F4U-1 Structural Framework

[cvairwerks]

Ambaryerno: What is the drawing number for the one with the ordinates? Easier for me to work with the full drawing as I might need to pop over to other referenced ones to determine answers. I'm pretty sure I know what the answer is going to be, but need to verify from the print first. Hate giving out erroneous info....

I missed seeing the last post about the tape sketch you did. Have a number of posts on this board and another that I didn't get notifications on. I'm sorry that I'm so late answering. To your question, the tape should be running with the 1.5" dimension the same as the 3 3/8" dimension on the tube. Sometimes, not all the fabrication instructions are on the prints and some things are simply assumed. I can't be sure if the tape was supposed to be applied to the tube itself or the strap. The drawing doesn't specify and that information may have been given in the assembly paperwork that the factory person was working off of. The reason for that tape is to proved a cushion and an electrical break between the strap and the tube to prevent galvanic corrosion.

 

[Ambaryerno]

C cvairwerks The drawing with the ordinates is 10201.

I've actually more or less been able to move on from the tape issue. Basically, I'm not going to bother with it because it honestly wouldn't be visible. I'm going to be simplifying where I can, IE by not modeling bolts and rivets in interior areas that wouldn't be visible.

 

[MIflyer]

Here is something.

 

[cvairwerks]

No sweat on the tape stuff.

I can see what they are doing, but need some time to figure out how to describe it and not sound like an idiot! Give me a couple of days.

 

[Ambaryerno]

My thought is if I can figure out how to layout the shape from the ordinates, I can then use that to create a curve I can then set as a path for Blender to extrude the cross section around. I just have to get past that first part. There are also CAD modeling plugins for Blender if that would help facilitate this.

I FEEL like I'm close to having it; The grid shown in the drawings does appear to coincide with the actual scale in inches (thus 40U = 40in above the horizontal reference). There's just something missing in my by brain about connecting the ordinate to the correct respective abscissa.

 

[Ambaryerno]

I actually think I've got it. I was looking at it wrong, and trying to match the written ordinate with a written abscissa.

Instead, the column headings are the respective ordinate/abscissa for the indicated point. That's what covers the points that don't neatly line up on the grid. I just tested with Excel and it works.

All I have to do is make the line, and then bring it in the thickness of the skin to find where the actual curve of the frame is.

 

[cvairwerks]

Think I've got it... Have to divorce the ordinate and the abscissa charts from each other. They are plotted based on different 0 references. If you plot the ordinate chart, you get the upright OML, while if you plot the abscissa chart, you get the OML on it's side, looking from the rear to the forward. and the ordinate chart doesn't care about the viewing direction for a single line set.

Plot the ordinate chart, using the ordinate reference number as the Y axis and the decimal number for the X axis. For the abscissa chart, do it the opposite...plot the abscissa as the X and the decimal as the Y value.

The screen grab is just a reference to tell you the orientation of the coordinate system for whichever set of lines you want to plot. That allows you to overlay the various stations on the same system and get a visual reference to how the fuselage contours fit together.

 

[cvairwerks]

Looks like we both came to the same basic answer about the same time.....

For ref..in this, the OML is of the fuselage structure and would be the same as the IML of the skin.

 

[Ambaryerno]

Ta da. Bulkhead 186. The hardest part is indexing the X and Y axes and not reading the wrong line or column. Also, some of the numbers are slightly smudged/excessively thick making them hard to read.

With this, I think I can now get my frames and bulkheads correct (I MAY need to revisit some of the other parts because I was trying to manually kludge a few things when they didn't fit as expected). I now just need to model this in Blender, covert from line to curve, and array my cross-section piece to follow it around. I can then cut out the parts where it crosses the longerons, and separate it into the left/right, bottom, and turtledeck segments (I want to make it modular so I can "swap out" parts to account for changes over the course of development, IE the later turtledeck without the windows).

 

[GregP]

You can get a pretty good idea here:

 

[BobB]

A guy who worked in the Bell Bomber Plant in Georgia on B-29's told me that their offices were not air conditioned and by afternoon you would find that the drawing paper had stretched or shrunk enough that you could see the measurements were off on linework that you had done in the morning. Designers were given loft lines that they traced onto their drawings. Ideally, Tooling would be given metal plates that the loft line drawings had been photographically transferred to and would use those in building their tooling but sometimes the tooling wasn't perfect. If the tooling and drawing didn't match, you were building parts to the tooling, not the drawing. If a problem became obvious, the tooling might be fixed or it might be decided that the drawing had to be changed to maintain interchangeability with all the parts already made.

 

[Ambaryerno]

So here's a conundrum:

I've been working on remodeling what I already have to match the ordinates given in the blueprints, and the actual measurements give on the parts sheet. The bulkhead itself worked out just fine, but I'm running into problems with the armor plate and its formers.

You can see here the contour for Station 186 itself, and the window cutout. These lines are drawn in using the ordinates themselves. The armor plate was modeled using the measurements given in the blueprints. Which means this SHOULD be accurate. The problem is that it's leaving a quite noticeable gap at the top (about 3/8in). However, you can clearly see there's no such gap in the actual machine:

The former is especially a problem because going by the measurements given on the part sheet, the bolts that ought to be holding it to the back of the armor plate wouldn't even pass through them!

So the question is what gives? Did I actually model something wrong that I'm just missing, or is this an error in the blueprints? Or is the countour given in the ordinance flexible and can be adjusted to the actual shape of the bulkhead and formers?

 

[cvairwerks]

Looks like for the early s/n airframes, the armor plate was floated in with using the side windows and frames as the locating points. 02449, which the photos you reference, is c/n of 297, so armor installation on the 186 bulkhead should be via drawing VS-10266. Local notes at C12 and D12 give the jigging info. I suspect that there was a bit of variation in getting all the tooling built for the various production locations and there was a bit of parts floating that had to be done until everything was on hard tooling for all vendor locations.

 

[Ambaryerno]

Looks like for the early s/n airframes, the armor plate was floated in with using the side windows and frames as the locating points. 02449, which the photos you reference, is c/n of 297, so armor installation on the 186 bulkhead should be via drawing VS-10266. Local notes at C12 and D12 give the jigging info. I suspect that there was a bit of variation in getting all the tooling built for the various production locations and there was a bit of parts floating that had to be done until everything was on hard tooling for all vendor locations.

So if I'm following you, model the parts per the sheet and adjust the final positions and contour of the skin to fit?

 

[cvairwerks]

Hard to tell for sure. By the notes, it looks like the armor plate was floated in to the bulkhead using the two side glasses to provide the final vertical location. Kinda hard to be sure after all these years and not being a Vought guy.
Vultee, Stinson, Consolidated, Convair, GD and now some Lockheed, are in my normal work wheelhouse. Everything else I deal with is based on industry practices and known historical information for the build times, combined with historical company processes and practices and guidance from other restoration guys. Been doing this since 1980, but still lots to learn and have better understanding of. I do make mistakes and sometimes have different understandings than what the original design guys were thinking. It sometimes is hard to figure this stuff out simply from drawings and not having parts to play with, but it's the best we can do. If your aren't building a flyer, then close enough can be good enough....Remember that perfection is the enemy of progress! Create on!

 

[Ambaryerno]

Well, this is what I've got now:

I've reached out to the guys working on that Birdcage, as well, to see if they could shed some further light on it.

 

[cvairwerks]

Chuck and his team are great guys.

 

[Ambaryerno]

So does anyone have any suggestion for resources when Aircorps Library either doesn't have a drawing at all, or what they have is so faded as to be illegible?

 

[bse7entn]

You can try reaching out to Ester with the sheet number but chances are if it's not online, they don't have it. Still may be worth asking the question.

For faded drawings you can try going into an image editor and see if there's any information to bring out through levels adjustments, find edges, unsharp filter, or even just inverting the image. Sometimes it's helpful, sometimes not.

 

[Ambaryerno]

They suspect those drawings were never scanned to microfilm, so short of finding someone who actually has a complete set of originals that somehow survived I'm probably SOL there.

My next thought was someone who actually has access to one of the actual Corsairs to see if I can get photos/drawings from them. I've tried reaching out to Chuck and his team but haven't heard back yet. Classic Jet Fighter Museum in Australia recently restored a very early Birdcage, but their website isn't working, unless someone has contact information for them.