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Author Topic: weight  (Read 5691 times)

dougal99

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Re: weight
« Reply #25 on: January 02, 2009, 02:07:53 PM »

On the other hand one has to wonder why some people will build model narrowboats and then operate them at speeds that would put a small budgie into orbit. 

Barry M

Sticky thumb (ugh) or the Captain wants to water ski  {-) {-)
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Ghost in the shell

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Re: weight
« Reply #26 on: January 02, 2009, 02:37:06 PM »

In my opinion, though chances are, that I am probably very wrong, At a scale speed, a ship like Nord Icelandia, at her scale, she should just be developing a bow wave, rather than having her anchors swept under.  maximum speed for a vessel like her would be around 10 to 15 knots, which would be somewhere around 20km/h, and she wouldn't put a 6 foot wave on her bow. 

I have tried to set her EPA up so that at full speed she is at scale full speed

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malcolmfrary

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Re: weight
« Reply #27 on: January 02, 2009, 03:09:36 PM »

There is indeed a calculation for speed but most people feel that a scale boat doing scale speed doesn't look right or give the correct wave formation.

Colin

Why?  too slow?



A lot of people think that scale speed is the speed of the original divided by the scale, when it should be the original speed divided by the square root of the scale.  When your scale boat is producing a believable wave pattern, this is the speed it is doing.  Incidentally, the power required to do this is closely related to dividing the original's power (converted to watts) by the cube of the scale.  Because inefficiencies in a model are greater, you usually need to add a considerable percentage, but it gets you into the right area.
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Ghost in the shell

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Re: weight
« Reply #28 on: January 02, 2009, 03:27:10 PM »

based on a 1/87th scale, 20km/h max speed.

scale speed using sq/rt gives 4.5km/h, which would be comfortable walking pace at just over 2.3/4 mph

scale speed using scale of speed (20km/h divided by 87) 0.22km/h, 0.13mph

to put that into perspective,
at 220m/hr (722ft/hr) she would take over 4 hours to cover 1 kilometer, and probably 9 hours to cover 1 mile! even nasa's crawler that carries the space shuttle from the Vehicle assembly building to the launch pad would be faster CARRYING THE SHUTTLE, and that little baby weights in at 6,000,000lbs (2,721 tonnes!) and can do 1.6km/h.

imagine taking 5 hours to walk the length of southport pier. 
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Tester

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Re: weight
« Reply #29 on: January 02, 2009, 03:58:09 PM »

Just a quick point but isn't the scale speed of 20 kph at 1:87 around 2.15 kph ie 20 / 9.32 (square root of the scale) which is around 1.5 mph.

Or have i got the wrong end of the stick  {:-{ {:-{


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malcolmfrary

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Re: weight
« Reply #30 on: January 03, 2009, 10:16:56 AM »

Tester, you have the right end of the stick.  Hang on to it.
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TCC

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Re: weight
« Reply #31 on: January 03, 2009, 02:44:00 PM »

On the other hand one has to wonder why some people will build model narrowboats and then operate them at speeds that would put a small budgie into orbit. 

Barry M

Like this ->

http://uk.youtube.com/watch?v=lBoPmaRl4q8

 ok2

Someone should show this guy the speed calculation. :-)
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Ghost in the shell

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Re: weight
« Reply #32 on: January 03, 2009, 02:54:01 PM »

thats a tad quick for a DD
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catengineman

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Re: weight
« Reply #33 on: January 03, 2009, 05:06:08 PM »

Scare the pants off any ennemy  :-))

having that running at you full tilt you would worry that the reactions of the helmsman were razor sharp  O0
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TCC

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Re: weight
« Reply #34 on: January 03, 2009, 07:19:38 PM »

It's the only model of a destroyer I've ever seen that leans into curves like a motorbike.

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catengineman

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Re: weight
« Reply #35 on: January 03, 2009, 07:22:48 PM »

Helps keep the coffee in the cup while on the bridge  :D

It's the only model of a destroyer I've ever seen that leans into curves like a motorbike.



Cookie is happy as well  :-))
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Bryan Young

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Re: weight
« Reply #36 on: January 10, 2009, 06:13:20 PM »

I could be wrong here (again), but if you really want to get a scale speed then consider the following:-
No mathematics required. And this is all hypothetical:-
If a 500ft long ship was to take 50 seconds to travel its own length then wouldn't a 1:50th model of the same ship take 10 seconds to cover the distance? I'm sure somebody will point out the error of my thinking!.BY.
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Reade Models

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Re: weight
« Reply #37 on: January 10, 2009, 06:22:48 PM »

What!  500 feet in 10 seconds - that's going some! {-) {-)

Malc


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malcolmfrary

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Re: weight
« Reply #38 on: January 11, 2009, 11:30:47 AM »

The 1:10 model would be 50ft long.  (Big shed needed). The model speed would be based on the square root of the scale, so 1:10 equates to 1:3.16 for the model, original speed is 6.8 mph,  model speed is 2.16 mph, or 3.16 ft/sec, which works out at 15.8sec to cover 50 ft.
For your crew, time is passing rather faster than it is for us, based on the same rules.  Sorry about the maths, but its maths and not magic.
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Bryan Young

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Re: weight
« Reply #39 on: January 11, 2009, 06:54:24 PM »

I just knew it! But at least I was working on the same lines. Anyway, rather than get involved with semantics, I normally drive model ships at a slow(ish) walking pace. Looks OK. We have one guy in the club who drives a Liberty ship (10 knots real speed) at a scale speed of around 100mph. And he doesn't give a rats....he also has the anchors draped over the bulwarks. Oh well. Win some and lose some. BY.
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