33% Zlin 24 Krajanek

[johnndeanna]

Well,

I believe I am ready to start a build thread since I have finally decided on a first sailplane. AS the title indicates I am going to be building a Zlin 24 Krajanek as my first plane. I chose this plane for a number of reasons, and many of them are due to the high number of firsts with this plane. It will be my first glider, my first large scale model, and my first complete scratchbuild. For my first build I felt it was important to keep my interest high throughout the build. The plane has a relatively low parts count as compared to some other planes, and it is a very good looking plane. It will help a lot to have the low parts count so that I can make good progress in order to get in the air quickly. I consider this a building block to more complicated builds down the line so it's important that I use this as a learning tool rather than feel overwhelmed with it.

This weekend construction begins with the building of the main workbench. I have a 10'x12' bench along the walls right now, but want a bench I can access from all sides to help with construction of the larger assemblies. Going to be 30"x8', which should give me ample room for most any planes I will likely build (due to size of space and transport constraints). I am really looking forward to getting started. Please feel free to tag along as I proceed and I welcome and concerns or comments along the way. I'll be picking up a new bench sander and scroll saw tomorrow after work so I will be ready to go come this weekend. Going to be a fun time I think.

John

[ARUP]

That will be a great sailplane! Aerobatics will be 'scale' with it, too!

[lenb]

Need photos

[Tom]

Good choice!

[johnndeanna]

Michael, I thought so too.

Len, absolutely.

Tom, the exact plane I was looking to replicate. I do have a photo pack of that particular plane which leads me to my first question.

The plans I have (from Jim Owen at Scale Soaring UK) do not specifiy skin material. What thickness of plywood should I use to skin the fuse to replicate that particular plane? I'm thinking 1/16" would be sufficient but wondered about weight gain aft of the CG. And after skinning would you just stain and varnish or would you glass and epoxy over it?


John

[johnndeanna]

Question 2, what would the object in front of the cockpit be used for?

(edit) I answered my own question. Pitot tube.

[lenb]

Grunau Baby twin?

Cool choice. Looking forward to the build and lurking in the dark corner.

[Tom]

Michael, I thought so too.

Len, absolutely.

Tom, the exact plane I was looking to replicate. I do have a photo pack of that particular plane which leads me to my first question.

The plans I have (from Jim Owen at Scale Soaring UK) do not specifiy skin material. What thickness of plywood should I use to skin the fuse to replicate that particular plane? I'm thinking 1/16" would be sufficient but wondered about weight gain aft of the CG. And after skinning would you just stain and varnish or would you glass and epoxy over it?


John

Plywood choice should be 1/16” on the forward part of the fuse......aft of the CG switch to 1/32”. For that aircraft with its natural finish I would glass the interior of the 1/16” sheeted area and then stain and varnish......that way the front end is reinforced where needed. You could also stain everything first and then glass it all with .75oz glass but that will only add weight.

[Dave Smith]

Video here:

https://www.youtube.com/watch?v=JGNip3vjv64

[ARUP]

Nice vid! Good tips for construction of model if you 'freeze frame' the structure shots in the vid!

[johnndeanna]

Plywood choice should be 1/16” on the forward part of the fuse......aft of the CG switch to 1/32”. For that aircraft with its natural finish I would glass the interior of the 1/16” sheeted area and then stain and varnish......that way the front end is reinforced where needed. You could also stain everything first and then glass it all with .75oz glass but that will only add weight.

Thanks Tom. I'll follow your recommendation and glass the interior and go with varnish for the rest of the plane aft of the cockpit. I would think that given how thin the plywood is I wouldn't need to shim the 1/32" to match the 1/16" outer surface? Doubt 1/32" difference would be noticeable at all where the two thicknesses join.

I am starting to get really stoked about getting started. While I don't want to spend all my time in the garage, I should get at 90 minutes in the evening a few times a week, plus I have my lunch hour at work every day, and I arrive in the office 90 minutes early every day so I'm not sitting in traffic, so I probably have 2 full hours a day at work I can do something, plus another 10 hours a week at home minimum. With that sort of time I should make pretty steady progress. Nothing like enjoying spring SC weather on the top of the parking deck at work sanding ribs and notching for spars. I could have all the ribs done in a week at work once I get the outlines cut on the scroll saw. Going to be a lot of fun.

[ARUP]

Definitely use thicker marine grade ply on the bottom at least to the end of skid. Balsa shims aft of that will 'fair' the thinner ply to the thicker ply. FWIW, I use 1/64" ply on my vintage birds almost exclusively. I do put thicker stock on the bottom so that the rare rock or stump (corn field stubble) won't punch through. The skid hard points are usually located at a scale location where vertical formers are located. The landing loads are transmitted through these and dispersed throughout the local structure. Study that video! It' pure gold! Carbon fiber tow with epoxy is used to tie parts together like the tow release loop into the nose or wing hold pylon into the fuselage.

[Al_M]

Nice looking sailplane. Excellent choice! It has a strong resemblance to the Grunau Baby, but I guess that has alteady been noted. I will be following your build with enthusiasm. Good luck!