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Old Aug 21, 2007, 11:09 AM
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huber, Thanks for the great discussion on oscillation! You sound like you have lots of canard knowledge and I assume experience with flying them. John 235, I changed post 981 to say that the control surfaces were changed to zero trim and the oscillation stopped and the model returned to smooth attitude.{what I meant to convey} Your model reminds me of my Shinden which was designed to go after B29 super fortresses at 479mph. I started with 2 cells with the 20% canard with the CoG back about 1.25" from the main LE. The model had to fly nose high at full UP elevator. It was really just flying on the main wing. I added a cell and three plus square inches to the canard which put the CoG just where yours is at the LE. It is a different plane now and is fun to fly. I have considered putting more area on the canard but it may not be worth the effort. This model just needs lots of power like huber referred to for snappy performance.The canard incidence could be increased for slow flying. I fly with UP trim. It's remarkable how models perform like their big brothers. Charles
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Old Aug 21, 2007, 02:20 PM
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The F-88 Sabre Canard is now ready to fly.I'll get video of the maiden or even if it's just an attempt,but luckily we have a 600 foot paved runway to fly it off of since when calculating the cg ,I also found out the stall speed is 27 mph! and the cg is 12.35 back from the canard LE. Maiden is set for 5:30pm,wish me luck
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Old Aug 21, 2007, 02:58 PM
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Luck !
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Old Aug 21, 2007, 03:14 PM
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thanks John, I did some taxi testing and she gets squirrely fast but will keep a straightline fairly well,had to reinforce the canards with strapping tape and carbon,should be fine now.
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Old Aug 21, 2007, 04:36 PM
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D Squared Winglet change

I'm pulling for you ACE! You must be on the way to the field now and you deserve a reward for all your inovation and hard work. I took the D Delta to a soccer field last evening for a trial with UP trim. The practice teams allowed me to have 1/2 the field to practice on. At 1/2 of my elevator trim used the model looked stable for a change in level 1-1/2" tall grass but was begging for more up. There was no bouncing and it looked like it wanted to jump into the air. I gave full UP trim and it looked like it was just skimming the tops of the grass. When the power was cut and the model slowed, it seemed to need more yaw stability. I have not been happy with the winglets because they just look too small to have good control at low speed. I have added highth and depth to the tune of about 7 sq. ins. each. I now feel sure that like the chuck glider, 3.5 degrees canard incidence is barely adequate at nose down glide. Since the soccer field is much too small to fly a two pound canard from, I had to resist adding power and pulling the elevator control back because a canard can suddenly leap 10 feet into the air in level flight when the drag from the grass is removed and both wings have high lift. This happened to me there one day when the grass was twice as tall and it took full power and lots of UP elevator to lift off. I suddenly was in a maiden with my first balsa canard G1 yellow and red. All I could do was to cut power and try to land in a circle within the fences. After 180 degrees of turning, the right wing touched the fence at about three feet and caused a couple of hours repair work. The model handled very well and has not been changed since then. Charles
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Old Aug 21, 2007, 08:35 PM
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Sabre canard was a sucess,despite a small repair job needed. Took her to OFMC at 5:30 and a few friends also met me there.Set her on the runway with a Tanic 1760 3 cell installed and the cg marked at 12.35 in accordance with the CG calc. Started the rollout and turned around and taxied back to take off position. Throttled up carefully holding a slight amount of up elevator and let her gain groundspeed until it was sufficient,lifted off flying out no more than 5 feet off the ground for probably 200 feet trying to climb with no luck so I set her down and she looked like she flipped in the tall grass. Upon closer inspection only the nose gear and gear servo were loose so we brought it back and taped it straight but it wouldn't track straight down the runway so I decided to try a handlaunch. Before that though we taped three quarters on the tail since it seemed very nose heavy. I tried a handlaunch and holding FULL up elevator only saw a extended glide once again.We then decided to wattmeter the 1760 and a 2070 3 cell. With the 1760 I was only seeing 160 watts,that explains the "extended glide flight" I had during the first and second attempts.However with the 2070 we were up to 290 watts and a significant thrust increase,so I gave it another shot again with a handlaunch since the front gear was collapsed.For some odd reason I launched FULL THROTTLE(BAD! idea for small stubby winged edf's and I knew it just wasn't thinking)so it rolled onto it's back and hit the grass breaking the nose and canard torque arm. Overall, I'm pretty happy that it did infact fly despite being practically a cousin to the F-104 starfighter due to it's small wings,mine only measure 18 inches. She will fly again soon,and I will ROG next time.

BTW thanks yet again Charles, but I believe you deserve the reward, I'm just messing with EDF canards, while your the master at them period
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Old Aug 22, 2007, 07:57 AM
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No Challenge = No Fun

Your getting there Mustang Ace! My guess is that you need a little more canard area to hold the front end up. The area at the tips may be too small.I am moved and deeply grateful that you think of me so highly but master, I am not and never will be. We are having a complete party doing this and it is because we are NOT masters. We just take what others have done and attempt to change and improve. If we could solve the infinite number of problems with flying machines we would get bored and just quit. There are some in the hobby who buy a ready made machine and get really good at operating it and quit because their challenge has been met. The biggest kick comes when you put your ideas together and make them work. Then you try to improve it to work even better. I am lucky to love model planes and also the construction and piloting of them. This subject would make a great thread and might bring out some interesting angles. Speaking of a master,The fellow who designed the Douglas DC3 airliner in the 30's was getting close. Charles
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Old Aug 22, 2007, 08:30 AM
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Quote:
Originally Posted by canard addict
John 235, I changed post 981 to say that the control surfaces were changed to zero trim and the oscillation stopped and the model returned to smooth attitude.{what I meant to convey}
Thanks for the clarification. Still, I don't see how that can explain the behavoir of the model. If the only thing that changed was the elevator trim, it shouldn't affect the pitch stability. Anyway, as long as you are ok to keep flying it and give some flight reports, thats ok with me.

On my calculations, my canard area is 20%, although the Shinden looks smaller than that.... and I remember you posted to say that mine looks larger than 20%. Well, I am not saying that one of us is mistaken, but I think the Shinden's canard span looks smaller relative to the span of the main wing. My canard span is is 37cm vs main span of 80cm. If I do end up having a lack of elevator authority, I have two possible solutions in mind. The most obvious one is to build a new canard wing with more area, but the more interesting option is to mix some elevator into ailerons.
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Old Aug 22, 2007, 08:53 AM
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Quote:
Originally Posted by canard addict
The biggest kick comes when you put your ideas together and make them work. Then you try to improve it to work even better. I am lucky to love model planes and also the construction and piloting of them.
I would have to wholeheartedly agree!! Well said, Charles.
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Old Aug 22, 2007, 09:14 AM
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Great explanation Charles,any way you look at it you are my hero when it comes to canards. When I met you two years ago in Apopka I could tell you were a great person and I wish we could have spent more time talking,but I was younger and didn't realize at the time just who you were.
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Old Aug 22, 2007, 12:15 PM
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Let's have a friendly discussion about canard characteristics so that all may join to agree or disagree all in the interest fun and education. I have attached the Shinden CoG data as it was out of the box. The canard looks small but is shown at 44.8 sq. ins. which is 20.3% of the wing at 220.4. On the other hand, John235's model seems to have a larger canard but I calculated it from his plans to be at 20% of his wing as he said it was. Note that the Shinden's CoG point is 0.53 behind the wings LE. With 2 cell power the model was sluggish and was in need of speed. The additional cell made it fun to fly. On the subject of canard design, I went back to Andy Lennon's book and found that at low Reynolds numbers the airfoil can lose lift around 6 degrees AOA, angle of attack, and stall at 8 degrees. The canard wing must be in control of the model and never allow the main wing to stall.To load the canard properly and using huber's balancing act on my designs, I increased the area of the canard which moved the CoG well forward of the main wing. This gave a see saw action around the CoG in my mind which apparently gives the canard more ability to handle vertical action. I noticed that many canards, the Sig Tri-Star for one, gives the pilot one chance to flare on landing before stalling out. With a forward CoG, I get all the repeated nose control needed for a smooth landing. On the subject of oscillation on my D. Delta,since both wings have elevons,DOWN trim took lift away from the canard and added it to the main wing. This seems to give the main more control of the model which resulted in problems. At speed the high AOA of the canard lifted the nose which gave the main more AOA which caused the rear of the model to rise up which killed the AOA of the canard causing it to drop which killed some lift of the main. At this point, the nose wheel touches the ground,springs back and bounces the nose up and the process repeats. I have had this problem on new designs in neutral trim and have cured it with more power, more canard area and a lower incidence on the main wing. You just can't allow the main wing to overpower the model. John 235, I believe that elevons will do great things for your design. Charles
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Old Aug 22, 2007, 03:38 PM
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D Squared has Larger Winglets

The larger winglets were just added today and each went from 6 to 8 grams. The model was a little extra nose heavy and seemed to want more UP trim to fly so the CoG can afford to be back a tad more. The winglets just looked too small to work at slow speeds and yaw stability seemed lacking at the beginning and end of a fast taxi. I see no reason how the larger area can hurt the model's performance. Charles
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Old Aug 22, 2007, 06:15 PM
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Vertical fin and moment arm?

I was looking at John235's side view, and agree:
"The tail fin looks a bit tall..."
That reminded me of something I'd read in Lennon's chapter on canards and vertical surfaces:
"Another disadvantage of a small canard and rearward CG is reduction in moment arm to the MAC of the vertical tail surface(s); it necessitates very large vertical areas. Burt Rutan solved this problem by using aft-wing sweepback and placing the vertical surfaces at the wingtips. This substantially increases the moment arm." (p105)
The notion of "moment arm" (as best I can fathom) has to do with the distance between the calculated mean aerodynamic chords of the wing and the tail. Reducing the moment arm is like shortening a lever ... making the aircraft (in this example) sensitive around the yaw axis.
So ... perhaps John235 might consider dividing the vertical area between two "winglets", as you've done on the Double-Delta, Charles? More stability from vertical surfaces that appear more in proportion to the rest of the airplane?

pjw
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Old Aug 22, 2007, 09:56 PM
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Who knows pjw? Lennon speaks of a canard at 15% with the CoG back into the wing to carry the motor load. John 235 has compiled a canard which has features found on successful canards which have been shown here and elsewhere. I know what he is up against at this point and feel he must carry out his feelings as they were developed. My Delta may end up a failure while John's may fly like a dream. On my designs which have been successful, from the CoG to the center of the winglets is from 13 to 15". From the CoG to the canard LE is about 20".The CoG is about 4" ahead of the main wing. On the Delta, the first measurement is 13" and the latter is 13.5". How will this compact little model handle in the air? I feel it will certainly get right into the air but may be a hand full to land. I may have the chance to maiden it this weekend at the RAMS meet at King, NC. Charles
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Old Aug 22, 2007, 10:31 PM
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I was able to repair the Sabre Canard,added a 1/2" extension to both canards and modified the nose gear to strengthen it and give better steering control and nothing was stopping me from trying another test flight......

Took it to the park and found a long strech of sidewalk
"runway" to take off from and set up for takeoff with a few clicks of up trim on the canard and both ailerons with up reflex from yesterday. With a 30c 2000 3 cell poly rc pack she ran along the ground for maybe 75 feet and lifted off at close to a 70 degree angle. I was impressed! I then flew her around trimming the ailerons(actual ail. trim on radio died so i subtrim,a pain in the air) making wide turns to keep the airspeed up and not stall with the short wings. After a few circuits I pulled the power all the way back and she started to glide straight ahead and level,so I kept power around 50% and she was still moving right along. I then did a few rolls and they were fairly axial but I had to coax it back to level(thinking to noseheavy although it kept a slightly nose high altitude the whole flight after leveling the elev. trim). I also tried a loop but she didn't want to complete so at the vert. pull I rolled into an Immelman. Dives are good and it doesn't tuck like the firebat just pulls out straight. After probably 5 minutes I greased the first landing onto the grass. I then took off again since i still had battery left and flew around some more and tryed another landing gliding in this time but knocked the gear out again so back to the gorilla glue,now I'm very happy with the design and it should get better every time I fly it. I managed to get a crappy cellphone pic of it but since I was alone that's the best I could do and keep control of the plane at the same time
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