Canard Forum: Show,Discuss, Learn - Page 76 - RC Groups
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Sep 18, 2007, 02:18 PM
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Thank you, Don. You probably just saved me lots of time and money. Charles
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Sep 18, 2007, 06:29 PM
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John235's Avatar
For me it is just an experiment, I don't have any serious aspirations other than sport flying to start off with. Especially since I have never caught a thermal in my life. There is a local competition for 7cell NiMH thermal gliders in Australia. There is a really wide range of models that are entered. Some people are quite serious about the models, but most of them just do it because they enjoy the flying whether they are competitive or not. There is one flyer at my club who competed with a Multiplex easy glider with an upgraded motor. The results were respectable since he is a good pilot.
Sep 18, 2007, 10:10 PM
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I went to a competition once and found out that I had 30 seconds to get my geared speed 400 into a thermal. One flyer was happy to burn out a brushless motor if necessary to get up in a hurry. What an eye opener that was to me. It was beautiful to watch national contenders go up and down and spot land within seconds of the alloted time. I just love to gently climb into rising air with my Graupner 2M and do loops on the way down. Charles
Sep 19, 2007, 03:45 AM
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John235's Avatar

Powered maiden flight

When I fitted out the motor and controller it came out 30g heavier than I expected. I can't believe that I used that much Velcro tape, wire and solder, so I must have got my previous AUW wrong somehow. Even with the battery right under the canard, I needed another 25g of nose weight. The AUW for the powered maiden flight was 485g (17.1oz).

I had two flights today. The first was with the 30% elevator to flap mixing as before, and the COG set between 7% and 10% static margin. The flight was nicely uneventful, but the model didn't give me much confidence at low speeds. I felt I was doing a bit of work to keep constant altitude in the turns. Maybe the ailerons were losing a bit of authority at low speeds as well. Disturbingly, at certain points during low speed passes, the model would rock from side to side, with a gentle oscillation. The good news is that the problems disappear at higher speeds. Although the model is faster than I expected, its flies very well at speed and is very predictable. I didn't find this problems during the test glides, possibly because the model was about 24% lighter, and I was more being careful to keep the speed up.

For the second flight I disabled the elevator to flap mixing, so I was relying purely on the canard elevator for pitch control. The roll axis oscillation no longer occured. I figure the oscillation was caused by some sort of tip stalling behavior when down elevator was applied through the ailerons. I did some testing of the stall behavior, brief vertical climbs, nice round loops, fast diving passes and fast turns. The behavior was all very nice so far. Slow speed flight is quite ok when flying straight, but low speed turns still didn't give me much confidence. I am guessing the problems occur because I was too close to the stall speed of the main wing. I think that moving the CG forward to at least 10% static margin will help prevent this situation. If there are still problems I may also look at changing the canard airfoil section to one with less camber. Comments and suggestions are welcome.
Sep 19, 2007, 08:40 AM
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Congratulations John! and thanks for the detailed report. I wish I could have seen it fly. Any chance of a video? About how fast is it? Your conclusion to increase the SM to 10% should add a more solid feel to the flight. It sounds just like my original Duck design which was recently changed over to a Lipo battery which resulted in more SM and a lighter AUW. Going from 9.6 to 11.1 volts made a big difference in performance. It also was at about 5% SM and tended to rock the wings when placed in a nose UP climb. The increased power and weight shift made it a joy to fly. Charles
Sep 19, 2007, 01:36 PM
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Captain Canardly's Avatar
Thanks Don! and Charles!
these were strictly 'sperimental' as my interest (was ) mosltly edf if I was to move to elictric flight. in about 3 minutes, the "first" bird got to about a couple hundred feet.When I moved to the pair of props, 20 seconds and a "very cold' in comparrison battery later attained the same altitude. as a soaring machine goes, both kill the L/D beyond a drastic amount, but the twin 50 mm was like a barn door.
I'm just trying to employ a 90 mm fan to somethin'! I was down a couple days from a thunderstorm, and hopefully if the goofy weather behaves to our advantage, I will continue where I left off with the ribbon shots- my thermal bird has a higher dihedral on it, so I will check out both .
Sep 20, 2007, 01:32 AM
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John235's Avatar
Charles, I don't have much experience guessing the speed of the models. I think it might be in the range of 40 to 50MPH full throttle with a shallow dive. I have seen parkzone stryker foamys that are faster, certianly some with big motor upgrades are a lot faster. The stall speed isn't too bad, its just had more "go" at full power than I expected. That was a pleasant surprise because I like to build models that have a wide speed range. It just the low speed handling that needs to be sorted out. The canard is mounted slightly lower than the main wing, since I believe that is the way to minimise drag. Last night it occured to me that when the canard starts to stall it probably creates a lot of turbulence that could result in poor lift from the main wing. For future models, I might try putting some dihedral into the canard to see if it can offer any improvement. I can't see any simple way of adding canard deihedral to this model without adding a second elevator servo.

Captain, In general, how do you find the handling of your Blue/yellow/red electric sailplane that you used for testing with the streamers? Is that one around 80" span? It looks like the canard has a wider chord and lower aspect ratio that some of your other designs. Do you think this has any effect on the performance or stall behavior?
Sep 20, 2007, 03:20 AM
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John235's Avatar
Charles, Its very intersting to note your GA goose also had the same rocking motion with insufficient static margin. I thought it might be related to my fin location, but since yours has the winglets, it cannot be. I have never seen any model with this rocking motion before. Maybe it is unique to canards..
Sep 20, 2007, 03:38 AM
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John, You have dihedral action because of the swept back wings. I have had low speed rocking on two models and both have parallel wing edges on the canards with dihedral. My cango had a short main wing because I wanted a fast roll.I added 2.75" to each wing tip and reduced the rock to acceptable level. The Soar Star Canard has a full wing with no rock. A little wash out in the wing tips may also be helpful for you. I do know that you will never see a rocking action on a long wing model like a glider. Both of my models that rocked had shorter coupled wings than the more stable ones. When the Cango wings were lengthened, it reduced the relative area of the canard and it still has good elevator action. D Squared is short coupled but is rock solid at all speeds.When proving in the yellow and red Ga. Duck, ten sq. inches were added to the canard to avoid the hopping ground action probably due to marginal power and that resulted in reduced SM which probably caused more instability. When the new battery was added, it increased the power and the SM which had good effects. Charles
Sep 20, 2007, 03:55 AM
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John, Maybe with nose UP condition with slow speed the wake of the canard allows alternate tip stall or even inner wing stall. Don??? Charles
Sep 20, 2007, 03:58 AM
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Bill Covert's Avatar
If you really want to give it a shot:

You can take ANY plane, reverse the prop, and see what happens.

If it flys, its a canard.

.....just don't use the ailerons, and expect the rudder to be REAL responsive.

BTW, the problem with the SF Models canard is that the pilot can't see where he's going.
Sep 20, 2007, 04:36 AM
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Welcome, Bill. Have you tried to see out of a J3 Cub? I believe that seeing from a Long EZ would be better. On the subject of wing rocking, it seems that I have seen a short winged biplane model rock. The Pitts Special comes to mind. Charles
Sep 20, 2007, 06:54 AM
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John 235
Try to increase the size of the fin. When in turn or at higher angle of attack your fin is being blanked off by turbulence coming off the wing.
Other solution would be to have winglets on the wing tips.
Sep 20, 2007, 07:09 AM
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pjwright's Avatar
John235 - I'm wondering if the relatively small vertical fin factors in to slow-speed oscillations? At some point in the speed envelope, doesn't the fin lose effect over yaw? You may be seeing incipient dutch roll.
As Lennon's book points out:
"Canards, particularly those with small foreplanes and pusher engines, do not have adequate moment arms [to sustain positive directional control]."
Lennon recommends swept wings and large vertical fins ... or fins placed at the wing tips.
Don Stackhouse's website (Ask J&D) had an interesting note about yaw stability and dutch roll that may apply here (in that canards and flying wings have much in common):
"Flying wings get especially tricky on this issue. Yaw stability is generally tough to come by for them. Lots of sweep is one way to do it, but that also adds to dihedral effect at most airspeeds. The result can be a bad dutch roll problem, from too much dihedral effect and not enough fin effect to balance it. Tip fins add to yaw stability without significantly adding to dihedral effect."
Food for thought before you start monkeying with the canard airfoil?

Sep 20, 2007, 07:21 AM
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John235's Avatar
Hi Laddie, Thanks for your post. I think the the cyclic rocking must be a chain of two events. I am am pretty sure that one of them is the tip stall. The other one might be the yaw correction due to the fin as you say, or some other interacation as charles suggested. I am less concerned about it now, because I have now resolved the issue with effectively more washout in the wing due to disabling the elevator->flap mixing. Apart from that, the effect you wrote about might be contributing to some of the problems I have with low speed flight. There are a few simple changes I can try on my next day at the field, adding winglets might be the next thing to do if I stil have problems. So my approach might be like this:
1st Revise CG for larger static margin.
2nd Set elevator->flap mixing to 25% for up elevator, but disabled (0%) for down elevator.
3rd Add more canard decalage.
4th Add winglets to main wing.
Last edited by John235; Sep 20, 2007 at 07:39 AM. Reason: Added 3rd option

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