Conversion Table

[bruce martin]

Again I am having one of those SENIOR moments I thought for sure I had read some where on this forum, that some one had posted a table of conversion numbers. I to am going to be working on the IJN - 53 , to convert it to an I-58 . So there are some parts that I need to down sized and reconfigured and cast up. So if anyone remembers where it was , can you point me in the right direction .
Thanks .
Later Bruce

[Ralph --- SSBN 598]

Re: Conversion Table

Maybe this is it.

I have an Excel Spreadsheet that will do conversions.
Just look for the conversion you want on the tabs.

It does feet to inches & millimeters.
It does millimeters to feet and inches.

You can get it here. Alma 1891 build

[bruce martin]

Re: Conversion Table

Thanks Ralph, that is the one I was looking for. I knew that someone out there would have it.
Thanks again.

Later Bruce

[Ralph --- SSBN 598]

Re: Conversion Table

You are welcome. I do have a request....... If you find any errors when using the spread sheet, let me know so I can go in and correct it.

[ober freak]

Re: Conversion Table

Hi Ralph,

Nice spread sheet! But your model speed calculation is wrong.
Based on the laws of Froude (water) and Reynolds (air) the model speed is calculated in this way:
Model speed = Original speed / sqrt(scale)

As the Model reacts like the Real one when Fr / Re-Numbers are the same on both. Also the waves around your model and the resulting drag are in direct scale then.

http://en.wikipedia.org/wiki/Froude_number

http://en.wikipedia.org/wiki/Reynolds_number

Marco

[Ralph --- SSBN 598]

Re: Conversion Table

The old discussion on "What is Scale Speed?"

You two links are correct as far as they go.
My calculator did have an error in it and I thank you for your post because it caused me to look at the thing again.
The Speed Calculator had an incorrect formula given an incorrect ressult.
I think I fixed. ? ?

Now back to the discussion.
Your links go to the issue of what is Scale Speed in regards to bow wave and trailing wakes.
All the formulas address this issue so the model can produce scale looking bow waves and trailing wakes.
This issue also comes up in Reynolds numbers. Scaling in air. Lift vs Drag.
The formulas resulted from wanting scale models to produce waves from model motion. This results in the model traveling faster to generate the scale waves.
These formulas are very good from the perspective of the model at the model.
The reason models must move faster to generate the scale waves it the water media can not be scaled.
If the boat is scaled smaller then the water needed to have it's molecules closer together to have the same effect on it as the full scale in it's water media.

Airplanes that are scaled the same as full size do not fly well as the shape of the wing is not sufficient to give the same lift.

Example: say full scale air has molecules at 1 per every inch. On a model at 1/4 scale would have to have air molecules at 4 per every inch to have the same effect from the air.
We can not scale air or water. Well we could fly airplanes in a room that the air pressure has been risen to multiply the air density to the scale.

The two formulas are to scale the craft to the real world air and water to give the same drag and lift at the models point of view.
================================
But when we run our boats or airplanes the perspective is not from the craft's point of view.
It's from our point of view on the ground look out to the craft.
We still can not scale water or air when we run our crafts but we can scale the visual speed.
If the real craft travels 1 mile in 1 hour then the scale model should travel the same distance that meets the scale of the craft in the same amount of time.

1 real mile when scaled to 1/10 model would be 1/10 of a mile.
So the distance traveled at a given scale speed is the real distance divided by the scale.

The Calculator does nothing more than convert real distance vs time in to scale distance for the same time.
It does not consider water or air density or the look of the scale bow wave and trailing wakes. Or lift vs drag.

Froude (water) and Reynolds (air) formulas are for engineers to figure out the best design for a given model scale to produce full side reactions to the medium they are being tested in.

I am a builder and runner of models.
Running from point A to point B at the scale my model is, should take as long as the real boat covering the same real distance.

If I/you want the bow wave and trailing wake to look scale then I/you will need to run your models a little faster than the scale speed to get the look.

Either way...All is Good!

[ober freak]

Re: Conversion Table

Running from point A to point B at the scale my model is, should take as long as the real boat covering the same real distance.

This is true if we also scale down the surrounding scenery like on a larger model railway or something similar. "Miniatur Wunderland" in Hamburg for example who are also trying to implement ships in their 87th scale world.

But as we mostly sail our models in the real open world the "look an feel" lives much more from the effects the model produces like waves or leaning to the side on turns, but this is a ride on the knife edge for not going to fast.
On an open lake a larger ship can drift from the wind sideways in nearly similar speed than your calculated speed which also doesn't look very true.

So we both are right in some way and not in an other, depending on the surrounding of the model I think.
As I always say: you build the model to your likes and handle it in the way you want for your own satisfaction, regardless what the others think.

The big problem we have is we can't scale down everything as you already stated.

[Ralph --- SSBN 598]

Re: Conversion Table

You pointed out the wind.

That is another issue where the real wind speed needs to be scaled in your mind for your boat's scale.
A light breeze could translate in to a gale force wind at scale.
------------------
I like the "scale down the surrounding scenery."

We can choose a scale to build our boats at. Everything else is on it's own.
It's easier to just ignore the surroundings.

Though I have seen photos of some clubs who have their own pond and go to great lengths to build scale seaside towns and commercial docks.

This also is a problem. What Scale do you build at your club?
This sets a scale that everyone needs to build to if they want to stay in scale.

Australia has a suggested standard scale of 1/72.
----------------
Things built in scale.

I compete in the shooting sport of cowboy action shooting. A few years back, one of the clubs I belong to, decided to build a full scale western town with a 320' main street to hold our matches in.
We call our little town, Chimney Rock after the local natural monument in the area and the history of the area. Last known fight between settlers and indians in southern California.