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Old Jan 05, 2013, 03:51 AM
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Build Log
Valmet L-70 Vinka Scratch build (1.45m / 57")

Hello everyone,

today's dish is scratch build of Valmet L-70 Vinka basic military trainer from 70's. This is rather nice looking plane which is said to be nice to fly. That is, the 1:1 plane is nice to fly. This is (to my best knowledge) first ever attempt to kit it to park-flying size, traditional balsa building way. Interesting thing is that it is loved plane, but only really limited nr. of build attempts exist. I'll give it try.

Original plane was designed in 70's and then taken into operational use in 80's. 30 of these were built and they are still in full use. As this is quite recent plane there is whopping amount of pictures around internjet, just use google to see those. I will enclose some pics here to save your efforts, but ... there are zillion more .

Also, it has wiki-pages in several languages, you could try following : english, german, finnish etc..

Tuomas
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Old Jan 05, 2013, 03:59 AM
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Then to design

I used some rainy days last summer to design this model and other projects have stopped me building it. Actually two of my pals are building proto's also, so they have headstart to me, but my aim is to be faster... I must be, because I have promised guy's that I will make canopies etc. plastic stuff for the planes.

This is not my first venture into designing model aeroplanes, check www.iwaru.fi for more designs and links to build logs. If everything works like in movies this model will be kitted.

Vinka has nice, simple curves, there are no exotic structures or forms. Just your average balsa bashing. My aim was to make smallish light park flyer so it means somewhat fragile plane.

Draft plans below.

Tuomas
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Old Jan 05, 2013, 06:46 AM
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A very good looking plane! Well proportioned for modelling. I will watch the progress with interest.

Geoff
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Old Jan 05, 2013, 12:10 PM
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elev

Thanks Geoff!

First in order is elevator.

Tuomas
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Old Jan 05, 2013, 02:10 PM
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It will be interesting to see this one come together.

Larry
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Old Jan 06, 2013, 01:20 PM
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Wings..

Thanks,

Todays steps are covered in couple next messages.

First - wing. Which is quite basic. Nothing fancy, only thing is the forward moving LE at root. Airfoil is Clark-Y so LE must be supported, but apart from that it is flat.

Tuomas
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Old Jan 06, 2013, 01:27 PM
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Basic fus stuff, formers

Then to fuselage.

As I do all designing in cad it allows fancy things, like split C-formers. I mean; the formers which normally are like C-characters tend to break due the balsa grain. So I have used following technique in couple planes. I simple split formers into 3 parts which are aligned according grain. They are pretty easy then to assemble. Only irritating thing is laser gap which is approx. 0.1-0.2mm. So I must make minor adjustment for those joining parts. Unless done there will be error of couple 0.1 at the end.

For strength I use doubler spar on formers around cockpit opening. I could have used same tech as with C-formers, but in cockpit area there is need for additional strength.

This all is a bit complicated to explain but pics tell everything.

Tuomas
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Old Jan 06, 2013, 01:34 PM
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Then to main event

Okay, now it's time to build fus. Structure is your average 'guillows'-style fus, but with additional box-structure to keep wing in one place.

I really have to admit that designing this type planes is all too easy and you can make mind boggling complex structures in cad which are interesting to build. I think that some details of this build are just a bit too ... interesting. But I can manage them.

Tuomas
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Old Jan 08, 2013, 02:30 PM
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Then to wing centerpiece

Ok, next one is seemingly simple but it is actually most difficult part in this project. Not because it's structures, they are simple. Challenge here is that if there is even minute twist or inconsistency in previous fus. phases this will not work at all...

Actually everything fit quite well. There were approx ~0.2 width error but that was easily sanded.

I was quite worried about possibility of internal box twist but no real problems...

Tuomas
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Old Jan 13, 2013, 03:57 PM
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that other build mentioned couple messages ago

I have been enjoying long weekend at my summer cottage (what - summer? it is winter here..) so no building. But peekoo, a pal of mine who is building same plane sent me couple pics of his status.

He is slightly ahead of me... That looks sooo nice.

Tuomas
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Old Jan 20, 2013, 01:20 PM
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I had to spend one day cleaning my shop.. But still did something.

Fixing one wing half.

Tuomas
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Old Jan 20, 2013, 01:40 PM
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meanwhile elsewhere..

You might remember that in the beginning of thread I mentioned that there are three simultaneous builds of this plane.
  1. mine which is pictured in this thread
  2. Peekoo who is slightly ahead of me, for his status see pic below
  3. Hsk is building his plane in .... just a bit more through way. He has managed to build full moving scale flaps in his wing. Picture below, for more see Hsk's website here http://www.elisanet.fi/~g631808/vinka/

Hsk's way of doing flaps deserves applause and I am quite anxious to see how it performs.

Tuomas
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Old Jan 21, 2013, 11:20 AM
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This is starting to look like it might have a very light wing loading... What's the weight at this point in the build?

James
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