F4U-1 Structural Framework

[cvairwerks]

- CATIA V5 25 years ago - are you sure about this???

CATIA V5 was publicly released in 1998. Because we were early adopters, we got an initial version in 1997. We probably had between 10 and 20,000 users in the company.

 

[J_P_C]

CATIA V5 was publicly released in 1998. Because we were early adopters, we got an initial version in 1997. We probably had between 10 and 20,000 users in the company.

thanks for information - i thought with 15 years of experience i'm old user

 

[Ambaryerno]

I've got some good progress coming along now. To do the structural framework I've decided to "build" it the way the real thing was, so I'm modeling each part separately and "assembling" them. However, I've got one part I'm having a bit of trouble with:

I'm currently working on part # VS-17579. It's the mount for the boresight on the Birdcage models, and I'm having a bit of trouble trying to read the drawings. Especially the socket/receiver part of the assembly.

Based on the parts list, the assembly has three components: 17579-1, 17579-2, and a cotter pin. 17579-2 is clearly marked on the drawings, but unless I'm missing something 17579-1 isn't. On most of the assembly parts I've had so far, each part is shown separately on the drawing, but that's not the case here.

I was hoping photos of the actual part could help me interpret what I'm seeing, but I'm having no luck at all finding any.

Has anyone actually seen pictures of this assembly that might be helpful in understanding the drawings?

 

[cvairwerks]

This is an easy one that trips newbies up quite often. If you look at the parts list, right above the title block, for the -1, to the right there is a note that say to make the -1 from a -2 casting. The -2 is a raw casting, as it comes from the foundry and would have had the sprue and the parting lines already trimmed to a point, but not flushed, as that would be taken care of as the part was machined.

There is also a note down in the effectivity box that has you look at specific note #6 and that tell you that for F4U-1 construction number 325 and on, the next assembly rolls to another part number, VS-19380, even though the effectivity box says something different. That means that there was an engineering change, and rather than revise the drawing and run thru the full release cycle, Engineering approved an assembly roll with a break in at #325 and any further changes to the drawing, would then incorporate all the revisions at one time and go thru the full release cycle at that point. It was a cost and time saving measure, as a release cycle could take as long as a couple of weeks or more.

 

[Ambaryerno]

I'm specifically modeling an early F4U-1 from that 1-324 range, and am aware of the change in #325 (though I may model parts for that range, as well).

So -1 isn't actually a separate part? It's just something being machined out of the casting?

I'd still like to see an actual photo of the real part as a visual reference.

 

[cvairwerks]

The -1 is the completely machined casting. If you look at the table, it shows that a -1 contains only one item....a -2 casting. Then look at the VS-17579 Assembly, it contains two parts.... a -1 and the AN380 cotter pin. If you were looking at it as a modern standard parts tree you would see:

VS-17579 Assembly (1) (my notes here...Contains: )
.... VS-17579-1 Fitting (1) (Contains: )
... ...VS-17579-2 (1)
.... AN380-3C-5 .... .. . (1)

To wrap it up, a -2 raw casting is machined to make a -1 fitting. The -1 fitting is combined with an AN380 cotter key to make a VS-17579 Assembly... It gets complicated when there are a large number of assemblies that make up an even larger assembly. In those cases, the individual components that make up the smaller assemblies are omitted from the parts tree for the top assembly, but are included in the lower level assembly drawing for each sub assembly.
Keep after it, you are starting to understand it all!

Excuse the periods in the last three part numbers, had to do that due to formatting issues with the forum software.

 

[Ambaryerno]

I was able to get some photos of the original part, and what I had was pretty close as it was. I've now completed it to my satisfaction. I do wonder what the point of the cotter pin actually is. It's not supporting another part or locking a nut in place, and the threaded part part is only half an inch deep so it wouldn't be able to secure the boresight itself (plus, this would all be covered by the outer skin with only the threads accessible, so it couldn't be inserted in the first place unless you were to get down into the cockpit tub and feed it through from under the seat).

 

[cvairwerks]

With a little digging....The 17579 is the 186 bulkhead bore sighting tool mount. Look at 17569, as it's the fabrication drawings for the bore sight "T" that fits that socket. The cotter key is used to orient the "T" in the correct position and the entire "T" is locked into place for gun firing by the nut that screws into the bottom of the 17579 fitting. Had to run thru the maintenance manual to find the bore sight procedure and it gave the drawing number for the bore sight tool installations.

Sometimes you have to follow a breadcrumb trail to find the info or data you need...

 

[bse7entn]

Was going to mention that you could do yourself a favor and not even bother with holes in parts if you don't plan on showing pins and bolts removing. Save on polys that aren't necessary. You could add a temp Empty just to point where the pin goes for later.

 

[Ambaryerno]

With a little digging....The 17579 is the 186 bulkhead bore sighting tool mount. Look at 17569, as it's the fabrication drawings for the bore sight "T" that fits that socket. The cotter key is used to orient the "T" in the correct position and the entire "T" is locked into place for gun firing by the nut that screws into the bottom of the 17579 fitting. Had to run thru the maintenance manual to find the bore sight procedure and it gave the drawing number for the bore sight tool installations.

Sometimes you have to follow a breadcrumb trail to find the info or data you need...

I know WHAT the part itself is. The issue is how would you get TO it? The boresight mount is buried inside the aircraft and couldn't be reached easily, unless there's an access panel for it I haven't gotten to yet.

 

[cvairwerks]

The maintenance manual section for the bore sight set up, says to unscrew the rubber plug from the fitting. The plug covers the hole in the belly skin.

The mount is attached to the 186 bulkhead at butt line 0 and is flushed to the bulkhead face, which in turn makes it flush to the IML of the fuselage skin at that location. Go to either 10256 or 19380 and look at the main view. It's looking aft at the bulkhead and if you look right above that, there is a view of the bulkhead, looking from the right. The fitting is at the right edge of the view, and various reference lines are carried up from the view looking aft. Vought didn't use water line/butt line on all of their drawings, so it makes it a little harder to give you a 3D location.

 

[Ambaryerno]

Was going to mention that you could do yourself a favor and not even bother with holes in parts if you don't plan on showing pins and bolts removing. Save on polys that aren't necessary. You could add a temp Empty just to point where the pin goes for later.

I'm only modeling holes that would in some way actually be visible because they're not covered by bolts, washers, etc.

The maintenance manual section for the bore sight set up, says to unscrew the rubber plug from the fitting. The plug covers the hole in the belly skin.

The mount is attached to the 186 bulkhead at butt line 0 and is flushed to the bulkhead face, which in turn makes it flush to the IML of the fuselage skin at that location. Go to either 10256 or 19380 and look at the main view. It's looking aft at the bulkhead and if you look right above that, there is a view of the bulkhead, looking from the right. The fitting is at the right edge of the view, and various reference lines are carried up from the view looking aft. Vought didn't use water line/butt line on all of their drawings, so it makes it a little harder to give you a 3D location.

We seem to be having a problem communicating.

The hole for the cotter pin is at the TOP of the socket of the boresight mount, and would be out of reach.

That's the part I'm trying to figure out. How do you insert the pin when its buried behind a body panel, and there's just a small plug in the belly skin?

 

[cvairwerks]

The cotter pin is permanently installed before the casting is drilled to the bulkhead. Should it get damaged after the aircraft is skinned, then a mechanic would have to climb into the belly of the fuselage, after removing whatever equipment he needed to for access, and then replace the cotter key and then reinstall everything that had been removed.

 

[cvairwerks]

As a general aside, when you look at an assembly drawing, unless there is a notation about only temporarily installing some part or hardware, it's meant to be permanently installed if it's shown on that drawing.

In the case of my job, we have quite a few things that our books tell us to only temporarily install them, as there are additional rigging tasks that can cause those items to have to be disassembled and adjusted. Once final rig is complete, it will detail going back and completing final torques, installing safety wiring or cables or other locking methods and then doing verification checks to see that the final installation meets the documents. A good example is all of our gear door mechanisms.

 

[larrymc]

I'm looking for good cross-section/blueprints of the F4U-1's structural framework for a 3D modeling project. There was a previous thread here a while back about it, but all the sources provided there are now defunct.

I've got good elevation drawings for the exterior shape, but nothing for the internal skeleton. Does anyone have scans/copies of the material cited in the old thread, or anything that would be of use?

Depending on your desired precision and accuracy, the attached cutaway may be of help. It is of a later mark, but I doubt the locations of bulkheads, etc, changed very much.
A detailed elevation with station marks will allow you to determine which parts are stringers, longerons, formers or bulkheads. Your envelope drawing will allow you to make authentic, if not make-it-and-build-it-accurate drawings for the structural pieces. Mostly, it would be "subtract skin thickness for the outline dimension, then graft in the cross-section of the material the structural piece is formed from.
It's been 50+ years since I wrote an IPB, but the descriptions in the replies seem pretty good. But unless you are looking for buildable accuracy, your envelope drawings, an elevation with station locations marked and some knowledge of the kind of extruded or stamped sections should be able to give you something that looks very right.

 

[Ambaryerno]

Things are coming along pretty nicely on the first bulkhead, but I've got a spot that I can't really figure out:

This is part of the cradle for the oxygen bottle. Specifically, I'm looking at CVC-3006-5-12. The drawing calls for 8 pieces of insulation tape, measured at 1.25in x 1.5in. It's pointing to this area here:

This assembly holds the lower and middle pair of straps in place (there's also rivets I don't have modeled yet). However, I can't tell on the drawing what exactly the tape is for, and that's the only place in the drawing the tape even gets called out. I don't think it goes between the tube and the inside of the strap end because there's no tolerance there for it. Does anyone have any ideas about this?

 

[cvairwerks]

The tape is wrapped around the spacer and between it and the bracket. The rivet goes thru all three parts. It's purpose is to allow the spacer to slide slightly on the structure as the tank strap is tensioned or released. It also provides some chafe protection, as the strap will move ever so slightly during flight.

 

[Ambaryerno]

The tape is wrapped around the spacer and between it and the bracket. The rivet goes thru all three parts. It's purpose is to allow the spacer to slide slightly on the structure as the tank strap is tensioned or released. It also provides some chafe protection, as the strap will move ever so slightly during flight.

Is there a way you can illustrate what you're talking about? It might help me see it better.

If it's supposed to go like this:

Can you see where there's a small problem with the lack of space? That loop of the strap is given a diameter of .75in, which is the same as the outer diameter of the tube it's going around (the tape is measured at .017in thick). And the strap itself is given as steel sheet at .035in thick, so it's not going to have a lot of give.

Also note the rivets don't go through the tape. They're too far apart.

 

[Ambaryerno]

Bringing back this thread. I stepped away from the Corsair for a bit for other things, and am back to it again now. This is where I currently stand:

Not pictured is the skin, and that's where I've got a bit of a problem:

I'm using the blueprints on aircorpslibrary.com, and the measurements for individual parts have been useful...when they actually provide them. However, for parts like the bulkhead and frame the blueprints themselves don't provide measurements I can really use to shape the curve. So instead, I'd been using screen shots imported into Blender as references, and shaping them over the drawings.
Therein lies the problem: Because these were hand-drawn, they're often not completely accurate. As a result, I'm not getting a nice, smooth curve on the skin between the frames, because the angles don't quite match up right.

The blueprints do have a page consisting of ordinates and abscissa, but I'm having problems making heads or tails of it. For example, it shows this as a reference:

My reading of it is to start with, say, 0, and find the ordinate that matches that position, and use that to place a vertex. Then do the same for 2, offsetting it to the left by the abscissa. The problem is there's places where the coordinates meet that don't correspond to the actual curve of the shape (in fact pretty much all of them don't). So I'm not sure how to actually use this to plot the shape of the curve for a given frame.

 

[SaparotRob]

I can't help you but that stuff looks cool.