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Old Jul 31, 2015, 02:29 PM
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Flying frog, I would normally agree with your assessment of the area penalty for flying wings, but lately I started to re-think my design philosophy for gliders and electric aircraft. We may be working under an erroneous belief that reflexed wing tailless aircraft are inferior in efficiency to conventional aircraft, at least when airfoils of moderate camber are used for both.

I have been designing RC models for 30 years, with a lot of them being gliders with high camber airfoils. The last 8 or so years I have designed a number of tailless models, including the airfoils which are specifically designed for them.
I recently finished a 60 inch span model with quite a high (14 oz) wing loading and was testing it one nice sunny day last fall. As a joke I climbed to 400 feet and chopped the throttle and let the prop fold to see if I could work a thermal for a few minutes.
Imagine my surprise when it started climbing at a rate like one of my lightly loaded gliders! Granted it was a good day, but after 30 minutes at 1500 feet cruising from thermal to thermal I was convinced that we were missing out on a viable alternate platform for thermal flying because of opinions/experiences from the past. Not only did the thermal performance excel for such a heavy model with a short span, the handling in lift was every bit as good as my regular gliders.

I believe the purpose designed airfoils made all the difference. I was pretty much forced to come up with something using Profili after finding very little in the way of reflexed airfoils with zero pitching moment.
Not too big a wonder that I have become a fan of flying wings/tailless models in the past few years, I especially like their stability, it makes the the whole flying experience that much more relaxing.

With the results I have had with the 'wings' I would not hesitate to build a large ship for dedicated thermal flying. When I feel a desire to add another thermal ship to the stable, a tailless will be first choice.
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Old Jul 31, 2015, 03:16 PM
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wings

hi Dave
do you use cad like auto cad or the like if so i will knock out a sketch as several folks want a drawing or (and ) could do a jpeg with the the diams on it what span do you want this one is 77.5".
clear sky
nic
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Old Jul 31, 2015, 07:15 PM
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The UnFlinch - Combat Hybrid

I am a huge fan of SweepWings Flinch, even for combat, but have grown weary of using blunt center sections for combat; a great fpv design, but too many compromises for lightweight combat machines. As I just finished a Juggernaut without the center section and love it, decided to use that center section in a Flinch, move forward and make a "V" out of it. Net result is motor and CG further back, much lighter battery: 2200 vs 3600 and structurally more sound - spars a simple triangle instead of odd angles to accommodate blunt nose. Huge success, a major badass wing. Here is video and carnage from hit during video. Hit at 2:47 just below view of camera. Whacked a much larger wing.

Unflinch Maiden (3 min 39 sec)


Combat Carnage - Old Guys (0 min 38 sec)
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Old Aug 01, 2015, 12:10 PM
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design

good morning builder
like you i am a long time builder and and have been designing flying wing and testing starting in 1985. i started building in 1965, started flying r/c in 1977. if you would like to study high performance wings look to what our brothers in europe are doing.
as far is heavily load air craft (r/c) i have thermaled 7lbs ugly sticks for 20 to 30 min a number of times, and a 14lbs senior Telamaster equipped with glider wracks and a super tiger 3000 in the nose. the Telamaster was by far easier to thermal but you have to have just the right conditions or it just wont happen. in the first half of 1990's my forward swept wings were winning and placeing in td contests. i still have a love song that i keep in contest condition to compare my wings to the wings must at least match the songs performance in ALL conditions to be considered a valid design in my list of projects. with more than 45 designs in 30 years using the 75% rule to get a the loading on the wing, if it is not the same or lower than the songs 10ozsqft it just will not perform on a consistant basics. best of luck wit your work and when you are able to get the heavy loading to work i will want to build one also. clear sky and smooth air
nic
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Old Aug 01, 2015, 04:25 PM
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flyingfrog50:

Hi Nic. I have Draftsight software which allows me to view and manipulate .dwg files. So a CAD drawing would be great!

Many thanks;

Dave-
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Old Aug 01, 2015, 05:06 PM
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draft site

Hi Dave
i need a few days to draw what i built. I have draft site also but have not used it much, how do you like it?
smooth air
nic
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Old Aug 01, 2015, 08:37 PM
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Nic:

I find draftsight very intuitive for a rank amateur. Photoshop was the program I used as a printer. I can probably display the .dwg file and export it as a. pdf. Then resize it from there to fit my needs. Once converted to a .pdf I can do what ever I need to. As I have time, I will do my best to learn cad. That is on my bucket list...

Regards;

Dave-
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Old Aug 01, 2015, 10:35 PM
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Flying frog, do you have any pictures of your TD wings? Why use forward sweep? A friend built a 2m forward swept wing for the slope many years ago using the E-186. It seemed to be quite efficient but the handling was unremarkable.

All of the old farts (myself included) around here are transitioning to motor gliders for all the TD flying, nobody wants to set up a high start or winch anymore. Not much of a weight penalty now over pure sailplanes, we sure have come a long way from brushed motors and nicad batteries for our power systems.
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Old Aug 02, 2015, 12:02 PM
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forward swept

Hi Builder
Why forward swept? First we want to stop span wise flow. fws of 1deg to no more than 2deg does this very well. (tuft testing on a bicycle mount is where i got these #'s from) More forward sweep only causes inboard flow that causes a high pressure zone aft of 50% of the root on the bottom side, this forces you to carry a lot more up trim, up trim = drag, also drag from stagnated flow at root under side and vortex development on top at root. Extending the fin forward only gets you 2 vortexes to deal with.
No tip stall you can hook a low slow tightining turn with out fear.
No spin out of a thermal. less loses in the climb phase.
Nose pitches up when in lift a more efficiant entry to lift as you tend to put in down elevator and reduce drag at that moment an gain more altitude.
Forward swept wings (fsw) tend to self center in lit and stay there, more relaxed flying.
If you want to build fsw do not use airfoils designed for planks or aft swept they will get you close but will have large drag buckets at increased AoA. the reflex in the top of the airfoil causes recirculation of air and thickens the airflow a lot . You need a section that has a nearly flat line on the top aft 30 to 40% of the wing. look at the sections on the drawing i sent a long you may need to down load it and use picture viewer to zoom in to see what i mean.
forward sweep also seams to reduce the pitching moment of the section, allowing less reflex to be needed.

I wish i still had the pictures of the tuft testing and the ships but those boxes of pic's were lost in the move severial boxes including 3 airplanes and a wench were also lost.

the 2 meter ship was my fav it had a zoom you had to see to believe at a contest in 95 i heard some one say that i had a rocket hidden in there.

if you have a cad program i can send you some of the airfoils i use.
I hope this helps and does not sound like a lecture.
have a great next flying day
nic
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Old Aug 02, 2015, 12:50 PM
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Quote:
Originally Posted by builder View Post
We may be working under an erroneous belief that reflexed wing tailless aircraft are inferior in efficiency to conventional aircraft, at least when airfoils of moderate camber are used for both.
I also believe that flying wings can every bit as efficient for gliding/cruising as tailed aircraft. The lack of fuselage and tailplane is certainly an advantage, and modern airfoils are excellent. For maneuvering performance I subtract 1.5 times the elevon area to calculate the effective wing loading. I have also done a lot of experimenting with flying wings and find that the total necessary elevon area can be a lot less than some might think. I use about 10% max.

I also design and build glow powered wings with 25 oz wing loading and they fly like pattern planes and glide forever.

My main point however was to point you to Peter Wick's airfoils, which are simply excellent for high lift and low drag. You can find lots of info in RC Groups and elsewhere.
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Old Aug 02, 2015, 10:03 PM
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Nic, I have a cad program and I use Profili to develop the 'foils, so DXF files would be great if you want to share.
I have not yet played with forward sweep, just sweep back and straight taper, a couple of examples shown here. The swept back one has slightly more stability in roll and yaw, otherwise not much difference between the two as far as handling goes. They use the same family of airfoils, so this might be the deciding factor.
Your 2m has very similar area to one of my ships, I used larger than normal chords as well. Are you a fan of using large chords for your wings?

Erwin
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Old Yesterday, 12:48 PM
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wide cord

good morning Builder
nice birds very nice.
For flying wings most of mine are wide cord to the newest being very wide cord. the most recent is a 77.5" span with a root of 22.75" and tips at 14.25" with 2deg. of forward sweep on the l.e.
The wide cord seams to smooth out the pitch and allows the wing to slow down to take advantage of small thermals + the extra area allows for lower loading. The ability to run out of sink with less loss of altitude is an unexpected beniefitt .
Another thing i am finding is that the lower loading means we can use a lower camber section that's thinner, for lower drag. park fliers like the nutt ball, or pizza box flyers are a riot to fly i think its due to low wing loading and plenty of power.
have a great day
nic
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