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Old Sep 20, 2007, 07:34 AM
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Quote:
Originally Posted by canard addict
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
This seems plausible. The chain of events could be as follows:
1) One wing tip experiences a tip stall.
2) It falls out of upwash region beyond the canard span.
3) The AOA will then be reduced, so it becomes unstalled.
<EDIT> Meanwhile the alternate tip reaches a tip stall.
5) The cycle repeats.
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Last edited by John235; Sep 21, 2007 at 02:37 AM. Reason: Flawed logic!
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Old Sep 20, 2007, 09:57 AM
who has rabbit ears down
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235!
To your first question, I uasually go between 6 and 8 for a canard's aspect R. and as for difference in stall types, that would rely more on the 'foil and leading edge roundness . the multi colored bird is a 6 footer.
I believe you have good ratios for your tri color setup, there,and i would be using an incidence meter to the finest line i can "read" in accuracies of differential wing/ canard incidences. I do know that the smaller the canard, the less forgiveness you will get in the stability department.
Johnny
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Old Sep 20, 2007, 12:53 PM
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John, When the canard elevator goes DOWN, the ailerons go UP? Just checking. The discussion is great!! My yellow canard rocked with winglets after adding ten sq. inches to the canard and it went past 30% of the wing. Both canard and main wing had dihedral. My next model, the red and white Ga. Goose, used the same wing plan with no dihedral, a 6 inch longer nose and a swept back canard and the problem was solved.With full UP elevator and low power, the canard gently falls and recovers with no tip stall. Charles
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Old Sep 20, 2007, 08:15 PM
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Captain, thanks for the info. So far my drawing for the 2m(78.5") glider, it has AR=7.4 for the canard, whereas the main wing will have AR=10. I am looking at a canard span of 30". I intend to use SA7036 airfoil on the main wing, and probably E205 for the canard, maybe with some leading edge modification. I will use hinged canard elevators, ailerons and rudder. Please let me know any comments.
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Old Sep 20, 2007, 09:10 PM
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Charles, When the rocking occurred, the mixing caused the ailerons move up when the canard elevator goes down, as you said, and vice-versa for down elevator.

My thinking is that tip-stalling and subsequent rocking can be completely avoided by using washout in the main wing. I have a degree or two in the main wing but it was cancelled out because the elevator->flap mixing causes the ailerons droop down when down elevator is applied. Next time I will try adding the mix for up elevator only, so the ailerons can go up for extra control authority for up elevator, but never drop lower to avoid the tip stall problem. It is a non-linear control response, so I will start out with small mixing ratio and some exponentional to avoid any weirdness around neutral.

I am looking at canard dihedral to change the canard wake flow over the main wing. I would like to get some improvement in overall lift and better pitch stability at high AOA. I have seen models with conventional layouts that suffer pitching issues when the wake of the main wing momentarily flows over the horizontal stabilser. I think its possible that my model may be suffering similar issues at low speeds, when the canard creates the most turbulence. For conventional layout aircraft, the soution is normally to reposition the horizontal stabiliser, change to a V-tail, or use anhedral on the tail as done with some full size jet fighters. Placing the canard above the main wing like your Egret and D^2 seems like a simple solution, but I don't know if there might be other factors to consider in this choice.
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Old Sep 21, 2007, 08:47 PM
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Rocking at Slow Speed

John, since the model is finished, you are limited in things to try. BTW, I found that my Cango did not rock in smooth air and thought that a forward shift in the CoG had fixed it until it flew again in bumpy air. I then extended the wing span for performance that could be tolerated. Why not add weight up front and see what happens? If that does not work, then maybe you could add another section to each wing tip with a trailing edge upturn for wash out. A longer distance between leading edges could be used on your next design. I believe my D Squared would rock if it did not have a 14" chord at the wing center which makes it more like the Long EZ shape. Your rocking at low speed reminds me of a conventional model with the CoG aft. Is your main wing at zero with the thrust line? Perhaps lowering the LE of the main wing may help. Good luck with it. Charles
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Old Sep 21, 2007, 10:16 PM
INDORUS EXPARAMINTO
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Springfield, Missouri, United States
Joined Jul 2002
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Anyone need a Rare Kit
St. Croix Models 1/5 scale LONG EZ kit NIB - balsa with fiberglass parts.
Sized for a .40 2 stroke. Beautiful kit, hate to part with it, I should just keep it.
Have had it for many moons and have always wanting to convert it to electric using an AXI and some Lipolys but with the new baby I see I will never get around to it.
Thinking around $200 shipped
Will take more pictures of it if interested

Larry
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Old Sep 21, 2007, 10:21 PM
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The incidence of the main wing is set at 0.5 degrees. As you suggested, moving the CG forward will be the first thing I try to improve the low speed handling. As it stands, the model dosen't rock once the mixing was disabled, so that isn't worrying me too much unless it is going to make a comeback as you found with your model. My comments above are just ideas that I am considering for my next model, which is probably going to be a 2m glider. Have you noticed any issues in low speed handling where the canard is mounted lower than the main wing?

In the past I have been frustrated when I made wings that were so strong it was impossible to add washout or correct warping by re-shinking the covering. For this wing, I decided not to sheet the entire "D secition" of the wing, so the torsional strength is reduced. I am optimistic that I would be able to add more washout if needed.
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Old Sep 22, 2007, 04:37 AM
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My two that have the rocking tendency have a shorter distance between the leading edges and have low canards like 4" below the wing. The Cango has larger aspect ratios. Charles
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Last edited by canard addict; Sep 22, 2007 at 04:52 AM.
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Old Sep 22, 2007, 04:50 AM
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SE-Flyer, I have that kit. It was produced up near Oshkosh where the Rutan home builts meet and I believe is probably the most accurate to scale ever made. Even the cowls on each side of the engine are included and look authentic. Charles
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Old Sep 22, 2007, 09:46 PM
It Wasn't Me!!!!
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PMPJOHN Long-EZ ready for maiden

Charles,
Just completed the foam Long-EZ Beta build from pmpjohn cut depron.
If the weather cooperates tomorrow I will try to get her into the air.
AUW 14oz, 36.4" WS, BP21 outrunner, GWS 8040 prop, 1300Mha Apex 3S, GWS 15A ESC, AR6100 rcvr., 3 HS55 servos.
I have attached a few photos for your viewing pleasure.
C-YA RL
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Old Sep 22, 2007, 10:38 PM
Dr John
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Inspector

That's looking pretty good. It will look even better once you finish shaping the canopy and cowling. I hope the weather holds for tomorro. If so I'll see you at the field. I would like to see how this one flies compared to the small one.

John
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Old Sep 22, 2007, 11:29 PM
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Hey Inspector, You're back and with a neat canard. Hope you and PMP will make it happen tomorrow! Charles
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Old Sep 23, 2007, 02:35 AM
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This morning I flew my model again with the CG further forward. I added only 5g (0.2oz) to the nose which moved the CG to 4mm (5/32") in front of the 10% static margin point. There were no problems of any sort. I happily flew low circuits, and the landing approach was a joy. It had a good combination of elevator authority and safe stall behavior. I used 30% elevator->flap mix to work for "up elevator" control only, activated by a switch. I flew with the mixing turned on the entire two flights. There was no reason to turn it off because it was flying nicely, maybe next time I'll try switching it off. Anyway it was good because I could make very tight turns without feeling as though it was about to drop out of the sky like before. I have the impression that changes to CG and mixing program were both contributing to this. I also flew a circuit of inverted flight, which was fine, as well as some tidy rolls as I got more confident on the second flight. Overall its been a good experience and I am pretty sure there will be more canard models in my future.
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Last edited by John235; Sep 23, 2007 at 03:28 AM. Reason: typos
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Old Sep 23, 2007, 01:47 PM
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I'm really going to work on my Long EZ to have it this weekend at the Georgia E flyin.
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