This blocks were made at a CNC shop in my neighbourhood. I handed over
to them only a hand-scribbled sketch and got back beautifully precision-grinded
masterpieces. All four cost me $60. I'm very satisfied for what I got for
the money.Wing Attach Blocks (Jan. 15th, 2002)
The wing attach blocks carry the wing attach bolts which connect both halves of the wing. These are one of the most stressed components of the airplane. The Sonex plans ask for extruded rectangular 6061-T6 material for the attach blocks. I will deviate in this point and will use instead chromoly (42CrMo4 or as DIN-ISO code: 1.7225) steel. This will make the drilling of the bolt holes more complicated, but I think it's worth the effort (I suspect the aluminum blocks may wear out by the time).
This blocks were made at a CNC shop in my neighbourhood. I handed over
to them only a hand-scribbled sketch and got back beautifully precision-grinded
masterpieces. All four cost me $60. I'm very satisfied for what I got for
the money.
The 4.8mm x 4.8mm chamfer at the long side as specified by the plans is not sufficient to make the blocks sit flush inside of the aluminum angle. Either I'll have to convert the chamfer to a radius or increase the chamfer.
The drilling procedure was extensively discussed at the Sonex email list in the past. Also here I'll deviate from the common path. I think the commonly-used pilot-drilling method is not good here. It probably will be best to drill only one block at each side to 3/16" (or nearest metric equivalent) and then use this block as a drill guide for the opposite block. I'll also buy a real reamer when it's time for installation and also use close-tolerance bolts.
=====================================================================
Fitting the Wingribs (Jan. 13th, 2002)
From the beginning of this project I planned to use flush solid rivets, especially where minimizing of drag is concerned.
This particularily has to be considered when skinning the wing. Unfortunately the Soenx wing-mainspar contains no lightening holes. So there is no acces for a bucking bar to the wing's nose when the spar is attached. I now developed a concept of a mixed solid/blind/flush/protruding solution in order to make use of the best of all worlds.
The protruding blind rivets were chosen according to the plans in order not to sacrify the spar's strength by countersinking the sparcaps.
The riveting-concept is a follows:
1. nose-skin pre-bent, all wing components cleaned, alodined and primed. All rivet-locations drilled and dimpled where necesssary, everything de-clocoed
2. noseribs will be attached to the pre-bent forward wingskin
This should be easy, because the prebent skin opens up about 80 degrees and so allows easy access with rivet-gun. I'll use a concave grinded bucking bar which blends into the wing nose's curvature. My highest concern goes to the airflow of the top forward skin, which is most susceptible to imperfections.
3. next the lower part of the forward wingskin will attached to the noserib
Because the inside of the nosecone is too tight for the rivet-gun, I'll rivet the lower part conventionally.
4. when this is done, the mainspar will be attached to forward and aft wingribs.
5. top-aft wingskin will be installed next. Back-riveting should be not a problem (easy access for rivet-gun
6. when bottom-aft wingskin will be attached, it's questionable if arm and bucket bar can reach thru the open aft end to the most forward rivet locations. If so then flush solid rivets can be used, otherwise the forward rivets will be flush blind rivets.
7. last job is to rivet the overlayed skins to the forward flange of the sparcap. At this time there's no more access to inside of the wing's nose. So I have to bite the bullet and use protruding blind rivets (maybe I have to install some drain-holes into the bottom of the forward wing section...)
all comments and suggestions welcome
=====================================================================
Fitting the Wingribs (Jan. 5th, 2002)
Tonight I pilot-drilled the lefthand outboard wingribs to the mainspar (mainspar still clecoed only).
So far, so good. When I adjusted the rib's position, I clamped two steel-rulers to the rib's flanges in order to simulate the curvature of the wingskin.
You can see here how the forward wingskin will overlaps the aftskin. I'm not totally satisfied with this transition. I made the sparcap distance (= mainspar-height) exactly to the plan's 193.1mm. The ribs I have hammered over the Sonex' original formblocks, so this should be all to dimension and fit nicely. However I think the ribs should be about 1.5 to 2 mm less in total height. If this will pose problems when I lateron hit the rivet line at the sparcap, then I'll insert a 1/2" strip of 0.032" mateial over the whole spar-length between sparcap and wingskin. This should be a simple cure.
