruising revs 1600, gear ration 4:1, twin blade. Blade size?, pitch?, ratio?, Speed is totally unimportant, as long it moves. I am 72, I have seen everything ,why should I rush?.

    By the way, my daughter wants to go to San Fransisco,LA,Las Vegas, Reno back to San Fransisco in May 2013, (17 days) where is there a nice boating shop for me to fluff around. Also what should she see, what is a must in LA, San Fransisco and which nature park is the nicest close to San-Fransisco. Secondly, my wife wants to go for a ski holiday, we will not go and ski, but just for the atmosphere in December 2013 in Northern Italy. We like Italy, but have never been in the winter resorts of Italy. Any recommendations Frosty? Bert
     
  10. Richard Woods
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    Richard Woods Woods Designs

    The Blue Pelican in Alameda is a great marine consignment store

    Hearst Castle is a must on the drive south

    Yosemite is a bit inland but the best National Park. Whilst in that area you can ski and sail at Lake Tahoe. Mona Lake is interesting if you like birds and salt crystals pillars. Bodie a bit north of there is an old gold mining town and the first place that had electricity bought in from a distance on HT wires. So it has the worlds first transformer (only of interest if you are an electrician)

    The smog is good in LA, as are the 8 lane freeways. Otherwise just try to find the Hollywood sign

    Richard Woods of Woods Designs

    www.sailingcatamarans.com
     
  11. johneck
    Joined: Nov 2011
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    johneck Senior Member

    The prop is about the right diameter, I would say optimal is about 17", 430mm. The pitch for your diameter should be about 320mm. A constant pitch prop will work fine, but not one that is a constant pitch angle. The pitch angle for any radius can be calculated as
    pitchangle=arctan((P/D)/(pi*r/R))

    where
    p/d is pitch to diameter ratio, 320/480 in this case
    r/R is the non dimensional radius, so starting at about 0.10 at the hub up to 1.0 at the tip
    So in this case the pitch angle at the root should be about 65 degrees and about 12 degrees at the tip.
    the pitch angle is measured from a plane normal to the shaft axis.

    Looking at your picture, it seems that the root may be OK, but since the blade is flat the tip will have far too much pitch. I assume that is why you are looking at twisting the tip. The blade needs to be twisted about an axis that is radially outward thru the center of the blade so as to reduce the angle at the tip down to somewhere in the vicintiy of 12 degrees. If you do not twist it enough, you will overload the motor and not go anywhere. If you twist it too much the motor will spin freelybut you will not produce as much thrust as you might like.
    With the power this low, a two bladed prop should work fine if you can get it close the correct pitch. One technique to check would be to set the prop on the fwd end of the hub and make some properly angled blocks and use a level. This may get you close enough to make it work.
    Have fun, let us know how you make out.
     
  12. Frosty

    Frosty Previous Member

    If you going to make a prop like this and tweak it then making a mould of the original is a good idea for somewhere to return to.

    This is as simple as a bowl of cement and settle it in and remove before it hardens.

    You can then always see where you were or to save a good one.

    It would be a good check of your work if the prop can be fitted in any position perfectly and would indicate if your blades are equal .
     
  13. BertKu
    Joined: May 2009
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    BertKu Senior Member

    Thank you John, much appreciated. It confirms my output of the software program. However, Propcalc has some badly errors at low power like 1Hp, thus I did not trust it anymore. Thanks again.

    Richard Woods, thank you for the tips given. I will certainly visit the sites proposed. My motherboard packed uplast night at 23h00 and I tried everything to make it half work, but at 01h00 I had to give up. Nothing worked anymore, not even my bootup display. I have borrowed a laptop to respond to all of you. With the summer holiday here, 30 degrees Celsius (86F ?) the yearend festivities, I have no hope to have it sorted out by the 5th of 2013

    Frosty, I don't have a prop to make a mould from. It is much more fun to ensure that the 16 odd permitations are eliminated and the one which is the correct one, is made. i.e. the front bending in the wrong way, the back bending in the wrong way, the blade welding in the wrong way etc.etc.

    All of you a very enjoyable new years eve.
    Bert
     
  14. BertKu
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    BertKu Senior Member

    Folks am I on the right track?? (I was allowed to keep the laptop a little longer)
    Bert
     

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  15. daiquiri
    Joined: May 2004
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    daiquiri Engineering and Design

    If the red disc is facing forward, then you are still not. :)

    Namely, it is not very clear from the last two photos if the leading edge of the blade is correctly facing forward.

    You can recognize the leading edge by the fact it has a pronounced concave curvature, like this one:

    LE-TE.jpg
    - I have indicated the leading edge with red line.

    In your last photo it looks like you have turned the leading edge (red) of the prop in the wrong direction (assuming that the red disc is facing forward - is it?):

    120-1.jpg

    If it is so, the blade should be flipped by 180°, in order to let the correct edge face forward during the prop rotation.

    Cheers
     
    Last edited: Dec 29, 2012
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