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Old Dec 11, 2011, 12:11 PM
Grumpy old git.. Who me?
JetPlaneFlyer's Avatar
Aberdeen
Joined Mar 2006
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I just posted my KFm3 vs. Drela AG12/13/14 DLG flight test results: http://www.rcgroups.com/forums/showt...1542598&page=2

Thoughts / suggestions?

Steve
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Old Jan 01, 2012, 10:45 PM
Microbiology at it's best.
beerbrewer's Avatar
Waverly, Nebr.
Joined Apr 2009
250 Posts
Gathering test equipment

I am new these this foam and electric things and have been fastenated with the Geobat concept from it's very beginning. I want to build one with a KFm? and it's unique shape really makes a person wonder: How do you turn parallel straight lines into a cresent and keep that profile?

I started reading this thread for educational purposes and it tells me I have tons yet to learn.

What if I have axcess to is a smaller wind tunnel that is just sitting idle. The test chamber is approx. an 18" cube and could fit wing sections of that length. I will have to ask, but it is possible. Any modifications to it would cost dearly so a person would have to work with what they got. It has been used for modeling of cooling of food products.

Does anyone have axcess to a 3D printer to make perfect and repeatable sections?

What about monitoring and camera equipment near SE Nebr?

Equipment would have to be designed and built specifically for this tunnel. Smoke delivery by what means? It would have to all be custom built.

I am positive that the "yes" person is going to ask "What is in it for me and what will it cost?"

There has got to be an angle to do a good study. It does not matter if it is grant funded or just a bunch of hobbiests getting together to have fun. I would need to present a proposal for this to work. Who would be doing what and who is paying for it?

I have a wind tunnel, pretty much nothing else.
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Old Jan 05, 2012, 08:41 PM
In Rc for a LONG TIME FFAA#1
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Canada, ON, Ottawa
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I have asked some of my robotics pals that have a 3d printer and hope to get some sections of the kfm foils made and will see about them into a water tunnel / wind tunnel
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Old Jan 07, 2012, 06:13 PM
In Rc for a LONG TIME FFAA#1
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if some one could do some profiles of the following kfm's a 2 3 4 with a 10 in cord I will be able to get some made and get them to anyone that has a wind / water tunnel for testing

Jim
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Old Jan 08, 2012, 07:58 AM
Grumpy old git.. Who me?
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Aberdeen
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Jim / Beerbrewer

One of the problems with testing KFm airfoils (and Dick Kline's original KF patent come to that) is that there are no coordinates defined for the various KF/KFm airfoil types. For instance a 'KFm 1' is just wing that has a step (of indeterminate size) 'somewhere' on the bottom surface, pretty much everything else is at the total discretion of the builder. Similar story for all the KFm airfoils, the only thing that's defined is the number of steps and if they are placed on the top or bottom, all else is subject to infinite variation according to personal preferences, skill levels and material/method of construction.

What this means in practise is whatever shape you use, the results of any testing will be discredited/ignored/ridiculed by some because the airfoil doesnt agree with what 'they' think that particular KFm should look like (ask me how I know)

I've come to the conclusion that it's a futile (and quite frustrating) exercise to do any testing on 'KFm' airfoil until there is a consensus on the precise coordinates for the shape of each type. It's crazy to even try when you think about it.. Would you go and test a 'conventional' airfoil using only the description that 'it has a curved bit on top and an almost flat bit on the bottom'? Until then I think it's best to forget scientific testing and just accept that KFm airfoils are simple, cheap and quick to build and perform perfectly adequately for sports/fun RC models.

Steve
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Old Jan 08, 2012, 11:01 AM
In Rc for a LONG TIME FFAA#1
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jpf , I just want to have a generic set of foils such as the ones from tony's b.b. And the kfm 4 so I will get them made if I can and then we can see what's happening

Jim
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Old Jan 08, 2012, 11:30 AM
Jack
USA, ME, Ellsworth
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Quote:
Originally Posted by laserman View Post
jpf , I just want to have a generic set of foils such as the ones from tony's b.b. And the kfm 4 so I will get them made if I can and then we can see what's happening

Jim
So you need them to be about 10" in chord? And how much length or span do you want?

I sure we could work up some samples from the more commonly used materials and for the more commonly built foils (using Dow FFF for example). Those would seem to offer a fairly consistent and widely applicable (for a starting point at least) model.

I'll even volunteer myself to provide some to you at no expense to you...

Jack
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Old Jan 08, 2012, 01:05 PM
Grumpy old git.. Who me?
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Aberdeen
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Jim,

If all you need is a image that you can produce a 3D model from to feed into your 3D printer then the basic 'November/07' line drawings of the KFm1 to KFm4 shown in post #2 of this very thread are as good as anything: http://www.rcgroups.com/forums/showp...90&postcount=2

Of course many builders don't use actually use the folded construction shown on those images. Laminated foam sheet construction seems more common and that tends to give a different shape to the LE. As I said in the last post, there are countless variations on the 'KFm theme' even within each KFm type designation, but the ones in post #2 are as good as any.

IMHO the 'curved' versions shown in the same post aren't really representative of what's being built and flown.

Steve
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Old Jan 09, 2012, 01:04 PM
RC beginner
New York
Joined Oct 2008
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ill bet it turns out early separation is responsible for the characteristic slow glide, friendly stall, and unfortunately increased drag too. for wind tunnel flow tests its easy to make samples from copy paper webs glues to profiles cut from postscript printouts made by programs like plotfoil. takes minutes instead of hours.
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Old Jan 09, 2012, 01:07 PM
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I don't know how early the separation is, but the videos I took of the KF test plane with tufts did indeed show the reversed flow characteristic of separation at high angles of attack.

Roger
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Old Jan 09, 2012, 01:18 PM
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i cant do youtube but would very much like to see that. i dont suppose you could capure and post a pic or two sometime?
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Old Jan 09, 2012, 01:28 PM
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Unfortunatley, I have to agree with Steve. There are as many variations of KF airfoil as there are modelers making them. I am among those who prefer to have a true airfoil shape to my foam wings. Many choose to glue the sheets of foam together as slabs or wedges, and just round the leading edge.

I found that the KF worked for me on the many FFF aircraft I built over the years. All had one thing in common: they were relatively low speed high drag designs to begin with. The higher drag of the KF airfoil did not have much impact. I do still claim that the KF airfoils as I constructed them, did provide much better flying characteristics than a flat plate or under cambered wing would. Would they have flown better with the same airfoil without the step or with different steps? That is what I was attempting to learn with the test plane. Unfortunately it is no more. A low level inverted pass combined with lack of practice destroyed the test plane fuselage, and rendered the wing useful only for a Frankenplane. The KF test plane MK2 is one of this winters projects.

My recommendation for airfoils is to try the MH32 with variations on the step. Also try flat plates with steps and a radiused leading edge. The two airfoils would give a "best" and worst case airfoil. You might also try wedge KF airfoils to see what happens.

Roger
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Old Jan 10, 2012, 07:31 AM
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Joined Mar 2011
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hello all,

if i may i would like to say that everyone agrees the KF seems to be great for flat wings. my interest is WIG(Wing In Ground effect) which needs to be flat bottomed, very stable, able to resist wind gusts and work well for low aspect ratio type flying wing.

has anyone on this forum with a low AR delta tried taking off and see if the wing remains IGE(In Ground Effect) until they actually pull it up into a climb?

some deltas may actually rotate and then level off at between 1/2 and 1 wingspan hands off.

cheers

armour.
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Old Jan 10, 2012, 11:18 AM
United States, FL, Hollywood
Joined Sep 2003
285 Posts
Would you guys please recommend me an airfoil for a 96" motor glider.
Thanks
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Old Jan 10, 2012, 12:14 PM
Jack
USA, ME, Ellsworth
Joined May 2008
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The KFm9 (three steps on top, flat bottom) worked good for me on the Big Blu 96" glider:

http://www.rcgroups.com/forums/showthread.php?t=1470211

Jack
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