FTFF 2015 Scratch Build: Sikorsky S-39

[willsonman]

The polls have closed and the decision is in. The Bugatti lost out due to cost and I'm not about to ask a community based on being cheap for handouts. The subject for my build at the Flite Test Flight Fest 2015 will be the Sikorsky S-39. Its an interesting subject that has a great place in the history of aviation. I've never been particularly fond of the look but I love the history.

First thing to address is size. The plans I have are for a 76 inch wingspan. Too big? Too small? Having to transport this thing home from the event I have to say I'm not really willing to go bigger. At any size the wings will be hot wire cut from 2" pink insulation foam. Covering will be tissue and WBPU. Floats will be made from the same foam. Fuselage can go either way. Solid foam hot wire sections, or formers that are sheeted. Size will also dictate the size of motor and cell count. At 76 inch span the max prop size is 12 inches. Maybe a .46 size on 4S. Plans call for a .60 size motor but Mine will not be as heavy

Next is the issue of landing gear. I have to say that I do not do float planes. I have no place locally to really fly them. Landing gear will be fixed despite early indications that I would make them retract. Its just not worth the effort as I would only fly this off grass. It also makes waterproofing a non-issue.

I have sourced plastic parts for the dummy 9-cylinder radial and a plastic nacelle cover from Park Flyer plastics. With the majority of electronics going into the wing, I'll need access to them. I'll have to get creative to get the tail wheel servo wire connected. The main positive and negative battery lines will run down the fore struts for the wing. I'll use brass tubing and solder screw-down plates to secure them. The battery will then be in the fuselage. More than likely servos and their wires will be embedded into the wing. Rudder functionality still needs to be engineered. the 76 inch plan calls for booms of 28 inches long. A perfect candidate for carbon fiber arrow shafts. I'll build a box around them to get the right shape. Elevator control will run through one of them leaving the other for possible rudder control.

We have a looong time to develop a plan and I FULLY expect input and criticism from you all. If you have an idea or want to contribute anything, I need it! This is something that was asked for and I fully intend to deliver.

 

[Craftydan]

Have you considered "removable" LG with hatches to cover the bays?

I'm kind in the same boat (yup, pun intended) as far as water locations, but I do happen to fly at a site or two that does . . . I imagine the same is true for you, especially since the next FTFF is roumored to have a water feature

Your build, your plane, but it would be awesome to maiden it from the water at FTFF

 

[AkimboGlueGuns]

For the landing gear, you could modify Flying Penguin's removable wire landing gear. I would do the 76" wing span, No modding the plans then. Good Luck! looking forward to seeing this thing.

 

[willsonman]

Dan, if that is in the rumor mill then I may reconsider. The issue stems from having the lever arm for the retract leave an open hole in the fuselage for water to get into the battery compartment. The other option (not gonna happen) is to use micro air cylinders.

Akimbo, yes, I am leaning toward that way too. I may have to make the wing in three pieces and use wing tubes just to get the thing home.

 

[earthsciteach]

Dan beat me to it. Yep - removable gear. Just do away with the recesses in the hull.

 

[willsonman]

I may go that way or a simple pin to adjust the landing gear on the ground. Another option to resolve the tail wheel steering is to have a separate rx and a BEC going to the battery plug. Both rxs would be bound and operate at the same time. I would be using Lemon recievers so we are talking about an addition $10 or so for the rx and BEC.

 

[Waffleman]

For the tailwheel, instead of running a BEC to a separate receiver, you COULD just run the servo wire a bit longer to the main RX. Seems simple to me... You will have to run the battery wires from the hull to the wing anyways.

 

[willsonman]

Yes but there will be no room in the brass tubes for anything other than 12AWG wire. I thought about down one of the struts but nah. Rather keep it simple.

 

[willsonman]

Ok, I think I will go with the 76" plan as-is. The outboard floats may have to be removable which will involve screws and hard points. I'll be needing lots of brass strips and my soldering torch to make light work of them. Looking at quite a bit of light ply too, 1/8" thick should suffice for everything. I'll embed ply plates into the foam core wing for mounting. At this size, with all the hardware I think we can do this build at around 6 pounds AUW. That means only 600W or so are needed for flying. A .46 size will do well here. I have one but The bearings are not good so I'll get a Tacon from HobbyPartz. Love Tacons. Its rated for 800W and will swing the 12" prop fine. A 12x6 or 12x8 should do fine. Not looking for speed but thrust for getting off step on water.

With the spar on the wing I am thinking I will go with a wooden spar. This will allow me to drill a hole in each side to key in the booms. There will be lots of hardware involved. With all the struts, wire landing gear, and complex tail control surfaces this really will be pushing the time line.

The main hull is 6.9"W x 7.3"H x 33"L. That will be the most complex "building" portion. I'm considering sourcing a solid foam block, if I can find one, and sculpt it to shape. I can then cut it in two and then hollow it out. I can layer 2" foam board as well for this. It will make a holy mess but I can work around a trash can for the sculpting. Doing it this way will allow me to knock it out in a few hours rather than an entire day. Adding hard points to the fuselage for gear and wing mounting will not be bad. I can insert a ply spine at the tail for the tail wheel assembly and spar connection. Finishing will more than likely be glass and WBPU. With all the compound curves the glass will be more forgiving rather than tissue. I'll have to spend time filling the weave with baby powder and WBPU. Lots more sanding. It will also help with rigidity.

 

[Craftydan]

So . . . how many time will you have built this plane in your head before FTFF15?

 

[willsonman]

LOL, at least 100. I've done it at least 1/2 a dozen currently. I'll need to in order to make sure I have every piece of hardware, tool, oz of glue, etc. packed in the car and ready to go. With this build I'm already looking at packing up 3/4 of my shop. Between the hot wire tools( 3 bows, power supply and backup wire), soldering tools, carving and sanding tools (files, paper, blocks), Foam (pink and DTFB), 2 sets of plans, glue, tissue paper, WBPU, spackle, glass cloth, carbon fiber, paint, tools (screwdrivers, drill and bits, saws, clamps), and other things I've forgotten I'm already looking at quite the car full. Then camping gear too. I've already started a word doc listing out materials I'll need to buy with web links. Its still looking at about a $100 build which is not bad.

 

[willsonman]

Coming to my senses here. I have a Tacon .32 size motor that is good for 700W. With a 12x8 prop Its a good fit theoretically. Smaller bell for fitting in the dummy radial too. I may get flak from Asbjorn for this but it may just be the ticket.

 

[willsonman]

Printed plans last night while I re-built the front end of my Storch. Printed two sets. One for reference and building and another for cutting up and template making. At 93" long its a big plan. The wing chord is 11 inches. There will be plenty of wing area. Any suggestions for the struts? There are essentially two types: round and flat. The flat ones protrude from the base of the fuselage and connect to the outboard pontoons. The round ones are everywhere else. I'm thinking lots of coat hangars.

 

[AkimboGlueGuns]

coat hangers would work, but I would use LG wire (thicker, less bendy) to make the struts, then laminate the wire between two layers of de-papered foam. You could then sand them down to the shape that you need.

 

[willsonman]

I like the way you think. Mostly because that is what I was thinking too. I was thinking of using steel rods that you get at the Home depot. They are super strong and difficult to bend but we are talking about mostly horizontal lines. I can make fairings from foam around them. They do not need to be super stiff as they will be strutted to the wing. But tortionally they do need to be quite stiff on water landings for those pontoons.

 

[AkimboGlueGuns]

You could always try making fairings for the floats out of ply wood. If they only need to be stiff on the floats, then ply wood may be the best for stiffness to weight ratio.

 

[AkimboGlueGuns]

after looking at the picture, You may just want to reinforce the float with ply wood the you can anchor the wire into. Ply would be kinda ugly on a plane like this.

 

[willsonman]

after looking at the picture, You may just want to reinforce the float with ply wood the you can anchor the wire into. Ply would be kinda ugly on a plane like this.

This... exactly. Plan to do the float in foam and have a ply cap to anchor it all well.

 

[willsonman]

I have gotten a couple of questions about this project recently and the overarching theme has been "what have you gotten done?"

In a word... NOTHING.

I want to make it crystal clear... this is a BUILD for FTFF2015. I will NOT be bringing a completed plane. I will be packing up my entire shop and build the plane at FTFF. I will start with raw materials. I will not even pre-cut the plans. Every part of the build will be done at FTFF2015. This thread is for community suggestions to aid in planning and execution of the project. I do not want to share a plane at FTFF I want to share a build. The only way to do that is to build it there.

To summarize... I will build a 76-inch span SCALE Sikorsky S-39 at FTFF2015. No profile foamy, no box fuselage, no armin wing, NO COMPROMISES!

 

[Ron B]

WOW
When you do your packing list you had better include lots of caffeen and something to take to keep you awake as you are going to be building 24/4 on it. I hope you don't fall asleep after you get it in the air.