Scott Voigt's Build Logs

Thermic 50-X

Specifications:

Wingspan:     50" (48-3/4" tip-to-tip)
AUW:            7oz
R/C:             Rudder, Elevator
Launch:         Hand Tow

BUILD LOG - SCOTT VOIGT'S THERMIC 50X

BUILD LOG

This is a build log for Scott Voigt's Thermic 50x.

Introduction

This is the Thermic 50-X build log. I'm 14 years old and I'll be building the 50-X for R/C. It'll be my first build log and third R/C plane.

 

Thanks Grandpa for supplying the R/C equipment and wood and Mike for getting me going on this build log.

R/C Gear

2 Dymond D37 servos

Dymond Micro Lite 4S receiver

 

It's a 15.9 gram system without the battery. I'll trim and solder the cables and antenna once I know exactly where everything will go.

 

Shaping the boom

This design has a hardwood boom incorporated into the fuselage. The boom is included in the kit as stock and needs to be shaped. Once determining that the boom is a uniform taper I transferred the shape by lining up the boom over the plan and marking both at several locations along the length. Then I measured the width of the boom on the plan at the markings and transferred these to the marks on the wood. Then I faired the line and cut/planed/sanded it to shape.

 

Building the Fin and Rudder

Now the vertical fin assembly. It all fits perfectly. All I sand is the little burs off the laser-cut pieces. I used epoxy where large surfaces come together. That's mostly on the lower half of the fin. 

I've added a few small 3/32" sq. braces to provide a more solid base for the rudder.

I'm also going to add more stock to build up a surface to hinge into.

I made a slightly bigger rudder. For R/C I want to get more effect out of it.

I cut a flexible hinge in half for this job. The balsa I used is soft so I just cut slots with a knife.

Testing the fit:

I won't glue the hinges in until after covering.

Starting on the Pod

I made sure to get a strong, flat, and in-line bond between the fuse pod forms and the boom. Also, I sanded off extra glue from the face of the forms to let the bulkheads lie flat. The form extends up past the boom on top; at first I thought I made a mistake shaping but I realized it's supposed to be this way. The extra space is a clever way to hide the wing saddle parts.

I extended the former lines on the plan so I could see where they go with the pod form down.

The fuselage starts to take shape very quickly. The wing in the background is being dihedraled; my preferred order of build is "whatever's dry comes next".

Balsa stripping tool

My grandpa is on vacation and he took the Baker McMillen Cadet along to build. He also took the balsa stripper I used to get stock for the 50... and I've used the last of that wood.

I could either wait for him to get back, buy stock, buy a stripping tool, or make my own tool...

I used a very straight block of wood and used CA to hold the little shim in place. The block is long, so I slide the balsa past it rather than pass the tool along the balsa.

I was shocked when I tested it and a 3/32" sq. stringer came out perfectly. Now I'll add more wood behind the blade and strip some 5/32" sq. LE material for the wing.

The trick to this is straight wood, a solid shim to hold the blade out from the main block, and enormous clamping pressure. I upgraded the shim to basswood and the clamp to a "Pony" before stripping bigger pieces.

Wing Center Section - Part I

I started with the inner panels of the wing. The trailing edge and spars are supplied in the kit; the leading edge is 5/32” sq. strip.  A spruce LE could be used for extra strength, but I chose hard balsa.

I started by pinning the TE and spars. I won’t add the LE until the ribs are in place.

The ribs go in the notches perfectly, and the notches match the plan. I used thin CA here and the assembly took less than a minute.

With the main ribs in place, the LE can go on. I left a very small amount of extra on each end that I'll sand down before joining the wing. I waited until now to do the false ribs so I can glue them in front and back at the same time. This seems to help keep them straight. I used medium CA to give me time for positioning.

Wing Center Section - Part II

The middle of the wing has 1/32" ply dihedral braces that strengthen as well as set the angle for the joint. I installed these on one of the panels before adding the #2 ribs. These ribs have space in their spar notches to fit over the braces.

I left off ribs #1 and 2 until installing the braces. I should have left off the 2a ones too; I ended up relocating one to make room for a brace.

Braces in place with ribs down to #2 added:

The finished joint- braces, ribs, false ribs, gussets. Ready for sheeting.

Wing outer panels

Now I'll build the rest of the wing. I started by laying out the trailing edge, which is in three pieces.

The wingtips and spars are all laser-cut. They fit right over the plan.

The front spar is extra long and should extend past the wingtips some. It needs to be aligned perfectly over the plan where it joins the other panel, at its root. I cut the rear spar to fit the angle.

Adding the ribs. I started with the big ones to get the spars in line. I like the TE notches. They make this process easy and strengthen the glue joint.

All the ribs are in complete agreement with each other. The spars don't have to bend any to go through the rib holes.

The LE needs to have a small notch to fit over the wingtip.

   

Gusset Location

The gussets for this wing section (except for the one at the wingtip) need to be added after joining the wing panels, but I'm going to figure out which ones go where now. The only acute angle is the top one on the plan in this picture, so the acutely angled gusset furthest right of the three goes there. The lower gusset on the plan is biggest by far, making it the middle one on the wood. The one on the left has to go out by the wingtip.