2 Metre Constant Chord Thermal Wing - RC Groups
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Feb 24, 2013, 11:55 PM
Living on the Dark Side.
guitarcher's Avatar
Build Log

2 Metre Constant Chord Thermal Wing

Since acquiring my Alula HLG a year ago I have become totally obsessed with flying wings. I have sifted through the nurflugel and flying wing forums and decided I liked the wings of Miniphase and Penumbras and CO series.

I admire the wooden wonders that are displayed in the Nurflugel forum, particularly some of the Hortens but have chosen to build this wing from foam because this was an experimental build and I didn't want to spend a huge amount of time on something that might not fly.

The following build was completed in 2 days.

Specs: 2 Metre wingspan, coz thats what I can fit in my Land Rover Defender
diagonally between the seats.

235mm ( just over 9" ) constant chord, coz that's easy.

S 5010 profile as suggested in the airfoil database.

White EPS packaging foam as I got it from work for nil cost

Wing to be cut from 4 sections with 1 degree sweep in the inboard and
3 degrees in the outboard.

Carbon fibre spars with bidirectional filament tape reinforcing.

2812 motor form Hobbyking ( $6 ), 3S 1300 mAh battery.

8" x 6" folding prop from HK with the blades reversed for pusher

The templates were cut from 3mm aluminium with a bottom section for accurate alignment. I made a wooden frame bow from scrap timber with 24 gauge NiChrome wire using a 12 volt car battery for the power source.

After cutting the cores I laid them back in the beds and used hot melt glue to join the sections together. The control surfaces were then cut. I elected to go for flared elevons to help with reflex if necessary. Flaps were also cut. The flaps are shorter than the elevons to reduce pitch up on deployment. Control surfaces are bottom hinged.

An exacto knife was used to cut slits in the foam and yellow PVA glue to secure 6mm x 1mm carbon fibre spars. One in the top and bottom surface at 30%
chord and and several cross braces. Also a 3mm carbon spar 10mm from the control surface cuts to provide rigidity in that area. 3mm CF was also inserted into the elevons for the same reason.

Holes were cut in the top surface to receive the HK MG90 servos and hot glued in place. More slots were cut to bury the servo wires.

50mm bidirectional filament tape covered all spars and slits as well as leading and trailing edge and centre section strengthening. The centre section was further reinforced with A3 laminating film as there no full depth spars. 50mm tape was also used for the hinges and to fully wrap the control surfaces.

The wing tips were cut from foam to the TLAR principle and were eyeball sanded to a symmetrical shape similar to S 8020 about 20 mm thick at the base to provide some measure of inherent strength, tapering to 10 mm at the top. Tongues of 1.5mm acrylic were inserted into the bottom of the wingtips so I could attach them to the wing ends using double sided tape for easy removal. The tips also received the tape treatment.

Iron on film was applied to the skins to protect the filament tape and provide some torsional strength.

All up weight with battery came to 700 grams, which I was very happy with.

Initial flight tests were carried out over long grass,no motor, with minor adjustments necessary to provide an acceptable glide.

Motorised testing then ensued. A lot of down trim is needed under power with a tendency to nose up unexpectedly. This may be due to the motor being fitted so close to the CG. Climb rate was reasonable considering the small motor. I don't need to get up there fast anyhow. Motor off trim only required minor adjustments. Glide ratio is pretty good. Sharp angles of bank are not good with a tendency to spiral dive. Sometimes this is recoverable, other times not, depending on altitude. Impacts with the ground have so far caused no damage. Another reason why I like foam.

Flap deployment was very successful with slight nose down attitude. Flap angle is max servo travel, about 80 degrees with no elevon required.

I've had a couple of hours of flight time so far and apart from the dreaded spiraling issue I'm very happy. One other cause for concern is that even though I have bright colours on top and winglets with dark underside, the wing has a habit of disappearing from view at not very great heights. It gets side on and just vanishes. Many anxious moments pass before appearing in another part of the sky.......so far. I had hoped that the 2M wingspan would alleviate this tendency. Thermaling opportunity has been limited so far, but I will have to be careful to limit the height, but that's easier said than done.

All in all not bad for 2 days fun building and low cash invested.

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Feb 25, 2013, 03:25 AM
the answer 42 is
Nice looking plane, great color scheme as well

Feb 25, 2013, 09:01 PM
Registered User
slebetman's Avatar
Sweet! So, it's a one piece wing or is it detachable? My last 2m wing project failed due to severe flutter. I'm therefore very interested in your spar set-up. What kind of foam did you use? Does it thermal?

Looking at your AUW, I think I may have built mine too light - therefore not stiff enough. I was aiming at 400g. Hmmm.. I may have to restart that build or start another 2m project.

Thanks for sharing your wing.
Feb 26, 2013, 05:02 PM
Living on the Dark Side.
guitarcher's Avatar
Sweet! So, it's a one piece wing or is it detachable? My last 2m wing project failed due to severe flutter. I'm therefore very interested in your spar set-up. What kind of foam did you use? Does it thermal?
I have included a picture of the spar layout for you. As stated in the build log the taping and skinning of the wing give combined strength. I have not had any flutter issues yet, but only fly it slow for thermals.

The wing is one piece. The foam is open bead Styrofoam used in packaging and I used this because I got it for nothing and the plane was experimental. EPP will work and of course is much more resilient but very expensive.

It will thermal but thus far I have only flown it in light morning air before the wind gets up.

I also have built a Grim Reaper from Crash Test Hobbies and as I initially tried to build it as a thermal plane I used 6mm CF spars instead of the supplied fibreglass rods. I've since put on a big motor and prop and scream around the sky at breakneck speed and it is dead stable with no flutter. Go to their web site for great "how to videos"

Hope this helps, sfluck.
Feb 27, 2013, 11:57 AM
less is more
Knoll53's Avatar
Wow ! 2 day build...that's amazing. Nice model.

Spiral dive may be a tip stall? What do you think?

You might look at adjusting your CG and reducing the elevon deflections to the minimum allowable to provide adequate control. The thought being that may be large deflections are stalling the control surface.

If it is easy to do, it might be interesting to try the spiral dive testing with smaller winglets.

Last edited by Knoll53; Feb 27, 2013 at 12:06 PM.
Mar 08, 2013, 01:38 PM
Always great building with Toe Scale!
Mar 14, 2013, 08:51 AM
Auzzie built planks
timbuck's Avatar
Nice work Greg..
Paint the winglets flouro orange.

Latest blog entry: More colours

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