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Author Topic: Paddle Wheel size - is it important?  (Read 4527 times)

Offline kiwimodeller

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Paddle Wheel size - is it important?
« on: July 24, 2016, 06:47:46 PM »
I have been giving thought to building another side wheel paddler. I have a set of Graupener wheels and also a set of Barry's ones, both 140mm diameter. To build the size of boat I am thinking of (around 60" overall) the scale wheels would be a little under 120mm. What problems might the oversize wheels cause? I had thought I should make the hull a little deeper draught to ensure that the bottom of the wheels ended up in the correct relationship to the bottom of the hull. The original has the lowest point of the wheels just above the bottom of the hull so I would need to raise my wheel shaft height 10mm to keep the wheels correct. Any comments, advice or suggestions welcome. Cheers, Ian.
"Every time I think I see the light at the end of the tunnel it turns out to be some bastard with a train trying to run me down!"

Offline andy

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Re: Paddle Wheel size - is it important?
« Reply #1 on: July 25, 2016, 06:56:31 AM »
Bigger wheels are useful. Then the paddler also can drive on land as well.

Andy

Offline Mechanicboy

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Re: Paddle Wheel size - is it important?
« Reply #2 on: July 26, 2016, 12:50:44 AM »
Depending on how strong is the steam engine to produce enough torque to drive a big wheel paddler. Use long stroke steam engine to produce enough torque or use reductiongear to increase torque from a hi reving small steam engine. And the boiler must be big enoug to give steam engine enough torque to drive a big wheel paddle.

Offline Delaunay

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Re: Paddle Wheel size - is it important?
« Reply #3 on: July 26, 2016, 02:50:49 AM »
:) Good evening;
Too large wheels did not they risk conversely, braked mechanics and boat; At their lifts and their prey in the water ???

Offline Tomas Krejci

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Re: Paddle Wheel size - is it important?
« Reply #4 on: October 01, 2016, 03:42:54 AM »
Hi,
       Paddle wheel size is important,BUT ..
                                                                if the model is long as you write (60 '=> 152.4 cm) so change the wheel diameter from 120 mm to 140 mm (Graupner) I think it is insignificant,
  BUT - especially since the wheel are designed for the model paddlesteamer Glasgow

 Model ps Glasgow Specification
Length o.a. 1010 mm Width (beam) 388 mm Width (excl. paddle boxes) 200 mm Height 424 mm Draught 65 mm A. u. weight, incl. R/C gear 6.2 kg Weight, empty (without drive system, power supply and R/C gear) 1.8 kg Scale 1:40
I am rather worried that such a small paddlewheel on a  your big ship will have low efficiency .
Keep in mind that (I assume) the optimal speed for such wheel sizes range from 100 to 200 rpm. At higher speeds can such a model wheel lose effectiveness. This is due to circumferential speed at a certain size wheel ... I think here on Paddleducks on this theme you will find the answer too.
There is always a crucial question - you're building an accurate ("showcase") model, or RC model. with whom you want to go on the water.
If you want your model floated well, in many cases you'll have to settle for compromises. It concerns the size of the paddle wheels or propellers, it concerns the size of the rudder ,powerplant design ...
It is necessary to consider all the pros and cons.
In any case, I wish you success in building !

Greetings
Tom

Steam....GO!

Offline Tomas Krejci

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Re: Paddle Wheel size - is it important?
« Reply #5 on: October 05, 2016, 02:34:00 AM »
Hi Gents,
               I add here a few lines from old publications on the design and size paddle wheels for large ships.
Steam....GO!

Offline bill stafford

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Re: Paddle Wheel size - is it important?
« Reply #6 on: October 09, 2016, 11:27:21 AM »
very interesting discussion gents
I have long suspected the relationship between wheel diam. + width +depth of float , and it seems i was on the right track , thanks again .
 my experience was to lower the top of the float below the static water surface to allow the water scoop effect on paddlers not to reduce the effectence of the drive .
 i have also wondered about wheel diam , and how it effects drive , as most au paddle steamers who were used for towing logs , had large diam paddle wheels , or very wide floats , PS Adelaide and oscar W , my model wheels are set at least 6/10 mm below the static water line , and this does make a BIG difference
I have also talked to other modellers about size of the floats , mainly the depth of the float , and my experience is at 1/24 scale , i tend to go w 25 mm deep floats on my wheels , some modellers dont see it as a issue , i dont know .
 paddlers are a funny beast , and i know that heavy brass paddle wheels arnt a good idea , some of the larger models out here use aluminium, i now try to use barrys HIPS wheel kits , due to there very light weight and quality, a firm friend of mine , but not just a one eyed view , he does good work
i started on a model of the PS Rodney , using barrys wheels , but may increase the float size .
i drive my p addle wheels at 300/350 rpm , via tooth belts and gear boxes, trying to get a 540 type motor per wheel , but on fine days i throttle back to 200/250 rpm , but if the wind comes up , i need the  extra revs , even though it tends to froth and bubble , there is extra drive .also on this subject , there seems to be a maximum speed these hulls will travel at , them all we get is bubbles , but the real enemy is wind
I hope this helps and these are my experiences w a paddler for over 15+ yrs

Offline bill stafford

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Re: Paddle Wheel size - is it important?
« Reply #7 on: October 09, 2016, 11:35:05 AM »
on the subject of your problem , i wouldnt lift the paddle wheels up , on mine i had to lower them , look at the static water line , and set your floats so as the top of the float is about 10 mm below the static water line , this allows for the water scoop effect , this having the top of the floats below the water line , is critical , and makes a big difference

Offline Delaunay

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Re: Paddle Wheel size - is it important?
« Reply #8 on: October 09, 2016, 06:35:42 PM »
:) Bonjour ;
A lire vos remarques, il faudrait considérer que ( hormis un modèle à l'échelle ) le meilleur rendement d'une roue à aubes est obtenu avec:
- un grand diamètre
- un nombre conséquent de palles
- des palles de petite épaisseur ( à défauts de palles mobiles ) mais de grande largeur
- une vitesse de rotation de 200 à 400 rpm
- une profondeur ne dépassant pas le fond de coque ( ou elles deviennent des roues :whistle )
Esque je me trompe  :( ???


:) Hello ;
Read your comments, it should be considered that ( apart from a scale model [/ i]) the best performance of an impeller is obtained:
- A large diameter
- A significant number of paddles
- Thickness of small paddles ( to defects in mobile palles [/ i]) but very wide
- A rotational speed of 200 to 400 rpm
- A depth not exceeding the hull bottom ( or they become wheels [/ i]: whistle)
Esque I am wrong ??? :(

François

Offline derekwarner_decoy

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Re: Paddle Wheel size - is it important?
« Reply #9 on: October 09, 2016, 07:20:57 PM »
Hi PD's.......

An important element in the design of spoked wheels [land or water] is the need to minimise harmonic stress due to the rotational impact with the mating surface

Harmonic stress causes fatigue in mechanical structures which can lead to failure of the weakest point within the build

One of the simple principals employed here is the irregular or uneven number of elements [spokes] used in the design

This applies from bicycle wheels, to any gearing or chain in a power transmission drive......ie., the requirement of one uneven number of element [tooth, shaft or spoke] in the drive

So for our application this is why paddle wheels have 7, 9 or 11 spoke members in the design

We should also remember the rules of scale for [linear] movement being ..."the scale speed being the actual speed multiplied by the square root of the scale"

Derek
« Last Edit: October 09, 2016, 10:35:44 PM by derekwarner_decoy »
Derek Warner

Honorary Secretary [Retired]
Illawarra Live Steamers Co-op
Australia
www.ils.org.au

Offline Delaunay

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Re: Paddle Wheel size - is it important?
« Reply #10 on: October 09, 2016, 08:08:26 PM »
 :) Hello Derek ;
Merci de se complément qui m'avait complétement échappé .
Mais dans la théorie, combien devrait il y avoir de palles dans l'eau pour mouvoir le bateau, ou plus exactement combien de pourcentage des palles d'une roue devrait être immerger ?


Thank you to supplement that had completely escaped me.
But in theory, how should it be any paddles in the water to move the ship, or more exactly how much percentage of a wheel paddles should be immersed?

François

Offline bill stafford

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Re: Paddle Wheel size - is it important?
« Reply #11 on: October 09, 2016, 10:58:25 PM »
gday guys , theory is ok , but my paddler has being going for 15+, w 8 floats per side , no cracks no issues ,but room for improvement, hence my interest . the other way to improve paddlers is to reduce draft , but thats a hard one , as its all theory till floatation tests , dont forget to maintain paddle blade depth
regards  bill s

Offline derekwarner_decoy

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Re: Paddle Wheel size - is it important?
« Reply #12 on: October 10, 2016, 08:28:26 AM »
Morning Bill

Certainly not disputing that our model components will never be stressed [in loading or frequency] like the full size counterparts, simply mentioning the 'uneven number or unequal' element in design

Derek
Derek Warner

Honorary Secretary [Retired]
Illawarra Live Steamers Co-op
Australia
www.ils.org.au

Offline bill stafford

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Re: Paddle Wheel size - is it important?
« Reply #13 on: October 11, 2016, 10:09:40 PM »
fair enough derek, its good to see healthy discussion.
 from memory graupner paddle wheels are 8 floats, as are mine on my paddler, i think adelaide has 12/14 floats
this could be one of those things that matter full size , but not a issue on models.
 but i do believe there is a relation between diam and paddle blade float size =drive ,, put i havent built enough to say what it is, but there is a reason adelaide has large wheels w plenty of floats.
my area is windy , so i need all the drive i can get .I have even see my model almost blown backwards

 

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