canardlover

Hello out there, as a keen canard-designer I usually follow ”conventional canard wisdom” which goes something like this: ”...the canard foreplane MUST stall before the main wing to avoid the airplane to enter a superstall….” and further….” …usually the foreplane area loading of a canard should be about 150% of the main wing loading…”
Fair enough - this works pretty well if your canard relies solely on the foreplane flap to achieve pitch control. The backside of the coin is that with that high foreplane loading the prop wash of a tractor engine is instrumental in keeping the nose up. As soon as you approach for landing and shut down the engine the nose drops at a critical moment. Ask me, I have bent quite a few nose gear legs before learning the technique to land such a ship.
OK, after this little “lecture in canardology” I come to my real purpose of this thread which is to get your input on my new canard design taking shape in my shop (see pics) This is a different bird resembling the famous X-29 or Su-47 Berkut and having both a front and a rear flap for pitch control. In addition to that of course the possibility to use elevon mixing on the ailerons for additional pitch control.
Now to my question to you: What foreplane loading would you use on a machine like this and how would you configure the different flaps to achieve an airplane with a large speed envelope, good turning performance, no bent nose gears and no superstalls…???
Please let me “pick your brains” on this one before I decide and set her up for the maiden flight….Thank you…Cheers/Harald

PS...Moderator: maybe I misplaced this thread and it fits better under "Aerodynamics" if you agree, please move it...thanks..!..DS

All Day Dan

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Get this book, "Basics of R/C Model Aircraft Design" by Andy Lenon. It will help out a lot. I'll try to make a copy of the page you need. Dan.

allanflowers

I remember trying to take Lennon's theory into account on a canard project years back. I had no luck with it and decided it was hogwash, rather than downwash.
Of course I ended up with a canard raised up like yours, to help reduce any downstream effect on the main wing.
I finally ended up with about a 130% loading on the forewing, as I recall.
I will be watching with interest to see what you find out on this. There are a lot of bogus theories and formulas around on canards, as you surely know. Maybe you can resolve it for us all.

All Day Dan

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Allan, It's all in the first flight. If you survive that, you got it made. Try this website for some more information. I checked it out from my own experience and it was right on. Dan.
http://adamone.rchomepage.com/cg_canard.htm

Lnewqban

Canards are regular planes flying backwards; hence, everything works backwards

In this link page, find a five parts article with the following title: "Canard & Tandem"

http://www.rcmplans.com/index.php?main_page=page&id=18

BMatthews

I agree that this is far better in the Aerodynamics forum.

Yes you want the canard loaded so it stalls first. But then again it has a lower reynolds number and is suffering from being a shorter span so it has more effect from the tip vortices.

All in all it comes down to the old Hiesenburg Uncertainty Principle that says " We just don't know"

Would it be possible and practical to set this model up with some of the heavier bits arranged to be movable with an easily adjusted mechanism? If so you could alter the CG and thus the canard to rear wing loading ratio and try flying it with testing for the stall and steep banked "G" loaded turning behaviour and a host of other tests at both of the extreme ends of the speed range of the model.

I have to admit to only playing with a couple of canards in all my days. The last one was an old timer single pusher canard. I honestly never did get that one flying the way I would have liked. But keep in mind that to fly their best free flight models generally need to be on the ragged edge of almost being unstable. The model just didn't work that way. It seemed to be best when the canard was very heavily loaded. But then the fore wing was creating too much drag and the overall model performance suffered badly.

canardlover

Hi all and thanks for input and for replacing the thread.
DAN: I already have Andy Lennons book and he prescribes a "static margin" of 25% MAC of main wing (Fig.8, p.104) which is heavy loading.
The calculator is a bit more "daring" with a static margin of only 5-15% of MAC, I have that one too in my ´puter.

Lnewqban: I have most of Andy Lennons articles already and he elaborates only very little on static margin in there.

So we are stuck with "conventional canard wisdom" so far.
Let me give you an example of one of my creations (see pic) which superstalled twice for me at a foreplane loading of 180%....[:@]..! One of the superstalls was even inverted..Quite a show but only two broken fins. Had to increase up to 200% loading before that monster stalled with a "mush" of the nose.
And that behaviour is exactly what I want to avoid with this new FSW canard - hence this thread and the aft flap.

BMatthews: I have played with the idea to have the battery pack moving on a slide back and forth but it is rather cumbersome and requires much space so I hesitate.
Keep info flowing....Cheers/Harald

Lnewqban

Harald,

If I understand correctly, your problems come from the nose engine increasing the efficiency of the foreplane to the point of increasing the critical AOA and the stall resistance.

Such effect is gone when you reduce the throttle for landing, at which moment the foreplane is unable to keep proper pitch balance while flaps (in the main wing) are deployed.

Am I wrong?

canardlover

Lnewqban, your are quite right except that I did not deploy any flaps since that ship only had one single aileron on the main wing. Further as you can see I experimented with high and low placement of the foreplane but that did NOT help the "nosedropping". It all comes back to the very high foreplane loading with +3 degrees aoa. Of course you can reduce foreplane loading and its aoa and then fly the plane so fast that stalling is avoided. But then the speed envelope gets rather limited and the plane will become "divergent in pitch" and very tricky to fly provided you do NOT use elevons.

DAN, nice canards you have there, it appears you prefer a low foreplane but do you also have elevons...???

So I would like to move towards more flaps and much less foreplane loading but how far can you go in reducing foreplane loading in a canard model airplane..???
Modern fighter aircraft such as the swedish JAS 39 Gripen, the Sukhoi SU 47 or the X-29 probably have very little if any loading at all on the foreplane but they have powerful computers onboard and elevons to achieve pitch control....Cheers/Harald

All Day Dan

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Harald, Thank you for the compliment. I put the canard on the bottom at first for ease of construction. Whenever I pitched the nose up, during landing, the model always lost altitude. I thought this was because of blockage of the wing surface. I eventually relocated the canard to the top of the fuselage and got some better results but not much. The real trick was to land faster. I also had the canard set at +2 degrees. The wing was at 0 degrees. Here's an image of another one I designed. This was a great flyer. Unfortunately a midair led to an early demise. Dan.

Lnewqban

That is a very original project, Dan!

Harald,

What about increasing the elevator area and mixing elevator with throttle?

They would act like flaps of the canard for landing.

Split flaps for the canard would be an option if mixing is not desired.

The idea is to make the CL of the canard flexible, since the speed of the air over it is so variable.

Just a suggestion.

canardlover

Thanks all for more input. I think I will try 130% loading next time - good suggestion allanflowers.. And then I will skip elevons and just use the fore and aft flaps in parallell with a Y-cable for pitch control. I usually have main wing at +1 degr. and foreplane at +3 degr.Will start out without deplyment of landing/starting flaps. And then fly initially without forcing a stall until I get used to the ship.Waddayathink about that guys..???
Dan: nice "trike" you have there but I beat you with one engine................Cheers/Harald

All Day Dan

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Harald, Great plane! Had I thought of that configuration I would have gone for it. Thanks, Dan.

charlie111

I don't think the foreward wing is made for lifting More for control.But, If you were thinking about loading you would have to increase the size of the Forward wing and actually treat it as a seperate wing.To eliminate a stalling problem front Wing may have to be Larger than Rear?

canardlover

Dan: it appears from pics above that all three canards of yours have rather high foreplane loading..! I deduct that from your placement of the main gears. In particular the big one on the left in post #2 - still with the nosewheel on the ground..!! Is there any possibility for you (or me) to calculate your foreplane loadings..??
Regarding placement of the foreplane vs. the main wing "conventional canardology" maintains that a high foreplane is better since the downwash goes over the wing rather than under it.
Further as you so correctly said it: "the trick is to land faster"....I fully agree but I do not like that. Would be nice to be able to land it like a delta with very high aoa but that is not easy to obtain.
Please have a look at the Su 47 Berkut in this video:
http://www.youtube.com/watch?v=H1wXsygQTVA
and enjoy the slooooooow speed forward with high aoa and the canard flap just "flapping" like mad at 1 min 25 to 40 seconds into the video......nice..!
..Cheers/Harald

All Day Dan

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Harald, thanks for the video. I really can't tell you what the canard loadings were. All I did was get a hold of some equations from the magazines and balanced the models in accordance with them. I had a couple of real hairy first flights. The push pull model was so nose heavy that after I throttled back to land, the model developed a severe desire to nose right it. I saved it at the last second by applying full throttle and had to land by slowly decreasing the power while working the elevator. Luckily, I had a long runway to work with or else the plane would have been gone. It landed at about 50 miles per hour, maybe more. The last plane, you can tell by may age, was so tale heavy that I was in a crash mode all the time I wa making a 360 to get back to the runway. I could swear that the last few seconds was a crash but luckily, for some reason, it was a gentle one on its wheels. I did check the final CGs with this website I posted before and found it very accurate. Dan.
http://adamone.rchomepage.com/cg_canard.htm

Villa

I have been flying both a straight wing and a swept wing 46 size pusher Canard for about 9 years. I found a solution for a very serious problem and have wondered if others here have seen the same problem and come up with other solution. My landings are usually a little faster than none-Canard types, and very nose high. The problem that I saw was that if things go slightly wrong during the landing, the front gear may hit hard, and bounce high into the air. This is a disaster on a Canard, since the plane will immediately stall and nose in. After doing this many times I came up with my solution. I set up for my usual landing as described above; fast and nose high. If things do not look right I will abort. However, if things do not look right and I do not abort, I prepare to go to full down elevator as soon as the mains touch the ground. This has saved me many times since I fly in high wind conditions. I look forward to reading your comments on this maneuver. I totaled my swept wing pusher Canard about 6 months ago when it hit a telephone pole and I chose not to re-build it. I do have a straight wing pusher Canard which I'll get into the air soon.

canardlover

Villa, thanks for sharing your experience with us. It appears we all have the same problem with the risk for "nose in" during landings. I have not used the high alpha approach myself but it certainly looks cooler than just "greasing her in" at rather high speed like I do. I also give full down when nose wheel is on the grass.
Dan and Villa, if you have plans/drawings of your canards and know the c.g. position I can easily calculate the foreplane loading my way and share the results with you..?!?!
Attach a "nose in damage" pic....[&o]..!...Cheers/Harald

All Day Dan

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Harald, I thought I had them but I can't find the plans. They were designed in the pre-CAD days and were done by hand. The designs were published in the May 1982, November 1983 and March 1987 issues of Flying Models magazine. They may have some left. I can send you copies of the plans that appeared in the magazines and you would have to scale them up or use them as they are. I don't know if they were distorted to fit within the page of the magazine. Dan.
http://flying-models.com/

Villa

Hi canardlover
I use this calculator http://adamone.rchomepage.com/cg_canard.htm for the CG. It gives a safe nose heavy CG that I then adjust from flight tests. I'm not familiar with the % of foreplane loading method. From the very little interest in building Canards I have concluded that builders give up after the front end goes up 45 degrees during a landing and totals the plane. My Canards have all been made from Coroplast so the damage usually is minimal to none. My biggest problem has been a slight cyclic roll that becomes more pronounced with some up elevator input. I believe a lower Canard wing position would solve that since it appears that the Canard wing interferes with the airflow to the main wing. Plans and photos of my straight wing Canard are at http://www.rcuniverse.com/forum/m_3580825/tm.htm

canardlover

Villa, thanks a lot for your plans which I have missed. Made a quick calculation on the "Runard" and found that your foreplane is very lightly loaded. With the proposed c.g. at 3" ahead of the main wing L.E. you have a "static margin" of 3% MAC and a foreplane loading of 110% (see attached drawing) I hope I made it correctly it is sack time now here in Sweden.
Dan: would it be possible to do the same with some of your canards..?...Good night/Harald

All Day Dan

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Harald, Try this one. Dan.

canardlover

Dan, here is my calculation on your Sabrebat. Rather conventional but on the light side with a foreplane loading factor of 130%.
The problem with most calculations - mine and the linked calculator given by Villa - is that they do NOT take the lifting force of the fuselage into account. And most of the fuse is in front of the c.g. which means that Lf must compensate for that also. No problem with you Villa having an aluminium spar as fuselage......
That is the reason why Dan (and others) must load the foreplane more.
Now sack time again...Good night./ Harald

allanflowers

Here's another drawing if you want to calculate on it. The grid is 100mm. The CG is shown on the side view at the leading edge of the wing. It has a full flying canard, leading edge slats and flaperons - the last two features couldn't be used because I would run out of elevator to match the additional wing lift. This model was much too heavy (the wing complications and retracts didn't help) and, after a few flights, found its rightful place as a hanger queen.

All Day Dan

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Harald, Here's another one. Dan.