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Old Jan 06, 2011, 07:12 AM
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v-tail vs inverted v-tail

I would like some discussion on v-tails vs invert v's. Which allows for the best acrobatic manuevers and why? If you have a highly acrobatic plane, please let me know or post a video.
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Old Jan 06, 2011, 08:16 AM
gpw
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Inverted V tails drag on the ground... Look cool though !!!
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Old Jan 06, 2011, 08:23 AM
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V-tails produce a roll component in the "uncoordinated" direction with a turn.

Inverted V's produce a roll component in the "coordinated" direction.

For precise aerobatics you normally don't want any roll components from your yaw inputs.
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Old Jan 06, 2011, 08:41 AM
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thanks. I am still pursuing an idea with 3mm epp similar to the potato chip with an A tail on top to get roll in the direction of the turn. The wing would have some flex as well. Goofy more than precision is intended although I do wantb to fly well.
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Old Jan 06, 2011, 03:02 PM
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An A tail should handle maginally better than a V tail due to the proverse roll vs adverse roll.

But the difference is generally small, and generally can't alone justify the added complexity/weight of building one above the fuse or the hassel of landing damage to one below the fuse.

(BTW, a conventional vertical tail also creates adverse roll, just not as much. In order to eliminate it entirely you have to have a balanced rudder area and sweep above and below the CG)
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Old Jan 06, 2011, 05:18 PM
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Originally Posted by rdeis View Post
An A tail should handle maginally better than a V tail due to the proverse roll vs adverse roll.
...
(BTW, a conventional vertical tail also creates adverse roll, just not as much. In order to eliminate it entirely you have to have a balanced rudder area and sweep above and below the CG)
A question: V tails have the slant in the same direction as wing dihedral.
As far as I know, this dihedral helps with a turn (on a left turn, the dihedral causes a plane to roll left, etc.) and inverted dihedral hinders a turn
(on a left turn, the inverted dihedral causes a plane to roll right, etc.).

What am I missing on a V tail and conventional vertical tail creating adverse roll on a turn (and a /\ tail creating proverse roll)?
Is it something about moving a tail causes an opposite motion to the plane overall (like with an elevator or rudder)?

Thanks.
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Old Jan 06, 2011, 06:38 PM
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I really no nothing about these to speak of, but I was thinking that an /\ would be simple to affix to a foam 3mm epp wing roughly potato in shape that would have flex in the wing for built in dihedral like my new flex wing dart as a hand launch, not ROG. Same build technic as just the new wing here with some gear thrown on it in a slightly widened format of the wing of my squirt design. This is a continuation of several themes smashed into one.
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Old Jan 06, 2011, 06:54 PM
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This build technique for the wing: http://www.rcgroups.com/forums/showt...0#post16988392

This shape widened slightly for more natural flexing dihedra with the /\ on the backl: http://www.rcgroups.com/forums/showp...82&postcount=2

This for the inspiration http://www.rcgroups.com/forums/showthread.php?t=949444
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Old Jan 06, 2011, 11:52 PM
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Originally Posted by flying-llama View Post
What am I missing on a V tail and conventional vertical tail creating adverse roll on a turn (and a /\ tail creating proverse roll)?
Is it something about moving a tail causes an opposite motion to the plane overall (like with an elevator or rudder)?
First the simple case, single vertical tail fin:

With a conventional vertical tail, deflecting the rudder to the pilot's left generates a force to the pilot's right that is applied at the aerodynamic center of the fin/rudder. That center point is normally well behind, and slightly above, the CG of the aircraft. So the force causes a relatively large yaw moment to the left (by pushing the back of the airplane right) and a relatively small roll moment to the right (by pushing the top of the tail to the right). The roll and yaw are in opposite directions, so it's called "adverse roll"

If the vertical tail were to extend below the CG instead of above, like it does on some rocket launched models, then the force is applied below the CG, you get a yaw to the left (by pushing the back to the right) and also a roll to the left (by pushing the *bottom* to the right) The roll and yaw now compliment each other, so you get "proverse roll."

If the vertical tail is carefully centered vertically on the CG, you get no roll effect at all, just yaw. Some pattern planes, 3d aerobats do this to improve maneuver precision.
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Old Jan 07, 2011, 12:00 AM
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V tail adverse yaw

The same principles apply to the V tail, only doubled because you've got two surfaces. There's also a slight wrinkle from the way the two surfaces work together.

To turn left, the left ruddervator is deflected left/down, and the right ruddervator is deflected left/up. The left/left deflections yaw the airplane left, while the down and up deflection both tend to roll the airplane right. Depending the V angle, size, and location, you can get a lot of adverse roll.

An A tail, on the other hand, will have the left ruddervator deflect left/UP and the right one deflect left/DOWN because the angles are reversed from a V. (It's interesting to note that you don't have to move the tail with respect to the CG to get this change!) The opposing up/down moments now roll the aircraft in the correct direction to compliment the yaw, so you get proverse roll.
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Old Jan 07, 2011, 12:04 AM
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Originally Posted by tymbrewolf View Post
I really no nothing about these to speak of, but I was thinking that an /\ would be simple to affix to a foam 3mm epp wing roughly potato in shape that would have flex in the wing for built in dihedral like my new flex wing dart.
Neat idea, and lends itself to the A tail very nicely! (Conventional wing-and-tail designs usually end up needing twin tailbooms or other inefficient structures to avoid the droop, this one doesn't)

Make sure you get enough dihedral. I'm told by the old master that around 6* is the magic number, and that's always held true on my models.
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Old Jan 07, 2011, 12:19 AM
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Quote:
Originally Posted by rdeis View Post
First the simple case, single vertical tail fin:

With a conventional vertical tail, deflecting the rudder to the pilot's left generates a force to the pilot's right that is applied at the aerodynamic center of the fin/rudder. That center point is normally well behind, and slightly above, the CG of the aircraft. So the force causes a relatively large yaw moment to the left (by pushing the back of the airplane right) and a relatively small roll moment to the right (by pushing the top of the tail to the right)...
Ahh, in your scenario, my brain was fixated on the airflow coming in sideways as the airplane turns and pushing on the (conventional) v-stab to the left (and so rolling a little to the left).
I lost track of the rudder (behind the v-stab) being partially rolled to the right by the airflow coming from the airplane's front.
And similarly for the v-tail.

Now I get it. Thank you.
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Old Jan 07, 2011, 08:17 AM
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Originally Posted by flying-llama View Post
Ahh, in your scenario, my brain was fixated on the airflow coming in sideways as the airplane turns and pushing on the (conventional) v-stab to the left (and so rolling a little to the left).
I see. You're looking at the dihedral/anhedral effect after the airplane has already yawed. The adverse roll is a side effect of *introducing* the yaw.

On a conventional layout, the dihedral effect of the tail vs the wing is small because of the relative size of the surfaces and because the long tail moment makes the yaw correction much larver than the dihedral/anhedral roll effect.

On the disc wings he's talking about, though, you might be right-- the tails are much bigger and the tail moment is very short.
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Last edited by rdeis; Jan 07, 2011 at 09:56 AM. Reason: added dihedral discussion
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Old Jan 07, 2011, 01:41 PM
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I likea good discussion, although this one is getting over my head. Perhaps I will just do a normal ret configuration.
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Old Jan 07, 2011, 01:56 PM
An itch?. Scratch build.
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I must admit I can't quite see the point of a 'V' tail, either up or down, on an aerobatic plane.

Well if it's any good at aerobatics, it will probably spend almost as much time flying inverted as the right way up.

Now a 'Y' tail with 120deg spacing............
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