Hi all,

Fellow outdoors lover here working on a Super Stinson 108 in the Canadian amateur built category. I’m planning on doing some mods to modernize and extract more of the potential from this already decent backcountry aircraft. I’m also going to put it on floats at some point so some mods are specifically for that eventuality.

Skookumchuck means strong running water in Chinook Jargon for those wondering. The name reflects my deep love of the coastal northwest.

I bought the already started project a couple of years ago and have been working on it steadily. The fuselage and turtle decks were already stripped, repaired, epoxy primed and painted. The wings were as removed.

I’ve decided to incorporate the following mods:

Metal rear baggage compartment. Since this is a straight 108 or a 108-0 it didn’t come with a baggage compartment. The previous owner installed a metal one and I’m going to modify and lighten his design a bit.

O-540 B4B5 installation. One of the lightest O-540 models, I have a full suite of lightweight accessories for it.

Full chord droop tips. This is a kit that came with the plane. It was designed by Bob Reynolds and signed off by Chris Heintz of Zenair fame. It adds about 5 square feet of wing area including one square foot to each aileron. Although not in the plans, I’m extending the wing slats out to the tips. The added wing area is outboard of the slats and expanding them means more of the aileron will be covered.

One piece windshield.
Passenger side brake actuation.
Center stack instrument panel.
Heated pitot.
Cowl flaps.
NACA carb Intake scoop.
Control surface gap sealing.

I’m considering the following mods:

20 gallon onboard fuel increase. I am definitely adding some fuel capacity but have not decided which.
Leading edge cuff.
Larger flap skins: +3”.
Improved strut root fairings.
Cargo door on the pilot’s side for the rear passenger compartment to facilitate loading while on floats.


The priority right now is figuring out which fuel increase option to go with. The early 108s came with a 20 gallon tank in each wing for a total of 40 gallons. I’d like closer to 60 gallons, if possible. Some options are installing tanks from a 108-3 which are 25 gallons each totalling 50 gallons, additional similar wing tanks further outboard, leading edge tanks, tip tanks and a rear fuselage mount collector tank.

The rear tank is tempting but would probably require pumps, electrical and a lot of extra plumbing. I’m a big fan of simplicity, so until someone can convince me otherwise, I’m leaning away from this option.

Installing -3 tanks would be relatively simple but I’d like more than 50 gal and It just does not seem worth the investment.

Leading edge tanks are what I’m leaning towards now, in part because I can incorporate the leading edge cuff into the design.

Tip tanks inside the fibreglass droop tips might be an option but may not add much capacity. I have yet to calculate what’s possible.

Ultimately, I’d also love to install some kind of large cargo door for the passenger part of the cabin, but there’s an important fuselage cross member in the way which would require reinforcing around it or engineering some kind of skookum quick release there.

Right now, I’m working on the one piece windshield form. I’ll be draping that possibly next week. If all goes well, I may be offering to make them for other Stinson owners.

Anyway. Enough of the wordage. I’ll post some teaser pictures for now.

Cheers,
Marcus.

Hyas kloshe.

I think that 0-540 model was on early Pawnees and 235 hp. If so I liked that it was low compression and slower turning than the 250 hp and 260 hp models. Because the 12 volt battery was back under the horizontal stabilizer, line loss was considerable. It would start, however, if you could bump the start button enough to get a quarter blade. Or if you had to prop, that was easy as well.

Good engine!

Charly Center at Crosswind STOL was working on a leading edge cuff for Stinsons, and installed one on a 470 Stinson. I've read the flight test report and it was absolutely incredible!!!! You might try to bend his ear on that.
One solution to your fuel might be to split another tank and place half outboard of your present tanks, connected with a tube. No pumps, no gauges, just gravity.
One of the things I always said I'd do if I ever had the opportunity to do a project like you are, is to brace the horizontal stab. They take a good beating with a bigger engine, and especially on floats. They tend to crack spars right at the end of the doublers on the attach. I extended the doublers and so far that's worked well.
Sounds like a great project!!
John

Masiem, tcj!

Contactflying, that was the engine Bob suggested. Pretty bulletproof, runs on 87 mogas and it’s relatively light considering all of the cubic inches.

Hardtailjohn, I heard someone had a cuff for the Stinson but couldn’t remember who. Now I know. Thanks. I’ll look into that. I like the idea of a second tank outboard. The one issue with that is the drag wires migrate up the spar as you move outboard so it would have to be a shallower tank but gravity is the way. To avoid venting and overflow issues, I’m thinking it would need separate fuel lines and tee them above the door with separate shut off valves there. The stock L-OFF-R valve is problematic.
As for the horiz stab, I have made a doubler for the attach but I have not looked at the stab spar. I’ll do that ASAP.

VortexAlternator wrote:Masiem, tcj!
As for the horiz stab, I have made a doubler for the attach but I have not looked at the stab spar. I’ll do that ASAP.

Look on the back side and front, just under the doublers. It was tough to find the first one, but once we did, we started to see a few that way. Like I said, I ran the doublers out quite a ways...I'll try to grab some pictures for you.
John

VortexAlternator... That's funny.

I've been building an amateur built Stinson for a while. Got a set of cessna fowler flaps and custom tracks cut out. Currently extending the wings and putting another fuel tank outboard by using inboard tank ribs on the outboard section of the wing.

Fuselage structure is done. Float fittings, reinforcements for sea plane doors, etc.

Squared off ailerons. And working on full length leading edge slots. Lots of work and i seem to go in spurts.. trying to get back at it but my dad dragged one of the other Stinson's back from Texada Island and asked me to annual it first.

Between work and the fleet of planes that my dad, his good friend and i own, the project takes longer and longer.

That's life

mmartin1872: Another crazy Canuck? Whodaknownit? Where are you located?

Sounds and looks like an awesome project. Do you have a thread here? I’m curious how you are making your doors and reinforcing the fuselage. I dream of fowler flaps but I want to fly this century so that mod is off my list for now anyway hence the bigger skins plans.

Zzz. heh. You are the first to notice, so you are not sleeping after all.

hardtail: I’m going to look now.

mmartin. Found your thread. It is awesome. I was just in Chilliwack last week with Mike Jackman in his ivory -3.

Since we are both working on experimental super Stinsons, we have the higher engine weight W+B issue. Im sure you would like to avoid ballast as much as me. Would adding a ~3” leading edge cuff not move the MAC forward enough to compensate for the higher nose weight? My napkin calculations showed promise. l’m thinking of making a set of replacement ribs or leading edge fuel tanks with a droop built in. thoughts?

By the way, aren’t the flying wires in the way of the tank further outboard? Or are you moving them to the bottom of the spar?

This is going to get "interesting" dueling Stinson projects, bring it on boys lets see what ya got on the go.

Haha. Yeah. Could get ugly... We might have to arm wrestle over the next set of 2425’s that come up for sale.

I will be watching this and would like to know where you have other information posted. I have picked up a second -3 that was hit by a deer in Montana on take off. The fuse is in repairable shape, the horizontal can be fixed and I have an extra engine.

Cool stuff

I started a project thread at the Stinson owner’s site but it’s tumbleweeds and crickets over there. Good people, but they are mostly certified. Most of the action for that group is on Facebook.

My buddy Gary, has a set of 2425's for sale, in good shape. He just moved to Alberta, but he bought Dave Miller's Yellow Stinson with the Io-360 on it, a few years ago.

I've got a set of Amphibious floats for my project, Easy Lift Floats out of Quebec. (out of business now). Hoping they aren't too big, I increased the gross weight, with the extended wing, and the bigger fowler flaps, even if they are a little overfloated for 2500 lbs, I think they'll work with the 2900 lbs gross weight that I decided on for the 'homebuilt project.'

The outboard fuel tanks, I purchased a univair spar splice kit, in order to get the 'chinese blue print of the spar splice doublers, to ensure that I am able to carry the strength of the repair through the spars. This allowed me to reverse engineer the spar splices, in the extended section of the wing. I had a bunch of wings kicking around, so I was able to steal some drag wires, mounts, compression tube etc. Made the drag/antidrag wires basically match the inboard section of the win. g.

With a 3" leading edge extension, might give you the effect you want. I haven't been too concerned about 'moving the weight aft' at this point. I'm thinking that with full length slots, leading edge cuff and the fowler flaps - depending on if I can use all 35 degrees that I got machined into them, I might not need a lot of weight in the tail.. I've made provisions to install the 'survival kit 24 of beer' underneath the horizontal stabilizer. Just have to remember, to replace a beer, with a near the same weight rock, as it gets drunk.

The door reinforcement. I removed all the door 'trim metal' and welded a square tube at the top of the door cut out. I've fabricated new 'trim metal' to encapsulate the square tube, and the hinge material will get cherry max riveted to the 'trim metal and square tubing'. This allowed me to also start fresh where the door striker plates go, because the original metal was pretty beat up there. I'll have 2 striker plates, on the forward and aft side, one on the bottom. I've been designing a 'parachute ripcord' style of release mechanism to release the door in the event of an accident, to allow the door to fall out of the 'hole'.

The rear windows I fabricated bigger frames out of aluminum, and have acquired rubber seal, that is like the old car windshields, with the little v groove piece of rubber that holds the window in tight (some beavers/otters use the same seal for the roof e-exit). The rear windows, are just big enough, that in an emergency you could kick the plastic window out, and squeeze through.

But of course, I'm trying to reign in all my brilliant ideas, because each one adds 4 weeks of work onto the project. Which explains why, I'm 10 years into it already. Fuselage is substantially complete. Tail is substantially complete, 1 wing is call it 50%, 1 wings is 25%. 1 aileron is 90% complete, the other one hasn't been started. The 1 flap, has been modified to fit, and the other flap has 8 hours of work.

At this rate, I should be complete in 2025. Especially when my dad drags home other airplanes for me to fix on the weekends, rather than working on the project.

Thanks for the synopsis. That's epic, as the kids say.

I met Gary and his IO-360 super Stinson a couple of years ago at a YPK airshow. That's a great engine for a Super Stinson. I was considering an IO-360 for my plane but a good deal on an O-540 showed up. Being able to run 87 mogas will be worth it.

I was hoping to find a set of amphibs too but some 2425's would be good start. Are Gary's floats at Fort Langley?

Are your tanks way out in the wing extension?

"At this rate, I should be complete in 2025."

LOL. Yup. Same.

"I've made provisions to install the 'survival kit 24 of beer' underneath the horizontal stabilizer. "

That's Canuck AF. There's a microbrew for that: "Tail Ballast Stout"... because It's gotta be hefty.

I have a good set of 2425 floats that I will sell, It doesn't look like I am going to be able to get a new plane any time soon so the floats need to go to help finance a plane.
They are located in SouthEast Alaska so shipping is not real easy, We are on the road system so IF you can get through Canada you can drive in and pick them up.

Sounds tempting. I think we spoke about a year ago. I'm already in Canada. The problem for me is entering the US. I have a cabin in Washington state and I can't even go there to maintain it!

Working on "fowlerizing" the Flaps. Adds about 2" of wing area and I'm making the max extension 40 deg. I will have to extend the Flap lever arm and mount the assembly higher in the frame. The bellcrank, pushrod flap mount arms and ears all need extending. The bellcrank brackets are just reversed between wings as they are offset and I need the opposite offset to make room for the bellcrank extension. It will take more umph to extend the flaps. Does not require the sector to be modified. The forces on the flaps will be only slightly higher.

Big dump of updates. Been busy. Lots of irons in fires. Will be starting on the tip tanks soon.

Floor boards cut out. Need to finish them. Will be coated in epoxy with a topcoat of polyurethane.



Windshield drape mould before fairing.



Wing / fuselage rotisserie



Machining an extra flap notch.



Panel rough in.



Aileron extension.



Com button installation.

My Stinson did not come with the passenger side brake actuators. Everyone wants them so finding them used is not easy and Univair wants $3500 USD or so for their kit. That's 40,000 Canuckistani Kopecks! I decided to make my own. I had to base my parts on drawings and measurements from other installed sets. It would have been much easier if I had a set to clone but alas... They are not too hard to fabricate but there are a lot of small parts and the assembly is pretty tight so it all has to mesh. Had the things in and out of the plane way too many times but that's easier than fixing problems later. I kept the early style pedals and modded them to work because they are beautiful and have the Stinson logo on them. That added to the workload but worth it IMHO.