Next FT model: David W.'s Saab Viggen!

FOGeologist

Member
I received an FT Viggen from Da Boys last week, and got the 70mm EDF (QX Motor QF 2827 (2227)-2800KV) today. I bought a ZTW Beatles 70A SBEC and a Lemon RX top-pin with stab last week. This evening I purchased a China Hobby Line 3000 mAh 4s battery from CHL themselves. It should be here Wednesday or so.
electronics.jpg
 
I put gear and a steerable nose gear on ours. We got some attention when we ran it down the runway and took to the air. It is still flying today one year later.
 

Russtynailz

Member
I love the Viggen! I have built 7 of them, and they fly great!! They love the wind and if set up right can even hover in the wind and vertical land. (Takes practice) I just finished building one for Flite Fest next week. Good luck and enjoy it, I know I do.
 

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FOGeologist

Member
Well, the Lemon RX managed to die on me within about 4 minutes of pairing it. It was working just fine, then I permanently mounted the ESC, and... no motor or anything, just a red light on the receiver.

Kept trying to get some kind of function, and I was thinking it was my ESC that failed. I tried another ESC and it wasn't working, either. I futzed around with the wires hoping I'd maybe cold-soldered the extensions, but nope. Then I had a thought - "Maybe it's the rx?" Tried the one out of the long-lost 1/4 scale Cub and YEP, the system is working fine - this is my first Lemon that's been a "lemon."
 
That is rare, I don't buy any thing but Lemon receivers. I do stay away from the stabilization receivers. I have found them to be more trouble then they are worth.
 

Russtynailz

Member
I bought an eagle tree stabilizer once, I still have yet to install it to try it. (3 years at least I've had it.)
 

jaredstrees

Well-known member
I've got a 70mm EDF laying around I plan to use in a viggen, just many projects to do! I may have to build one after my current build. Everyone says they fly great! Good luck, look forward to seeing how it turns out.
 

FOGeologist

Member
I am really thinking of putting a folded wing on this bird. While it's great that David W. was thinking of a simple build, it seems... wrong? Is that it? Wrong, to put a flat airfoil on it?

Maybe I should just build it as it is? What do you guys think?
 

FOGeologist

Member
OK. Ship is built, photos taken of the process. Maiden flights are complete. Documenting of the build to follow.

It's a FLYER!! Initial flight was a bit of a sketchy affair, as I had the roll rates set to high (duhrrrr), but the ship floats extremely well. On the upwind portion of its flights, I had to roll off throttle, leading to floating, or put the nose down, which would really speed the ship up. You gain control over this bird by AOA (angle of attack) and thrust. It is wind-sensitive at these high AOAs. I had one bad launch that (inexplicably) had me launching at 3/4 throttle, and the bird settled onto the deck and took one roll. The nose was slightly scrunched, but not bad enough to prevent further flights. I put the ship up and tried my stabilization system in the Lemon Stabilized, but got the "alieron shakes" at high speed, same as always with every airframe. I will have to turn down the gain and see if I can get it tuned to work with this system. I placed the battery about an inch forward and got less float out of the ship and better speed.

You can get some airspeed with this bird! I made a couple of high-speed medium-altitude passes with it and was amazed at how fast it will go. I'm not a super high-speed flier and I like making controlled flight maneuvers and basic aerobatics with RC aircraft. I did several faultless and "cordless drill" style aileron rolls with it and an Immelman, and it does nice maneuvers, although I have plenty of room to improve, once I get used to the airframe's performance.

Tonight I will fix the nose and put together a scale paint job for this ship.
 

FOGeologist

Member
OK.

Pretend it's Saturday the 8th, and I'm posting a blow-by-blow account of the build. Regenerate your suspense over whether "that idiot's going to mess this one up good, LET'S KEEP UP A DEATH-WATCH!" Go ahead, start a betting-pool over when I mess up so bad I'll get video evidence of a crash...
 

DamoRC

Elite member
Mentor
Congrats on the maiden - yep- its a good ship. Used to be one of DamoRC Jnr's go-to planes. As a pusher he liked to try to cut the grass with it.

Pics of the finished bird would be nice before you "mess up so bad I'll get video evidence of a crash... " ;)

DamoRC
 

FOGeologist

Member
The first puzzle - how should I make the wing? I could build up the wing on the original, giving it a profile. By default, it will be a flat-bottomed airfoil, but that might be OK.

To begin with, maybe I need to build a dummy wing to see what will happen.
wing_dummies.JPG
 
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FOGeologist

Member
Congrats on the maiden - yep- its a good ship. Used to be one of DamoRC Jnr's go-to planes. As a pusher he liked to try to cut the grass with it.

Pics of the finished bird would be nice before you "mess up so bad I'll get video evidence of a crash... " ;)

DamoRC
We'll get there, brother. I'ma make it happen! Tomorrow the ship's in the garage for finishing. I gotta un-ding the nose, thank the Big Guy for lightweight spackle and sandpaper.
 

FOGeologist

Member
I designed some wing ribs. I did not use a known NACA profile, as I anticipated that the ribs would merely provide structure and a generalized airfoil shape. I used Inkscape to create a bezier line, measuring the cord at four probable locations, and created the wing rib shape based upon estimated shape of the airfoil at the wing root and at the tip.
wing ribs.JPG
 

FOGeologist

Member
In general when you fold one of these foamboard wings, you place the longest straight edge abutting the itself, cut about halfway down, fold it back on itself and bevel both sides. If you do it right, when you fold it you will get a nice airfoil shape around the central spar.

But what happens when you have a reverse-triple-delta shape (I think this is the correct terminology)? The leading edge shapes are impossible to line up, so you have to come up with a way to fold them where they will meet without too much thickness, and with a sound enough edge where the ship can take a little damage.

Here's what I did:
first fold.JPG

I deeply beveled the edges of both wings (inspired by Our Sublime Leader, Nic Lechner). I tried pinching them together after a shot of hot glue; I found two 2" pine flats in the garage to get the pinch even and to avoid burns. This worked OK; the soft foam was dented in areas where I additionally added strong clamps to keep the long flats even. Fingers worked better - the price was PAIN!

leadingedge.JPG
 

FOGeologist

Member
What to do at the aft end of the wing, where the trailing edge leads to the control surface? On the dummy wing, I thought I could deeply bevel the surface faces and get them to form a low-angle trailing edge.

Sorry for the out-of-focus pic:

dummy wing from control surface.JPG

You will notice that I have a brown paper piece covering the leading edge joints.


dummy wing top view.JPG

This is exactly what you think it is: It's kraft paper, soaked in my infamous thinned Titebond Wood Glue mixture, and applied like a tape over the edge. This stuff shrinks when it cures and lashes itself to the paper and foam pretty aggressively, providing protection and a smooth surface.