SZD-22 Mucha 1/4

[mlachow]

SZD-22 Mucha 1:4

Wingspan 3.75m

Length 1.75m

Weight 5kg

Manufacturer - Oldgliders.com

Web Site - https://oldgliders.com/en/offer/szd-22-mucha-14-kit/

Main Wings - Two Piece

Main Wing Materials - Balsa / Ply / Pine / CF Joiner

Airfoil HQ 2.5/12

Fuselage Single piece, single wheel

Tail Removable stab, Balsa, Ply, Pine

Control Surfaces Ailerons(2), Spoilers (2) Rudder, Elevator(2), Tow Release


Well things are quiet on the forums, so time to enter a new build. I actually started doing a little bit of work on the model back in May. Just basic framing on the tail and fuselage. Things got started again in November after I finished painting project that taking up part of the workshop. So now it's back to making some more balsa dust.

Video Documentation - https://www.youtube.com/watch?v=s9rDpsOEI28
Mucha Standard SP-2117 - YouTube

[mlachow]

First step on the tail is to build the frame out of the machined parts.

And the rudder.

[mlachow]

The rudder post and elevators are all drilled for the hinges before building everything. That way things are aligned.

A false LE gets added to the stab. Then the stab gets sheeted with 2mm balsa. I picked through the sheets for the lightest ones. After that, the LE can get added to the stab.

The rudder and elevators get the front LE added, some 10mm balsa. This gets slotted later to expose the hinge point holes again.




Next the rest of the sheeting is added to the elevators and rudder. The angled pieces are installed as larger rectangles. Then they get trimmed to shape after the cap strips are fitted. Markings were made on the drawings to record where the hinge points are located and where the balsa fill is located for the control horns. I will probably install some small micro wing servos each side of the elevator.



The rudder fits on the fin. The stab bolts in from the top. There is a fiberglass fairing that gets put on when you install the stab. This is going to be a pain if the stab gets removed. It mighty require a little creativity with some magnets.




If you really want a lighter model, then these tails reallly need to made out of all balsa instead of the light ply. My Zugvogel stab is way lighter. It is made out of balsa, with 1.5mm (1/16) sheeting

[mlachow]

The fuselage needs a building fixture. It gets cut to the basic bottom outline, with a few vertical supports added to hold the top outline. Most parts interlock together. I cut and fitted wheel mounts from aluminum before assembling everything.

I used a mix of balsa and spruce strips. A few are spruce but most of the in between strips are balsa to save a little weight.


I did the stab mount bolt work before sheeting everything. While the oldgliders build photos show most of the fuselage planking as pieces between each former, I used longer pieces. I tried to mix the overlaps every two formers. I also scarf the ends of each piece. Probably not necessary but it should add a little extra strength. Some of the 2.5mm balsa sheeting was on the heavy side. I used some thicker 1/8 sheeting that I considered scrap. I had an order of balsa come in and it was cut from a pretty thin balsa log. The sheeting looked like a potato chip and it was not flat anywhere on the sheet. So as a piece of 4 x 48 1/8 balsa it was useless. It did cut up nicely into smaller pieces to bend over this fuselage. I used good quality sheeting on the fin.

At this point the top is mostly sheeted. The next step is to work on the motor mount up front. Then finish up the rear sheeting and the part of the fin that extends in front of the stab on the Mucha. After that I will flip the fuselage over in some cradles to finish up the bottom sheeting and landing gear.

[stevekremer]

Looks nice Mike!

[SMYK]

Why 1/4 scale and not 1/3 scale?
Binio has bigger one
SZD 22 is called MUCHA STD
There was a MUCHA ter as well. Older sister

Mike

[mlachow]

It all comes down to what you can haul around. For my van, with two 1/3 scale models, I can fit at least 3 1/4 scale models. I plan to put a motor in it so with a bungee or winch take off I can fly it at home. And the 1/4 models often fit with the tail attached to reduce setup time.


The SZD-12 would have been nicer to look at. There is one really nice restoration I have seen pictures of. There aren't many 3.5 scale kits/plans out there. Plus there aren't any SZD-22's flying around so I'm trying to keep some variety and color on the field. Everyone else can squint and say is that a JS-3 or a Diana-4.

What are you building?

[mlachow]

The wing starts out with getting all the ribs ready and getting the building shims cut. Plus cutting all the strip wood for spars, LE, aileron hinge line.

I also used some scrap plywood to create some alignment guides for all the ribs. The first step was gluing the ribs to the bottom spar. Then I add the shims and glue in the bottom of the TE and the aileron hinge line.


The shims are tapered and covered with flash break tape. Great for taping on wings and for building.
The aileron hinge line has some 10mm balsa and I glued the 2mm skin piece to that ahead of time.

I only used some of the ply ribs for the ailerons. I replaced the rest of the diagonals with balsa pieces. No need for all that plywood and the balsa pieces are probably stronger anyway.

[mlachow]

Now I can get ready for the top spar and the webs. Some balsa was shaped to fill in between the spars and the wing tube at the root. I also added the rear spar to the wing. You just have to be careful on the inner two ribs. They are much wider and don't follow the straight taper of the wing.



After that dries it's time to start adding the webbing. Most of it is balsa. But at the root I switched to 1.5mm plywood. The tubing is a little wider than the spar. So those webs by the tubing require an extra 0.8mm ply spacer. SInce the aileron ribs are all done, I also added the top TE strip. In the root area, there is some balsa filler in there to add a little strength. Otherwise the 1mm pine can be damaged with fat fingers trying to move the model by the TE between ribs.

[mlachow]

The final step after putting the ply webs on the root is doing an extra wrap with kevlar. The model us under 4 meters so I didn't wrap the full spar Only the center. After applying epoxy to the kevlar, wipe off the excess then wrap it with electrical tape to keep it flat and smooth until it cures.




Now the wing sheeting and cap strips can start. Sometimes I iron it on, sometimes I use pins on smaller, flatter areas. The caps have an extra bit at the front edge. That starts out as a rectangle which is trimmed down to the rest of the cap strip behind it. Technically it is supposed to be a radius but a simple angle is good enough.

[mlachow]

Progressing along with sheeting and cap stripping the wing. First the top is sheeted then the bottom. Cap strips also need to be added.

The TE sheeting at the root, behind the 1mm pine TE strip was made from 0.4mm (1/64) ply and 1/32 balsa laminated over it. I cut four pieces so the other two are ready for the second wing panel.

I am putting in the wing wires now. A section of tubing was run near the root to keep that part of the cable in place Since it is just two channels, there will be just two regular servo wires.

The ply frame for a servo opening for the spoilers is huge. I have no idea why it is that wide. I will cut a piece to reduce that down to half the size. You don't need much room for an MKS6110HV servo.

The spoiler is not really scale. It should be upper and lower surfaces and 3 rib bays wide. The one they supplied is 3 1/2 bays wide.

The aileron is very long and narrow. It appears to be stiff enough with the diagonals.



It looks like I am almost ready to start the second wing panel.

[mlachow]

OK, second wing panel is started. This should be faster since I have any strips prepared and the root TE piece and joiner rod filler.

[Sinkhappens86]

You're making quick work of this one!

[mlachow]

Quick work on the second wing panel. Tomorrow might be slower since it looks like some mid-day flying weather.

Second wing panel has all the ribs, spars, webs, subLE top of TE, aileron ribs put together. Next step is spar wrap and the bottom rear spars. Then I can proceed with the sheeting and cap strips.

[mlachow]

The second wing has been sheeted on top. I still need to complete the bottom sheeting. So the new years eve plane drop is below.