FTFF 2015 Scratch Build: Sikorsky S-39

[willsonman]

Its really a true challenge. My builds typically take between 100-150 hours to complete. I'll have 78 (assuming I sleep 3 6-hour nights) . BUT they should be mostly un-interrupted stints of building. A lot of the build flow here at home stems from working on the project.... life.... ok where was I? Developing a solid plan here will drastically help. Not to mention the size of the model. Building something this big and detailed in 4 days is a bit over the top for a one-man-show. I hope I can pull it off.

 

[willsonman]

Been thinking more on this one lately as we are now down to 8-months away. I took another look at my material inventory again and am still not thinking of anything I am missing... except a big one.

I am having trouble visualizing how to attach the two main struts at the front of the wing that I will run my main power wires through. I was thinking I could do a wrap of copper or brass strip and solder to make a strap to screw to a bulkhead. I would like to make it servicable but maybe someone else has a better idea? I'm thinking I should probably leave the center section with booms all attached and just make the outer portion of the wing and floats removable to transport home. I really could use some ideas here guys.

 

[willsonman]

Continuing plans for the build here. I had a great conversation with my wife. For those who do not know she is a graphic artist who tolerates my use of her equipment and skills for my hobby. For simplicity I've decided to go with the classic Shell oil scheme. My wife has agreed to draw op some vector files from the plans based on the attached photo. All the cuts will be in red and I can get them cut from Callie's Graphics for a reasonable price. That way I can buy a few rattle cans of yellow and apply the vinyl directly once cured out. I do plan to do rivets on the fuselage if time allows.

 

[AkimboGlueGuns]

Haven't seen that scheme on a S-39 before. Is that modeled after a full scale?

 

[willsonman]

I believe so. Even if its not. It about the simplest I can go. Anything else that I have found will require a lot more work.

 

[AkimboGlueGuns]

Yeah, the leopard spots would be a pain to make and apply. Regardless the plane should look very good in those colors.

 

[AkimboGlueGuns]

This airplane was painted like that, but is now being restored to original colors.

 

[willsonman]

Well, we are drawing closer to this event and planning of the building area has begun. To facilitate the desire of onlookers to follow the build I am putting together a schedule. This is not just for getting others to see what I will be doing and when but to allocate time and plan more effectively. Right now I have just run through my first day (Thursday) from 7am until midnight. It will consist of the bulk of creating the shapes of the plane. The wings, fuselage, tail planes, pontoons. I plan to start work on the wings and hot wire cutting at around 8. There will be 4 sections to cut. With a flat-bottom airfoil this will go quick. I'll be doing fuselage sculpting after that followed by tail planes and pontoons to follow after that.

As I complete the list I will post it in this thread.

 

[AkimboGlueGuns]

Sounds good, I'll be checking this project fairly regularly to see progress. Let me know if you ever need an extra set of hands.

 

[willsonman]

Went through and made a lot of additions to my supplies checklist. After looking over the plans a lot of the mounts will be simple 1/8 music rods with electrical ring terminals soldered on. It makes it simple and fast. I can apply "fairings" via foamboard and gorilla glue to gussy them up. In total I need 208 inches of wire... That is quite a bit of weight but most of it is around the CG.

I've decided to simply make the booms from their intended 1/8 ply. It will be strong and simple. No need to incorporate additional engineering into the spar as well. As this will not be a high-power speed demon I decided to use 12AWG wire for the power leads through the motor mount tubes. These will have brass strips soldered to them for securing to the motor mount and fuselage. I will still be running two Rxs. One in the wing and one in the fuselage. The one in the fuselage will have a BEC and run the tail wheel servo only. The wing will be VERY tedious to work on before covering with glass. There will be multiple hard points for strut installation, engine mount, spar, aileron servo, elevator servo, rudder servo, ESC, and aileron pushrods and bell cranks all stuffed inside the thing. I will fabricate styrene sheet hatches for each component for service and they will be secured via screws. Again, ALL of the landing gear will be fabricated from scratch. If you have never seen this kind of solder work done be sure to watch. Its stupid easy and very strong.

Lots of decisions being made now so keep checking for updates.

 

[Gryf]

Just for fun, here's some great footage of a real S-39 in action, thanks to Kermit Weeks at Fantasy of Flight.

https://www.youtube.com/watch?v=A-CCkwPRYrA

Gryf

 

[willsonman]

As we enter the final quarter of the year prior to FTFF 2015 I have started placing my orders. Orders to Hobby King, Tower Hobby, and Park Flyer Plastics are placed. Running total for the project is now at $109 with shipping.

My big concern right now is the separation of the wing panels. Essentially I will be building the wings in 4 sections to make 3 panels. The center panel will be secured to the fuselage and house pretty much all of the electronics. At nearly 2" thick it will be sufficient but the real issue is... the outer wing panels. The center section will be two roughly 25" panels to make about 50" span. The outer panels will be about 13" each. The ailerons will be split and when the wing sections are secured together there will be a centering pin to lock the two parts of the aileron together. This way, the aileron servo and all mechanisms will be contained in the wing and make joining simple... maybe.

The issue is to tie in the main spar. The plan calls for 3/8" balsa spars. Easy. I can use locator dowels (or pins) to make the alignment right on the balsa end caps of the foam for the joining. I am having a hard time figuring out what I want to do to join the spars to give the needed strength needed at those tips. No struts attached at this point.

My initial idea was to use CF tubing. Use a larger ID above the spar and secure it all into the foam using gorilla glue. Then use a smaller OD tube to slip into the tubes to tie in the strength. The question is how far does this CF spar need to go into each wing panel? Further into the center section or outer section? Plan calls for 9" of spar into the outer section. I was thinking that maybe 5 or 6" would be enough.

Really would like community thoughts on this.

 

[wilmracer]

I've had good luck with aluminum tube for the outside and CF arrow shafts for the inside. For a wing this size I'd do a pair oriented vertically. I can't remember if this is a built up or solid foam wing. If is is build up I would definitely add sheer webbing between the shafts.

I would think 4-5" would be enough as long as you're not planning on pushing the envelope with speed or maneuvers.

 

[willsonman]

Foam core wing. No shear webbing required. I fly scale so I do not plan to do any crazy maneuvers.

 

[earthsciteach]

What is the length of the outer section?

 

[willsonman]

The outer panels will be about 13" each.

ADD kicking in?

 

[wilmracer]

ADD kicking in?

So... I know 26" is quite a bit, but does it make it impossible to do a 1 piece wing and still transport it? I only bring it up because this is a BIG build to attempt in a short timeframe. I know you've planned out every step and I think you can get it done, but removing the complexity of a multi-panel wing would probably save you at least an hour or two. Or if you build like me a day or two

 

[willsonman]

I've really thought about it. The issue becomes, plane setup becomes more work than getting a flight or two in. The booms for the tail tie in directly with the wing. So, in addition to removal of 16 struts I would have to make the tail removable as well with disconnects of the servo connections as well. So then, I would have to somehow keep the struts organized while the plane is disassembled. This way is much simpler for transport. Simply remove the wing tips and in the back of the car it goes. The other interesting issue will be getting the thing home. With essentially my entire workshop packed up in the car, the materials for the build will take up considerably less space than an airplane.

I am considering making 4 even 18" panels for the wing. This would bring the broken down span to only 36". This would mean that I would have a set of struts on each panel to screw in and the side pontoons could also have to be removed. This could add some strength to that joint. Keep in mind that there are a total of 24 struts on the entire plane. For this dis-assembly I would remove the 4 struts from the pontoons to the wing and the 3 struts from the pontoon to the fuselage... 14 struts total. That adds up to 12 screw points the way the plane is designed.

So, the options are 46" span broken down with minimal re-assembly, or 36" span broken down with a lot of re-assembly.

 

[Craftydan]

Wilsonman, ol' buddy, ol' pal! The solution is simple!

You can make space for your beautiful new plane by sending your hot wire rig home with me

 

[willsonman]

LOL! Well, the rig consists of a car battery charger, dimmer switch, a large bow, a small bow, and a "scroll saw" type bow. It really doe not take up that much space. Although I have considered donating it to someone... no clue who or by what criteria.