Why a Y-tail?

[turaboy]

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?

[Sparky Paul]

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.

[turaboy]

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!

[No Step]

Dare I drag this thread back to life?,..... sure :D !

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

[HugePanic]

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....

[No Step]

"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.

[eflightray]

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. :)

[turaboy]

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...

[Ralph Walton]

I've seen guys do it for greater yaw stability.

[JoeSantora]

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