The View Up Here

Random scribblings about kites, photography, machining, and anything else

Finishing the Le Fish

Posted by Tom Benedict on 22/07/2013

Now that I have a slope I can fly from, I’m at full-throttle trying to finish my Le Fish. Unfortunately, despite having cameras and loving photography in general, I did a lousy job of documenting my progress as I went. Stopping to take pictures always gets in the way of the build!

I finished my Le Fish over the weekend. For now I have a 4xAAA KAP battery pack powering the thing. I’d like to switch to a 2S LiPoly with 6V UBEC, but for now it’s in and it’s flying. The all-up weight came in at 24.4oz, so right at the bottom end of what’s considered a midweight build (25-30oz). Since we can sometimes get a fair bit of wind at our local flying spots, I may need to add a ballast tube at the CG point so I can dial it up to the 35-40oz of a traditional build weight when conditions warrant.

Here are the details:

Wing

I built out the wing as a mix between the kit’s contents (no instructions on this plane) and Steve Lange’s original build. The wing cores that came with this kit were made from 1.9oz EPP foam, not the lighter foam used in the ultralight kit. I glued the wing cores together with 3M Super 77, similar to how my Zagi went together. The wing is reinforced top and bottom with 6mm carbon fiber tube, joined by external aluminum ferrules at the wing root. I glued these in using white Gorilla Glue. (Note to the reader: I later read on Steve Lange’s Swiss Fish Build that he used white Gorilla Glue throughout, and skipped a lot of the other adhesives. DOH!) I did keep one aspect of his Swiss Fish build, though: Rather than use the two basswood spars that came with the kit for reinforcing the subtrailing edge, I used a single 8mmx1mm carbon fiber ribbon (part number T733L6 from CSTsales.com). This gives the wing a very solid base against flexing. Steve Lange used one of these in place of the two 6mm tube spars when he built his Swiss Fish. I wish I’d gone that route as well, but c’est la vie.

I covered the entire wing with 1.7mil CP “New Stuff” laminate from Aloft Hobbies. I then built up the leading edge D-box with an additional layer of 3mil film from the same source. This is straight out of Steve’s Swiss Fish Build. I sanded a bevel on the control surfaces so they’d get a full 45 degrees of swing up and down, covered them in 1.7mil laminate, and hinged them with 3mil laminate top and bottom. This made for a very solid, if slightly heavy wing.

Tail

The tail group is all balsa. Steve Lange built a new tail group out of Depron for his Swiss Fish, but since I’m not actively trying to shave weight, I kept the balsa tail that came with the kit. The tail was sanded to shape and covered in 1.7mil laminate. Hinges were made out of the same material, just like the wing. I glued the tail on using white Gorilla Glue. (See the pattern? With one exception, it’s the only adhesive I used on this plane. I love this stuff!)

In the event this tail is damaged or torn off, I plan to replace it with a Depron tail. I wound up needing a little bit of nose weight to bring the CG where I wanted it, and this would let me remove it. Besides, it’s easier to cut Depron than balsa.

Servos

I followed the recommendations for servos from the Leading Edge Gliders site, but I mixed and matched where they went. The site recommended Hitec HS-85MG for the flaperons, and standard servos for the rudder and elevator. I used Hitec HS-85MG for the rudder and elevator, and Hitec HS-325HB BB Deluxe servos (standard servos) for the flaperons. In retrospect I wish I’d picked up four of the HS-85MG servos and used them for everything. The fuselage of the Le Fish is barely wide enough to stack two standard servos side-by-side. I would’ve preferred more options in how I mounted them.

I wound up mounting the flaperon servos inside the fuselage, very similar to how Steve Lange mounted his on his Swiss Fish. The only difference is that he mounted his horizontally, with the shafts extending sideways out of the fuselage. I mounted mine vertically, but upside-down, with the shaft running perpendicular to the wing. The servo arms protrude out the side of the fuselage. I think Steve’s arrangement is cleaner, but it requires the smaller HS-85MG servos to pull off.

The rudder and elevator servos are mounted vertically just in front of the flaperon servos. One points up, the other points down. One control rod goes over the wing, one under. It’s a little awkward, but it kept everything inside the fuselage, with just the tail linkages poking out.

This arrangement put all four servos in as small a volume as possible, located just in front of the wing. This keeps the mass fairly central, so it should minimize the rotational moment of inertia in all three axes. All four servos were wrapped in blue painter’s tape and mounted using white Gorilla Glue. Fairly standard fare these days. It holds well, and by peeling off the tape later, the servos can be removed or replaced.

Radio

When I got my Turnigy 9XR radio several months back, I picked up a FrSky DJT 2.4GHz module and a stack of FrSky V8FR II receivers. An eight channel receiver is massive overkill for a four channel plane, but since I have these installed in my other three planes it keeps everything consistent between them. The receiver is mounted just forward of the tail servos using blue painter’s tape and white Gorilla Glue.

The V8FR II has two antennas. The idea is to place them away from everything else made of metal, away from each other (spatial diversity), and at ninety degrees to each other (orientation diversity). I put the horizontal antenna at the top of the fuselage, maybe half an inch below the surface. The vertical antenna is at the bottom of the fuse, poking out between the radio and the tail servos. It’s not ideal, but the active portion is completely clear of the electronics. I should get full range out of the radio with this arrangement. Considering I plan to use my LeFish for in-your-face aerobatics, range is probably the least of my worries.

Battery

I’m still on the fence about the battery. I like LiPo chemistry, but I’m already so tail-heavy, I need more weight in the nose than an appropriately sized LiPo battery and UBEC would provide. So I made the battery compartment so it could house a 4xAAA NiMH pack, plus room for ballast. I may still wind up using a 2S LiPo and UBEC, but that’s down the road. For now nothing is set in stone. Contrary to how most folks build their LeFish, I took yet another cue from Steve Lange and made a battery hatch on the port side of the fuselage. That way I can change my mind later on. I’m not happy with how I’ve hinged it, and there’s no real clasp to keep it closed, so there’s some work left to be done on it. I’ll probably take yet another clue from Steve and use magnets as latches.

What’s Left?

Aesthetically there’s still some work to be done. Right now the plane is as bare-bones as any plane could be: white foam covered with laminate, and unpainted balsa covered with laminate. The only splotches of color are some exposed carbon spars in the wing and the blue blocks of the tape-wrapped flaperon servos. It sounds like a minor thing, but this plane needs some color! Without some telling color on a plane, it’s hard to look up and instantly know if a plane is right side up, upside down, coming toward you, moving away, etc. Contrasting patterns on the upper and lower surfaces of the wings, a stripe on the vertical stabilizer, or a blocked out canopy shape – a trademark of the Le Fish design! – are all visual cues that let the pilot know which direction the plane is facing. So I plan to give the aesthetics some careful thought.

Then all that’s left is balance and maiden flight. But that’s a story for another day.

– Tom

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