WWII aircraft dimensioning question.
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I am looking at a set of WWII aircraft plans and some of the dimensions are fractional and some are decimal. Can anybody fill me in on why?
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I have no idea. But I´m wondering if those are P-40 plans
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Which is easier to write...
40/1000" or 0.040"
In fact what you'll notice is aircraft dimensioning is based around bolt sizes. So seeing fractions less than 1/32" is rare. It's to do with TPI on bolts because you can't get less than 3/32" diameter fasteners then it changes it's numbering system to reflect really tiny bolts used in electrical systems etc.
Also as an aircraft ages it's constantly compared to it original design. So if it's skin thickness begins at 0.125" and corrosion is removed in maintenance then it needs to be accurately measured. So the fractional method is too obtuse.
Finally, to bore you even more all Detailed/Fab Drawings by engineers will be in decimal because of tolerances blah blah blah
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@numbthumb said:
I have no idea. But I´m wondering if those are P-40 plans
What would make you think that?
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@unknownuser said:
Which is easier to write...
40/1000" or 0.040"
In fact what you'll notice is aircraft dimensioning is based around bolt sizes. So seeing fractions less than 1/32" is rare. It's to do with TPI on bolts because you can't get less than 3/32" diameter fasteners then it changes it's numbering system to reflect really tiny bolts used in electrical systems etc.
Also as an aircraft ages it's constantly compared to it original design. So if it's skin thickness begins at 0.125" and corrosion is removed in maintenance then it needs to be accurately measured. So the fractional method is too obtuse.
Finally, to bore you even more all Detailed/Fab Drawings by engineers will be in decimal because of tolerances blah blah blah
So a WWII plane might be designed with tolerances down to 1/64th but later more precision measurement of skin thickness might account for areas of skin or airframe wear? What I am dealing with are station drawing of the airframe and the dimensioning seems to be a random mix of fractions down to 1/32nd and decimals to 2point precision. If I understand the story the selling nation was selling equipment that was out of spec and the buyer was re-machining to a higher tolerance.
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What you could be dealing with is revised drawings. If there's a title block on the drawing, lower right, you'll see the info regards the revisions. If you've got a complete drawing it should have a separate page with flag notes detailing the revisions.
What's important about WWII aircraft is that they copied boat building standards then refined them to suit the higher tolerances needed for aviation. So seeing a mix of dimensions would be normal.
Sounds like an interesting project
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Interesting, yes. However trying to pick up differentiate a 3, 8, 5, on a coffee stained bluprint that has been photostated at small scale and then xeroxed and the scotch taped together is not fun.
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@numbthumb said:
@roger said:
What would make you think that?
Oh,just a hunch
This in fact: http://www.network54.com/Forum/149674/message/1317706027/Help+Need+info+ASAP,+Curtiss+blueprints+---Mixed+fractional+and+decimal+dimensioning--Why-Special agent numbthumb.
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At your service
Knowing how much details went into El Tigre, I really hope you´re planning on modeling that Flying Tiger. It would make a terrific model. -
@roger said:
What would make you think that?
Oh, just a hunch
This in fact: http://www.network54.com/Forum/149674/message/1317706027/Help+Need+info+ASAP,+Curtiss+blueprints+---Mixed+fractional+and+decimal+dimensioning--Why- -
@numbthumb said:
At your service
Knowing how much details went into El Tigre, I really hope you´re planning on modeling that Flying Tiger. It would make a terrific model.I am on my way to Thailand to meet up with a college friend whose father was a photographer with the American Volunteer Group of the Flying Tigers. He spent about 1,000 hours modeling a P40. I think I will not do any physical building myself.
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It looks like WWII and its high accuracy / high volume production was a tipping point between the low tech world and a high tech world. Planes designed at the beginning of the war were done on Inch fractions down to 1/32 or 1/64. However, anything done outside that fraction world was done in decimals. But it was not long before everyone went decimal. And finally, the hand held calculator put the final decimal nail in the fractional coffin.
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Here's more boring trivia...
WWII caused aviation to make a 25 year leap in 9 years. After the war USA identified that airspace had changed forever. They held the Chicago Convention whereby 52 countries (Allies) agreed to operate commercial aviation under one common standard. Whether manufacturing or maintaing an aircraft it abides to the same principals.
The US realised that the end of the war meant lots of pilots, airfields and airplanes would be useful for commercial transport. What's interesting from all this it that no matter what aircraft you work on it's maintenance manual chapters are the same. So repairing a Boeing structure is Chapter 52 or repairing a Cessna structure is Chapter 52. In essence, a mechanic/technician in aviation should be able maintain any aircraft according to these basic principals.
I need a life
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Rich, it is neither boring nor trivia. It is a fascinating insight into the dynamic relationships in history. But then, I think you knew that.
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@roger said:
I am on my way to Thailand to meet up with a college friend whose father was a photographer with the American Volunteer Group of the Flying Tigers. He spent about 1,000 hours modeling a P40. I think I will not do any physical building myself.
Any chances to see that model? Do you happen to have any pics of it, or are there any available on the internet?
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I will send an email and see if I can get a copy to post. I am not sure if the model still exists. It could have been destroyed or lost in a move, but I will ask.
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Thanks!
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Sad news folks the plane was stomped by a former spouse. Se la vie. But the good news is I will be able to show some photos one of these days.
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And sadly, instead of modeling I am going blind entering almost invisible data into a spread sheet so I can model, model model instead of read/model, read/model, read/model.
"Accountants and grocers, they weigh everything." --Zorba the Greek from the movie "Never on a Sunday"
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