Finishing the Aft-Wingribs (Dec. 28th, 2001)

After cutting and pounding was done, the raw aft-wingribs were sitting at the shelf for about a year or more. However before I can mount then at the wingspar some finishing-work has to be done.

I'll put two indendations in each of the aft-ribs. Most of the spamcans have them and they considerably increase the stiffness (=increase buckling resistance). A nice side-aspect is that I have to pay no weight penalty for this type of improvement.

This shows how I grinded the negative matrix into the formblock. I used a router and a spherical bit. The edges are radiused and waxed so the sheet can nicely 'flow' in.

 

 

 

 

 

 

 

This shows how I clamped the matrices. There's a kindof 'aluminum-cigar' tool which actually will make the dent. The tight clamping is to avoid distortions of the rib.

 

 

 

 

 

 

Two blows are quite right for the shallow indentation. The wooden block distributes the force evenly onto the forming tool.

 

 

 

 

 

 

 

 

 

Doesn't look so bad (the dents appear more pronounced at the pic as they're actually are [only about 3mm deep]). Now I have also to do the indentations at the mainspar-side and then form the flanges at the lightening holes. After this the flanges will be bent to exactly 90 degrees and any 'banana' effect will be removed by enlarging or reducing the flutes.

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Tuning the Nose-Wingribs (Dec. 24th, 2001)

The spars seem under control now. Unfortunately I don't have the material for the center-web at hand. So the spars are on a temporary hold.

What I can do now (without writing order checks) is mounting the wingribs to the spars. I'll start with the noseribs.

First task is to straighten and adjust the ribs. The flanges should be 90 degrees. When the ribs come off from the formblock, they're about 80 degrees and the whole rib looks more like a banana.

I made a simple tool (no, not my own idea). It's a piece of wood with a saw-cut at the small side as deep as the flange's width. The tool slips over the flange and serves as an lever to 'fine-tune' the flange. Astonishingly, after I got the flanges perpendicular, the banana-effect was gone and the rib was laying dead-flat at the table! Anyway this is hell of a work. I spend half an hour for the first rib. So there are another 29 noseribs left and also another 30 aft-ribs (which are more twice the size) this job will keep me busy for the next 30 to 50 hours (or for almost the whole month of January).

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TheMainspars (Dec. 23th, 2001)

This is how ~my~ spars intersect.

If there will be no more unexpected surprises this appears to work.

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The Mirror-Inverted Mainspar (Dec. 20th, 2001)

The vertical stabilizer found a dry and warm place below the ceiling of my workshop.

There it will stay until next spring when outside temperatures allow for spray-priming the inside of the skins and the rib-construction

 

 

 

 

 

My next endeavour is the mainspar-assembly. The sparcaps are already cut, also the main-sparwebs. Then I'll test-fit the wingribs. Materials for the center-web I'll oder at a later time. Also this part has to wait for priming until springtime.

---W A R N I N G --- DO NOT LOOK TOO CLOSE to these pics!

Only until I tried to assemble the spars I realized that I made all four sparcaps ~mirror-inverted~. I think there's not a single Sonex builder who didn't once made two left parts instead of a left and right one, or a mirror- inverted one. But ALL FOUR of these very expensive parts - I think this is good for the Guiness Book of Records.

How could this happen?

Besides of intergalactic stupidity there may be probably also another explanation:

When I was a student, I learned technical drawing the traditional way (pencil and fountain-pen). When I drew 3-vies of a part then there was (and still is) a standard (DIN) which tells how the views have to be positioned at the page: first you draw the front view, then rotate the part 90 deg down, this is the top view, turn it back and then 90 deg to the right, this is the side-view. I never had any problems to decipher a plan using this style. The Sonex plans are different. Often the views are located just where there is space at the page (or at least I could not discover a consistent method and also my builder buddies couldn't). Often the only way you can find out what side the plan shows is looking for hidden lines.

Now that the disaster has happened, what can be done?

- trashing the sparcaps and buy new ready-machined ones (unhappily Sonex doesn't sell the raw material anymore)? - would cost a little fortune, there's no budget for this

- burying the whole project? - I'm not far away from this solution

- build the spar as it is: mirror-inverted? - as strange as this solution looks at the first view, it seems do-able.

The spars are identical to the 'real' ones except that the 'handshake-part' where the spar-halves meet is inverted. Where the plan shows the left spar in front of the right one it is inverse for mine. Now I have to look out like hell not to make other faults which would finally ruin the spars (and probably 50 hours of hard work).

This is my left spar flying behind of the right spar.

more to come...

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Is there any Simple Thing in this project? (Dec. 11th, 2001)

Have just match-drilled the the second set of the left horizontal tail skin. My method works - but I'm still not really satisfied. Some of the rib flanges I couldn't hit dead-center. Max runout is about 1.5 mm. Usable (I think), but far from perfect. Doesn't this leading edge look sexy? no distortions, no dents (so far). How will this part look first when it's polished to a mirror-like gloss! I still sympathize with solid-flush riveting the top surface. However I'm a bit hesitant with that - one bad blow with the rivet gun could ruin (not only) my whole day. An alternative would be using flush blind rivets. But I doubt if on a rainy day my horizontal stabilizer would not fill with water (solid rivets are water-tight).

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Refining the Horizontal Stabilizer (Dec. 8th, 2001)

Now that I have two horizontal tailskins left over for training, I test-bent the leading edge of the right skin with hands only. This is what came out

The light reflections tell that the leading edge is not of uniform radius. The skin fits nicely and at other lighting conditions the deviation from the theoretical radius is almost invisible. The next skin I'll test-bend I'll use a solid wooden plank.

This is my refined sequence of building (so far):

1. at first I'll bend the undrilled skin

2. then attach skin at rear spar (arrow shows pilot holes alread drilled)

3. mark the rib locations on inside if skin

4. center-punch the rivet holes on inside of skin

5. drill from inside of box wherever possible. The skin can be lifted up enough without distorting the leading edge

5. where drilling from the inside is not possible, I'll use the centerpunch-marks which are visible at the outside, counter- center-punch and then drill from the outside.

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Building the Horizontal Stabilizer (Dec. 5th, 2001)

The tailfeathers are some of the easier parts to build. This is one of the reasons you can buy 'tail-kits' from several kitplane manufacturers (RV, Zenair). If you stumble with the tail then you probably better cancel the idea of building a complete airplane. After this introduction here's what I experienced:

Some months ago I already had cut and pilot-drilled the horizontal tail skins. I had some doubts if all these rivet holes will at a later time line up with the rib flanges...

Then I build the horizontal tail's internal truss construction.

At first I draw the main lines on the table, then clecoed everything nicely together. I'm sure the thing is within 1 to 2 mm of precision. All ribs are perpendicular to the table's surface. There's no internal tension in this construction.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

So I test-fitted the skin tonight

The deviation of the pilot-holes of the skins are also less than 2mm from the plan's dimensions. Before I will start drilling, I decided to mark the skin's holes using a sharpie pin on the rib's flanges at first. This was a very good idea. Most of the skin's holes were centered at the rib flanges -

 

 

 

 

 

 

 

 

 

BUT some like this one...

 

...or this one

 

So the consequences are clear like a German November's day: throw another two squaremeters of aluminum sheet onto the scrap pile and start over again. Actually common sense could tell me that this way of construction will fail. Luckily I'm not a fast-build assembler. This poor guys are bound to the laser-drilled pilot holes of the skins and have no way out of such a misery. Making another two skins will take three or four days - actually nothing to worry for me.

This is my building sequence which luckily will prevent the above disaster:

I think the above sequence is as fool proof as it could be.

Lessons learned:

NEVER drill anything if it's not required for the actual building task. There's always a big temptation to 'finish' a part. As this example shows this habit may cause a lot of extra work.