Scratch build : V-Tail size

[Zak]

Hi,

I am building my first model from scratch and i would like
to use a v-tail instead of the more popular 'T' config.

Specifications of the model:

Wingspan: 39 inches
Foil type: Flat-bottomed Clark Y with dyhedral
Wing chord: 6 inches
Model type: Slowflyer
Target AUW: 6 to 8 ounces
Fuselage: Carbon fiber wrapped tube
Motor: GWS DX-A or M-100
Batteries: Kokam LiPo 1020's


Now, how do i calculate the size of the V-tail and the flaps (?) ?

I am not looking for scientific formulas, only an approximate
size in inches or a ratio that is proven to work.

Thanks! :)

[Zak]

Oups!

I forgot to ask:

What is the best angle for the 'V'.

45 deg. ? Less ?

Thanks! :)

[Sparky Paul]

Yer gonna get the rigorous scientific approach irregardless! :D
http://www.charlesriverrc.org/articles/design/markdrela_vtailsizing.htm
.
Otherwise, if you know the normal horizontal span/area and vertical span/area, a workable solution is to make the 1/2 span of the vee equal to the diagonal of the "box" the horizontal 1/2 span and vertical 1/2 span make.
An included angle of 90 degrees between the surfaces emphasizes the rudder action.. opening the angle... 105-115 degree allows more elevator effect. A wide angle of 135 degrees gives a mild rudder and lots of elevator.
.
PJB's Seriously Aeronautical Stuff:
http://home.earthlink.net/~pjburke1/aindex.html
Sparky Paul:
http://www.angelfire.com/indie/aerostuff

[Zak]

Wow! Thanks Sparky Paul!

That will get me started :D

[Foxy]

For a rough estimate I and others I fly with use a vtail with 11% of the area of the wing. Seems to work well. We use a 110deg v.

[Dave Hederich]

>> vtail with 11% of the area of the wing.

Isn't the area of the tail feathers vs. the area of the wing dependent on fuselage length, i.e. the closer the tail feathers to the wing, the larger they need to be for comparable "leverage?"

[Sparky Paul]

Originally posted by Dave Hederich
>> vtail with 11% of the area of the wing.

Isn't the area of the tail feathers vs. the area of the wing dependent on fuselage length, i.e. the closer the tail feathers to the wing, the larger they need to be for comparable "leverage?"
.
The horizontal area that provides "leverage" for a fun-flier will be quite different in size and location for one on a thermaller.
The 'need' is dictated by the flying requirements.
A standard kit SIG Kadet Senior for instance has about 300 sq. in. in the horizontal. The plane is fully aerobatic.
My Kadet Lifter which has only to takeoff, do 2 180s and land is quite content with 150 sq.in. at the same location moment wise.
.
PJB's Seriously Aeronautical Stuff:
http://home.earthlink.net/~pjburke1/aindex.html
Sparky Paul:
http://www.angelfire.com/indie/aerostuff

[PeterH]

I've had good success, at least for my purposes, in making the total area of a v-tail the same area as the sum of a conventional rudder/elevator empennage, but distributed among two surfaces instead of three. I also used 110 degrees between the panels from a SWAG analysis and subsequently found that Graupner sold v-tail control horns that are intended for 110-degree v-tails.

If you're rolling your own, go measure a known decent flyer with a conventional tail and do some 'figgering'. You'll get into the game just fine.

Enjoy.

[Sail 'n Soar]

Running the math, the total area of the V tail should be the same as the total tail area of the conventional tail. However, the included angle will depend on the application, e.g., ~90 degrees for a high aspect ratio glider. Take the square of the cosine of the angle between horizontal and the V tail times the total V tail area to determine the equavilent horizontal stab area and the square of the sign of that angle times the total V tail area to get the equivalent verticle stab area.

[Zak]

Great info, all !!!

Thanks!
:) :) :)