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Old Aug 25, 2010, 09:57 PM
just Some Useless Geek
Chicagoland
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Just as a side note, those who are interested in corollary might want to take a look at the aerospike as an alternative take on drag reduction through air-on-air bearing surfaces.
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Old Aug 26, 2010, 12:04 AM
Addicted to building...
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Omaha Nebraska
Joined Feb 2006
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23t23dS,

Great idea, and the wind tunnel is cool! Saw a lot of home brew wind tunnels in science fairs when I was a kid and wanted to make one too, just don't have the room for more 'creations". Hope you can build the plane for real world tests, or do you intend of seeking help? Would this be a group project, or a single effort?

A Useless Geek,

Love it! ever thought about the bom and what it was used for. Learning something new is cool! The corollation factor makes one think.......

Wonder if anyone has tried that no a EDF to see if they can increase the speed and duration.

Fred
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Old Aug 26, 2010, 09:28 AM
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23t23dS,

I'm really glad you are interested in helping. Now maybe we can make some progress. This is the best news we've had yet.

When you build your wind tunnel wings, I recommend using foam. Since you will be testing at airspeeds where the foam will not break apart. The reason I recommend foam, is that you will be able to accurately reproduce the airfoil shapes being used by modelers. I also recommend you test both the flat plate version of the airfoils and the curved airfoils like Viking60's above or mine below. My sample is of the center section of a biplane wing. The center section is about 1 1/2 inches shorter than the main wings, so the steps are actually further out than the 50% typical of a KFM2 airfoil. It is the curved shape that is important in the photo, not the step placement.

Welcome aboard. I look forward to your posts.

Roger
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Old Aug 26, 2010, 05:11 PM
Onward through the fog.
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Bohol Philippines
Joined Aug 2008
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Quote:
Originally Posted by maguro View Post
23t23dS,

I'm really glad you are interested in helping. Now maybe we can make some progress. This is the best news we've had yet.

When you build your wind tunnel wings, I recommend using foam. Since you will be testing at airspeeds where the foam will not break apart. The reason I recommend foam, is that you will be able to accurately reproduce the airfoil shapes being used by modelers. I also recommend you test both the flat plate version of the airfoils and the curved airfoils like Viking60's above or mine below. My sample is of the center section of a biplane wing. The center section is about 1 1/2 inches shorter than the main wings, so the steps are actually further out than the 50% typical of a KFM2 airfoil. It is the curved shape that is important in the photo, not the step placement.

Welcome aboard. I look forward to your posts.

Roger
Nice to see so much activity on the more technical/theoretical side of the KF issue.

Maguro,
If anyone does come up with access to a wind tunnel or builds one, I like the idea of using the flat plate as a "benchmark". It would be a good reference foil as a base-lline for the comparisons.

While I"m much more of a "foam-butcher" than an "egg-head" I'm really interested in seeing what kind of data you guys can come up with. We all agree that the KF foils work pretty well for our application. It would be nice to definitively be able to say "why", and to offer some sound evidence to the KFm detractors.

Onward through the fog.

Steve.
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Old Aug 26, 2010, 07:31 PM
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Quote:
Originally Posted by maguro View Post
23t23dS,

I'm really glad you are interested in helping. Now maybe we can make some progress. This is the best news we've had yet.

When you build your wind tunnel wings, I recommend using foam. Since you will be testing at airspeeds where the foam will not break apart. The reason I recommend foam, is that you will be able to accurately reproduce the airfoil shapes being used by modelers. I also recommend you test both the flat plate version of the airfoils and the curved airfoils like Viking60's above or mine below. My sample is of the center section of a biplane wing. The center section is about 1 1/2 inches shorter than the main wings, so the steps are actually further out than the 50% typical of a KFM2 airfoil. It is the curved shape that is important in the photo, not the step placement.

Welcome aboard. I look forward to your posts.

Roger
Thanks You,

Don't get your hopes too high thought, I'm just a (First Year ) AE student and it remains a fact that I know far more about model aircraft than about full scale and theory.

As for the school's wind tunnel, I've been told that it is not what I'm looking for, but I am, as i previously mentioned, hoping to get access to it to see what it can and cannot do. Then perhaps I will be able to work around what it can do, ie; build airfoil sections that will work within its limits.
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Old Aug 26, 2010, 08:19 PM
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As a first year student you may not get access to the wind tunnel. That was usually reserved for third and fourth years (at least it was 40 years ago when I was a student). Getting access to the fluid dynamics programs may be easier. For them you will have to do a different kind of modeling, you will have to build the airfoils numerically.

I've found a simple program on the Internet that I plan to use to try and model the KFM airfoils, both flat plate and airfoil shaped. I have no idea if the program will even be able to handle the discontinuity caused by the step. What ever happens, I'll post my results here.

Good luck with your studies.

Roger
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Old Aug 27, 2010, 06:34 AM
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Amsterdam
Joined Sep 2005
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very interesting..! I think birds have a similar mechanism build in in their feathery wings..

watch at 2.35:

Real birds eye view! Golden Eagle in flight - Animal Camera - BBC (3 min 9 sec)


and at 0.35
http://www.youtube.com/watch?v=MIn7K62DrB4&feature=related

maybe something like this could also work



I would love to try it..!

edit: trying it..! http://www.rcgroups.com/forums/showt...4#post15899050
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Old Aug 27, 2010, 10:29 AM
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Valley Village, CA
Joined Jan 2002
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Originally Posted by Johannez View Post
very interesting..! I think birds have a similar mechanism build in in their feathery wings..
...
Nice find Johannez. The regular shots from the ground camera are almost as interesting. Near the end of the first video you can clearly see the wing is an under-cambered airfoil, shaped in a slowly curving gull (higher in the middle, lower at the roots and tips), and can see that the wing tips have a much higher AOA then the roots.

Don't forget there is a fairly large KF ridge on the bottom of the wing as well.
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Old Aug 27, 2010, 11:50 AM
Jack
USA, ME, Ellsworth
Joined May 2008
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In the Building & Flying thread, within the last year I think, there are some reports, usually by DaveReap, of a KFm2 build that was made to look like a bird. It had a irregularly shaped edge on the back at the step, looking like the ends of a number of feathers.

Also the KFm strip on that plane was also rebated, there was unsupported area near the back of the strip with a empty area back up under it. It would look like this in cross section:

==== <--- KFm2 strip's rear edge, overhanging the support strip
== <--- rebated support strip under KFm2 strip
=========== <--- wing panel

That particular plane was made to look like a bird and it flew very well. If I remember right, not only did the overhang and undercut not hamper the flight characteristics, there was some speculation that it improved things.

Jack
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Old Aug 27, 2010, 05:25 PM
just Some Useless Geek
Chicagoland
Joined Oct 2008
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Originally Posted by Freddie B View Post
...Wonder if anyone has tried that on an EDF to see if they can increase the speed and duration.
Well, to be fair, the aerospike was meant to be used at supersonic and above speeds. ICBM reentry vehicles are coming back into the atmosphere at 20K kph and above. The aerospike was tested below those speeds, but was really only effective once your projectile got above the speed of sound.
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Old Aug 27, 2010, 06:14 PM
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Omaha Nebraska
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Quote:
Originally Posted by A Useless Geek View Post
Well, to be fair, the aerospike was meant to be used at supersonic and above speeds. ICBM reentry vehicles are coming back into the atmosphere at 20K kph and above. The aerospike was tested below those speeds, but was really only effective once your projectile got above the speed of sound.
Since the corollation on the aerospike and KFm airfoils is present, good thing the KFm does not need to go supersconic to become effective! Bet the distance of the boom on the aerospike was critical and fine tuned to the speed expected that it would impart it's effectivness.

It was just a random thought anyway, didn't think it would work or full scale jets would probably be using them.

Still thank you for the lesson by pointing out the aerospike.

Fred
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Old Sep 02, 2010, 05:07 AM
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Hi all,
Just new to the forum and am keen on the information in the current thread. It's a bit off topic however I thought I would share my findings at a recent boat show in Melbourne Australia.

http://veem.com.au/props_interceptor.php

It appears that the Kf theory has gone commercial in the performance propeller industry.
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Old Sep 02, 2010, 06:39 AM
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jj604's Avatar
Melbourne, Australia
Joined Jul 2005
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That's interesting. Good find.

However if you you look carefully at the rotation direction of the prop, these are different thickness strips right on the TRAILING edge of the blade. May well be similar in principle but it's not the same effect. What little it says on the web site suggests it is changing the effective pitch of the blade by thickening the trailing edge. This is different from changing the lift and stall point of a wing by inducing some sort of vortices and turbulence. Certainly the Reynolds Number regime is quite different. Any boat experts out there who know more??

John
Quote:
Originally Posted by Shanothegreat View Post
Hi all,
Just new to the forum and am keen on the information in the current thread. It's a bit off topic however I thought I would share my findings at a recent boat show in Melbourne Australia.

http://veem.com.au/props_interceptor.php

It appears that the Kf theory has gone commercial in the performance propeller industry.
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Old Sep 02, 2010, 07:13 AM
Jack
USA, ME, Ellsworth
Joined May 2008
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I don't really know more but the link prompted my curiosity. This wiki link on cavitation in marine propellers is interesting reading:

http://en.wikipedia.org/wiki/Propell...ler_cavitation

And it will offer you links to some fascinating videos like this one that shows tip cavitation on a marine propeller:

Propeller tip cavitation (0 min 18 sec)


The thing about the Interceptor Technology props that sort of baffles me is that the strips are going to change things as the water is coming off of the trailing edge of the prop whereas the most important work of driving the boat is done on the suction side of the upstream edge of the prop.

I'm not making any accusations here but I can't help but wonder if I don't smell a little bit of snake oil being sold here?

Jack
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Old Sep 02, 2010, 11:21 AM
just Some Useless Geek
Chicagoland
Joined Oct 2008
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Your sense of smell is as keen as ever, Jack. These Veem guys apparently wanted to use the KF without crediting its creators, and without paying any royalties. So, they flopped the KF on its head and tried to create a "variable pitch" system via synthesized stimulated cavitation. Great.

I smell it, too.
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