Question on a Novel Concept

[Joexer]

I have always wanted effective yaw for flying wing type design, but all of the "traditional" ways of handling this axis have major drawbacks. Drag Rudders are complicated, Differential Thrust is (IMO) crude and inelegant, Rudders don't have an effective moment. I began looking at flying wing designs and I for a brief moment turned to gliders. Which gave me the Idea of splitting the Elevons on a flying wing into two control surfaces and using Crow/Butterfly Braking on one side of the model at a time on a partial mix (to maintain control) to the (now split) Elevons. Of course this concept has some drawbacks, as does everything. Some of them I can think of are 4 Servos, A very complicated mix, and absolutely required to have near equal effectiveness on both parts of the split elevons. Has anyone tried something like this? Does it seem "Sound" to do this? Are there any Downsides I haven't taken into account? Image below.

Also I realize that the forces would need to be balanced very carefully

 

[bracesport]

There is only one way to know for sure and if the Yaw is not so effective you will still have some crow to try!

 

[Monte.C]

Yeah that's a tough one.

To rotate about the yaw axis, any drag on one side will be effective, but if they're the same area as each other then the outer one has a significantly greater moment about the roll axis than the inner one. They're the same area but at different distances from the roll axis. So if the outer control surface is smaller than the inner one they can counteract the tendency to roll, but they need to be at exactly the right surface area ratio, one to the other.

 

[Monte.C]

(Who else here does their best thinking in the shower?)

How's your algebra?
Figuring out the required geometry of the two ailerons can be done in two equations with two unknowns. I can draw you a diagram if you like.

 

[Monte.C]

And I might have gotten them reversed, inner & outer...

 

[Merv]

Does it seem "Sound" to do this?

It looks like it it should work. I’m not sure this would be any easier than drag rudders. Put a rudder on each wing tip, on the vertical fin. The trick is to deploy only one at a time. To yaw right only deploy the right rudder, yaw left, deploy only the left rudder.

 

[Monte.C]

I know how we can simplify this - if you want to use the trick with two ailerons. Make them any size you want, they can be the same size, and just vary the throw on the inner one at the field until you've dialed it in.
But merv's solution looks good.

 

[NickRehm]

I know how we can simplify this - if you want to use the trick with two ailerons. Make them any size you want, they can be the same size, and just vary the throw on the inner one at the field until you've dialed it in.
But merv's solution looks good.

I would do that too... There's too much coupling of roll and yaw (and even pitch) to figure it out on the ground. Best you can do is guestimate it--outer portions probably 40% the size of the inner portions) and then adjust the relative throws after flight testing the yaw response.

 

[Monte.C]

I would do that too... There's too much coupling of roll and yaw (and even pitch) to figure it out on the ground. Best you can do is guestimate it--outer portions probably 40% the size of the inner portions) and then adjust the relative throws after flight testing the yaw response.

Yeah I was trying to figure it just like a lever arm torquing about the roll axis, to make them equal against each other, outer vs inner. (Distance x surface area.) It seems like it should work but I might be confusing myself there. Much easier this way. Adjust the inner one until you achieve a zero-roll torque effect. Just make sure you have enough on the outer one for normal flight.

 

[Hondo76251]

Looks to me like it should induce yaw, but I suspect that the disturbance on the affected wing will also reduce lift causing not just yaw, but also bank, which might not be all bad actually.

I've never been a fan of wings myself, and the only ones I've liked were because I had twin motors and differential thrust! lol

would be interesting to see this plan of yours in action!

 

[quorneng]

Wings require aerodynamic reflex for longitudinal stability. There would be a danger that using 'crow' would impinge on that resulting in unwelcome behaviour when entering a turn.
If you are going to have divided control surfaces it would be simpler to have elevators inboard and ailerons outboard so the basic reflex is not altered applying a roll force. You would also have the option to programme in differential movement ultimately 100% so only 'up' aileron and the resulting drag would be applied.
Just my observation.

 

[Tech3811]

Honestly, my strategy is to just try it out!

 

[CarolineTyler]

I would have thought the best place for a rudder is on the wingtips, you get plenty of moment there and it seems to work fine for a canard plane, which has a very simuliar wing.