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Author Topic: Sikorsky S-39 "Spirit of Africa"  (Read 9113 times)
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billdennis747
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« Reply #125 on: October 05, 2018, 04:11:07 PM »

Hi Bill, I imagine it should work in theory,

the only suitable tubing I have is 1,48mm o.d./0,8mm i.d., so by the time it gets to the outer diameter I want, I might be having a bigger inner diameter as well, leaving me with a very thin walled tube. Practically I imagine the inside will not get as much corroded, so that may not be an issue.

Issue nr. 2, Is caustic soda all that is needed? I might have some in Greece, so I could give it a try as an alternative solution. Never done it...

Thanks for the suggestion,

George
Block the ends! This from another thread:

Briefly, strong solution of caustic soda in plastic tub, outside, latex gloves, preferably goggles, tweezers, separate tub of water to dip in.
Put the sheet in and agitate and turn over while it fizzes. Take it out out occasionally, dip in water and check. Keep going until it's as thin as you want. Don't get distracted, it will disappear altogether and that's too thin.
If you look at some of Terry Manley's models from the 70s (FK8, Vimy, Blackburn Swift, Sprat) the beautiful metalwork was done like this

Keep weighing it to follow progress. Yes, just caustic soda
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OZPAF
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« Reply #126 on: October 05, 2018, 08:24:02 PM »

it's amazing how much complexity can be hidden in an apparently simple Mechanism. Entertaining and instructional - thanks George.

John
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g_kandylakis
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« Reply #127 on: October 30, 2018, 06:39:38 AM »

Late reply, as usual...

thanks for the comments and also (Bill) for the solution to my tube problem. Have not tried it yet, but will when I 'll need the parts and have the time.

In the begining of the month I posted the jig and was about to make the actuation mechanism.

Solution #1 is finished and was tested on the jig, with one side of the landing gear. This has two side effects. First the load is only 50%, second the servo receives an unequal side load. Both give me some questions about the end result.

It seems to be working well, although not as smooth as I had expexted. When I compared again the manual (hand) activation, it was much smoother. It turns out that I am deforming the push-pull wire quite a lot and this causes extra friction. So, back to the drawing board.  Version #2 is almost finished, should be much smoother, I hope...

https://youtu.be/BxGDlQ3McFw

Not much to explain, I hope the photos and video do that for me, but if there are any questions, please shoot freely  Wink

George
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rgroener
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« Reply #128 on: October 31, 2018, 02:05:37 AM »

George, very nice progress. This will be an other impressive ship you build.
The mechanism for the gear seems to work quite well. It's always interesting what complex things you can achieve with simple materials.
Roman
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g_kandylakis
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« Reply #129 on: November 19, 2018, 05:01:06 PM »

Thanks for the kind words, Roman...

Yes, everything seems possible, it would be even easier if one had the proper tools for the job. Else you have to improvise a lot...

As I wrote, I tried a slightly different approach with my second attempt, but that turned out to be a complete failure. It would not move at all, too much strain on the servo. The only way for this to work is to have zero friction resistance.

This shouldn't be a problem, theoretically it is supposed to operate only when the model is airborne so the landing gear will be under no load.
I bet though that there will be many rectractions before take off and many landings with gear up  Grin. Murphy's law will definetely want to come to play...

So, after some figuring out I went to attempt #3, which was in effect similar to the first, but with improvements to enable smoother running.

I am glad to say that it seems to work as hoped for. I also opted to use a slightly better servo, 0,2 gr heavier, but stronger (100gr force compared to 75), but I can always try with the lighter one, when completely finished.

Here is a video of the various test runs at different speed settings. Not as smooth at very low speed, but still working properly.

https://www.youtube.com/watch?v=e4g3imkE_b0&t=8s
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Mefot
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« Reply #130 on: November 19, 2018, 05:39:22 PM »

I'm really enjoying this build. An education in keeping going until it's perfect instead of the " that will do" attitude !!!

I may have missed this in an earlier post so please forgive me if you have already answered the question before.

When you fly this freeflight will you replace the receiver with a programmer to control the motor and activate the retracts ?  Smiley
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g_kandylakis
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« Reply #131 on: November 19, 2018, 05:50:48 PM »

When you fly this freeflight will you replace the receiver with a programmer to control the motor and activate the retracts ?  Smiley

Yes, that is the plan. There is one already available from SAMS, but I have something else in mind, which is still in the works...
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« Reply #132 on: November 19, 2018, 05:59:11 PM »

I am looking forward to seeing the "something else " with eager anticipation  Smiley
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g_kandylakis
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« Reply #133 on: November 19, 2018, 06:00:07 PM »

yeah, me too  Grin

Not in my hands though...  Wink
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« Reply #134 on: November 19, 2018, 06:02:27 PM »

 Grin Grin Grin Grin Grin !!!!!
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g_kandylakis
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« Reply #135 on: November 19, 2018, 06:04:37 PM »

And time to get out of the test phase with a mockup and see it on the model. Again. only 50% done, left side only...

In the photos you can see the 3 different versions. The second had an interesting advantage with the servo closer to the CG, but it did not work, so, who cares...

And a short video... The model is doing some push-ups as well  Grin

https://youtu.be/--5LTDT3djg

I should finish the parts for the other side, I guess Roll Eyes

George
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« Reply #136 on: November 19, 2018, 09:03:44 PM »

Loving it, George  Smiley

My anticipation is also eager as I wait to see your final control system!
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Glenn (gravitywell) Reach
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« Reply #137 on: November 19, 2018, 11:58:25 PM »

Man!  How do you guys come up with this stuff!  I must have only half a brain or something! LOL
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« Reply #138 on: November 20, 2018, 11:53:26 PM »

Exceptionally cool George!!  Beautiful design and great work.
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« Reply #139 on: November 22, 2018, 12:14:56 AM »

Clever and still simple enough to be hand made. Very nicely engineered. Re the slight lack of smoothness at slow speeds - I suspect this is probably a limitation of the servo resolution. They are probably not made to the standards you set yourself Smiley

What material are you using for your pull cord? Spectra?

John
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g_kandylakis
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« Reply #140 on: November 22, 2018, 12:49:58 AM »

Hi John,

Yes, from a point on it is indeed a servo limitation. I will send my complaints to the manufacturers  Grin

As for the cord, it is actually a pull-push cord, it has to lower the gear too. I made it out of 0,2mm music wire. Flexible enough to bend but not so weak as to bend under load

George
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« Reply #141 on: May 13, 2019, 03:04:39 PM »

Wow, so much dust...

Almost 6 months have passed, not a single update was posted. Not that there was any update at all to post  Grin.

Busy times, first with end of the year from business and family point of view, then a 3-view research project took over, then work again and only in April was it possible to get my hands on the model again.

And still so, not much done, just the final main components missing, struts and side floats. Major incentive here was to make bare bone pictures, so that helped a bit.

But first the floats...

Nothing spectacular, made of sheet wood and then any excess wood was removed for lightness. I doubt they will float as they are, unless some skinning is applied  Grin. And no, it is not intented fo water flying, I am not that crazy.

Fun fact, I ended up making 5 floats in total. The first two turned up a little heavier and not as clean as I wanted, then two more were made to my satisfaction, plus one to be used as a vacuum forming plug for the underside.
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« Reply #142 on: May 13, 2019, 03:07:03 PM »

not much, but some more float pictures...

These are the final ones. Bare weight is ok, although the plastic skinning is already causing me worries in terms of weight.
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« Reply #143 on: May 13, 2019, 03:11:59 PM »

And here the fun ones...

All struts will be basswood. In the picture the "hull to wing struts" are the only ones done. Hull to floats were done too, only to discover they are too short  Angry. The sanding of basswood in streamline shape is a very-very-very boring thing to do...

The remainder were simply cut from balsa strip, just for the shake of the assembly...
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« Reply #144 on: May 13, 2019, 03:18:57 PM »

and some close-ups. Not very impressive as photographs I am afraid.

The weight at the moment tells very little, as all 4 servos were in place, so probably the frame weight should be close to 17-18 grams.

I keep track of the weight budget, and hope to be ok, although there is serious fear of getting infected with Monzitis, depending on how much the plastic will add. Depending on the outcome, I may start removing items, such as servos, to the delight of the FF purists  Wink

So, that is it for now, more in November  Grin

George
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« Reply #145 on: May 13, 2019, 03:58:20 PM »

Great work, George, really amazing.
Where do you hide the helium bag to achieve such a low weight Huh
And dont let us wait till November for an update...  Cheesy

Urs
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« Reply #146 on: May 13, 2019, 04:06:27 PM »

custom made, inside the leading edge sheeting  Grin
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« Reply #147 on: May 13, 2019, 04:08:41 PM »

NEWS FLASH!

Secret informer has revealed dastardly plans of a Sikorsky S-39 to invade the 2019 IIFI in the Netherlands!  Watch this channel for further details as the story unfolds! Grin Cheesy
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« Reply #148 on: May 13, 2019, 04:12:22 PM »

2029 is more likely... Unless someone else beats me to it this year...
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« Reply #149 on: May 13, 2019, 04:27:05 PM »

Not very impressive as photographs I am afraid.
I beg to differ! That structure is just gorgeous, George. As ever, I’m in complete awe at your skill and workmanship!
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