Can yall verify rib form block size ?

[fairchild]

I will be making my first rib form blocks next week. (I hope)
Do I remember someone here saying that when Bob designed the master rib form (drawing sheet #4- on the mylar) that he intended that the form block
dimensions be exactly the same as the master rib ? That is--- route the blocks right off your master rib 2-nd copy so the form blocks and the master rib
are exactly the same size.........(and the finished ribs will be .050 inch taller (.025 x 2) than the form blocks and also therefore the master rib pattern)

I looked and looked and couldnt find the post that had that comment......
Just wanted to make sure before I make chips !
Thanks ahead of time !
Tim

[Bcone1381]

My belief is that the sheet 4 mylar represents the finished wing profile. I picture the skin of the airfoil shape represented by the outer black line on the drawing. Your form blocks are going to be duplicates of your master rib. So, if the master rib is .050 smaller than the finished airfoil shape, the finished skinned wing will duplicate the exact dimension of the mylar sheet. But, if one made the form block to conform with the mylar sheet, leaving the black line, I don't think its enough to affect the outcome.

[Chris In Milwaukee]

Either way, you're building a one-of-a-kind wing for your plane. As long as everything you build is based on the forms that *you* built, then everything will be just fine. If you were using nose ribs built from my forms, ailerons from Brooks' form, and center ribs from the factory, and bought spar blanks from another builder, then you may run into some dimensional inconsistencies.

So don't dwell too much on it. Start cutting and bending parts, and life will be good!

[Glenn Patterson]

All our templates were made to the line and with the thicknesses of material the variance is 2 layers thicker on each side. We built following the methods of the day.This may be worth a conversation with Barrow's if no one has a definitive answer. If the template is the skin line then that would take .096 out of the rib and is a weight savings considering the number of ribs. Bob is good to talk with and has helped with some of our questions along the way. My first question was the angle of the lightening hole as I could make 45 degree dies with available router bits. He said don't worry it springs back some and it will be good. He helped with sizing the tubes to mount our re-purposed Cessna 337 engine bed mount for a Continental IO-360. And few other queries along the way.
Maintaining the wing shape and especially getting the leading edge tight to the wing shape is critical. The shape is critical and if it is adjusted by thicknesses it still is the required shape. Make profile blocks of the spar shape for your wing rib shape & height so that the ribs fit the spars. The comes comes the next question of joggle the rib to tuck the flanges under the spar or have the flanges go over. Either way is okay. We made the spar flanges matched to the rib flange so the ribs were joggled to tuck between the spar flanges.

[S Lathrop]

I made the rib forming blocks to Mylar drawing. I found that my spars matched the ribs just fine. This was true of both spars and the spars for the ailerons and flaps.

You can confirm this by checking the drawings for the spars against the rib form block.

[fairchild]

i think i understand that if the wing "shape" is scaled up or down- it is still the same airfoil. However there are lots of other internal wing parts which probably have
dimensions called out somewhere on the plans.... so i dont want to accidentally scale up JUST the ribs. Perhaps i will E-Mail Bob if no one has a definite answer.
It would SEEM logical that Bob may have down-sized the rib form specifically so we WOULD use it to copy via router the form blocks. But maybe not---- only guessing.

In a related question--- drawing 3b which shows the ribs (1/2 scale) shows a drawing of the rose rib. If drawing 3b is to correct dimention--- I should be able to
compare the nose rib outline with the master rib and see if my master rib outline (page #4) is slightly (.050) undersize or if it is exactly the same size----- RIGHT ?
EXCEPT---- at the bottom of page 3b (rib drawing) bob has written

"see full size wing rib form block drawing #4 --- scale drawing for dimensions not shown"

Is Bob telling us by this that the drawing of rib on 3b is NOT an accurate outline for the rib--- and to refer back to the master rib for exact geometrical shape ?
That looks like to me what he is saying.

And to determine the front to back length of the nose rib---- the rear edge appears to butt up against the forward spar web plate. (and get riveted to the attach angle)
When I look at the master rib drawing #4----- there is a line labeled "main spar". But the main spar is a sandwitch ---- which layer of the sandwitch does that single
line correspond to ? The .032 bent "C" channel ? Is that taken to be the "center" of the spar sandwitch and what he used for the line on drawing #4 ????
Which layer I take the be the line on drawing 4 will determine how much sheet metal tail sticks rearward on the nose rib --- right ?
It looks like it would have helped is Bob had been slightly more verbose on his notations. But i am new to blueprint reading ......

so I guess the operative question is---- is drawing #4 the finnished outer shape of the wing after skinning ? or the form for the rib form blocks having the various
outer sheet metal layers all ready subtracted out ?

Tim

PS- looking at Eric's page---- he sanded his master rib form to the INSIDE of the line on the mylar. i shot for the outside of the line-
but im probably between the outside and the middle of the line. Then he mad his dorm block to match his master form.
Wonder if I need to sand to the inside of the line ????

PPS- I had drawing 3 - showing the ribs--- enlarged at the blueprint place to full size. I just laid the mylar rib form (#4) over top of the
full size enlargement of #3----- its fairly close -- but the pin holes dont line up--- off by 1/4 to 1/2 from one end to the other.
So it APPEARS that the drawings on page #3 are sketches and not exact accurate precise drawings. Thats assuming my blow-up
of drawing 3 didnt get distorted during the blow-up process.

[Glenn Patterson]

Use the mylar full pattern for the wing rib patterns. We made a mylar copy on a light table and glued that to the template. 3M 77 spray adhesive works perfect to secure the mylar pattern to the MDF. I did manual engineering drawings for years and a person tries to be accurate but the work is human based. Most engineering drawings came with a std disclaimer to follow the drawing measurements and not to scale the drawing. When CAD came along it was easy to transfer a part page to page and adjust it for the detail. We had a large format copier for drawings that gave a minor distortion & if copies of copies get made then more distortion creeps in. The BH drawings that arrived were large format copies that are likely copies of copies.

We drilled the jig pin holes in the master wing template and that way any pattern spun off was made using the jig pin holes for drill guides. Using the master will give consistency for the locations for all the parts. Bushings are discretionary as the holes are only used maybe 3 or 4 times and they will be fine without bushing if used with care. We used 3/16 screws with the head inset on the backside, fender washers and wing nuts for the jig pins. The master template is a good place to mark the rivet lines on so that they are carried onto the hammer form. The rivet rows are marked on the hammer form & the rivet rows marked on the rib as they are formed w/ magic marker. A person can see where the rivets rows are on the rib flanges & can safely flute between the marks to stay away from the rivets. The marker comes off with alcohol.

I found the when scale did not agree with the measurements for the tail feathers & rudder then I used the grid method to scale the drawings. For example if it said 12" and scaled at 11" then the grid is done by drawing parallel lines on the 12" measurements then the the ruler is inclined so the 0 &12inch are on the parallel lines lines then the inches marked off. Same in the opposite direction. This puts the grid on the drawing at increments that make the drawing scalable to the designers intent. The work table was painted white then a white one inch grid applied. This allows part to be drawn the full scale on the table using the grid on the marked up drawing. The critical dimensions are followed and the curves made by the way they cut the lines on the grids. This works good even if the hand drawn part is to scale and has to be blown up exponentially for a construction pattern. The horizontal stab & elevator was drawn as an assembly on the table. The same pattern make identical left and right parts.