PS Reliant - paddlewheel rotation

[Derek Warner]

on Wednesday, February 27, 2002 "Stuart Badger" <106160.2011@compuserve.com
wrote
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
> As to the rotational speed of the paddle wheels I am not too worried. One
> of the BIG advantages of steam power is that steam engines give maximum
> torque at zero revolutions. Provided the wheels are geared down so that
the
> resistance to rotation is not more than the power of the engine (I will be
> using a 4 to 1 reduction) then the speed of the wheels can be simply
> regulated by the throttle. The engines I have chosen use one channel of
the
> radio for speed control and forward and reverse - neutral on the radio
stick
> being 'off'.
>
> I expect the paddle wheels to turn at ABOUT 50 rpm. One of the main
reasons
> for instability on paddler models (sidewheelers) is that they are simply
> travelling too fast! So I think about 50rpm is the maximum I would want
them
> to turn. I am hoping that as the model is fairly large she should be a
good
> deal less tender than a smaller model. The 26inch model I built some years
> ago of the same boat was fairly worrying on the water
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
Thanks Stuart - we all look forward to your postings on Reliants progress!!,
however I must question the 50 shaft RPM of the model - would 50 shaft RPM
been more like the actual?

Have a look at PD messages 116, 133, 775, 779, 781 & 892. I think they may
offer some alternate thoughts

With PS Decoy I have been considering reducing the paddle blade height so as
to be able to maintain say 180 RPM (full speed) which is somewhere near
actual
multiplied by the scale factor noted in one of the above postings (if it is
correct)

Apart from this (speed increase) do we not also get a gyroscopic or
(stabilizing)
effect based on each rotating mass close in by of the hull? - or does this
same
gyroscopic effect work against us??

I looked at a link to Chedders model engines some weeks ago, but will wait &
look forward to your confirmation of power plant chosen

best regards Derek

[Paulrjordan]

(Snip)
> however I must question the 50 shaft RPM of the model - would 50
shaft RPM been more like the actual?

I must say that I too was a little concerned when I read that Stuart
is considering a rotation of 50 beats a minute, so thanks for bringing
this up, Derek.

Remembering that water is not scalable, I'm also wondering if the 50
rpm, which is close to prototypical, will drive "Reliant" at a
satisfactory speed. I experimented with a number of different rotation
speeds until I achieved the scale speed I wanted, and I ended up at
120 beats in the water. (180 rpm with no load) I realize this is
probably twice as fast as the prototype and the only option to
reducing paddle wheel rotation to a more realistic scale speed is to
exaggerate the float area. I did this and it had the effect of 1)
slightly slowing the paddles down and 2) increasing the speed. In
fact the percentage increase in speed "appeared" to be closely
proportionate to the percentage increase in float area. Once again..I
am reminded water is NOT scalable in density and we are forced to use
little "cheats" to replicate prototype performance in models. I would
also say that I have only ONCE read of a modeler who claims that
feathering blades in smaller models replicate the increase in
performance of the prototypes. I have no idea at what scale this
efficiency would "kick in" but at some point it must.

I'm so keen to talk to Bill Wilkinson (the giant Paddle Tug guru in
the UK) about this whole power transfer issue as it's one of the
"biggies" in our hobby.

I have attempted to read all kinds of technical material on this
subject..but I just end up confusing myself...the proof of the pudding
(paddling)is in the WATER and that's about the only "theory" I can
relate to. As you know, I am a great fan of thorough bath/tank/pond
testing of the hull, mechanical and control systems before the
superstructure is even started. It will be fascinating to see how
Stuart's lovely tug performs, and I don't foresee any problem so long
as he provides capacity for increased revs in case the 50 rpm is too
slow to push her along to his satisfaction.

Please keep the info coming in so we can add to our knowledge base of
this..and also don't forget the note book and pencil at ALL tests to
record changes to configuration and results.

PJ

[Stuart Badger]

Paul and all!

I have just turned the model of Old Trafford (Reliant) over to do the final
clean up on the hull and put the finish coat on. I have uploaded shots to
the photo section of
her hull 'turned turtle' so that you can see why I am a little concerned
about the weight of the sponsons hanging over the hull!! Goodness they is
BIG!!!

Just hope the view in the photos is NOT one that is repeated at the pond!

And - yes - I really MUST have a tidy up in the workshop now I'm up to the
fiddly stage!

Stuart