ChocoFly 1:3 ASW-17S 7M GPS Racer now in stock in USA

[tewatson]

After the loss of my LET JS-1 about a year ago, and my beloved FW Model ASW-17 this past July, started looking at options to get back on the GPS course in early 2021. Was lucky enough to find a Choco ASW-17s on the ground here in California, completely untouched. Even better, it was complete with FES system, servos, and IDS sets for the wing/stab. Finally started the build earlier this month, with the goal of being ready by Spring 2021.

I thought of skipping the build log thing, but since more of these will no doubt start appearing, figured it might benefit someone. This will differ somewhat from my previous build documentaries, in that it will be real-time, with likely long-ish periods between updates. Did the last two pretty much after most of the work was done. So...onward.

[tewatson]

The stab is first up. It uses two servos, and IDS linkages with CNC-cut carbon surface horns and links. One nice feature of this airframe is the drag spar slots and internal surface horn locations are already opened up, drastically reducing the amount of dangerous Dremel root canal surgery. The servo bays are sized with very tight clearances - making it impossible to slip the assembled frame and servo in as a unit, complicating the install a bit.

First step was to open the servo bays, and cut the wipers/lower skin for horn clearance, then secure the horns while ensuring the IDS arm is exactly perpendicular to the hinge line. The horns were also positioned so the hinge pin is removable (it just slips under the wiper on the inside). Very important for serviceability.

Since the frame had to be inserted in the bay first, then the servo, it was essentially impossible to glue things using the "normal" process without creating a huge mess and most likely getting epoxy where it's not wanted. There was also no room to add glue around the frame perimeter with the servo and linkage in place. So, drilled three small holes in the frame flanges, then slipped the frame into position, installed the servo, and connected the linkage for proper positioning. Once everything was aligned, put a single drop of thick CA into each frame hole, waited for it to cure and removed the servo. This opened up access to permanently secure the frame with epoxy where required.

The elevator linkage is very precise and completely slop-free.

[tewatson]

On a related note, I still hate those OEM phillips head sheet metal screws for servo frames. Continuing to use my retrofit process for 3mm machine screws:

https://forum.scalesoaring.com/forum...ounting-screws

[tewatson]

Landing gear setup is next. The retract linkage is straightforward, although the actuating arm is blank (no holes) which requires one to determine the appropriate linkage point, then drill and tap. No huge deal; in fact this is an advantage as you have options.

The wheel brake is standard paddle style and designed for an unusual (to me) actuating setup. Modified an aluminum servo horn, and used spectra line for the connection. Time will tell on durability.

Note for FES-equipped planes: the gear has two "down" positions, one normal, and one hyper-extended for FES takeoffs. It's a clever design as there are no additional moving parts. The procedure to extend to the second position is simple and can be done with either a three-position gear switch (to stop it at the halfway-extended point), or manually with everything powered off. Basically, you grab the wheel at the halfway point and pull it forward while extending the rest of the way. It will retract normally, and when extended for landing will revert to the normal position.

During the retract setup, noticed the gear would almost always hyperextend itself with normal (or close to normal) servo speeds. Don't know why...maybe something to do with the spring tension and a bit of "bounce" when cycling. I don't like slamming the gear up and down, so I always set a slower speed. Interesting behavior though.

[lenb]

This is great timing Tom. Mine has finally arrived here on the Eastern Seaboard and will be assembled over the winter as well. Thanks for taking the time to post updates.

len

[tewatson]

On to the rudder. As the linkage is a very close fit inside the fuse blister, be sure the tail group fit is correct and the fin/rudder seats completely before starting any linkage work. You can gauge this by any gap remaining between the aft portion of the fin and the fuse. On mine, there was a blob of epoxy on the wood platform in the fuse where the vertical joiner seats, and the joiner itself was a bit long.

The next step is to cut an access hole in the rudder post. This needs to be large enough to allow your servo of choice to pass through. Servo sits on top of the tray, and the mounting screws pass through the tray from underneath and into wood blocks on the opposite side of the servo lugs.

The supplied servo tray is laser-cut ply, laminated with what looks like silver carbon cloth. The servo cutout is sized for a 20x40mm servo and I used the Hitec D945TW with 300+ oz. in. of torque. My first thought was 'why do I need such a large servo' and initially planned to use a smaller 15mm size. But, after seeing another Choco 17 with FES that required some tail weight, went the easy route and used the OEM tray and bigger servo. Extra torque for this huge rudder can't hurt, either.

The tray as supplied was too long, as it would have positioned the servo where you could not access the forward mounting screws. So, trimmed the aft end for proper fore-aft position, after which a linkage mock-up helped define exactly what vertical positioning was required. When dressing the tray sides, be careful not to remove too much as having a snug fit is just about mandatory in these tight quarters, so it will hold itself in place for gluing. I tacked it in place with a drop of thick CA at the corners, then when satisfied with the positioning, ran a bead of MGS epoxy thickened with chopped glass and silica along the edges, top and bottom.

My linkage uses a clevis at the servo, 3mm rod, and a Dubro 3mm ball joint at the rudder, mounted to a 3mm threaded brass insert. Pay attention to the linkage geometry/servo horn length, as you want the rod essentially parallel to the fuse blister profile when viewed from underneath (see pic). Watch for binding inside the fuse blister, and between the rudder/ball joint body with throw opposite the linkage side (e.g., left rudder throw with a right-side linkage setup). There is no clearance, Clarence...so you will also need to slightly shave the ball joint body in a couple spots.

Another way to do this might be with a clevis at the rudder. I'm not a fan of repeatedly levering a clevis on and off so didn't even consider it. Another factor is the geometry involved with the linkage not perpendicular to the hinge line; with reference to the linkage plane, the attachment point moves up and down with right and left rudder throw, respectively. This would put twisting forces on a clevis arrangement. YMMV.

[JimD]

Hi Bruce, in my effort to get the www.ScaleSoaring.com website up-to-date, I posted info for this model and your contact on the HOME page. Let me know if the links are okay, or if you would like some other link.

[tewatson]

Currently working on the wings. Some additional info in response to post #8 on IDS component sizing... The ASW-17 wing has four control surfaces each side; two flaps and two ailerons. The supplied IDS kits are sized according to the requirements for each surface. The inner and outer flaps, as well as the inner ailerons, use CNC carbon surface horns/links (very burly). Flap link pins are 2mm hardened steel, inner ailerons use 1.5mm pins. Only the outer ailerons (which, at 65cm length and 4cm chord, are far smaller than ailerons on 4m F3J ships) use the IDS setup pictured in post #5.

So, while not machined aluminum a la Baudis, the supplied control mechanisms are more than up to the task.

[tewatson]

Working on flap servos in the main wing panels. The ASW-17 wing has four separate flap surfaces, and the supplied Servorahmen frames are for MKS HV747 servos. As mentioned earlier, the IDS components are beefy, with 2mm hardened steel link pins and CNC carbon surface horns/links. Prepping the control surface horns and installing them is straightforward but rather fiddly. The pockets in the surfaces are opened to rough dimensions from the factory but need final sizing/fitting, and same with the drag spar slots where the links pass through. Some of this work is ticklish business, as it's easy to let your attention lapse and cause ancillary damage. Install the horns with the links connected, so you can verify they are perpendicular to the hinge line. I use MGS epoxy, thickened with chopped glass and silica. The arrangements obviously also need to match on both sides.

When prepping the frames, pay attention to possible distortion when assembling. In my case, the servo horn bearing posts were just long enough to bottom in the frame bearing cavity before the servo was completely seated. Tightening the mounting tabs/screws bowed the frame as the servo lugs were pushed tight against their mounting flanges. The solution was to shorten the horn bearing post about 1mm (see pic). I also drilled small holes at key points in the frame, to allow epoxy to ooze through and act like a rivet.

The wing profile and servo bay size makes it all but impossible to install servos the usual way (dropping an assembled servo and frame into the bay with epoxy). My workaround is to dry-fit everything and mark the frame position so it can first be accurately placed in the bay with epoxy, then add the servo, and finally the link. Secure the control surface at neutral, power up the servo for precise positioning, check for square, and weigh down for curing. This allows you to avoid sliding the assembly all over the place and getting epoxy everywhere it isn't wanted.

The result is a clean install and very tight, slop free surfaces.

[tewatson]

Moving to the outer wing panels. Installed the inner aileron servos using a process similar to the stab servos. Secured the surface horns while ensuring the IDS arm was exactly perpendicular to the hinge line. The horns were also positioned so the hinge pin is removable (it just slips under the wiper on the inside). Important serviceability detail.

Next, drilled three small holes in the frame flanges, put the frame into position, connected the linkage, added the servo, and powered it up for proper positioning. A single drop of thick CA into each flange hole secured it, then after it cured went back and added thickened epoxy along the frame sides. The result is very tight, slop free surfaces.

Next are the outer ailerons where things get really crowded, and a whole new servo install plan.

[tewatson]

The outer aileron servos and linkage configuration was a special challenge, as the wing is extremely thin. The aft edge of the servo bay is just 8mm deep, and of course gets thinner towards the drag spar and forward edge of the aileron itself. Chocofly sets the wing up for all-internal linkages, and the main issue with such an arrangement is the resulting geometry, giving no more than 4mm of moment arm at the surface. With a 3.5mm servo horn, this requires dialing the servo throw way back, losing effective torque and relative precision.

My solution is to take the surface horn slightly above the top skin, and while not as visually clean as all-internal, it allows for 6mm of moment arm. It may not sound like much, but a 50% increase is fairly substantial and should head off potential issues. Custom surface horns were thus required, and I fashioned these from the same material used for the others. Installation followed the same procedure as before - with links connected, to verify they are perpendicular to the hinge line, and MGS epoxy thickened with chopped glass and silica.

Next is servo frame prep...

[Scalesoaring]

Hi Tom,

The Aluminum IDS servo arms are enroute from Switzerland. Hope to have them in a couple of weeks - FYI.

Bruce

[tewatson]

Prepping the outer aileron servo frames required an extra step - as the frames are reversible, they have two horn bearing post holes. One of the holes (for a left side servo arrangement) was molded off-position and would not allow the servo to seat squarely. If left uncorrected and forced into place, it would put a tremendous lever force on the horn and probably cause binding, then eventual horn failure. I briefly contemplated making ply frames and using some standalone bearing supports, but finally settled on a simple fix. Drilled the bearing hole oversize, and epoxied in a brass bushing using the servo to hold proper alignment. Ghettaux? Maybe, but works perfectly.

Otherwise. just some basic trimming for proper fit in the wing, and my usual heli-coiled screw inserts.

[jgallacher]

Beautiful work Tom can't wait to see it.

[tewatson]

Outer aileron servo final install followed the same procedure as with the horizontal stab - put the frame into place, then the servo, connected the linkage, and powered it up for proper positioning. With everything aligned, put a single drop of thick CA into each frame hole, waited for it to cure and removed the servo. This provided access to permanently secure the frame with epoxy where required. The result is very tight, slop free surfaces. As a plus, servo throw is at 95%.