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I always wanted a forward swept wing...

jamesomega

Junior Member
#1
But I haven't actually seen an Alulah up close before and while all of the flight videos and photos looked great via google, I really didn't like the idea of having to stare through a prop if I was ever going to try to FPV it. So, I decided to scratch build a pusher 48" version from a single $6ish sheet of 4'x2'x2" Insulfoam EPS R-tech from Home Depot (hot wire setup not included). Since EPS is a rigid/brittle/flimsy/light weight material, it really needs to be sparred ($4 fiberglass arrowshafts) and skinned (scotch heavy duty shipping tape) in order to compete against any g-forces. I've found that a properly tape skinned and sparred EPS wing will typically out perform EPP setups in cost, weight savings (speed and endurance), and g-tolerances at the cost of durability/crash recovery, but each pilot's mileage may vary. In any case, this is my first attempt at a forward sweep design.

The build was relatively easy- hot wire the wings out, low temp hot glue them together, cut out the curves, sand it smooth and skin it in tape with a gift card. I didn't take any build photos unfortunately since I thought it wasn't going to fly at first, but I'll try to put together a build guide when I get V2 going. I'm still messing around with wing and airfoil (PW51) AoA and the overall CoG placement between different motor/battery combos, but I believe a 35mm (3530-ish) should balance out the battery and GoPro. V2 will have a different fuselage design once I find an optimal motor/prop combo, but this one is a little nose heavy and was just quick and dirty.

Here's prototype so far:



Specs & Electronics as follows:

Wing geometry: 48" span, 10 3/16" root chord + 1 1/8th in front for forward sweep, 6.5" tip chord. CoG: somewhere around 1.5" from the leading edge of where they come together. Elevons start at 2.5" from the trailing edge at the root chord and taper to 1.5" at the tip chord. Airfoil used was a modified PW51 with a 1/4" vertical insert to bring it up to 1.5" root thickness. Straight front angle, no dihedral.

Motor: Trusty/cheap Suppo BL2212-6 2200kv
Prop: 6x5.5 APC
ESC: Turnigy 40amp Plush (w/ braking)
Servos: Started with Coronoa DS-939MG but they have too much slack in their heads and recently swapped them out for HK 922, lesser torque threshold but no slack.
AUW: 634g (1.4ish lbs) - oh snap.
Batteries: 2650mah 35-70C 3S nanotech flat packs or 45C 2200mah 3S nanotechs / need more flights to get the best CoG.
Radio Setup: Hitec A9 & Optima 6 with SPC for voltage telemetry.
Endurance varies: but on a Suppo 1250kv BL-2217/7 running a 9x6 APC (too much for the motor), I was able to get 7.5 minutes worth of fast and unlimited burst climb at 75% throttle and 50m33s of total flight time down to 11.2v thermal-ing around Natomas Field on a particular hot day. I haven't tested the 2200kv setup just yet, but I expect some inefficiency.

Some additional pictures:













After I re-maiden this thing, I'll see if I can get my buddy to record a flight video for me so I can show off its flight characteristics. It's EXTREMELY aerobatic.
 
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jamesomega

Junior Member
#6
I'm charging up 2200mah 3S's and 2650mah 3S's for the maiden today! I'm pretty excited, but my buddy's going to have to throw it for me first in case it needs some wild trimming.
 

jamesomega

Junior Member
#7
The winds were kinda nasty and I wish I had brought a camera with a zoom lens, but you can still kinda see it flipping around in 1080p.

 

Craftydan

Hostage Taker of Quads
Moderator
Mentor
#8
The winds were kinda nasty and I wish I had brought a camera with a zoom lens, but you can still kinda see it flipping around in 1080p.
Vid is fine -- plenty clear enough to see you're having a blast!

She looks pretty in the air, but how does it glide?

Can't tell from the vid when the motor is on/off, but for a lot of the vid it's pretty clear you're pushing it like a sport plane, not a power glider. It looks fun to fly as either, but wondering how well she'd take on her glider heritage.

BTW, what's your run time on the 2200s (or the 2650)?
 
#10
She looks pretty in the air, but how does it glide?

Can't tell from the vid when the motor is on/off, but for a lot of the vid it's pretty clear you're pushing it like a sport plane, not a power glider. It looks fun to fly as either, but wondering how well she'd take on her glider heritage.

BTW, what's your run time on the 2200s (or the 2650)?
I should had added some more annotations for when i had the throttle on and off. If the wind is up like it was yesterday, then I might be able to take it slope soaring so folks can see how it does.

The flight times have been all over the map so far.

On a 2200, I'm able to get about 7 minute of high running throttle, but depending on weather and wind conditions, I can keep it in the air for 20-40 minutes.

I got my longest flight on a 2650 pack with 8 minutes of throttle and 50 minutes of gliding/thermal hunting at the same location. My city is very flat, so I have to drive a while to hills to fly.
 
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#11
SSC Combat?

Great VID and nice build for V1. I am looking for pusher wing options for a SSC Combat plane. Will be trying coroplast so it won't look as nice as your glider but it needs to survive mid-airs and lawn dart landings. Like the way you have battery protected and out front for balance.