What is this appendage called, and why does my plane fly better with it?

[Vimana89]

I'm a better RC pilot, designer, and builder than when I started, but I'm still very much learning, including when it comes to aerodynamics theory. I'm a hands on trial and error kind of guy, so sometimes I just grab something I see and try it. I saw this article on a proposed low aspect NASA design that is what I call a "tail topper", a small, swept horizontal plane atop the vertical stabilizer, but not a full t tail. What is the proper name for this, and what are the aerodynamic principles behind it? The maiden flight of my RET extra slender delta was super sketchy, but on a repair I stuck one of these thingies on it just to see what would happen, and it's been handling so much smoother ever since.

 

[Vimana89]

They really need a specific sub board for general and specific aerodynamics related topics

 

[Vimana89]

I'm going to try to do some research myelf, but my main questions are:
*What's this thing called
*What purpose is it supposed to serve in aerodynamics(which leads into question three)
* How and why did adding this to my plane seem to make it handle better and more stable

 

[Vimana89]

After some search Kung-Fu...nothing. The closest thing I could find a reference on is T tails, which this is not a full T tail, being much smaller and the elevator being located on the main tail plane on the NASA configuration, and at the rear of the wing in my own tailless design. It might as well be called a dinglebop or a squeedlyspootch. I'll just call it a horizontal stabilizer, because that's a neutral term that can refer to a regular tail plane, the tail plane on a T tail configuration, or I guess this, although this setup is not a full tail plane in any way.

 

[JTarmstr]

Ok, so that is the NASA Silent Supersonic concept plane. Basically it is a jet designed to minimize the effects of sonic boom. If you notice, there are also baby canards the wing is warped with special bulges and there is a little baby T tail. I would guess that all those pieces are for minimizing the sonic boom and provide no large benefits to a small RC plane that wont exceed 40 MPH. I have never seen a tail design like that before so I think that solidifies my hypothesis.

EDIT: as for stabilizing your plane, adding any sort of stabilizer will make your plane more stable, especially a delta design like that. Think of stability as trying to balance a marble on a bowl, with an unstable design the bowl is upside down with the marble on top. Any sort of action will make the marble fall off (and the plane will go into a flat spin and crash).

With a stable design, the marble is in the bowl, and every input stabilizes itself unless you add some sort of correction thus no flat spin unless you change the aerodynamic surfaces to manually go into a flatspin. Adding any more horizontal or vertical stabilizers will make the walls of the bowl higher, and make it more stable.

I hope this helps make sense of it. i would also point out that aerodynamic rules, air viscosity and other sciency stuff changes in the transonic region, so jets designed to be efficient while past Mach 1 have features that wont be useful at Mach .05

 

[Vimana89]

Ok, so that is the NASA Silent Supersonic concept plane. Basically it is a jet designed to minimize the effects of sonic boom. If you notice, there are also baby canards the wing is warped with special bulges and there is a little baby T tail. I would guess that all those pieces are for minimizing the sonic boom and provide no large benefits to a small RC plane that wont exceed 40 MPH. I have never seen a tail design like that before so I think that solidifies my hypothesis.

EDIT: as for stabilizing your plane, adding any sort of stabilizer will make your plane more stable, especially a delta design like that. Think of stability as trying to balance a marble on a bowl, with an unstable design the bowl is upside down with the marble on top. Any sort of action will make the marble fall off (and the plane will go into a flat spin and crash).

With a stable design, the marble is in the bowl, and every input stabilizes itself unless you add some sort of correction thus no flat spin unless you change the aerodynamic surfaces to manually go into a flatspin. Adding any more horizontal or vertical stabilizers will make the walls of the bowl higher, and make it more stable.

I hope this helps make sense of it. i would also point out that aerodynamic rules, air viscosity and other sciency stuff changes in the transonic region, so jets designed to be efficient while past Mach 1 have features that wont be useful at Mach .05

I have noticed no down sides to having it, and what you said about stability makes sense. I think it ended up helping a bit, or at least not hurting. That is true that the NASA plane is specifically designed for supersonic. My plane is more like the HP-115 that topped out at under 300 MPH, it has the super slender wing more to play with lower speed handling and high alpha using the huge vortex lift.