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Nov 01, 2018, 05:52 PM
http://bit.ly/2zm6gK7
Discussion

KF Airfoils - Understanding the Basics First


I have this posted over in 'Modelling Science' but since I have used these airfoils on my foamie scratchbuilds, I figured it belongs over here too. Hopefully you can find this beneficial (:

I recently had a renewed interest in KF airfoils, and plan to do ALOT of testing (CFD and real-world, and maybe some wind-tunnel) to optimize these airfoils for some planes I want to build. But before we can answer all of the questions like "Is it better than a NACAxxxx airfoil" or "What wing loading is it best for" etc etc., we need to understand the basics of what makes these airfoils so special.

KF Airfoils 1.0 - Introduction and Preliminary CFD Research (22 min 15 sec)



Now. What are YOUR thoughts on these airfoils? I have had great experiences years ago when I was building more, and I look forward to doing that again very soon.

What is something you wonder about in relation to KF airfoils and their performance?
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Nov 01, 2018, 07:15 PM
Build straight - Fly twisty
Whiskers's Avatar
Actually you talked way too much.
A Clark-Y airfoil is only flat on the bottom aft of the 25% line.
A genetic totally flat bottomed airfoil is NOT a Clark-Y, it is more like the Aquila airfoil: https://www.google.com.au/search?q=a...w=1366&bih=695
This airfoil is noted for having an inferior performance relative to the Clark-Y, and the Clark-Y really needs to be thinned to perform well at model sizes.
The KFm airfoil you tested bears little resemblance to any that I have seen.
The very sharp leading edge and that huge step are not usually employed.
It should be noted that the KFm profiles shown in the listing of the various types are also very different to those that are actually built by the people who employ them.
It should also be noted that there is no category of model airplane competition where KFm airfoils are employed, and absolutely no category where a KFm must be used in order to be competitive.
Last edited by Whiskers; Nov 01, 2018 at 09:56 PM. Reason: Fixed grammatical error
Nov 01, 2018, 09:14 PM
flyin' fool
goldguy's Avatar
Most all you need to know has already been discussed at the beginning of these threads, some including input from the inventor himself.
Nov 01, 2018, 09:32 PM
Registered User
juzchillin's Avatar
whisk and gold are both right.
for one, way too long winded , 2 its all been gone over before

don't remember who said it but the best explanation i can remember went something like this

You put the lime in the coconut , ya mix em both together
oh and i think he was standing in a hot tub at the time !
Nov 02, 2018, 01:16 AM
http://bit.ly/2zm6gK7
Quote:
Originally Posted by Whiskers
Actually you talked way too much.
A Clark-Y airfoil is only flat on the bottom aft of the 25% line.
A genetic totally flat bottomed airfoil is NOT a Clark-Y, it is more like the Aquila airfoil: https://www.google.com.au/search?q=a...w=1366&bih=695
This airfoil is noted for having an inferior performance relative to the Clark-Y, and the Clark-Y really needs to be thinned to perform well at model sizes.
The KFm airfoil you tested bears little resemblance to any that I have seen.
The very sharp leading edge and that huge step are not usually employed.
It should be noted that the KFm profiles shown in the listing of the various types are also very different to those that are actually built by the people who employ them.
It should also be noted that there is no category of model airplane competition where KFm airfoils are employed, and absolutely no category where a KFm must be used in order to be competitive.
Like I said, I modeled the Kf2 airfoil how I build them. When you fold foam board it doesn't look like the drawings on Wikipedia.

Sorry you thought i talked too much. Aerodynamics is not a trivial topic although I do try to condense as much as possible. Besides I really get going when I'm interested in something
Nov 02, 2018, 01:17 AM
http://bit.ly/2zm6gK7
Quote:
Originally Posted by juzchillin
whisk and gold are both right.
for one, way too long winded , 2 its all been gone over before

don't remember who said it but the best explanation i can remember went something like this

You put the lime in the coconut , ya mix em both together
oh and i think he was standing in a hot tub at the time !
Because it's been done before, no further research or discussion should go into it?

This forum would be pretty stagnant if that were the case...
Nov 02, 2018, 03:07 AM
flyin' fool
goldguy's Avatar
There are already two established ongoing threads on the subject of the KF airfoil here. So why not just post your input there? The active community has already been posting ideas, research, findings and discussion for many year, all endorsed by 'Dickeroo', the inventor of the airfoil.

Besides that, there's hundreds of successful design posted for comparing ideas, building techniques and real world results.

Wikipedia knows diddly on how it's used successfully on model aircraft.
Nov 02, 2018, 03:19 AM
Build straight - Fly twisty
Whiskers's Avatar
Are you going to stop calling an Aquila airfoil a Clark-Y.
As an aerodynamicist you should know better, especially as you are setting out to inform people.
It is wrong to teach misinformation.

See what happens when you stir up a Grumpy Old Man?

Nov 02, 2018, 04:06 AM
flyin' fool
goldguy's Avatar
I always thought that about you. It takes one to know one you know.

This whole scenario is like this ……………..

A bunch of old dudes that have belonged to the same model airplane club for many years, are all good friends and after flying sit around the coffee shop/pub BSn' about the KF airfoil. One of these guys is also the inventor, pioneer and champion of this unique idea. Many facts, graphs, charts, doodles, videos and endless theories have been laid out on the table during the thousands of chit chats about it. Everyone and anyone is invited to sit around the table and join in.

Nobody has raised their voice, been offended or gotten a back eye over it all.

Then...………..

This new guys comes along and wants to start the discussion all over again, when in fact he should be showing a bit of respect for those who came before him.
Last edited by goldguy; Nov 02, 2018 at 04:19 AM.
Nov 02, 2018, 04:34 AM
Wake up, feel pulse, be happy!
Piece's Avatar
I only watched the video until the part where you repeatedly said "vorticeee" instead of "vortex".

The RCG-edition story of the KF airfoil boils down to this: "It's simple to make, so we're going to paint the science as rosy as we can to make it seem like our best option."

In reality, the KF airfoil provides the mechanical strength benefits of a traditional wing cross section while staying almost as easy to build as a flat plate design. Aerodynamically, it's certainly better than a blocky rectangular cross section or a flat plate with dowel spars glued on bottom, but far inferior to specialized foils designed for model aircraft, and not even as good as foils designed for full-scale craft shrunk to model size.

So it's not exactly a scientific breakthrough, but it beautifully solves the problems of A) shaping 50 individual ribs and assembling them into a wing, and/or B) trying to structurally reinforce a single-thickness sheet of fanfold without adding immense drag and weight.

The messenger is bulletproof; fire when ready
Latest blog entry: Jeti ESC resto-mod
Nov 02, 2018, 01:29 PM
http://bit.ly/2zm6gK7
Quote:
There are already two established ongoing threads on the subject of the KF airfoil here. So why not just post your input there? The active community has already been posting ideas, research, findings and discussion for many year, all endorsed by 'Dickeroo', the inventor of the airfoil.
Yes you are right, and perhaps in the future I should share there. However, since this video is geared towards ‘beginners’, (as I said, its an INTRODUCTION), most beginners are NOT going to scroll through 2000 pages of technical talk.


Quote:
Are you going to stop calling an Aquila airfoil a Clark-Y.
Honestly you have a good point here. Even though most people (as you pointed out, incorrectly use) call fold-over, flat-bottomed foamboard wings a ‘Clark Y’ I will make sure to not make this mistake in the future. Thank you for pointing this out.


Quote:
This new guys comes along and wants to start the discussion all over again, when in fact he should be showing a bit of respect for those who came before him.
Seriously? By going over what is typically ‘common knowledge’ to more ‘advanced’ modelers, I am not respecting those who came before me? This one really gets me going so… I will say no more on the subject.


Quote:
I only watched the video until the part where you repeatedly said "vorticeee" instead of "vortex".
You’re right, that is not a word haha. There were times where two VORTICES would form in the step region, so I began blurring the two words together lol. Good catch; although I’d hope this wouldn’t be enough to disqualify the rest of the information in this video.

Quote:
The RCG-edition story of the KF airfoil boils down to this: "It's simple to make, so we're going to paint the science as rosy as we can to make it seem like our best option."
I have seen that for the last 6 years that I’ve been using these airfoils lol. Although, I feel like because of their ease of use, and because there is really still a lot of unknown variables here, they deserve some more study (especially with the rise of small UAS over the last decade and moving forward).


In summary, I am kind of disappointed. Not by the feedback, that is welcome. But more by the delivery; it’s stuff like this that makes me want to stay out of these forums (unless I have a question, which is met a lot more graciously than when I offer some piece of information myself).
I don’t want to waste anyone’s time with my own complaints so I won’t post any other responses like this, but do feel free to continue to add to the conversation if you feel so inclined. And I truly do appreciate the responses regardless!
Nov 02, 2018, 05:00 PM
Wake up, feel pulse, be happy!
Piece's Avatar
Lulz, I'm sure your information is good, or at least better than 75% of the garbage and pseudoscience that a beginner would have to wade through in the "technical" KF threads.

Except nobody really comes to Scratchbuilt Foamies for technical discussion. Maybe you can see why. If they do, they get a swift kick in the ribs for trying to overcomplicate things, or for exceeding the base knowledge of the local watchdogs. This thread's course is nothing unusual.
Latest blog entry: Jeti ESC resto-mod
Nov 02, 2018, 05:01 PM
Build straight - Fly twisty
Whiskers's Avatar
A robust discourse is an integral part of science. It's a mechanism to keep us all on track.
Long may it continue...
Nov 02, 2018, 09:47 PM
flyin' fool
goldguy's Avatar
I did say 'everyone and anyone' was welcomed to pipe in on the discussion. Starting a new thread on the same subject is what I was referring to in regards to 'consideration'. The information as it has been presented on the KF in those threads is both simplified for the beginner and technical for the advanced thinker too. Yes, even understanding the basics first from the inventor himself.…….https://www.rcgroups.com/forums/show...91&postcount=3

It's already been studied, picked at, probed, analyzed and dissected, and still continues. But then again, so has the Bernoulli effect and the jury is still out on that one too.

It's all there, even some input that's dead wrong. Although, having the strength in numbers, it's gets critiqued and corrected quickly.

No thread is ever too long, even for the beginner. Either use the search function or post a question, it's that simple.

Anyhoo, back to my latest KF build mixed with a little black magic ………………...
Last edited by goldguy; Nov 02, 2018 at 11:07 PM.
Nov 03, 2018, 10:38 AM
treefinder
springer's Avatar
Corsair, i have to admit i haven't watched your video yet, but allowing for the editing of other posters, think that if you are/can run studies of KFM wings the way we actually build them at size and speed we actually fly them that would be valuable. (And present your results, of course). While we "all" have our anecdotal, empirical data that we rely on for our opinions of the value of KFM it would be nice to see data from the "official" math side of it all. That has been the missing piece of the puzzle to me. Even the work by maguro et al used an implementation that no one i know actually uses (step in mh32 airfoil). If you have the time and access to the cfd tools, it would provide some interesting info and you could format it in a way to guide noobs into best imementations. As others have said most folk use kfm because it is dead easy to build, and flys surprisingly well, perhaps even better than conventional, in the characteristics that help beginner flyers stay aloft (not neccessarily in efficiency).


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