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Old Jan 01, 2014, 10:32 PM
Thermal Wrangler
DrFragnasty's Avatar
Launceston Tasmania
Joined Mar 2004
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4M Lunak

Just acquired my first Lunak. Always loved the shape of these ships. It's a Reichard 4M I gather.

This'll be a slow build with a view to making it a slope weapon and aerotow aerobat.

Replacing the tailplane is #1 priority since it weighs a tonne! I'm exploring options here; vac-bagged blue foam tails with elevator servos mounted in the fuz is the way I'd prefer.

The wing is almost complete except for tip damage but I'm worried about the weight of the wings. The roll-rate must be near-glacial. The TE is as thick as your little finger. Maybe a new set of wings with a HQW 2.5? MH32?

The fuz however is spot-on. Not sure about the canopy lip. What's the extra "step" for?
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Old Jan 01, 2014, 11:44 PM
EvShaw
South Africa, GP, Lethabong
Joined Sep 2007
4 Posts
My 2 cents worth!... If I may? One of my favorite airfoils is the SD7037. It has a nice speed range and seems to be able to carry weight extremely well!
Enjoy the build!
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Old Jan 02, 2014, 01:09 AM
Will fly for food
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Bellevue WA,
Joined Dec 2003
6,608 Posts
Don't worry about the weight. Without it, penetration will be hindered. I flew mine quite often on the slope with a 2.5lb ballast weight. When coupling the mid flaps with the ailerons the roll rate is very good. Here is a vid from many years ago when I got the chance to fly a buddies Lunak at Eagle Butte. I was trying to stay away from the other slopers.

Lunak (4 min 2 sec)
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Old Jan 02, 2014, 01:09 AM
Registered User
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Nice bit of glass work that, do you have access to the moulds?
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Old Jan 02, 2014, 02:38 AM
Thermal Wrangler
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Launceston Tasmania
Joined Mar 2004
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Moulds? No, but I can ask. As for wing section, 7037 at 12-13% root would be good. What's a tip section to transition to?

The fuselage root moulding is 375 mm, 45mm thick presently and looks like an HQ section.

EDIT: It could be the E211 section as noted on Esprit Model:

http://www.espritmodel.com/lf107-lunak-arf.aspx
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Old Jan 02, 2014, 04:49 AM
Thermal Wrangler
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Launceston Tasmania
Joined Mar 2004
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Retroplane Reference Photos

Found some excellent reference photos of the Lunak on retroplane:

http://www.retroplane.net/romanin/romanin.htm
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Old Jan 02, 2014, 10:06 AM
bie
maidenflight-postponer
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Germany
Joined Oct 2004
787 Posts
Hi,

had one Reichard-Lunak a couple of years ago and wrote a review about it for the August 2005-edition of german magazine Modellflug International. Sadly I lost the Lunak in June 2009 due to my inability of reading the thermals right at the Colli San Fermo in Italy...

Even a big bird like that can become very small, when the lady whispers in your ear: „Minus 400 meters..."

Just my 2 cents: No need to build a new tailplane or a new set of wings, if you want to have a very good allrounder with aerobatic capabilities. You can have a lot of fun as well in flat land thermal conditions after aerotowing as you can have at the slope or in alpine conditions.

Don’t worry about the weight: 8 kg (plus) are required for good penetration and they are relatively easy to handle when thermalling.

Flaps, flaperons and ailerons give you plenty of possibilities to get a decent rollrate and to land safely.

I built two servos into the elevator, one for each half. If you like to, you can use them additionally to aileron/flaperon when doing a roll - one half down, one half up. I didn’t use it, it wasn’t necessary for my style of flying.

Anyway: Have fun!!!

By the way: Have a look at Lunak.de...

Andy
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Old Jan 02, 2014, 12:46 PM
Paul
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Mold UK
Joined Apr 2005
123 Posts
Andy is right, the stock Reichard Lunak is good for aerobatics, as per the full size and doesn't need major surgery.

The odd tweak won't go astray however. Plenty of info here http://scalesoaring.co.uk/cgi-bin/ya...m=1270226171/5
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Old Jan 02, 2014, 01:17 PM
Thermal Wrangler
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Launceston Tasmania
Joined Mar 2004
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Thanks for the link Andy, lots of useful photos there:



Ditto Slopeangel; the top-drive flap mod in that thread is something I'd definitely do.
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Old Mar 06, 2014, 03:16 AM
Thermal Wrangler
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Launceston Tasmania
Joined Mar 2004
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Lunak Attack

Progress is slow but now the backlog of lazing around over summer is cleared it's under way again.

Goal for this re-build is to keep it light at the extremities especially the tail. This will be flown off less than ideal slopes and aerotowed so a wide flight envelope is needed.

Not much I can do about the wing structure unless I make another. I'll try it as is.

The Ideal Scratch-Built Wing
Ideally I'd have a vac-bagged, peel ply hinged wing using 93g plain weave carbon under a thin veneer skin (Mulitplex-esque) and housing a light but unbendable carbon spar with rectangular joiner boxes.

But, I already have the stock wing, I'll see how this goes as-is.

Elevator servos relocated into the fuz and using one rather than two elevator servos. Plug-in tail halves will be easy to do but the rudder needs to removable because of this. Elevators are heavy but I'll try it as stock.

Next up is laying-up some elevator joiner rod tubes that get set permanently into the fuz.
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Old Mar 07, 2014, 07:02 AM
Thermal Wrangler
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Launceston Tasmania
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Tailplane joiner housing

Tailplane joiner housing done.
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Old Mar 08, 2014, 03:47 AM
Thermal Wrangler
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Launceston Tasmania
Joined Mar 2004
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Joiner housing curing

Decided against making the fuz holes bigger to accommodate tube housing and instead cut them to fit flush on the inside.

Joiners waxed and inserted to help locate tube housing then a bog mix (cotton flock) anchors them.

Currently curing with tail taped into position.
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Old Mar 10, 2014, 04:12 PM
Thermal Wrangler
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Launceston Tasmania
Joined Mar 2004
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Elevator Drive

Elevator drive is aluminium extrusion located permanently in the fuz, floating and housed in carbon boxes within each elevator half.

This is where the gap-filling properties of resin / bog compensate for any errors I make.

Elevator drive sanded with 1000grit, waxed then wrapped with 2 wraps of baking paper for clearance then wrapped with wet-out plain weave 93g carbon and taped to maintain pressure.

Once cured, cut and sanded, each box is glued into an elevator half and that's the elevator drive crank. No bearing support needed because the hinges provide that.

Just an opening in each fuz side for clearance.
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Old Mar 14, 2014, 05:24 AM
Thermal Wrangler
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Launceston Tasmania
Joined Mar 2004
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Elevator Drive

Elevator Drive Done
  • Cured and trimmed elevator drive boxes.
  • Trimmed alum drive to fit and drilled a few lightning hole in it.
  • Had a spare Blaster 2 DLG elevator horn. Trimmed to fit.
  • Drilled / countersunk alum drive to fit the horn.

Upon closer inspection one elevator half had the brass joiner tube pushed deep into the tailplane. Surprised it actually received the joiner rod.

Brass tube removed ready to be replaced with lighter tube.

Removed redundant servo mount material both sides. The weight loss was significant.

So far lost 93g from the tailplane and that doesn't include servos / clevises / pushrods.

Next-up install alum drive in permanently.
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Old Mar 14, 2014, 08:45 AM
bie
maidenflight-postponer
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Germany
Joined Oct 2004
787 Posts
Hey Doc,

though I really respect your craftmanship and follow this thread closely, I don’t get the idea behind all the mods you’re doing or planning to do with the Reichard-Lunak to lose weight on that ship.

I mean: The Lunak has a bulky fuselage, a big wing area and kind of an outdated airfoil (that nevertheless works fine on this glider).

This means, it needs a healthy AUW for decent flying characteristics, starting at around 8 kilogram (that’s around 17,5 lb).

So, again: What’s your intention? I can’t imagine better flying characteristics in this case with less weight. So, what’s your aim in terms of weight? And why?

No harm intended - just curiosity!

Regards,

Andy
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