V-Tail
11-10-2002, 12:48 PM
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V-Tail
The Vee Tail area was explained to me this way (Rightly or wrongly). If you were looking at the flat side view drawing of the airplane then the view on the tail should equal the area of the vertical stab that would normally be used for that airplane. I am not going to argue about it. It works on my design.
My Vee angle is 120 degrees between the two halves. Now I know that everybody with an opinion will jump on this and argue about a degree here and a couple of degrees there. Again, it works on my design.
Ed S
My Vee angle is 120 degrees between the two halves. Now I know that everybody with an opinion will jump on this and argue about a degree here and a couple of degrees there. Again, it works on my design.
Ed S
11-10-2002, 03:00 PM
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V-Tail
The relative tail areas of the vertical and horizontal tails of conventional cross-tail planes vary over a wide range. So can the angles between the halves of V-tails. The problem in either case is to harmonize the tail design with the design objectives of the model in question.
Generally speaking the total area of the V-tail should be the same as the area of a conventional tail for the same model. There are two possible criteria for sizing the V- tail: control authority and stability. Either one of which could have higher priority depending on the purpose of the model.
One peculiarity of the V-tail is that it has a yaw to roll coupling that is undesirable in aerobatic aircraft. Another pecularity is that the up- going control surface is a bit more effective than the down going surface due to the end plate effect of the other half of the tail. This results in a slight yaw to pitch coupling which can be eliminated by differential with less up than down going travel. In a yaw, one side partially blankets the other side reducing the effectiveness of the V-tail a little in yaw. This can be overcome by reducing the angle between the halves of the tail a bit but, then you have to increase the area a bit so as not to affect the pitch response. Yet another peculiarity of V-tails is that they torque the aft fuselage of the model when operated differentially for yaw so that the torsional strength and stiffness of the fuselage aft end must be designed accordingly.
For a given CG location, the tail moment arm, angle between the halves of the tail and tail area will determine the stability and damping in pitch and yaw. The design of the yaw and pitch responses are both affected by the selection of the angle between the halves of the tail thus complicating the design process.
See: http://www.charlesriverrc.org/articles_modeldesign.htm and scroll down to tail design and structure.
Ed,
Just as a range of tail sizes can be made to work using conventional cross-tail configurations so, can a range of V-tail configurations and sizes be made to work. If the criteria is that it work "well enough" then you need go no farther. If the criterion is "what works best" then you may not have looked deeply enough. The even trickier question is the definition of "best" which varies depending on the purpose of the model.
Generally speaking the total area of the V-tail should be the same as the area of a conventional tail for the same model. There are two possible criteria for sizing the V- tail: control authority and stability. Either one of which could have higher priority depending on the purpose of the model.
One peculiarity of the V-tail is that it has a yaw to roll coupling that is undesirable in aerobatic aircraft. Another pecularity is that the up- going control surface is a bit more effective than the down going surface due to the end plate effect of the other half of the tail. This results in a slight yaw to pitch coupling which can be eliminated by differential with less up than down going travel. In a yaw, one side partially blankets the other side reducing the effectiveness of the V-tail a little in yaw. This can be overcome by reducing the angle between the halves of the tail a bit but, then you have to increase the area a bit so as not to affect the pitch response. Yet another peculiarity of V-tails is that they torque the aft fuselage of the model when operated differentially for yaw so that the torsional strength and stiffness of the fuselage aft end must be designed accordingly.
For a given CG location, the tail moment arm, angle between the halves of the tail and tail area will determine the stability and damping in pitch and yaw. The design of the yaw and pitch responses are both affected by the selection of the angle between the halves of the tail thus complicating the design process.
See: http://www.charlesriverrc.org/articles_modeldesign.htm and scroll down to tail design and structure.
Ed,
Just as a range of tail sizes can be made to work using conventional cross-tail configurations so, can a range of V-tail configurations and sizes be made to work. If the criteria is that it work "well enough" then you need go no farther. If the criterion is "what works best" then you may not have looked deeply enough. The even trickier question is the definition of "best" which varies depending on the purpose of the model.
