Canard difficulty

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Rktman

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I need some advice from the experts here on how best to solve the stalling problem on my scratch built canard. It trims out nicely and glides beautifully on hand tosses but porpoises like crazy when launched. I added nose weight and it helped some but it still dives and recovers in large 4' loops. I used an online CG calculator to get an estimate and it's within 1/8" of where trimming tosses result in a nice glide (also input a 10% static margin). The canard wing is airfoiled and fixed.

From what I gather on other forum threads the canard's incidence may be too much (it looks like it's at about 5° or 6° instead of the 3° it was at before I reglued it back on after it snapped off on a trimming toss). I can either add more weight to the nose (simpler fix but adds a ton of weight) or rip it off and put on a new one at the correct angle. Or I might be diagnosing the problem wrong. If it isn't already obvious, I'm a total newbie at this so any advice/guidance/suggestions (in layman's terms) would be very much appreciated!
 

XolveJohn

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Confused. When you say porpoises like crazy when launched, do you mean it does that when it goes to glide, but does not do that with a hand launch?

Canards are different, I would reduce the incidence and go back to hand launch tests. Even with normal gliders, hand results often differ from performance after an actual launch. Adds to the fun.

I am of the school that believes canards do not perform as well as normal gliders, but you may prove that wrong. They are usually delta wings, which clearly can't glide as well as a decent aspect ratio sailplane type wing.

I do know that in the old days, folks making flexwings, found that they could not make them glide right without having another tiny flex wing, or CANARD at the front set properly. Another thing problematic to build, the flexwing. Note the Rogallo wing for Gemini recovery had to be cancelled, they said due to unreliable deployment from pyro problems, but I think it was just a mess. Parachutes have enough problems to solve.
 

Richard K.

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What is the name of your Rocket Glider? I am getting ready to start building the "Sky Blaster" designed by Larry Renger maybe we can compare notes. This is my first attempt although I have built several control line planes.
 

papabatman

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i am a every day rc flyer when you say porpoises it means tail heavy. verified your cg. you alsp might want to turn down your throw and add expo/
 

Rktman

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Confused. When you say porpoises like crazy when launched, do you mean it does that when it goes to glide, but does not do that with a hand launch?

Canards are different, I would reduce the incidence and go back to hand launch tests. Even with normal gliders, hand results often differ from performance after an actual launch. Adds to the fun.

I am of the school that believes canards do not perform as well as normal gliders, but you may prove that wrong. They are usually delta wings, which clearly can't glide as well as a decent aspect ratio sailplane type wing.

I do know that in the old days, folks making flexwings, found that they could not make them glide right without having another tiny flex wing, or CANARD at the front set properly. Another thing problematic to build, the flexwing. Note the Rogallo wing for Gemini recovery had to be cancelled, they said due to unreliable deployment from pyro problems, but I think it was just a mess. Parachutes have enough problems to solve.
Yup does beautifully when hand-launched, but it's a different animal once rocket-launched and it goes into glide mode. It's stalls pretty bad, dropping maybe 4 feet before it recovers and then goes into another loop. Adding nose weight helped a little but I suspect the canard incidence angle is too great (glopped on too much glue when I reattached it after a trimming mishap, so instead of being at 3 degrees it's now closer to five or six degrees).

Agree that canards are harder to sort out then "conventional" gliders, though I've only built/flown 4 canards, one of which far outperforms my other wing-in-front-tail-in-back gliders (maybe cause it's small and light).

Being that this is my first attempt at designing and building one, it's a learning experience so I expect problems and I'm surprised there aren't more.
 

Rktman

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What is the name of your Rocket Glider? I am getting ready to start building the "Sky Blaster" designed by Larry Renger maybe we can compare notes. This is my first attempt although I have built several control line planes.
I'd like that, think we both could benefit. Mine is a self-designed scratch-built. Are you doing the RC version? That's a pretty challenging build. Think I could learn a lot by following your build thread, can you send me a link?
 

Rktman

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i am a every day rc flyer when you say porpoises it means tail heavy. verified your cg. you alsp might want to turn down your throw and add expo/
Mine is free-flight so once it's launched it's entirely on its own. Confirmed CG and removed tail weight and added quite a bit to the nose but the problem didn't go away. That's why I now suspect there's too much incidence in the canard wing.
 

XolveJohn

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Google HOW TO TRIM A CANARD GLIDER and I bet you turn up lots of good info, like from model plane sources. They have been messing with them for 50 years +. But it seems the "normal" wing/tail config still dominates. I don't remember Cessna coming out with a canard light plane. Just Burt Rutans Veri Easy canard that John Denver pranged. Well at least it could not stall. :(
 

Richard K.

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I am just starting to make working drawings from the plans and so far I am not sure if I will include the RC equipment as I have very little experience with it and none with the Rocket engines. Also the cost of adding all the RC gear would really put a dent in my retirement income. I don't fly control line anymore and just build for my own amusement. I found the plan for the Rocket Blaster on E Bay while looking for something different to build.
I have never used the Canard style wing & just assume that it should be on center with the wing and I don't know what effect that not using the RC controlled elevator will have on it & the wing. I was thinking I would make it to use the rocket engine & follow you in making it free flight from there.
What size/type of engine are you using? My plans call for a D size but going up to E size gives better performance. Also I am not very good on the computers so I won't be making a build thread, just use this forum or E mail.
 

XolveJohn

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You might try the Turnigy 5X radio system from Hobbyking. Xmtr and Rcvr costs $25 total. I have been using on RC BG. I use the tiny indoor servos on C birds, see my Rumblebee construction thread. They are a bit difficult to wire up, as you need to solder very fine wires, and run on only a single lithium batt, 4V. But you can run it on 5V with tiny normal servos. Can't beat the price of that radio, but does not have any fancy features like expensive systems. The rcvr is quite tiny and light, though.

Oh, and it seems only to be available from the China warehouse. They won't stock it in the US ones because it will compete with their clunky house brand radios. 3 day shipping is about $15 or more.
 

Rktman

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Google HOW TO TRIM A CANARD GLIDER and I bet you turn up lots of good info, like from model plane sources. They have been messing with them for 50 years +. But it seems the "normal" wing/tail config still dominates. I don't remember Cessna coming out with a canard light plane. Just Burt Rutans Veri Easy canard that John Denver pranged. Well at least it could not stall. :(
Thanks for the tip, will do. Didn't know that's how John Denver ended. I know the Monterey Bay area where he went down from when I lived in Cali. Very sad way to go.
 

XolveJohn

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They say the guy who built the plane put the valve for one of the tanks on the wrong side, to turn it he had to lean over, and accidently pushed one of the rudder pedals, and put it into a spin, which was not recovered from. Needed one of those cool rocket fired E-chutes.
 

Rktman

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I am just starting to make working drawings from the plans and so far I am not sure if I will include the RC equipment as I have very little experience with it and none with the Rocket engines. Also the cost of adding all the RC gear would really put a dent in my retirement income. I don't fly control line anymore and just build for my own amusement. I found the plan for the Rocket Blaster on E Bay while looking for something different to build.
I have never used the Canard style wing & just assume that it should be on center with the wing and I don't know what effect that not using the RC controlled elevator will have on it & the wing. I was thinking I would make it to use the rocket engine & follow you in making it free flight from there.
What size/type of engine are you using? My plans call for a D size but going up to E size gives better performance. Also I am not very good on the computers so I won't be making a build thread, just use this forum or E mail.
It doesn't seem to make a difference whether the canard wing is in line with the main wing or not as I have 3 canards and 2 of them have the canard mounted on top and the wing on the bottom. Having said that though I'd stick with your plan layout, as it uses a thicker built up body vs the thin stick fuselages on my gliders, and that may make a difference. I'm not all that knowledgeable--yet--and learning as I go so the Forum is a great place to get feedback from folks who are engineers or just have a ton of knowledge and building experience with gliders.

The Sky Blaster is a really great looking glider and should do well as a free flight if the CG is where it should be (do the plans specify where it's located? If not there's an online canard CG calculator here: https://rcplanes.online/cg_canard.htm that may be of help.

My scratch-built "Kestral" is fairly light weight and I've been using just B4-2s while I sort things out. Once I do that I'll move up to a C6-3, which should put it up high enough for some decent glide times (I'd be satisfied with a minute and a half, as I tend to lose gliders that stay up any longer than that).

Kestral.JPG
 

Rktman

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They say the guy who built the plane put the valve for one of the tanks on the wrong side, to turn it he had to lean over, and accidently pushed one of the rudder pedals, and put it into a spin, which was not recovered from. Needed one of those cool rocket fired E-chutes.
Not the way I want to shuffle off this mortal coil. Not that I could afford a private plane, but as something of an acrophobic I don't think I'd want one even if I could. :eek:
 

XolveJohn

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After watching the TV show MAYDAY, I am not eager to hop on an airliner anymore. Even if they are more reliable than elevators.

Here is some data on canard use, judge for yourself. Many think they just open a can of worms on your aircraft.

https://www.boldmethod.com/learn-to-fly/aircraft-systems/canards/

http://www.apollocanard.com/4_canard myths.htm

Yes it is an interesting, "different" configuration, but they can cause certain problems, as you are noticing. Having the wing in front of the tail gives it clean air, for example, no turbulence from a canard hanging out front. I guess I would blame the Wright bro's for starting this. I have read that their planes were pretty squirrelly to fly. Wing warping sounds awful to implement.
wright.jpg
 

Richard K.

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Hello John, I just skimmed thru " What are Canards...." by Aleks Udris and came to the conclusion that he stated in the last line, Canards just look good!
In fact that's what gave me the impulse to build the "Sky Baster".

Thanks for posting, Richard K.
 

burkefj

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I've only done one canard, but did not put pitch controls on it, just used elevons on the wing, my main reason was to move the cp forward so the natural cg would be in the right spot without needing tail weight. I placed the canard in line with wing with zero incidence on either wing or canard.
IMG_20180216_171205411.jpg
 
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Richard K.

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I just started on my first Rocket/Glider the "Sky Blaster", so hang on its going to be a wild ride!

I started building & flying as a kid in the 1950's and retired a few years ago & started building to fill some time. I haven't flown anything in many years & have no experience with Rockets or RC only Control Line.

I started making some working drawings of the wing & fuselage and I'll warn you all now that I take some liberty with the plans. Its not that I know anything but only trying to make things a little easier for me! LOL. I am doing some research on the types of rocket engines & equipment needed. I am going to look at RC stuff but on my retirement budget I don't think I'll go that far.
So here are some pictures of the former's and 1/16 sheets for the top & bottom.
20181230_115152.jpg
20181230_113850.jpg
 

burkefj

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I believe this became the astro blaster from estes, or was a parent, with modern equipment and a long burn motor it should be nice, at the time motors and rc equipme limited me to sub 30 second flights. I got to meet larry at naram this year, didnt know the name and his pioneering history before. I think plans are available for download. https://freercplans.com/plan-sky-blaster-3215.htm
 
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Rktman

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I just started on my first Rocket/Glider the "Sky Blaster", so hang on its going to be a wild ride!

I started building & flying as a kid in the 1950's and retired a few years ago & started building to fill some time. I haven't flown anything in many years & have no experience with Rockets or RC only Control Line.

I started making some working drawings of the wing & fuselage and I'll warn you all now that I take some liberty with the plans. Its not that I know anything but only trying to make things a little easier for me! LOL. I am doing some research on the types of rocket engines & equipment needed. I am going to look at RC stuff but on my retirement budget I don't think I'll go that far.
So here are some pictures of the former's and 1/16 sheets for the top & bottom. View attachment 370156 View attachment 370157
Your experience building balsa planes serves you well, you've got some great fabrication skills there. I have 0 experience doing so and this would be a daunting build for me. Glad to ride along and see how it's done.
 

Rktman

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Thanks for those links. The articles seem to agree that canards ARE fraught with complications (though they're referring to full sized planes. Methinks the smaller scale of rocket powered canards probably makes them a somewhat related but different animal). Since I've got far more conventional gliders in my fleet I do agree that they're easier to understand and get decent flights out of. Canards seem to be more finicky, but then I've only had 4 counting this one to try and get my head around what makes them tick.

As a relative newbie why tackle a canard? Well, quite aside from the coolness factor, I wanted to try something different that was more of a challenge (or maybe I'm just a masochist). Getting something difficult to work is just more satisfying than building something easy I guess. That and for me mistakes are a great way to learn how stuff works.
 
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Rktman

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I'm leaning toward tearing off the canard wing and setting a new one in at a lesser incidence, unless someone else chimes in with an alternate assessment of what the problem is and how to fix it.

The other thing rattling around at the back of my head is that the canard wing might possibly be too small. It's a tad shy of 30% of the main wing area so I'm considering a modest size increase. I could be totally off on this...but I guess I'll find out.
 

georgegassaway

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Please post a couple of photos, and how much incidence you have. What kind of airfoil does the canard have, and what kind does the main wing have? Key thing about a canard is that it needs to stall before the main wing stalls. So it's better for our size of models if the canard airfoil is say rounded while the main wing has at least "some" airfoiling to it, a flat bottom-ish type airfoil. In any case, canards are sorta tricky.
 

smk99

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You are correct that the canard incidence is probably too high. Canard incidence sets the airspeed where the aircraft is in trim (pitching moment is zero). Higher incidence yields slower trim speed. I suspect that the trim speed associated with 5 deg canard incidence is below the stall speed of your model. So the model tries to slow down to the trim speed, stalls, nose drops (good) to break the stall, and the whole sequence repeats. Adding nose weight increases stability which helps, but what you are really after is a change in trim speed. This requires reclocking the canard as you suggested. Another option is to add a trailing edge control to the canard. Positioning the added control surface 5 to 10 deg trailing edge up would likely produce a trim speed that is above stall speed.
 

Rktman

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Please post a couple of photos, and how much incidence you have. What kind of airfoil does the canard have, and what kind does the main wing have? Key thing about a canard is that it needs to stall before the main wing stalls. So it's better for our size of models if the canard airfoil is say rounded while the main wing has at least "some" airfoiling to it, a flat bottom-ish type airfoil. In any case, canards are sorta tricky.
I didn't airfoil the main wings and the canard has a moderate airfoil since it's only 1/16" balsa. Since I'm going to tear it off and put on a new one I'll just round off the edges as you advise.
IMG_2230.JPG


I thought I had remounted the canard at 5° or 6° incidence but according to the photo I just took, it's at 3°, the same angle I've used on other (smaller and larger) canard gliders successfully. Now I'm not so sure too much incidence is the problem that's causing the pronounced stalling...but then I don't know what else it could be.
canard wing.png
 

Rktman

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Maybe you can set up a variable adjustment on the canard. Makes sense.

The only "real" canard aircraft that seems cool is this:
But it still has a tail. The pusher props allow the wings to get calm air, it is supposed to be quiet, also.

https://en.wikipedia.org/wiki/Piaggio_P.180_Avanti

View attachment 370205
Since I'll probably end up tearing off the existing canard wing, that's a good suggestion to make the whole wing adjustable or have flaps I can set to test different incidence angles until it flies right.
 

Rktman

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You are correct that the canard incidence is probably too high. Canard incidence sets the airspeed where the aircraft is in trim (pitching moment is zero). Higher incidence yields slower trim speed. I suspect that the trim speed associated with 5 deg canard incidence is below the stall speed of your model. So the model tries to slow down to the trim speed, stalls, nose drops (good) to break the stall, and the whole sequence repeats. Adding nose weight increases stability which helps, but what you are really after is a change in trim speed. This requires reclocking the canard as you suggested. Another option is to add a trailing edge control to the canard. Positioning the added control surface 5 to 10 deg trailing edge up would likely produce a trim speed that is above stall speed.
Took a photo this morning so I could measure the incidence angle better. Seems my original assumption that the canard wing has too much incidence might be wrong. It's only at 3°, which is not all that much. Now I'm more confused what could be causing such severe stalling.
 

smk99

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Do you have a picture showing the center of gravity location?
 
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