Airfoil Advice for a Freewing model

[lostrider]

Im going to build my first freewing with a GWS B geared 300 size motor to test&see what i can get with that airframe: Freewing Scorpion from scratch

Wing span will be ~120 cm, with the 400-550 gram of total flying weight.
Foam is the main component for the all body and wings, with some balsa & rods.

I need airfoil advices for a Freewing Scorpion like model,
Also i dont have any plan but just info from some pdf&photos, if anyone has much more information about the scorpion, i'll be happy to see.

Im a real fan of the planes which have real low stall speed characteristics like that. Some people loves the speed and acrobatics. I love the perfect landings-take off's and stability.





Also what if i choose an under chambered wing profile with this type of plane?
Which is works and best for freewing? flat bottom, symmetric or under-chambered,
I feel like i need to go with symmetric airfoil but i have a medium under-chambered ready wing, and if its possible to use it with the freewing, i'll go with it.
But as i know, under chambered wing profiles doesnt have a stable airflow at bottom,
So it will create a bad effect on the freewing thing.
Is that correct?

And thanks to the designer of scorpion for a thing like that.
Freewing is a real nice thing, besides it looks like State of art as a plane.

[BMatthews]

Because the freewing is free floating I'm pretty sure it needs to use an airfoil that is self stabilizing. That means anything with reflex such as used on plank style (non swept) flying wings.

Check out the MH110 for one option.

[lostrider]

thanks, Great
MH110
http://www.mh-aerotools.de/airfoils/mh110koo.htm

Besides it says MH102 for root sections of windmills,

http://www.mh-aerotools.de/airfoils/mh102koo.htm


its (MH 102 ... 110) for entire windmill blade,

MH110 looks good; like the wings of birds;

but i feel i need a little thick airfoil

(because with the variable AOA, i dont want a airfoil which will move up and down too much with of all little turbulances and gusts),(Also i dont want to fill the wings with carbon rods, so i need a thick foam wing profile)
so whats about MH 104? or MH102?


MH 104 http://www.mh-aerotools.de/airfoils/mh104koo.htm
MH 102 http://www.mh-aerotools.de/airfoils/mh102koo.htm

and its about windmill airfoils
http://www.mh-aerotools.de/airfoils/windmill.htm


And it says about this type of blades will stall at high speeds
(maybe it isnt related to airfoil, maybe they are talking about the entire blade design, but i want to put as a note.

--
To avoid destruction of the windmill due to over speed caused by high wind speeds, it was decided to direct the aerodynamic layout towards a stall regulated machine. (such a windmill has no variable pitch blades to control the mill at higher wind speeds; instead, the airfoils are designed to stall sharply when the operating limits are exceeded, thus limiting the power output).
--

So i guess i'll make something like MH104, with a little flat bottom (from middle of the airfoil - to the ailerons)
?

[lostrider]

besides this stall means not a stall like low speed, just the loose of some lift.
well its not hard to see the elevon sides of this airfoil is little up, so its how it does the balance thing,

also with a thick reflex shape like MH104, it will nicely meet with different AOA, is that correct?

so i can make it with the full span elevons? like in scorpion?

here an image from Freewing

[BMatthews]

Find another way. Airfoils over 12% start to get rather draggy at model airspeeds and by the time you're up around 15% you're pretty much at the limit for models.

[lostrider]

Thanks for that. so MH110 is the only option with thickness as %10.
so if my wing root span is 16 cm, thickness must be 1.6 cm at the roots...
i will need carbon rods...

[BMatthews]

Either carbon for caps or if you were to skin the foam with water based polyurethane and something like newsprint you can double and triple layer the max thickness point to form a pretty good spar equivalent. I did some control line combat models years ago and it worked fantastic.

You'd need to use something to help support the tube with bearings in it anyhow. Just a slip fit of a rod in a tube will be too much friction. To work well you need the hinge to be really free. Almost any sticktion at all and it'll be like you've got ailerons on all the time and the direction is constantly wandering around.

[lostrider]

i love the polyurethane, and yes i can try that. newsprint. very nice :D

also its lighter then epoxy so why not.
and i will cut the end of airfoil, about 5 cm width and i will replace with balsa for aileron.
Now it looks like it will be ~25 dm2 wing area with my calculations, after the balsa ailerons.
50 cm wingspan per one left and right, 21 cm wing root span, 18 cm wing tip span (before 8 cm of tips) and 25 cm mainframe span.
so foam core thickness is ~21 mm & ~2 mm skin

i'll try to keep the skin thing below 50 gr with some light paper

[lostrider]

You'd need to use something to help support the tube with bearings in it anyhow. Just a slip fit of a rod in a tube will be too much friction. To work well you need the hinge to be really free. Almost any sticktion at all and it'll be like you've got ailerons on all the time and the direction is constantly wandering around.

yes im looking for some plastic bearings, or i'll make my own bearings to avoid extra weight.

[lostrider]

and a light tube for ailerons, because they will be real wide. something like that:

[lostrider]

whats about V-tail?
theres some scorpion models with V-tail but i dont know if its have a disadvantage on freewing.

(with v tail i'll get less drag&little less weight, but i'll loose some tail authority, but i really dont want a complicated tail, so i can easily repair or replace the tail after damages, and its more safely.)

i dont need a rudder and elevator so its an option.

--
Well now im reading their history again, and they have a V-tail prototype at 1994, but i cant see any v tail in newer models, in '97,'98, and 1999.
I'll give a try anyhow.

[lostrider]

http://www.aerodesign.de/english/profile/profile_s.htm#sipkill

[BMatthews]

Even plastic bearings may have too much sticktion. But I'd be happy to be proven wrong. You may need a ball shell bearing at the root and perhaps a reduced pin to a regular ball bearing at the end of the joiner rod or tube.

As for the rest of those oddball V's, struts and sun worshiping propeller spinners you're on your own....

Good luck on what promises to be a unique project.

[lostrider]

Thanks!
Im going with a larger chord size.
21 cm root chord
16.5 cm tip chord
48 cm span for this part.


I've decided to work with sipkill1710b airfoil.
Im using 9v 1Ah adapter with 60 cm wire.
I want to cut very slow because of the thin airfoil, also i've started to cut from weak places.
Later i'll replace the elevon sides with balsa.
Here after a little sanding.

[feihu]

lostrider:
I just came across your thread and wish you success in your endevour. I've read the posts in this thread but I have not been able to download the internet address in your post # 12. Nor have I been able to find what a Scorpion looks like.
I investigated the free wing concept about 25 years ago as it pertained to full size general aviation airplanes for the purpose of gust alleviation which is the greatest potential of the free wing.
So regarding your project, the airfoil is the least of the problems you are faced with, so your wing as shown in your post # 14 may be OK, and I would suggest some washout.
It is important that the wing pivot location be at a point that provides sufficient static margin (perhaps 15-20%mac) and be Friction Free; and the control surface for elevons be of the correct size and deflections for aoa and roll control. You will need a fifth radio channel for fuselage trim control.
Good luck,
feihu

[Texas Buzzard]

I've been building and designing powered model aircraft since 1951. I have read almost every issue of RCM and MA ( from AMA ). In the early 70s I built an experimental A/C - the Pietenpol Aircamper w/ 65 H.S. Lycoming engine.
I have not seen that term until I clicked onto this site. It's new to me.

What is a "FREE WING"? In simple language what are its strong points?

[feihu]

Texas Buzzard:

The attachments are excerpts form papers that were presented at an engineering symposium back in 1978. These will give you a general idea of what the free wing potential benefits are. The figure 1 referred to in the text is similar that shown in the post #4 of this thread. An RC version of a free wing using a free canard to control the AOA of the wing was successfully flown by NASA back in 1977.

Hope this helps

feihu

[Texas Buzzard]

Feihu, Thank You so very much - this paper is excellent!

I was ignorant of the term FREE WING.

It was thoughtful of you to take the time to present this paper.

Now my mind is over loaded - - - let's see, just how many proposed projects do I have in front of me? I had worked some with two RC Canards copied from published plans. They were .25 glow sized ships. The main thing I was interested in was the fact that they tend not to stall but just start to "hunt" as the stick is pulled back at lower power.

But a successful non - stalling scratch built was Barnaby Wanfain's odd looking FMX-4 or the "FACETMOBILE". When you give some up and reduce throttle it just rocks a Little and "hunts in the vertical axis - a bit like a falling leaf. Hit power and away she goes - mine has a 30" width and 32" length. it was a balsa/ply build w/ a strong AXI motor.