Hey guys. I have just got back into this hobby, and want to build a glider. I used to have a ton of gliders (among 20 other planes) and enjoyed flying them. The this is, all my models have been out of kits and what-not, i want to make my own this time. (more or less)

I went up to my addic/storage place in my house, or as i like to call ... the "graveyard" and in the heap of wings and bodies i found an old glider that i used to love. This thing spaned 14 or so ft. It was a beast, and had some great features, Including "flaperons". Anyway, the prob is, is the fuse is broken in half and unrepairable. Im going to use the wings though.

The point is, im making a new body, that will have a V-tail design, which i always wanted to have, but never did. I know how to set it up mechanically and everything, But...i dont really know how big/long each tail piece should be. I was just thinking about going with the good ol' "TLAR" way (that looks about right), but thought i better make sure 1st.

So, is there any equation, or rule-of-thumb for V-tails? Like wing span vs tail span? Sq. inch vs ___ ????

Thanks for the help. ~Dylan Shine

Do a search here for "v-tail" and "vee-tail".
It's the subject of many a thread and message.

the rule of thumb i was told is draw up the standard tail, put a box around it and take the V to the top corners

I couldnt really find anything in the search.

Put it in a box? Like an outline where all lines are touching a side? Then bring it up to the corner where is isnt touching?

Could you explain is a little more, i dont think i follow. Thanks.

i'm about as clear as a stagnant pond sometimes

OK, if you look at the tail or a normal layout you have a upside down T shape, if you put this in a box with the tail at the bottom and the sides at the tips, then the top is at the high point of the rudder. The V-tail should be in the top corners, this makes sure its the right angle and size. it has more area than the tailplane and if you have a high fin the V-angle is greater to give greater stability as the fin would have. A large span tail gives a shallower angle which gives the V more pitch stability.

Now.. how you work out what the normal tail section should be is a different matter.

If you just want to throw something on, make each V 20%ish greater in span than what you would use for each side of the tailplane, then use an angle of 110 degrees ish between the V.
In the past i've done things like this more by looks than using any formula. its worked so far

Hey thanks a lot, thats just what i needed to know.

Here's a sketch of what philly is talking about.

There are some practical advantages to v-tails, like only building 2 surfaces, keeping the surfaces out of the grass on landing, etc. However, the idea that there are efficiency gains is largely myth. The only aerodynamic advantage that I've heard of is that the tail cannot be completely blanketed by wing wake on a quickie racer.

People that claim to see a difference often have built the v-tail smaller than the equivalent conventional setup - then claim less drag.

It's a cool style choice though, so if you want one - make one.

Good grief that was weird. I just went on MS Paint, where rough scketches of my plane are, and i drew up that exact picture. Black box, with red and blue lines...looking exactly like that. I got back on here and thought somehow i already posted that or something...lol anyway.

Yeah i think they are just cool, i have always wanted to make one. One thing i would really like to do, not with this plane, but maybe a future one, is the V-swept forward. Like very forward...i think that would look awsome.

Thanks again for the help guys.

It makes no difference to the way you work it out. like the claimed efficiency gains of a V it does little extra. i believe its to do with the fact that vortices's cant move forwards just outwards therefore making it more efficient

.
I got 13 pages of hits just on "v-tail"!

Go to the D&J Aerotech site, click on ask Joe and Don, and search v-tail. There is a lot of info by guys who know a lot about v-tail sailplanes. They say the surface area of the 2 V surfaces should equal the total surface area of the 3 surfaces in an X tail.

This "tail in the box" rule is also known as "grandma's rule". Whatever you call it, it's bogus. It will produce a badly undersized V-tail.

For simple sizing V-tails, see http://www.charlesriverrc.org/articl...tailsizing.htm
The DJ Aerotech site has similar stuff.

The most detailed V-tail info I know of is here:
http://www.fmsg-alling.de/vtail.htm
but it's probabably more than most people want to deal with.