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Delt Wing - Looking for some advise....

jd7792

Senior Member
#1
Hi guy's,

Still waiting on hardware and electronics to finish this project, but in the mean time I thought I would seek some advise about my wings profile. As you can see in the two photos below the shape is basicall the same as most wings. It has a wing span of 30" a wing depth of 9.5" and a centre length from nose to motor mount of 11".

I notice that a lot of people use pink foam to make their KF Air Foil, but I have been limited with the foam that I have available. So I decided to use two extra pieces of depron to built the density up. While I was playing with the first part of the Air Foil I found a 3rd piece of foam that was thinner than the original foil. I cleaned it up and came up with the idea that is in the attached photo's. As it is I have a two step AF Air Foil, but I am not sure how that will work so now I need some advise before I glue everything together.

So my question is, "Will a two step AF Air Foil work?" If so can anyone tell me how it will effect the overall wing?

Please let me know what you think...:confused:

IMG_1445.JPG IMG_1446.JPG
 
#2
Here is the basic sheet on KF characteristics. Most people use Kfm2 or 4 on their flying wings - 2 because it gives it a floaty feel and 4 because it is locked in for speed with good glide. 3 is mostly for gliders as attached because it generates good lift, but you do not need this for a flying wing. You can try it as an experiment? I would stick with what you got at the mo because you can always add more steps later.

kfm-family-descriptions3.jpg


Jim
 

jd7792

Senior Member
#3
Thanks Jim,
I have actually seen something like you posted before, but 1) I couldn't find it and 2) I don't think it had the third foil on it. I really appreciate your help. I am hopeful that someone, somewhere has done something similar and can give me an idea whether to keep going or change it before I make it permanent.

Thanks again

JD
 

earthsciteach

Moderator
Moderator
#5
Also, consider covering the entire wing with either poster laminate or something like econokote. It adds a tremendous amount of strenth!

Looks good! The wing sweep looks pretty good for a decent cg.
 

teflyer

Full Circle
#7
If I may ask, what percentage of the wing chord did you put the steps?
When you fly it, I would suggest putting a little reflex just in case.
 

earthsciteach

Moderator
Moderator
#10
Yep. I find a good ol' Clark Y works just fine with the elevons trimmed up! Now, the one I'm working on at this very moment will have reflex built into the airfoil profile. Just because.
 

jd7792

Senior Member
#11
If I may ask, what percentage of the wing chord did you put the steps?
When you fly it, I would suggest putting a little reflex just in case.
I started off with the full measurement from leading edge to the back edge of the elevon (23cm) the first step at 1/2 of that (11.5) however the second step is slightly different. The fact of the matter was one of the pieces I had wasn't exactly parallel, so by the time I finished luck had it that it was 1/2 of the first step at the nose but only 5cm wide at the outer edge. At this point you have to remember that the foam sheets are $15 each (Thats the best I can get!) So I wanted to use every piece I could.
IMG_1447.JPG

Can you also explain what you mean by "Putting a little reflex"? This is the first play with Delta Wings so I have a lot to learn!

Also remember that at this stage the wing hasn't been sanded into shape along the leading edge and I haven't glued anything in place yet. I am still waiting on some parts so I can't go too much further until they arrive.
 
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jd7792

Senior Member
#12
Search for articles and posts from Schraut5 he has built several similar type wings
It is actually Schraut5 that has been my insperation on this build. I started off with his basic outline measurements. I was very impressed with his Wing that he posted the build to. Once I finish this build, and hopefully it is successful, I will post a build log of each step. I'll be sure to credit Schraut5 when I do it.
 

earthsciteach

Moderator
Moderator
#13
Reflex, um, in my own words, means that the trailing edge of the airfoil bends slightly up. This is done to overcome the natural pitching down moment inherent to the shape of an asymmetrical airfoil. In conventional aircraft, this pitching moment is overcome by the horizontal tail surface. Some planes utilize a canard to do the same instead of a tail.

Here's a link with a couple of diagrams showing the difference between an airfoil on a plane with tail surface or canard and that of an airfoil for a flying wing.
http://www.mh-aerotools.de/airfoils/flywing1.htm

It is my understanding, based on teflyer's experience that the KF-3 (what you have) has a pretty forceful nose down moment. You can easily overcome this by setting the "neutral" position of the elevons slightly up. Let me know if I didn't explain it clear enough. Simple idea, hard to describe in words!
 

colorex

Rotor Riot!
Mentor
#16
Down elevator surfaces go down.
Up elevator surfaces go up.

Add uptrim to add more reflex.
You're right, I'm wrong - but I'll eat my shame with an excuse:

"Oh, sorry - should have been more specific. Down elevator stick surfaces go up - Up elevator stick​ surfaces go down."
 

jd7792

Senior Member
#17
Reflex, um, in my own words, means that the trailing edge of the airfoil bends slightly up. This is done to overcome the natural pitching down moment inherent to the shape of an asymmetrical airfoil. In conventional aircraft, this pitching moment is overcome by the horizontal tail surface. Some planes utilize a canard to do the same instead of a tail.

Here's a link with a couple of diagrams showing the difference between an airfoil on a plane with tail surface or canard and that of an airfoil for a flying wing.
http://www.mh-aerotools.de/airfoils/flywing1.htm

It is my understanding, based on teflyer's experience that the KF-3 (what you have) has a pretty forceful nose down moment. You can easily overcome this by setting the "neutral" position of the elevons slightly up. Let me know if I didn't explain it clear enough. Simple idea, hard to describe in words!
Thanks for your help. The attached page was pretty hard going but I understand your explanation. My next question will obviously be "How do I work out the CG, taking into consideration the effect of the airfoil and the required reflex I will have to add?" or "Does this have an effect on the CG at all?"

Do you have an opinion of where the CG should be? The wingspan is 30"
 

earthsciteach

Moderator
Moderator
#18
You can use this to find the cg: http://fwcg.3dzone.dk/

Yes, reflex will have some impact on cg location. But, don't worry about it, because you can't account for it when you are balancing the plane (unless you have a wind tunnel!). I guess you could, but it would require some computational fluid dynamics to determine the force exerted by the reflex while in flight. :p

Use the cg locator in the link with the cg set to 15% or 20%. This should get you in the air. You can tweak the cg by moving the battery slightly forward or back from there. Keep in mind, at that point you will have 2 variables you can mess with, 1) CG location by moving components and 2) reflex by trimming the elevon neutral position. The pain in the butt factor increases exponentially with the number of variables. So, 2 variables = 4 x the pain in the butt factor!

Here's my take on that:
1) arrange components so that the wing's cg is where the program says it should be.
2) Test flight. If you have to hold 'up' elevon to keep it in the air, bring it in and set the elevon position up by adjusting the clevis on the control rod.
3) If it flies tail heavy, move the cg forward and repeat steps 1 thru 3.

Hope that helps!
 

PaulT

New member
Mentor
#19
On the subject of cog and using the calculator as per the teach, my Tek Sumo that I fly is a about 40%.
Am I measuring correctly?
Calculator at 25% says 5.5 inches when in fact mine is about 8.5 (40%)
Am I wrong or is there some magical pixie dust on the Tek. (It flies awesome, by the way.)
 

earthsciteach

Moderator
Moderator
#20
Oh - and the 15-25% given by the program is % of Mean Aerodynamic Chord, not from LE.

If you do the calcs for the default wing numbers on the program, it places the cg at 20% of MAC. This equates to about 60% of Root Chord.
 
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