I think lack of airfoil on the main wing, and airfoiling on the canard is part of the problem.
As I said, canard designs need for the canard to stall first, and main wing stall last. I think your is having the main wing stall before the canard sometimes, yet perhaps the canard stall other times depending on the angle or attack and airspeed. No airfoiling always stalls before an airfoil does. Oddly enough, if your canard was say half (or 2/3) of its current area but twice (or 1.5 times) as much angle of incidence, it would tend to stall the canard more easily due to the higher angle of attack (incidence). While the higher angle of incidence would make the canard create more lift. Compare the canard size/area of a couple of well known old B/G's, the Mini-Dactyl and the Delta-Katt. Pretty small canards with a lot of incidence.
Delta Katt: note fuselage angle to wing, canard is straight (zero incidence) to the fuselage, the pop-pod was mounted parallel to the wing. This pic from a 2.9X scale-up article: https://www.rocketreviews.com/scratch-groovy-katt-by-geof-givens.html
Mini-Dactyl: it also had the same sort of fuselage set-up as the Delta-Katt, though the pod was parallel to the fuselage not the wing. If this was scaled up for C size or lager, it might have some problems with pitching up on boost unless it was built to roll (easy way is to angle the pod "crooked" in yaw about 3 degrees, causing a roll on boost without messing up glide trim like rudder trim for boost would.
PLANS from JimZ's site (The above is from part of the instructions): https://www.spacemodeling.org/jimz/km-6.htm
BTW - Aerodynamic scaling related to "Reynolds Number", is that the smaller an aerodynamic surface is, the less effective it is (smaller = lower Reynolds Number). Because air molecules are a constant size, if air was instead small particles of rock, full size planes would fly thru sand while smaller models fly thru gravel and smaller thru pea gravel, and really tiny models fly thru "boulders", in a relative sense of size. That is a wild oversimplification of course (no plane could "fly" thru sand) but a way to get across the idea of air molecules of constant size vs how the airflow behaves with smaller and smaller models . Suffice to say that the smaller size of a canard will tend for it to stall sooner than a larger one, everything else being equal. https://en.wikipedia.org/wiki/Reynolds_number
Also, don't give the canard an airfoil, round it only. And try to do what you can to sand some airfoiling into the main wing. Even if it's pretty much rounding the leading edge and sanding a crude taper into the UPPER part of the trailing edge (don't taper the underside of the trailing edge).
Another thing to try would be to add a turbulator strip at 25% of the main wing chord (on top of the wing, not bottom). That "trips" the boundary layer early, causing it to remain attached longer at higher angles of attack than without it. I have used turbulator strips n some of my R/C sailplanes and a few R/C rocket boosted gliders to reduce/solve tip-stall problems (wingtip on one side stalling, causing the glider to veer to one side and begin a dive rather than stall straight ahead like a well behaved R/C model should. This alone might solve your problem right now. Vinyl tape about 3/32" - 1/8" across would be about right. I say vinyl, like electrical tape or repair tape, since that would be about the right thickness, thinner tape would not work as well. Needs to be thick enough to have a significant "bump" to trip the boundary layer. The image below is for a more advanced full size airfoil and shows the turbulator farther back than 25%, but 25% generally works well for our size of models.
As I said, canard designs need for the canard to stall first, and main wing stall last. I think your is having the main wing stall before the canard sometimes, yet perhaps the canard stall other times depending on the angle or attack and airspeed. No airfoiling always stalls before an airfoil does. Oddly enough, if your canard was say half (or 2/3) of its current area but twice (or 1.5 times) as much angle of incidence, it would tend to stall the canard more easily due to the higher angle of attack (incidence). While the higher angle of incidence would make the canard create more lift. Compare the canard size/area of a couple of well known old B/G's, the Mini-Dactyl and the Delta-Katt. Pretty small canards with a lot of incidence.
Delta Katt: note fuselage angle to wing, canard is straight (zero incidence) to the fuselage, the pop-pod was mounted parallel to the wing. This pic from a 2.9X scale-up article: https://www.rocketreviews.com/scratch-groovy-katt-by-geof-givens.html
Mini-Dactyl: it also had the same sort of fuselage set-up as the Delta-Katt, though the pod was parallel to the fuselage not the wing. If this was scaled up for C size or lager, it might have some problems with pitching up on boost unless it was built to roll (easy way is to angle the pod "crooked" in yaw about 3 degrees, causing a roll on boost without messing up glide trim like rudder trim for boost would.
BTW - Aerodynamic scaling related to "Reynolds Number", is that the smaller an aerodynamic surface is, the less effective it is (smaller = lower Reynolds Number). Because air molecules are a constant size, if air was instead small particles of rock, full size planes would fly thru sand while smaller models fly thru gravel and smaller thru pea gravel, and really tiny models fly thru "boulders", in a relative sense of size. That is a wild oversimplification of course (no plane could "fly" thru sand) but a way to get across the idea of air molecules of constant size vs how the airflow behaves with smaller and smaller models . Suffice to say that the smaller size of a canard will tend for it to stall sooner than a larger one, everything else being equal. https://en.wikipedia.org/wiki/Reynolds_number
Also, don't give the canard an airfoil, round it only. And try to do what you can to sand some airfoiling into the main wing. Even if it's pretty much rounding the leading edge and sanding a crude taper into the UPPER part of the trailing edge (don't taper the underside of the trailing edge).
Another thing to try would be to add a turbulator strip at 25% of the main wing chord (on top of the wing, not bottom). That "trips" the boundary layer early, causing it to remain attached longer at higher angles of attack than without it. I have used turbulator strips n some of my R/C sailplanes and a few R/C rocket boosted gliders to reduce/solve tip-stall problems (wingtip on one side stalling, causing the glider to veer to one side and begin a dive rather than stall straight ahead like a well behaved R/C model should. This alone might solve your problem right now. Vinyl tape about 3/32" - 1/8" across would be about right. I say vinyl, like electrical tape or repair tape, since that would be about the right thickness, thinner tape would not work as well. Needs to be thick enough to have a significant "bump" to trip the boundary layer. The image below is for a more advanced full size airfoil and shows the turbulator farther back than 25%, but 25% generally works well for our size of models.
Probably woulda been OK at 3.0 (less noseweight) or 4.0 degrees (more noseweight)
Yes, follow the curve, proportionally (25%).
And do it full span, since the issue being tackled here is not tip-stalling, but apparently the whole main (rear) wing stalling before the canard is (or main sometimes stalling or sometimes not, inconsistently, making trimming very hard).
So, you want the whole wing to be able to handle a higher angle of attack before stalling than it seems to be doing now.
Since the LE and TE are square.... i just occurred to me you might need to make the turbulator strips extra thick. So if you do not see much improvement in trim stability with one layer of vinyl tape, try 2 to 3 layers. On my R/C gliders I had 2 to 3 layers (laid atop each other onto plastic the cut to width with a ruler and model knife), but those were bigger wings with larger chords.
Another thing I'll note on my experience with Canards, is that sometime they need to be more nose-heavy than I would trim normal gliders. Sometimes a "fine line" between having a good pitch trim that does not want to stall, but glides level, versus being too nose-heavy where it isn't actively trying to "dive" into the ground. BUT it is definitely in a bit of a shallow dive - if it sped up then the canard would give enough lift to pull the nose up, from diving, but at the steady-state glide velocity it's more nose-down than a normal glider would be. Sorta hard to explain it until you experience it. One of several reasons why I have rarely done canard models, other than proven good designs/kits (Like Edmonds, and the Mini-Dactyl. Even the Delta-Katt was a bit tricky).
I did make up a Canard design a few years ago for an easy-build glider for club members. Some info on on it in this post:
https://www.rocketryforum.com/threads/canard-glider-plans.142817/#post-1737448
And the plans. Not exactly the coolest glider design, but it worked. The Canard angle was "TLAR" (That Looks About Right), 1/8" over 2" which only now did I calculate to discover it's 3.58 degrees. Had the prototype seemed to have needed more or less than that after glide trim throws, I would have changed the angle, but it was in the ballpark. Of course that angle is all relative to the canard area, wing area, and distance between them for this design which is OK with it, so do not presume 3.58 degrees is some magic angle.
Yes, follow the curve, proportionally (25%).
And do it full span, since the issue being tackled here is not tip-stalling, but apparently the whole main (rear) wing stalling before the canard is (or main sometimes stalling or sometimes not, inconsistently, making trimming very hard).
So, you want the whole wing to be able to handle a higher angle of attack before stalling than it seems to be doing now.
Since the LE and TE are square.... i just occurred to me you might need to make the turbulator strips extra thick. So if you do not see much improvement in trim stability with one layer of vinyl tape, try 2 to 3 layers. On my R/C gliders I had 2 to 3 layers (laid atop each other onto plastic the cut to width with a ruler and model knife), but those were bigger wings with larger chords.
Another thing I'll note on my experience with Canards, is that sometime they need to be more nose-heavy than I would trim normal gliders. Sometimes a "fine line" between having a good pitch trim that does not want to stall, but glides level, versus being too nose-heavy where it isn't actively trying to "dive" into the ground. BUT it is definitely in a bit of a shallow dive - if it sped up then the canard would give enough lift to pull the nose up, from diving, but at the steady-state glide velocity it's more nose-down than a normal glider would be. Sorta hard to explain it until you experience it. One of several reasons why I have rarely done canard models, other than proven good designs/kits (Like Edmonds, and the Mini-Dactyl. Even the Delta-Katt was a bit tricky).
I did make up a Canard design a few years ago for an easy-build glider for club members. Some info on on it in this post:
https://www.rocketryforum.com/threads/canard-glider-plans.142817/#post-1737448
And the plans. Not exactly the coolest glider design, but it worked. The Canard angle was "TLAR" (That Looks About Right), 1/8" over 2" which only now did I calculate to discover it's 3.58 degrees. Had the prototype seemed to have needed more or less than that after glide trim throws, I would have changed the angle, but it was in the ballpark. Of course that angle is all relative to the canard area, wing area, and distance between them for this design which is OK with it, so do not presume 3.58 degrees is some magic angle.
"Flaps" on an airplane wing allows the wing to fly slower without stalling. So my concern is that adding an adjustable flap flap on the canard will mean the canard may not stall until reaching an even higher angle of attack than it is reaching now before it stalls. Which means the main wing will be more likely to stall first. So, I'd keep it flat, with the rounded edges, no flap.
I'd suggest "tack gluing" the canard on with a two drops of CA, one front and one rear of the canard. And if you think it needs more angle then use a razor blade to slice the glue joint under the front, then put a shim of 1/64 or 1/32 plywood under the front, another drop of CA, and try again. And so on. Once you reach an angle that seems right, then permanently glue.
Now, I know that full size aircraft have control surfaces on the canard, but they are designed very well (often have turbulators) and have much better Reynolds numbers (flying thru "sand", "not rocks"). The Astro Blaster I had......always flew sorta funky, and it did have a canard with a "elevator" (pitch control) surface on it. But also it was just 1/8" balsa with rounded edges, while the main wing had a flat bottom airfoil, so it didn't exactly have a stalling problem but just handled different than the other R/C models I've flown. I even converted it to electric R/C a few years ago and while it flew.... again it wasn't a comfortable "fun" model to fly.
As in contrast to some flying wing models I have flown, also unconventional, that flew very honestly and consistently. BTW - do not take that as as suggestion to switch to a flying wing, as those can be just as troublesome to design from scratch. The ones I speak of R/C wise were mostly highly popular Flying Wing kits or ARF's that the designers nailed just right (the ones that suck usually don't become popular. Usually). And one designed by a Mr Vern Estes ad John Shulz in 1961, the Astron Space Plane kit (not R/C of course). I scaled that up 4X as an R/C RBG and the glide handling was SO sweet once trimmed that a beginner could fly it in glide.
Oh, I recalled a canard Boost Glider I did long ago that had a canard flap because it moved from flat on boost to down for glide. Bruce Blackistone's "Disaster 17B Valkyrie". It had very flaky trim. Like I said designs usually do not become popular unless they fly well - "usually". This didn't exactly become "popular", but it was a plan in Model Rocketry Magazine. In those days there were not a lot of glider plans, and this stood out as a "different" glider when seen at some big contests (where IIRC he never had much success in scoring well with it). Blackistone made several big versions of the Valkyrie, using engine choices (not many options in the early to mid 1970's) that were often at the heart of why they failed before even having chance to glide. F67 Shred. F100 shred. Three D12 cluster Shred. D20 staged to F7, D20 boosted it to 50 feet, ignited the 7 second burn low thrust F7 which slowly pitched over and gravity-turned into the ground to crash become burnout.
An article here about a scaled up big (2X) one that Bob Koenn built. https://archive.rocketreviews.com/reviews/all/scratch_valkyrie.shtml
Absolutely!
