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108 amateur build project. What Have I done?

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Robert Picard
(@bob-picard)
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Joined: 4 years ago
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My O-540 was done by a one time STC in 1979, or somewhere thereabouts. At that time, all parts of the STC get approved. When I replaced the engine last year, I sent my mount in to have it inspected and they said I had a bent mount giving the engine a slight twist. They told me that the mount tubing was too light for an O-540. Understandably, operating on floats really puts the mount to a stressful beating, so I wasn't surprised that the lighter tubing bent. I had them make a new mount out of the proper size tubing and it fit perfectly. All of a sudden the engine fit much better and the clearances between the engine and the cowling improved. So to answer your friend about an approved motor mount, that happens as part of whatever method he uses to get the whole O-540 installation done, usually a one time STC or using someone's multiple STC. If he uses someone else's multiple STC he must use what is specified in that particular STC, if stated. The mount will either be included in some kind of kit, or it just may be a drawing. If it's just a drawing, he can have EAMF make it to that drawing. If he goes for a one time STC, he can use whatever he can get approved. I hope I have helped.

Bob PicardN6346M Stinson 108-3 Floats/Skis/Wheels
N48923 Taylorcraft L-2B skis/WheelsAnchor Point, Alaska


   
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orange4sky
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Do you still have the docs from your STC? We are in Canada and I believe Transport Canada recognizes US STCs My friend might be able to use yours if you were willing to share/sell it.

Marcus Sabathil: Owner of Skookumchuck Voyageur 108


   
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Robert Picard
(@bob-picard)
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Marcus,
Get ready for a long-winded reply. The STC belongs to a person or entity, not the airplane. When a one time STC'd airplane is sold, the ownership of the STC itself still belongs to the holder of record and does not transfer with the airplane. I don't understand why it doesn't transfer with the airplane since it is for a one time one serial number only and wouldn't be any good to anyone else.
The airplane owner gets a copy of the fancy looking front page of the STC that basically describes the modifications made and whatever restrictions and flight manual supplements are required. The airplane will also come with flight manual supplements (if required) a FAA 337 indicating how the STC was installed, a log book entry and Instructions for Continued Airworthiness (ICA). My STC was issued long before ICAs were required. I now understand why the FAA requires it because before ICAs came along the airplane owner, or mechanic for that matter, had no idea what was used to make the modification or how to maintain it. For example, not too long after I acquired the airplane (the engine STC was already done when I bought it), I decided that the "Lord" mounts were beginning to sag a little and that I would replace them. I had no idea what part number to order for replacements. The mounts themselves are not marked with a part number and when I tried to look up a parts list, I found out just how many different "Lord" mounts there are for a Lycoming O-540. I tracked down the owner of the STC and asked him if he was interested in selling it to me and he said no. I contacted the FAA Aircraft Certification Office (ACO) and asked them if they could give me any information and they said that STC information is proprietary and they couldn't help. I ended up using Commanche 250 mounts.
The engine upgrade for my Stinson was, I believe, one of the first ones to be approved. I'm sure a lot has been done to improve upon what I have. I have made several significant changes to the original STC via field approvals. I have improved the fit and integrity of the engine to cowling baffling, removed an unnecessary second oil cooler and was able to delete a climb restriction for cooling purposes. I have replaced the propeller and governor with a unit that recommends a specific motor mount cushion so now I know what to use. I have replaced the exhaust system that looked like it was made by a Midas muffler apprentice from scraps of automotive exhaust pipes with a new modified Maule system that fits and works beautifully. I have replaced the intake/carb-heat with a much improved unit.
I'm pretty certain that if your friend could get a hold of my airplane's STC it probably wouldn't do him much good anyway. Although it may have been good enough to meet 1979 criteria, I doubt if it would meet today's standards.

Bob PicardN6346M Stinson 108-3 Floats/Skis/Wheels
N48923 Taylorcraft L-2B skis/WheelsAnchor Point, Alaska


   
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orange4sky
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Whew. Ok. So basically: Bureaucratic clusterfrack.

What are you running as a prop? I will also need to get mounts. I'm going to be running a Harzell HC C2YK - 1BF

Marcus Sabathil: Owner of Skookumchuck Voyageur 108


   
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Robert Picard
(@bob-picard)
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Poor Marcus, you must think I have nothing but long-winded replies. Here goes. When Hartzell came out with that horrible and expensive AD on the old steel hub prop., the Piper Comanche community was devastated. It looked like an extremely costly AD that could ground the entire fleet. They cut a deal with McCauley and got them to come up with an STC'd replacement prop. Apparently they guaranteed a certain number of buyers to make it worth McCauley's effort. The STC they came out with is a 3 blade Black Mac prop conversion and at that time it became the only other prop legally used on the 250 Comanche. It was also specially priced for the Comanche because of the large number in the fleet that needed conversion. Even then I considered it a bargain at $6000 including the STC the prop, backing plate and spinner and a new governor. The estimate to fix my old Hartzell was around $8000 and required a repetitive five year compliance of the AD whether it flew or not. I couldn't even keep it hermetically sealed as a spare in my hangar without having it redone every five years. I wound up giving it away. . The 3 blade prop is more efficient in pulling me out of the water, it is shorter in diameter and picks up less spray on the water and pebbles on dirt strips, and significantly reduces your noise signature, making your neighbors happy.

Bob PicardN6346M Stinson 108-3 Floats/Skis/Wheels
N48923 Taylorcraft L-2B skis/WheelsAnchor Point, Alaska


   
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Robert Picard
(@bob-picard)
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By the way the new 3 blade prop wound up being only one lb heavier than the two blade prop it replaced.

Bob PicardN6346M Stinson 108-3 Floats/Skis/Wheels
N48923 Taylorcraft L-2B skis/WheelsAnchor Point, Alaska


   
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orange4sky
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HaHa. It must be karma as I'm not known for my brevity in other spheres. No. That's all interesting information. I love learning, so fill your boots. Pixels are cheap but I do appreciate your time.

I like the advantages of a three bladed prop and I'm considering a three bladed Catto composite for float flying down the road. The fixed vs CS debate is a weight vs efficiency vs cost triad of conundrums but I enjoy the mental exercise.

I imagine that the same mounts would work for me in this instance.

Cheers.

Marcus Sabathil: Owner of Skookumchuck Voyageur 108


   
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orange4sky
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Busy on the project. Big dump of progress photos.

Detail of the teak floorboards

Glue up of spline and facing

Making rub strips from delrin

Delrin fairleads

Bits for extending the ailerons for the full chord droop tips.

Leaky O-540 gasket. You can see how the gasket was sucked into the sump along the top edge.

Waiting for paint.

Waltham CDIA clock that needs TLC.

Out of kilter balance wheel.

Some polishing done.

Marcus Sabathil: Owner of Skookumchuck Voyageur 108


   
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orange4sky
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Flush gas caps. I'll be venting the tank another way.

Parasite drag begone!

For the great thirsty lump.

to make way for the new caps I had to cut this open. It had a fair bit of corrosion. The rest of the tank has very little corrosion.

Satisfying to have these done. I was concerned about welding the alloy but it was very easy to TIG. I used 5256 rod which is ductile and very resistant to cracking. The manual mentions that it's S2-1/2H. Anyone know the equivalent to modern alloys?

Finally getting to the wing mods.

Tips fit very nicely.

Deburred, etched, Alodined and ready for primer.

Dreaming of a tank nestled in between the drag wires. Need to re-engineer the compression tube/s. Moved to top and bottom of spar with tank between perhaps? I like the simplicity of just adding a passive gravity feed tank out here instead of one over the baggage compartment which would need a pump and complicated filler, electrical, etc. OTOH, If I need ballast in the tail for the O-540 then a tank back there would mitigate that.

 

Marcus Sabathil: Owner of Skookumchuck Voyageur 108


   
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Bob
 Bob
(@rjpustellgmail-com)
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Wow! Just wow.......... Oh, to be able to build a Stinson (or any other number of wonderful old airplanes) as an Experimental! One could use factory parts when convenient and available and fabricate or adapt things as needed. Dont' do anything stupid and don't bother with Forms 337 and negotiations with the Feds all the time. Nice!

Your project is a work of art and love. Keep us updated. I am drooling.

Bob and Pat and the two Stinsons


   
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orange4sky
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Thanks Bob! Glad you are enjoying the posts.

Marcus Sabathil: Owner of Skookumchuck Voyageur 108


   
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Will Ware (Webmaster ISC)
(@stinsono)
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@orange4sky, How are you doing this as an experimental? Just trying to understand the “specifics” of how that works...Thanks


   
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domurray
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He is building it in Canada. Different rules.


   
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orange4sky
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In Canada we have special certificates of airworthiness for amateur-built aircraft similar to the US. I refer to "experimental" sometimes because it's a lot easier than typing "amateur-built category".

It's very similar to the FAA amateur-built category in that you have to prove it's 51% + owner built.

Marcus Sabathil: Owner of Skookumchuck Voyageur 108


   
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orange4sky
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I have decided to extend the slots to the end of the wing. It's very easy to do this at this point and seems like a good idea from a safety perspective as the existing slots have moved inwards relative to the wing tips. Luckily, I now have a donor wing for parts thanks to the local Stinson community. Unfortunately it's a damaged wing so there are no "slats" (108-1811300-2) Once I find a pair, they will have to be shortened by about 1/4 to fit.

Finished fabricating the end braces. The drawings called for a single AN4 rivet at the end of each brace but elsewhere on the wing they use two AN3 rivets which seems like a better arrangement to me. less possibility to loosen from flex.

 

Marcus Sabathil: Owner of Skookumchuck Voyageur 108


   
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