The View Up Here

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

Archive for July, 2013

Ember – Last Dash

Posted by Tom Benedict on 31/07/2013

We dropped Ember off this morning for his last bout of surgery.

Ember Pre-Surgery

His bladder is healed, his urethra is healed, and all five fractures in his femur appear to be healing nicely. All that’s left is to remove all of the external hardware, staple the holes shut where the pins have been, and attempt to fix his kneecap.

His vet thinks the tendons attached to his kneecap were scarred as a result of the impact, and may have re-attached to his femur at the scar locations. This is what she thinks is limiting motion in his knee. If this is the case, she’s planing to attempt to scrape the scar tissue free, restoring some or all of the motion in his knee. Afterward he’s going to go through hell’s own physical therapy regimen to retain and possibly expand on his range of motion.

Ember is on the last dash of this race to get his health back. If last night is any indicator, he’s ready. We had to take him off all solid food at 6pm in anticipation of his surgery this morning. I put all the food away (all four cats had to suffer through this), and only left their water. As soon as I put the food in the cabinet, I heard a loud scrabbling sound coming from the kitchen. I spun around to find Ember finishing a very undignified jump onto the counter in search of something to eat. Cripes! Busted leg and all, he still managed to jump up there.

Yeah, in case you’re wondering, I didn’t sleep much last night. Between his bashing around trying to find food and the other three yowling at the tops of their lungs most of the night, no one in the house got much rest. It may sound callous, but we were all glad to drop him off at the vet and bust out the cat food for the other three cats.

– Tom

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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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A Slope At Last

Posted by Tom Benedict on 14/07/2013

I’m almost done building my Le Fish glider. The Le Fish was designed by Steve Lange, an avid slope soarer and aerobaticist (if that’s even a word). He’s one of the big movers and shakers in the American VTPR or “in your face” aerobatics movement. Rather than try to describe it in words, this video explains VTPR and the Le Fish better than I could:

As I said, I’m almost done building mine. I’ve been “almost done” for over a month. Why so slow? Because up ’till now the only slope I’d really flown from successfully was an unforested cindercone near Kailua-Kona. It’s a great site. It gets fantastic wind. But the ground is cinder with almost no vegetation at all. Any landing results in damage to the aircraft. It’s like landing on chopped up razor blades. Something is going to get cut.

So when I was invited to fly somewhere on the green side of the island, I jumped at the chance. GRASS!

At the Slope

A bunch of us went out together with our Zagi 5C flying wings, and spent the afternoon flying, crashing, laughing, and running up and down the slope retrieving airplanes and getting generally exhausted. It was GREAT!

The lift wasn’t as good as the other spot I’ve flown, but according to one of the guys there, the wind was a little lower than when he’d flown there before. Even so, I had one flight that lasted well over half an hour. Plenty of time to explore the lift and figure out where the problem areas are. Unfortunately it’s a fairly narrow zone with vortices on either side. One side catches rotor off a nearby hill, and the other has some kind of vortex that I haven’t entirely figured out yet. Turn too sharply, though, and your plane goes into a spin you can’t pull out of. All four of us fell for it, and only a couple of times were we able to pull off a save.

But the best lift was right in front of where we were standing, right next to the ground. In your face aerobatics? PERFECT!

So I’m back on the path to finishing my Le Fish. The wing is built, the tail is built, the fuselage is shaped and reinforced. I’ve even plumbed half the servos. All that’s left is to cut out the radio/battery bay, mount the last servo, and run the control rods. I may not be able to pull it off in a week, but I’m determined to try! Finally, finally, I’ve got a slope I can fly this on.

Flying Zagis
– Tom

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Raptor 2000 Advance – A Maiden At Last

Posted by Tom Benedict on 05/07/2013

Despite having flown the Raptor several times, I didn’t really consider any of those a real maiden flight. The first set was hand-thrown gliding tests, just to make sure I got all the controls moving the right way, and to make sure I could land. The second set was powered flights, but the controls were so squirrelly and the plane flew so poorly, it was all I could do to bring it down in a reasonably safe manner. Even then, I wound up snapping off one of the tail feathers.

It wasn’t until yesterday that I did what I considered to be a real maiden flight: powered takeoff, long gliding flight, and a safe landing. But to get there I had to answer the remaining questions from the earlier flights: why was I rolling off to one side, and why did the plane pitch up violently under power? It turns out both had the same root cause: the removable tail.

The Raptor 2000 Advance is a V-tail motor glider. The tail is removable, and the control surfaces must be unlinked before removal. When the tail is put back on, there is nothing to indicate proper setting of the control surfaces. They have to be dialed back in every time. Yesterday and today I flew the Raptor, and each time I installed the tail to the best of my abilities. The flight characteristics were wildly different each time.

Yesterday’s flights were almost dream-like. The plane had no noticeable P-factor (the tendency for the plane to roll when power is applied), and it flew clean and level while gliding. This morning’s first flight was the exact opposite: it had a strong tendency to roll to the left, and rolled harder under power. It also pitched up, constantly trying to do loops. Under power the plane pointed straight up in the air and went ballistic at wide open throttle.

I traced the problem back to the tail. After looking at the setup, I noticed both control surfaces were angled up by about 2mm. I zeroed them to the best of my abilities, and with my heart in my throat I tossed the plane into the air a second time. That time it flew beautifully, just like yesterday.

Long-term I’d like to either make an alignment jig that lets me center the controls accurately every time, or replace the control rod ends with threaded clevises I can Loctite in place. In the short-term I’m just not removing the tail now that I have it set properly.

The one other piece I knew I needed was some form of airbrake. The field where I fly is quite small, and the Raptor loves to glide and glide and glide. I needed some way to stop it in the air and bring it down. So I added adjustable crow.

The idea with crow – or butterfly as it’s also called – is that you bring the flaps down, and at the same time you bring the ailerons up. This increases camber at the root of the wing, and reduces it at the wing tips. Overall it adds drag, which slows the plane down. But an over-cambered wing will stall before an under-cambered one, so this makes sure the wing root stalls before the wing tips. This keeps the pilot in control, and makes a stall a less violent maneuver than if the camber was reversed.

I tested the idea on my Bixler 2 first: The three position switch on my transmitter controls whether I’m using flaps, crow, or keeping the trailing edge neutral. With the switch all the way up, the flaps are centered and the ailerons work normally. One click down, and the flaps can be controlled via a knob. Two clicks down and that same knob controls the amount of crow. This lets me hit the brakes, and dial in how strong the brakes are.

And a good thing, too! On the Bixler 2, five to ten degrees of crow is enough to dump speed and bring it down in a hurry. On the Raptor 2000 Advance, I had the flaps 45 degrees down before it visibly slowed. With the plane at a nice safe altitude, I tried bringing the flaps 90 degrees down and the ailerons 30 degrees up. WHOMP! It slowed down FAST. Having the ability to dial in the brakes during approach was a must.

In the end, it worked like a charm. Every landing was smooth, and at the end of the day I went home with two undamaged airplanes, ready to fly!

Enjoy the video:

– Tom

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