"SOARBIRD", a hawk-like slow flyer / thermal glider, Bluecor & EPP - Page 4 - RC Groups
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Nov 13, 2006, 06:52 AM
“There’s no place like Foam”
gpw's Avatar
Viking , having built quite a number of those airfoils and Evans designs in the gas days (eps Foam wings ) I think it would be workable with the required "holy trinity"of tailless FW design.. Sweepback , Dihedral ,and Washout . "Pure " (no verticals) wings were built from box store Foamie wings with the 3 "laws", all flew fine .... It is a good airfoil that's got a good speed range , and gentle characteristics...just an idea for better handling ...
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Nov 13, 2006, 08:15 AM
High Altitude Flyer
viking60's Avatar
GPW, The ESA40 looks like a good airfoil to use for a new design project if I were looking to make up the cutting templates & go into hot wireing a foam core... but that's a lot of setup time for just one wing for anyone who does not have a CNC foam cutter. With my shortage of building time these days, I'll keep it simpler for now.


SOARBIRD's Design & Performance Envelope Concepts:

Stylized Bird-Like Silhouette
Light Weight, Low Wing Loading
Stable Flying; Thermal & light wind slope soaring capability
Capable of Very Slow Flight & Landing Anywhere; Durability
Adequate power to climb quickly, loop, handle some winds
K.I.S.S. approach: Simple Build Techniques

With a BlueCor wing, the 61" SOARBIRD is flying at under 11 ounces, & the 53" prototype SOARBIRD II will include an elevator, & still be under 11 ounces. It's wing is relatively quick & easy to build. (Tail-less was never a design factor in achieving SOARBIRD's bird-like flying profile - it needed a tail to complete the look anyway.)

Thanks to everyone for all of your feedback, suggestions, & encouragement! I'll post updates on SOARBIRD II's progress soon.


Last edited by viking60; Nov 18, 2006 at 01:58 PM.
Nov 13, 2006, 12:35 PM
High Altitude Flyer
viking60's Avatar

SOARBIRD II Shaping up


Here's a preview of SOARBIRD II

The wing has less leading edge sweep, the outer wing joints are moved inboard substantially, the wing tips / elevons are reshaped and stretched back inboard significantly, and the wing's inboard trailing edge has been reshaped into a more curvilinear profile (which should look good in the air.)

Span is at 53-1/2", chord is reduced at the root by about an inch.

The body / fuselage is just slightly shorter with a somewhat shortened head; the EPP foam head around the motor is somewhat slimmer so that the Multiplex folding prop should sit folded a bit closer in glide mode. The tail is actually stretched for now, with an elevator hinged in place.

More later!

Nov 13, 2006, 05:05 PM
Glider guider
Speedo125's Avatar
It's lookin' better all the time Bruce! I'll be waiting to hear a flight report with that new wing. It certainly looks more "scale-like". When you have the design finalized, I'll carve a fuse' from blue foam and give it a light coat of FG/Polycrylic.
A former 14'er bagger.
Nov 15, 2006, 04:01 PM
High Altitude Flyer
viking60's Avatar

SOARBIR II dimensions

SOARBIRD II's wing is 52-1/8" span at the trailing edge. The wing root chord (center) is 12-7/8"; if the leading edge were extended out to a line parallel to the root, the tip chord would be 6-7/8". The elevon wing tips add on beyond this, for a bit more area than what is removed from the front outer corner of the wing; the total wing area comes out to close to 500 square inches, about 3.4 square feet. This amount of BlueCor weighs 2-5/8 ounces. The spars add another 5/8 ounces.

At a flying weight of about 10-3/4 ounces, this comes out to a wing loading of just over 3 ounces per square foot. That's a light bird!

The solid EPP foam body is made from a block of 1.3# density foam that is 2-3/8" wide, 2-3/4" high, and 18-5/8" long, shaped by band-sawing & then carving with a sharp fillet knife before sanding, to end up looking somewhat like a bird's body. After shaping, & with the motor mount shaft and wing mount plates epoxied in place, the body weight only 1.0 ounce. (The tail group, assembled, glued, & painted, weighs 1/2 ounce.)

More Later!

Last edited by viking60; Nov 18, 2006 at 02:00 PM.
Nov 17, 2006, 11:49 PM
High Altitude Flyer
viking60's Avatar

SOARBIRD II's fuselage

SOARBIRD II's fuselage is about ready for flight. The electronics all are mounted or embedded in the EPP foam where the wing will cover them. Final work on the new wing will be completed this evening, ready to fly tomorrow. I'll post more photos soon, & then the flight report.

Nov 18, 2006, 12:54 PM
High Altitude Flyer
viking60's Avatar

SOARBIRD II is ready to fly


Soarbird II is now ready to fly! Flying weight is at 10-3/4 ounces after the wing was painted; that's a weight gain of 3/8 ounces over the unpainted wing. (The added elevator and it's servo and linkage are part of the weight tradeoff while shrinking & changing the shaping of the wing from the first prototype SOARBIRD.)

3 Blue Bird BMS308BB servos are used; therse have coreless motors, offer 17 ounce-inches of torque @ 4.8V, and weigh only 6.2 grams each. The Corona RD620 receiver allows use of two aileron / flaperon servos; flaperon setup allows for programmable & switchable aileron reflex trimming for cruising, slow floating, or landing modes.

Winds are, unfortunately, holding at about 20 MPH in South Park today, with higher gusts forecast... far less than ideal conditions for doing the trim flights on an aircraft with a undercambered airfoil and just a little over 3 ounces per square foot wing loading!

More soon!

Nov 18, 2006, 09:34 PM
High Altitude Flyer
viking60's Avatar

Here are a couple more photos of the SOARBIRDS. The first is of the original SOARBIRD gliding off a slope flying site recently. There was a distinct lack of thermal lift that afternoon, cold air, and what breezes wer moving were not oriented into the hill, so I'm looking forward to better light wind slope flying conditions another day. I'll comment that the heavily reflexed wing tips are not ideal for either high speed climbing, or for clean efficient gliding; my impression is that there's a lot of drag.

OH- one hawk & a couple more crows cruised by to check out the new bird in the neighborhood, but none of them crowded SOARBIRD too closely.

SOARBIRD II has radio range issues; I'd run the antenna in the EPP foam fuselage, but it's now being moved out & onto the underside of the wing. I'll replace the .032" music wire elevator control rod with a C.F. rod, too, to minimize the possibility that it is a specific sub-harmonic length of the 72 MHz carrier, and may therefore be masking the antenna's ability to pick up a good signal.

This newer wing design & setup is VERY promising! There's very little aileron reflex being used in the minimum flaperon setting, and it's definitely an improvement over the much higher aileron / elevon reflex initially set up on SOARBIRD I. I'll write more on this later once I've done more test flying & setup tweaking.

The second photo is of the two SOARBIRDS together. (The angle of the photo isn't the best to give a comparative perspective... )

It's indoor flying for the slow flyers tomorrow morning for some of the local flyers; I'll also see about getting some test flying done on SOARBIRD II if conditions allow.

Last edited by viking60; Nov 18, 2006 at 09:43 PM.
Nov 18, 2006, 10:55 PM
Registered User
praymond's Avatar
Nice looking Birds!! And what a beautiful backdrop for flying!! WOW

I built the noodle board variant beagle, use it for vids with a 5in1 cam. Looking forward to your reports on SoarbirdII. Would love to freak out the turkey vultures and seagulls that fly where I do!!
Nov 19, 2006, 10:37 AM
Robots... robots everywhere
minifly's Avatar
Just an idea about the vertical tail area...

How about putting some clear (perspex, or mylar) material fot the vertical tail, so you can keep it looking flat?

Looking awsome though.

Nov 20, 2006, 12:04 AM
High Altitude Flyer
viking60's Avatar

Down the road, clear material would be a nice touch; I do not have any suitable material on hand at this time. I'm still at the stage of optimizing the wing and tailgroup geometry & control system setup details, so it's really quick & easy to build out prototype tail groups from Bluecor for now.

Today's flying indicates that SOARBIRD II's wing is performing well, and the ~4 degree downthrust on the motor mount installation is better than without; my impression is that this bird would still like to have more positive wing incidence relative to the tail. I'll have materials along & be prepared to do further testing to attempt to define the optimum incidence on my next test flying opportunity.

Nov 21, 2006, 08:07 PM
Happy Trees
m4rs's Avatar
Hey Bruce, looking cool. Had any locals come by/after it? If not I want to be there when it happens..calling now.
Nov 22, 2006, 07:41 AM
J. Titors gr8 grandson...
Sonofagun's Avatar
I glassed a 4' version top and partial bottom. That extra weight along with a more rearward cg (less reflex) and less camber seemed to really help the glide.
The wing loading is still ridiculously low. After I glue the 2 halves together I bend a flat carbon strip around nose along LE. Post us a short video Vik. if/when you get a chance.
Nov 22, 2006, 11:09 AM
High Altitude Flyer
viking60's Avatar

Wing likes to be set at positive incidence relative to the tail


thanks for the comments! A full airfoil wing would have advantages; I'll likely end up hot-wiring EPP foam cores when I jump to that stage. (Keeping a large single surface Bluecor wing aligned req

The undercambered Bluecor wing requires some positive wing incidence, relative to the tail / horizontal stabilizer, to fly with less aileron reflex (for a cleaner, more efficient glide.) I shimmed the wing's leading edge up about 9/16" ; than might come out to about 2 degrees of positive incidence, typical for Jedesky type airfoils. I still am flying with some up elevator trim... the ideal / most efficient setup would have SOARBIRD flying with zero up elevator trim....

The Motor was acting less than happy recently, & finally gave up; I'd built & flown it without a vented can... this I now realize was a mistake; 19 winds on 3S LiPoly, trying to run the LARGE 9.5x6.5 Multiplex folding prop, definitely generated an excess of heat, & I'm now rewinding the motor to 21 wraps of 26 gauge [Y termination.] I'll be using one of the http://www.StrongRCmotors.com/Cans.htm vented cans when SOARBIRD II goes back into the air, and using a CC Thunderbird 9 ESC. More flight / setup testing & optimization will be possible after that motor rewind is completed.

I'm considering slightly reflexing the entire trailing edge of SOARBIRD II's wing to equalize out the effects of the undercamber, & thereby increase the glide efficiency. I'll report on the results of this experiment when it's done.

Video?... I do most of my flying alone, but eventually I may have a friend along who can shoot some video.

I will report that SOARBIRD II is climbing well, looping tightly- (4 to 5 foot loops), & able to roll OK in it's present configuration; it was never meant to fly upside down, but it can easily do enough of the crazy maneuvers to possibly scare off agressive hawks. So far, the hawks that have cruised by have been only curious, and have shown no agressive tendancies... that should be expected to change in the spring, however, when flying near nesting areas. The ravens always come over to check out the new bird in the neighborhood, but while they talk the trash talk, they also have not been agressive- they do sometimes stay around SOARBIRD longer than the hawks.

Last edited by viking60; Nov 22, 2006 at 02:44 PM.
Nov 26, 2006, 07:31 PM
High Altitude Flyer
viking60's Avatar

SOARBIRD II Flight Report: Variable Reflex Control for Ailerons


SOARBIRD II, with the added elevator and the spoileron control of the aileron reflex, is definitely out-performing the first prototype. (I flew them both again today in gusty, variable wind conditions; without the elevator, SOARBIRD just is not happy in gusty winds- especially when compared with the quick responsiveness of SOARBIRD II.)

So before long, SOARBIRD I will get another updated tail and an elevator & servo. I'll upgrade it's receiver to a Corona RS 610, so I can use the flap switch to change the aileron / wing tip reflex.

For flying SOARBIRTD II, I have the (spoileron control) flap switch in the minimum aileron reflex position for launch under power, & the elevator is trimmed for good climb without zoom; once I've climbed to altitude (or punched out in front of the slope a comfortable distance when flying slope winds with this lightly loaded bird) and I cut the throttle, I'll switch in the up reflex for more efficient gliding. [Reflex amount is programmable on the RD8000 radio I'm using.] It's working NICELY!!!

Last edited by viking60; Nov 26, 2006 at 07:37 PM.

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