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Old Sep 04, 2012, 06:58 PM
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Don if I may, do the aft undercamber (look like a couple degrees of flaps deployed) airfoils exhibit similar pitch up at stall behavior?
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Old Sep 04, 2012, 09:01 PM
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Originally Posted by captarmour View Post
Don if I may, do the aft undercamber (look like a couple degrees of flaps deployed) airfoils exhibit similar pitch up at stall behavior?
Not necessarily. It's all about the shape of the upper surface. If the stall begins very gradually and progressively, starting at the trailing edge, then you probably won't see a lot of sudden pitch-up. However, if a whole section of the trailing edge lets go all at once, then there will probably be a pitch-up, depending of course on the details of the rest of the plane's design.

One way for that to happen is if a large portion of the rear part of the airfoil is seeing about the same amount of adverse pressure gradient (a grossly oversimplified way to look at that is if that whole portion has about the same slope on the upper surface, i.e.: it's "flat", as I discussed before). When that portion reaches enough angle of attack ("alpha") that the adverse pressure gradient is more than the airflow can overcome, then the flow over that entire portion of the airfoil has to separate before the flow finds a region forward of there with less slope, and less adverse pressure gradient, where it can successfully stay attached.
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Old Sep 05, 2012, 02:23 AM
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Ok understood. Thanks a mil.

I will do some more research on the stalling characteristics of airfoils with flaps deployed.

Cheers
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Old Sep 18, 2012, 06:11 PM
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Originally Posted by canard addict View Post
Don, Thank you for the discussion. Lady Luck must have been with me on the Twin. The canard data is: Symmetrical airfoil, three degrees positive incidence, 8.25 inch center chord, 16 degree LE sweep back and 50% of the main wing's area.

The main wing's data is: Semi-symmetrical airfoil, zero incidence, 9 inch center chord, 12 degree LE sweep back.

At low cruising speed and full UP elevator it gently drops the nose to prevent main wing stall.

It seems that my Delta Duck had two degrees incidence on the canard with front motor and large delta main wing which would mush rather than stall.

Charles
Hello Charles,

Once again I have to admire your delta ducks.

As I may have said before I am using a somewhat similar design to fly in ground effect.

Flying close to the surface at speed I was thinking of a way to climb and descend for wave/obstacle clearance without changing pitch.

If I were to have all moving canards with your planforms, coupled with oversized elevons pivoting in the same direction, so that nose and tail will climb or descend together causing gain/loss in height with little or no pitch change.

Has anyone tried that before? As they say, "...nothing new under the sun."

Regards

David.

Ps I looked at you delta duck # two on YouTube, very nice anymore vids?
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Old Sep 22, 2012, 05:56 PM
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Captamour, please forgive the slow reply since I have been away. Thank you for liking the Ducks. The original version had a 30" span and a video is shown of it on the second flight on the same battery on page 341 , post 5101. The second version had a 36" span with a larger rudder and was more visible with the lighter colors on the side view. It also had a 5 degree down thrust to hold down the rapid climb at speed. I do not see why your idea would not work with proper sizing and throws on the control surfaces. Lowering the canard AOA from 2 to 1 degree may be better. I seems that I gave lots of dimensions of Duck one since Nickchud was building it. It seems that the time frame was late 2010 to mid 2011. I can review data and take pictures if you need more.

Charles
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Old Sep 22, 2012, 06:35 PM
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Delta Duck

Here are the digital drawings I made, copying from the dimensions Charles gave me. It was September 2010. I had a lot of fun with both versions I built but, if you're thinking of GE I'm sure you will have less damage sticking with Charles' original high-mounted canard version.

An excellent design, thoroughly recommended. Post #4466.

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Old Sep 28, 2012, 11:28 AM
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thanks guys,

on my next model i will try the canard and elevons moving in the same direction. in the meantime i am trying to get the same characteristics on my present model as the last one. i made a few changes and it is misbehaving compared to the last, massive phugoid IGE. as they say 'do not trouble trouble' but again without trying we will never know.

im still trying to get my head around why nick's duck with the low mounted canards performed better than the high mounted. was everything else the same? my research indicates for mutual interference the high mounted(probably just a bit lower) makes more lift than the lower position.

charles looking at the width of your fuse if it were scaled up to 22.5 inches wide, which is reasonable width to be comfortable, your wingspan will be 37.5 feet! man o man that would be a low wing loading with all that wing area. i am figuring that as an ultralight something as small as a 15ft wingspan may work. the dyke delta is a 22 ft wingspan.

as a single seater the cockpit may have to be quite a bit farther back, probably mid root chord, to balance the engine.

as far as i remember symmetrical wings do not need much reflex, if any, so with an all moving 'control' canard these wings should work very nice.

some time ago we had a discussion on the all moving canard as regarding stall recovery. recently on my maiden i almost lost it in a gust and overcontrolled by flaring way too high and she just hung there about 5 ft off the ground, so i added power and did a perfect landing. we were amazed at how slow she was flying. the next day i removed the close coupled canard and talk about high speed stall! it seemed that the canard downwash caused the airflow to remain attached to the wing and drastically reduced the slow-flight speed.

charles, this reminds me of the 'mush' you talk about when you describe your landings, she wants to keep flying post stall and remain controllable.

what do you think?

i'll look up the posts, thanks again.

cheers

david.
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Old Oct 01, 2012, 12:04 PM
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David, Captarmour, Thanks for the long post which is packed with thought provoking ideas. I hope that my head will work today as I sit here watching a
very wet situation outside with little hope of getting out all day.

David
Quote:
i'm still trying to get my head around why nick's duck with the low mounted canards performed better than the high mounted. was everything else the same? my research indicates for mutual interference the high mounted(probably just a bit lower) makes more lift than the lower position.
I see no difference in model performance with all positions. Rutan used in line configuration with the great Long EZ.

David
Quote:
some time ago we had a discussion on the all moving canard as regarding stall recovery. recently on my maiden i almost lost it in a gust and over controlled by flaring way too high and she just hung there about 5 ft off the ground, so i added power and did a perfect landing. we were amazed at how slow she was flying. the next day i removed the close coupled canard and talk about high speed stall! it seemed that the canard down wash caused the airflow to remain attached to the wing and drastically reduced the slow-flight speed.
Strip elevators at about 1/4 average chord width are my choice. They seem to work like adding exponential control for smoothness. If costs are ignored, the canard adjustable stabilizer may prove valuable to trim a full scale version.

David
Quote:
charles looking at the width of your fuse if it were scaled up to 22.5 inches wide, which is reasonable width to be comfortable, your wingspan will be 37.5 feet! man o man that would be a low wing loading with all that wing area. i am figuring that as an ultralight something as small as a 15ft wingspan may work. the dyke delta is a 22 ft wingspan.
This makes me wonder if full scale designers consider models before tackling their projects. Rutan did and his accomplishments reflect it. It seems that Don, with his background would have no trouble with full scale design.

David
Quote:
charles, this reminds me of the 'mush' you talk about when you describe your landings, she wants to keep flying post stall and remain controllable.
This was discussed in the thread. It describes the turbulence on top of the wing after stall adding lift.
I'm glad that you like the Duck's design. A full sized version would have to add room in front of the pilot for an engine compartment.

Charles
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Old Oct 01, 2012, 06:32 PM
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David and Charles, hi!

I've been reading back through the posts on this thread in Sept, Oct of 2010. fascinating and very informative stuff, specially from Don, John and Charles.

I definitely did have more success with the low canard, as in the plan below:


Though, I have to confess that things like pilot error, bad luck and strong winds probably contributed to my difficulties with the original high canard version. The field behind my house has many humps, bumps, dips, hedges and trees, which make it unwise to fly on windy days.

Best of luck to you both and congratulations Charles on the on-going success of this thread. See you in Georgia at Christmas time, I hope!

Cheers

Nick

PS I've been searching for a build thread for one of the canard Wright Flyers, 1905/6/7. There are several postings on this thread, eg Galaxiex. But I haven't found a link to a build thread or plans. Any ideas?
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Old Oct 02, 2012, 04:38 AM
Ikaruswannab
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Hi,
I went thru this thread by browsing the pictures that i liked most and reading what ever was written about them as the whole thread is to big to read for a quick question that i have.
I am trying to build my first canard from salvaged parts of other planes just for the fun of it and i have seen a lot designs that confused me.
So is there an answer to what AoA the front canard must have?
Is it supposed to be parallel to the main wing or not?
Regards,
Theo
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Old Oct 02, 2012, 07:43 AM
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[QUOTE=nickchud;22886469]David and Charles, hi!

I've been reading back through the posts on this thread in Sept, Oct of 2010. fascinating and very informative stuff, specially from Don, John and Charles.

I definitely did have more success with the low canard, as in the plan below:


Hi Nick,

Interestingly although it looks lower your canard is actually in line with the wing, in flight it will actually be a bit above the wing due to the aoa. In that case it may interact with the wing to create mutual interferance to a greater degree than the high mounted position which may be a little too high.

More interestingly the incidence is the same as the wing but the local airflow would probably increase its aoa to above that of the wing, creating enough decalage for stability.

I can't put my hand on it now but I've seen studies that show the highest lift position was like the Saab gripen and rafale, ie, just above and ahead of the wing.

Rgds
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Old Oct 02, 2012, 08:01 AM
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Originally Posted by teopbako View Post
Hi,
I went thru this thread by browsing the pictures that i liked most and reading what ever was written about them as the whole thread is to big to read for a quick question that i have.
I am trying to build my first canard from salvaged parts of other planes just for the fun of it and i have seen a lot designs that confused me.
So is there an answer to what AoA the front canard must have?
Is it supposed to be parallel to the main wing or not?
Regards,
Theo
Hi Theo,

The AoA depends on the airflow. For stability the forward wing should have a higher AoA. In the drawing above although there is no decalage, that is the incidence of both wings are the same, the upwash of the wing will cause the canard to have a higher aoa.

To answer your question it can be parallel, but the farther away from the wing the more we should consider adding decalage.

When you look at different designs look at them from this point of view and you will be able to make a better decision.

My 2cents.
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Old Oct 02, 2012, 08:17 AM
Ikaruswannab
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Thank you captamour.
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Old Oct 02, 2012, 08:34 AM
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Thanks Charles,

Re full size ultralight the pilot being almost as heavy as the entire aircraft would have to balance the engine to keep cg correct. As I mentioned a quick guess would put him probably midpoint of of root chord.

I was looking at your video again with the larger duck and you get a bad phugoid on landing roll suggesting for my application I would need a larger canard with more decalage.

I'll try a small glider test model and see what happens in ground effect.

For just an ultralight application it would be close in the standard config.

Rgds
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Old Oct 02, 2012, 11:09 AM
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Canard AOA

teopbako, Theo
Quote:
So is there an answer to what AoA the front canard must have?
Is it supposed to be parallel to the main wing or not?
Regards,
Theo, I do not consider my Delta Duck with the motor up front to be a canard or to depend on the front wing to stall first to keep the main wing flying. The model is really just a flying wing with added control up front with elevons front and back.
In a climb, the motor adds a bit of lift which will keep the front wing from dropping.
To prevent rapid climb at speed, I added 5 degrees of down thrust and shimmed up the TE of the front wing to a very low AOA. If you build a true canard type with rear motor, you will have to protect the main wing from stalling by giving the canard wing about 3.5 degrees more of positive AOA than the main wing has. This assures that the canard wing will stall first with the CG in the correct position. Please use the Canard center of gravity calculator. I feel that similar airfoils of almost any type will work. The front of this thread gets most of the questions answered. The steep canard angle applies to models with the power applied from the CG and rearward. My feeling is that high speed canards may be OK with smaller area and lower AOA up front although this may be open for discussion.

Charles
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