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Author Topic: Taking a second look at the Plexiglas pieces - 2-3-V-2  (Read 60653 times)

Neff Jacobs

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Re: Taking a second look at the Plexiglas pieces - 2-3-V-2
« Reply #45 on: February 01, 2016, 03:09:15 PM »

OK, the edge you are comparing is 6cm call it 2.375. 
This means the difference in offset between 12 in radius and 18 in radius is now less than the line thickness.
So,  Lay a nice straight edge say an engineer's scale across the ends of the 2.375 inner chord and then use a caliper probe to the centre, the point of maximum deflection called offset.   If the offset is around .060 it's 12 inch radius and matches the radius of the Drawing.
If offset is more than .066 or less than .054  that's outside 10% and would appear to me to preclude it matching the drawing. 
Luck
Neff
« Last Edit: February 01, 2016, 03:10:47 PM by Neff Jacobs »
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Ric Gillespie

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Re: Taking a second look at the Plexiglas pieces - 2-3-V-2
« Reply #46 on: February 01, 2016, 03:28:38 PM »

If the offset is around .060 it's 12 inch radius and matches the radius of the Drawing.
If offset is more than .066 or less than .054  that's outside 10% and would appear to me to preclude it matching the drawing. 

Doing as you describe there's an element of "eyeballing" involved (my micrometer is too thick to fit inside a space that small) but the offset is between .056 and .058.
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Jeff Palshook

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Re: Taking a second look at the Plexiglas pieces - 2-3-V-2
« Reply #47 on: February 01, 2016, 04:09:43 PM »

Dick Janson has favored us by expressing his concerns that the artifact is appearently being compared at 1.5:1 here.   Surely it is worth a little time to rule in or out the one and only artifact we have, that I know of, that has a simple in or out cartiera.

I did as you requested and spent more than a little time trying to figure out how to double-check the initial analysis of the artifact.  We no longer have access to a Lockheed 10 window so I can't duplicate that comparison.  I agree with the need to make sure that the comparison of the curvature of the artifact with the curvature on the Lockheed engineering drawing needs to be at a 1:1 scale. The problem is, the paper drawings, if they still exist, are not accessible.  The best we can do is a photocopy made from microfilm of the drawings at the NASM Archive, but how do we make sure we're looking at a 1:1 print out?  I reasoned that if I scaled the curvature cross-section on the drawing to a 1/8th inch thickness for the plexiglas, the drawing would, by definition, be at 1:1 scale.  I did that and then compared the curvature of the artifact to the curvature on the drawing by overlaying the artifact on the scaled 1:1 drawing.  The results are shown below.


Ric,

Look again at your photo scaled+curve.jpg.  Closer examination of it shows quite obviously, I think, that the scale of the copy of the Lockheed drawing you are using is not 1:1.  The full-scale distance between each of the "station" lines showing distance between a chord line and the outer edge of the window glass (e.g., 1-7/16 in., 1-31/64 in., 1-17/32 in.) is 1 in.  Measure any one of these 1-in. distances with your ruler and you get about 3/4 in.  Or, take the the 1-7/16 in. measurement on the drawing (or any of the other chord line-to-outer window edge measuremennts) and measure it with your ruler.  For the 1-7/16 in. measurement labeled on the drawing, it measures about 1-1/8 in. using your ruler.

The ratio between drawing's labelled measurement and measurement by your ruler is about the same in both examples I've given:

3/4 in. divided by 1 in. = 0.75
1-1/8 in. divided by 1-7/16 in. = 0.78

Clearly, the copy of the Lockheed drawing you are using to compare the artifact to is not 1:1 scale.

This doesn't necessarily mean the curvature of your plexiglas artifact does not match the curvature shown in the Lockheed drawing.  Looking at the chord line-to-outer window edge measurements for the entire window as shown in your TIGHAR Tracks report on the plexiglas artifact, the measurements are slightly different for the bottom half and top half of the window glass.  The top and bottom halves of the window glass may not have had the same curvature.  The curvature of your piece of plexiglas might match the other half of the window glass.

Jeff P.
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Ric Gillespie

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Re: Taking a second look at the Plexiglas pieces - 2-3-V-2
« Reply #48 on: February 01, 2016, 04:32:18 PM »

The full-scale distance between each of the "station" lines showing distance between a chord line and the outer edge of the window glass (e.g., 1-7/16 in., 1-31/64 in., 1-17/32 in.) is 1 in.  Measure any one of these 1-in. distances with your ruler and you get about 3/4 in.

You're right, but if I scale the drawing to match the 1 inch station lines, the thickness of the plexi will be larger than the 1/8 inch specified. Are we to assume that the thickness of the plexi shown in the drawing is not drawn to scale?
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Neff Jacobs

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Re: Taking a second look at the Plexiglas pieces - 2-3-V-2
« Reply #49 on: February 01, 2016, 05:04:05 PM »

Ric,
Thank you  for your time and trouble.  I am satisfied  that the piece of plexiglass is approximately 12 inch radius which is the same radius and thickness of the Electra side windows in the drawing.  I think probably worth filing the photo against the 1.5:1 drawing and the rebuttal that radius was confirmed by the middle ordinate method.

As far as the drawing, in that era the drawing was likely a pen and ink drawing on tracing paper or vellum so blueprints  of the drawing for production work could be easily made.  In the case of an engineering change the thickness of the window being hard to draw with .070 ink lines may have been left slightly oversize since what the document was depicting was inner radius.

I would always advise use of written dimension  over drawn dimension especially in older documents.   
Neff
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Ric Gillespie

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Re: Taking a second look at the Plexiglas pieces - 2-3-V-2
« Reply #50 on: February 01, 2016, 05:39:07 PM »

Clearly, the copy of the Lockheed drawing you are using to compare the artifact to is not 1:1 scale

Okay.  Once more with feeling. I scaled up the drawing to match the 1" station lines and the curvature of the artifact is still bang-on.

Can we all agree that wherever the hell this piece of plexi came from it has the same thickness and curvature as Lockheed Part Number 40552 effective 1-15-37?

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Ric Gillespie

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Re: Taking a second look at the Plexiglas pieces - 2-3-V-2
« Reply #51 on: February 01, 2016, 05:40:43 PM »

I am satisfied  that the piece of plexiglass is approximately 12 inch radius which is the same radius and thickness of the Electra side windows in the drawing.

Thank you.
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Ric Gillespie

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Re: Taking a second look at the Plexiglas pieces - 2-3-V-2
« Reply #52 on: February 01, 2016, 05:56:01 PM »

By the same extension, then, it doesn't make sense to continue discussing anything else TIGHAR has found on Niku, does it?

Sure it does.  We do it all the time.

I originally expressed enthusiasm for going full court press on 2-3-V-2 because I believe that if it did come from Amelia's Electra, it could be a diagnostic artifact.

The problem in this case was that your premise was invalid. 2-3-V-2 never had the potential for being a diagnostic artifact.

Nonetheless, I think the re-examination you prompted had value.
« Last Edit: February 01, 2016, 05:58:15 PM by Ric Gillespie »
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Monty Fowler

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Re: Taking a second look at the Plexiglas pieces - 2-3-V-2
« Reply #53 on: February 06, 2016, 05:59:36 AM »

Something seems to be missing?

LTM,
Monty Fowler, TIGHAR No. 2189 EC
Ex-TIGHAR member No. 2189 E C R SP, 1998-2016
 
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Ric Gillespie

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Re: Taking a second look at the Plexiglas pieces - 2-3-V-2
« Reply #54 on: February 06, 2016, 01:29:23 PM »

Something seems to be missing?

Yes, an inappropriate posting was removed.  A Forum subscriber read a critique on another forum critical of our recent discussion here about Artifact 2-3-V-2.  He said that the critique raised several points that have not been discussed here.  Rather than raise those points himself he posted a link to the critique.   
I've read the critique in question.  The author's argument is that the "shatterproof glass" specified in the Lockheed engineering drawing is glass, not Plexiglas, but he offers nothing to support that contention but his own opinions and assumptions.  Plexiglas was certainly in use in aircraft applications as early as March 1936 when NACA began testing it in response to concerns about crazing (see http://nvlpubs.nist.gov/nistpubs/jres/19/jresv19n4p367_A1b.pdf) and Rohm & Haas was advertising its use in Lockheed aircraft in 1937. 
« Last Edit: February 06, 2016, 04:01:02 PM by Ric Gillespie »
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Jeff Palshook

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Re: Taking a second look at the Plexiglas pieces - 2-3-V-2
« Reply #55 on: February 07, 2016, 10:50:11 AM »

The full-scale distance between each of the "station" lines showing distance between a chord line and the outer edge of the window glass (e.g., 1-7/16 in., 1-31/64 in., 1-17/32 in.) is 1 in.  Measure any one of these 1-in. distances with your ruler and you get about 3/4 in.

You're right, but if I scale the drawing to match the 1 inch station lines, the thickness of the plexi will be larger than the 1/8 inch specified. Are we to assume that the thickness of the plexi shown in the drawing is not drawn to scale?

Ric,

Trying to tie up a loose end from the earlier discussion in this thread about the scale of the copy of the Lockheed drawing you have ....

I think I have figured out why your approach of measuring the thickness of the window on your copy of the drawing didn't work.  Looking again at your photo "scaled curve.jpg" back in Reply #40 in this thread, the thickness of the window you measured on your copy of the drawing appears to be slightly less than 1/8 inch, by perhaps 1/64-th of an inch.  Possibly the difference from 1/8 in. is smaller less than that.

The text of the 1996 TIGHAR report on the pieces of plexiglas (http://tighar.org/Publications/TTracks/1996Vol_12/40552.pdf and http://tighar.org/Publications/TTracks/12_1/PartNumber.html) says that Lockheed Drawing No. 40552 shows a change, dated 15 January 1937, of the thickness of the window glass from the previous 5/32 in. to 1/8 in.

Assume the drawing was drawn showing the window thickness as 5/32 in.  I argued up-thread that your copy of the drawing is 3/4 the size of full-scale.  This would make the thickness of the window  as measured on the copy of the drawing

    5/32  X 3/4  = 15/128 in.

This is slightly less than 1/8 = 4/32 = 8/64 = 16/128 in. and seems to approximately match what you measured for the window thickness on the copy of the drawing, as shown in your photo "scaled curve.jpg".

The thickness of the window should obviously be shown somewhere on Drawing No. 40552.  Note in "scaled curve.jpg" that there are two arrows on the drawing immediately to the right of the word "glass" in the "shatter proof glass" label which are set up to show the thickness of the glass.  If the writing to the immediate left of the upper arrow in this pair is the actual measurement, it is unreadable.  However, note that there is a circled letter "A" immediately to the right of the word "shatter" and also a circled letter "D" below and to the right of the circled "A".  These refer to notes A and D in the "changes" section of the title block of the drawing.  These notes were apparently used to track the changes in the thickness of the window (and also changes in the window material) rather than changing the actual drawing each time to show the new window thickness.  (At the very top center of "scaled curve.jpg", there is also visible what looks to be one half of a circle, probably another circled letter indicating another change note.  My guess would be this is circled "C", which would correspond to change note "C", indicating the change from plate glass to shatterproof glass.)

In doing this little study of the drawing, I noticed a couple errors in your transcription of the dimensions on the drawing and some other possible errors:

(1) In the transcribed version of the changes section of the drawing, Note D reads "thickness 1/8 was 1/32".  Based on the information in the text, Note D almost certainly should read "thickness 1/8 was 5/32".

(2) In the transcribed version, near the center of the drawing showing the curvature of the window, the overall height of the window is shown as "12-15/64  +0, -1/16".  However, all distances between "stations" for the window are shown as 1 inch except the bottom-most one, which is shown in the transcribed version as "31/64".  So either the fractional portion of the overall window height should be 31/64, or the bottom-most station measurement should be 51/64 -- can't tell which one is correct.

(3) (Possible errors in transcription)  At the top of the window, the transcribed measurements for the chord line-to-outer window surface are shown as 1-9/64, 1-13/64, 1-23/64, and 1-29/64 inches for the first four window "stations".  The corresponding differences between these measurements are 4/64, 10/64, and 6/64 inches.  This doesn't seem to make sense for a smoothly curved window surface -- the 10/64 difference looks to be out of place, making the chord line-to-outer window surface transcribed measurements suspect..

Jeff P.


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Ric Gillespie

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Re: Taking a second look at the Plexiglas pieces - 2-3-V-2
« Reply #56 on: February 07, 2016, 11:11:15 AM »

Thanks Jeff.  I think that all makes sense.
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Monty Fowler

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Re: Taking a second look at the Plexiglas pieces - 2-3-V-2
« Reply #57 on: February 07, 2016, 02:54:20 PM »

I'm glad you chose to moderate the language in your reply to my query, since I'm the one who started that discussion over in the other forum.

LTM,
Monty Fowler, TIGHAR No. 2189 EC
Ex-TIGHAR member No. 2189 E C R SP, 1998-2016
 
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Ric Gillespie

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Re: Taking a second look at the Plexiglas pieces - 2-3-V-2
« Reply #58 on: February 07, 2016, 04:37:44 PM »

I'm glad you chose to moderate the language in your reply to my query, since I'm the one who started that discussion over in the other forum.

I'm glad you're glad.  I have never been accused of being a moderate person and I am occasionally excessively immoderate.  I'm trying to improve. 
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Ric Gillespie

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Re: Taking a second look at the Plexiglas pieces - 2-3-V-2
« Reply #59 on: February 08, 2016, 09:06:56 AM »

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