Canard Size?

[LaGaffe]

Greeting,

From what I've read and heard to get a canard (and three surface plane) to work well you shouldn't build it too small (foreplane chord no smaller than 4~5"), but on the other hand there is Chris Golds' Shinden and TurnKeyRC's XP-55 which if I'm not mistaken are smaller. So, from practical experience, what is a sensible minimum canard size?

Soft Landings
Torbjörn

[Marion]

I do not know the answer to your question. But I sure would like to know the answer !!

In times past, I have made small (6 to 10 inch) sheet balsa size glider models of the design in question, and tested them. It is a place to start. It can, however, be misleading at times, because of the aerodynamic differences due to the small size.

For starters, I would make the canard about 25% of the wing area -- and see what happens with the flight of the small test model. It is easy to make changes with the sheet balsa model.

Let us know what happens...

Crazy Marion

[LaGaffe]

Ah, I think a clarification is in place: the question I would appreciate an answer to is: What's - from practical experience - a reasonable minimum absolute canard/foreplane size (chord, or rather Re I guess)?

Another question is: What a practical minimum size of the foreplane as a fraction of the main wing? Wouldn't mind an answer to that one as well.

/Torbjörn

[Sparky Paul]

Andy Lennon, who works with odd shapes, recommends a canard of no smaller than 15% of the wing, with 30% being better, AND a chord of 5 inches or more, due to the special demands on a canard... it's more highly loaded than an aft horizontal, being a lifting surface; it must stall before the main wing, otherwise the pitch-up can be uncontrollable; the main wing must arrive at its angle of zero lift before the front wing does, otherwise the dive can be uncontrollable.
and for me, it's at the wrong end of the airplane for a structure which will contact terra firma first some (most) of the time.:)
.
* his italics

[LaGaffe]

I've read Andy Lennon's book at least trice, but if I'm not completely mistaken the canards of Chris Golds' Shinden, TurnKeyRC's XP-55, and some others I cannot remember the names of are smaller, which made me curious of actual practical experinces of small sized canards. A well founded second opinion is always interesting (and e.g. Martin Simons made a rather good job at demolishing the CLA theory IMHO). Someone in another forum recommended a chord of at leas 4.5", and my latest doodles had a thirty odd percent canard with sqrt(24) inch chord (don't ask why :-)

[Ollie]

You can make the aft wing go through zero lift first by making its airfoil of lower mean camber than the fore wing airfoil. Just compare the zero lift angles of attack allowing for decalage.

You can make the fore wing stall first by making the aspect ratio of the aft wing low enough to delay its stall until after the fore wing stalls. Enough difference between the fore wing's induced angle of attack and the aft wing's induced angle of attack will serve, allowing for down wash angle and decalage.

[Marion]

For what it's worth....

Full scale areodymanics books of the 1950's (yes, I am that old ) made the lateral centroid a much more complicated matter than the CLA described by Lennon (and lots of others too). I used the full scale theories to calculate the necessary size of a vertical stabilizer on my model during that time period. It looked so small, that I simply increased the area by 60%. All worked well in flight.

Apparently both the CLA and other methods have been used successfully.

[Sparky Paul]

CLA is really a subset of "neutral point", applied to the side view.
There might be flaws in it but the way I think of it, arrows need feathers at the REAR... :)
And tubular missiles need the c.g. ahead of the center of the surface area.
"static margin"... :)

[LaGaffe]

Yes, but if I understand Simons correctly, if you use CLA to design you end up with a working conventional plane, but it might not work for something more out of the ordinary, and if fig 12.14 on p158 (Model Aircraft Aerodynamics, 4th ed) is to be believed, according to CLA some planes wouldn't need a fin to fly (CG well ahead of CLA without a fin) :D. My approach is to collect TVCs of similar models that are supposed to fly and play with Plane Geometry ...

Before this thread derails any further, my point was that taking any one persons writings as The Truth might not be a good idea... Whether CLA is more, less, or not at all correct has very little to do with an emprically based estimate of a reasonable minimal size/Re for a canard (for RC - FFers seems to get away with even peanut canards). Isn't there anyone actually building canards?

[Sparky Paul]

You have posted your answer to your question.
There are successful models of canards with smaller than -recommended- canard surfaces.
But also you're looking for the Truth in relation.
There isn't any!
Unless you know the constraints -some- authorities such as Lennon and Simons place on what -they- feel is reasonable and recommend as such, since are no absolutes in anything, and you have full freedom to try what appeals to you.
The surface area police won't come by and lock you.
Mother Nature might slap your creation out of the sky as unworkable, but that's between you and Ma Nature. :)
Then you change something, and offer it again. :)
And after enough work, youwill probably find the small part works best at the back, for several reasons.. the primary being "Don't make your smallest surface work the hardest! "

[LaGaffe]

Nope Sir, I most certainly isn't after The Truth (as far as I'm concernerd there ain't no such thing). What has The Truth whatever that is to do with actual experiences? I know there are plans for small size canards - I have a few of them - what I don't know is how they actually fly. The designer is obviously partial (at least I am :)), someone in another forum stated that a canard that according to the unnamed designer flew well actually flew like a dog, and some published plans are lemons. I don't mind experimenting, I don't fly anything except own designs, but I do like to have at least some knowns among the unknowns :D.

[Rotozuk]

I have built a couple of conard slope gliders in the the past.

The first one I knew very little about what a canard should be, and it flew very well, but by nature of the conard, did not pull well in stall turns that were a popular flight pattern of the time. Thus I could not fly it with the normal PSS glider of the day.

The second model I did a lot of research, and wanted to improve on the flight habbits of the glider. I followed what I had read (I think it was Lennon's book) and that plane was a PIG and never flew well at all.

I stopped messing with the conard layout as it did not perform well in a glider format. I personally do not feel that they are a good format for model aviation. Heck, I hardly see a good appilcation in any form of aviation. The "safety feature" comes at a high cost to performance in one way or another. Either you have a bland handling, or a long take off and landing roll out, or all of the above.

And this is from a guy that has flown in LongEZs, etc.

-Wayne

[LaGaffe]

Not being interested in glider of any sorts or description (with the exception of Horten style wings), I've not read those PSS articles, which I obviously should have. Bland behaviour? Not a problem - wht you expect from a transport style plane. Long take off and landing roll out is more of an issue, but being the weirdo that I am, I was considering a canard - or three surface - flying boat. And I get at least as much pleasure out of designing the planes as I get from flying them.

Andy Lennon (I'd assume that his advice despite some unusual designs where on the safe side, that is, if you followed his procedures you end up with something that flies reasonable well) suggests Eppler airfoils, but there are others, and if I'm not mistaken, some better suited for low Re? Any suggestions for canard and three surface airfoils?

[Sparky Paul]

Lennon is one of the few reliable sources for the odd stuff. And he mentions the warts as well as the kudos for oddness.
I'm working up a tandem wing plane based on his R/CM&E design of 1988.. having found a couple of unbuilt wing kits.
Won't be the same as his, but the configuration police won't be coming to my door to tell it mustn't be done! :)
That's true with any of this. Find what has worked, and either use it as is or change something.
It either works or it doesn't. The only judge is Ma Nature. If she likes it, OK, if she doesn't, she'll let you know. :)