Thinking about trying a free floating canard.

The Rocketry Forum

Help Support The Rocketry Forum:

tab28682

Well-Known Member
TRF Supporter
Joined
Jul 30, 2014
Messages
1,704
Reaction score
244
Have been mulling over a couple of simple fun scale rocket glider projects that would need a canard to look right.

A fixed canard with no pitch control (as well as a full flying one or one with pitch control surfaces) causes the CP to move forward, all else being equal, which means more nose weight for the typical RC rocket glider with the motor in the rear.

A free floating (full flying) canard would have the effect of removing the vast majority of the canard forward area effects from the aircraft and would reduce the amount of needed nose ballast.

Has been proven to work on canard equipped missile models like the Sidewinder and the later versions of the Python from Israel. There is also some data in various NACA wild tunnel tests on missiles with free floating canards.

Thinking about a RC rocket glider version of the Von Braun Ferry Rocket, the one with a large swept wing and canard. I am sure it will fly quite decently as a elevon controlled flying wing, if you removed the canard completely, given the generous wing sweep and area.

Ergo, the same model with a free floating canard, full flying on a pivot, properly balanced and with the pivot in the right place to avoid flutter should look right and end up being lighter with a reduced amount of nose weight.

Have sketched up a smallish one for the 18mm D2.3 reload, so saving a little nose weight is useful at this level of power.
 
Last edited:

burkefj

Well-Known Member
TRF Supporter
Joined
Jan 27, 2009
Messages
3,332
Reaction score
789
Tom I think for a horizontally gliding rocket you'd need to balance such that gravity does not want to rotate the canard and provide any pitch effect, to do this I think the pivot point will be in the non optimum location for a vertically launching rocket which is typically further forward than the neutral pivot point and gravity keeps it pointing vertically for the most part. I know you say "properly balanced"....I'm not sure what that means for a horizontally flying airplane.....maybe have the pivot forward for vertical boost and free floating, then locked in place via a servo once in glide mode?

Frank


Have been mulling over a couple of simple fun scale rocket glider projects that would need a canard to look right.

A fixed canard with no pitch control (as well as a full flying one or one with pitch control surfaces) causes the CP to move forward, all else being equal, which means more nose weight for the typical RC rocket glider with the motor in the rear.

A free floating (full flying) canard would have the effect of removing the vast majority of the canard forward area effects from the aircraft and would reduce the amount of needed nose ballast.

Has been proven to work on canard equipped missile models like the Sidewinder and the later versions of the Python from Israel. There is also some data in various NACA wild tunnel tests on missiles with free floating canards.

Thinking about a RC rocket glider version of the Von Braun Ferry Rocket, the one with a large swept wing and canard. I am sure it will fly quite decently as a elevon controlled flying wing, if you removed the canard completely, given the generous wing sweep and area.

Ergo, the same model with a free floating canard, full flying on a pivot, properly balanced and with the pivot in the right place to avoid flutter should look right and end up being lighter with a reduced amount of nose weight.

Have sketched up a smallish one for the 18mm D2.3 reload, so saving a little nose weight is useful at this level of power.
 

tab28682

Well-Known Member
TRF Supporter
Joined
Jul 30, 2014
Messages
1,704
Reaction score
244
A featherweight canard will not droop enough when flying to have any appreciable effect on things. The relative airflow will keep it in line, torsion free and trim effects free. Will balance so it will not flutter and give it a try. If you lock it in place with a servo when gliding it becomes a normal fixed canard and the CG will have to be moved forward appropriately.

I can always piggyback the model one my large Carbon Z Carbon Cub, as I did with the A4b and glide test it before a launch.

I have flown a couple of different mostly flying wing models with a canard added. On one of them I could turn the canard action on and off. Model flew fine either way.

A thin balsa or Depron chuck glider would prove the idea before making the larger model...might do that.
 

burkefj

Well-Known Member
TRF Supporter
Joined
Jan 27, 2009
Messages
3,332
Reaction score
789
yeah, you'll need to calculate some portion/% of the area forward of the pivot as the % that contributes to CP I believe, when I was looking at vertical launched rockets we were using about 20% area pivot point so that you had to assume that forward 20% will still contribute to forward cg movement I think....still a reduction in having to move the CG forward as much, but not zero...will be interesting to see how it works out, I agree on something like an XB-70 which will fly fine with just elevons would look better with large forward canards... I think it would be hard to have a 20% pivot for a horizontal glider even weighted to stay neutral...I've never tried or thought about this much..

Frank
 

hornet driver

Well-Known Member
Joined
May 2, 2011
Messages
4,637
Reaction score
7
Hey tab, I'm not sure what your trying to accomplish short of just running the experiment.. One thing to think about. Ok, maybe a couple things. If you use elevators on the main wing and have a floating canard, Your killing some lift off the main wing, although the canards are free floating, your gonna need a little more stick input to pull the nose up versus having a fixed canard which would deflect airflow and require a shallower AOA--BUT !! It can be like sitting on a razor and you can develop porpoising as you try to correct for the fixed canard overwhelming the main wing. STALL--CATCH IT--STALL --CATCH IT--You get the point. A true canard (as a lifting device) stalls before the main wing at high AOA and sort of mushes through so they don't depart flight. If you look at aircraft like the Vari-eze or Starship you'll notice that the canard has a completely different cross section than the main wing. Aircraft like the Grippen and Vigin are not canards in the true sense. Their canards are more oriented as control surfaces and the XB-70 falls somewhere in the middle since it was a wave rider and the canards provided lift at high speeds and were deflective at lower speeds. OK, if you wrapped your head around that, it can be confusing, a rocket with canards( deflective surfaces not lifting) that are fixed does require more nose weight to counteract the CP shift and make it stable. But that does not mean more overall weight. You just need to move the gear forward--the farther you move it forward the more impact it has on the CG and you don't gain weight--See where I'm going with this? On Timberwolf (not RC) I had full moving canard with a fixed position after ejection--it porpoised but I was able to tune some of that out over time with less deflection. I would think that a committed RCBG with a full moving canard as a deflective device would be more effective than the other options from a glide perspective. You'll need a lot less input so it's more a matter of trimming than muscling it around the sky---Just my thoughts---H
 

tab28682

Well-Known Member
TRF Supporter
Joined
Jul 30, 2014
Messages
1,704
Reaction score
244
Believe me: I have my mind wrapped around what you are saying and then some...:)

The goal is to have the CG further back and keep the model lighter overall.

The planform of the Von Braun Ferry, as mentioned, will likely fly perfectly as a flying wing with the canard removed. It will have PLENTY of pitch authority with elevons. With a fixed canard, full flying servo controlled canard or a canard with a hinged elevator, the CG difference might be as much as .5"-.75" on the planned model.

The planned model will have a span of about 24" and design weight will be about 6oz on the pad with a D2.3. The radio gear weight will be about a 16-18 grams: two 3.5 gram servos, a 4 gram RX and a small single cell lipo. Not enough radio weight to do much CG shifting. The two elevon servos will be mounted on the wing and cannot be moved forward without increasing linkage weight, both length and stiffness.

Pretty well known in the RC world that small full flying canards do NOT work well, and small canards with a hinged pitch surface do not fare a whole lot better, at the size model I am looking at.

The proof will be easy to determine. I will build the wing and canard, attach them to a profile and planform fuse and test it, with the canard fixed and with the canard free floating. Measure the needed CG for each version. See if it saves enough weight to be worthwhile.
 

hornet driver

Well-Known Member
Joined
May 2, 2011
Messages
4,637
Reaction score
7
OK , I got ya. I guess one thing I wasn't clear on, when I said move the gear forward I meant use the canards and not the wing elevators. Looking forward to your results.--H
 

Latest posts

Top