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Old Jun 05, 2004, 01:22 PM
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turaboy's Avatar
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Question
Why a Y-tail?

I am working on the configuration for a small UAV, and am wondering about the advantages of the Y-tail. Two UAVs, the Desert Hawk and the Predator B, both use Y-tail pusher configurations. I also found a few more airplanes that use this configuration.

What are its advantages and disadvantages?
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Old Jun 05, 2004, 01:48 PM
Ascended Master
Sparky Paul's Avatar
Palmdale, CA
Joined Oct 2000
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The vertical leg of the Y--
Advantages: keeps the prop off the ground
Keeps the propwash from interfering with the optics.
.
Disadvantages: limits takeoff and landing pitch angles.
Lots of stuff aft of the c.g.
Which means the nose must be longer
which means the side area aft of the c.g. must be greater to balance the nose area..
Puts the delicate parts at the initial impact location.
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Old Jun 05, 2004, 03:27 PM
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Paul,

Thanks for the help! I wonder about the prop, though. Most RC flying wings are pushers, and they don't (usually) have problems with ground strikes.

And I am not following your propwash comment. Particularly in the Desert Hawk (first pic above), the optical payload is pretty far in front of the tail...

Is there an aerodynamic advantage to having that vertical leg of the Y, particularly when compared to a V-tail? It doesn't look like it has a control surface on the Hawk (I see flaps and V-tail aerosurfaces); maybe it's just a skid?

In contrast, the Predator B and the Bugatti do both have rudders in the vertical leg of the Y...curiouser and curiouser!
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Old Dec 22, 2008, 12:10 AM
My Hangar is full
No Step's Avatar
Everett, Washington
Joined May 2003
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Dare I drag this thread back to life?,..... sure !

I'm building a Moni motor glider. It has a Y-tail. The lower vertical "Rudder" is mixed with the V-tail somehow. Anyone have ideas how to do that. I was going to try mixing a third servo to the rudder component of the V-tail but I don't know if that would work unless the V-tail travels, "up and down", were equal. I gotta do something because I the steerable tail wheel is "connected' to the sub rudder.

As a general rule do V-tails have equal travel up and down for controlling Yaw? or is there differential involved usually? I've only had one V-tail long ago and I can't remember
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Old Dec 22, 2008, 12:43 AM
German Engineering.......
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Auxsburg
Joined Dec 2007
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they "should" do the same angle for both controlsurfaces...

otherwise you are mixing elevator and rudder....

you could off course mix rudder & elevator to improve handling. like pull a bit when the rudder is used to keep the nose up while turning, but i don't think that was your question....
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Old Dec 22, 2008, 01:07 AM
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"they "should" do the same angle for both controlsurfaces"

That would be good. If the travel up and down for rudder input are equal on the V-tail, then I could easily mix a second Rudder servo (lower "rudder") to the V-tail "rudder" servo.
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Old Dec 23, 2008, 03:53 AM
An itch?. Scratch build.
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South Wales U.K.
Joined Mar 2003
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Reminds me to some degree about my early introduction to model aircraft and single channel RC, back in the 50's.

Not 'Y' tail, but a sort of 'T' tail. The tail plane, (horizontal stab) was set on top of the fuselage, with the fin, (vertical stab), set underneath, an under slung fin. A low 'T' ?

The reasons explained to me at that time were, it allowed the tail plane to be right at the back, (maximum moment arm), and still be removable for transporting the model, but left the fin in place for strength, alignment, and for any control connections. Back then many fliers carried their models in narrow boxes, and cycled to flying sites, so if the model packed almost flat more could be taken along.

Another 'reason', but more like just luck, was that with an under slung fin when the model lands, (no U/C), the fin pushes the nose down reducing the landing 'belly slide' and risk of the model getting flipped over by any wind.

I can remember my first free flight glider, (an A2 size Revenge), a couple of FF rubber jobs, and my first two single channel RC models all having under slung fins.

Some threads just trigger some old memories, thanks.
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Old Dec 23, 2008, 06:57 AM
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Wow, I did not expect to see action on this topic again! Thank you for all the great thoughts. I don't have any new ones, unfortunately, still just pondering...
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Old Dec 29, 2008, 05:12 AM
The Flying Kiwi
Mt Maunganui New Zealand
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I've seen guys do it for greater yaw stability.
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Old Jan 01, 2009, 02:13 PM
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USA, CO, Lakewood
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Quote:
Originally Posted by No Step
As a general rule do V-tails have equal travel up and down for controlling Yaw? or is there differential involved usually?
V-tails do indeed use differential. The up V has more authority than the down so without diff. you'll get a pitching up with just rudder imput.

Joe
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Old Nov 27, 2012, 10:48 AM
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Y-tail aerodynamics and stability derivatives

Hi,

What will be the "gross" aerodynamics(coefficients) of a plane with a Y-Tail?

and, what will be its stability and control derivatives (in terms of magnitude and sign conventions)?

Best regards
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Old Nov 27, 2012, 12:36 PM
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"The up V has more authority than the down so without diff. you'll get a pitching up with just rudder imput."

I think it's exactly opposite: the Down V needs more movement than the Up V, so that there is no pitching with rudder input. Maybe that's so with the Moni. Maybe the Moni's V-tail movements for yaw are reduced, and the lower rudder restores the yaw authority...

Jim R....
...whose authority in yaw, pitch, or roll is much in question.
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Old Nov 29, 2012, 06:11 PM
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The Perigee Y-tail

Back in the 1980s, I designed, built and flew my tail-pusher "Perigee" (N9XH): a tail-pusher tail-dragger airplane with a Y-tail..

I chose a Y-tail for the practical reason of protecting the tail-pusher prop and I needed a good place to put the tailwheel anyway.

I overcame the reduced rotation angle problem mentioned earlier by setting the wing on the fuselage to just-below the airfoil stall angle whilst the airplane was in the tail-down (three-point) position. Takeoff run does not require doing anything but keeping the airplane straight with the tailwheel and rudder, which is very easy with the aft propeller providing additional effective aft lateral area. Lift off comes about all by itself when sufficient airspeed is obtained, which is above stall speed. Takeoff run is still quite short.

Another advantage not mentioned by other contributors was an increased effective-aft lateral area from the upper components of the Y-tail (compared to a zero-dihedral horizontal tail configuration).
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Last edited by AirJer; Nov 29, 2012 at 09:08 PM. Reason: clarified wing to fuselage comment
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