"SOARBIRD", a hawk-like slow flyer / thermal glider, Bluecor & EPP - Page 3 - RC Groups
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Nov 11, 2006, 06:49 AM
Crash Master
Gene Bond's Avatar
I believe you about the rigidity. 48 or so may be the extent of single surface's capability, that's even pushing it, IMO... The problem is it's not as easy to just roll the LE over on a swept planform to use a Jedesky-style airfoil on a swept wing.

Keep the faith! The goal is worthy of the quest
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Nov 11, 2006, 06:58 AM
registered foam addict
chara's Avatar
vik, nice project!
I love the bird like models.
I've build one a while ago. wanted to have one that could compete with the buzzards that are flying around in light lift.
it was all made of 3mm depron (AUW 120g). jedelsky profile. aileron, elevator control. crucifix tail like yours.
it didn't fly so well: was a bit tricky to balance, wings were too flimsy (had no stiffening spar) and were flapping wildly Roll control was miserable...

If I build it again I willgo with RET (rudder elevator thrust) control.

good luck with your next flight! it's absolutely cool1
Nov 11, 2006, 02:33 PM
High Altitude Flyer
viking60's Avatar

SOARBIRD is flying very well!


I finally got a morning without gusty winds, so even though the thermometer was sitting on 11 degrees early, I headed out to work out SOARBIRD's setup / flying details.

The first two packs were flown with the BPHobbies 8x6 folding prop, but it was quite obvious by the end of those flights that, even on the 3S LiPoly packs, this prop was not generating enough thrust- SOARBIRD was climbing anemicly and stalling repeatedly.

The fix? I quickly ran back to the shop and installed the MULTIPLEX 9.5x6.5 folding prop. (By the time I was heading back down to the flying area, the thermometer had made it up to 25 degrees... balmy!)

What A DIFFERENCE a prop makes!!!

This prop REALLY generates a lot more thrust, and SOAREBIRD was off & climbing nicely!

I played with battery positioning / balance and elevon reflex, ending up with the amount of reflex shown in the last photo below.

Four ravens cruised by to check out the new bird in the neighborhood, and while I think they were trading derisive remarks among themselves about SOARBIRD's flying style, they did not crowd him too closely.

After running back to the shop once more to do a quick job on the elevon linkages & wing tip tempering, I decided to finish off my morning by flying some gusty crossing winds in the small bowl just across the road from my house. It handled the challenge well, but as the wind direction was continuing to shift even farther around to an unfavorable direction, I decided to call it enough for the morning... (it was time to recharge all of the batteries again, anyway...)

I did stiffen the elevon linkages before the last flight- (I added a section of carbon fiber rod, bound to the 1/32" music wire with kevlar thread & thin Cya glue), and it did help. At high speeds / full throttle with the Multiplex folding prop, there had been a tendancy to induce some oscilations / flutter into the wing tips. I also used the heat gun judiciously to 'temper' some of the BlueCor in the wing tip area before that last flight in the gusty crossing winds, and I'd say it did improve control response, as it resulted in a bit more rigidity in those areas.

By the way: I mounted the Multiplex folding prop on a prop saver, which works great! - K.I.S.S. RULES!!!

Final assessment after this morning's flying?


Last edited by viking60; Nov 11, 2006 at 02:44 PM.
Nov 11, 2006, 06:05 PM
skumgummi dave
Great thread Viking! Really enjoying your progress.........

Nov 11, 2006, 09:18 PM
Registered User
Congratulations Bruce on your Soarbird. Perhaps it could be a bird of prey and you can bring it over to my place in the summer to take out all the gophers on Lost Creek International Airpark. Maybe you can take it bird hunting also for pheasants and grouse . Anyway the rest of your flying friends here over the pass are anxious to see your bird.
Nov 12, 2006, 07:22 AM
“There’s no place like Foam”
gpw's Avatar
Great News about the flying , WAAAY COOL !!!
Nov 12, 2006, 09:34 AM
Glider guider
Speedo125's Avatar
Lookin' good Bruce!
I'm following this one closely. It's just what I've been searching for. I sure do miss CO. I never should've let the missus talk me into moving. It looks like you're near treeline. That would put you at about 10.5K to 11K, right? I imagine it will really float down here near sea level.
What do you think about a very light FG skin (applied with Polycrylic) over those wings to add some stiffness? It would also reinforce that dihedral joint. The small amount of added weight would improve penetration in those gusty conditions too.
Nov 12, 2006, 10:00 AM
Dismembered Member...
arx_n_sparx's Avatar
You could stiffen the wings a lot more by closing in the bottoms of them. This would help the penetration much more as well.

Nov 12, 2006, 10:06 AM
Looks Great
I knew you could do it.
I debated once about trying to hot-wire some foam wings in this shape but it was a bit beyond my skill and patient level. A man just about need to make up about 3 sections per side to get all the curves, sweep, and reflex.
That's where bluecore works great. Just needed to be stiffened up some.
Great job Viking

Nov 12, 2006, 10:24 AM
Registered User
kimhey's Avatar

Talking about InspirationBoost..!!

Thanks for sharing this bird with us all.

Nov 12, 2006, 11:53 AM
High Altitude Flyer
viking60's Avatar

My home sits at 10,300 feet; this flying site in the flats is just about 10,100 feet elevation... (Sherman is one of Colorado's many 14'ers.)

Brad & Speedo & SPFD,

I'm inclined to build out another different high speed / high wind wing version, and leave this wing very light; [the heat tempering of the BlueCor foam in the wing tip area, along with stiffening the elevon linkages, did add enough more rigidity to have it handling the gusty cross-winds in the tight tree-lined bowl just in front of my house quite well...]

Heavily undercambered airfoils are not really good above certain speeds, so Brad's sugestion of closing in the bottom of a Bluecor wing, or SPFD's comment on hot-wiring a wing would probably be more appropriate than just stiffening the Bluecor single layer wing. A BlueCor wing closed off on the bottom with DocuLam film might be a good next design step for SOARBIRD.

SOARBIRD is really quite flyable as it is, within it's own performance envelope limitations.

I've cut some EPP wings with hot wire, (*kitted a couple of designs on a limited basis) and am definitely thinking of going that way on a later generation; this build log thread is focused on a more simple undercambered Bluecor winged slow flyer / cruiser that most builders can knock out without going into hot-wire techniques & equipment.

Hey!- the snowfall stopped, sun's out, & the winds aren't blowing- time to get off the computer soon & get out & FLY... I'll go find a slope for SOARBIRD to cruise today!

SOARBIRD does now have it's own page on my web site; I'll be adding new information there, as well as on this discussion thread:



Last edited by viking60; Nov 12, 2006 at 12:33 PM.
Nov 12, 2006, 03:54 PM
Crash Master
Gene Bond's Avatar
Congrats Bruce. Looks like another winner.
Nov 12, 2006, 07:43 PM
“There’s no place like Foam”
gpw's Avatar
If you guys want a nice airfoil for hot wiring , please check out the Bill Evans(Scimitar, Slo Mo , Seirra Trainer) airfoil ... just really a great airfoil for these types of FW .... Looks like a whale to me , but flies super , very gentle with a good speed range ...
Nov 12, 2006, 11:48 PM
High Altitude Flyer
viking60's Avatar
Originally Posted by gpw
If you guys want a nice airfoil for hot wiring , please check out the Bill Evans(Scimitar, Slo Mo , Seirra Trainer) airfoil ... just really a great airfoil for these types of FW .... Looks like a whale to me , but flies super , very gentle with a good speed range ...

From what I've dug up so far, it looks like the airfoil Bill Evans used was similar to an ESA40; here's a link to one page in the NASG Airfoil Database on it:


Looks like a good flying wing airfoil with a reflexed trailing edge; no horizontal stabilizers were used, but very large vertical stabilizers were always used in Bill Evans' designs. Here's a link to a thread with a lot of his plans:


Last edited by viking60; Nov 12, 2006 at 11:56 PM.
Nov 12, 2006, 11:55 PM
High Altitude Flyer
viking60's Avatar

53" Wingspan SOARBIRD now in the works

I ended up back in the shop instead of out flying on Sunday.
I'm already building another prototype SOARBIRD. This one is being built with a 53" span, and I'm also adding an elevator on the bird's tail, so I can test that variant for control response / stability in higher winds & gusty wind conditions, in comparison to the first SOARBIRD. Both will be in the air next weekend if all goes well.

I've built in about three to four degrees downthrust into the motor installation on this new body / fuselage. Either wing will mount on either fuselage, as they will have the same root chord and mount spacing, so I'll be able to swap out parts & test all of the variations.

More Later!

Last edited by viking60; Nov 13, 2006 at 07:21 AM.

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