Notes on Forming Patrol Wing Ribs (Plus Side-Bar On Rib Fit to Spars)

[sjt]

Bob recommends gluing mylar to 032. The mylar has parallel lines representing spars.
I used a table saw to cut mdf with parallel sides that were 32 -0.032 (patrol spar center line is 32 inches apart).
I then layed mylar on top of parallel side mdf.
The parallel lines can be lined up and over the parallel sides of the mdf .
They should be exact match.

Drill the tooling holes to forever match the mylar template with the mdf form.

I would recommend the tooling holes to be a little distance away from spar. I am trying to make sure there are no future issues with rivet to edge distances.
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I use the word parallel to emphasize how the parallel sides are of use during assembly


image_11022.jpg Those parallel sides are at right angles to the table during the assembly phase.


Rough mark the top and bottom of the airfoil. Use a jig saw to cut close to the edge. Routers only can take off a little at a time.

After routing - the mdf form has two parallel sides that are exact, and two routed sides that follow the mylar - aluminum template.

I even made mdf forms that had notches for the flutes.
In the picture below form block 3 has two dowel pins holding aluminum horizontally. The rubber holds aluminum down.
Using a wood dowel flutes can be made. The assembly is held firm with the press.

LIke Spruceforest above a lever can be used to make sure flanges are 90 degrees.

notches.jpg

Fluting pliers will work. You will find that the first rib will take an hour to flute. Once you get the hang of it , it will only take two minutes.



Consider investing in a company that makes mdf:

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[geraldmorrissey]

Does my heart good to see scratch building skills being passed on. On other hombuilding sites I visit, old timers complain that scratch building is dead and gone. Not among the Bearhawkers.
Gerry

[LBayliff]

I'm just starting a Patrol scratch build and am planning my manufacturing process for the wing components. I have a stupid question regarding bend dimensions on the wing rib flanges. What are the finished dimensions on the bent flanges meant to be?

On drawing 3 Bob specifies 9/16" flanges bent at 90 degrees however, in the booklet he recommends offsetting the rib form profile by 9/16" from the form block to draw the flat pattern for the ribs. In this case, the bent flanges would be slightly less than 9/16" due to the material consumed in the bend. Furthermore, I don't see bend radius specified for the rib flanges, although I would assume it would be the same as that of the spars at 0.1".

Thanks for posting your notes and Youtube videos of your build! They've been a great resource.

-Lane

[sjt]

I found this youtube video:

https://www.youtube.com/watch?v=h9fxo95D4Ik

a number 7 drill has about the right radius.


anyways the radius chamfer is a short cut , a square edge is longer distance.

If anything, the flange would be the tiny bit longer then 9/16 if you use the washer trick.

[sjt]

The question we all get stuck on is :

Are you supposed to cut the master template on the inside or the outside of the line.

The answer is neither . It is the middle of the line.


Also I like the spray on 77 for attaching the mylar to a piece of 032.
77.jpg

I cut to the outside of the line and slowly file to the middle of the line. You must leave some of the line.
Others might do it differently.

I also am very fond of 1 inch mdf as compared to the 3/4 inch stuff



As a rule we all start out with O.C.D. You have to remember we are building the wing with a plastic mallet.

hammer.jpg

[LBayliff]

Thanks for your reply Stan. That's all good information and clears things up for me. I realized I had gotten things mixed up with the bend acting as a shortcut, it makes sense the way you explained it.

How did you set the bend radius? I suppose one option would be to router the edge of the form block with a router using a 0.1" radius bit. In Bob's booklet he indicates setting a radius but doesn't give a dimension. The only radius dimension listed is on the wrong side of the from block and at 1/32" which would be too tight for the material:

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I'm also realizing the OCD needs to take a back seat to practicality at times. Maybe I'm overthinking this. Thanks again for your input.

-Lane
Alexis Creek, BC

[sjt]

If you buy the 1 inch sheet, you can make one form block instead of two. You can use both sides for forming left and right versions of the wing rib.
No need for a router just round off the hard edge with a sanding block.

Some times Bob says things that might mean something different that what you think.
I would take the 1/32 as an absolute minimum Not as a goal.
Another example is he gives the decimal distance for rivet spacing (1.021 inches). What he real means is 12 rivets in the 12 1/4 inch rib spacing. You need to make sure that the rib locations are 12 1/4 inches apart. And by the way you use 12 rivets. Get the 12 1/4 locations right. And then maybe use a rivet fan or a ruler.



I would buy a 4x8 sheet of quality 1 inch mdf from a store that sells hardwood (oak) and cabinet maker supplies. You will need every bit of a 4x8 sheet for making the form blocks.
Use some cheap 3/4 inch mdf (lowes or home depot or Canada equivalent) for things like the Backup block that holds the material still while whacking it.



mdf.jpg

I might have used a router on what Bob calls the backup block. I wanted to hit with the plastic mallet with a glancing blow.

I used a flexible ruler and a rivet fan for rivet locations along rib.

Bob says he wants a 1.5 inch spacing. So I figure how many rivets are used to to span the distance between the center of the C-web Spars. The number of rivets is what ever it takes such that the distance between rivet holes is about the 1.5 inches. Not exactly 1.5 inches.
fan.jpg

[sjt]

In some ways it is harder to make an airplane by hand if you grew up around a machine shop.

The truth is we use rubber mallets to make the wing. Sometimes I have been known to use a wood stick.

For me, I control the accuracy of my measurements by using a single tape measure. I hide the tape measure from my son so he does not use it as a hammer.

For the patrol the ribs are spaced 12 1/4. This single tape measure sets the 12 1/4 rivet distance across the entire spar. I will try to get the in between rivets right because I have OCD but
it does not matter. A rivet fan could have done the job with the required precision.

Is my tape measure accurate? Don't know. I do know I use it in the same way for front and rear spar and that is all that is important.

tape.jpg

[SpruceForest]

Bend radius in .032 2024T3/4 is 2x bare minimum and 4x desired. Any larger than 4x and you start running out of edge clearance for rivets, so I targeted .1 in 025 and .1-.125 in .032 stuff. If you rout at .1" (~3x), actual radius after forming against the grain will be closer to .125 in .032, which is ~4x. 1/10" in .025 or .020 will get you to pretty much .1 formed radius.

Forming to 2x risks cracks in thicker stuff or ripping of material in thinner stuff. If in doubt, buy a radius gauge set (good to have in any case) and check what you are producing off a sample form block. I NDI'd my first couple nose and center ribs... easy to do and helps with piece of mind where it's going to be a challenge to set eyes on once the skin is on. Same goes for all the bends on flatwork in the flaps and ailerons - avoid too tight or too loose a radius. Finally, what Bob says is generally good guidance and 1/10" seems to be about where he draws the line for wing ribs.

Inexpensive .01-.5 in gauge set:

https://www.amazon.com/dp/B01E633F8U

[LBayliff]

Thank you, this is the information I was looking for. I'll purchase a radius gauge like you recommended for the bends. I'm considering investing in a cnc router to produce the rib profiles and other sheet metal aluminum parts. There are some good hobby grade options out there nowadays for under 10k and it seems the savings in time would make sense. As per your notes regarding precision craftsmanship, I'd like to eliminate as much human error as possible from my parts.

Thanks again for your input, I appreciate the effort you put into documenting your work.

-Lane

[Bcone1381]

As you progress with drilling I am reminded of a reason why I quite scratch building. Make drilling jigs to drill all repeatable holes so you have some repeatable dimensions established. I'd make one for that 12-1/2 inch spacing with the 12 equally spaced holes.

I did not do this. When I made my rib attach angles, I match drilled them so I had no repeatable standard to them and each angle "belonged" to a specfic rib and specific backer plate at a specific location on my spar. Keeping track of that was impossible. Your goal is to have a box of attach angles and 1/2 x 1/8" backer plates that are identical to each other and will fit every rib and every spar backer plate. It needs to be drilled with a jig.

[sjt]

patrol is 12 1/4

[sjt]

I copied N3uw with his "story pole " idea.
I bought an extra length of capstrip material and made a template. The important thing is getting the 12 1/4 spacing correct.

You can never have enough clamps.

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I made a transfer punch to make a dimple

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