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Old Nov 29, 2010, 03:57 PM
Reap the wild wind
headlessagain's Avatar
Bristol,UK
Joined Feb 2007
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Dan
Here is the Piranha thread http://www.rcgroups.com/forums/showt...860561&page=10. See post 500 for my build & pictures. It's more of a mid wing KF4 aerobatic model which flys really well at all speeds apart from trying to turn at zero airspeed
Here is some flying footage
Piranha RC plane 11Jun2010 HC PK.AVI (4 min 2 sec)
!
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Old Nov 29, 2010, 04:41 PM
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Cleveland
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Jack,
Thanks for response and what your saying makes a lot of sense. I have always appreciated the KF airfoils from a far and never really tried one out for myself. Well, I guess there's a first time for eveything, right?

I will openly admit to my airfoil ignorance but am trying to learn as much as I can.

The Herr line of kits tend to be "boxy" in shape. While very sturdy and durable, they are more functional than asthetically pleasing. My prototype is exactly that as well. Perhaps some pictures would help. Give me a minute or two....

Dan
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Old Nov 29, 2010, 05:29 PM
Jack
USA, ME, Ellsworth
Joined May 2008
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I was over looking at the Herr line, I had not realized that they are a division of SIG:

http://www.sigmfg.com/cgi-bin/dpsmar...nuF.html?E+Sig

One of the planes I mentioned was a SIG Rascal 40. It had been a fuel plane and I came into it used and converted it to electric. That was the 72" 7 pound plane and it was a lovely thing. I had enough power in it that it was a sporty flier when I turned up the wick but I loved it just for it's size and smooth flying style. It was a plane that really responded to to the use of coordinated controls and helped me get settled down on flying with ailerons and using the rudder too. A receiver failure took here away from me... Sob!

Jack
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Old Nov 29, 2010, 07:57 PM
Onward through the fog.
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Bohol Philippines
Joined Aug 2008
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UP-date

The Taubenator has been flown and crashed. (Repairs Made!) The receiver quit listening to the transmitter. Still looking into that problem and it looks like the ESC/Receiver connector or one of the servo extensions from the tail area has an intermittent disconnect, but, when working OK it flies well and can be brought to a very slow speed. The Vee-Tail seems to be working OK but perhaps on the next one a bit more dihedral would be a good idea. I have removed the BP21 and replaced it with a Blue-Wonder, which i think will be enough since I was flying on about 1/3 throttle with good results.
No video because the batteries in the camera died and the plane was down before Edna could reload.

I have added a camera mount that allows 360deg rotation but no tilt adjustment. My current leaning is to a nice Vee-Tail copy of some local bird as a AP ship to try and get some video of the local birds should they choose to come over and have a look-see at what I'm doing.

The attempted maiden was at 6am and now it's 9:20 and windy. I may try again if the wind dies a bit.

Dan,
I echo what Jack has told you. The KF wings are a good choice and for a few bucks worth of foam and glue it's worth your time to give it a try. You may become a convert. Specially when you see how easy they are to put together and how well they work compared to a conventional foil.
Good luck with your efforts. I hope it all works out good for you and keep us updated on your progress.

Steve.
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Old Nov 29, 2010, 08:30 PM
Jack
USA, ME, Ellsworth
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Headless,

That is a lovely flight demo there, I had forgotten how nicely the Piranhas can fly. And your plane has my nomination for the prettiest build to date, you really did a nice job on that.

Dan,

If you didn't look at that video that Headless put a link to, do that. The Piranha with it's mid wing and KFm4 airfoil is without a doubt the most aerobatic of all the various KFm builds.

My FB, Jerry_in_Maine, built one too and it was exactly the same way. It would do anything you asked of it, but was also very mellow when you weren't doing that. You could run it up to where it was about to speck out and and it had a very respectable glide too.

Jack
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Old Nov 30, 2010, 01:04 AM
Reap the wild wind
headlessagain's Avatar
Bristol,UK
Joined Feb 2007
3,762 Posts
Jack
thanks for your kind comments
Dan
when you build your KF wing you can save some time and money by using spray adhesive. You don't need an expensive 3M product, just look one suitable for foam backed carpet.
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Old Nov 30, 2010, 12:19 PM
Addicted to building...
Freddie B's Avatar
Omaha Nebraska
Joined Feb 2006
5,992 Posts
Another great glue for laminating the wings is Elmer's Rubber Cement, like they use in schools. Brush on both sides, wait until dry, about 10 minutes, press together and it will never come apart. Elmer's is safe on all foams too! You can place a piece of wax paper over one side as you align the parts, and slide the wax paper out. Once the 2 glued sides touch you are never going to get them apart again! $1.35 a bottle too!

Fred
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Old Nov 30, 2010, 08:02 PM
Onward through the fog.
Cybernaught's Avatar
Bohol Philippines
Joined Aug 2008
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Taubenator Maiden and first AP vid.

I've been messing with the Taube type planes quite a bit lately and here is the maiden of the Taubenator.
Taubenator Maiden b.wmv (1 min 38 sec)

It is the second attempt to maiden and was quite successful. the first time I tried, yesterday morning, I had an electrical problem that resulted in a burned out ESC and a crash landing so that doesn't count. The plane is flying on a BW-1500 motor with a 7x6 SF prop and I'm using a heavy 1300mah 3s battery so the flight times should be excellent specially since it cruises in no wind at half throttle. Probably around 4amps or less but that's just a guess.

This is my first AP video with the Tabuenator and it's a composite of 3 flights with the cam rotated to front, back and left-side. The performance with the Vee-Tail is good and it glides surprisingly well on the KFm2 with the Philips entry. the friction fit is snug and should be OK. I will avoid any wild maneuvers when using the camera. Here is my first AP vid with this plane. You may recognize the area from my previous aerial videos. Swimming is very minimal.
Taubenator AP1 b (2 min 47 sec)


I will post these videos on both the Taube COOP and the KF Build threads, since the wing is my favorite KFm2 and the bird is Etrich Taube inspired with Gene Bond's wing profile.

I hope you find it interesting and to those of you who are in the grip of winter's frigid clutch perhaps this will offer a vicarious visit to a warmer environment. I"m tempted to clean up the sailing punt and go for a jaunt when the tide raises a bit, but I'm out of sunscreen at the moment. Anyway it's 10am and the wind is up but there are rain clouds threatening. That's why I did the maiden at 6am.

Steve.
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Old Nov 30, 2010, 09:46 PM
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opinion

New hear to this thread, but I have been lurking here alot.

Building a 36" wing span flat kfm2 with ailerons controled by seperate servos.

This is my 2nd attempt. Still tuning the kfm3 with ails I built last week.

8" root chord, 6.5" tip, (made a goof while cutting, thought good time to try more taper.) I used the calculator and since tapered chord, I avg it to 7.4" although not precise, because I left the area above the fuse 2.25 at the full 8" t.e.. It tells me that the overall step hieght should be .0614, so a little less than 5/8".

To keep it easier, I left the step at 50% of the tip straight across, so the 50% gradually decreases till it hits 41% at the fuse.

I mitred the step leading edge, and used a .125 wood dowel that is set in a groove sanded into the bottom of the step surface and the top of the main. the 2 pieces fit together nicely at the leading edge. And for the step spacer I used a .125 carbon fiber tube 24" long and centered. I hot wire miter cut 2 6" strips to fill the gap at the wing tips where the cf tube spar ends. they ramp up to a max of .125 so as to support step at the tips. The space between the le and the step edge will hopefully be filled by the foaming action of the PU glue.

The ailerons will be 12" x 1.25" and will start in from the tips about 1.25" servos recessed into bottom as far as step will allow. The blue tape in the pics show where ails will be.

It will mount to a 33" blue baby with a blue wonder 1700kvt motor. I hope to stay with 2s batteries, but will try 3s if needed.

Nothingn is glued together yet so good time to ask:

How do the experts here think it will work?

2, will the taper and varying step/chord% have a negative affect?

3 will it benefit from end plates?

4 Does anyone know how much weight servo extensions will add? I can skip them and move servos in, but, this will put the horns at the inboard end, and ails will likely twist.

Thanks for your opinions.

Pat
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Old Dec 01, 2010, 08:20 AM
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Fairplay, South Park, CO
Joined Sep 2005
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Pat,

You asked a few specific questions:

2, will the taper and varying step/chord% have a negative affect?

I typically like to have the step at about 50% of chord in the wing's center, and at no more than 50% of chord at the wing tips; on many builds these days, I prefer to taper the step back to 40% of chord at the wing tips... (It will fly as you have it, but maybe not quite as well as it could.) I am also of the opinion that reducing the height of the step as it approaches the wing tips does reduce drag, and I think that's what you said that you did; if so, that will possibly work better than a taller step at 50% of chord at the wing tips. (You could always add a bit of an upper layer extension at the center of the wing to bring it back to 50% of chord in that area if you want.)

3 will it benefit from end plates?

Definitely! I would suggest that you make them to extend at least 9/16" to 5/8" above and below the wing surface from about 30% of chord on back to just ~1/4" past the trailing edge. You can taper the contour down from the 30% point forward to the leading edge. (I've included the first photo below as an example.)

4 Does anyone know how much weight servo extensions will add? I can skip them and move servos in, but, this will put the horns at the inboard end, and ails will likely twist.

One trick you can use to stiffen foam ailerons is to iron on a full layer of low temp covering material around the entire aileron. This will give it enough twist resistance for the flight loads of a lightweight foamie aircraft. (I've also used tapered balsa aileron stock on some of my longer wing builds, in place of the foam.)

Aileron differential is useful on a wing like this to minimize adverse yaw... you want more up travel than down travel. I've found that using a single center-mounted servo, with the linkages angling out to the inner ends of the ailerons can result in a nice amount of differential. (You can get an idea of what I'm talking about in the first photo below.)

The second photo below demonstrates something else you can do to improve the performance of your wing: Shaping the leading edge. This is done to end up with the entry point of the leading edge at from 24% to 30% of the airfoil's total thickness. I sometimes carve & sand away excess foam, then use a covering iron the finish heat-forming the sanded foam. This heat forming actually firms and 'tempers' the foam nicely. The result is a wing which flies better and glides better with a bit less drag.

The DANCER discussion thread has more of the 'why this works' type of discussions, so I won't go into more here. I hope these suggestions help- good luck with your project!

VIKING
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Old Dec 01, 2010, 05:19 PM
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Thanks Viking, i was hoping you would opine.

Actually the step filler is the cf tube spar. so the step height is constant. But what do you think of this option. I re-cut the step with a taper like you recommend, and move the tube forward a quarter inch or so. the spar will remain straight across while the step will taper from 50% at the fuse and taper out to say 45% or so at the 6.5" tips. Since the spar tube is moved forward, the step in the center would extend past the spar probably 3/8th of an inch. This would leave some of the step unsupported, I could add some foam tapered shims if the blank space is a problem aerodynamically. And by extending past the spar, the step is taller in the middle and by virtue of the taper, it is lower out near the tips because there it stops at the spar and goes no further aft.

On end plates, good ty, thats what I wanted was some known successful dimensions. I had a feeling they help... but not if you make them the wrong shape or size.

Ail flex, check..... differential, check. I used a single servo on the kfm3 last week, we are still tweeking that. It has some adverse yaw. Even with 5/8" up and 1/4" down. That is why I wanted to do 2 servos on separate channels so I can just adjust differential and rates (if needed jack) in the mix of the programable radio.! Should be fun to play with and get a good grip on what works and what does not. Logic would tell me that I should have done the dual servo one first, then I would have know the geometry for the fixed single servo later... oh well live and learn the hard way for me.!

Leading edge shaping. This is where I was a little confused. I mean I know, I think, what your refering to, but just giving a % of thickness leaves too much to my imagination. Can you show me a shape? You meant carve it down to a point right?

And this point, would it be symetrical from the center? or remain as flat as possible on the bottom? Also, you showed a pic of a wing that has a 3 to 4" radius cut on the l.e. outer corners, did you mean for me to do this also??

I like that you mentioned 'tempering' the foam with heat, because it was noticeable, the difference between cutting the fff pieces with my hot wire, and with a razor blade. Especially the control surfaces. A hot wire cut aileron is stiffer than the same one cut with a knife, the heat forms a crust if you will along the edge. Someone teased me for taking the time to cut foamy pieces on a hot wire, till I handed them 2 strips, one knife cut and one blade cut. It was obvious.


Gotta get cutting. and gluing hopefully.

Pat.
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Old Dec 01, 2010, 07:51 PM
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Fairplay, South Park, CO
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Pat wrote: Thanks Viking, i was hoping you would opine.

Actually the step filler is the cf tube spar. so the step height is constant. But what do you think of this option. I re-cut the step with a taper like you recommend, and move the tube forward a quarter inch or so. the spar will remain straight across while the step will taper from 50% at the fuse and taper out to say 45% or so at the 6.5" tips. Since the spar tube is moved forward, the step in the center would extend past the spar probably 3/8th of an inch. This would leave some of the step unsupported, I could add some foam tapered shims if the blank space is a problem aerodynamically. And by extending past the spar, the step is taller in the middle and by virtue of the taper, it is lower out near the tips because there it stops at the spar and goes no further aft.

Sounds like that approach should work well.

On end plates, good ty, thats what I wanted was some known successful dimensions. I had a feeling they help... but not if you make them the wrong shape or size.


Ail flex, check..... differential, check. I used a single servo on the kfm3 last week, we are still tweeking that. It has some adverse yaw. Even with 5/8" up and 1/4" down. That is why I wanted to do 2 servos on separate channels so I can just adjust differential and rates (if needed jack) in the mix of the programmable radio.! Should be fun to play with and get a good grip on what works and what does not. Logic would tell me that I should have done the dual servo one first, then I would have know the geometry for the fixed single servo later... oh well live and learn the hard way for me.!

Leading edge shaping. This is where I was a little confused. I mean I know, I think, what your referring to, but just giving a % of thickness leaves too much to my imagination. Can you show me a shape? You meant carve it down to a point right?

And this point, would it be symmetrical from the center? or remain as flat as possible on the bottom? Also, you showed a pic of a wing that has a 3 to 4" radius cut on the l.e. outer corners, did you mean for me to do this also??

The previous photo just happened to be one I pulled from my one of my DANCER wings that shows some of the leading edge- (forget my wing tips for now.)

The idea is to not make a sharp leading edge (which can become overly pitch sensitive) but to lower the entry pointof the airfoil... not symmetrical, but rounded down from the upper surface quite a bit, & rounded up from the underside too, resulting in what's referred to as more of a 'Phillips Entry'. Below is a drawing of a 9% thick KFm3 from the earlier DANCER wing that I pulled out of my archives, based on the RG15 airfoil profile. Maybe this will help to show what I'm talking about in dropping the entry point of the leading edge, and thereby creating a bit of 'camber' to the wing.

The "Camber Line" is an imaginary line half way between the wing's upper and lower surfaces... behind the top KF step, there's another invisible line, the 'virtual upper airfoil surface', which is the boundary layer between the the trapped recirculating vortex and the air that flows past over it.

I like that you mentioned 'tempering' the foam with heat, because it was noticeable, the difference between cutting the fff pieces with my hot wire, and with a razor blade. Especially the control surfaces. A hot wire cut aileron is stiffer than the same one cut with a knife, the heat forms a crust if you will along the edge. Someone teased me for taking the time to cut foamy pieces on a hot wire, till I handed them 2 strips, one knife cut and one blade cut. It was obvious.

I'm a big fan and advocate of heat-forming & tempering... using those techniques, you can transform a marginally structural foam material into a very good structural member for the size & weight we're dealing with. I'm also a big fan of Carbon Fiber rods & tubes, as they offer so much structural strength at so little weight... and in my thinking, that's 'getting a lot of bang for your buck', too!

VIKING
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Old Dec 01, 2010, 09:45 PM
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Thanks Viking, my wood dowel is right there on the inside where the step piece joins the main piece. But I will try to get a better shape that resembles that one. If I gorilla glue the dowel and 2 pieces, I should be able to sand as one.

My overhang, that is, the part of the step that hangs past the spacer in the middle, like above the fuse, is 1" It decreases as you move out toward tips. Do I need to fill this or can I leave it open? Might it affect lift? Maybe a narrow strip of tape, that goes straight down vertical from the back of the step to the top surface of the main wing.?

I'm happy with how the new tapered step looks. Thanks for the advise on that. I ended up with 43% from LE at the tips and 50% at the root. And the step height at the root is a little less than 1/8" taller than at the tip.

P.
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Old Dec 01, 2010, 10:12 PM
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Fairplay, South Park, CO
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Quote:
Originally Posted by wheelspinner20 View Post
Thanks Viking, my wood dowel is right there on the inside where the step piece joins the main piece. But I will try to get a better shape that resembles that one. If I gorilla glue the dowel and 2 pieces, I should be able to sand as one.

My overhang, that is, the part of the step that hangs past the spacer in the middle, like above the fuse, is 1" It decreases as you move out toward tips. Do I need to fill this or can I leave it open? Might it affect lift? Maybe a narrow strip of tape, that goes straight down vertical from the back of the step to the top surface of the main wing.?

I'm happy with how the new tapered step looks. Thanks for the advise on that. I ended up with 43% from LE at the tips and 50% at the root. And the step height at the root is a little less than 1/8" taller than at the tip.

P.
Pat,

Others have tried the 'overhang' on some designs, but I have not... My impression is that it can not really enhance the trapping of the recirculating vortex behind the step, and that it might possibly increase the drag by a bit. It would be interesting to fly it first with the overhang open, then cover it with the tape later to see if you can detect a difference.

VIKING
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Old Dec 02, 2010, 03:51 AM
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Ashford. Kent. England
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Nice videos steve... you in your shorts and sunshine whilst I an indoors watching my car gradually get buried under the snow... its ******* cold outside... and flying is definitely not on for today...
Next job... make some of Vikings skis
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