This & That, May. 28th, 2001

I ~almost~ bought this engine tonight

It was on Ebay Germany. It is a Type 4 engine. It's still originally packed by the factory and sat unnoticed for decades. I offered $200 however at the last second I was outbid. It went away for about $700, still a good bargain I think.

I started drilling out rivets at bulkhead #3 tonight. Here's a little tutorial for renoving solid rivets:

at first I centerpunch the rivet heads. I use the small dot on the rivet. Its's too small to guide the drill alone.

then I drill through the whole rivet using a #30 drill. This weakens the stem and maks driving out the stem later much easier.

after this I enlarge the hole to about 3mm depth using a 3mm drill. This will provide 0.1mm safety distance at left and rigt of the rivet. After this I use a punch and wiggle the head two or three times until its breaks off

at last I use the punch to drive the stem out. Even tho I did not damage the holes, the holes are a bit enlarged now. I think this came when the rivet expanded when I set it. So I will open up the holes and use 5/32" rivets now instead of the original 1/8".

After this 'operation' I installed turtledeck formers #3 temporarily. If you try to do this almost perfectly, it takes ~a lot~ of time. I spend the rest of the evening with this task. Critical is the transition where the rounded turtledeck goes over to the straight side panels. If this is not perfectly aligned, then it will show up on the skin surface. We'll see how this works out...

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Still more (or less) on Aft Fuselage Construction, May. 27th, 2001

It took the whole weekend to adjust and cleco the forward and aft turtledeck formers (including turtledeck splice channel). Problem is that the aft former has to be square to fuse, forward former has to be 60 deg and formers are flush to side panels. Distance between forward and aft formers has to be exact so that pilot holes of turtledeck skin will fit (so I had to scrap 5 clips until I got it right). Now (Sunday 22:00 local time) everyting is perfect >>>EXCEPT<<<

!Adrenaline Shot! Scroll down and whatch the nicely riveted bulkheads. What I did ~not~ take into account was that also turtledeck formers will be attached to the bulkheads!

The encircled rivets have to be REMOVED. This means 7 rivets per bulkehad side x 2 sides x 3 bulkheads = 42 rivets to be drilled out. If this goes on like that I'll become the rivet removing master of all times :(((

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More on Aft Fuselage Construction, May. 26th, 2001

This is the way I true out the aft fuselage bulkheads before riveting.

All the bulkheads can be sub-assembled outside of the fuselage. This is much easier than riveting the verticals and crossties directly to the wall skins. Once all bulkheads are square the whole tailcone will become square automatically. I also dimpled the rivet locations at the bulkhead verticals and sidewall for use of flush solid rivets.

The bulkheads and sidewalls can be stored at a very limited space for further use. The holes for the elevator pushrod and rudder cable fairleads are only pilot drilled. I will align these holes when the tail is installed using a cheap laser pointer.

Apropos elevator pushrod support: I don't like this particular solution of plastic snap-bushings. Caused by the circular motion of the pushrod idler the pushrod itself does not only move linear back and forth but also a bit up and down, thus causing unneccessary friction at these plastic bushings. I'm still looking for a better solution here.

Deviating from the suggested order of construction I first clamped the front and rear turtledeck formers and the skin splice channel temporarily in place.

This 1/4" gap at the top joint of turtledeck formers #1 I have no explanation what that's good for (anyone out there has an explanation?). For 'Sonex illiterates' this looks as if I would have cut the formers too short.

Hint:

When installing the splice channel like suggested, it's very hard to get a flush fit of the channel's clips to the forward and rear former. It's better to install the clips at first at the formers and the clamp the channel in-between.

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The Beauty of Bucketed Rivets, May. 15th, 2001

The green of the primer an the golden shine of the MS20470 AD4 rivets are a great match. Have just riveted the longerons to the fuse sidewalls. Actually driving solid rivets is not as far as difficult as I had expected. I had about 2 to 3% of bad rivets, mostly because I accidentally hit the same rivet a second time thus flattening the shop head bejond usability. Drilling out bucketed rivets is ~much~ easier than drilling out stainless blind rivets.

Another advantage of solid rivets is the ability that they can be cut to exact length (material thickness plus 1.5 times the rivet diameter). This makes very reproducible shop heads. With blind rivets this is not possible.

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Green Parts, May. 12th, 2001

Most of this parts belong to the rear fueselage (large sidewalls and longerons not shown, they're already back in the workshop). The result was not as I expected.Watch the bottom left part. It shows some dull and some shiny spots. The shiny spots is where too much primer went on. Three parts stuck to the foil and the coating peeled off when I pulled them apart. So I used lacqueur thinner and removed the primer again. These parts will be redone tomorrow.

The priming alone took one Saturday (spray top, wait for drying, spray bottom, wait). Total work for cleaning, etching, alodining and priming of the rear fuse parts accounted to almost 50 extra hours. I expect the corrosion protection for the complete plane will be about 200 hours (where the wings will be the most laboursome).

One problem I'm still looking for a solution: All the parts were marked wit the SNX-xxx designations before cleaning/priming. After priming all marks are gone. It will be a lot of puzzling to get all the pieces back to the right location.

I raise my hat for all the RV guys who do this job for the inside AND outside of the plane.

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Can One Improve the Sonex Design?, May. 10th, 2001

The last days my project came to a hold. All these alodined parts around and the weather so bad that I can't prime-spray them in the garden (temperature about 10 degC).

So I made some of the last parts (Outboard Rear Spar Channel / SNX-W12-03) I still had material for (and which did not take much space on the working table).

From the Sonex builder's email list I remembered that this part could be improved. The plans show the spar 'U' channel and a small angle riveted at the outboard end. This angle will hold the tip rib.

Someone suggested to save this small angle...

...and instead do a third bend at the W13-03 instead. I had already made this small piece - but to hell with it. What a great solution: stronger, lighter, elegant. Let's first say that making this angle and riveting it on the W13-03 would be a peanut - 15 minutes of simple work. But now my way to do it:

This third bend could not easily done at the bending brake. So the first thing was to fabricate a forming tool form particle board. Sides nicely filed to 7 deg and 11 deg respectively and bending edge radiused to the usual 1/8".

The bending brake I disassembled and put it together in such a way that I could bend over the forming tool (I don't like hammering because of the 'banana' effect - see previous notes)

Next problem showed up immediately: Because of the bend angles of 97 and 101 degrees the third bend would interfer with the upper and lower flange (B). So hurry, take some paper, calculater to figure out the slope of the edges. A little filing and - voila - problem solved.

BUT when I would bend the lower flange the lower end of the third flange would be damaged by the brake. So hurry file the lower third flange such that it won't interfer with the lower bend (A)

Next problem: if I would cut the piece to final length and then make the third bend the part may become too small if the bend-allowance is not calculated correctly (my weak point). So better leave the part a bit bigger and file to size after the bend has been made. BUT this is not so easy. So hurry and make a fixture where I can clamp the part without damaging the part's flanges when filing it to size. Puh - this all took the whole evening.

The part is ~perfect~ and ~elegant~ and took about five times as if I would have made it according to the plans. This is the price to pay if you think you could improve the Sonex design. BUT this is an experimental aircraft - isn't it?

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Elevator Ribs, May. 1st, 2001

The elevator skin which I purchased prebend from Sonex is the next I'll put hands on. The elevator ribs I already had made before. So I fitted the elevator root rib now. The result was not much satisfying.

If the rib is flush at the leading edge at the elevator, then the trailing end looks above the elevator skin. This comes from the 'banana effect'. This effect is unavoidable if the rib flanges are driven with the plastic hammer. The flange stretches and the rib bows up. This is a big disadvantage of this type of forming technique.

This picture shows a left and right rib held together. The effect is duplicated and obvious.

This is how the elevator root rib looks if made per the plans. What I also dislike is this opening at the trailing edge. I suspect the opening may produce a whistling noise. So it's time to build these ribs once more...

Isn't this perfect? The flanges are made with my 'forming tool & bending breake' process. Look for April 28th note for details.

I found this electronic compass at a German mailorder tools company (Westfalia). Price is about US$ 40. The compass is electronically damped and self-compensating. The compass works with a 3V Lithium watch battery. I removed this battery, soldered a 3V Zener diode in and connected a cable for connection to 14V board voltage. I will chain a 1KOhm resistor directly at the bus connection, so the power supply will become short-circuit protected (maximal current is then about 14mA).

A drawback may be the build-in power saving feature. If the compass is stationary for about 10 minutes the display will be switched off. So I hanged the thing with a string to the ceiling and let it swing in the Spring breeze. Seems the display remains on.