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Old Apr 12, 2012, 12:06 PM
Jack
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Dick,

If you exchange email with D Abhinav, maybe you can invite him to come here and discuss this further? If he wants to do that of course.

The stuff looks interesting from a layman's viewpoint. Maybe this is a good start on getting some real data on the performance of the KF foils.

Jack
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Old Apr 12, 2012, 12:33 PM
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Mach .3 is about 230 mph. That's a bit fast for a glider. I wonder why they tested at that speed?
230mph is hard to achieve on a 75meter course with rubber band power. i suspect those plots are unrelated to real world performance. very attractive but maybe not of too much interest to rc hobbyists.

btw dickeroo, hope your recovery was successful and youre feeling well.
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Old Apr 12, 2012, 01:27 PM
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230mph is hard to achieve on a 75meter course with rubber band power. i suspect those plots are unrelated to real world performance. very attractive but maybe not of too much interest to rc hobbyists.

btw dickeroo, hope your recovery was successful and youre feeling well.
Thank you for asking, Dave.
Yes, I'm on the mend and doing extremely well. I was operated on just a little over a month ago and I have healed nicely. Right now, I'm doing Outpatient therapy twice a week. I have been very fortunate in that there was a minimum amount of pain and the knee is responding very well to therapy. It is amazing what they can do today. I saw so many, many people with knee, hip and shoulder problems. As we all age, there will be many more people in need of this type of procedure.

Dick
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Old Apr 19, 2012, 05:30 AM
gpw
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Glad you’re OK !!!!
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Old Apr 25, 2012, 01:52 PM
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Originally Posted by jackerbes View Post
Dick,

If you exchange email with D Abhinav, maybe you can invite him to come here and discuss this further? If he wants to do that of course.
hello again guys....

Jack, this is a good suggestion, or maybe Dick can pass a few observations back . I've got a few things that it would be interesting to get answers on:
  • This is computerised simulation (Fluent CFD software). Has any validation of the results been done against wind tunnel tests for stepped airfoils?
  • No mention was made of the lift/drag performance. The L/D vs α graph seems to show a LD of about 26 for the NACA symmetrical airfoil but only about 6 or 7 for the KFm3. Comments?
  • The Cm vs α graph shows an erratic but generally strongly negative Cm value, for the KFm3 airfoil. Would this not result in instability in pitch?
  • What does the comparison look like if an airfoil better suited to a normal aircraft wing was used rather than a symmetrical NACA airfoil, i.e. one with some positive camber, something like an SD7037 or maybe even the good old Clark-Y.

Steve

PS.. Dick, i hope you are back to full fitness very soon.
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Old Apr 25, 2012, 04:08 PM
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Originally Posted by JetPlaneFlyer View Post
hello again guys....

Jack, this is a good suggestion, or maybe Dick can pass a few observations back . I've got a few things that it would be interesting to get answers on:
  • This is computerised simulation (Fluent CFD software). Has any validation of the results been done against wind tunnel tests for stepped airfoils?
  • No mention was made of the lift/drag performance. The L/D vs α graph seems to show a LD of about 26 for the NACA symmetrical airfoil but only about 6 or 7 for the KFm3. Comments?
  • The Cm vs α graph shows an erratic but generally strongly negative Cm value, for the KFm3 airfoil. Would this not result in instability in pitch?
  • What does the comparison look like if an airfoil better suited to a normal aircraft wing was used rather than a symmetrical NACA airfoil, i.e. one with some positive camber, something like an SD7037 or maybe even the good old Clark-Y.


Steve

PS.. Dick, i hope you are back to full fitness very soon.
Hi Steve... My right knee replacement has worked extremely well. I feel that I have regained the quality of my life back. Now I will need to get the left one done in September. It's been a month and a half since the surgery and I can now walk without a cane. In fact, I even forget that I had a problem. Amazing what they can do these days.

The young man who sent me the file on his KF testing has told me that as soon as he has a chance he will do further testing. When ever he sends me the file,
I will post here as soon as I receive it.

I hope that all is well with you and your family.

Dick
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Old Apr 25, 2012, 07:17 PM
Jack
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Dick,

It is good to hear you're doing so well.

If you think the guy might not be aware of it and might like to do it, tell him his presence here would be welcome. There is always room for one more here.

Jack
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Old Apr 25, 2012, 07:45 PM
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Dick,

It is good to hear you're doing so well.

If you think the guy might not be aware of it and might like to do it, tell him his presence here would be welcome. There is always room for one more here.

Jack
Jack...

This young man is currently traveling. As soon as he can he will attempt to do more testing. I have managed to put him in touch with Frank White who wrote the book called Fluid Mechanics. He is updating his book and would like to include whatever testing of the KF he can. This would certainly be of benefit to the young man.

Here is D Abhinav's web page...

https://sites.google.com/site/abhinavdasari/

I will invite him to post here as well.

Dick
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Old Apr 25, 2012, 08:25 PM
Jack
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Thanks, Dick.

Looking forward to learning more about all of this science stuff...

Jack
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Old May 06, 2012, 09:56 PM
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Hi Ive been reading with interest about the KF airfoils. Some time ago around 1988 to 1994 I develped an interest in alternative airfoil methods of design and lift etc as there were certain airflow problems with conventional airfoil design. To cut a long story short I ended up over several years testing different airfoil designs and I finally ended up with airfoils similar to the one I have uploaded which are similar to the KF airfoils. Back in the early 1990s there wasnt much internet in Australia so to speak therefore, I wasnt really aware of airfoils such as the KF etc. Due to the general lack of enthusiasm directed toward my airfoils here at the time I sort of gave up and put all of my work under my house. It is only recently I have regenerated interest after visiting this site many times and seeing that some people are actually into using these type of airfoils. I plan on building an rc plane soon so I can finally see how my airfoils go. Apart from my facebook page this is the first time I have posted any of my work on the internet. If anyones interested I have a lot of data on the foils that I tested in the low speed wind tunnel at Sydney University. Thanks.
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Old May 07, 2012, 01:47 PM
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Gary,

Very interesting. What do you see as the pros and cons of your design compared to a good conventional airfoil?

Any more data you can share from the wind tunnel? I see Cl and Cm but no data for Cd.. and of course Cd tends to be the challenge with these non-conventional airfoils.

Steve
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Old May 07, 2012, 09:56 PM
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Hi Steve, thanks for your reply. In answer to your question re pros and cons I will try and answer the best I can - Firstly I have a pilot license but I am not an aeronautical engineer as such. I had developed an interest about the actual flow around wings and especially high speed flow and transonic shock wave formation and flow separation etc a long time ago during my flight training. After about 12 months of (constantly) approaching Sydney University to let me use the wind tunnel, Doug Auld the head of the aero dep't finally caved in and said ok - but with the caveat "if it doesn't impress me I don't want to see you again. So my first wind tunnel foray actually involved modifying a naca 0012 foil by placing a flexible/resilient trailing edge surface along the entire trailing edge. This was done to try and mimic the row of hairs that can be seen along the trailing edges of some insect wings. He thought the experiment was interesting and although it wasn't really what I was looking for, it allowed me the opportunity to access the wind tunnel facilities over the next 10 years when I needed them. So to cut a long story a bit shorter, my initial work had no resemblance to what evolved over the next ten years. I began working with another type of foil mathematics and the sections that were being generated from this were unusual to say the least - having abrupt surface profile diversions at the position of maximum airfoil thickness (see posted pics). Most of my work was done with sharp leading edge foils, however only in low speed wind tunnel flows. There are many very good conventional airfoils out there, although I see a need though for airfoil types that can operate at higher speeds without the associated adverse flow effects. Maybe with some modifications this concave arc stepping may be of help in there. On the other hand the lift curves that were being generated by the above airfoil are ok and the stalling angles are ok too, so it would appear that this type of thing may be suitable for low speed applications. As far as drag goes after taking into account wind tunnel support drag and the low aspect ratio of my test sections and the endplates the drag is ok. Just a note - I have also tested the rectangular type step cut-out and these are a bit draggy - also tested were steps using 45 degree wedge cut-outs and these were a bit less draggy than the rectangular step cut-outs - the concave arc steps definitely improve drag conditions ( I think that golf ball dimples operate on samelike principles ?) . Also the aerodynamic centre seems to be further aft than conventional design. I have a stack of data packed away so if you or anyone else is interested then I can dig it out so to speak, no problem. Thanks.
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Old May 08, 2012, 06:09 AM
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Most of my work was done with sharp leading edge foils, however only in low speed wind tunnel flows. There are many very good conventional airfoils out there, although I see a need though for airfoil types that can operate at higher speeds without the associated adverse flow effects.
we would probably agree your test section would not perform well in glider competitions. however super slow flight is what impresses most kf enthusiasts (many may not admit that ) so it would be interesting to see what happens in a real plane. specially since your profile resembles the structure of dicks original paper airplane in some ways. im assuming with a more reasonable aspect ratio and with the advent of nodern foam building materials that might not be too hard to implement.

ps gary, one or two crlf might help make your posts easier on the eyes. lol!
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Old May 08, 2012, 06:32 AM
Jack
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"..we would probably agree your test section would not perform well in glider competitions..."

Dave is right of course. But that does not mean that you are not having fun. And part of the fun would be showing up and flying a plane with about $10 worth of material in it. That will drive the guys with the $600 glass slippers a little nuts and it would be worth it just for that reason alone.

To my knowledge, the following post may represent one of the few efforts that has been made to date to collect some data on a KF winged glider (KFm9 in this case) and compare the sink rates from that to other high performance gliders:

http://www.rcgroups.com/forums/showp...2&postcount=39

My effort was less than that of a knowledgeable scientist and more of a seat of the pants flying guy with a little extra instrumentation. No wind tunnels but it was in the real world so that is a some value.

I was using a sink rate of 1.0 FPS as the "gold standard" and Big Blu 96 had a best descent in the tests there of 2.8 FPS. So that certainly lowers the threat level to the glass slipper crowd.

There is still room for considerable improvement there in the KF glider, it had a un-faired motor mounting and the Eagle Tree eLogger was strapped to the top of the wing and inducing more drag as there was not room for it inside the fuselage. And I have a lot of room left for improving the streamlining on the rather blunt entry on the leading edge and thinning the tips a little too.

So if anyone wants to insist that their $600 glass slipper from some far off land is almost three times as good as a KF winged glider, I'll not argue the point. But just the joys of building it myself and flying it made it priceless to me! And that is worth something.

Jack
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Old May 08, 2012, 09:52 AM
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personally id have to agree with pretty much every thing you said about fun and making comparisons. i found your thread at least as interesting as jetplaneflyers. your glider is a work of art (and technology). thanks for the link. it might be interesting to see how different numbers of steps effect glide too.
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