RCU Forums - Vee Tail sizing

RCU Forums (https://www.rcuniverse.com/forum/)

- Aerodynamics (https://www.rcuniverse.com/forum/aerodynamics-76/)

- - Vee Tail sizing (https://www.rcuniverse.com/forum/aerodynamics-76/1465336-vee-tail-sizing.html)

RE: Vee Tail sizing

That would give twice the vertical area as original.

RE: Vee Tail sizing

Quote:

ORIGINAL: Jim Thomerson

Seems to me that you would design a V tail so that whem you looked down on it, it would look the same as a horizontal stab and elevator, and when you look at it from the side, it looks like a regular vertical rudder, more or less.

What you're describing is the projected area. For the stabilizer area you're very right and "what you see is what you get". But as HighPlains notes from the side view it's a little more complex. When you do the simple WYSIWYG projected area thing you're only seeing the one side and there's another projected fin on the other side that the near one is blocking.

It may help if you think of a V tail as being more of a twin fin tail. Looking down you see one stabilizer. But looking from the side you only see one of the two fins.

RE: Vee Tail sizing

Quote:

ORIGINAL: MikeFreas

I'm going to dig this up in the hopes I can get some input and help.

I'm currently converting my ARF Senior Telemaster to a V tail. I have removed the stock stab in one piece and used one of the ribs as a template for my new stab. I scatch built two halfs with the same cord and length as the stock horizontal stab at 17". Today at the field a guy warned me that my surfaces may not be big enough and that was confirmed by BMathews via a PM. I have the ability to extened each side about another 3 inches which is roughly 20% more surface.

Now I consider myself a smart guy but I can't figure out the actual formula.

Any help or advise would be great.

Just use the Pythagorean theorem. A^2 + B^2 = C^2. For example, if your horizontal stab half is 4 inches long and the vertical stab is 3 inches high, the length of the v-tail half should be the the square root of (3^2 + 4^2) = the square root of 25 = 5 inches. The angle up from horizontal would then be the arcsine of 3/5, but why figure it out when you can get that angle by jigging the v-tail so that the tips are 3 inches higher than the root.

RE: Vee Tail sizing

Quote:

Yup, but keep in mind that the side view that showed area like the regular vertical rudder, is a view of one regular hiding a 2nd one sticking out the other direction. Good thing is that rudder area isn't really a critical detail. (pun intended)

RE: Vee Tail sizing

Yes, please note the "more or less".;)

RE: Vee Tail sizing

Quote:

ORIGINAL: HighPlains

I was thinking that the Telemaster uses a lifting horizontal stablizer? That might make it interesting.

Formulas:

Measure the areas of the original design's vertical and hoizontal surfaces.

A lot of sport models use about 1/3 of the horizontal area for the vertical area. To figure the angle the following example shows the basic math for such a ratio.

Once the ratio of vertical to horizontal surface area is determined, it becomes a simple math problem to calculate the angle of the V, as well as the area.

The basic trigonometric function is : Sin^2  + Cos^2  = 1

{This should read Sine squared Theta + Cosine squared Theta equals one}

If we want the ratio to be 1:3, then Theta () needs to result in:
0.25 + 0.75 =1

The square root of 0.25 is 0.5, and the square root of 0.75 is .866

The arc-sine or inverse of the sine function of 0.5 gives 30 degrees.
The arc-cosine or inverse of the cosine function of .866 also gives 30 degrees.

Thus, for an equivalent ratio of 1:3 for the vertical to horizontal area, the angle of each half of the V-tail need to be 30 degrees above the horizontal plane. Since the angle between the V is typically called out, it becomes 120 degrees (180 – 2(30)).

There is some disagreement as to the area required. They range from:
a) using the same size as the existing horizontal stab area
b) using the projected stab area of the V the same as original
c) using the same total area as the combined area of the original tail
d) using the square root of the sum of the squares of areas of the vertical and horizontal

Gliders often use very acute angles (90-110 degrees), because they need a lot of rudder authority.
Pylon racers often use (110-120), I’ll reserve comment as to why.

Thanks for the explanation and the math. Saying to me "it's a simple trig function" is like saying brain surgery is easy.

The stab is built so it's to late now. Yes it's still a lifting configuration. Overall length is about 2" longer per side then the stock one I pulled off. Angle sits right about 110. All I have to do now is clean it up and sheet the top and build the "cradle" it's gonig to fit in on the tail. Remember that this is the ARF version so I have been working on strengthing the entire tail. The stock build quality and design sucks and relies on the sheeting for almost all the strength of the tail.

Rember also that this is going to have twin motors. I think I have decided to fly the V tail with one motor installed in the stock location and my spare wing to make sure it will fly.