Flat turns? Rudder with Zero Roll

Hey all,

I am making a flying wing or lifting body and wish to have it 'flat turn' in Yaw with rudder input.

Pretty difficult. I havent round a way yet. I remember someone did this in a Helio years ago in FS2004 days. At one point, I had it figured out, but that was perhaps over 12 years ago. Any clues? Any idea's? Do I need to incorporate a 'SimConnect' thing to do this?

The rudders are plates that slide up (glider spoilers style) on the back sides of the lifting body and give the body a thrust like rotation to either side. Its a bit like a mix between the B2 flying wing and a Schweizer glider with angled ailerons that grip the air and cause yaw input, pulling the wing back.

A thousand thanks for any input and idea's.


Note that the angle of the Yaw Thrusters (plates that slide outwards, top and bottom) are angled to help create a Yaw moment, a pressing towards the center of the vehicle in a Yaw axis.

Roy Holmes

Resource contributor
Your wing appears to be fitted with no aerodynamic surfaces to make it fly in any particular direction, it would have no directional stability as depicted.
That means it would be totally uncontrollable in the conventional sense.
Any yaw from using your Yaw Thrusters would set it rotating about its center of gravity with no natural tendency to stop.
You could stabilize it with a fly by wire system using thruster jets but does it have any propulsion to generate gas for thrusters?
If on the other hand you want it to behave like a normal airplane except for unbanked turning you could do that in the sim, it would just be totally unreal/fictional.
Hey Roy,

It has ailerons at the wingtips of the lifting body. It has clamshells at the tail for elevators; top for up and bottom for down. The Space Shuttle had similar. Mine is like this so I didnt have a gigantic assembly that hinged, but shells instead, so I could have structure inside. Probably creates some drag though. The rudder control is the same as the B2 flying wing, but theirs is clamshell while mine are glider versions, and at an angle for rake to input a torsional force, similar to glider alinerons in German and Swiss gliders.

The design is basically a modernized version of the German Arup. Below is a version of the Arup made by a test pilot of that company. Mine has the rudder removed and fans (props) moved to the wingtips (hinged wingtips instead of trailing aileron edges) and the tips can be raised up for a STOL take-off mode system. Similar to the top photo below, but bigger. Motors are located farther in the aeroshell, not in the wingtips (thruster pods). I am sure there is a huge gyro issue there, putting the fans in moving aileron structures. No models presently to test this.

Anyways.. Thats my design so far and some background in similar versions that I base my design direction on.

Vought V-173.JPG
NOTE and Edit; The 'first version' glider Space Shuttle had a giant rear flap at the engines that was the elevator. It later was a pure delta wing, but the prototype used a giant flap assembly in the back of the fuselage (only the fuselage area, that width zone, under the engine bells). That was what I meant by the Space Shuttle in comparing mine with that. But I changed my version to clam shells because the huge elevator structure looked hideous... grim... horrible...
If you take photo number two (above, second one down) and curved the leading edge more and put V-173 prop booms on it, that is my girl.



Resource contributor
The design is basically a modernized version of the German Arup. Below is a version of the Arup made by a test pilot of that company. Mine has the rudder removed and fans (props) moved to the wingtips
But Bill, why did Arup have a fin and rudder in the first place? Also, say one of these wingtip thrusters fails, what is to keep the a/c flying straight? Methinks it will spin like a sycamore seed?
All good points.. And hey, Tom. :)

The V-173 Flying Flapjack used a cross drive shaft joining the two engines via a clutch system. One engine could run both fans.

On Beechcraft twins, (and other twin engine planes), they teach you how to fly with one engine. This might be possible. Model testing required.

The B2, and birds, and flying wings, do not have rudders. Not that I hate rudders, but tend to thing they arent that necessary if you have other means to control yaw. In my case, slats that come up out of the aeroshell.

But these things aside... How in the world could I do flat turns with rudder input.

Rob Barendregt did one for the Haunebu project. He used his VTOL system to bring that into play, enabling the saucer to have flat turn capabilities.

I need to be able to give this girl rudder with 'zero roll' occurring....

I have lowered the rudder down to the tail, at one point, having it under the tail. (bad idea). I have tried quite a few things. Nothing really worked, but I did increase Rake and lowered rudder area and that helped it have a realistic feedback, but I still get Roll...
The problem you'll have executing a flat turn is that the wing on the outside of the turn will be going faster and therefore generating more lift, leading to roll. This is that secondary effect of controls thing flying instructors are always going on about.
I guess theoretically you could feed in some corrective aileron to reduce lift on the outer wing and increase it on the inner one, but that will induce some yaw in the opposite direction to the one you want to turn...
Ultimately the problem isn't the lack of vertical control surface, it's wanting to conduct a zero roll turning manoeuvre.
I don't think a flying body can turn if it does not have any bank. My understanding is that the bank points the lift component toward the inside of the turn pulling the craft left or right. As SkippyBing says above you get that bank with the roll induced but the inside wing going slower (less lift) and outside wing going faster (more lift) and the yaw from the induced drag of the down going aileron, hence the need for rudder input in a coordinated turn.

So flat turns with rudder only, will only point the aircraft nose left or right of the overall heading/direction the craft is going. The thrust component may now also push/pull the craft left or right. So maybe a very slow flat turn rate?? Unless the craft's nose is pointing almost 90 degrees left or right of the direction of flight.

I don't think the flight dynamics of FSX, P3D or x-Plane can handle that configuration.

Roy Holmes

Resource contributor
The reason all those airplanes turn is that they bank.

Turning is not just a question of controls.

The rudder by itself does not create a turn, it creates a yaw. That means the airplane is pointing away from the direction it is going. If it has some natural directional stability caused by something like a fin there will be a side force which will help it turn.

Drag from spoilers out near the wing tips does not create a turn, however the loss of lift creates a bank and that is mainly what makes the airplane turn.

The airplanes that do not have fins/rudders almost certainly have fly by wire systems to control them because they have no natural stability.

Anything that hovers can yaw and face any direction it can then move in that direction so it has done a flat turn. Anything that relies on wing lift to stay in the air could do a flat turn, but it would be very slow.

The Space Shuttle has a very big fin. When in space it turns, pitches and rolls by reaction jets. When actually flying like on the approach it flies conventionally.

The fact is that it does not matter what a sim model looks like because it has zero influence on how it flies. You could have no wing, but provided the aircraft.cfg shows some wing area and wing span plus the air file has the necessary content it will fly. That is why actually putting the rudder under the tail did nothing. You would have to change the yaw and side force coefficients in the air file to get any change.

To turn you need a substantial side force. Probably the best way would be to use differential prop thrust. If you increase power on the left engine it will create yaw, but more importantly it will offset its thrust from the direction the airplane is travelling and "pull" it into a slow turn to the right. That probably would not work without some natural directional stability to stop it just yawing out of control, but it's worth a try. Since you want a flat turn you would also have to counter the bank created by the left wing flying faster than the right one and creating more lift
PS Why do you want a flat turn?


Resource contributor
Birds don't have rudders, but they do have tails - highly mobile tails which do more than hinge up and down. Their wings also flap, which flying wing aircraft don't, unless they're breaking up in mid-air :eek:. However, like aircraft, birds turn by banking.

Ah, the siren call of the flying wing! Stop your ears to it Bill, listen to Skippy and Roy whose beards are greyer than mine and thine, as befits much wisdom. hint: other modellers have built flying wing flight models with a bit of tail included: it just didn't show on the visual model, but keep that under your hat. :tapedshut

Roy Holmes

Resource contributor
Use any airplane's flight dynamics and animate the whole model so that it stays flat in a turn, i.e if you bank 30 right, roll the body 30 left.
Just don't ask me to test fly it.
Many thanks guys for your input.

Very true on the plane not 'actually turning' into its input direction with rudder only in a situation like this with a lifting body. It would only turn the attitude of the plane on its Y axis and when you released rudder, it would go back to where it was (attitude or aim into direction of flight) with little to no change in direction of flight. I just need it to do so without rolling.

Basically it would be acting like a hovercraft when you go to turn at good speed. It changes its direction its facing, but continues going straight ahead unless you have some sort of force that can push it into the new direction you need. Banking would be needed, and it does that well. I just need a flat turn input. :)
I am making a flying wing or lifting body and wish to have it 'flat turn' in Yaw with rudder input.
If you are using a 'conventional' airfile there are basically two entries in section 1101 which control roll when yawing/applying rudder.
Cl_dr roll moment rudder and Cl_r roll moment yaw rate. Btw, when Dornier developed the Do 27, it was a design criterion that the aircraft must not roll when applying rudder.
Most aircraft are capable of performing flat turns, although at a rather slow rate of course….
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Super video, Bernt. The Royal Jordanian Falcons were flying Extras like these at a recent airshow and pulling all these manoeuvres short of flying backwards in level flight, but their sideslips were what caught the eye when landing in formation. Wild!