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Old Nov 26, 2012, 10:18 PM
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I don't know canard from barnyard

The lack of leverage in the vertical stab's (as measured by the distance from the cg backwards to them) just seems like the canard wouldn't want to point the nose into the wind. The side area forward of the cg would seem to overwhelm the vert'l stab. I could see it working at high speeds, but not at the relatively slow speeds of some slope flying.
I have plenty of experience with slope flying, just haven't seen any canards, except for the Astro Blaster (it's fins were out at the tips, and farther behind than the Shinden)
Belly landing can be tough on canards, too. I remember repairing them even after decent landings.
Your bottom line does suggest some inherent yaw instability.
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Old Nov 26, 2012, 10:24 PM
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If there is not enough fin area, speed isn't likely to help.
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Old Nov 27, 2012, 02:17 AM
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Belly landing can be tough on canards, too. I remember repairing them even after decent landings.
Yes, maybe the Starship would be a good scale slope soaring project? Mine has no landing gear and I've learnt to land it with the canard swept back at the last moment, after a few of those repairs.

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Old Nov 27, 2012, 06:11 AM
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Tick Point
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he lack of leverage in the vertical stab's (as measured by the distance from the cg backwards to them) just seems like the canard wouldn't want to point the nose into the wind. The side area forward of the cg would seem to overwhelm the vert'l stab.
I believe that you are correct on this Tick Point. The Shinden needs a modification or two when you want to shrink it down to a model. As I see it, the canard area is too small and the CG is too far rearward. To correct this, you can add about 20% more length to the fuselage, increase the canard chord to get it's area to 30% of the wing area. The wing area could also stand to be reduced. With a more forward CG and a bit more vertical fin area, the yaw instability should be corrected. If you could raise the canard to a higher position it would help on landings. The model would still look like a Shinden and you would have the fun of making it work. BTW, to assure that the canard stalls first, you could add as much as 3.5 degrees incidence to it.

Conehead Orrin, I have missed you and it was good to hear that you are back.

Charles
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Old Nov 27, 2012, 06:54 AM
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The problem is that by the time you make those changes, it will not look like a Shinden any more. It will look like a plane in a fun-house mirror.

Looking at it with 20/20 hindsight:

Yaw stability is yaw stability. No easy way around it. You might be able to help things by slimming the forward fuselage, but you will have to add more vertical fin area, Adding it to the trailing edge also helps get the area a little further aft, giving a little more moment arm. Every little bit helps. Adding it mostly below the wing will make it less conspicuous.

As far as pitch stability and stall characteristics, a better approach might be to just forget the canard. Treat it as a flying wing, which happens to have an insignificant little "trim tab" on the nose. Put enough washout in the wing that it can stabilize itself, and rig the outboard control surfaces to act as elevons. It might not even be worth the trouble to put an elevator on the canard, just leave it a fixed surface.
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Old Nov 27, 2012, 08:36 AM
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Originally Posted by canard addict View Post
Tick Point


I believe that you are correct on this Tick Point. The Shinden needs a modification or two when you want to shrink it down to a model. As I see it, the canard area is too small and the CG is too far rearward. To correct this, you can add about 20% more length to the fuselage, increase the canard chord to get it's area to 30% of the wing area. The wing area could also stand to be reduced. With a more forward CG and a bit more vertical fin area, the yaw instability should be corrected. If you could raise the canard to a higher position it would help on landings. The model would still look like a Shinden and you would have the fun of making it work. BTW, to assure that the canard stalls first, you could add as much as 3.5 degrees incidence to it.

Conehead Orrin, I have missed you and it was good to hear that you are back.

Charles
I agree. Same with the very similar Curtiss XP-55 Ascender from 1941. They considered it a flying wing with a full flying front elevator. However, when shrunk down to the size of a model, the plane benefits by making it into a canard and grow the front canard larger than stock. So what you end up with is a stand-off scale that actually works rather than a model that is more unstable than the original.

The original XP-55 had terrible low speed handling qualities and if allowed to stall, would be nearly unrecoverable. One of the prototypes ended up falling inverted for 16,000 ft and the pilot couldn't save it, so he bailed out. I would imagine the Shinden might have experienced similar problems, but not sure without reading more about it. Either one would have been a lot more stable if built as a real canard.
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Old Nov 27, 2012, 02:56 PM
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I am willing to stray quite a bit from scale on this Shinden. My avatar is a "black bullet" with a significantly larger wing and it flies great. It looks like it hails from the future!
For the shinden, I could use the same airfoil (MH45) that has the reflex needed. I was planning to do a full flying canard (forewing) instead of an elevator.
The big surprise is that I expect to mount a GoPro in the cowling. I think I need an active forewing for pitch control to handle the added moment from the weight of the camera and tilt/pan I made.
I think I can keep the forewing to scale because if it's too small, I'll be relying more on the elevons for control anyway.
I am willing to increase the wing area by a lot, 80% even. The unique look of a canard, and the added lift of a big wing would make for a good sloper.
I really appreciate all your input. I'll send a photo of the 39" fusey I've already shaped and the tilt/pan camera.
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Old Nov 28, 2012, 12:39 PM
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Tick Point, Please do design your model as you feel it should be done and enjoy your own creation. If we take the inputs of others in a cheerful way and mold their ideas into our way of thinking, then we can come up with lots of good models. I have found that one good model will plant the seed for the next one which can only keep the hobby exciting. Please do continue and send us pictures of what you are doing. My modeling has been delayed for about one week but I look forward to getting back to the table soon.

builderdude, Thank you for the interesting post on the XP-55. The designers may have depended too much on the rear wing.

Charles
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Old Nov 28, 2012, 01:21 PM
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One thing I might caution is to maintain the same wing/stabilizer ratio or even improve on it by increasing stabilizer size. My concern is that if you increase wing area without also increasing stabilizer area to maintain the same ratio, you could end up reducing your plane's stability.

You could build yourself a balsa or depron glider of exactly a scale size of your full-size plane and then use it to determine what it needs to be stable. I built a balsa sheet glider of my XP-55 before building the full-size RC model and incorporated a movable front canard stabilizer, and it glides beautifully. Plus it's a lot cheaper to crash than the full size RC plane would be. Mine required some "up-canard" to glide correctly, which is why I mention making it movable, like with a dowel or something.
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Old Nov 28, 2012, 02:34 PM
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I fly inverted, but I didn't mean to with my camera, oops.

This is a camera plane, disguised as a PSS. My hope is to fly high, not fast, and capture quality video with the setting sun behind me and warbirds pumping half-pipes below, with pilots below them. The cam tilts 45 degrees and pans 30.
Wouldn't an enlarged flying wing (with airfoil MH45) and a somewhat undersized forewing be stable? Apparently sizing the forewing is much more important for a canard than sizing a conventional rear tail.
What happens if you add a forewing to a Zagi? That might be my quickest test before I commit to fiberglassing, or, just build it and see.
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Old Nov 28, 2012, 03:26 PM
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Why the obsession with adding a canard? Flying wings, if properly designed, are adequately stable, both statically and dynamically. Aft-tails, properly designed, are also stable, both statically and dynamically, and the design work required to achieve that is fairly simple.

Canard aircraft can be statically and dynamically stable, but the design and development effort required to achieve that is somewhat more difficult and elaborate than achieving the same thing with an aft tail. In particular, the stall characteristics of the canard need to be carefully tuned so that the canard ALWAYS stalls before the wing. Simply setting the canard at a higher incidence angle than the wing will NOT guarantee this, and precisely predicting the exact stall characteristics of a flying surface, especially a small one, is difficult and uncertain at best. Also, the compromises needed to achieve that plus static stability almost always results in a loss of aircraft efficiency.
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Old Nov 28, 2012, 04:29 PM
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I want to shoot my camera out the back without a conventional tail getting in the way. If I use a flying wing with the camera in the back (and add nose weight), I'm concerned that the wing loses pitch stability with that weight fore and aft. I figured a canard would add pitch control.
Now that I'm hearing how critical size is for the forewing....hmmm.
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Old Nov 28, 2012, 04:39 PM
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I may make the main wing enormously out of scale (with elevon), the forewing to scale, and later enlarge the forewing if it lacks pitch control.

A large flying wing may be the easiest solution, just not as cool.
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Old Nov 28, 2012, 04:43 PM
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What's the difference between statically and dynamically? Aren't flying things always in a dynamic state?
Statically is just flying straight and Dynamically is a change in direction?
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Old Nov 28, 2012, 05:06 PM
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Good, interesting stuff.

Here's a flying wing with a detachable canard.. The first time I flew it, the wing started to lift before the canard, that's even more destructive than when the canard stalls first.

It features in this video, if you have the patience to wait a couple of minutes...
Canards Taking off.wmv (3 min 54 sec)
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