Choco Fly SB 14 6m Build Thread

[Soaranator]

Sorry for the delay in posting this – I had to have a herniated disc in my neck removed between C5 and C6 and a bone spacer graft and a titanium spacer installed. Finally feeling healed enough to write this, and starting to work on the SB14 again.

So, on to installing the Torcman drive system. I've attached instructions from Torcman that explains the entire process at the bottom of this page. Before I started, I taped all of the openings in the motor and its' bearings over with blue tape, along with the front bearing on both sides to keep construction detritus. After the install was complete I used my dental picks to remove the blue tape from the front bearing. The motor mount ring I have is round and the SB14 fuse is somewhat oval, so I made a cresent-shaped filler out of plywood and glued/screwed/laminated it to the top/front of the motor mount ring. I used carbon powder in the resin used with the fiberglass cloth so it would match the carbon used in the mount ring.

I used my Robart incidence meter to align my fuse on the bench with the wing at +3 degrees. I taped a spirit bubble to a 3/16 square piece of spruce and taped it to the motor. I lightly clamped the motor shaft to my workbench and then used a shim to make the spirit bubble parallel to the shaft since the motor housing is slightly bell shaped and adjusted the mounts for it to be level. Now, the motor will have 3 degrees of downthrust with the fuse at 0 degrees. The motor mount ring got tacked in with a few drops of 15 minute epoxy, then the front bearing was also tacked in. Then the motor was carefully removed and thickened West Systems epoxy was filleted in on both mounts front and rear. During this phase the motor shaft was also cut to length.

From Florian Schambeck is a really nice tow release. This all aluminum jewel is a low profile unit that also serves as a servo mount. Schambeck recommends a KST DS125MG servo – I didn't have one on hand and substituted a KST X10 mini. I mounted it as far forward as I could while making sure it cleared the motor. I transferred the tow release opening from the release using a piece of blue tape. I pressed it around the opening, then cut out the material using an Xacto knife. Using a flashlight, I transferred the opening location from the inside to the outside by shining a light thru the fuse and put a dot on the outside of the fuse where the opening needed to be. On this model the fuse seam is on the centerline of the fuse making it easier to center and locate.













[ATTACH]n48373[/ATTACH]

[Steve P]

Lookin’ good! Glad you’re feeling better and back on the build. Thanks for the Valenta build “helpline” call earlier today. I was stumped. I’d give you five stars on a customer survey.

[Soaranator]

After laying out the airborne radio gear next to the fuse I decided to see how it was going to balance and where everything would fit. With all the batteries, 2-5000mah 2s packs for the airborne and 2-5000mah 5s packs for the motor, there was no way it would balance with all the batteries in the cockpit. I got in touch with Bruce DeVisser at Rosenthal Models to find out how the Chocofly guys do it. The answer is a “10s Long Pack” (something that is apparently popular in Europe but unknown here...) that slides into the tailboom behind the landing gear. The diameter of the SB 14 fuselage gets small very quickly aft of the cockpit. At the trailing edge of the wing it is smaller than my 3.5 scale ASH 31. Because of this, there is not the usual room under the wing or above/next to the landing gear as in most other 1/3 scale gliders. This means the two 5s packs need to be joined into a “long“ nose-to-tail pack. I did so using 1/8” lite ply and fiberglass strapping tape. The two pieces of EPP foam on the back of the pack support the rear of the battery as the fuse is even smaller back there. The inside of the fuse is rather abrasive raw carbon fiber, so the rear end of the battery pack has a couple of layers of polyurethane tape (used protect the leading edge of wooden propellers) to protect it. Something to keep an eye on...

With a bit of trial and error I ended up modifying a battery tray and holder kit (again from Rosenthal USA) so the motor batteries can be installed and removed with the wing joiner in place and the landing gear down. It is a tight fit. To install, I rotate the batteries 90 degrees and push it on until the foam blocks clear the wing joiner. Then, I rotate it right side up and slide it into the locking mount. The extension cable has to be in place and it has a holder to keep it out of the landing gear operating area.

One of the 5000mah 2s packs is mounted to the side of the landing gear using velcro, the other is industrial strength velcro mounted just ahead of the landing gear bulkhead. Velcro should be “activated” by pushing it together and twisting it slightly to engage the hooks and loops. I use a paint stirring stick to separate the velcro and remove the batteries. Credit cards work too.,

I am using the Elite Falcon 130HV which provides plenty of power for the Torcman motor and full telemetry for my Jeti radio. It also features propeller positioning which I will set up later. I want to get this plane ready to fly at the November aerotow at Cumberland since that will be my last chance to fly it this year so I omitted a couple of features. To mount the ESC, I used thumb nuts and taped over the bottom of the nuts to keep epoxy out. Then put blobs of thickened epoxy on the bottom of them and positioned in the fuse. After that epoxy cured I added more thickened epoxy to get a good mechanical bond on the brass nuts.

The Jeti CB220 is mounted to spruce rails, Then the three receivers and antennas were mounted. One of the RX is used as a switch to turn the model on and off via the transmitter and I simply coiled the antennas for that one.

Time to re-check the CG and start programming! CG was right on. Tips the scales at 26.3 lbs all up. I put 1.5 oz in the nose for insurance as I have become allergic to tail heavy planes in my old age...

The only problem I had was with the Ceflix landing gear – it has a “V” shaped actuation slot in the swing arm. It worked perfectly on the bench laying on its side, but in the plane it wouldn't completely retract and lock. I found that the lever for the brake was jamming up against the back of the actuator arm, preventing it from any further travel. (I didn't hook up the brake as I removed the brake servo mount from the side of the retract so the airborne battery would fit there.) This was quickly remedied by using some 1/3 scale safety wire. Now it locks up and down. I'm using round elastic cord from the fabric supply store to close the gear doors. I found two holes in the retract and used two “bowsies” from my rc sailboat parts bin to have adjustable gear door closers. One of my objectives in this build is to make everything “Field Servicable.” There is nothing worse than driving 10 hours anticipating 4 days of aerotowing only to be grounded by a failed part that cannot be removed and replaced on the first day.

Another mod for the gear is that is uses some sort of elastic bands to connect the rear of the retract to hooks laminated into the fuselage. I has some rubber bands and they do support the model, but are not as durable as a short section of a bicycle inner tube.

The last thing I did was to make the winglets removable. Len Buffinton has a great how-to over on Scale Soaring. Here's the link.




https://forum.scalesoaring.com/forum...ng-them-back-o




Time to go fly it!

[Soaranator]

Forgot to mention how I did the CG. First, since the wings on the SB 14 sweep forward very slightly, I joined them together with the wing rod and placed the upside down, supporting the wing rod. I measured and marked the cg location on the wing roots, then placed a 3' straight edge on the wings to get a line 90 degrees to the centerline of the fuse by measuring an equal distance from the end of the yardstick to the leading edge of the wing. I transferred this line to the first 6” of the bottom of the wing. Then, cut a Forum pencil into two 2” pieces. Using strong double stick tape they were attached to the wing centered on the line I just drew and covered with blue tape. Next, the airplane was assembled. Next, I screwed a one foot square piece of flat wood to one end of each sawhorse – two pieces of wood, two sawhorses. I then placed them such that they were parallel to the wing roots and far enough apart for the fuse to fit between them. I got a stool to place the tailwheel on and lowered the fuse between the pieces of wood. The stool keeps the trailing edge of the wing from damage if the plane is too tail heavy. Add or subtract weight as needed.

The rudder servo mount is another really nice item from Schambeck that provides a clean and efficient mount for wherever you need to mount a servo inside a fuselage. The push-pull rudder cable that was moulded in the fuse is a fiberglass rod covered in softer plastic. I used one of my cable crimpers to crimp the clevis on the servo end, being careful to apply enough force to crimp the clevis without damaging the pushrod.