Canard Gliders

[AFlyingMonkey]

I'm building a sail wing type glider with a canard front. If these are supposed to be lifting canards, and the wings are 13 inches long how big should the canards be?

[mycrofte]

Are you talking about a rocket boosted R/C?

Mine is just a rocket glider with a total wing span of 12.5"! But the canards have a root of 1.25" and are each 2.125" wide.

[AFlyingMonkey]

well I'm considering making an RC but for now in the testing phase I want it to be just a FF glider. Its a swing flop at the moment but I've made the canards the same size as I would a standard rear horizontal stabilizer, but the nose is jerking up and it'll pull a full loop from a hand toss then stabilize out to a steady glide after the loop. my thought process is telling me that the canards are too big at the moment. I created them with 1/3rd the size of the wing, which in my mind's eye is telling me its too big. I think I'm going to drop them to a 1/4 of the wing size to see if that makes a difference. I'm just refining a design here and wanted some general thoughts.

[georgegassaway]

Its a swing flop at the moment but I've made the canards the same size as I would a standard rear horizontal stabilizer, but the nose is jerking up and it'll pull a full loop from a hand toss then stabilize out to a steady glide after the loop. my thought process is telling me that the canards are too big at the moment. I created them with 1/3rd the size of the wing, which in my mind's eye is telling me its too big. I think I'm going to drop them to a 1/4 of the wing size to see if that makes a difference. I'm just refining a design here and wanted some general thoughts.
Well, I am a bit confused here. If it stabilizes into a steady glide, what is the problem? ANY Free Flight glider that will transition to a steady glide is going to pull the nose pitch-up when it is thrown faster than its steady-state glide speed. Though the greater the angle of incidence, the more it will pitch up. Also a larger tail or canard will make it pitch up more.

But, Canards are unusual beasts when it comes to glide trim. So, perhaps a smaller canard will work. BUT, if it is indeed going into a steady state glide with the 1/3 size canard (I presume therefore 10-11% the area of the wing), then with a 1/4 sized canard (6.25% the area of the wing) the glider will either tend to dive a bit or you will have to remove a lot of noseweight or add tailweight.

Now if you had described the model as stalling too much or needing a LOT of noseweight to get it to go into a steady glide, I would have agreed with you first impression to change the canard in some manner (either smaller size, or to lower the angle of incidence).

And now that I said incidence, that would be another way to make a change, and might be the real issue if indeed the glider is pitching up excessively. Indeed since you say “Loop” on a hand launch, the smaller the radius of the loop (tighter it is), then that indicates there is a lot of incidence angle between the wing and canard (or wing and stab for a normal model).

Do take note that I have only addressed the glide and hand launch part of the issue. Rocket boost is something else. Since you said this model is a swing flop wing, yet is a Canard design, that is really odd. Could you post photos of it in both boost and glide configurations? With pop-pod (boost mode) if it uses a pop-pod? The only canard swing-wing I have heard of before is one that was so skinny that it boosted up inside of a clamshell rocket (Steve Behrends’ “Spread Beaver” design), so that is why the canard was not an issue on boost (even so the whole glider was installed backwards in the clamshell, so the canard was at the bottom of the clamshell compartment for boost because the canard stuck out the sides of the clamshell).

- George Gassaway

[mycrofte]

While I would go with smaller canards, it sounds like you are just hand launching it to hard. If you can find a long sloping hill (or a 2 story building), try a launch closer to glide speed and see how it does.

Other than that, try a swing test to double check your balance point. After a few "whirling loops of death" I have come to rely on those...

[georgegassaway]

BTW - you had said this was a "Sail-wing". But later described it as a swing-flop wing, so I went with that.

But by sail-wing, did you really mean "Flex-wing"?

I've done lots of flex-wings, nearly all of them Rogallo-style with no tail or canard. But I did do a very complex one for FAI rules 20 years ago, for Boost Glide, which was a Canard type (and also flopped the main flex-wing spars). That one used exactly a 1/3 sized canard. But being a flex-wing, there would never be any reason to try to throw it hard enough to loop, and even if I did try, it was too draggy to maintain momentum to loop.

Two photos below, when I last flew one of those special canard types at NARAM-34 in 1992. The glide photo shows only one half of the canard deployed. The model still glided on that flight, but in a very shallow dive due to loss of half of the lift. It's other flight was a very good one. BTW - that entire glider folded up inside of 15" space of BT-20 (18mm tubing), though it had a wingspan of about 48". The canard was pivoted 180 degrees backwards after folding its spars, and the main wing was a flop-wing (28" main spars that folded at about 14.5").

Anyway, I really figured you must have meant something else. But did want to follow-up on clearing up what you meant by "sail-wing". Indeed that is yet another reason that photos would be useful.

- George Gassaway

[AFlyingMonkey]

I'm looking at the wing span as something closer to like an actually tow glider. Here I'll post a pic of a real one. I'm designing something that has about a 10-1 lift ratio if I can. I'm just doing some experimenting for now, when I've got something to show I'll get it posted. My associate and I are working on a canard design because we believe that they tend to do better with a smaller engine size, (A, 1/2A, and 1/4A) if you can get them to work properly. I'm thinking of the Voyager Plane of my youth. The more effecent I can get the wing after boost, the better the plane will fly overall. The swing flop part of it is to get the wing past the boost phase.

[georgegassaway]

I'm pressed for time today, so I won't be able to reply again till Tuesday.

Attached is a pic representative of a swing-wing glider. In this case it is a really big one, 6.5 foot wingspan, main wings 36" x 3" chord each (plus 6" at the hinges).

Actually two models. One was my first one at 6 foot span or more, in 1972, as a B/G. I made the rest as R/G's. The more modern one is one I built in 1992, as a clone of one of my best from 1976. In 2007, I modified it to use rudder-only radio gear, and it sure flew great as a rudder-only R/C bird.

But it is proportionally similar to other swing-wings, the old Jon Robbins "Groundhog" used wings 1.5" chord by 18" for about 36" span, powered by B & C engines. I made some as small as 1" chord by 24" span for 1/2A size.

When you say "swing flop", do you just mean "swing"? There is such a things as a "flop-wing" which is totally different, where the outer wing panels folds chord-wise (if the wingspan span was say 24", then it folds into almost half that, say 12.5"). The wings fold 180 degrees, and fold the other way so the airfoils touch bottom to bottom, to be symmetrical.

If you really do mean a model that FLOPS the wing panels in addition to being a swing-wing, there are extra complexities to that which I do not think you'd really want to get into, at least not until well after perfecting "just" the swing-wing part (One time, I tried flop tips on a swing wing. But the boost airflow grabbed them and pried them open, and that action pried the tail off. I never tried that again).

- George Gassaway

[AFlyingMonkey]

George,

I've actually gotten the swing and flop part down pretty pat. It's the canards I'm trying to get my head around. I'm wanting to keep the weight down as much as possible, but also keep it flying straight. well the wing is actually been cut into three sections. The actuall tips ae being used as partial vertical stabizers, then the second part has a 2 degree up for added dehydral, then the last is just flat. Now that I've added extra vertical stabilizer to it and reduced the amount of canard on it, it flies really well. I'll find a picture of something that looks close to what I'm doing. The Venus Giblet is close to what i'm working with. Mine just has just 2 more hinges.