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Author Topic: Something a little different....  (Read 716 times)
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Sundancer
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« on: April 16, 2014, 11:44:16 AM »

Normally my builds appear in the "Stick and tissue" forum; however, although this one is all balsa, it is more sheet than stick and is covered in film, so as it is electric maybe this is the best place for it.

The subject is a fairly heavily modified version of a plan published in the March 1970 issue of the UK R.C.M. & E magazine called the "Can Can".  The original was a single channel model powered by a pusher .049.  My version has pitch control via an all-moving fore plane plus twin rudders and is electric with a 140 watt out runner and 3S 1800 lipo.

Built with incidences as shown on the plan (+6 on the wing and +12 on the canard) and with the CG position (which is not shown) calculated using a canard CG calculator available on-line at http://adamone.rchomepage.com/cg_canard.htm, it was hopelessly either nose heavy or under elevated.  As a result the 1:3.6 all sheet chuck glider shown in one of the photos was made and after juggling the incidences on this to make it fly OK the big model was re-rigged with the main wing at zero and the fore plane at +3 degrees (subsequently re-trimmed in flight to -2 degrees!) with the CG as calculated (3" in front of the wing LE).

It now flies very well, with an excellent glide (AUW 24 ounces, loading 11 ounces/square foot), an extremely rapid climb at full throttle and a blistering turn of speed if held level at full chat.  It is also VERY sensitive to rudder inputs and is flown with minimum rates and a lot of exponential on this function - with higher rate on rudder it will do an amazing axial roll, but is just too twitchy for normal flying.  Despite the incidence difference between the wing and canard being the "wrong way round" according to normal advice, it displays the classic canard refusal to stall, simply flying along with the nose nodding up and down as the canard stalls and un-stalls.  After being initially not too keen I am now quite getting to like the appearance in flight which is quite "futuristic" (for Star Trek fans think Klingon Bird of Prey!).  However, I cannot see how it could have possibly flown with the incidence set-up shown on the plan.
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Dave Andreski
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« Reply #1 on: April 16, 2014, 03:38:26 PM »

Very nice results!
Dave
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Konrad
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« Reply #2 on: May 10, 2014, 09:33:56 PM »

Fantastic!! I would never have thought that the rudders would have been very effective. I've seen what you are seeing with the front stab when she is as large as yours. Can't explain it. Do you have any reflex in the airfoil? I have found that setting up my canards as if they were flying wings seems to tame them down yet give me a broader speed range than true flying wings or classically trimmed canards.

Looking real good. Kind of reminds me of the Boeing Sonic Cruiser.

All the best,
Konrad
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OZPAF
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« Reply #3 on: May 11, 2014, 05:42:52 AM »

5 deg decalage would seem to be close to what's required as the performance would seem to indicate. The incidence angles of the original seem way off the map and it is likely that the canard was on the point of stalling.
I'm glad you have sorted it out and thanks for sharing.
John
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Sundancer
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« Reply #4 on: May 16, 2014, 03:37:56 AM »

Fantastic!! I would never have thought that the rudders would have been very effective. I've seen what you are seeing with the front stab when she is as large as yours. Can't explain it. Do you have any reflex in the airfoil? I have found that setting up my canards as if they were flying wings seems to tame them down yet give me a broader speed range than true flying wings or classically trimmed canards.

Looking real good. Kind of reminds me of the Boeing Sonic Cruiser.

All the best,
Konrad

Hi Konrad

Interesting that you have observed this.  I am still puzzled as to why the settings on the plan should be so far removed from my final set-up, but no matter, it flies well now!  Re the rudder effectiveness - yes this caught me unawares at first,I had what I thought was a modest amount of movement set up and this proved to be way too much.  Whether this is due to the twin rudder layout or not I don't know, but once I toned the movement down it handles very nicely and is very agile.

There is no reflex on the wing section, it is a straight forward flat bottom 10% thick "zip-zip" section.  I take your point about setting a canard up like a flying wing, but I don't think this would work with this model without building in considerable washout to the main wing.  My experiments with moving the CG back resulted in the model being unflyable with the CG still a little in front of the wing, pitch response was so sensitive as to make control impossible.
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