Tweet
For stab linkage, used a Z-bend at the servo and an L-bend at the surface, made long enough such that it cannot become disengaged with the stab mounted. The arrangement is rock-solid with no slop whatsoever.
-
-
Looking good, Tom!Comment
-
Simple and extremely reliable setup Tom, Thanks for posting the pictures, I know Rick was explaining the setup but his photos didn't show on the forum...Len Buffinton
Team Horizon HobbyComment
-
Tip on installing/removing the stab with this arrangement: Before disassembling, input full "up" and then power off the plane. The rearward position of the surface horn and link makes it easier to access.
TomComment
-
Nice work! Scale Models just keep getting better and better. We are so lucky in this hobby. Having the wing servos preinstalled was a good idea. I don't enjoy wing servo installation on a 10 servo wing...Comment
-
The rudder servo bracket, pushrod and control surface horn are factory-installed. It was just a matter of mounting the servo and connecting the pushrod ends. Kept things simple with a clevis at the rudder and a Z-bend at the servo.TomComment
-
Landing gear setup was next. The retract assembly is a work of art. It looks to be superbly engineered with a drum brake, integral servo mounts and carbon fender. The retract servo is factory-installed with linkage fully adjusted. The gear door spring arrangement is left to the builder.
Completing the retract assembly setup just required mounting a brake servo and connecting the cable. I used a 4-40 clevis and rigging coupler for adjustability, with the cable secured by dual crimp ferrules and a dab of JB Weld to ensure nothing slips.
TomComment
-
Landing gear door springs required a bit of thought, as there was no room at the forward end of the retract assembly, and limited room at the rear. Tried mocking up a torsion spring, but the full-length hinge setup resulted in too much physical spring displacement for that to work. My pal Dennis Brandt suggested coil springs with an overhead support rod, so did a test setup and it worked perfectly.
Used a small-diameter carbon tube with ply support blocks on both sides (one side is captured, other side is slotted to allow removal), soft long-throw springs for light but even tension, and #1 dress hooks on the doors. Very simple and functional. The final assembly will include a larger tube over the support rod, in between the springs, to maintain proper spacing.
TomComment
-
Moving forward to the nose area, poached an idea from Steve Condon's JS-1 and fabricated a tray arrangement that mounts the tow release servo and batteries, while also providing a compartment for nose weight. Aircraft ply bulkheads hold a removable ply shelf with a dado slot at the forward end, and socket screws at the aft end.TomComment
-
With the major fuse arrangements solved, it's time to finalize and secure the wiring. Using the PowerBox Champion SRS unit for battery and RX management, with dual (redundant) JR DMSS RXs. The unit accommodates serial bus communications with multiple radio brands, so it does not lock you into using just one manufacturer's equipment. This is a huge advantage for future flexibility. More on this unit later when the cockpit area is finished out.
The retract is reinstalled and all wiring harnesses are routed and connected. Everything is secure, and arranged such that maintenance will be easier. RX and battery placement is next up.
TomComment
-
Using dual redundant JR 812BX DMSS serial bus RXs, with additional diversity satellites, for a total of eight antennas. Protective sleeves (un-shrinked shrink tubing) are used where other wires could touch the exposed coax ends. These pics also show the power/programming switch for the PowerBox unit mounted to the battery tray. It is bulkier than standard switches, but another feature I like is it cannot be inadvertently switched on/off; it requires pushing two buttons simultaneously to operate.TomComment
-
On to the wings... As previously mentioned, this is where a lot of work was required. There were two key problems:
First, as delivered, all of the flap and aileron wipers were severely oversized and mis-shaped, which bound the surfaces up tight (they sounded like old rusty door hinges when moved, and on Steve Condon's plane one of the aileron servo horns stripped out its spline teeth upon initial movement testing.) Instead of being properly radiused around the hinge line, the wipers were an oblong profile which resulted in more resistance as the surface deflected downward and the wiper exerted upward pressure on the sub-TE. They were also far too thick, compounding the shape effects.
Second, all of the linkages were designed to be completely internal. Not a bad concept, but with a wing this thin, the available section height out at the ailerons resulted in very little moment arm or mechanical advantage at the surface horns. This only allowed absolute minimal servo throw to be used, thus extreme imprecision in surface movement and significant double-centering (about 5-6mm for the outer ailerons.) It was also impossible to get more than ~9mm of upward throw, while the setup specs call for 15mm.
These two factors combined were completely unacceptable, if not downright unflyable. I can appreciate the out-of-the-box thinking on a clean airframe here, but give LET an "F-" on execution, and the wings required a fair amount of work to correct all of this. Again, not insurmountable problems, but it is disappointing that the planes were actually shipped that way. The wing servos and LDS-style linkages were all factory installed and there is no way this could not have been noticed. Another puzzling aspect is that the full-size JS-1 has linkage blisters on top of the wing, so eliminating them was also very non-scale.
Onward, as we dive into the outer wing panels...stay tuned.Last edited by tewatson; 01-25-2019, 01:35 AM.TomComment
-
The outer wing panels had three problems: Incorrectly molded wipers, incorrect linkage geometry, and excess sub-TE overhang. These factors resulted in significant double-centering, excessive load on the servo, limited upward surface movement, and a fair amount of surface slop. As designed, the aileron and flap surface horns are steel barrels that pivot in a brass bushing on either side; they are cross-drilled and threaded to accept a linkage rod, and the whole assembly is epoxied in right under the wiper. For the tip ailerons, this provided about 3mm of moment arm. Not good. So, to prepare the panel for a new linkage design, the OEM equipment had to come out, the wiper needed re-shaping for free(er) surface movement, and the sub-TE overhang depth needed to be slightly reduced to allow adequate upward surface movement.
First step was to remove the surface "horn" mechanism. This of course required disconnecting the linkage rod, and then pivoting the aileron down about 70-80 degrees to expose the wiper underside plus a safety gap. Secured in this position, a thin Dremel cutoff wheel made short work of the epoxy holding the bushings in. Extreme care was used to avoid slipping and other unpleasantness (like a spinning cutoff disk skating across the wing.)
Next was to re-radius the wiper (to the extent possible.) With the aileron secured in the down position, the wiper was then extensively block-sanded with 180 grit to a more functional contour, then finished with 220 grit. One positive build aspect here is the wipers have a carbon base layer (really just an extension of the upper control surface skin), so they will not fracture like those made strictly with molded spooge. However, they are still molded with the wrong profile, so re-shaping ability is somewhat limited.
Finally, the sub-TE overhang was reduced approximately 1mm by marking the new profile with blue tape, and then using a thin sanding block to sand the edge to the new line.Last edited by tewatson; 01-27-2019, 05:33 PM.TomComment
-
The tip ailerons needed more surface horn moment arm, to provide mechanical advantage and allow more of the available servo throw to be used, thus increasing movement precision, improving centering, and reducing slop. This would require the linkage to protrude slightly from the upper skin; however, this is far preferable to the alternative.
The thin wing section somewhat limits what can be done, although to be effective the new surface horn did not have to be all that much longer. Based on the thickness and servo placement, I could double the surface moment arm (increase it to 6mm) without difficulty. After a couple mockups using cardboard horns to gauge linkage geometry, settled on a horn design and clevis arrangement. This allowed me to use the OEM linkage rod and LDS servo connector by shortening the rod and using MP Jet nylon clevises (these are the removable brass pin design, so no need for a wider skin slot to accommodate the "spread" required to install a traditional metal clevis.)
Once the design was finalized, I crafted horns from G10 and tacked them in for a final position check, then secured them using MGS epoxy mixed with chopped glass fibers and a bit of silica. With the horns permanently in, it was then just a matter of gradually opening the top skin slot to provide operating clearance. My pal Steve Condon went through all of this with his JS-1 as well, and he made a mold for some linkage fairings. I have a set of those on order to cover the exposed clevis...full-scale style.
The result is what should have been in the first place: Proper tip aileron movement, adequate servo throw, excellent centering and essentially zero slop. Inner ailerons are up next...Last edited by tewatson; 01-27-2019, 06:10 PM.TomComment
Comment