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Old Feb 04, 2013, 10:30 PM
Build straight - Fly twisty
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Originally Posted by jackerbes View Post
I was perfectly happy with the amount of performance I got from Big Blu and thoroughly enjoyed flying it. Regardless of the opinions of the "real" glider pilots and their "real" gliders.
There is no doubt that good fun can be had with such a glider even though it is 'falling out of the sky' relative to a 'real' glider.
You just have to be skilled in finding strong thermals.
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Old Feb 05, 2013, 06:49 AM
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Originally Posted by Dickeroo View Post
Just a guess on my part....

The KFm2 traps a rotating vortex behind the step that lowers the air pressure over the upper surface. Since this is occurring behind the step in the second half of the chord, the COG has to be further back.

I don't have a clue as to how the KFm1 generates lift.
Doesn't the KFm1 gets its lift by acting as a wedge, forcing down air?
(Which would be why the NASA report said the KFm1 acted somewhat like a flate plate airfoil)
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Old Feb 05, 2013, 08:08 AM
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Originally Posted by g828 View Post
Doesn't the KFm1 gets its lift by acting as a wedge, forcing down air?
(Which would be why the NASA report said the KFm1 acted somewhat like a flate plate airfoil)
The problem with the NASA report on the KF was this: they followed our patent drawing out the window and got poor results.

Here was our thinking at the time we filed for a patent. We only wanted to patent a step or discontinuity, not an entire profile. The reason was that we knew it worked in so many different ways we couldn't patent them all. Our patent drawing showed a flat upper surface with a sharp leading edge and a step on the bottom 50% back from the leading edge.

Why on the bottom? Because we knew that the step on top showed higher L/D than the step on the bottom. We also believed that when an aircraft goes from subsonic to supersonic the characteristics reverse themselves. Thus, we showed it on the bottom wanting to pick up the higher numbers supersonicly.

Inspite of the sharp leading edge and the step on the bottom, the KF airfoil still refused to stall out beyond 50 degrees AOA, while other NASA airfoils were all losing lift much earlier. There is a diagram that shows this in the book Fluid Dynamics by Frank White which was published in 2004.

This is basically what led to how things on the KF evolved. Our purpose was to patent just a step which would trap a vortex and provide greater stability and stall resistance.
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Old Feb 05, 2013, 08:16 AM
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Here is the page from Fluid Mechanics...
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Old Feb 05, 2013, 11:41 AM
KlonWarz
Joined Dec 2012
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67degree aoa

I went to look at the information posted from that page of Fluid mechanics, Dick...

In part, it's misleading...

In reference to the X-29 'flying' at a high, 67degree aoa...

Hogwash!

I watched the vid of the x-29 in action and reviewed some of the specs...

They have control surfaces ALL OVER that aircraft, and are controlling it by computer !

Oh.... HUGE thrust ! It's possible to fly a brick with enough thrust!

In the vid I watched, it's obvious the canard is in what we might consider to be an acceptable aoa... and they've also got strake flaps on it, at the rear of the craft.
...probably close to vectored thrust!

No doubt they were able to garner much valuable information from sensors placed on the aircraft while they were bashing it about the sky, but they were NOT flying that wing! lol
I wouldn't doubt it was much more than an impediment for much of what was going on.

....they were seeing how far, and what they could do with those fancy swept forward wings stuck on the sides of the fuselage!

IF I had any sort of specialized training I'd really be able to shred that part of the presentation in the book... just because something made it into print does NOT mean it is gospel !
There's most likely a ton of literature out there from the Flat Earth Society. :-)

IMO, with NO scientific background or certification of competence, support for the KF step would most likely be found in data compiled on turbulators.
KF step is a full - length turbulator.

Perhaps there may be support in the work of Rutan.

Best
rc

EDIT!!! I really mangled that statement! What I meant to say was, IMO, (I have NO scientific background or Certification of Competence), KF theory is probably related to turbulators. ..that part was meant to be my own personal limitation...
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Old Feb 05, 2013, 08:19 PM
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Originally Posted by rusty case View Post
IMO, with NO scientific background or certification of competence, support for the KF step would most likely be found in data compiled on turbulators.
KF step is a full - length turbulator.

Perhaps there may be support in the work of Rutan.

Best
rc
I agree with rusty case. The step probably does act as a turbulator, which would most likely be the best use of it in full scale aeronautics. The question is whether on not making the KF step into a wing is more worth it than sticking rectangular pieces of metal on a wing (which turbulators pretty much are)

The idea that the KF step could possibly be acting as a turbulator was the primary reason I chose a thick airfoil in my wind tunnel test.

Also when I did the wind tunnel testing of the KFm4 airfoil, I did not find that it had a huge improvement in terms of stall angles as that book claims. Rather I found it stalled perhaps 4 or 5 degrees above the control airfoil.
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Old Feb 05, 2013, 08:57 PM
Build straight - Fly twisty
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40% seems to be the preferred position for a KF step.
Turbulators are usually deployed further forward.
My theory is that for 'our size' wings we need to consider the airflow, not around the airfoil itself, but the airflow over the boundary layer. The boundary layer and flows adjacent to it form a Virtual Wing Section which is variable and adaptive.
On a full-size wing the boundary layer is a small fraction of the cord. In 'our' size it has much more significance.
This theory can help to explain how wing-sections that literally would not get off the ground in full-size aviation work OK for us. I am referring here to horrors like the thick, sharp edged purely rectangular "wing sections" that some guys chop out of foam and fly quite successfully.
In the case of my little test glider the airflow over the boundary layer of the rear part on the Ca section was probably very similar to the airflow over the boundary layer of the turbulent air behind the step.
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Old Feb 05, 2013, 09:24 PM
KlonWarz
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Originally Posted by g828 View Post
....the primary reason I chose a thick airfoil in my wind tunnel test.

....when I did the wind tunnel testing of the KFm4 airfoil....
may I ask if you have posted any of your results elsewhere on the forum????
rc
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Old Feb 05, 2013, 09:25 PM
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btw, I made a mistake, I meant the KF airfoil should act as a vortex generator (slight difference, similar effect)

But anyway, wouldn't the success of the barn door wings be more mainly due to the amount of power/weight ratio the RC community has access to so that the R/C plane can power through the relatively high amount of drag?
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Old Feb 05, 2013, 09:26 PM
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Originally Posted by rusty case View Post
may I ask if you have posted any of your results elsewhere on the forum????
rc
uh... no.... sorry.
Reason is that my report for high school is still being submitted so I don't want to release the data until later....

The only thing I did do was post a video of my tests
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Old Feb 05, 2013, 09:43 PM
KlonWarz
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Originally Posted by Whiskers View Post
...horrors like the thick, sharp edged purely rectangular "wing sections" that some guys chop out of foam and fly quite successfully...
:-)

Yes, I'd have to agree with that, W....

I think.... what many rc fellows fly today resembles the equivalent of the GeeBee racer. and I've also watched those awesome vids of fellows hanging on their props, tail tapping!!! Wowee! What fun they are!

I really should study turbulators more... I'm aware they exist, and that's about it.

For lift, my preference would be a retractable leading edge slat and Junkers styled flaps... and as you mentioned with scale, I am not aware of how a fixed leading edge slat could be practical on an inexpensive model craft.

(There's apparently someone up in Alaska installing slats on SuperCubs)

All told, the KFm airfoil step is a wonderful opportunity to experiment !
rc
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Old Feb 05, 2013, 09:52 PM
KlonWarz
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Originally Posted by g828 View Post

The only thing I did do was post a video of my tests
may we watch your vid? :-)

I've said so in some prior post... much of my knowledge of turbulators comes from an AOPA article on Rutan's Boomerang.

You may wish to see if it is available.

There was also a bit of hush-hush mention of Rutan's crew quietly discussing "Thrust inducing vortices".

You might find that particularly interesting????
rc
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Old Feb 06, 2013, 04:55 AM
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KFm4 Airfoil Testing (2 min 22 sec)


It's nothing too special. Just showing airflow around the airfoil. But if you look closely, you can see a big blob of smoke shedding and then reforming rapidly, which I assumed were the vortices shedding and then reforming.
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Old Feb 06, 2013, 11:13 AM
just Some Useless Geek
Chicagoland
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Originally Posted by rusty case View Post
...what many rc fellows fly today resembles the equivalent of the GeeBee racer. And I've also watched those awesome vids of fellows hanging on their props, tail tapping!
If you've seen any of the vid capture of my Longhorns transitioning from horizontal flight to prop hanging then you'd see the effects of P/W ratio. A purely flat plate wing can produce "lift" by simply deflecting the apparent wind downward. The KF wings produce actual lift at lower airspeeds and lower AoA. Obviously we're still trying to noodle out what's happening, but the net effects are visible to the most casual of observers. You can't deny that KFs offer lift. Drag, too, but let's not discount the lift.
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Old Feb 06, 2013, 12:29 PM
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personally in my tests there was no increase in lift. imo the biggest benefit is stall resistance. i never get tired of seeing my kf foamy float along unbelievably slow at crazy aoa. at least compared to uc w/o the strips.
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