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Old Mar 06, 2011, 05:54 AM
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Yes, John, The Duck spins better with the larger wing. At first it did a nose down tail spin but after moving the battery rearward by 3/4 inch, the flat spin worked really well. It is different from Duck 1 because it required no right aileron for a full left rudder spin. So far I have tried full left rudder and full up elevator with moderate throttle. The spin is rather floaty with very low descent rate. The landings are gentle but with positive nose up stability for three points. With less canard influence, incidence and motor down thrust, it flies fast without climb, flies inverted with less forward stick and with better visibility it meets all demands that I was hoping for. Maybe a video later if my man is for it.
Charles, Thats great news! It sure sounds like you have it sorted. From what you wrote it sounds like the symmetrical airfoil on the canard is working well for you - especially for inverted flight. I know you moved the CG further back for the Duck 2. That unloads the canard wing slightly, but I was wondering if that would translate into a noticably lower stall speed.

I am really looking forard to the video. I think you will have a challenge to put on a better show than the video of the first Duck. I hope you don't mind me reposting it here, because I think its really good viewing.

Canard Addict's Delta Duck (2 min 6 sec)
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Old Mar 08, 2011, 05:36 PM
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John 235
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Charles, Thats great news! It sure sounds like you have it sorted. From what you wrote it sounds like the symmetrical airfoil on the canard is working well for you - especially for inverted flight. I know you moved the CG further back for the Duck 2. That unloads the canard wing slightly, but I was wondering if that would translate into a noticably lower stall speed.

I am really looking forard to the video. I think you will have a challenge to put on a better show than the video of the first Duck. I hope you don't mind me reposting it here, because I think its really good viewing.
John, Sorry for the slow response. I appreciate your interest and challenging questions. It was fun to see the video again and I have contacted the same gentleman to see if he will do a rerun. I was sold on the high lift flat bottom airfoils for years and noted their stall characteristics and inability to do things such as inverted flight and outside loops. The symmetrical airfoils seem so smooth for models that it makes me wonder what purpose that anything in between the two styles would serve. I want to stay with the tear drop style a bit longer just for fun. The speed of the model can be adjusted with drag from thin to thick versions. Regarding the performance with fore vs aft CG, I found that with forward CG the nose of the Duck wanted to droop which could not be fixed well with UP trim. The landings were hard to the point of bending the landing gears. I feared that the canard area should have been increased but by moving the CG back by only 3/4 inch, the model turned into a delightful floater with great flight characteristics. I think of the Duck as a large equilateral delta which includes both wings. The stall is really not well defined but with nose high, it turns into a mush with added lift from turbulence for smooth landings. At present, I am toying with the thought of making a twin motor taildragger with swept back in-line wings similar to the Georgia Goose with a prominent rudder and no horizontal tail. What do you all think it should look like?
Charles
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Old Mar 10, 2011, 12:54 AM
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Check the canard action out on this Russian jet.
Charles


http://www.virtualaces.net/phpBB3/vi...php?f=2&t=3466
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Old Mar 10, 2011, 06:01 AM
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John 235
John, Sorry for the slow response. I appreciate your interest and challenging questions. It was fun to see the video again and I have contacted the same gentleman to see if he will do a rerun. I was sold on the high lift flat bottom airfoils for years and noted their stall characteristics and inability to do things such as inverted flight and outside loops. The symmetrical airfoils seem so smooth for models that it makes me wonder what purpose that anything in between the two styles would serve.
From your comments, the Duck 2 sounds like a very enjoyable flyer. I can't wait to see the video. The gent who shot the first video certainly did a great job of it.

I think the symmetrical airfoil is perfect for the Duck style model because of the low aspect ratio main wing. Low aspect ratio makes it harder to stall the main wing, so you are less likely to come into issues with the stall characteristics of the symmetrical airfoil. If you increase the aspect ratio of the main wing with all else being equal you will push the main wing towards the AoA where it will stall. That is the reason why I expected the 36" span Duck 2 to spin more easily than the 30" version.

Applying the same reasoning to a symmetrical airfoil on the George Goose style model without other changes might suggest the possibility of problematic stall characteristics. So I think this is one case where it might be good to compromise between the fully symmetrical and flat bottomed airfoils. A semi-symmetrical airfoil, eg. NACA2412 as shown in several examples from Andy Lennons book might be one to consider. Not really a compromise, but the best of both worlds perhaps?

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At present, I am toying with the thought of making a twin motor taildragger with swept back in-line wings similar to the Georgia Goose with a prominent rudder and no horizontal tail. What do you all think it should look like?
Charles
Should I visualise something like this? Or maybe you would prefer to use a longer tail moment.
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Old Mar 10, 2011, 11:59 AM
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CA and John 235
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Quote:
Originally Posted by canard addict
At present, I am toying with the thought of making a twin motor taildragger with swept back in-line wings similar to the Georgia Goose with a prominent rudder and no horizontal tail. What do you all think it should look like?
Charles

Should I visualise something like this? Or maybe you would prefer to use a longer tail moment.
That beautiful model must have been lurking in my subconscious mind all along because my preliminary sketches are very close to it except for a different cockpit and tail dragger LG. Also both wings will be swept back with straight trailing edges. Regarding airfoils, there has been success in using identical ones front and rear as Lennon did on his Canada Goose. After looking them over in his book, it seems that a symmetrical one up front with it's abrupt stall at about alpha 10 and one similar to the Eppler 197 for the rear with it's gentle loss of lift would be good as shown on page 6 figure 5. BTW, Lennon used 3.5 degrees AOA on the canard wing to assure it would stall first.

So far there has not been a response from the video photographer but it may be a good while before we can depend on the weather.
Charles
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Old Mar 10, 2011, 12:56 PM
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...BTW, Lennon used 3.5 degrees AOA on the canard wing to assure it would stall first...
As we have discussed here before, simply setting the incidence of the canard at 3.5 degrees, without also taking into account the other parameters involved, will NOT guarantee that the canard stalls first. You have to take the entire combination into account, not just one parameter.
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Old Mar 11, 2011, 07:59 AM
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Don, with this canard incidence business, I think what happens is that we usually set our C/G to give us a static margin of 10%. Then, with the canard area at about 20% of the main wing and the airfoils we commonly use, we find that the flying trim ends up with the canard incidence (both stabiliser and elevator together) at somewhere from 2 -4 degrees.

This suggests that we have correctly loaded the canard to carry more than its fair share of the weight and we have been getting good flying results across a range of designs. Given that we often commit to the relative incidences at an early stage in the build, it seems to me a good idea to anticipate this setting, knowing that we can fine tune it in flight. The aim being to get the trim setting with the least elevator deflection and without altering the static margin.

Here's another discussion that's cropped up in an aeromodelling magazine between serious academics in your field. They're arguing about whether it's Bernoulli or Newton who explains why planes fly. Bernoulli says the pressure difference between top and bottom of the wing is caused by the speed of airflow. Newton says it's the change in momentum caused by deflecting the air. My guess is that it's a bit of each and possibly more of the latter. On the other hand, Newton came first, so somebody must have thought that Bernoulli could explain something that Newton could not.

What do you think, and does it matter?

Cheers

Nick
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Old Mar 11, 2011, 09:20 AM
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I've covered this quite a few times in a variety of forums, including recently.

There is no conflict between them.

A wing makes lift by grabbing chunks of air and shoving them downwards.

Bernoulli explains how the wing can grab hold of something as insubstantial as air, in order for it to do that shoving.

The whole Bernoulli-vs-Newton argument makes about as much sense as arguing about which is the source of a wing spar's strength, the spar caps, or the glue that holds them to the shear webs. Neither is much good without the other.
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Old Mar 11, 2011, 09:26 AM
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For more on this (a LOT more), you might take a look at this:

http://www.rcgroups.com/forums/showt...oo+big&page=24

There are also some subsequent discussions on the following page that you might find useful.
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Old Mar 11, 2011, 05:28 PM
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Don:
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Neither is much good without the other.
So, I was right, Newton does not provide all the answers. And the guy who wrote this to the RCME magazine, criticising the article by Prof.David Burton is mistaken...
Quote:
As a practicing aerospace engineer.... with degrees in aerospace engineering and computational fluid dynamics, I am very familiar with the physics of flight.. etc,etc The phenomenon that results in lift is simply momentum. Air has mass and when accelerated it has momentum.
It aint that simple. His name is Harold Peeling.

Cheers

Nick
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Old Mar 11, 2011, 07:29 PM
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Depending on your point of view, both could be construed as correct, in at least a narrow, limited sense. It IS Newton that makes the lift. However, in this specific case it is Bernoulli that makes Newton possible.
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Old Mar 13, 2011, 08:37 PM
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Canard RC Plane Flying Through a Rainbow

RC Plane Flying Through a Rainbow (2 min 18 sec)
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Old Mar 14, 2011, 04:59 PM
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Thank you, budkeywest, a good job with the camera and the transmitter!
That was a great flying canard. Can you give us a little data on it?
Charles
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Old Mar 20, 2011, 10:58 PM
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Hi guys!
I'm working on a new design with a canard. On Charles' Egret, is the nose rudder steerable? I'm considering doing something similar in order to avoid using separate servos for rudder and nose wheel because the there is no direct route between the vert stab and nose.

Thanks for the help!

Paul
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Old Mar 21, 2011, 07:33 PM
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Idriveaboxter Paul
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Hi guys!
I'm working on a new design with a canard. On Charles' Egret, is the nose rudder steerable? I'm considering doing something similar in order to avoid using separate servos for rudder and nose wheel because the there is no direct route between the vert stab and nose.
Yes, Paul, The steerable nose gear is just extended up about 2-3/4 inches so that when the nose gear moves the rudder moves with it. The wire is 3/32 inch spring steel with a single coil below the steering arm which is a Carl Goldberg part. The wire was easily bent in a vise. The rudder measures 3 by 2 or 6 sq. inches. At first it was a triangle of half the size but did not work.
I can now do turns with level wings and a knife edge as long as the model turns a bit on elevator. I will attach a picture of the Egret and will be happy to supply any further information.There may be pictures of the Egret build. Just go to the last sentence of post no. one for a reference to an index post.
Charles
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