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Posted by Wormboy | Jul 12, 2014 @ 01:28 AM | 1,937 Views
Well the maiden went reasonably well.

She survived the first flight with out sustaining any damage other than a little paintwork scrape on the bottom of the hull. Which is to be expected I suppose.

First flights were very hairy due to a pronounced nose up tendency.
CG was as per the plans but I think the wing incidence is to blame. Even moving the CG 15mm forward of that marked on the plan, and well forward of what I would have expected, she flew very tail heavy.

When scaling down the plan, I didn't decrease the incidence angle of the motor and wing. I think it was 5 deg from memory, which I think is too much now that the plane is lighter and smaller.

I plan to push the CG a little further forward and shim the motor down a bit to see if that will help the situation any. Unfortunately the Horizontal stabiliser / wing angle is set in epoxy now.

On the bright side, water handling was excellent, power is great and she lives to fly another day!

Pics attached and video below. Thanks MrWaz, for making her look even better than in real life

Please feel free to exmine the evidence and post your advice or comments re the pitching issue, I'm very much open to suggestions.

MrWaz haz done quite a good job of making my flight look a lot smoother than it actually was (or at least felt). I will post up a "warts and all" video for critique.

Sikorsky S-39 Spirit of Africa - maiden flight (2 min 55 sec)


Uncut version for analysis.

Sikorsky S-39 "Spirit of Africa" maiden flight - uncut version (4 min 14 sec)

-Mat-
Posted by Wormboy | Jun 14, 2014 @ 01:43 AM | 2,013 Views
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...Continue Reading