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Jun 14, 2014, 12:43 AM
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Sikorsky S39 build "Spirit of Africa"


Well it's not so much of a build log as the build is almost complete.
I just thought I'd take the opportunity to post up a couple of pictures of my Sikorsky S39 build, started in September 2013 and hopefully finished within a 12 month period. Span is 1.4m (55" in imperial speak).

I got hooked on the design when I saw the Spirit of Igor online. It is just such a distinctive plane I couldn't resist. Now that the registration numbers are on, I've got to follow through with all those giraffe spots

My version is a reduced version of the Bob Rich design. I couldn't fit an orginal sized one so I reduced it down to 55" to be able to get it in my car.
My target weight is 38oz to give a wing loading of 12.4 oz/sq ft.
Power train will be electic and draw about 500w on a 4S system. This should be well over powered and I want to just be able to putt around on 1/2 throttle and keep the amps minimal.


The pictures are pretty self explanatory...

I had a real hassle with a couple of parts of the build that are a worth noting for any future builders.

1) As I scaled down the original plans I ran into issues with the rudder linkage. The design called for a flexible cable routed down a boom. With the reduced size of the plane the rudder linkage radius also shrunk, meaning that it bound terribly. I have figured out a pull pull system that will work better and is strangely similar to the full size plane through sheer coincidence.

2) The tip floats I found were too fragile, after crushing one while screwing in a strut. I ended up just making some from blue foam, which was then balsa sheeted and glassing. They wont crush or sink now.

3) The struts too were lots of fun.. harder to keep straight than a box of springs.
I eventually went with streamline aluminium tube with brass inserts for attachments. The inserts were squeezed in with compressed balsa either side to a friction fit. I then screwed all the parts together and pushed and pulled the friction fits to make everything right. Then wicked thin CA into the balsa to firm it all up. we'll see if it stands up to the inevitable abuse I will give it.

Watch this space for the build completion and maiden.

-Mat-
Last edited by Wormboy; Jun 14, 2014 at 12:54 AM.
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Jul 07, 2014, 06:57 PM
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Sikorsty S39 - Spots


Well the spots are painted on now. I know it's is not strictly scale as I have missed a couple of features and the spot design is not quite the same. Nevertheless, it is unmistakably the Spirit of Africa now.

All that remains is glazing the windows, hooking up the ESC and motor, finishing off a spacer ring for the radial and final assembly.

Weather permitting, the maiden will be this weekend!
Wish me "happy landings".
Jul 10, 2014, 02:01 PM
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Very nice! I made one from foam a couple years ago. Mine's slightly smaller at 52", about 32oz, and I flew it on 3S. I also ran the elevator pull-pull inside the booms, and I ran the rudder pull-pull from a servo in the nacelle.

https://www.rcgroups.com/forums/show....php?t=1015724
Jul 12, 2014, 01:18 AM
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Quote:
Originally Posted by warhead_71
Very nice! I made one from foam a couple years ago. Mine's slightly smaller at 52", about 32oz, and I flew it on 3S. I also ran the elevator pull-pull inside the booms, and I ran the rudder pull-pull from a servo in the nacelle.

https://www.rcgroups.com/forums/show....php?t=1015724
Hi Warhead,
Yes, I have seen your build, great job. I hope yours is still flying.
With a bit of luck I will be able to make mine fly as smoothly as yours.

I could have easily gone with the 3S or 4S setups
However, my cooling ventilation is limited so I went for a higher volts / lower amps option. This way the whole power train has heaps of headroom on amps draw, keeping the need for cooling to a minimum.
Jul 21, 2014, 12:36 PM
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If I recall, I think I ended up putting the ESC inside the fuselage. I think it would work out well to use thermal compound to "glue" a tall aluminum heatsink to your ESC, letting the heatsink protrude through the fuselage into the airflow (or even mounted to the bottom of the plane, behind the step, so it can be cooled by water -- being very careful to seal around it).

https://www.rcgroups.com/forums/show...7&postcount=20
Oct 11, 2016, 05:23 AM
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Fantastic plane


I know, it's a while ago, since you posted this "build log" but I have a question anyway. Do you have a picture of the leading edge of the main wing before sheeting?

I'm plan to build the same bird, maybe a little bit smaller (1:12 scale) and so I am doing a bit of research.

Cheers Jannick
Oct 11, 2016, 07:31 AM
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Thanks Jannick,
I would certainly recommend the S 39. It's a great little plane. I do have a couple of things I would do differently and if you go ahead with yours I am happy to go through them for you.

I have been through my photos and can't see a pic of the wing before the sheeting was added. Sorry.
If you have a set of the same plans then the wing is built mostly as layed out. IIRC

EDIT: After consulting the plans again you're right, my leading edge is formed differently.
I used an oversize leading edge with sheeting butted in behind then the whole lot sanded to shape instead of the original round dowel leading edge.

Cheers,
Mat
Last edited by Wormboy; Oct 11, 2016 at 08:53 AM.
Oct 11, 2016, 07:36 AM
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Here are a couple of recent photos of my S39 ... just to keep you interested
Oct 12, 2016, 09:29 AM
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Like.
Jan 09, 2017, 11:12 AM
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mmalmsten's Avatar
Nice job! This is going to be my next build and am glad to find some references.

Mike
Jan 09, 2017, 07:34 PM
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Quote:
Originally Posted by mmalmsten
Nice job! This is going to be my next build and am glad to find some references.

Mike
Nice one Mike, she's a great plane and you'll love it.
There is another one being built here.
https://www.rcgroups.com/forums/show...d-from-Scratch
If you have questions I can help you with just ask. Do you have a build thread yet?

Mat
Jan 10, 2017, 06:52 AM
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Not yet, I have to finish up a hydroplane and rescue tug build before I get to this one. I have a set of drawings and a plans for it that I am modifying/tweaking while I finish up the boats.

I will start a build log and am sure I will be reaching out to you at some point. Thanks for the offer.

Mike


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