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Hi Everyone;

Something has been bothering me lately.  I have seen many check the accuracy of their model to various drawings.  The question comes to me, which is accurate?  There are as many drawings if not more than there are kits.  Especially with the latest kits, I would trust the developers to make accurate research.  The same however is true to the drafters.  I'm sure they also research prior to creating drawings.

 

How do you gauge between the two?

 

Do you have a 'reliable' source of drawings for your projects?

 

Cheers

 

Al

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There's no such thing as reliable drawings. The kind of drawings modelers think about (multi-view orthographic projections) are not produced by aircraft manufacturers. They have no need for them. Any such drawings are produced, hopefully, with reference to a lot of manufacturer dimensional data and photographs of the real thing, but that's open to a lot of interpretation.

 

Here's an example: Let's say for the sake of argument that I was able to produce a four-view orthographic projection drawing of the Mumblypudge Fudrucker Mk.I, down to three decimal places of perfect accuracy. The drawing is *absolutely* a scale reproduction of the real thing, down to the last itty bitty detail. Then I inadvertently move the battery access hatch 0.0001 mm aft without realizing it. Boom. Now the drawing is no longer accurate.

 

Yes, that's an extreme example, but the idea is, there's really no such thing as “accurate†drawings. The only truly accurate drawings of any aircraft are those produced by the manufacturer used to produce the real thing. And that includes drawings of each individual part of the aircraft, one by one, and subassembly and major assembly drawings. Some model drawings are, to be sure, a whole lot better than others. But even the ones that are widely touted as being “really accurate†may fall down when subjected to intense scrutiny. The overall shapes may be great, but the details may be less than accurate. Or the details may be spot-on, but with errors in major shapes. You could spend a lifetime on one set of drawings and still not have them “accurateâ€. An intimate, highly detailed knowledge of the real airplane is required to produce really good drawings, which isn't something that a lot of draftsmen have or have the ability to gain.

 

The problem is, unless you embark on a detailed study of the subject at hand, and have access to all the detailed dimensional data and thousands of photos of the real thing, you really have no way to ascertain which drawings are good, which ones are bad, and which ones fall somewhere in between.

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Al,

 

Checking kit parts directly against drawings is something that seems to be reasonably common in the modeling world.

 

There are lots of factors that make the practice a bit questionable if your searching for ultimate accuracy plus in 25+ years in engineering I've never seen anyone place a component on a production drawing as a method of assessing its final accuracy.

 

Modellers however for the most part are not engineers. I'm currently using a set of Bentley plans in my 1/32 Typhoon build. I find those very good.

 

I think that well used drawings can be really helpful. Plonking a kit fuselage 1/2 on a ‘scale' drawing and then bemoaning a minor difference is possibly not the best use or practice. Doing that to get a general idea for shape is possibly useful.

 

HTH

 

John

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The only drawings you can absolutely scale from are produced on velum and are used in lofting.  Velum does not suffer from the affects of humidity nor does it distort lines.  I worked aircraft production for several years and the guys in lofting (prototyping) could only scale off velum.  If you handed them a paper drawing and told them to build something, they'd hand it back to you with some choice words to the effect of "Do it your self cause there's no way we're doing it off that stuff."  We built the aiframe for this:

 

eJRgDmC.jpg

 

I had the distinct honor of helping (very minor help) to construct the airframe for this speedy guy.  It doesn't hold the world record for the fastest helicopter any longer (Thanks Eurocopter) but the Eurocopter won't be in the Udvar-Hazy National Air and Space Museum either.  When I saw it in the UH facility I said "Holy Sh*t!"  I had a hand in building that thing!  My DNA is in that airframe!  My wife was actually impressed with me for about 10 minutes.  I found it odd that the rotor blades on this helicoper only flex about 1/4" (6.3 mm) when in flight.  The counter rotating rotors took care of the lift problem of the retreating blade when the aircraft speed approached that of the rotor blades. 

 

Everything that was measured, cut, drilled, shaped or otherwise worked on this airframe was done based on drawings produced on velum (when it was at our facility).  Sikorsky did the high speed runs down in Florida if memory serves.  It first flew at the Schweizer Aircraft facility in Horseheads, NY with yours truly in attendance. 

Edited by Juggernut

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I agree with the above posts. Drawings are good for reference only.Photos are even worse. As far as accurate goes Jennings is correct.  Manufacturers produce thousand of drawings of individual parts and sub assemblies to produce an aircraft. If like me you build ships that then becomes 100's of thousands. I have yet to find one ship drawing that is accurate to the ship as commissioned.

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There are many variables operating here.

Are the draftsman's original source of the drawings all that accurate to begin with? During the war some parts of the drawings were modified to protect secrets. Some drawings had original errors which were propagated over time. Some changes were not recorded properly on the drawings. There are many reasons for official drawings to be full of errors. Especially under the pressures of wartime conditions. 

When  you make xerox copies the dimensions in one direction are distorted purposefully to prevent people from making copies of paper money. The written dimensions may be correct but the paper is distorted. 

As a professional designer/draftsman I've been making mechanical drawings all my life. I could tell you stories about drafting errors that would curl your hair. In general, I caution you that the closer to the time of war that the drawings were made the higher the possibility that they are full of errors. 

In general, it is like religion. Belief of accuracy a matter of faith. 

:punk:

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Hi

I did some drawings (5 views) myself and from pictures, manufacturers drawings and measurements, I was "guessing" my accuracy around 95 %, not more.

However, I did also some 3D drawings based on 3D measurements, that has also some "it is about...) and I'm guessing the accuracy around 98 %and could never find the official wingspan from a few mm (in scale 1)

18042008330023927215677212.png

cheers

Norbert

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The only drawings you can absolutely scale from are produced on velum and are used in lofting.  

 

 

Right up to the point that the aeroplane goes into production, especially in war. After that, unless there's a really tight process of capturing production changes back into the original drawings - forget it

 

Modellers drawings are a 2D model of the aeroplane. The best are based on extensive research and careful interpretation

 

Richard

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Accuracy of drawings in scale modelling of assembly kits is more of a philosophical question, not a technical one. You need to think like a dressmaker or tailor and less like a architect.

 

The problem occurs with scratchbuilding or making vacform models, where you can't really tape much together to get a feel of the completed thing so work a great deal from drawings making subassemblies that you hope fit together.

 

I'm therefore of the opinion that the best "plans" are therefore card models.

 

Tony

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Right up to the point that the aeroplane goes into production, especially in war. After that, unless there's a really tight process of capturing production changes back into the original drawings - forget it

 

Modellers drawings are a 2D model of the aeroplane. The best are based on extensive research and careful interpretation

 

Richard

 

 

After prototyping, the lofting department turns the vellum drawings over tothe tooling department that makes the  tooling, jigs and fixtures so the production aircraft is true to the drawings, modifications and all.  We then can use paper drawings to actually build the aircraft.  The critical measurements are already established in the tooling, fixtures and jigs.  Been there, done that....  Got several Sikorsky T-shirts.

 

LOL... Depending on the scope of the modification, it usually gets prototyped right on the production line.  Design Engineering normally lags behind a month or two in producing/updating the drawings.  Production gets released to the floor in the form of written ECO's (Engineering Change Orders).  Sometimes these come with rudimentary drawings, sometimes not but all the information to do the modification is contained in the ECO (which us what drives the drawing changes)

Edited by Juggernut

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i usually compare drawings and model to scaled real plane pictures. as many i have as better. most drawings i have checked have problems.i agree with you that 100% is impossible. but in scale models its impossible to replicate everything at such a levell. i wish tamiya is doing all subjects i want to build.

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After prototyping, the lofting department turns the vellum drawings over tothe tooling department that makes the  tooling, jigs and fixtures so the production aircraft is true to the drawings, modifications and all.  We then can use paper drawings to actually build the aircraft.  The critical measurements are already established in the tooling, fixtures and jigs.  Been there, done that....  Got several Sikorsky T-shirts.

 

Try facelifting a car when half the CAD models don't match what's in production.

 

My favourite was a car that moved factory, then the bumpers wouldn't fit. One factory had been building with the front members out, one down one up. So they bodged the tooling to make it work. When it moved factory they fixed the tooling...

 

Another thing on checking kits against drawings - are you checking against the drawing that the kit tooling was made from? If so, maybe both are wrong

 

I think it's best to find something that matches the dimensions then work using as many photos as possible

 

Unless you want to avoid hassle that is, then choose something with as few photos as possible - then no-one can prove you wrong

 

Richard

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As a general rule, I wouldn't trust any drawings 100%. Having worked as a mechanical drafter/designer for many many years, I can say that drawings quite frequently don't match what's actually produced. I played with the idea of creating a drawing in 1:1 scale of the Jagdtiger, and actually made some decent progress on it, but really accurate dimensional data of components used, is just about impossible for me to find, so I stopped working on it.

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It's very difficult to trace drawings of actual aircraft manufacturers even if they are known to exist. The warbirds community constantly churn out rebuilds and replicas of aircraft but how and what drawings they are using seem to be a closely guarded secret.

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If you can find out the frame and rib locations, usually they are identifed by their distance from a datum point somewhere in space, these can be very useful in plotting out your own drawings or CAD, then it is a bit like joining up the dots. Sometimes you hit gold like the Montfortan book on the Spitfire, but otherwise if you want the ultimate data, be prepared for hundreds of hours of research....

 

Or a LIDAR scanner!!

Edited by wunwinglow

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