Wing Rib Template

[Wolfpilot]

Greetings.

I apologize if this has been previously over discussed :-)

We started on the project this weekend. We are creating a master template in aluminum with the Mylar glues to it. So far we have rough cut it to within 1/16” and ready to trim finish to Mylar lines. Bob does not say in his manual, I reviewed past comments in the forum and Eric Newton’s Builder’s Manual but I am still confused if it really matters if the template (not MDF form) should be trimmed to inside the line or outside?

In Eric’s Builders’ Manual:
“…2. Using a band saw, cut the form block carefully, staying just to the outside of the line.”

But I am making a template, not the form block.

I completely understand the concept that this is our plane and as this is the template, all ribs will match. However will it make any difference further down the line as things come together? I know we are only talking about the width of the drawn line on the form and I do not want to over think it. But?

So in summary, in making a master template does it matter?

Thank you in advance.

Rocky & Angela

[geraldmorrissey]

Split the curve.
Gerry
Patrol #30

[sjt]

Middle of line is correct answer. You can see it latter on when you make a part that is to be made 31.66 inches (bearhawk patrol steel supports inside wing) . The driving spec is 32 inces between front and rear spar.

But if you take into account that 31.66+ 0.0625 rear capstrip+ 0.25 main spar capstrip + 0.032/2(half a main spar) + 0.032/2(half of rear spar) You get the sum 32 to center of spars.

I used a file to finish my template to the center of ink line. Half of the ink is gone - not all.

[sjt]

I am sure the correct answer is the middle. However, I do not think it really matters. You make the ribs first, then you bend the spar c-channels to fit whatever the ribs ended up being.

It is very hard for someone with a machinist background to get their head around the fact that airplanes are made with rubber mallets. When Bob has a number like 31.66 a machinst assumes it has to be made with high precision. The number is an artifact of the thickness of capstrips and half spar width. Bob just wants the center of the spars to be 32 inches apart.

You also see it in the rivet spacing spec. Bob calls out (patrol) 1.021 rivet spacing. What Bob is really saying is that the ribs are 12 1/4 apart and he wants 11 rivets in between ribs. You should try really hard to make the rivet location used for the ribs every 12 1/4 inches. After all the rivet holes for ribs are located on 12 1/4 centers put 11 rivets in between rivet holes for ribs.

That is a lot of words. Instead Bob just says 1.021 which is 12.25 / 12

p.s.
You do not always put rivets every 1.021 apart because sometimes there is something else that is more important like at the spar splices.

[Wolfpilot]

Thank you for the feedback. I am well aware of the old saying "You are not building a swiss watch, you are building an airplane." I just know it can't help to get some opinions before ending up with a lot of re-do as well.

Rocky & Angela

[Glenn Patterson]

A person can over think this until their head hurts. Take it just to the line is perfect. The math is very simple. Set the spars parallel and level at 32" centers in the wing jig by measuring from the topside of the rear spar web to topside of the front spar web at 32". It is the same as 32"c-c of the spars. Clean and simple. It also is much easier than trying to split a line or risk losing the line. We built our wing that way and it came out perfect and dead straight. Taking the pattern to the line and leaving the full line width visible will give the same exact same wing form. You are right in that it is not a Swiss watch. Keep it simple and most of all keep moving. It is easier to put a copy of the mylar wing form on MDF as copies can be spun off easily with a flush cut or template router bit with a router table. That will give an exact hammer form and one can make a spare full size working reference board that can be abused to layout jig pin holes & to cut up for spar bending templates etc. The master can can hang up and stay in good shape. I made a bunch of leading edge reinforcements out of MDF to keep the ribs from bending when the skin is wrapped tight around the leading edge. So a lot of value in an mdf pattern.

[Wolfpilot]

Again, Thanks for the feedback. Template completed and MDF templates and forms in process.

Rocky & Angela
Full Project Log is at:

https://eaabuilderslog.org/?s=AR-PATROL

[Frank]

The mylar drawing was made by running a pen around a template (labeled "Full Size Wing Rib Formblock Layout). My job was to reproduce that template, not make one that is .5 mm larger. The test would be to run a pen around my template to see if it matches the mylar, and it does. I'm working on the LSA and the prototype is noted for its light weight.

[Gr8apmech]

Bottom line, other parts must fit the master. Use same method you used to loft the wing rib when you loft the other parts. Measure measure measure.