ululi1970

I am working on my first flying wing. It is a swept wing with fins at the wing tips, sort of like a Zagi on steroid.
I have working split airbrakes and I was wondering if they can be used to
control yaw in flight. The idea would be to deploy the airbrake on one wing to increase the drag on the wing and induce yaw. I have already set up the radio for that, but before I give it an actual try I'd like to hear from people with more experience.
Thank you

Lnewqban

I believe that that is the way in which B-2 bombers control the yaw, with some help of differential thrust.

Lifer

My Feedback: (1)

I believe they use a device call clamshell rudders.

sensei

Certainly it will work, my dad was controlling yaw in his RC version of his later full scale home built design of the Sawyer Skyjacker II back in 1974, you can see the yaw control door towards the leading edge in the first picture on the left, and it was really nothing more then an air brake. The doors in flight are flush but as rudder peddle is applied the doors are independently deployed up to about 45 degees and are very effective in yaw control.



Bob

UStik

Whatever they are called - they actually work. I'm not the one with experience but before there is no information for you I'll rather contribute my second-hand knowledge. In a former post (http://www.rcuniverse.com/forum/aero...l#post10581301) I gave two links to Web pages of a very skilled modeler who made these "spoilerons" for a model of a stork which obviously has no vetical tail. He even used a rate gyro coupled to the spoilerons to emulate the yaw damping effect of a fin. Follow the two links and look at the pictures, which are all in English as opposed to the German text. Unfortunately, this brilliant modeler passed away a few years ago so we can not ask him any questions.

Probably you would not need a rate gyro if you are only looking for some rudder effect. But consider that split ailerons come out thin and flexible and are more prone to flutter than conventional ones. So you would need to build complex but rigid aileron halves, not to mention the cost and weight of four servos and the complex mixer in the transmitter or an airborne unit.

da Rock

A lot of big commercial jets use spoilers instead of ailerons. They often have both, but use the spoilers for turns while cruising to change directions with the least affect on airspeed.

The P61 Blackwidow of WWII was designed to rely on spoilers instead of ailerons. They were called spoilerons.

Lifer

My Feedback: (1)

Very true, but they are not used for yaw.

ululi1970

Well, the model I have (which is already built) is a Ligthning Dart. The split airbrakes are inboard of the ailerons, you can see the horns acting on the top part in the picture.
I realize that being close to the center they may not be as effective as when they are placed near the tip... Right now a single servo in each wing operates both halves.
With some investment in time and money, I could install 4 slim servos to operate the top and bottom part independently. I own a Taranis radio, whose programming capabilities
are practically limitless, so that is not much of a problem...

da Rock

In fact, they are used because they do yaw as well a induce roll. The commercial application of spoilers for turning is the spoiler on the inside of the desired turn creates drag which induces yaw in the desired direction. Aileron deflections require perfect differential to provide equal "steering" for the same drag.

Of course it's true their purpose isn't yaw, but then ailerons purpose isn't either.

UStik

Sounds really interesting, especially the Taranis part, and with a (admittedly complex) gyro it could even make for additional yaw damping. I would go for it just for the fun of it if it were not the inboard airbrakes; that looks a bit disappointing to me.

By the way, I don't care much about the name of the things, even though Spoilerons seems very apt to me. After all for instance on gliders, spoilers are used for their drag and less lift is only an unwanted by-product. And those split ailerons have been used full-size as speed brakes and named spoilerons before.

ululi1970

Unfortunately it is an ARF that I picked up for not much money, so that limits what can be done (though there is always the possibility of bashing it).
It is made by avia-richmodel, but now it is discontinued.
It is my first foray into flying wings and I may just take it easy for now.
It flies well, though ground handling is a bit of an issue. Right now I am waiting for some oleo struts to replace the crappy front wheel
gear that bends where it attaches to the frame with every landing...

Bax

My Feedback: (11)

There's a major thing to consider: without some kind of augmented stability device on board the model, what will keep the rear of the model behind the front? If you are going to have no vertical fin, but use differential drag to control yaw, you will most certainly need a gyro of some type to keep applying control action as the model is disturbed by currents in the air. The B-2 cannot fly without its control computers operating...there's nothing else to give it yaw stability. A fin is used to move the lateral center of pressure behind the center of gravity. With no fin, the center of pressure could be anywhere, and the model will not have any kind of yaw stability. The alternative would to have a swept wing with split ailerons that are split at all times to have enough drag at all times to keep the trailing edge aft of the nose.

Without something to hold the rear behind the model, it won't fly well at all. That's why planes have crashed when their vertical fins have been ripped off...the B-70 suffered the same fate when it lost its vertical fins.

BMatthews

Bax, the tip fins will provide enough yaw stability to keep it from swapping ends. Check the pictures.

ululi1970

Speaking of B-2, I ran into this this afternoon
http://www.generalhobby.com/stealth-...cts-p-525.html

So it looks like a model B-2 can fly without fins and the sophisticated electronics of the real one. Looking at the pictures it shows
the tip split aribrakes...

iron eagel

Here is how it's done.

http://www.youtube.com/watch?v=E-5ctTWQODk

UStik

But the split ailerons don't need to be open all time. Proof is on the web pages I mentioned above.

Bax

My Feedback: (11)

OK, I saw the tip fins....funny how things in plain sight can be missed! I somehow was thinking about a finless flying wing model where split ailerons are used to control yaw. There, you need an active stability system to keep the airplane right-end to!

nitrosportsandrunner

couldn't you make only half of the aileron a clamshell rudder...and the other half normal? say, only the outer 1/3rd of the aileron be able to split open, the other 2/3 of the aileron would be solid. I would think that would less on the need for the clamshell halves to be super strong, since most of the aileron function is achieved by the first 2/3 of it. just a thought.

iron eagel

You need to have both an upper and lower surface moving or you have it changing the camber and acting as an elevator.

nitrosportsandrunner

tried to draw my idea.
the air brakes would need their own servo
and if you wanted to, you could have the clamshell on one side open and the other stay closed....this would act like a rudder.

iron eagel

Your right that is exactly how they need to be.
In the video which I posted the link for in post #15 you will see that's exactly how they are setup.

abelard

The B-52 uses spoilers for roll control too. A disadvantage is that if you push over into a zero-G condition, no lift on the wings, they become ineffective. This was a factor in a spectacular crash at Fairchild AFB in 1994:

https://www.youtube.com/watch?v=FUEhNKBi4DY

ululi1970

Thanks for all your ideas. Unfortunately, my set up has the airbrakes inboard relative to the ailerons. So they would probably be not very effective so close to the center of the wing. I guess next time...
It was an interesting discussion.

iron eagel

They may not be as effective but they should still work to some small degree.
One thing to note for future reference, from what I have seen done. The method of choice now is more like a spoiler setup top and bottom on the wingtips as opposed to the clam shell arrangement.

bpbrinson

I used a Klingberg wing type of yaw dampening system on early Zagi's, both slope and powered. Worked well. Klingberg yaw dampening is very simple. Small, very undersized, hinged tip verticals. I used 20 mil mylar. When the airframe would yaw, the leading wingtip yaw dampener would hit the stop (wing tip) and the trailing would hing to stay aligned to the airflow causing more drag on the leading wing tip than the trailing wing tip. Very simple.