Scale plans - Are they really true to scale?

[Cheshiretaurus]

Do you ever check your scale plans or just assume they are correct?

After ordering plans for various subjects, It became apparent that either the kit was wrong or the plans were. A bit of googling of wingspans etc and getting the calculator out revealed some plans had shrunk in the wash, others have grown.

So how would you know?

First thing to do is check the scale on the plan usually they show 3 meters & 10ft, in 1:72 scale 10ft = 1.67" or 42.33mm, measure this on the plans, you might be surprised.

Looks like this ones a bit small, 96% too small to be exact.

So what can you do about it

Well if you have access to a scaling photocopier or scanner & printer, your done

For this one the scale measured 40.6mm so 42.33/40.6=1.042 (104%) set your copier to this and away you go.

or scan it best just use black & white setting (no grey scale ) and rescale the image in a photo editing package, then re print them.

After you have printed your new plans, re-measure them just to be sure, find out what the wingspan or length should be to and measure that too for good measure (pun intended)

I've found lots of plans like this even some printed in magazines, so before beginning cutting plastic, it might be worth a bit of time checking and verifying your working to correct plans.

Measure twice cut once.

Happy building

Mark

[Tailspin Turtle]

It gets worse. Sometimes the drawing is stretched or shrunk differently in the vertical axis than the horizontal axis. I recommend starting with the wing span (reliable) and overall fuselage length with respect to a dimensioned drawing (problematic) to insure that the drawing is properly scaled in both axes instead of beginning with that little scale and then checking the span/length. Also, occasionally one of the views is a slightly different scale in its entirety than the others on the page although this generally only occurs with SAC drawings when the three view is being laid out. Also see http://tailhooktopics.blogspot.com/2012/05/accurate-three-view-drawings.html

[Iain Ogilvie]

Simple answer - no...

And, IIRC, the scaling on Aviation News was always out.

Of course checking the scale does not necessarily make them accurate!

I'm always extremely wary when someone states 'well, I checked it against plans and the kit is 3mm short in chord.' Really???

It scares me what faith some people generally put in printed drawings - but of course there are those with an excellent provenance by the likes of Bentley et al. Even than - reproduction/print methods can add some variance as Tailspin mentions...

Iain

Edited February 17, 2013 by Iain (32SIG)

[Cheshiretaurus]

Tailspin Turtle,

Yes I've found a few with the distortion you describe. Needs much more in depth attention.- the fix I use for them is to scan then crop the individual images right upto the nose to tail and wing tip to tip, work out how many pixels that should be (I scan at 1200DPI) then resize each image length & width accordingly.

[BritJet]

Totally agree with previous posts, they can't be anything other than a guide.

There's also the added complication of errors being deliberately made on drawings as an attempt to identify unathorised copying - a lot of the Aviation News drawings come under that.

Steve