tail!?

[mohammad_sa39]

hi

what is the best position for the tail of an model(indoor for example)

my mean is what is better for the tail when i put it on the model

does it need for any angle of attack?if so, negative or positive?

does it need for any arc?

what kind of shape is better for it

thanks for any help.

Mohammad

[Sparky Paul]

A typical indoor duration model looks like this.. from Frank Zaic's Yearbooks..
The sizes of the wing and tail aren't unique to this airplane, most similar planes look the same, with minor differences.

[mohammad_sa39]

thanks my friend for the pic but i couldnt get my answers from the pic i think
but i dont know cool info about the tails and need for someone to tell me about them and specially an answer for that qquestions i asked

i saw some of tails but dont know any thing about them and their capabelity

[Sparky Paul]

The answers you seek and need to have aren't available in a "painless" :) form here on the 'net..
For the very basics of airplane design, two books relating to models are:
"Model Aircraft Aerodynamics" by Martin Simons
And
"Basics of R/C Model Aircraft Design" by Andy Lennon
.
These two should tell you most of what you need. The rest comes with experience.

[mohammad_sa39]

ok thank you for yor answers
but noone cant give me dirct answers abou my questions?

i think any normal tail will works but dont know about BEST tail and dont know about
its angle of attack and the camber(if it needs for)
thanks alot my friend

[Sparky Paul]

The easy answer to your tail question is in the image..
Put a tail about that size about that distance from the wing, with the wing at the angle of incidence shown, the c.g. is found by flying, and will be around the 35% point, for that configuration..
The tail has zero incidence.
This will work for a surprisingly large range of airplanes, from indoors to outdoors.
There is very little in model aviation that -must- be precise..
Only the location of the center of gravity is of primary importance.

[BMatthews]

---what is the best position for the tail of an model(indoor for example)

There is no "best" place for it. Low, high or T tail makes no difference in how it flies. However structural considerations may make your decision for you.

---does it need for any angle of attack?if so, negative or positive?

Usually between 1 and 3 degrees negative COMPARED TO THE WING depending on how you intend to fly it. Indoor models like that shown in the picture above typically use very close to 0 degrees.

---does it need for any arc?

No. Often free flight duration models do use an airfoil or arc like shown above because they typically use a very rearward balance point so the tail is lifting upwards... but not as much as the wing so the general response is still stable. But the model will still fly with no arc but perhaps duration will suffer slightly.

---what kind of shape is better for it

Doesn't matter but don't make it too extreme either way. Generallly if the tail is a smaller aspect ratio than the wing that is a good thing. Aspect ratio = span / avg chord.

[mohammad_sa39]

thanks for cool answers

BMatthews,is this all thing i must know?or onother think is need for the tail?

thanks alot

[BMatthews]

The only factor that is missing that I can think of is the size of the stabilizer compared to the wing. Normally the stabilizer area is between 12 and 20% of the wing area depending on the airfoil used and how the model will be flown and the length between the wing and the tail. But for free flight we often make the stabilizer much larger to work better with the very rearward balance point. It's not uncommon to see the stabilizer on free flight indoor models being up to 50% of the wing area. But 30% is much more typical.

With the tail area that large it's possible to balance the model back around 60 to 90% of the wing chord behind the leading edge. There is a method that indoor modellers use to find the correct balance point location but it's been years since I used it so the formula is lost to me. However if you can find an indoor model discussion area they will know. It was called the CMOS or Centered Margin Of Stability. Another term was the Zero Margin of Stability balance location. Both methods set the balance point right on the neutral point of the model and rely on the high drag center of the pylon mounted wing for stability. You can't use this method unless it has a very high wing location. Normally the balance point needs to be a few % in front of the neutral point.