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Old May 14, 2011, 05:55 PM
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Twin Duck design points

John 235 and all:

The model was visualized as a next step forward in my quest for canards.
Like the British Miles bomber, I wanted a twin powered unit which had the motors positioned at the CG to avoid extra ballast. Other goals were:

1: Pleasing appearance
2: A taildragger for fun landings
3: CG at the center of the fuselage
4: A canard sized to hold the nose high on landings with adequate leverage
over the main wing.
If the goals are met, the landing gear may be stable on the take off run without ground looping. This is up for discussion.

For a pleasing appearance the nose had to be shortened which IMO might
jeopardize stability by losing canard effectiveness and risk rocking and/or tail wagging.

To position the CG at the center, The wing area was reduced, the canard area was increased an it was moved forward.

John 235
Quote:
I want to say that I can't get used to the look of the large size canard on your Duck Twin. I am still curious about the reason you deviated from your previous 'rule of thumb' for 30 - 35% canard size relative to the main wing area. I'd expect to loose efficiency due to the larger canard, although maybe that's not a priority for this design. The glide ratio may be a bit like a biplane if you know what I mean.
The large canard will carry it's share of the load based on it's area. It is at 51.6% of the main wing and has 1/7 more leverage than the wing does.
As mentioned before, due to the airfoils and incidence angles,it should stall before the main wing. The chuck glider has a gentle stall when thrown hard
and slightly up. It turns into a floater quickly with small amounts of nose weight removed.
The 30% canard area was used as advised in Lennon's book for the Georgia Goose style long nosed model. I promoted it to give others a starting point for getting a design into the air.
As for efficiency, it seems that both wings will hold the plane up well but the main wing can never be fully loaded as you know.

More thoughts are welcomed.

Charles
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Old May 15, 2011, 03:54 PM
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Andy Lennon's 'Canada Goose'

I was bundling old magazines, and came across this construction article that you'uns may find of interest.

Canada Goose MAN Jan1981

Andy Lennon's classic canard, the 'Canada Goose' - basis, I believe, for Charles' 'Georgia Goose'. From the January 1981 issue of Model Airplane News.
;-)
PJ
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Old May 15, 2011, 05:53 PM
nickeast
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pjwright

Do you have a copy of MAN Nov 1969? I'm looking for a glider called "NAUGE"...
Can't find the plans, but I think they were in that issue.... Any help is greatly appreciated.

Nick
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Old May 15, 2011, 06:30 PM
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Nick, I remember that airplane, in fact I made a little indoor FF "bedroom glider" (gliders I flew in my bedroom) of it. It was the "Nuage" (as in "new age"), not "Nauge". That may be why you couldn't find it.

The designer apparently failed high school physics, he was convinced he could turn into the wind while pulling up sharply, and use that trick repeatedly to gain altitude. I guess he also believed in perpetual motion.

However, the glider flew fine, or at least my little model of the model did. Those first thirteen bedroom gliders were the "first generation", and an aerodynamic puzzle posed by two of them showed me one of the clues to figuring out how to get good performance at low Reynolds numbers. The "second generation" bedroom gliders confirmed that theory, and later on I learned the airfoil theory that explained why. That eventually formed the basis of the original airfoils on our Monarch RCHLG, which lead to the founding of our company, and also a paradigm shift in model sailplane design that continues today in all classes, not just RCHLG. Not too bad for a few scraps of balsa.

I eventually made a mobile of those first thirteen bedroom gliders. We used it as part of the Christmas party decorations for the Soaring Society of Dayton Christmas party (I believe that was in 1969 or '70), hanging in the stairwell of the Engineers' Club in Dayton. The air currents kept the planes moving like they were in a thermal all evening, and folks stood mezmerized watching them the whole time. It became a standard feature of the party for a number of years after that.

Today it hangs in my office at our farm. I've attached a pic. The Nuage is the fairly conventional looking V-tailed one in that group of three off to the right, near the middle.

The two that eventually triggered the revelation for me are at or near the very top.
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Old May 15, 2011, 07:17 PM
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Twin duck comments.

Charles, Your criteria about ground-looping with the tail-dragger landing gear is an interesting one. The COG further forward will help the yaw stability in flight and reduce the potenital of ground looping. I think your concept using a large canard area is an effective way to achieve this.

One alternative I thought about was to change to a 3-surface layout with tail-dragger landing gear. Using a shorter canard moment and a longer tail moment should be workable with tail dragger gear, but it would be a pretty radical departure from your original concept.
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Old May 16, 2011, 05:10 AM
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Sorry, Nick - January 1970 was my oldest edition of MAN.
Have FM going back into the 60's...
:-/
PJ
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Old May 16, 2011, 03:34 PM
nickeast
Stuart,FL
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Don and PJ,

Thanks for the replies... "NAUGE" was a typo... I searched for the file "Nuage, MAN plan #FSP11692" from airage store with no luck... I also built a 60" version from the magazine plan (just took measurements from the plan in the mag) and came up with the 60" version. I used a Cox .049 in it to get up to altitude and after the motor died I was in shape for a great glide. I build the wings from "white foam" that I hot wired and covered with 1/32" balsa. In my 2nd childhood I thought it would be fun to do a "real one"... If anybody has a lead on the mag or plans I would really appreciate the help.

nick
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Old May 21, 2011, 06:01 PM
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Here's Charles' latest creation, watch in HD:
Charles Canard (1 min 52 sec)


..a
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Old May 22, 2011, 02:47 AM
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Wow!

That's fantastic, brilliant!

Congratulations Charles, another triumph.

Nick
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Old May 22, 2011, 11:28 AM
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Andy, Many thanks for the video. The Electric fun fly was held at Fort Payne, Alabama. It is one of the year's best which attracts fine modelers from several States as well as the top brass from SEFF. They give awards for the pilot's choice model which after six years makes for tough competition.

Charles
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Old May 24, 2011, 06:20 AM
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Charles, What a lovely model. The quality of the finish looks flawless in the video - Very impressive!

Very nice flying model too. It looks different from the Mk I duck because of the way it can be slowed down. It shows the effect of the extra 6" of wingspan. This one seems to float a bit on landing whereas the previous one came down in much more 'purposeful' way. It looks like a lot of fun, and no doubt its a bit more relaxing than the Mk I version.

Thanks for the video.
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Old May 24, 2011, 11:16 AM
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John, Thank you. Your remarks just make it all worth while.

John 235
Quote:
Very nice flying model too. It looks different from the Mk I duck because of the way it can be slowed down. It shows the effect of the extra 6" of wingspan. This one seems to float a bit on landing whereas the previous one came down in much more 'purposeful' way. It looks like a lot of fun, and no doubt its a bit more relaxing than the Mk I version.
You are so right! I have not flown Duck 1 since number 2 maidened. Not only did the larger wing and vertical stab help but I simply cannot see the all red profile of Mk1 from far away.

Copies of the Twin Duck's ribs were made onto card stock to trace onto the full sized drawings. The reduced fuselage side view will be shown soon.
My time has been spent recently on home improvements during fair weather.

Charles
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Old May 25, 2011, 03:39 PM
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Twin Duck

Here is a much corrected side view of the Twin Duck. It is at 1/3 of full scale.
The wing span will be at 43 inches as I recall which will be the same as the Egret. It will be easy to carry in the trunk of my sedan.The full sized version
may turn out a bit different after building the wings first.

The ground handling stability is a concern. Can the landing gear be moved further forward without ground looping on fast taxi? I have hopes that the large vertical stabilizer and two wing-lets will hold it steady. I do hate a model which veers on take off run. It seems that conventional types with small rudders, lots of mass behind the CG and which sit with a high angle of attack on the main wing are the worst to ground loop. Any comments?

Charles
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Old May 25, 2011, 05:41 PM
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With that long nose moment, and mains WAAYYY ahead of the C/G, it's gonna be a ground-loopin' fool.

Ground handling has a lot to do with dynamic stability. For example, the Spitfire has small tail surfaces on an unusually long tail moment arm, giving it average static stability but unusually good dynamic stability. Contrary to popular belief, not only is it delightful in the air, but it also has (according to folks like Jeff Ethel, who really knew their stuff about this) some of the best ground handling of any of the WW II taildragger fighters. The ground handling of our Roadkill Series Spitfire is also excellent.

Your airplane is likely to have marginal dynamic stability. More tail area is a very poor substitute for more tail moment arm.

If anything, you need to move the mains aft to about halfway between the C/G and where they are now, maybe more. Even so, the various prop effects on that long nose are likely to make your life, shall we say, "interesting".

Plot the location of the C/G in the side view, accurate in both the longitudinal and vertical directions. Draw a downward line from it, angled forward at least 5 (less ground looping) and not more than 15 (less nose-over tendency) degrees. Put the main wheels on that line, at a location that gives you adequate ground clearance with the plane level.

Make the tailwheel long enough to put the plane at the stall angle when in a 3-point attitude.
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Old May 25, 2011, 11:13 PM
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Charles, I love the new plane! Great work and a beautiful finish!
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