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Old Feb 06, 2011, 12:53 PM
Visitor from Reality
United States, VA, Arlington
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Caish
Okay, no technical terms here as I'm only a bystander to the canardly lot.

Ignore the early version of this post - a search on 'Canard Stik' proved my fuzzy memory was right:

http://www.rcuniverse.com/forum/m_33...tm.htm#5753337

Seems 'Canard Stik' was the name of the device - as featured in my new book 'How to miss the completely obvious' There's some good 'reverse donkey' reading in the thread the link points to.

The e-powered canard made up from a Sig Four Star 40 wing and a wooden medical crutch flew fine - it was second generation to a glow powered one - so your 'Kits Ylgu' should be (relatively ) easy going.

D
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Last edited by Dereck; Feb 06, 2011 at 12:59 PM. Reason: Further research
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Old Feb 06, 2011, 10:10 PM
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Dereck, It was fun to look back to the Ugly Stik Canard thread which you referred to and especially to the pictures near the end. Thanks

Caish, I am sorry that you may have been misled by my off topic discussion of my Great Planes Electrostik shown on page 273, post 4092. A canard version was considered but never designed by me. It would be a good candidate for a low wing canard with a larger front wing with a symmetrical airfoil and adequate power.
Charles
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Old Feb 08, 2011, 11:45 AM
What could possibly go wrong?
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Market Harborough
Joined Apr 2006
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Triple Wot

The Triple Wot flew again today! Three times altogether, each flight ended in an uncrontrollable flat spin. No serious damage till the third one. As long as she kept going in a steady, straight climb she was OK. But almost any turn went faster and faster.

Reminds me of my Catalina. With that plane, turns were easy, but it was necessary to centre the ailerons or even reverse them after initiating the turns.

Anyway, the experiment was interesting. The last, longest flight went on for about a minute and I had quite a long walk to fetch the bits. I wonder if I've broken a record by smashing up 3 planes all at once. The real killer for this project was that it needed a runway, therefore dismantling to put in the car and it took about 10 minutes to assemble each time.

So, I shan't be trying that again. I should be able to make one good plane out of the remains! hey-ho!

Nick
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Old Feb 08, 2011, 11:56 AM
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Quote:
Originally Posted by nickchud View Post
...Reminds me of my Catalina. With that plane, turns were easy, but it was necessary to centre the ailerons or even reverse them after initiating the turns....
You SHOULD have to center or reverse the ailerons once the bank angle for the turn is established, on just about any airplane. In a coordinated turn, the weight of the plane and the centrifugal force of the turn combine into a net force that is perpendicular to the wings. This makes the plane (and any human pilot, in the case of full-scale aircraft) "think" the plane is in level flight, despite the bank angle.

This is not a car, and you do not steer it the same way as a car. You use aileron into the turn to create the desired bank angle, center the ailerons (other than a small amount one way or the other if needed to hold the bank angle constant) during the turn, and then you use opposite aileron at the end of the turn to roll the plane back to level flight.

The reason that you may need to hold some opposite aileron during the turn is because the wing tip on the inside of the turn has a slower airspeed than the one on the outside of the turn, so you need a bit of "top" aileron to make the lifts of the two wingtips equal.

My guess is you just need more vertical tail on the aft airplane. Your model had insufficient static yaw stability.
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Old Feb 08, 2011, 12:04 PM
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Originally Posted by canard addict View Post
Caish, Thanks for the extra info. With a 48 by 12 wing the area is 576. With a 30% canard it would be 25 by 7. For the distance between LE's you can judge the proportions by the pictures but it seems that 26 inches is about right. The canard needs to be well above the ground to keep it safe. The CG needs to be about at the center of the fuselage. You can move it forward by increasing the area of the canard or extending it forward. The motor needs to be close in for good balance. Final balance can be achieved by choosing the battery weight. I like long ailerons and canard elevators. Remember that down elevators will cause a climb. The main LG should be about even with the wing's LE. I like about 100 watts per pound but keep it light as possible.
The above is what my mind's eye interprets now. Please keep us informed.
Charles
Your wingspan is wrong but I can work with the numbers.
Its going to be partial ugly stick wings, so they're bound in the middle. I haven't measured it but its going to be fairly short, 24 to 28" but still the full chord.
I'm thinking of a twin slightly V'd vertical stabs also.
How do they fly without a rudder just Aileron and Elevator?
I'll have to work on the light part a little, but it will still be very light. Hybrid foam fuselage, and balsa monokote covered wing.

Thanks again.
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Old Feb 08, 2011, 12:23 PM
What could possibly go wrong?
nickchud's Avatar
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Quote:
You SHOULD have to center or reverse the ailerons once the bank angle for the turn is established, on just about any airplane.
Yes, I knew that Don. It's just that some planes respond differently from others. I really enjoy juggling the rudder and ailerons with the various Delta Duck incarnations I have flown. The Catalina, like other flying boats has a huge tail fin.

The Triple Wot exaggerates the wingspan and maybe also the turning inertia, so perhaps I could have saved it by using much bigger fins. I did reduce the fin on the font plane by removing the rudder altogether. Anyway, I like to try these things but the real killer was the kerfuffle of putting it all together and plugging everything in each time.

Cheers

Nick
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Old Feb 08, 2011, 12:46 PM
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I suspect what might be the root of your problem is the slab-sided fuselages. Those can have surprisingly strong fin effects of their own. The forward fuseage is way ahead of the C/G, so its fin effect is overwhelming the fins and aft fuselages on the two aft airplanes, resulting in insufficient (perhaps even negative) yaw stability.

If your "flying formation" had two side-by-side airplanes in front, and one behind, so the one with all the moment arm was behind the C/G, you probably would have been OK.
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Old Feb 08, 2011, 04:48 PM
What could possibly go wrong?
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Quote:
two side-by-side airplanes in front, and one behind,
I see. Basically, I had double the lateral area behind the CG, but double the moment arm in front of it. That's just not enough at the back is it!

Nick
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Old Feb 08, 2011, 05:09 PM
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Static stability is linearly proportional to the moment arm and to the area, so half as much on twice as far from the C/G is a break-even situation.

However, dynamic stability is linearly proportional to the area, but to the square of the moment arm. Half as much area on twice the moment arm (the forward fuselage) is twice as effective as the two aft fuselages on half the moment arm. Get an oscillation going and the one in front will determine what happens. That's not good.

The net result is a plane that is at best marginal in static yaw stability, but dynamically divergent in the dynamic yaw stability. The flight behavior you described sounds entirely in keeping with that situation.
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Old Feb 08, 2011, 10:32 PM
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Delta Duck 2

The revised Duck #2 is finally finished. Duck #1 is small, quick and hard to see from the side with all red showing. The main wing span was increased from
30 to 36 inches which raised it's area by 55 sq. inches. The rudder was enlarged by 8 sq. inches to assure yaw stability of the longer and more massive wing. The landing gear is wider and taller. With more main wing area,
the CG moved rearward by 5/8 inch or 16 mm which gave more nose down leverage to the motor and ESC than could be counteracted by the larger wing and rudder with their reduced moment arm. The good news is that the model less battery now balances on the CG. The moment arms for the canard, rear elevons and rudder are 8, 11 and 18.5 inches respectively. The Duck #2 weighs in almost 2 ounces heavier at 29.5 ounces. We are entering the windy season at below average temperatures which subdues my hopes for a maiden flight any time soon. It will be nice to have sitting around and I hope to take some comparison pictures outdoors soon.
Charles
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Old Feb 08, 2011, 11:34 PM
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Very impressive model! The quality of the fit and finish looks amazing.

It looks like you did the right thing with the larger fin/rudder. Against the increased wingspan, I wouldn't have picked it as having been enlarged. More pictures would be very welcome.
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Old Feb 09, 2011, 01:58 AM
What could possibly go wrong?
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Quote:
The quality of the fit and finish looks amazing.
I can confirm that, John.

Lovely plane Charles. Only 2 oz heavier, but 55 sq" more wing area! She'll give you hours of interesting and fun flying.

Good luck with the maiden!

Nick
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Old Feb 09, 2011, 05:39 AM
What could possibly go wrong?
nickchud's Avatar
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Don
Quote:
dynamic stability is linearly proportional to the area, but to the square of the moment arm.
Aha! the penny drops. I'll pay a lot more attention to lateral area in future.

I remember something from Any Lennon's book, roughly: "The centre of lateral area should be 25% behind the centre of gravity." And he describes a good trick for locating it. Using card, you cut out a side view profile of the plane, anything like twin fins, cut 2 of them. Cut 2 pieces to allow for the side view of any dihedral. With a dab of Pritstick, fix the double pieces on the side in the corresponding places. Then put a pin through the nose and hang it up. If you have a weighted thread hanging down from the pin, you can draw a vertical line that will pass through the centre of lateral area. Move the pin back a few inches along the top of the profile and repeat the process. The point we're looking for will be where the new vertical line crosses the first one. If this point is too far back, cut something off the fins. Too far forward: make them bigger. I believe that too far back also makes handling difficult by introducing spiral instability.

I'm working from memory here, so please correct me if necessary. But that's what I'll do with any future designs, when I get round to them.

cheers

Nick

PS It seems to me that this hanging up method does allow for the fact that a small fin a long way back is more effective than a large fin with less distance. BUT it doesn't allow for the exponential effect as speed increases. So the 25% figure is just another of those ubiquitous rules of thumb. For a fast flying plane it might need to be more, and vice versa. A bit like "static margin" when you choose a CoG point in front of the Neutral Point.
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Old Feb 09, 2011, 05:52 AM
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[QUOTE=nickchud;17355801
"dynamic stability is linearly proportional to the area, but to the square of the moment arm."
Aha! the penny drops. I'll pay a lot more attention to lateral area in future.
[/QUOTE]

I had a similar reaction. I'm now pretty well convinced that this is why the Each Way Bet wouldn't fly, but the Stanger biplane with similar dimensions was rock steady. The big difference between them (apart from weight) was the fuselage structure - open framework for the Stanger, vertical and horizontal Depron sheets for the EWB.

Thanks for keeping the learning process going yet again Don!
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Old Feb 09, 2011, 08:53 AM
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I appreciate the kind comments fellows and will enjoy my dine out breakfast even more. The stability discussion as applied to the WOT, Each Way Bet and Duck 2 cover a lot of ground. Thanks to each of you for making our hobby even more interesting.
Charles
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