Making a New Turtledeck Skin, ( July 31st, 2001
The bad skin I used to mark the new skin - very speedy. At one side (arrow) I cut a 90mm x 2000mm strip which will become the new splice channel.
This is how the new laterally split turtledeck parts look like. This is a very rough cut. I will first fit and pilot-drill and at last cut/file to size.
What I also like is the 'grain' is perpendicular to the bent.
=====================================================
The Turtledeck Skin goes to the Junkjard :,( July 28th, 2001
My turtledeck skin assembly looks quite well from the outside (and if you are standing not very close)
Even the rivetet joint doesn't look so bad from outside
After all this cutting, fitting, drilling, dimpling, cleaning, priming, polishing at least 50 working hours went into this subassembly.
The whole mess started when I dimpled the 1/8" holes where the two pieces are joined. I pilot drilled, final drilled using a #30 drill, then dimpled both skins and the splice channel. While doing this, the holes expanded to about 3.5mm and so were out of tolerance for AD4 rivets.
First aid was to further dimple and bore skins and splice channel to 5/32 and then use the next larger size (AD5) flush rivets. So far so good. Today I set a couple of this AD5's using my BIG back-riveting tool ;))
back-riveting tool (my feet for comparison [it's 34 deg C / 93 deg F outside today])
What came out was a ~great~ disappointment. Most of the shop heads bent to one side (no, the rivets weren't too long, the extending part was exactly 1.5 times the diameter [6mm]).
The problem was that you cannot or can only with LOTS of experience (even with the slightly bented rivet set) work nicely inside this U-profile splice channel. So what to do? The question always is: is it good enough? The turtledeck got no structural loads to bear (except when you ground-loop the thing). I have decided for trashing the part. The next/new turtledeck will be split laterally as I mentioned previously. Then the two pieces are more compact, more easily to handle, join and fit. This time I will pilot-drill (2.4mm) and then [without final-drilling] dimple for 1/8" flush rivets using my ground-down dimpling dies. The AD4's are MUCH easier to set at this thin metal.
better news to follow soon (I hope)
=====================================================
The Inspector was here today, July 21st, 2001
He checked almost all of the 462 parts I made so far and signed them off in the plans. Measured many of them, compared to the plans, counted rivet locations, matched left and right parts.
Only three parts were wrong: two brackets had wrong hole distances, one part was drilled mirror-inverted. So my error rate is 0.65% - not bad for a bloody beginner (and not counting the 'practice parts' in the scrap bin...). My workmanship was regarded as 'above average' (with lots more effort involved as actually necessary). Inspector asked if it is a seaplane because of the intense corrosion treatment.
Inspector praised the quality of the plans (kudos to Monnett &Co). I'm one of the few builders here who does not follow the 'quick-build' lane (how long did it take to pound all these ribs out?) He reported from another builder like me who owns 5 hand-drawn sheets and builds for 7 years now - still no end in sight.
Next inspection is to be expected before closing wings.
=====================================================
I'll build a Total Lift Indicator!, July 20th, 2001
Why ~build~ such an instrument?
- because it's one of the most advantageous dials
- because it's a dirt-simple construction
- because it's almost fool-proof and failsafe
- because it costs only about $100 to make
The instrument consists of a differential pressure probe (0.5" X 1" X 6" 6061-T6 flat bar with four holes drilled in it) plus a Dwyer(R) Series 5000 Minihelic II differential pressure gauge of 0..2" water coloum (or equivalent of 0..500 Pascal for all those living in metric world).
The gauge looks suitable for the job. The case is made of fiber reinforced plastic. Outside diameter is 73.9mm, case diameter is 65.5mm and depth is 55.8mm (including tube studs which are 6.3mm in outside diameter). Weight is about 120 grams (6 Oz). The instrument will be mounted from the rear using a bracket.
So it will NOT fit into a standard aircraft-instrument hole! Do not unscrew the rear part (as I did). The instrument may loose its zero adjustment (which isn't a big problem, read on...).
The pointer is quite sensible (which is usual for such a sensitive instrument).
The front bezel holding the plastic glass can be unscrewed (with quite a lot of force).
The front bezel is sealed against the case with an O-ring (1) (which is responsible for resistance of removal). Once the instrument is open, you can adjust the pointer's zero position using a small allen wrench (2) which is provided with the instrument. This will be necessary for the Sonex's 60 deg tilted instrument panel.
The instrument face is fixed with two small phillips-head screws. So another face can be installed easily.
Instrument with face removed. Arrows locate the reception of the phillips screwas.
This instrument fits ~perfectly~ into a 'unox' champignon mushroom soup can. Give it a try if your US tomatoe soup cans are also usable ;)))
... to be continued...
=====================================================
More about Fitting the Turtledeck Skin, July 11th, 2001
My first t'deck fit uncovered two (three) problem areas:
problem areas encircled
My first idea was to 'pre-form' the t'deck and so take some of the force away. However the email group discouraged me to do this (thanks guys for the lively discussion about turtledeck fitting).
What I will do now is laying the skin sides 1/2" over the table edge and by using a soft-wood-block bending the edges about 10 deg. down. I hope this will contribute to a better fit.
If I would have to build another Sonex, I would build this part totally different: Instead if joining two halves at the top, I would join the two pieces laterally at bulkhead #3 - much cleaner and easier installation (no splice channel required).
=====================================================
Fitting Turtledeck Skin, July 9th, 2001
When building the rear fuse I deviated from the Sonex' recommended assembly procedure. Sonex suggests to assemble the turtledeck skin first, then cleco the wobbly skin to both sidewalls, then install the turtledeck formers.
For the following reasons I didn't like this procedure:
- I would have to work inside the tight, dark confinement installing the bulkheads. Possible for the blind riveting guys, - not good for hitting solid flush rivets.
- My nicely primed parts would most probably be scratched during this installation procedure
- I don't trust pilot-drilling the turtledeck skin and then praying that the bulkhead flanges will fit. I needed a more fault-tolerant method (because another shipment of 4ft x 6ft sheet metal from the US I can't afford [at this ridiculous xchange rate])
So what I did is the following:
- build the aft fuse sidewalls first (skin and longerons), test-fit bulkheads, pilot and finally drilled, dimpled, primed inside, polished outside
- build the complete bulkhead assemblies (the rectangular part and the turtledeck former attached), however leave the splice channel clips off. This way the bulkheads can easily be squared (see previous reports), dimple, prime bulkheads
- cutout the turtledeck skin with 20mm oversize, drilled turtledeck skin together with splice channel, dimpled turtledeck skins and splice channel
- adjusted and pilot-drilled the bulkhead flanges
- clecoed the bulkheads and test-fitted the turtledeck skins, marked the final cutlines of the turtledeck skin, disassembled
- final cut, prime, rivet the turtledeck skin together with splice channel
- finally rivet the (rectangular) aft fuse box (turn fuse box such that skin lies flat on tabletop, flush-back-rivet bulkheads)
- cleco turtledeck skin, drill rivet holes from inside thru former flanges and turtledeck skin
- disassemble again, dimple bulkead flanges and turtledeck skin
- finally rivet turtledeck skin
It is obvious that the priming and dimpling requires several more assemblies and disassemblies. My estimate is that the 'traditional' aircraft building method compared to the Sonex fast&easy method requires almost twice the building effort.
first test-fitting of the turtledeck skin
=====================================================
Joint of Forward Turtledeck Former, July 3rd, 2001
Aren't these jewels?
...no these are polished solid rivet heads - next is gold-plating ;)))