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Old Sep 28, 2009, 10:01 PM
Crash Master
Gene Bond's Avatar
Indianapolis, IN
Joined Sep 2001
16,632 Posts
Agreed, Jack. That's basically what I've done. Although, I'm working on one now that I somehow screwed up the filler, so I had to cut a custom spar on the band saw
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Old Sep 28, 2009, 10:27 PM
Geaux Saints
Hopalong X's Avatar
Grafton, Il
Joined Nov 2007
1,913 Posts
Quote:
Originally Posted by ookid
There is no place that I can see on the KF step calculator to enter sweep. The calculated MAC stays the same whether I enter the sweep as positive or negative. Is there something that I am missing? I don't want to brag but I tend to do well in math and this has me stumped.
Sweep isn't part of it.
It is supposed to work straight or swept wing
I have a different calculator than that let me run your numbers thru it.

Mike

You posted this but I'm not sure what it is with the run together numbers?

Base foam thickness- .335"8.58.5


This is the software below.

At the bottom left of page after it is open Click "English Example" if not already done, The instructions are under the Input and Output boxes.
When your ready to try using it look by "English Example" in bottom left corner click "English" or "Metric" according to what you want to use.

Enter your info into input and output comes up.
Use the major chord.
If you wish to taper the thickness of the step enter the minor chord seperately and you will have your maximum thickness for the center of the plane and then the wing tip with the minor chord.

PS- This one actually works it is the updated version.
If you still have problems I need the foam thickness. I'm not sure of your posting.

I forgot something, it has been a while since I used this.
If you still come up with negative numbers then you don't need a spacer between the steps.
Your chord length with the thickness of foam you are using means you have plenty of step already just with 2 pieces of foam stacked. So it shows negative numbers.

Steve/ Cybernaught builds all his planes with thick foam with no spacer and would show negative numbers on ALL his builds.
Some of his are two pieces of 1/2" stacked which is more than optimal of a step per the software or the 9-11% we usually try to maintain.
That is the only foam he has available.... but all his planes fly.
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Last edited by Hopalong X; Sep 29, 2009 at 07:35 AM.
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Old Sep 29, 2009, 01:00 AM
just Some Useless Geek
Chicagoland
Joined Oct 2008
2,543 Posts
Quote:
Originally Posted by jackerbes
OK, I give up, I can't find a build called an "XYZ" here in the forum or on the net.
Yeeeeah. Soory aboot that, eh? My fault entirely. I thought that I had posted pics and build info on the XYZ prototype I built last year, but apparently not.

The XYZ is supposed to be a family of park jets based on a construction method I came up with. The idea is to build a cruciform airframe in an X shape and enclose the airframe space with flat panels across the top and bottom and joining the wings to the frame panel both above and below the wing. It's a little hard to describe this adequately, and I never transferred my hand drawings to machine readable form. I have a pile of pictures of the original XYZ both under construction and in flyable form, but those images are apparently on my currently out-of-service Win2K Server machine. D'oh!

Anyway, the XYZ was a very fast park jet that didn't have enough control authority and a good pair of thumbs behind it. I crashed it a few too many times, the last one being nearly straight into the dirt at about 60-70 MPH. Oh, well. Had I only backed the throttle off a second earlier...
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Old Sep 29, 2009, 02:45 AM
Onward through the fog.
Cybernaught's Avatar
Bohol Philippines
Joined Aug 2008
1,566 Posts
A funny thing happened on the way to the flying field...

Well I have good weather for flying but....

See pictures!

Steve.
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Old Sep 29, 2009, 07:44 AM
Geaux Saints
Hopalong X's Avatar
Grafton, Il
Joined Nov 2007
1,913 Posts
It just needs a little bailing wire and Gorilla Glue that is all!

Better have them check the other side it might be ready to go also.

Mike
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Old Sep 29, 2009, 08:04 AM
Geaux Saints
Hopalong X's Avatar
Grafton, Il
Joined Nov 2007
1,913 Posts
ookid

Here is what I came up with.
.1 inch spacer for 9%.
.01 inch spacer for 8%.
Neg number for 7%.

So you don't need a spacer.
Just use 2 layers of foam with the 8.5" chord.

Mike
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Last edited by Hopalong X; Sep 29, 2009 at 08:38 AM.
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Old Sep 29, 2009, 09:09 AM
"Watch out for...CRUNCH!!
Modarius's Avatar
United States, UT, Provo
Joined Jul 2008
218 Posts
OK I edited my post, it should be .335" thick. Thanks for doing the calculations, I figured out what was wrong. The total step thickness that it was putting out was positive but only the spacer was negative. Thanks all for your help Its a bit too early to be waking up for me...
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Last edited by Modarius; Sep 29, 2009 at 09:20 AM.
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Old Oct 01, 2009, 10:25 PM
Geaux Saints
Hopalong X's Avatar
Grafton, Il
Joined Nov 2007
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Where is everybody?
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Old Oct 01, 2009, 10:40 PM
Registered User
j2m2t2's Avatar
AZ
Joined Feb 2007
542 Posts
Is there a difference between the folded leading edge and a KF-m step? Does the spacer make the foil? The pic below shows fold and KF, do they perform differently?
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Old Oct 02, 2009, 07:20 AM
Crash Master
Gene Bond's Avatar
Indianapolis, IN
Joined Sep 2001
16,632 Posts
Yes, they are different for a couple of reasons:

- the filled in step ruins the bubble area on the top foil. It will act more like a flat-plate.

- the additional thickness (to a point) of the step helps build a bigger bubble, which helps maintain lift at higher AoA's.
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Old Oct 02, 2009, 07:53 AM
Jack
USA, ME, Ellsworth
Joined May 2008
17,219 Posts
And I think having the 1/4" square spar in between the layers and bonded to both layers by the glue contributes a lot to stiffness. And, like Gene says, it is a better flyer in most cases.

There is a dubious building technique shown in that lower figure in that the spar is pushed forward up under the KFm strip and the step is rebated a little. I don't know that that is a good idea. And it would leave that unsupported part of the strip as fragile and vulnerable to being broken in handling.

I built the Zagnutz 48" flying wing as per the plans and it had a wing much like the lower figure. The 1/4" square was brought back even with the edge of the foam and both were at the 40% line.

That was my introduction to flying wings and it was one of the sweetest flying things. I was thrilled when I maidened it. I was test gliding it for the CG, increased the power a little more than intended, and it slowly and gracefully simply flew straight away from me at eye level.

The only issue I had with the Zagnutz wing was that the combination of the butt joint with back sweep in the spar, combined with the 48" span, worked the joint pretty hard. And the spar being on the bottom put the joint under a tension strain in flight so the wing got a litte over stressed and folded on the center line.

But I evolved it to a KFm4 and stiffened up the center section and my present Zagnutz has been flown regularly for several months now.

Jack
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Old Oct 02, 2009, 08:03 AM
Jack
USA, ME, Ellsworth
Joined May 2008
17,219 Posts
I've added another figure to post #2 that shows the taping and folding instructions for typical KFm2 and KFm3 wings, that also shows details that can be used as far as the arrangement of the spars and KFm strips.

And I also added a link to a brief history of the Kline-Fogelman airfoil there. Those are required reading for all true KF aficianados.

http://www.rcgroups.com/forums/showp...48&postcount=2

Jack
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Old Oct 02, 2009, 10:28 AM
Registered User
j2m2t2's Avatar
AZ
Joined Feb 2007
542 Posts
Thanks guys. Ive used the KF per others plans and it does add plenty of stiffness but Im struggling with it on a glider design.

According to the KF calc my 9mm epp can be doubled up to make the step without a spar. However the glider has a bad tendency to float down instead of glide. Kind of strange actually it stays horizontal and floats down at a 45.

This is ookid post with a response, he is building same glider:

Here is what I came up with.
.1 inch spacer for 9%.
.01 inch spacer for 8%.
Neg number for 7%.

So you don't need a spacer.
Just use 2 layers of foam with the 8.5" chord.

Mike
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Old Oct 02, 2009, 10:53 AM
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Ashford. Kent. England
Joined Feb 2005
7,022 Posts
I am not sure that using that thickness of foam will produce a good glider wing... My best results have come from 3mm and 6mm depron with KFm or 3 sections.. A 9mm main layer with another 9mm top step layer doesnt sound or feel right..
Steve gets away with 12mm thick layers on his powered KFm4 builds, but I am not sure if they glide well (compared to a normal glider) or need some power on for their landings.
I can say that using 6mm and just two layers produces a good sloper wing.. see the Revert...but overall that wing is only 12mm thick.
My KFm4 wing glides well enough to slope, 6mm main layer with 3mm top and bottom layers on 1/4 thick balsa spars..but I wouldnt equate it to a proper thermal type glider
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Old Oct 02, 2009, 11:03 AM
gpw
“There’s no place like Foam”
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United States, LA, New Orleans
Joined Jul 2002
24,200 Posts
Having flown many gliders over the years , we believe that long thin wings are the best and the airfoil should be set up for a reasonable glide speed , which seems to produce a shallower sink rate ... gliders seem to have a "cruise" speed which produces the best glide ... any slower and it just drops out of the sky... Done that a LOT!!! Bad when you can't make 3 min . off the winch !!! Thinking the more complicated KFM3 would be Super to try out on a glider wing , no ailerons , just RET... with FFF we could bend in nice elliptical dihedral too .. Just haven't got a round tuit !!!
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