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Old Oct 05, 2010, 10:14 AM
Jack
USA, ME, Ellsworth
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Great reports and details, Roger.

I've been encouraging some of the Blu Baby builders that want to move on to ailerons to start building flat wings for that. There is a long standing mortal terror about flat wings and the lack of dihedral that I think can be discarded with the KFm wings. At least that is my experience.

Flat KFm wings do not require the full time attention that some suspect they will. It is almost like they are inherently stable or something. And building flat gets you stronger wings and takes you away from all of the issues of trying to get good aileron performance from a wing that wants to be inherently stable. You can skip a lot of the differential experiments as you pursue rolls.

If you do more videos, and want to do it, treat us to some roll rate experiments. You'll probably find that it will get more axial as the speed increases but I'll bet they won't be bad at all from what I saw there in the video.

And then there is the thing where an inverted KFm2 or KFm3 seems to need very little assistance from the elevator to stay in inverted flight. I think that explains why the KFm1 seemed to fly just about as well as the KFm2.

I'll bet if you start experimenting more with coordinating rudder and ailerons in turns you're going to see some amazing things there too. The low wing loses much less lift in the turn and, at least for me, the flying characteristics take on a majestic quality. Some of the yankers and bankers don't get it but that is OK.

And to me there is nothing prettier than the long gliding, flat but all crossed up, crosswind approaches you can get with coordinated controls.

Jack
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Old Oct 05, 2010, 01:07 PM
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Here is a video I just made of the most recent flight of the KF SE5a. It doesn't really belong here, but we were discussing it's handling qualities, so I thought I'd let you see how it flies. Please note that I'm an old stick and rudder guy. My aerobatics was 25 years ago, and mostly in Citabrias and Decathlons. I mostly fly R/C sailplanes now. Flying R/C aerobatics is new to me, and it shows.

The video is silent. I stripped off the music for YouTube. Too bad it flows much better with the Bare Naked Ladies singing "One little Slip" and Robin Williams singing "My Way" in Spanish.

Roger

R/C Se5a Biplane Aerobatics (4 min 36 sec)
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Old Oct 05, 2010, 04:52 PM
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Joined Feb 2006
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Roger,

Thanks for the pilot perspectives, and flight reports. All makes sense to some of the things I've been noticing too. Also the SE-5 Video too. The SE-5 glides really well, power off, for a biplane. I would have expected a steeper glide, and a ground loop (almost), but not! Well done. KFm reacts and fly's differnt than conventional airfoils in many subtle ways. A lot depends on design and related build features too.

Thanks again,

Fred
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Old Oct 06, 2010, 09:05 PM
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Some people have been asking questions about the KF stick so I thought I'd provide some photos and descriptions.

The first photo is a modification of Vikings KFM3 drawing, that I am using as a basis for the all the KFM wing (except the KFM4). You can also see the outline of the control airfoil I will build to compare against.

The next photo is of the under side of the beast. The third photo is a close-up of the electronics. Starting from right to left the red rectangle is the transmitter for the FDR. Next is the FDR itself. You can see the pitot and static lines going into the FDR. The static splits in two, because the FDR has separate ports for airspeed and altitude static sources. The bottoms of the rudder and elevator servos are almost visible under the mess of wires to the left of the FDR. Next is the receiver. The receiver antenna wires have two layers of heat shrink tubing on them in an effort to keep them from continuously being crumpled while handling the airplane. Next you can see a couple of Deans connectors connected by a bit of wire. Harder to see is the coil around one of the wires (black with white stripe). This connects between the ESC and the battery, and is where the FDR gets the battery voltage and current data. The ESC is on top of the "fuse" just in front of the wing.

The last photo is of the GPS that connects to the FDR. It is in top the fuse aft of the wing. I hove no idea what I might use the GPS data for, but I have the GPS, and it weights almost nothing. So why not use it?

Roger
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Old Oct 20, 2010, 09:59 AM
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I got some FDR data from the Slow Stick. I think I'm going to have to get another more powerful motor (this will be the fourth in the life of the airplane). Top speed in level flight averages about 25 mph. I think that 50 MPH would be a better top speed for data gathering, but I don't know how fast I can make the Stick without also making it so heavy It isn't capable of reasonable slow flight.

If anyone is interested in the early raw data, let me know, and I'll zip it up, and post it.

Testing is on hold for now. I need to find a new motor, and a new receiver. I stole the 2.4 receiver from the Slow Stick to put in my new Spitfire. It was an early birthday present from my wife. I couldn't very well disappoint her, could I?

Roger
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Old Oct 20, 2010, 10:48 AM
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Maguro,

I'm certainly interested in whatever information you can derive with your FDR approach. I've been wondering if there's a way to install the pitot tubes & all of the electronics on the fuselage (or on a slight 'appendage' to the fuselage), rather than having to build them into the structure of each test wing? The readings would at least be comparable as far as airspeed, no matter what wing you were testing, and it might leave the wing building simplified to that extent. Maybe there are issues which I'm not aware of, so I thought I'd ask the question.

I also think you're right about wanting a higher top speed... there may be data variances between the different wing configurations which will be more apparent at higher air speeds. I expect that there will also be subjective handling / responsiveness evaluations which you'll be able to make while flying each of the variations which may correlate with the current consumption / drag affect data that's recorded.

We know all of this simply takes time to get set up. And then, of course, you're looking for some good flying conditions to do the test flying & data gathering. So we'll be grateful for whatever you can end up with from this process.

VIKING
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Old Oct 20, 2010, 12:53 PM
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I certainly second Viking60's motion to let us look at the data that you collected, Roger. We'll take the good, bad and the ugly.
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Old Oct 20, 2010, 03:10 PM
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Viking, The Pitot and static ports have to be outside the prop blast. They do not need to be on the wing. Models with the motor/jet on the rear usually put the pitot/static tube on the nose. I now have a Prandtl tube (combined pitot/static). It makes location a lot easier even though it still requires two separate air lines back to the FDR.

On my sailplanes, I put the static port flush with the fuselage and taped the air line and the pitot to the bottom of the wing. With the sailplanes I'm not concerned with accurate airspeed readings when the motor is running, only when actually soaring. The air line causes some additional drag, but I am not such a good a sailplane pilot that it makes all that much difference.

On the Slow Stick I fed the the air lines in the wing, because I didn't want them to mess up our readings. All the other hardware is strapped onto the fuselage. Moving the pitot/static from the wings on the slow stick would require putting it on a boom about 8 inches above the wing.

Speaking of which. I did some tests of the key chain camera, and it will have to be suspended from a boom in order to get a good view of the tufts on the wing from the root to the tip. If anyone has a good idea for a design for a boom to get the camera about 8-10 inches above the center of the wing opposite the one being photographed, please let me know.

Attached is a zip file containing the last three flights. I got a few good straight and level laps per flight after that I'd break down an do some loops and rolls.

Roger
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Old Oct 21, 2010, 11:23 AM
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Turbulator Structures

Friends,

KF stepped discontinuities are a type / class of turbulating structure which is very easily implemented when building with layers of flat foam sheet, FFF, etc..... but we may need to do some re-thinking, and be careful so that we don't fall into the trap of letting the commonly used material dimmensions dictate what shape / depth these structures assume.

KF steps are 'innies' - they are structures where the wing surface drops away from the contour of wing surface in front of it, forming a 'pocket' behind the KF step. This is a surface discontinuity where, in some cases, a circulating vortex may be captured while the wing is in flight.

Effective air boundary layer turbulating structures on a wing's surface can be either 'innies', or 'outies', and in some cases they can be merely more angular changes in the surface of a wing.

Old-timer & sailplane designers have known for a looooong time that using turbulator spar structures and 'trip strips' ('outies') on an airfoil's surface improves the performance of a wing. And the key to this is that even very minimal height / depth structures- (only 1/32" height for a trip strip) very effectively turbulate the boundary layer air flow, reducing surface layer separation bubbles across a wider range of angles of attack, and across a wider air speed range [for a given wing loading.]

How deep of a KF step / pocket we might want to use on various aircraft types for various desired flight performance envelopes is still a question that bears a lot of closer scrutiny and experimentation.

My recent testing on 'KF3" variant wing prototypes has been evaluating whether shallow depth KF variant stepped structures produce the same benefits (trapped circulating vortexes & turbulated boundary layer air flow) with less drag when compared to deeper stepped discontinuities. The subjective results of the KF3P prototype flight tests indicate that they do.

For making modifiable test wings where I can test deeper vs. shallower stepped structures, working with the various thicknesses of Depron & FFF is working well for me for now; I can add or change thicknesses by 1mm of foam at a time if I want, tape it in place, remove it again, and still keep a very clean and structurally sound wing structure throughout all of the various configurations. I can temporarily add other turbulator structures for some tests, too.

VIKING
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Old Oct 21, 2010, 12:12 PM
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Quote:
Originally Posted by viking60 View Post
Friends,

KF stepped discontinuities are a type / class of turbulating structure which is very easily implemented when building with layers of flat foam sheet, FFF, etc..... but we may need to do some re-thinking, and be careful so that we don't fall into the trap of letting the commonly used material dimmensions dictate what shape / depth these structures assume.

KF steps are 'innies' - they are structures where the wing surface drops away from the contour of wing surface in front of it, forming a 'pocket' behind the KF step. This is a surface discontinuity where, in some cases, a circulating vortex may be captured while the wing is in flight.

Effective air boundary layer turbulating structures on a wing's surface can be either 'innies', or 'outies', and in some cases they can be merely more angular changes in the surface of a wing.

Old-timer & sailplane designers have known for a looooong time that using turbulator spar structures and 'trip strips' ('outies') on an airfoil's surface improves the performance of a wing. And the key to this is that even very minimal height / depth structures- (only 1/32" height for a trip strip) very effectively turbulate the boundary layer air flow, reducing surface layer separation bubbles across a wider range of angles of attack, and across a wider air speed range [for a given wing loading.]

How deep of a KF step / pocket we might want to use on various aircraft types for various desired flight performance envelopes is still a question that bears a lot of closer scrutiny and experimentation.

My recent testing on 'KF3" variant wing prototypes has been evaluating whether shallow depth KF variant stepped structures produce the same benefits (trapped circulating vortexes & turbulated boundary layer air flow) with less drag when compared to deeper stepped discontinuities. The subjective results of the KF3P prototype flight tests indicate that they do.

For making modifiable test wings where I can test deeper vs. shallower stepped structures, working with the various thicknesses of Depron & FFF is working well for me for now; I can add or change thicknesses by 1mm of foam at a time if I want, tape it on place, remove it again, and still keep a very clean and structurally sound wing structure throughout all of the various configurations. I can temporarily add other turbulator structures for some tests, too.

VIKING
VIKING... I totally agree with your assessment. The steps do not have to be that deep. Below is my Condor with a rather small step. This is the plane I used to challenge the distance record for the first manned flight down at Kill Devil Hills, NC. If the step is too deep it creates a bigger vortex which then produces excess drag. The small step allows the vortex to remain attached and helps prevent separation. Your work on the step heights has greatly increased our knowledge about this phenomenon.

Dick
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Old Oct 21, 2010, 01:07 PM
just Some Useless Geek
Chicagoland
Joined Oct 2008
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Dick, are you still interested in pursuing the variable wing step idea? Perhaps we can get with Bruce and discuss some of the factors involved in deciding the step depth/position, then work out the actuators and control electronics. I imagine that Bruce is in a much better position to build flying prototypes than I am (totally broke and with clients who still owe me money). I can work out control and positioning algorythms, processing facilities, and software. Coordinated multi-axis motion control is a major part of the work I do.
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Old Oct 21, 2010, 01:34 PM
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Viking, If I could manage to talk Eagle Tree out of a loaner FDR, do you think you could/would use it in your testing? I think it would add significantly to our research.

Roger
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Old Oct 21, 2010, 02:44 PM
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Fairplay, South Park, CO
Joined Sep 2005
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Quote:
Originally Posted by maguro View Post
Viking, If I could manage to talk Eagle Tree out of a loaner FDR, do you think you could/would use it in your testing? I think it would add significantly to our research.

Roger
Roger,

Yes, that does sound like an interesting proposition! I'll need to look into the FDR's capabilities, and learn how to put it to use effectively. It would be very interesting in doing this.

I do have a very nice wide-open flying venue available, my 'Antelope Flats' site, which is within four miles of my house. It makes it possible to get out for a test flight without a lot of travel time, and the wind / weather conditions are very predictable before I ever leave home.

Bruce
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Old Oct 21, 2010, 09:23 PM
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Quote:
Originally Posted by A Useless Geek View Post
Dick, are you still interested in pursuing the variable wing step idea? Perhaps we can get with Bruce and discuss some of the factors involved in deciding the step depth/position, then work out the actuators and control electronics. I imagine that Bruce is in a much better position to build flying prototypes than I am (totally broke and with clients who still owe me money). I can work out control and positioning algorythms, processing facilities, and software. Coordinated multi-axis motion control is a major part of the work I do.
Yes, that would be useful, but I don't know if Bruce has the time. I've felt that a variable step on a carrier jet would make for better control landings without being too hard on the struts and tires which need to be frequently replaced. And, that's very expensive. These jets landing on the deck of a carrier are doing controlled crashes and the components take a severe beating. But, I digress. I'm just thinking too far ahead in terms of making it financially viable. We still have a very long way to go...
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Old Oct 22, 2010, 02:06 AM
it WILL fly! someday....
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Slovakia
Joined Aug 2008
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Can't make drawing right now, but I'll try to describe my idea of variable step mechanism (I can't remember original author of variable step height, It was here on RCG some time ago.)

Hotwired solid foam wing core with rather deep step, maybe 50%. Area from step to TE/aileron would be covered with depron strip, hinged on TE. Servo arm (or some clever linkage) placed under the depron strip "LE" at wing root, to raise it up/down, changing step height. LE of depron cover strip should be reinforced with CF or wood, so it won't bend. It would be fixed at wing tip, to prevent flutter and to get step height taper.

Makes any sense?
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