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Oct 25, 2016, 11:11 PM
treefinder
springer's Avatar
Thread OP
Build Log

7 foot span wing - MPF and wood


I decided that this bird deserves it's own thread. I've been discussing it on the SEMFF thread so far, but with a successful video flight, I think I can let her show her stuff.

The idea was to do a full scratch built design, no plans, nothing worked out in Sketchup (my normal way of doing it). I decided to use two sheets of foam, and cut a diagonal on each to form the top and bottom skins. Ribs came from the left over pieces that were scrap when I cut the sweep angle into center and tips. Main spar is two pieces of quarter inch square wood. ( I I think it's pine, but may be maple - fine grain light color wood.) The ribs are glued to the spars at 6" intervals. Airfoil is a generic symmetrical foil - didn't try to exactly duplicate a specific one. Once the spars and ribs are glued, i glued beaverboard (tablet backs type cardboard) to each side of the wood to make a box section. It is an amazing stiffener! The spar assembly was originally pretty flexy, but with the side webs is rigid. I glued the spar assemblies together using the two center ribs on each half, then glued the resulting assembly to the wing bottom halves. When I did this, I laid some open weave ribbon material on the 1.5" aft at TE area and weighted down the two halves to make a solid portion that ultimately became elevons. I did this on the floor of my work room, and it had an interesting effect on the final shape. The wing being symmetrical, and laying it "flat" on the floor, resulted in a warpage that adds what seems the right amount of twist to achieve good washout. Once tops are added, I glued a LE spar (this of basswood) and shaped the LE to a nice LE. The outer portion of the span on each side was shaped down some to enhance the washout (kinda like cuffs).
Last edited by springer; Sep 19, 2018 at 08:08 AM.
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Oct 25, 2016, 11:15 PM
treefinder
springer's Avatar
Thread OP
Specs:
wing span: 7'
AUW without lipo approximately 26oz.

Motor: Banggood DYS D2830-8 1300kv, 52gm 275 watt brushless
Prop: APC style 8x6
ESC: HobbyKing red brick 30amp I had laying around
Battery: Zippy compact 2200mah 3s pack
Servos: two 9 gram hextronic HXT900s

Here's the flight video:
(1 min 43 sec)
Oct 26, 2016, 12:36 AM
If it flies - I want one!
Petem's Avatar

Sweet!


An interesting build concept - thank you!
Oct 26, 2016, 01:31 AM
Build straight - Fly twisty
Whiskers's Avatar
Excellent!
Plans? Who needs plans?
Oct 26, 2016, 05:36 AM
gpw
gpw
“There’s no place like Foam”
gpw's Avatar
Bigger flies Better ...
Latest blog entry: Lost plans
Oct 26, 2016, 05:53 AM
You sabotaged my plane.
eliworm's Avatar
Very nice. I have wanted to do a large wing for a while now. Wish I had more time.

Jim

How about calling it the "Sensor".
Last edited by eliworm; Oct 26, 2016 at 06:11 AM.
Oct 26, 2016, 06:57 AM
Laughs at un-boxing videos...
basicguy's Avatar
I like the straight wing with no vertical stabilizers. Congrats.
Oct 26, 2016, 10:02 AM
treefinder
springer's Avatar
Thread OP
Thanks guys. It came together surprisingly well, considering the minimal design planning (for me). Doing it on the fly (pun intended) has been refreshing. All along I figured I would have to include some vertical tip surfaces for yaw stability, but the several flights in recent days showed only a little wobble, so the need seems much less than I thought. I think I will take my older bro's guidance and make up some tips to attach with magnets just to see how they change behavior.
Oct 26, 2016, 10:04 AM
treefinder
springer's Avatar
Thread OP
Quote:
Originally Posted by eliworm
Very nice. I have wanted to do a large wing for a while now. Wish I had more time.

Jim

How about calling it the "Sensor".
Interesting name, wat prompted that particular name?

Heh, so many planes, so little time!
Oct 26, 2016, 10:11 AM
AKA Don
Magnets? Better hope it will fly well with one on and one off!

Maybe tape or Velcro for a trial.
Oct 26, 2016, 10:16 AM
low tech high tech
vtdiy's Avatar
Nice wing , Springer! And fun to be able to just start building, and using up scrap. I'm curious to see whether it thermals well. Seems like it should!
Oct 26, 2016, 10:28 AM
treefinder
springer's Avatar
Thread OP
While the video showed a nice gentle launch, I should note that the first launches on maiden day were anything but! I had dutifully run the dimensions through a cg calculator (couldn't find the link for the wing calculator, so left tail dims at zero in the adamone calc that most folk use - it seemed to work). Set the balance point margin at 15%. All gear on, battery hatch taped in place, out to maiden. First thing I found was my idea to side arm discus launch was not gonna work. I could hold the wing at one tip, but couldn't lift it off the ground with one hand. So a grip about quarter span LE and an awkward side arm launch was used. Could not get a straight launch, plane was rolling right each time. I think it was hitting/deflecting off my arm. Eventually got it airborne with power on - instant loop, cartwheel. (Fortunately no damage, spar holding). Second throw I was ready: release, down elevator, throttle back - she flys! Well, as I mentioned in SEMFF thread I managed to move her through the air, barely in control most of the time to a less than smooth landing. Hmmm some work to do. Back inside i looked her over and discovered that I had set motor mount angle at 90° - to fuse bottom. The angle to the wing neutral line was more like 10° positive (motor shaft aft end up) so I had set her up for continuous loops by "design"! Took a 5/32 tapered shim to get angle back to ~0°. I addressed the take off issue by getting a length of 3/4 PVC pipe and repurposing the PVC display rack I use for my onesheeters at shows to make the 5' rails. Next launch was much more controlled, flight pretty well controlled as well. But I still felt she would still do odd things at times. No verticals or cg aft? Figured moving cg fwd wouldn't hurt, so I moved the battery pocket forward about 3/4" and reinforced it with more cardboard. The video is this final configuration. I am pretty happy with how she flys now.
Last edited by springer; Oct 26, 2016 at 10:45 AM.
Oct 26, 2016, 10:35 AM
treefinder
springer's Avatar
Thread OP
Quote:
Originally Posted by bz1mcr
Magnets? Better hope it will fly well with one on and one off!

Maybe tape or Velcro for a trial.
We discussed Velcro, I think I will probably use some tape too on first try just to keep things in place! With Velcro I will have to make a positive mount so the Velcro only retains, with enough magnets I might do a butt joint. We'll see. . .
Oct 26, 2016, 10:41 AM
treefinder
springer's Avatar
Thread OP
Quote:
Originally Posted by vtdiy
Nice wing , Springer! And fun to be able to just start building, and using up scrap. I'm curious to see whether it thermals well. Seems like it should!
Definitely floaty enough. The one flight in moderate winds, I powered her up a good ways and cut throttle(brake isn't on, so prop windmilling) and she hung up there for a looking time, several minutes to glide down. I don't think there was any lift, just flat glide. This morning I flew her and found out how low the ceiling was. I climbed up and watched her start to disappear. White plane,white clouds, not good. Fortunately clouds were thin and I dove her out of them.
Oct 26, 2016, 11:30 AM
You sabotaged my plane.
eliworm's Avatar
Quote:
Originally Posted by springer
Interesting name, wat prompted that particular name?

Heh, so many planes, so little time!

Back in my Hang Gliding days there was a wing called the Sensor. Always thought that was a cool name for a wing.

Jim


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