Adjust CG in flight or adjust wing arrangement in flight?

[perhapsleiana]

As a 3D and experimental pilot/designer I've always wanted to be able to flip a switch or hold a button on my transmitter and have the CG slide back temporarily to an unstable position. At first I imagined a sliding battery holder, but I'm realizing it might be easier to use slats or swing wings or something.
Pros/cons to sliding weight vs moving wing?

 

[Flying Monkey fab]

I have mulled this over myself and in the end, if you move the wing forward and aft you are doing virtually the same thing as moving the battery. Now slats, swing, etc. I think you'd have to look at the individual virtues and problems of each.
Just want to adjust stability? I'd move the battery. Want to futz with bigger things like slow speed vs. high speeds? Maybe something else.

 

[perhapsleiana]

I have mulled this over myself and in the end, if you move the wing forward and aft you are doing virtually the same thing as moving the battery. Now slats, swing, etc. I think you'd have to look at the individual virtues and problems of each.
Just want to adjust stability? I'd move the battery. Want to futz with bigger things like slow speed vs. high speeds? Maybe something else.

The battery weigh more than the wings, and I think swing would be nice- it also opens up the possibility of independent swing. I fly in a sort of dance-like style when I do 3D, with a higher wing loading and higher thrust to weight ratio than most builds, because since I’m flying 3D style, I don’t necessarily need a low wing loading to fly slow. I’m wondering if independent wing swing would help with yaw-intensive maneuvers like a knife edge spin

 

[Flying Monkey fab]

. I’m wondering if independent wing swing would help with yaw-intensive maneuvers like a knife edge spin

Well, you very much have my attention! If you try something like this I want to hear about it. If you have any luck with it I bet NASA would like to hear about it as well. To the best of my knowledge, asymmetrical swing hasn't been tried.

 

[perhapsleiana]

Asymmetrical swing has been tried, I remember a rotating-wing plane some point… in the 60s or 70s?
Anyway, I’m considering building a twin fuse Edge or similar with full-moving outboard wings that can swing independently if this proof of concept pans out well. Do you know any readily available assemblies for this? Leaning toward using a tube spar and having the wing twist around it, but are there like, hinged tube mounts for where the sweeping spar meets the fuse? Maybe some modifications to a vectoring firewall would do it.

 

[perhapsleiana]

For reference, this is the flying style I use, more or less:

 

[Ketchup]

Well, you very much have my attention! If you try something like this I want to hear about it. If you have any luck with it I bet NASA would like to hear about it as well. To the best of my knowledge, asymmetrical swing hasn't been tried.

Actually it has been tried! The NASA AD-1 was made as a testbed for an oblique wing aircraft.
I forgot exactly why it was developed, but I do remember that when the wing was rotated enough the aircraft gained the tendency to roll when elevator input was applied. I also wouldn't expect the stall characteristics to be good; if I remember correctly, when a wing is swept the edge further back will stall first (part of why NASA tested forward sweep with X-29 was to make the wing root stall first). With an asymmetrically swept wing I would think that you'd get some aggressive stall tendencies and tip stalls that would be tough to recover from without enough control authority.

 

[perhapsleiana]

Actually it has been tried! The NASA AD-1 was made as a testbed for an oblique wing aircraft.
I forgot exactly why it was developed, but I do remember that when the wing was rotated enough the aircraft gained the tendency to roll when elevator input was applied. I also wouldn't expect the stall characteristics to be good; if I remember correctly, when a wing is swept the edge further back will stall first (part of why NASA tested forward sweep with X-29 was to make the wing root stall first). With an asymmetrically swept wing I would think that you'd get some aggressive stall tendencies and tip stalls that would be tough to recover from without enough control authority.

That's more or less what I'd be going for, actually- an oblique sweep of the wing would be used to deliberately enter a spin- and in my style of flying, I like planes that have ridiculous amounts of control authority and enough power to perform a flat spin that doesn't lose altitude.
The tendency to enter a spin on an oblique wing could be use to accentuate, weaken, or possibly cancel the tip-stall of a snap roll.

 

[Flying Monkey fab]

For reference, this is the flying style I use, more or less:

Beautiful flying! I congratulate myself when I simply stop a roll where I meant to or come out on heading after a loop.

Actually it has been tried! The NASA AD-1 was made as a testbed for an oblique wing aircraft.

Okay, yes, I know about this but thought she was talking more like a F-111 able to tuck one wing at a time.

 

[Flying Monkey fab]

Okay, so the way I was thinking has been tried!

 

[perhapsleiana]

Asymmetrical swing has been tried, I remember a rotating-wing plane some point… in the 60s or 70s?
Anyway, I’m considering building a twin fuse Edge or similar with full-moving outboard wings that can swing independently if this proof of concept pans out well. Do you know any readily available assemblies for this? Leaning toward using a tube spar and having the wing twist around it, but are there like, hinged tube mounts for where the sweeping spar meets the fuse? Maybe some modifications to a vectoring firewall would do it.

wow I'm dumb, it took me this long to realize i could just drill a hole in a round spar and have the wing pivot around it.

Anyway first concept test is on the EPP foamy Yak- the same one that’s in the video I posted earlier in the thread. Just finished doing all the modifications, and let me tell you I absolutely have a favorite cheap servo now: 17g digital metal gear with the square top. Comes in several different labels.

 

[perhapsleiana]

built a symmetrical swing setup and flew it today, but one of the wing hinges came half undone. Alignment of the wing hinges is very important without full-moving wings for ailerons.
Also in the modifications were inboard leading-edge “ailerons” that I put in for scenarios like this, and I think they gave me some of the control authority I needed to wrestle the plane safely back down.

Forward wing position was notably less stable but had far better stall characteristics. I think I’ll keep this testbed around for future experiments, but frankly by now it looks pretty ugly, and it’s time for a new build. I’m thinking of using an FT Edge and locking the ailerons down for a full-moving wing roll control setup. I’ll probably order the plans from a print shop tonight.

 

[LitterBug]

Any Pictures? We love to see what everyone is working on!

Cheers!
LitterBug

 

[perhapsleiana]

Any Pictures? We love to see what everyone is working on!

Cheers!
LitterBug

None yet, will start taking them with this next scratch build.

 

[perhapsleiana]

decided the convenience of the speed build kit of the FT Edge would be worth the price, and when I checked the clearance section of the FT store, there was a FT hoodie in my size for 20 bucks? Snagged that too lol

 

[L Edge]

decided the convenience of the speed build kit of the FT Edge would be worth the price, and when I checked the clearance section of the FT store, there was a FT hoodie in my size for 20 bucks? Snagged that too lol

Have you looked at 4D or tried it?

 

[L Edge]

Problems of the swing wing is fighting the torque, bending, and twist of the wing structurally.

Also explored this one and destroyed models approaching from unfolded to folded(reversed order) making the shift in a close to zero G maneuver at low speeds.

How about some pictures of yours?

 

[perhapsleiana]

Have you looked at 4D or tried it?

Have looked at it, haven’t tried it other than flying helicopters. I’d love to but I’ve never found a good enough variable pitch assembly that didn’t cost over 200 usd.

View attachment 243003

Problems of the swing wing is fighting the torque, bending, and twist of the wing structurally.

Also explored this one and destroyed models approaching from unfolded to folded(reversed order) making the shift in a close to zero G maneuver at low speeds.

How about some pictures of yours?

I saw your thread on this! My approach is to taper the wings enough and have the pivot far enough forward that I don’t run into much wing twist. I’m not doing more than 10 degrees of swing here. Also, my next build will have full-moving “ailerons” for wings, which should help as well.

In your setup, it looks a lot like folding the wings at low speed would be risky enough, and adding in the neutral alpha/beta tendency to chatter on any backlash would certainly make the plane feel unstable. I generally build my planes with a slightly aft CG, so I was able to land safely… especially when the pivot pin for my sweep mechanism came loose on one side.
I’ve been flying for 14 years, and in the past 4 years I’ve landed some seemingly impossible in-flight failures. An experience with an extremely aft CG due to a battery sliding back taught me that an aft enough CG makes a plane feel almost “reverse stable,” where the plane has a tendency to pitch away from the ground in upright or inverted orientations. My goal is to have a plane that can go from stable to reverse stable/hover stable using wing sweep.

 

[L Edge]

If you are doing a sweep of only ten degrees, the CG is really not the problem. I did that with an offset asymmetrical wing of ten degrees and it was under control, but not any 3D. It's the structural stuff that needs addressing like the pivit pin for the sweep mechanism and stripped servos and the wing.

How about some pictures of your setup?

 

[tamuct01]

Some people have noticed the CG change between the F-14 with wings out vs wings swept. I've seen some examples of a sliding battery tray coupled with the wing mechanism to slide fore and aft as the wings sweep.