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Old Mar 31, 2007, 09:02 PM
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Voyager Decalage

pjw, My views on the wing angles are given on page30, post438. I agree with the motor down thrust and the incidence of the main wing but my canard wing has a steeper angle of incidence than the main wing which gives a positive decalage. I feel that the Voyagers are consistant in allignment and wing angles. I wish that the main wing and motor could be brought down to zero incidence. Then we could put the ailerons at normal and not have to shim the canard. All of our Voyagers fly like dreams thanks to our collective efforts. I am going to try less reflex in the ailerons and move the COG back a bit. The EZ, in my opinion is Rutan's most popular and I intend to keep mine as long as it or I can last. I know of no erratic behavior in any Voyager except the one with the outrunner extending rearward which,I believe, makes it able to spin. Concerning the canard incidence, if the canard flat bottom is placed on a horizontal plain, you would have positive incidence since the LE would have to go negative for zero lift. These are only my views and are up for discussion. The views of Don and pjw make great food for thought. CA
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Old Apr 01, 2007, 09:07 AM
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Thanks, Charles -- I've been re-reading Andy Lennon's work on r/c model design and the peculiarities of canard-equipped aircraft, which reinforces Don's observations above (and your earlier calculations).

Mr. Lennon's basic criteria for a successful canard are:
(a) the foreplane must stall before the main wing; and
(b) the main wing must arrive at its angle of zero lift before the foreplane.

From those two criteria comes all the discussion about CG, neutral point, static margin, decalage, etc. In the spirit of 'thinking out loud', this is how I'm seeing it:

The combined 'mean aerodynamic chord' (MAC) of the two lifting surfaces is the so-called 'neutral point' (NP) of the aircraft. As I understand it, the center of gravity (CG) should be located in front of this neutral point to assure that the model has inherent pitch stability. The distance between the CG and NP is called the 'static margin'. If the margin is zero, the plane will be very twitchy. Your calculations were working with a 10% static margin (considered 'stable' by Mr. Lennon) to locate the desired CG. That came out around 15.5" - 16" aft of the canard LE.

The larger the foreplane is in proportion to the main wing, the farther foreward the CG and NP will be - an important consideration when balancing out all the 'stuff' that goes into the model. More weight in the butt means a smaller canard is called for, seems to be the drift. You found the Voyager's foreplane to be 26% of the main wing, as I recall.

Now, to deal with the desired decalage it gets hairy (as Don hinted) - first calculating the respective wing loading, then the lift coefficients of the airfoils, and finally the correct angle of attack for both lifting surfaces to meet the two criteria for success. Suffice it to say that the Voyager has been engineered to have the right amount of lifting area; the foreplane's cambered airfoil generates more lift than the main wing; and the only question appears to be whether the optimal angle of attack is built in to the design. Test flying appears to suggest a minor increase in the foreplane's AoA is needed...and Don suggests that elevator trim can overcome this without undue 'trim drag'.

That's my synthesis of what I've gotten out of this really helpful thread (with a bit of help from Mr. Lennon).

pjw
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Old Apr 01, 2007, 07:18 PM
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Voyager Trim Talk

Quoteb) the main wing must arrive at its angle of zero lift before the foreplane.
pjw, I believe we have an error in Mr. Lennon's book here.Edit: No error in the book,only my misconception. CA... His second sentence is correct and figure 4 is correct. Quote: More weight in the butt means a smaller canard is called for, seems to be the drift.....Yes, you have to make use of that large main wing area to carry the load. The full scale canard with the seemingly higher aspect ratio than is on our Voyager assures it will stall first. The full scale Shinden also has a small canard with the main wing carrying most of the load. But these are real aircraft with large areas and high reynolds numbers and fly very fast. For model planes with their low reynolds numbers, we seem to need more area up front (30%) to behave at 25 mph. This together with a 4 degree incidence puts the canard in a position to stall first. So to make our Voyager fly better, we take a little lift from the main wing, add some lift to the canard and move the COG back to shift the load rearward. I love the discussion and these thoughts are only mine. Sorry for the errors on my part. Charles
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Old Apr 02, 2007, 07:58 AM
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Zero Lift vs. Stall

I had to puzzle through that statement as well, Charles. It does sound counterintuitive. But the accompanying graphic depicting how the foreplane airfoil and mainplane airfoil reacted at different angles of attack made it clear (?) for me.

In the attached graphic, the solid line is a heavily-cambered Eppler 214 airfoil - the recommended foreplane (canard). The dashed line is a moderatedly-cambered Eppler 197 airfoil - the recommended mainplane.

What this depicts is the pitch attitude of the aircraft. In a negative pitch moment (going left of center) the mainplane reaches zero lift (-2 degrees) before the foreplane (-5 degrees). In other words, as the aircraft descends in a nose-down attitude, the main wing stops lifting before the canard. If the reverse were true, the plane would pitch down violently (or is that 'catastrophically'?).

In a positive pitch moment (going to the right) the foreplane reaches stall (around +9 degrees) before the mainplane (around +14 degrees). So, as the aircraft ascends in a nose-up attitude, the canard stalls first, and the nose drops gently allowing the aircraft to safely recover from the incipient stall.

Again, this reinforces (to me) the importance of airfoil selection and relative wing incidence in models such as our Voyager Long EZ.
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Old Apr 02, 2007, 08:17 AM
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All of that said, and it is very interesting, did the designer of our Voyager's use the correct airfoils, or something close? Mine is being test flown this morning. Wish me luk. Tom
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Old Apr 02, 2007, 08:57 PM
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Thanks,pjw, I finally understand that story. It seems to me that to achieve that -2 and -5 attack angle on the airfoils, the model would have to be following an outside arc or constantly changing almost as in the outside loop because you would have to keep the air coming in toward the top of the airfoil for zero lift to occur. Andy Lennon Designed his Canada Goose with your two plots in mind and hit canard zero lift on approach. He had to reduce the canard area and revert to the main wing's airfoil for the canard. I will show his story here. My Shinden's canard will lose control in the outside loop because when I try to go under from verticle the model seems to flip upright from some sort of instability. From Lennon's experience, I used the same airfoils on all of my designs. I have no complaints or reason to change them. Tom, I need to here how your Voyager did. I'll bet it was a piece of cake. Charles
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Old Apr 03, 2007, 02:22 PM
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hey Charles ;has any one built a flat foamy/profile type, canard plane?I picked up a Hobby Lobby "Hot Rod" 3D ship at a swap meet for a couple bucks last week.Its sat on my table waiting for me to do something with it since then....when it occurred to me that if I were to reverse the ailerons on the wings and removed some of the elevator surface and repositioned the tail/stabilizer to the "front" it just might fly as a canard ship....any thoughts?
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Old Apr 03, 2007, 04:17 PM
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Yes, Daddiozz, It's all here in this thread. DangerBird has just what you need.I have, in this thread, shown construction details on the GWS Slow Stick and Pico Stick as canards. If you read the thread, you will pick up the design rules for canards and if you need help just ask and someone will reply. Charles
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Old Apr 03, 2007, 04:55 PM
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Quote:
Originally Posted by canard addict
Yes, Daddiozz, It's all here in this thread. DangerBird has just what you need.I have, in this thread, shown construction details on the GWS Slow Stick and Pico Stick as canards. If you read the thread, you will pick up the design rules for canards and if you need help just ask and someone will reply. Charles
..I have a slowstick canard right here in my shop;I must have missed the details on converting the 3D ship over ,I'll reread and go from there..thx

ok thats not exactly what i was looking for but its close;i'll play around with it and we'll see what happens...
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Old Apr 03, 2007, 08:30 PM
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Daddiozz, Sorry if we were not on the same track. Just make the canard wing area 30% of the main wing area, put it at 3.5 degrees positive to the wing and use the COG calculator to find the balance point.I always turn the wing around and make the motor a pusher. Charles
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Old Apr 04, 2007, 09:39 AM
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Airboat.
Does this help?
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Old Apr 04, 2007, 10:41 AM
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Cheers laddie and welcome ..Charles will love that any chance of an elargement of that three view
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Old Apr 04, 2007, 11:31 AM
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CAD threee view

Here's a pdf of the 3 view. It's in CAD so it can be scaled to any size.
Let me know if you want a bigger version.
Ivor
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Old Apr 04, 2007, 11:45 AM
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Quote:
Originally Posted by canard addict
Daddiozz, Sorry if we were not on the same track. Just make the canard wing area 30% of the main wing area, put it at 3.5 degrees positive to the wing and use the COG calculator to find the balance point.I always turn the wing around and make the motor a pusher. Charles
...thx ,Charles....any plans to compete in the annual soarstar/wingo race with the "mickey duck"? ...i like that ...and i just happen to have a soarstar laying around(pieces of one anyway)...I see yet another canard looming in my future..
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Old Apr 04, 2007, 10:17 PM
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Laddie, Thanks, The OMAC-1 inspired the Canada Goose per Lennon and both inspired me on my Ga. Goose. The top view looks much like the Long EZ. I also like the Vari Viggen which may be easier to copy. If only someone would do an ARF or plans for either plane. Daddiozz, I would not risk Mickey Duck in that race but it would surprise me if any standard type could keep up with it because of the stable and flat wind penetration of the canard type. For example, at the field when the wind is high and the guys put their models tail first into the wind when parked, I put my models canard first into the wind. When flying, the canard penetrates superbly and the elevator control works to hold the nose in place. On landing, when a good nose down glide is established, it is practically hands off until a little control is needed to cope with ground effect. The high thrust line of Mickey taught me to lower it on subsequent models because of the down pitching moment it causes. When trying to loop, the Duck becomes locked in a vertical position because it fights inside rotation. I just add aileron and do what I call a barrel roll and into inverted flight at times. The outside loop would be easy with different struts. Charles
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