Scaling down to size...got it. Weight?

Black Lion VF-213 · Post by **Black Lion VF-213** » Wed Dec 03, 2008 7:17 pm

This may sound like a dumb question. I know it's relatively simple to scale down a real aircraft to let's say 1/18. That HPH Tomcat is suredly 3.555 inches wingspan and 3.486 in length. How the heck do I scale down the Tomcat's weight to 1/18? Using the Tomcat's wingspan of extended sweep = 64 feet and dividing that by 18 I get 3.555. F-14 length is 62.75 feet. (6' 9").

But if I take a Tomcat's dry weight of 43,375 lbs and divide that by 18, I get 2,409.72 lbs!! If HPH were to properly scale that model of theirs by weight as well, who on Earth could lift it? That doesn't seem right.

Am I missing something, or was I right and I'm not fathoming just how heavy a Tomcat really is?

chunks · Post by **chunks** » Wed Dec 03, 2008 8:01 pm

length varies directly.
Area varies with the square.
Volume varies with the cube.

Weight, being dependent on volume, varies with the cube.

length is 1 dimensional: 18 ft scaled to 1/18 is 1 ft
Area, length times width is 2 dimensional: an 18 ft square (18 x 18 = 324 square ft) scaled to 1/18 is 1 square ft.

volume, length times height times width is 3 dimensional: an 18 ft cube (18 x 18 x 18 = 5832 cubic feet) scaled to 1/18 is 1 cubic foot.

volume is reduced much faster then area, which is itself reduced much faster then length at the same scale.

Hope this makes sense and hope I have this right, it's been a long time for thinking about this stuff.

Post by **aferguson** » Wed Dec 03, 2008 9:41 pm

divide the true weight by the cube of the scale. So, whatever the tomcat weighs/(18x18x18) and that's the scale weight.

I did this years ago for some smaller models i had and interestingly found it was impossible to make the tanks heavy enough (not enough room to cram in sufficient weight, even if i used lead) and impossible to make the planes light enough (the weight of the plastic model was already too much).

Threetoughtrucks · Post by **Threetoughtrucks** » Wed Dec 03, 2008 10:25 pm

Use this link to scale almost any size to any size:

http://www.printmini.com/calc.shtml

Save it, it comes in handy.

TTT

iflabs · Post by **iflabs** » Wed Dec 03, 2008 10:58 pm

Interesting, I never thought about the weight in proper scale. Very confusing.

immeww2 · Post by **immeww2** » Wed Dec 03, 2008 11:01 pm

Never thought it was so complicated.

pickelhaube · Post by **pickelhaube** » Thu Dec 04, 2008 5:59 am

immeww2 wrote:Never thought it was so complicated.

Your right

I think I will try to stick to dementional scale

Post by **aferguson** » Thu Dec 04, 2008 6:06 am

it's not complicated at all, you just divide the actual weight of the real thing by the cube of the scale you are working in. It's the cube because you're dealing with 3 dimensional objects, so you're essentially doing length x width x height..ie it's volume. That it's an irregular shape makes no difference since the model is the same irregular shape.

So if you wanted to find out the scale weight of a 1/32 FOV jagdpanther you just divide the actual weight of the vehicle by 32x32x32 and that's the scale weight.

Quite easy, really.

Black Lion VF-213 · Post by **Black Lion VF-213** » Thu Dec 04, 2008 9:27 am

I tried out the 18x18x18 formula and applied it to a dry weight P-51D. P-51D comes in at 7635lbs. 7635/5832 (18 to the third power) = 1.309 lbs. My goodness even our 1/18 BBI & 21st Mustangs are a little overweight!!

Post by **aferguson** » Thu Dec 04, 2008 11:28 am

makes you appreciate just how lightly built aircraft are, doesn't it. Try it for a tiger tank. I bet you'd be hard pressed to make it heavy enough.

Killerf6 · Post by **Killerf6** » Thu Dec 04, 2008 7:05 pm

I think you have to take the cube root, then divide by the scale.

IE cube root of 7,635lbs is 19.69lbs, divided by 18, is 1.1lbs.

pickelhaube · Post by **pickelhaube** » Thu Dec 04, 2008 7:18 pm

So how much will the weight of a 1/18 Tiger be ?

Killerf6 · Post by **Killerf6** » Thu Dec 04, 2008 7:20 pm

How much does a 1:1 tiger weigh?

pickelhaube · Post by **pickelhaube** » Thu Dec 04, 2008 7:23 pm

Killerf6 wrote:How much does a 1:1 tiger weigh?

56.9 metric tons

normandy · Post by **normandy** » Thu Dec 04, 2008 7:36 pm

Tiger I or King Tiger

Tiger I 57 tons

King Tiger 68 tons ...............

Killerf6 · Post by **Killerf6** » Thu Dec 04, 2008 7:38 pm

About 6lbs. or 2.7kilos.

correction I used 2000 kilos=metric ton in my first calculation, which is in error 1000 kilos=metric ton.

The correct answer is 4.7lbs, or 2.1 kilos

This is for the tank that weighs 56.9 metric tons

Killerf6 · Post by **Killerf6** » Thu Dec 04, 2008 7:59 pm

To answer the original question 1.95lbs would be the dry weight of an 1:18 F-14 to scale.

Post by **aferguson** » Thu Dec 04, 2008 8:02 pm

why would you take the cube root of the weight? Think of it as a big cube made up of little cubes and you'll see that you just divide the weight by the scale cubed.

The Tiger I would weigh 21.5 pounds in 1/18....ie at 1/18th it's size.

To look at it another weigh: to build a tiger tank out of little models of a tiger tank you would lay 18 end to end, 18 on top of each other and 18 side by side and then fill in the envelope of space they form with other little tiger tank models. Now of course you'd actually have to break the models into little tiny pieces to get the 1:1 tiger the correct shape but you get the idea. So, each little tiger would have to weigh 1/18x18x18 th the weight of the full size tiger.

Killerf6 · Post by **Killerf6** » Thu Dec 04, 2008 8:36 pm

It's old math classes kicking in. Any time I have an exponant I use the root of that exponant to find the recipricol. The cube root is the recipricol of the cube. Volume is expressed as a cube, to find the root you have to use the cube root. (18x18x18) is a cube of 18, or expressed 18^3= 5832. The cube root of 5832=18. The number 18 is the denominator of the scale though, not the root of the volume.

Truthfully it is just an approximation as volume and weight are not the same thing. We are saying (implied) that the weight of the object is equal to the weight per cubic dimension. Take our F-14 example: 43,375Lbs/cube dimension>cube root=35.13Lbs/dimension(note cube's cancel out) divide by 1/18 dimension = 1.95Lbs(note that the dimensions cancel each other out).

I may be all wet as it has been some time since I have taken a math class or done an excercise like this one, but I do believe that the equations are correct.

pickelhaube · Post by **pickelhaube** » Thu Dec 04, 2008 9:09 pm

Good God,
Both of you guys have my head spinning.

It feels like I am back in geometry class and Mr. Busher is stairing at me. That didn't help either. That was also back in '77.

Post by **aferguson** » Thu Dec 04, 2008 9:11 pm

weight is a function of the volume however. So something 1/18th the size of something else will have a volume 1/18x18x18 th that of the original and thus a weight of 1/5832th the original, assuming it has the same density, which is what it has to have if you want scale weight.

Going back to the example of a cube. Imagine a big cube 18 feet by 18 feet by 18 feet. A 1/18th model of it would be 1 foot by 1 foot by 1 foot. There would be 5832 1x1x1 cubes in the big cube. If the big cube weighed 5832 pounds then each little cube would weigh one pound. So the scale weight is the actual weight times the cube of the scale.

The fact that a tiger tank, or an f-14 are irregular shapes makes no difference since the scale model is the identical (hopefully) irregular shape. You could imagine the scale models as pixels that could be put together to form a 1:1 model of the full size original. And the weight would be 1/18x18x18 th.

flyboy_fx · Post by **flyboy_fx** » Thu Dec 04, 2008 9:53 pm

AHHH CRAP MATH 1+1= errrrrr
Im not so hot in math But history well wwii history Yea im on fire well for my age and dunt cureckt me spelzing ethear

FieroDude · Post by **FieroDude** » Thu Dec 04, 2008 10:03 pm

Just tell me that we aren't going to start beating up manufacturers for less than perfect weight accuracy, too. it's bad enough when we tell them to go back to the drawing board because the landing gear isn't exactly right for an unloaded plane, even though we will typically display the plane with a full ordinance load, or even more likely: FLYING!

flyboy_fx · Post by **flyboy_fx** » Thu Dec 04, 2008 10:17 pm

and if its to heavy ya cant hang it

iflabs · Post by **iflabs** » Fri Dec 05, 2008 1:02 pm

Someone should pull out a triple integral or something. But a dry weight of ~2lbs in scale for a F-14 is hilarious, friggin light.