Hi guys; I'm new to gliders but have a extreme interest in anything scale of historical significance to me. I just wanted to build something small and unusual. I decided after some contemplation on the SG-38 glider in Czech service. Since I build in two scales, 1/6 and 1/12, I started to build the little one and keep it as much as I could below 5oz.
I put certain restrictions on myself for the build.
1) Use Skyloft for covering
2) Use only Amrulose nitrocellulose adhesive for assembly.
3) Use only Nitrate dope.
4) Keep as close to scale as is reasonable in such small size.
6) 3ch RC

These restrictions which I put on myself did pose a few complications and some conflicted with others.
Here are my violations.
1) increase wing area slightly. ( increase cord by 3/16" and increase wingspan by 2" area should be 175 sq/in, increased to 187 sq/in
2) Increase rudder area by 5% geometric enlargement.

My wing area increase alloes me to go from a Cube loading of [email protected] to [email protected] This gives me a bit of mass to play with just in case I cant hold my 5oz limit.
I started doing the CAD for the model about two weeks ago and started construction last Sunday. I have been Taking pictures throughout the process which I will post. I will start at the beginning and go from there, since I am a ways along.

Here is the continuation part two.

Continuation part three.

Looks great, I love it! However, I prefer mine to be slightly larger.

Only a little larger, Is that 1:4? I don't think that I will build a larger one of these. My next "larger" glider will be a 1:6 Grunau Baby. But I think that a 1:12 LF-109 Pionyr might actually be my next. Or something power like an Avia BH-21 1:6 or 1:12 have not yet decided the next.

Here I am starting on the wing. The templates are made out of one of my favorite materials. "Garolite". In this situation it is XX. I am also using the same for my control horns. Templates are 1/16 and control horns are 1/32. These are just the full ribs inboard of the ailerons. The half ribs in front of the ailerons will be made separately.

Here is the Skyloft covered fin and starting the wing. As I mentioned in the first post, I will be adding one rib on the inboard side, equaling one inch per wing half. The other ribs are spaced about 1-1/8' apart.

Originally Posted by Otakar

Only a little larger, Is that 1:4? I don't think that I will build a larger one of these. My next "larger" glider will be a 1:6 Grunau Baby. But I think that a 1:12 LF-109 Pionyr might actually be my next. Or something power like an Avia BH-21 1:6 or 1:12 have not yet decided the next.

No, it's 1:3 scale. Bigger flys better!

So true. "bigger flys better". Too big for my back yard though.

In most cases, that's true with scale RC sailplanes but not the case when you are flying non scale sailplanes.

A 2 meter sailplane will almost always fly circles around a larger sized RC sailplane of the same name and stay up longer as well.

Originally Posted by Plantation Bruce

In most cases, that's true with scale RC sailplanes but not the case when you are flying non scale sailplanes.

A 2 meter sailplane will almost always fly circles around a larger sized RC sailplane of the same name and stay up longer as well.

Ah.......no. In fact the opposite is true.....more wing area is always going to preform better then less.......the larger wing area is going to have a lower wing loading most of the time which translates into better performance across the board.

Where is your CG on your SG-38. That is the "scale" airplane we are covering here. I know that my center of lift might be a bit different than yours due to a different airfoil. but it will give me a general idea. I can't find anything on the web.

here is a PDF of my fuselage CAD drawing with the CG where I "THINK it should be.

Originally Posted by Otakar

here is a PDF of my fuselage CAD drawing with the CG where I "THINK it should be.

That looks like the perfect starting point for the CG to me, lovely project and plan by the way, will you be sharing the wing plan as well ?

Originally Posted by Plantation Bruce

In most cases, that's true with scale RC sailplanes but not the case when you are flying non scale sailplanes.

A 2 meter sailplane will almost always fly circles around a larger sized RC sailplane of the same name and stay up longer as well.

If that was the case you'd see all the competition guys flying 2m or smaller, rather than flying 3.5-4m ships. The only reason the competition guys don't max out their wingspan at the 4m limit is that the shorter wings are more agile and flying a 3.5-3.8m can be an advantage over the larger 4m ships when down low and working small thermals.

Bigger is better, for a number of reasons.

For starters, going to a larger span lets you get a higher aspect ratio wing (which is more efficient) without dropping your reynolds numbers too low. RC gliders have severe issues with low reynolds numbers affecting wing performance, and that gets worse as your chord and flying speed drops. That's actually one reason why you see lower aspect ratio's at shorter spans, the designs are trying to keep the reynolds numbers up by keeping the chord large. Additionally, since larger ships can run higher wing loadings for the same soaring performance, you get more mass & inertia for the same soaring performance, reducing your ships sensitivity to turbulence. There's a number of other advantages as well.