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Old Jun 21, 2010, 06:27 AM
Flutter-Bys are fun
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nickchud,
Oh my, what a fun video to see. The water portion is really funny.
You really got stuck in the weeds.
Nice flying Long EZ with floats. Now that was very interesting to watch. When you sneezed and the camera didn't show the airplane, I wondered what would happen. Thanks for the show.
Conehead
Orrin Eldred
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Old Jun 21, 2010, 08:59 AM
What could possibly go wrong?
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Thanks for that Orrin!n I enjoyed it.

It was the photographer, not the pilot who sneezed! Luckily!

I've looked more closely at that crash landing. I think I cleared the weeds and caught the tip of the starboard float in the grass. Once again, my old problem of understimating the speed needed to keep the nose up. Made worse by flying with the C/G too far forward. Also made worse because I had intentionally left the piano wire at the front of the floats unbraced. I was hoping to settle on an optimum height after testing at speed on water. Also made worse by landing a little bit skew on uneven ground. No harm done.

That's the trouble with a Suck-It-And-See approach!

Nick, the slow learner.
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Old Jun 21, 2010, 01:50 PM
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Quote:
Originally Posted by mullinspsm View Post
I wouldn't think the canard would carry 1/2 the weight....maybe 30-35%. But since both surfaces are lifting they do contribute to effeciency. ...
I was looking at where the major masses are distributed in the airframe. Unless they're planning to put a lot of lead in the tail, the C/G is going to end up roughly halfway between the canard and the wing. That means the canard will be carrying half the weight, on a far smaller span and area. That means that less lift will be made by the larger, more efficient surface, and more will be made by the smaller, less efficient surface. That means that the total efficiency will have to go down.

I looked at their website and read some of their design rationale. They made appearance a primary design requirement, to the point of using it as the deciding factor in major decisions.

They also completely ignored propeller issues when they chose to use a pusher layout, basing the entire decision on the idea that getting the airframe out of the slipstream will save drag. In actual practice, only a few percent or less of airframe profile drag (and only about half that percentage of the plane's total drag) is influenced by the propeller slipstream, while 100% of the plane's thrust is influenced by the negative effects of airframe flow distortions and turbulence on propeller efficiency. The net result almost without exception ends up being a classic example of the expression "penny wise and pound foolish". You cannot throw away literally 10 to 20 percent of your propeller efficiency and then hope to gain it all back with an improvement of just one or two percent in the airframe efficiency.

As far as efficiency being helped by both surfaces lifting upwards, that doesn't hold up to scrutiny either. There will be strong downwash from that heavily loaded canard, which means the wing's middle portion (where it makes most of its lift) is constantly flying inside a downdraft created by the canard. This distorts the wing's lift distribution, increasing its induced drag, in addition to the detriment due to the downwash itself. The lift distortion can be compensated for in a narrow region of flight conditions by adjusting the wing twist, but then the lift distribution will be off of optimum at all other operating conditions, and there will still be the direct negative effects of the downwash at all flight conditions, even with adjusted wing twist.
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Old Jun 21, 2010, 03:50 PM
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Nick, That film was a movie adventure which was very entertaining. Maybe you missed your call and bypassed millions ha ha? You are also a fine looking energetic star! I can tell that your dog works with you and seems to enjoy your attention.

Don, How could Flight Science improve that design? They have the canard lower than the wing, have enlarged the area and moved it rearward which is what seemed to be needed by looking at the skinny original canard. I would guess that a lot depends on the speed.
Charles
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Old Jun 21, 2010, 07:15 PM
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Short answer: Put the canard behind the wing, and the prop on the front.

Longer answer: Make the canard much bigger, so that its size is closer to the size of the main wing, enough that its area loading and span loading is still higher than the wing's, but not by so much. Move it forward, not aft. Alternative is to move the C/G aft, but that raises other issues. Their three-surface arrangement that's shown as a preliminary concept on their website would probably be an improvement. Find a way to get a lot more moment arm for the vertical fins. Spend a LOT of effort on cleaning up the airflow into the prop.

Vertical location of the canard relative to the wing is not a big driver. The downwash field of the canard is roughly as high as its span, so unless the vertical separation is really large, the wing will still be flying through the canard's downwash.

Having the aft flying surface flying in the downwash of the forward surface is detrimental for a canard layout. It's actually beneficial for a conventional layout. For a given amount of static stability, the net induced drag ends up being about the same for the two arrangements, despite the canard lifting upwards and the aft tail lifting downwards.
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Old Jun 21, 2010, 10:38 PM
who has rabbit ears down
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Not to mention the areas alone are puny- too much Final Fantasy Art!
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Old Jun 22, 2010, 06:54 AM
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Don,

What is your experience with the Vari Viggen? It had the canard a lot higher than the main wing, which has a low wing placement. How did the canard interference influence the main wing. The Vari Viggen flew good as I understand.

Roger
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Old Jun 22, 2010, 07:31 AM
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I don't have any direct experience with the VariViggen, but I do have a partially completed full-scale VariEze out in the barn, I have been involved with a number of Rutan canards over the years including Voyager and the Starship, and I have some indirect knowledge of the VariViggen just from studying the Eze's, which are descendents of it.

Anything will fly if you put a big enough motor on it. The question isn't whether it flies "good" or "not good". The appropriate question is whether it would fly better if "this" or "that" were changed. Does the configuration of a specific feature, in combination with the rest of the plane, result in better overall mission performance?

As far as moving the canard up (VariViggen) or down (Quickie), the amounts of position change are not enough to get the wing clear of the canard's downwash field either way. The downwash field is a lot bigger than most folks realize.

The best way to maximize the efficiency of a canard layout is to make the canard as small as possible, which means also putting it on the longest possible moment arm in order to keep the same volume coefficient. The long moment arm also maximizes dynamic stability, which is linear with canard area, but proportional to the square of the moment arm.

For example, one of the canards I'm working on now uses a canard that is only 16% of the area of the wing, but on a very long moment arm. Static and dynamic stability are excellent, but the vast majority of the plane's weight is supported by the wing (the most efficient lift producer on the aircraft), and the detrimental effects on the wing of the little canard's airflow are minimal, all of which keeps the aircraft's overall efficiency high.
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Old Jun 23, 2010, 12:05 PM
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Delta Duck Build Log

The Delta Duck will be built here with the progress to be shown between our regular posts. Please continue to introduce your projects and comments as usual. Since the Delta Duck has not evolved from my proven designs, it's performance cannot be predicted by me. Unlike the D Squared, it will have symmetrical airfoils with the rear wing being much larger to do most of the flying. It will have elevon controls rear with simultaneous elevator up front for assistance. A rather large rudder will be well to the rear of the CG to provide stability and yaw control. With the CG back about 35% from the nose and well into the main wing, I expect the model to fly like a full delta with front elevator control. If the front wing stalls, it should not be a problem especially with tractor power. The tail dragger configuration with rudder will be a refreshing change with three point landings a possibility. The thrust line runs between the two wings with the main wing at zero to it and the front wing at plus 0.5 degrees. There will be no side or down thrust. The model glider performs well with it's CG very close to that of the Canard CG calculator. As the build continues, the motor and battery sizes will be decided for balancing. The battery hatch will be placed behind the front wing.
Charles
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Old Jun 25, 2010, 11:24 AM
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Delta Duck Front Wing

The Duck will carry the Spectrum AR 500 receiver which will respond to the DX-7 transmitter set on the Delta configuration. The Hitec 45-HB servos will operate the front elevators while Hitec 82-MG's handle the elevons on the main wing. The 1/16" top sheeting of the front wing provides a mounting surface for the servos to be glued to. After setting the DX-7 to DELTA and connecting the servos as shown in the manual, I was pleased that no adjustments to the transmitter were necessary.

It would be gratifying to receive any comments you may have on this project if for no other reason than to say you are watching it. At present, both wings have finished drawings. The fuselage and rudder have outlines only. Balancing the model without adding dead weight will influence the design.
Charles
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Last edited by canard addict; Jun 26, 2010 at 11:26 AM. Reason: Wiring Diagram incorrect removed
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Old Jun 25, 2010, 05:47 PM
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Here is some video of my latest canard.
"The Blade" First Flight of an Electric Canard Aircraft (8 min 21 sec)
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Old Jun 25, 2010, 06:52 PM
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Great maiden flight, Joel, you have a super performing canard on first try. With those puffy clouds around, I'm surprised that a thermal did not grab it away. Your site is informative and impressive here!

http://www.electricflights.com/planes.html

Have you considered a balsa and film covered canard? I believe you would love it.
Charles
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Old Jun 25, 2010, 08:24 PM
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Hi Charles, I'm watching your progress. The construction looks solid and straightforward like I'd expect of your project. One comment I have is about the connection diagram. It is confusing me because it gives the impression that 3 servos are wired to 2 channels on the receiver. Wouldn't you need three independant channels to control the canard elevator together with the elevons?
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Old Jun 25, 2010, 08:25 PM
Visitor from Reality
United States, VA, Arlington
Joined Dec 1996
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Hi Charles
DD looks like an interesting project indeed.

Love the simultaneous progression of plan and model - I tend to the other end of the spectrum and have to constantly remind myself that I don't have to completely lable the plan to aid the builder...

How your delta mainplane, close coupled canard and forward motor interact is going to be interesting also. Fingers crossed that it's in a good way.

Joel - fascinating model, ideal 'park flier' if ever there was.

Regards

Dereck
Who might actually be getting a new workshop (and the attendant condo ) next month...
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Old Jun 25, 2010, 10:43 PM
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John and Dereck, I am thrilled that two of the RC world's best are checking my work!!

John 235
Quote:
Hi Charles, I'm watching your progress. The construction looks solid and straightforward like I'd expect of your project. One comment I have is about the connection diagram. It is confusing me because it gives the impression that 3 servos are wired to 2 channels on the receiver. Wouldn't you need three independant channels to control the canard elevator together with the elevons?
When the elevator control is moved fore and aft, the elevators and elevons work together perfectly. When the control is moved side to side, the elevons work as ailerons but I am not really sure if the front wing's elevators remain in neutral since I was watching servos with the round wheels attached. Great observation, John. Tomorrow I will re-connect it all and check.

Dereck
Quote:
Love the simultaneous progression of plan and model - I tend to the other end of the spectrum and have to constantly remind myself that I don't have to completely lable the plan to aid the builder...
One thing that I dearly love about designing is that I can use a pencil and eraser to express ideas as they happen. It is a form of freedom to me.

Dereck
Quote:
How your delta mainplane, close coupled canard and forward motor interact is going to be interesting also. Fingers crossed that it's in a good way.
I picture the model as an overall Delta from the top view with the front raised for decalage and elevator control and not for canard action. The 1/2 degree incidence up front is just to give the main wing incentive to lift. I hope that makes sense. I do not like to trim the elevators for a good glide.

A new shop sounds exciting! I wish mine was a bit larger.

Charles
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