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Old Jun 05, 2011, 03:31 PM
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Build log PIK-7 Harakka II, 1:4 (2,65m) with free plan

Gentlemen,

just one (hopefully) quick build before summer holidays start here. That is 1st of of july.

This time it's slightly more vintage than my previous build (see here). Plane in question is PIK-7 Harakka II.

This plane has strange and murky history. It's origins come from World war II. Finnish forces took control of Russian occupied city of Äänislinna. And they noticed that there were an glider pilot school of sorts there. Along with some planes which were called UC-3. They were brought to Finland and put to display at victory fair .

Planes were then examined and found to be inferior in many ways. But.. prior to this Finns had used Grunau 9, Wronan, Hols der Teufel etc. which were quite complicated and heavy. ... One of these UC-3's were tested and strangely enough, found to be good flier, despite of inferior build quality and several shortcomings.

This UC-3 brought inspiration of building an similar type primary glider to replace Grunau's etc. Key idea was to make it extremely simple, light and easy to build in aviation clubs around Finland. So... Harakka was designed. Actually, according Jukka Raunio's book PIK-Sarjan lentokoneet (PIK-planes..) they did not even bother to make plans for prototype. Just sort of design as you build.

It must be stressed that despite the inspiration aspect of UC-3 the Harakka and UC-3 were totally different planes. (btw; harakka is magpie in english).

Key part of ideology was to build glider as light as possible. Empty weight of Harakka was only 92kg, compared to SG-38's 120kg. That leads to all kinds of benefits, like less sweat when you are hauling glider up to hill.

Ok. Now prototype was built, found to be good flier (better than Grunau's & SG's). As this was simple plane approx 28 were built. It was good primary glider at the end of WWII.

War ended and booming aviation clubs needed more primary gliders. And Harakka needed development and some upgrades. Local FAA ordered further development from PIK. Key designers were Juhani Heinonen and Raimo Häkkinen. New plane was called Harakka II and given PIK-serial number of 7.

Then there was further development with Harakka III, but only one was ever built. All in all 57 Harakka's were built (or started, some were not completed).

My motivation to this plane comes from technical challenge of trying to design an simple and easy to build glider. And it is not so easy as it seems. That aft fuz is quite difficult to get rigid enough as this thing has almost no rigging. Also I like that really clumsy looking plane. It has certain character..

I am aware of one previous modelling attempt, which is hanging from ceiling of Finnish aviation museum. I do not know whether is has ever flown, but it looks nice & it is very scale. My goal is to design & build an semiscale model of Harakka II. I will not even attempt to make moving pilot dolls and to hide all servos inside structures. I am just happy to get something remotely resembling Harakka II to air.

Tuomas
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Last edited by tuootal; Aug 14, 2011 at 01:55 AM. Reason: changed title
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Old Jun 05, 2011, 03:43 PM
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Ok. Some words about model itself. My aim was to make as simple and straightforward plane as possible. Only spruce & balsa. No complicated riggings etc.

Wingspan is 2,65m, despite the fact that this is 1:4. That wing is huge. If weight will be 2kg the wing loading will be approx 20g/dm2. That is typical loading for indoor featherweight planes. I will try to get this heavier as I do not want to end up with kite.

The aerodynamics etc. of this plane are bad. I do not expect it to be good flier. Hopefully it can circle one round around airfield after aerotow .

Tuomas
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Old Jun 13, 2011, 07:58 AM
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very nice I still have a japanese Hykari (distant relative) that 30 years on I still love to fly on special ocasions.
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Old Jun 13, 2011, 03:43 PM
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Japanese glider..

Thanks Big Nuts!

I tried to google Hykari, but all I got was ... well, nothing related to gliders . I then tried my favourite treasure trove of information (here..). I guess that you mean Hikari ? (that site has many errors, but the amount of information is out of this planet, over 3000 gliders!).

That Hikari is one cute plane. Much more appealing than this rather grunt Harakka.

It is quite wonderful to have rather large scaling factor (in my case 1:4) and end up with mere 2,6m plane. That is just slightly over 100". You could build 1:2 sized plane and end up with approx 5m size.

Btw, some Harakka's had also similar egg-shaped fairing. I have toyed with idea of making that fairing, but it has quite complex form. See here.

Tuomas
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Old Jun 18, 2011, 01:50 PM
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Amazing coincidence

You might remember that I commented in first message of this thread that there is (at least) one previous modelling attempt of Harakka. It is hanging from ceiling of Finnish aviation museum.

And I was not certain whether it has ever flown.

Well...

Some time ago I was browsing local ebay look-a-like (huuto.net) and I noticed old postcard. It pictures that same Harakka from museum up in air.

Postcard has text on its backside. It says 'Harakka II glider radio-controlled model 1:4, JÄMI 1987 (C) Suomen Lennokki Foto O. LUMES.'

So now I know that the plane in museum has been flying, ie. it is not just static model. I guess this proves that world is rather small place anyway.

Tuomas
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Old Jun 20, 2011, 03:45 PM
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build day #3,5

Upper & lower sheeting for wing #2 and LE of wing #1. Simple enough. No pics needed as this is identical to previous.

Just one comment regarding the size of wing. This is quite wide for such an small plane.

Tuomas
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Old Jun 22, 2011, 03:44 PM
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build day #4

Short session today. Added some root sheeting, wing tips, rib caps, LE for wing #2.

This is interesting project. All the time it feels that it is almost done. But there is still plenty things missing. Wing servo's, fastening, struts, finalizing elev (incl. pushrods), hinges, ailerons, ..... skid, bench etc. etc.

Tuomas
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Old Jun 26, 2011, 04:28 PM
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some beauty photos...

Had time to take some motivational pictures...

It is getting there, but... there is still some elevators, ailerons and covering missing. And zillion minor details not listed here....

Tuomas
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Old Jun 26, 2011, 10:27 PM
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Very Nice!
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Old Jun 27, 2011, 06:17 PM
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build day #5,5

(Thanks ARUP, I enjoyed your work with Prufling ... that plane has character ).

Today I had limited time and managed only to finalize wings (ie. rest of root sheeting, root plywood 'riblets', servo supports, strut hardpoints, sanding ... sanding ... sanding ...) and ailerons. No fancy stuff. I experimented with faster way to make top-hinged aileron hinges. It will be interesting to see whether they will last. But this is slow flying (hopefully) kite, so I hope that there will be no flutter ...

Still missing elevs, covering, radio inst., CG, etc. And skid. That is interesting.

I am aiming to get this done before Wredeby Aerotow event, which starts at friday. And I am forced to make an short business trip wed-thu. ... This will be tight.

Tuomas
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